Vascular Access Anatomy

1. Quick Answer

Vascular access anatomy encompasses the anatomical knowledge essential for safe insertion of central venous catheters (CVCs), arterial lines, dialysis catheters, and ECMO cannulae. The major access sites include the internal jugular, subclavian, and femoral veins for central venous access, and the radial, femoral, and brachial arteries for arterial access.

Key Anatomical Relationships:

• Internal jugular vein: Lies lateral to the carotid artery within the carotid sheath, posterior to the sternocleidomastoid muscle
• Subclavian vein: Courses anterior to the anterior scalene muscle, separated from the artery by this muscle; passes over the first rib behind the clavicle
• Femoral vein: Lies medial to the femoral artery (NAV = Nerve-Artery-Vein from lateral to medial) below the inguinal ligament

Critical Safety Points:

• Anatomical variations occur in 5-20% of patients and mandate ultrasound guidance (PMID: 22160196)
• The pleural dome extends 2-3cm above the medial clavicle - at risk during subclavian/supraclavicular approaches
• Compressibility is the cardinal ultrasound feature distinguishing veins from arteries

Exam Focus:

• CICM First Part examiners expect detailed knowledge of surface landmarks, anatomical relations, and ultrasound anatomy for each access site

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2. CICM First Part Exam Focus

What Examiners Expect

Written SAQ:

Common question stems:

• "Describe the anatomy relevant to internal jugular vein cannulation"
• "Outline the anatomical relations of the subclavian vein with particular reference to structures at risk during cannulation"
• "Describe the anatomy of the femoral triangle and its relevance to central venous access"
• "Compare the anatomical considerations for radial versus femoral arterial access"
• "Describe the anatomical basis of complications of central venous cannulation"

Expected depth:

• Precise anatomical relationships with named structures
• Surface landmarks for each access site
• Ultrasound anatomy (vessel characteristics, probe positioning)
• Anatomical variations with clinical significance
• Clear diagrams with accurate labeling
• Applied anatomy for safe cannulation technique

Written MCQ:

Common topics tested:

• Anatomical relations of major vessels (IJV to carotid, subclavian vein to artery)
• Surface anatomy and landmarks (triangle of the neck, inguinal ligament)
• Structures at risk during cannulation (pleural dome, nerves, arteries)
• Anatomical basis of complications (pneumothorax, carotid puncture)
• Ultrasound features distinguishing veins from arteries
• Anatomical variations and their frequencies

Difficulty level:

• Applied anatomical scenarios (e.g., "During left subclavian cannulation, which structure is at risk of injury?")
• Identification of structures from anatomical relationships
• Clinical consequences of anatomical variants

Oral Viva:

Expected discussion flow:

1. Define/Describe - Anatomy of the specific access site
2. Landmarks - Surface anatomy for safe insertion
3. Relations - Structures anterior, posterior, medial, lateral
4. Variations - Common anatomical variants and frequencies
5. Ultrasound - Appearance, probe positioning, confirmation
6. Complications - Anatomical basis of procedural complications
7. Compare - Alternative sites and their anatomical considerations

Common viva scenarios:

• "Walk me through the anatomy for right internal jugular vein cannulation"
• "Describe the structures you would pass through when inserting a subclavian line"
• "What anatomical structures are at risk during femoral venous access?"
• "Explain the anatomical basis for pneumothorax during CVC insertion"

Pass vs Fail Performance

Pass Standard:

• Accurate description of vessel course and relations for each major site
• Correct surface landmarks (SCM triangle, clavicle, inguinal ligament)
• Understanding of ultrasound anatomy (compressibility, pulsatility)
• Knowledge of key anatomical variations
• Clear understanding of complications and their anatomical basis
• Draws clear diagrams showing vessel relationships

Common Reasons for Failure:

• Confusing the relations of subclavian vein to artery (vein is ANTERIOR, not posterior)
• Incorrect NAV relationship at the femoral triangle
• Not knowing that the IJV lies LATERAL to the carotid in most patients
• Unable to describe the pleural dome and pneumothorax risk
• Poor understanding of anatomical variations and their frequencies
• Cannot describe ultrasound appearance of vessels

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3. Key Points

Must-Know Facts

1. Internal Jugular Vein Position: Lies lateral to the carotid artery in 95% of patients, but overlaps or lies medial in 5% - ultrasound mandatory to identify this variation (PMID: 22160196). The right IJV has a straighter course to the SVC, making it the preferred access site.

2. Subclavian Vein Course: Continuation of the axillary vein at the lateral border of the first rib. Passes ANTERIOR to the anterior scalene muscle (separating it from the subclavian artery which is posterior). Crosses over the first rib and under the clavicle to join the IJV, forming the brachiocephalic vein (PMID: 18439195).

3. Femoral Vein Relations: NAV from lateral to medial (Nerve-Artery-Vein) below the inguinal ligament. The femoral vein lies medial to the artery at the inguinal ligament but becomes posterior as it descends. The saphenofemoral junction is 4cm below the inguinal ligament (PMID: 16100523).

4. Pleural Dome Height: Extends 2-3cm above the medial clavicle, making it vulnerable during subclavian and supraclavicular approaches. Higher on the right side. Protected by Sibson's fascia (suprapleural membrane) (PMID: 24211056).

5. Carotid Sheath Contents: Contains the common carotid artery (medially), internal jugular vein (laterally), and vagus nerve (posteriorly in the groove between artery and vein). Ansa cervicalis is embedded in the anterior sheath (PMID: 30860207).

6. Anatomical Variations - IJV: Absent in 0.5%, thrombosed in 2-5%, lateral to SCM in 8%. Position relative to carotid varies - overlapping in 5%, anterior in 3%. Diameter varies from 5mm to 20mm (PMID: 11495610).

7. Allen's Test Anatomy: Tests collateral circulation between radial and ulnar arteries via the superficial and deep palmar arches. Ulnar artery is the main contributor to the superficial palmar arch; radial artery contributes to the deep arch (PMID: 14680706).

8. Ultrasound Characteristics: Veins are thin-walled, compressible, non-pulsatile (with respiratory variation), oval in cross-section, and have low-velocity flow on Doppler. Arteries are thick-walled, non-compressible, pulsatile, circular, and have high-velocity pulsatile flow (PMID: 20392326).

9. First Rib and Subclavian Vessels: The subclavian vein passes anterior to the anterior scalene muscle, which inserts on the scalene tubercle of the first rib. The subclavian artery passes posterior to the anterior scalene. Costoclavicular ligament is anterior to the vein (PMID: 15200590).

10. External Jugular Vein Valves: Contains 2 valves - one at the junction with the subclavian vein and one 4cm above the clavicle. These valves may impede guidewire advancement during EJV cannulation (PMID: 2914330).

Essential Anatomical Relationships

Internal Jugular Vein:

• Anterior: Sternocleidomastoid muscle (sternal and clavicular heads)
• Posterior: Prevertebral fascia, anterior scalene, phrenic nerve
• Medial: Common carotid artery, vagus nerve (posterior in carotid sheath)
• Lateral: Sternocleidomastoid muscle

Subclavian Vein:

• Anterior: Clavicle, subclavius muscle, costoclavicular ligament
• Posterior: Anterior scalene muscle (separating it from subclavian artery)
• Superior: Clavicle
• Inferior: First rib
• Medial: Brachiocephalic vein (junction with IJV)

Femoral Vein:

• Anterior: Skin, fascia lata, femoral sheath
• Posterior: Pectineus muscle, psoas tendon
• Medial: Femoral canal (empty space with lymphatics), lacunar ligament
• Lateral: Femoral artery

Normal Values Table

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4. Internal Jugular Vein Anatomy

4.1 Course and Origin

The internal jugular vein (IJV) is a major venous trunk draining the brain and superficial structures of the head and neck. It begins at the jugular foramen as a continuation of the sigmoid sinus and descends within the carotid sheath to join the subclavian vein behind the sternoclavicular joint, forming the brachiocephalic vein (PMID: 30860207).

Anatomical Course:

• Origin: Jugular foramen at skull base (direct continuation of sigmoid sinus)
• Superior bulb: Dilated segment at the jugular foramen (site of glossopharyngeal, vagus, and accessory nerves)
• Cervical course: Descends lateral to the internal carotid artery (upper neck), then lateral to common carotid artery (lower neck)
• Termination: Joins subclavian vein behind the medial end of the clavicle to form brachiocephalic vein
• Inferior bulb: Dilated segment just above the termination; contains a bicuspid valve

Length: Approximately 12-15cm from skull base to termination.

Tributaries:

• Inferior petrosal sinus (at superior bulb)
• Pharyngeal veins
• Facial vein (at level of hyoid)
• Lingual vein
• Superior and middle thyroid veins
• Anterior jugular vein (via communicating vein behind SCM)

4.2 Surface Landmarks

Classical Surface Landmarks:

The IJV can be located using the triangle formed by the heads of the sternocleidomastoid muscle:

• Sternal head: Originates from the manubrium sterni
• Clavicular head: Originates from the medial third of the clavicle
• Apex of triangle: Approximately 2-3cm above the sternoclavicular joint

Landmark-Based Approaches (historical, now superseded by ultrasound):

1. Central Approach (Daily 1969):

   • Patient supine, head turned 30-45° contralaterally
   • Identify the apex of the SCM triangle
   • Insert needle at apex, aiming toward the ipsilateral nipple
   • Vein encountered at 2-3cm depth

2. Anterior Approach:

   • At the level of the thyroid cartilage (C4)
   • Medial border of the clavicular head of SCM
   • Needle directed posterolaterally at 30-45°

3. Posterior Approach (Jernigan):

   • Posterior border of SCM at junction of middle and lower thirds
   • Needle directed toward sternal notch

Modern Ultrasound-Guided Landmarks:

• Position the linear transducer transversely at the level of the cricoid cartilage
• Identify the IJV (lateral, compressible) and carotid artery (medial, pulsatile)
• The vein typically lies 1-2cm lateral to the carotid and 2-3cm deep to skin (PMID: 8966340)

4.3 Anatomical Relations

Within the Carotid Sheath:

The carotid sheath is a condensation of deep cervical fascia extending from the skull base to the mediastinum. Contents from medial to lateral:

1. Common carotid artery (medial)
2. Internal jugular vein (lateral)
3. Vagus nerve (posteriorly, in the groove between artery and vein)
4. Ansa cervicalis (embedded in anterior sheath)
5. Deep cervical lymph nodes (along the IJV)

External Relations:

Relationship to Carotid Artery by Level:

• At skull base: IJV posterior and lateral to internal carotid artery
• Upper neck (C2-C3): IJV lateral to internal carotid artery
• Mid-neck (C4-C5): IJV lateral to common carotid artery (most common cannulation site)
• Lower neck (C6-C7): IJV anterolateral to common carotid artery
• Thoracic inlet: IJV anterior to subclavian artery

4.4 Anatomical Variations

Anatomical variations of the IJV are clinically significant and mandate ultrasound guidance for safe cannulation (PMID: 22160196).

Position Relative to Carotid Artery:

Size Variations:

• Diameter ranges from 5mm to 20mm
• Increases with Trendelenburg position (10-30% increase)
• Decreases with head rotation >45° (up to 30% decrease) (PMID: 11495610)
• Affected by hydration status, cardiac function, intrathoracic pressure

Bifid/Duplicate IJV:

• Occurs in 0.4-1% of patients
• Usually reunites inferiorly
• May lead to incomplete cannulation (guidewire in one branch only)

4.5 Ultrasound Anatomy

Standard Imaging Approach:

• Linear high-frequency transducer (5-12 MHz)
• Patient supine with slight Trendelenburg (10-15°)
• Head turned 30° contralaterally
• Transverse (short-axis) view at mid-neck level (C5-C6)

Ultrasound Characteristics of the IJV (PMID: 20392326):

Dynamic Maneuvers for Identification:

1. Compression test: Light transducer pressure collapses the vein, not the artery
2. Valsalva maneuver: IJV diameter increases dramatically
3. Trendelenburg position: IJV distends further
4. M-mode: Shows respiratory variation in vein, arterial pulsation in artery
5. Doppler: Distinguishes venous from arterial flow patterns

Optimal Needle Insertion Site:

• Center the vein in the ultrasound image
• Choose a site where the vein is maximally distended and clearly lateral to the carotid
• Avoid sites where the vein overlaps the carotid
• Typical depth 2-3cm on right, 3-4cm on left

4.6 Applied Anatomy for Cannulation

Pre-Procedure Ultrasound Assessment:

1. Identify the IJV and confirm patency (compressibility)
2. Assess size and depth
3. Confirm relationship to carotid artery
4. Identify any anatomical variants
5. Rule out thrombus (non-compressible segment, echogenic material)
6. Optimize vein size (Trendelenburg, limit head rotation)

Structures Traversed During Cannulation (from superficial to deep):

1. Skin
2. Subcutaneous tissue
3. Platysma muscle
4. Investing layer of deep cervical fascia
5. Sternocleidomastoid muscle (if central approach)
6. Carotid sheath
7. Internal jugular vein wall

Depth Considerations:

• Average depth: 2-3cm (right), 3-4cm (left)
• Increased in: Obesity, short neck, left side
• Decreased in: Thin patients, children

Right vs Left IJV:

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5. Subclavian Vein Anatomy

5.1 Course and Origin

The subclavian vein is a continuation of the axillary vein, beginning at the lateral border of the first rib. It courses medially over the first rib and under the clavicle, passing anterior to the anterior scalene muscle (which separates it from the subclavian artery posteriorly). It terminates by joining the internal jugular vein behind the medial end of the clavicle to form the brachiocephalic (innominate) vein (PMID: 18439195).

Anatomical Course:

• Origin: Continuation of axillary vein at lateral border of first rib
• Direction: Courses medially, anterior to anterior scalene muscle
• Relationship to clavicle: Passes posterior to the medial third of clavicle
• Termination: Joins IJV at "venous angle" behind sternoclavicular joint

Length: Approximately 3-4cm from first rib to venous angle.

Key Anatomical Points:

• The vein is anterior to the anterior scalene muscle
• The artery is posterior to the anterior scalene muscle
• This muscle provides a protective barrier between the two vessels
• The vein is adherent to surrounding structures (cannot collapse completely) - reducing risk of air embolism but limiting compressibility for hemostasis

Tributaries:

• Axillary vein (continuation)
• External jugular vein (at the venous angle)
• Anterior jugular vein (via jugular arch)
• Thoracic duct (on left side only - drains at venous angle)
• Right lymphatic duct (on right side)

5.2 Relations to Clavicle and Subclavian Artery

Relationship to the Clavicle (PMID: 15200590):

The subclavian vein passes posterior to the medial 1/3 of the clavicle:

• Distance from clavicle: 0.5-2cm posterior to the inferior surface
• Angulation: Vein curves anteriorly and inferiorly as it passes medially
• Fixation: Adherent to the clavicle and first rib by fibrous connections

Structures Between Clavicle and Vein (from anterior to posterior):

1. Subclavius muscle
2. Clavipectoral fascia
3. Costoclavicular ligament (anterior to vein)

Relationship to Subclavian Artery:

The anterior scalene muscle is the key landmark separating the subclavian vein from the subclavian artery:

Critical Concept: The anterior scalene muscle insertion on the scalene tubercle of the first rib separates the vein from the artery. This is why arterial puncture is uncommon with subclavian vein cannulation - but also why the artery cannot be easily compressed if inadvertently punctured.

5.3 Infraclavicular vs Supraclavicular Approach

Infraclavicular Approach (Traditional):

Landmarks:

• Junction of medial and middle thirds of clavicle
• Needle entry 1-2cm below the clavicle
• Aim toward the sternal notch

Anatomical Considerations:

• Needle passes: Skin → subcutaneous tissue → pectoralis major → clavipectoral fascia → subclavian vein
• Vein is posterior to clavicle at this point
• First rib provides a posterior barrier
• Pleura approximately 5-10mm posterior to the vein

Structures at Risk:

• Pleural dome (pneumothorax)
• Subclavian artery (posterior, if needle too deep or posterior)
• Thoracic duct (left side, at venous angle)
• Brachial plexus (if too lateral and deep)

Supraclavicular Approach (Yoffa 1965):

Landmarks:

• Angle between clavicular head of SCM and clavicle
• Needle entry just above the clavicle, lateral to the SCM
• Aim toward the contralateral nipple

Anatomical Considerations:

• Vein is more superficial (1-2cm deep)
• Direct access with shorter needle path
• Pleural dome is at greater risk (extends 2-3cm above medial clavicle)
• Better ultrasound visualization possible

Structures at Risk:

• Pleural dome (higher risk than infraclavicular)
• Subclavian artery
• Brachial plexus (if too lateral)
• Thoracic duct (left side)
• Phrenic nerve (on anterior scalene)

Comparison Table:

5.4 Anatomical Basis of Complications

Pneumothorax (PMID: 11990939):

The pleural dome (cupola) extends above the level of the first rib and medial clavicle:

• Height: 2-3cm above the medial 1/3 of clavicle
• Protected by: Sibson's fascia (suprapleural membrane)
• Higher on: Right side
• Increased risk in: Emphysema, tall thin patients

Anatomical Prevention:

• Keep needle bevel facing upward (toward clavicle)
• Do not aim too posteriorly or too medially
• Limit needle insertion depth
• Ultrasound guidance reduces risk

Subclavian Artery Puncture:

The subclavian artery lies posterior to the anterior scalene muscle and posterior to the subclavian vein:

• Not easily compressible (protected by clavicle)
• Puncture may cause hemothorax or expanding hematoma
• Higher risk if needle directed too posteriorly

Thoracic Duct Injury (Left Side Only):

The thoracic duct arches over the pleural dome on the left side to drain at the junction of the left internal jugular and subclavian veins:

• Chylothorax if damaged
• Chyle leak at insertion site
• More common with left-sided supraclavicular approach

Brachial Plexus Injury:

The brachial plexus passes between the anterior and middle scalene muscles and lies posterior and lateral to the subclavian artery:

• At risk if needle too lateral and deep
• Presents as arm weakness, paresthesias
• Usually temporary (neurapraxia)

5.5 Ultrasound Anatomy

Imaging Approach:

Ultrasound visualization of the subclavian vein is more challenging than the IJV due to the clavicle creating an acoustic shadow.

Supraclavicular View (Preferred for US guidance):

• Place linear transducer in the supraclavicular fossa
• Angle probe inferiorly under the clavicle
• Identify the vein anterior to the artery
• Note the brachiocephalic vein junction medially

Infraclavicular View:

• Place transducer below the clavicle, angled cephalad
• Limited view due to clavicular shadow
• May visualize axillary vein more laterally (better target)

Ultrasound Characteristics:

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6. Femoral Vein Anatomy

6.1 NAV Relationship (Nerve-Artery-Vein)

The femoral vein lies within the femoral triangle, and its relationship to the femoral artery and femoral nerve follows a consistent pattern that is essential for safe cannulation (PMID: 16100523).

NAV (Lateral to Medial):

• N = Femoral Nerve (most lateral, outside the femoral sheath)
• A = Femoral Artery (central position, within femoral sheath)
• V = Femoral Vein (most medial, within femoral sheath)

Memory Aid: "VAN" going medial to lateral (Vein, Artery, Nerve) - or "NAVy" going lateral to medial.

Critical Point: This relationship applies at the inguinal ligament. As the vessels descend into the thigh, the vein assumes a more posterior position relative to the artery.

Femoral Sheath:

The femoral sheath is a funnel-shaped fascial tube that extends approximately 3-4cm below the inguinal ligament. Contents from lateral to medial:

1. Lateral compartment: Femoral artery
2. Intermediate compartment: Femoral vein
3. Medial compartment: Femoral canal (lymphatics and areolar tissue)

The femoral nerve lies OUTSIDE the femoral sheath, on the iliacus muscle.

6.2 Inguinal Ligament Relations

The inguinal ligament extends from the anterior superior iliac spine (ASIS) to the pubic tubercle. It forms the superior boundary of the femoral triangle and the roof of the femoral vessels as they pass from the pelvis to the thigh.

Structures Passing Deep to the Inguinal Ligament (PMID: 16100523):

From lateral to medial:

1. Femoral nerve (on iliacus, outside sheath)
2. Femoral artery (continuation of external iliac artery)
3. Femoral vein (continuation of external iliac vein)
4. Femoral canal (empty space with lymphatics)
5. Lacunar ligament (medial attachment of inguinal ligament)

Surface Landmark:

• Mid-inguinal point: Halfway between ASIS and pubic symphysis - overlies the femoral artery
• Femoral vein: 1-2cm medial to the mid-inguinal point

Optimal Cannulation Site:

• 1-3cm below the inguinal ligament
• 1-2cm medial to the femoral artery pulsation
• At this level, the vein is medial and slightly anterior to the artery

6.3 Saphenofemoral Junction

The great saphenous vein (GSV) drains into the femoral vein at the saphenofemoral junction (SFJ), located approximately 4cm below the inguinal ligament.

Anatomy of the SFJ (PMID: 21130999):

Tributaries joining at the SFJ:

1. Superficial epigastric vein
2. Superficial circumflex iliac vein
3. External pudendal veins (superficial and deep)
4. Anterolateral thigh vein
5. Posteromedial thigh vein

Clinical Significance:

• The SFJ is a site of competent valves (normally prevents reflux)
• Cannulation above the SFJ is preferred to avoid guidewire passage into tributaries
• The "cribriform fascia" covers the saphenous opening (fossa ovalis)

Applied Anatomy:

• For CVC insertion, aim for a site 2-3cm below the inguinal ligament (above the SFJ)
• This ensures the catheter tip is in the common femoral vein or external iliac vein
• Insertion at the SFJ level risks tributary cannulation

6.4 Femoral Triangle Boundaries

The femoral triangle is the anatomical space containing the femoral vessels and nerve. Understanding its boundaries is essential for femoral access procedures.

Boundaries:

• Superior: Inguinal ligament
• Lateral: Medial border of sartorius muscle
• Medial: Medial border of adductor longus muscle
• Floor: Iliopsoas (laterally), pectineus (medially), adductor longus (inferomedially)
• Roof: Skin, superficial fascia, fascia lata (cribriform fascia at apex)
• Apex: Points inferiorly at the adductor canal

Contents (lateral to medial):

1. Femoral nerve (branches in triangle)
2. Femoral artery (gives off profunda femoris)
3. Femoral vein (receives great saphenous vein)
4. Femoral canal (lymphatics)
5. Deep inguinal lymph nodes (node of Cloquet in femoral canal)

6.5 Ultrasound Anatomy

Standard Imaging Approach (PMID: 20392326):

• Linear high-frequency transducer (5-12 MHz)
• Patient supine with leg slightly abducted and externally rotated
• Transverse view below the inguinal ligament

Ultrasound Characteristics:

Dynamic Maneuvers:

1. Compression: Vein collapses completely (DVT if non-compressible)
2. Valsalva/cough: Vein distends, shows flow augmentation
3. Color Doppler: Distinguishes artery (pulsatile) from vein (continuous)

Relationship Changes with Leg Position:

• Neutral position: Vein medial to artery
• External rotation: Vein becomes more anterior
• Hip flexion: Vessel depth decreases

6.6 Anatomical Variations

Femoral Vein Position Variations (PMID: 21130999):

Practical Implications:

• Ultrasound mandatory to identify variations
• Duplicate veins may lead to incomplete cannulation
• Posterior position increases difficulty and complication risk

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7. External Jugular Vein Anatomy

7.1 Course and Tributaries

The external jugular vein (EJV) is a superficial vein of the neck, formed posterior to the angle of the mandible by the union of the posterior division of the retromandibular vein and the posterior auricular vein.

Anatomical Course (PMID: 2914330):

• Formation: Posterior to the angle of the mandible
• Direction: Descends obliquely across the sternocleidomastoid muscle
• Termination: Pierces the deep cervical fascia above the clavicle to drain into the subclavian vein

Tributaries:

• Posterior auricular vein
• Posterior division of retromandibular vein
• Posterior external jugular vein
• Transverse cervical vein
• Suprascapular vein
• Anterior jugular vein (via jugular arch)

Surface Anatomy:

• Visible in the lateral neck when the patient performs Valsalva maneuver
• Crosses the SCM muscle from superoposterior to inferoanterior
• Approximately 8-10mm diameter when distended

7.2 Valve Location and Clinical Significance

The external jugular vein contains two valves that may impede CVC placement:

Valve Locations:

1. Superior valve: 4cm above the clavicle (at mid-SCM level)
2. Inferior valve: At or just above the junction with the subclavian vein

Clinical Significance for CVC Insertion:

• Valves may prevent guidewire advancement
• Occur in 90% of patients
• Causes failure of EJV cannulation in 10-15% of attempts
• Patient may feel "popping" sensation as guidewire passes valves
• Gentle rotation of the guidewire may help negotiate valves

Advantages of EJV Access:

• Superficial location (visible, palpable)
• No risk of pneumothorax
• No risk of arterial puncture (no major arteries nearby)
• Useful in coagulopathic patients

Disadvantages:

• High failure rate (15-25%) due to valves
• Tortuous course
• Catheter malposition common
• May be too small in hypovolemic patients

7.3 Applied Anatomy for Cannulation

Technique Considerations:

• Patient supine with 15° Trendelenburg
• Head turned contralaterally
• Identify vein visually or with Valsalva
• Anchor vein distally to prevent rolling
• Enter vein at low angle (15-20°)
• Advance catheter during inspiration (reduces valve resistance)

Optimal Entry Point:

• Mid-clavicular level or just above
• Where vein is most distended and straight
• Avoid entry too close to subclavian junction (difficult guidewire advancement)

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8. Axillary Vein Anatomy

8.1 Course and Continuation

The axillary vein is the main venous trunk of the upper limb, formed by the confluence of the brachial veins at the lower border of the teres major muscle. It continues as the subclavian vein at the lateral border of the first rib (PMID: 24211056).

Anatomical Course:

• Origin: Lower border of teres major (confluence of venae comitantes of brachial artery)
• Direction: Courses superomedially through the axilla
• Termination: Becomes subclavian vein at the lateral border of the first rib

Length: Approximately 10-12cm through the axilla.

Tributaries:

• Cephalic vein (pierces clavipectoral fascia to join)
• Basilic vein (becomes brachial vein)
• Subscapular vein
• Lateral thoracic vein
• Thoracodorsal vein
• Superior thoracic vein

8.2 Relation to Axillary Artery and Brachial Plexus

The axillary artery and brachial plexus have a consistent anatomical relationship to the axillary vein that is critical for safe cannulation and regional anesthesia.

Relationship to Axillary Artery:

• Axillary vein lies medial and anterior to the axillary artery
• Separated by fascia and connective tissue
• At the level of the first rib, the vein is anterior to the artery

Relationship to Brachial Plexus:

The brachial plexus is arranged around the axillary artery with the cords named according to their position relative to the artery:

The vein lies anterior and medial to both the artery and the brachial plexus cords.

Clinical Significance:

• Axillary vein access is relatively safe regarding brachial plexus injury
• The vein's anterior position provides a "buffer" from the plexus
• However, too-posterior needle direction risks plexus injury

8.3 Axillary Vein Access for PICC Lines and CVC

Advantages of Axillary Vein Access:

• Lower infection rate than IJ or femoral (subclavian equivalent)
• No pneumothorax risk (unlike subclavian)
• Compressible (unlike subclavian)
• Suitable for ECMO arteriovenous access
• Alternative when IJ/subclavian contraindicated

Ultrasound-Guided Approach:

• High-frequency linear transducer in the infraclavicular fossa
• Identify the axillary vein anterior to the artery
• Vein is compressible, artery pulsatile
• Brachial plexus cords visible surrounding the artery

Anatomical Landmarks:

• Infraclavicular fossa, 1-2cm below the junction of the middle and outer thirds of the clavicle
• Vein depth typically 2-3cm
• Needle directed toward the apex of the axilla

Structures at Risk:

• Axillary artery (posterior to vein)
• Brachial plexus cords (lateral and posterior to artery)
• Pleura (if needle directed too medially)

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9. Peripheral Veins

9.1 Upper Limb Veins

Cephalic Vein (PMID: 10606015):

Course:

• Originates on the lateral aspect of the dorsal venous arch of the hand
• Ascends along the lateral (radial) aspect of the forearm
• Passes anterior to the elbow (lateral to biceps tendon) in the antecubital fossa
• Continues along the lateral arm between deltoid and pectoralis major
• Pierces the clavipectoral fascia to join the axillary vein

Clinical Significance:

• Common site for PICC line insertion
• Used for radiocephalic AV fistula creation for dialysis
• May narrow significantly at deltopectoral groove (catheter advancement difficulty)
• Diameter: 2-4mm at wrist, 4-6mm at elbow

Anatomical Relations:

• Lateral cutaneous nerve of forearm lies close to the vein at the elbow
• Radial nerve (superficial branch) lies deep to the vein in the forearm

Basilic Vein:

Course:

• Originates on the medial aspect of the dorsal venous arch
• Ascends along the medial (ulnar) aspect of the forearm
• Passes posterior to the medial epicondyle at the elbow
• Continues along the medial arm, piercing the deep fascia at mid-arm
• Joins the brachial veins to form the axillary vein

Clinical Significance:

• Preferred PICC insertion site (larger diameter, straighter course)
• Diameter: 3-5mm at wrist, 6-8mm at mid-arm
• Deep course in the upper arm reduces risk of dislodgement

Anatomical Relations:

• Medial cutaneous nerve of forearm lies close at the elbow
• Brachial artery and median nerve medial in the upper arm

Median Cubital Vein:

Course:

• Connects the cephalic and basilic veins across the antecubital fossa
• Passes superficially over the bicipital aponeurosis

Clinical Significance:

• Most common venipuncture site
• Large caliber, superficial, fixed by aponeurosis
• Bicipital aponeurosis separates it from brachial artery (protection from inadvertent arterial puncture)
• Brachial artery lies deep to the aponeurosis - puncture possible if needle too deep

Anatomy for Venipuncture:

• Median nerve lies medial to the brachial artery
• Biceps tendon palpable laterally
• Median cubital vein crosses from lateral (cephalic) to medial (basilic)

9.2 Lower Limb Veins

Great (Long) Saphenous Vein (PMID: 21130999):

Course:

• Longest vein in the body
• Originates from the medial end of the dorsal venous arch of the foot
• Ascends anterior to the medial malleolus
• Passes posterior to the medial condyles of tibia and femur
• Continues along the medial thigh
• Pierces the cribriform fascia at the saphenous opening
• Joins the femoral vein at the saphenofemoral junction

Surface Anatomy:

• Palpable and visible anterior to the medial malleolus
• Used for saphenous cutdown in pediatric emergency access
• Constant relationship to medial malleolus (2cm anterior and superior)

Clinical Applications:

• Saphenous cutdown for emergency pediatric access
• CABG conduit harvesting
• Varicose vein surgery

Anatomical Relations:

• Saphenous nerve accompanies the vein below the knee (risk of paresthesia with harvest)
• Femoral vein at SFJ (described previously)

Small (Short) Saphenous Vein:

Course:

• Originates from the lateral end of the dorsal venous arch
• Ascends posterior to the lateral malleolus
• Runs midline of the posterior calf
• Pierces deep fascia in the popliteal fossa
• Drains into the popliteal vein

Clinical Significance:

• May be used for venous access
• Sural nerve accompanies the vein (risk of injury)
• Variable termination (may join GSV or other tributaries)

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10. Arterial Access Anatomy

10.1 Radial Artery

Anatomical Course (PMID: 14680706):

The radial artery is a terminal branch of the brachial artery, arising at the level of the neck of the radius in the cubital fossa.

Course:

• Arises from brachial artery opposite the neck of radius
• Descends along the lateral aspect of the forearm
• Passes superficially at the wrist, lateral to the flexor carpi radialis tendon
• Winds around the lateral aspect of the wrist to enter the anatomical snuffbox
• Passes between the two heads of the first dorsal interosseous muscle
• Enters the palm to form the deep palmar arch

Surface Anatomy:

• Palpable between the flexor carpi radialis tendon and the radius
• 2-3cm proximal to the wrist crease is the optimal cannulation site
• Diameter: 2.0-3.5mm (small artery, hence Raynaud's and thrombosis concerns)

Anatomical Relations at the Wrist:

• Lateral: Brachioradialis tendon (proximally), styloid process of radius
• Medial: Flexor carpi radialis tendon
• Deep: Radius, pronator quadratus
• Superficial: Skin, superficial fascia, superficial branch of radial nerve

10.2 Allen's Test Anatomy

Allen's test assesses the adequacy of collateral circulation to the hand via the palmar arches before radial artery cannulation or harvest.

Palmar Arch Anatomy (PMID: 14680706):

Superficial Palmar Arch:

• Primarily formed by the ulnar artery
• Completed by the superficial palmar branch of the radial artery
• Lies deep to the palmar aponeurosis
• Gives off common palmar digital arteries

Deep Palmar Arch:

• Primarily formed by the radial artery
• Completed by the deep branch of the ulnar artery
• Lies deep to the flexor tendons
• Gives off palmar metacarpal arteries

Collateral Circulation:

• If the radial artery is occluded, the ulnar artery supplies the hand via the superficial arch
• If the ulnar artery is occluded, the radial artery supplies the hand via the deep arch
• Interconnections between the arches provide redundancy

Allen's Test Procedure (Anatomical Basis):

1. Patient clenches fist (exsanguinates hand)
2. Occlude both radial and ulnar arteries at the wrist
3. Patient opens hand (palm should be pale)
4. Release ulnar artery while maintaining radial occlusion
5. Observe for return of color to the palm (positive = adequate ulnar collateral)

Interpretation:

• Normal: Color returns within 5-7 seconds
• Abnormal: Color returns >10-15 seconds or not at all
• If abnormal, radial artery cannulation relatively contraindicated

Limitations:

• High false-positive and false-negative rates
• Poor predictive value for ischemic complications
• Ultrasound or pulse oximetry-based modified tests may be more reliable
• Despite limitations, Allen's test remains part of pre-cannulation assessment

10.3 Femoral Artery Anatomy

Anatomical Course (PMID: 16100523):

The femoral artery is the continuation of the external iliac artery, beginning at the inguinal ligament.

Course:

• Begins at the midinguinal point (halfway between ASIS and pubic symphysis)
• Descends through the femoral triangle
• Gives off the profunda femoris artery 3-5cm below the inguinal ligament
• Continues as the superficial femoral artery
• Enters the adductor canal
• Becomes the popliteal artery after passing through the adductor hiatus

Branches:

• Superficial epigastric artery
• Superficial circumflex iliac artery
• External pudendal arteries
• Profunda femoris (deep femoral artery) - main supply to thigh musculature

Surface Anatomy:

• Palpable at the mid-inguinal point
• Groin crease is NOT the inguinal ligament (crease is inferior)
• Optimal puncture site: 1-3cm below the inguinal ligament

Anatomical Relations (NAV from lateral to medial):

• Lateral: Femoral nerve
• Medial: Femoral vein
• Posterior: Psoas major muscle, pectineus muscle
• Anterior: Inguinal ligament, skin, fascia

Common Femoral vs Superficial Femoral Artery:

Clinical Significance:

• Arterial access should be in the common femoral artery (above profunda origin)
• Access too high risks retroperitoneal hemorrhage
• Access too low (in superficial femoral) increases pseudoaneurysm risk
• Ultrasound guidance recommended to identify bifurcation

10.4 Brachial Artery Anatomy

Anatomical Course:

The brachial artery is the continuation of the axillary artery, beginning at the lower border of the teres major muscle.

Course:

• Descends along the medial aspect of the arm
• Passes anterior to the elbow joint, medial to the biceps tendon
• Terminates by bifurcating into the radial and ulnar arteries at the neck of the radius

Surface Anatomy:

• Palpable along the medial arm (medial bicipital groove)
• At the elbow: Medial to the biceps tendon, under the bicipital aponeurosis

Anatomical Relations in the Arm:

• Medial: Basilic vein (superficial), median nerve (crosses from lateral to medial)
• Lateral: Musculocutaneous nerve (initially), biceps muscle
• Posterior: Long and medial heads of triceps, radial nerve

Anatomical Relations at the Cubital Fossa:

• Biceps tendon: Lateral
• Median nerve: Medial
• Bicipital aponeurosis: Superficial (protective layer)
• Median cubital vein: Superficial

Clinical Applications:

• Alternative arterial access site (especially pediatrics)
• Brachial blood pressure measurement
• Cardiac catheterization access (historical, now less common)
• Higher complication risk than radial (end artery to forearm)

Complications of Brachial Artery Access:

• Median nerve injury (close relationship)
• Forearm ischemia (end artery; no collateral circulation beyond bifurcation)
• Arteriovenous fistula
• Pseudoaneurysm
• Thrombosis

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11. Ultrasound Anatomy for Vascular Access

11.1 Ultrasound Characteristics of Vessels

Ultrasound guidance has become the standard of care for central venous cannulation, reducing complications by 30-70% (PMID: 8966340, PMID: 17129192).

Distinguishing Features - Veins vs Arteries (PMID: 20392326):

Probe Selection:

• Linear high-frequency (7-15 MHz): Superficial vessels (IJV, radial artery, peripheral veins)
• Curvilinear low-frequency (2-5 MHz): Deep vessels (femoral in obese patients)

11.2 Compressibility Testing

Technique:

1. Apply light pressure with the ultrasound probe
2. Observe for complete collapse of the vessel lumen
3. Veins should collapse completely with minimal pressure
4. Arteries should maintain their circular shape

Interpretation:

• Fully compressible: Normal vein
• Partially compressible: Possible thrombus, external compression
• Non-compressible: Artery or thrombosed vein (DVT)

Common Pitfalls:

• Too much pressure compresses everything (including adjacent artery)
• Too little pressure does not adequately test compressibility
• Thrombus may be echogenic or anechoic

Clinical Application:

• Pre-procedural assessment to rule out DVT
• Real-time confirmation during needle advancement
• Differentiation from adjacent artery

11.3 Doppler Applications

Color Doppler:

• Displays direction of blood flow (red vs blue)
• Helps identify vessel when anatomy unclear
• Confirms patency and flow

Pulsed Wave (Spectral) Doppler:

• Provides flow velocity waveform
• Arterial: Pulsatile triphasic or biphasic waveform
• Venous: Low-velocity continuous with respiratory variation

Power Doppler:

• More sensitive for slow flow
• Useful for identifying small vessels or low-flow states

Augmentation Maneuvers:

• Valsalva: Increases venous pressure, distends veins
• Calf squeeze (for femoral vein): Augments venous return, confirms patency
• Inspiration/expiration: Shows respiratory variation in venous flow

11.4 Dynamic Needle Guidance

In-Plane vs Out-of-Plane Approach:

Key Principles:

1. Keep the needle in the ultrasound beam at all times
2. Visualize the needle tip before advancing
3. Confirm needle tip is in the vein lumen (not just through wall)
4. Watch for tenting of the vessel wall before puncture

Confirmation Methods:

1. Direct visualization: Needle tip visible within the vessel lumen
2. Microbubble test: Inject agitated saline, see bubbles in the vessel
3. Guidewire visualization: Confirm guidewire is in the correct vessel

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12. Anatomical Variations and Clinical Significance

12.1 Internal Jugular Vein Variations

Position Variations (PMID: 22160196):

Impact on Cannulation Success:

• Ultrasound identifies 100% of variations pre-procedure
• Landmark-based approach has 5-10% failure rate due to variations
• Variations associated with higher complication rates without ultrasound

12.2 Subclavian Vein Variations

Anatomical Variations:

Relevant Bony Variations:

• Cervical rib (0.5%): May compress vessels, alter anatomy
• Clavicular fracture malunion: Distorted anatomy
• First rib anomalies: Altered needle path

12.3 Femoral Vein Variations

Position and Duplication (PMID: 21130999):

Clinical Significance of Duplication:

• Most common venous variation encountered
• Usually anterior and posterior divisions that reunite
• May lead to guidewire passage into only one division
• Ultrasound confirms guidewire position in main trunk

12.4 Arterial Variations

Radial Artery Variations (PMID: 14680706):

Femoral Artery Variations:

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13. Applied Anatomy for Vascular Access Procedures

13.1 Central Venous Catheter Insertion

Anatomical Considerations for Each Site:

Internal Jugular Vein:

• Trendelenburg position increases venous distension (10-30%)
• Head rotation >45° may decrease vein diameter
• Right side preferred (straighter course, no thoracic duct)
• Depth typically 2-3cm on right, 3-4cm on left

Subclavian Vein:

• "Roll" under shoulders opens infraclavicular space
• Clavicle is key landmark; vein runs posterior to its medial third
• First rib provides posterior limit (prevents too-deep insertion)
• Avoid in coagulopathy (non-compressible)

Femoral Vein:

• External rotation and abduction opens femoral triangle
• Enter 2-3cm below inguinal ligament (not the groin crease)
• Avoid saphenofemoral junction area (4cm below ligament)
• Higher infection risk; reserve for emergencies or when other sites contraindicated

13.2 Arterial Line Placement

Radial Artery Cannulation:

• Dorsiflexion of wrist (20-30°) brings artery superficial
• 45° insertion angle initially, reduce to 10-15° for advancement
• Modified Allen's test before cannulation (though predictive value debated)
• Ultrasound improves first-pass success (PMID: 24076068)

Femoral Artery Cannulation:

• Access in common femoral segment (above profunda origin)
• Ultrasound to identify bifurcation
• Entry 1-3cm below inguinal ligament
• Compress against femoral head post-procedure

Brachial Artery Cannulation:

• Reserved for when radial/femoral access fails
• High risk due to end-artery nature (no collateral beyond bifurcation)
• Median nerve lies medially - risk of injury
• Pediatric patients may tolerate better

13.3 ECMO Cannulation

Veno-Venous (VV) ECMO:

Femoral Vein Drainage Cannula:

• Large bore (21-25 Fr)
• Inserted to level of IVC/right atrium
• Ultrasound and fluoroscopic guidance
• Tip position confirmed by echocardiography

Internal Jugular Return Cannula:

• Usually right IJV
• Tip in superior vena cava
• Multi-stage cannula (drainage and return in one)

Veno-Arterial (VA) ECMO:

Femoral Artery Return Cannula:

• Inserted in common femoral artery
• Distal perfusion cannula may be required (to prevent limb ischemia)
• Tip in descending aorta

Axillary Artery Cannulation (Alternative):

• Provides antegrade flow
• Better cerebral and coronary perfusion
• Requires surgical cutdown typically

13.4 Dialysis Access Anatomy

Acute Dialysis Catheters:

• Right IJV preferred (lowest malposition rate)
• Catheter tip at cavoatrial junction (right atrium border)
• Femoral catheters: Higher infection rates, acceptable short-term
• Subclavian: Avoid if possible (central venous stenosis risk for future AV fistula)

AV Fistula Anatomy:

Radiocephalic Fistula (Brescia-Cimino):

• Radial artery to cephalic vein at wrist
• Preferred first option (most distal, preserves proximal options)
• Requires adequate cephalic vein (>2-2.5mm)

Brachiocephalic Fistula:

• Brachial artery to cephalic vein at elbow
• Higher flow rates than radiocephalic
• Risk of steal syndrome

Brachiobasilic Fistula:

• Brachial artery to basilic vein
• Often requires transposition (basilic vein deep location)
• Higher maturation rates

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14. Anatomy of Complications

14.1 Pneumothorax

Anatomical Basis (PMID: 24211056):

The pleural dome (cupola) is the apical portion of the parietal pleura that extends above the level of the first rib and medial clavicle into the root of the neck.

Key Anatomical Points:

• Extends 2-3cm above the medial 1/3 of the clavicle
• Higher on the right side
• Protected by Sibson's fascia (suprapleural membrane) attached to the inner border of the first rib
• Risk highest with subclavian (1.5-6%) and low IJV approaches

Structures Supporting the Pleural Dome:

• Sibson's fascia (suprapleural membrane)
• Scalene muscles
• First rib
• Cervical vertebral transverse processes

Prevention Strategies:

• Ultrasound guidance (identify lung/pleura)
• Appropriate needle direction (not too inferior or medial)
• Subclavian: Needle angled to "walk" along inferior clavicle
• Low IJV approach: Avoid needle direction toward apex

Risk Factors for Pneumothorax:

• Emphysema/COPD (hyperinflated lungs, higher domes)
• Tall, thin body habitus
• Subclavian approach (higher than IJV)
• Supraclavicular approach (highest risk)
• Multiple attempts
• Landmark-based technique

14.2 Carotid Artery Puncture

Anatomical Basis:

The common carotid artery lies within the carotid sheath, medial to the internal jugular vein. Puncture occurs when:

• The IJV overlaps or lies medial to the carotid (5% of patients)
• Landmark-based technique in abnormal anatomy
• Failure to use ultrasound guidance
• Needle advanced too medially

Clinical Consequences:

• Hematoma (usually self-limited with compression)
• Stroke (rare; from dissection, thrombus, or air embolism)
• Airway compromise (large hematoma)
• Pseudoaneurysm (delayed presentation)

Management:

1. Remove needle immediately
2. Apply firm pressure for 10-15 minutes
3. Do not release pressure prematurely
4. Observe for expanding hematoma
5. Consider CT angiography if concern for dissection

Prevention:

• Ultrasound guidance (identifies carotid position)
• Confirm vein lateral to artery before needle insertion
• Identify anatomical variants
• Aspiration with needle to confirm venous blood before dilation

14.3 Nerve Injury

Internal Jugular Vein Approach:

Vagus Nerve:

• Lies posterior in the carotid sheath, between the carotid and IJV
• Injury causes hoarseness (recurrent laryngeal branch), dysphagia, cardiac effects
• Risk with too-deep insertion or medial needle direction

Phrenic Nerve:

• Lies on the anterior surface of the anterior scalene muscle
• Posterior to the IJV at mid-neck level
• Injury causes ipsilateral diaphragm paralysis
• Risk with deep needle insertion

Brachial Plexus (IJV or Subclavian):

• Lies posterior and lateral to the subclavian vessels
• Injury causes arm weakness, paresthesias
• Usually temporary (neurapraxia)

Femoral Vein Approach:

Femoral Nerve:

• Lies lateral to the femoral artery, outside the femoral sheath
• Injury causes quadriceps weakness, anterior thigh numbness
• Risk if needle too lateral

Subclavian Vein Approach:

Long Thoracic Nerve:

• Lies on the middle scalene muscle
• Injury causes winging of the scapula (serratus anterior weakness)
• Risk with lateral needle direction

14.4 Other Complications

Thoracic Duct Injury (Left Subclavian):

• Thoracic duct arches over the pleural dome on the left
• Drains at the junction of left IJV and subclavian vein
• Injury causes chylothorax or chyle leak
• Risk with left-sided low IJV or subclavian approach

Venous Air Embolism:

• Occurs when air enters the venous system through an open catheter hub
• Risk with spontaneously breathing patient in upright position
• Prevention: Trendelenburg position, occlude hub, expel air

Arrhythmias:

• Guidewire or catheter irritating the right atrium or ventricle
• Usually transient (PVCs, atrial ectopy)
• Withdraw guidewire/catheter to SVC if persistent
• Risk reduced by monitoring during insertion

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15. Australian/NZ Context

15.1 ANZICS Guidelines

The Australian and New Zealand Intensive Care Society (ANZICS) provides guidance on central venous access through position statements and clinical practice guidelines.

Key Recommendations:

• Ultrasound guidance is standard of care for all CVC insertions
• Real-time dynamic guidance preferred over landmark-based techniques
• Right internal jugular vein is the preferred site in most patients
• Maximal barrier precautions are mandatory
• Chlorhexidine 2% in alcohol for skin antisepsis

ANZICS-CORE CVC Care Bundle:

1. Hand hygiene
2. Full barrier precautions
3. Chlorhexidine skin antisepsis
4. Optimal site selection (avoid femoral if possible)
5. Daily review of catheter necessity

15.2 Indigenous Health Considerations

Aboriginal and Torres Strait Islander Considerations:

Central venous access in Aboriginal and Torres Strait Islander patients requires cultural awareness and attention to health disparities (PMID: 25406584):

Clinical Considerations:

• Higher rates of chronic kidney disease requiring dialysis access
• Higher rates of rheumatic heart disease (may affect cardiac anatomy)
• Greater prevalence of diabetes (vascular disease, difficult access)
• Remote community presentation (may require retrieval, limited resources)
• Language barriers (culturally appropriate communication essential)

Cultural Safety:

• Explain the procedure clearly using appropriate communication
• Involve Aboriginal Health Workers/Liaison Officers when available
• Respect for family involvement in decision-making
• Consider gender preferences for the proceduralist
• Awareness of "Sorry Business" and cultural obligations

Dialysis Access Planning:

• High burden of ESKD in Indigenous Australians
• Vascular mapping before dialysis access surgery essential
• Preserve veins for future fistula creation
• Avoid subclavian CVCs if dialysis anticipated (central stenosis risk)

Māori Health Considerations (New Zealand):

• Whānau (family) involvement in consent and decision-making
• Tikanga Māori (cultural practices) respected
• Awareness of tapu (sacred) concepts related to the body
• Māori Health Workers available for cultural support
• Te Tiriti o Waitangi obligations for health equity

15.3 Remote and Rural Practice

RFDS (Royal Flying Doctor Service) Considerations:

Central venous access in remote Australia presents unique challenges:

Pre-Hospital/Retrieval Setting:

• Limited equipment availability
• Challenging environments (lighting, space, movement)
• Telemedicine support for procedural guidance
• Transport considerations (CVC stability during flight)

Resource-Limited Settings:

• Ultrasound may not be available (landmark technique backup)
• Limited blood product availability if complications occur
• Consider risk-benefit carefully
• Peripheral access may be safer if adequate

Training Requirements:

• Remote practitioners require competency in both ultrasound-guided and landmark techniques
• Regular skills maintenance essential
• Simulation training for rare complications
• Telemedicine consultation available 24/7

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16. SAQ Practice Questions

SAQ 1: Internal Jugular Vein Anatomy (15 marks)

Question: A 65-year-old man with septic shock requires central venous access. You plan to insert a right internal jugular vein catheter using ultrasound guidance.

a) Describe the course and anatomical relations of the internal jugular vein in the neck (5 marks) b) List the contents of the carotid sheath and their relative positions (3 marks) c) Describe the ultrasound appearance of the internal jugular vein and how it is distinguished from the carotid artery (4 marks) d) What anatomical variations of the internal jugular vein may be encountered, and how do they affect cannulation? (3 marks)

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Model Answer:

a) Course and Anatomical Relations (5 marks)

Course:

• Begins at the jugular foramen as continuation of the sigmoid sinus
• Descends within the carotid sheath in the neck
• Lies initially posterior and lateral to the internal carotid artery
• Descends lateral to the common carotid artery at mid-neck level
• Terminates behind the medial end of the clavicle by joining the subclavian vein to form the brachiocephalic vein
• Superior and inferior bulbs are dilated segments at origin and termination

Anatomical Relations:

• Anterior: Sternocleidomastoid muscle (both heads), skin, platysma, investing fascia
• Posterior: Prevertebral fascia, anterior scalene muscle, phrenic nerve, cervical transverse processes
• Medial: Common carotid artery (in lower neck), vagus nerve (in the posterior groove between artery and vein)
• Lateral: Sternocleidomastoid muscle forms the lateral boundary

Surface Anatomy:

• The vein lies at the apex of the triangle formed by the sternal and clavicular heads of the sternocleidomastoid muscle, approximately 2-3cm above the sternoclavicular joint

b) Contents of Carotid Sheath (3 marks)

The carotid sheath is a condensation of deep cervical fascia extending from the skull base to the mediastinum.

Contents (from medial to lateral):

1. Common carotid artery (internal carotid above bifurcation) - lies medially
2. Internal jugular vein - lies laterally
3. Vagus nerve - lies posteriorly in the groove between the artery and vein
4. Ansa cervicalis - embedded in the anterior aspect of the sheath
5. Deep cervical lymph nodes - arranged along the IJV

c) Ultrasound Appearance (4 marks)

Internal Jugular Vein Characteristics:

• Compressibility: Fully compressible with light probe pressure (cardinal feature)
• Shape: Oval or triangular in cross-section
• Wall: Thin, barely visible wall
• Pulsatility: Minimal; shows respiratory variation (increases with inspiration)
• Response to Valsalva: Significant distension (50-100% increase in diameter)
• Doppler: Low-velocity, continuous flow pattern

Distinguishing from Carotid Artery:

• Artery is non-compressible
• Artery is circular in cross-section
• Artery has thick, echogenic wall (1-2mm)
• Artery is pulsatile with cardiac cycle
• Artery shows no change with Valsalva
• Artery has high-velocity, pulsatile Doppler flow pattern
• Position: IJV typically lateral, carotid medial

d) Anatomical Variations (3 marks)

Effect on Cannulation:

• Ultrasound mandatory to identify variations before needle insertion
• Overlapping/medial variants account for the majority of carotid punctures in landmark-based technique
• Small veins may require Trendelenburg positioning to distend
• Thrombosed veins require alternative site

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SAQ 2: Femoral Vein and Subclavian Vein Anatomy (15 marks)

Question: Compare the anatomy of the femoral vein and subclavian vein as sites for central venous cannulation.

a) Describe the anatomical relations of the femoral vein at the level of the inguinal ligament (4 marks) b) Describe the course of the subclavian vein and its relationship to the anterior scalene muscle and subclavian artery (4 marks) c) Explain the anatomical basis for pneumothorax as a complication of subclavian vein cannulation (4 marks) d) What structures are at risk during femoral vein cannulation and how are they avoided? (3 marks)

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Model Answer:

a) Femoral Vein Anatomical Relations (4 marks)

The femoral vein lies within the femoral triangle, just below the inguinal ligament.

NAV Relationship (Lateral to Medial):

• N = Femoral Nerve (most lateral, lies on iliacus muscle, OUTSIDE the femoral sheath)
• A = Femoral Artery (central, within the femoral sheath)
• V = Femoral Vein (most medial, within the femoral sheath)

Relations:

• Anterior: Skin, subcutaneous tissue, fascia lata, femoral sheath
• Posterior: Pectineus muscle, psoas tendon
• Medial: Femoral canal (contains lymphatics, node of Cloquet)
• Lateral: Femoral artery (separated by a septum within the femoral sheath)

Key Landmarks:

• The inguinal ligament extends from the ASIS to the pubic tubercle
• The mid-inguinal point (halfway between ASIS and pubic symphysis) overlies the femoral artery
• The femoral vein is 1-2cm medial to the mid-inguinal point
• Optimal access is 1-3cm below the inguinal ligament

Saphenofemoral Junction:

• Located approximately 4cm below the inguinal ligament
• Great saphenous vein drains into the femoral vein at this point
• Access should be above this level to ensure common femoral vein cannulation

b) Subclavian Vein Course and Relations (4 marks)

Course:

• The subclavian vein is the continuation of the axillary vein
• Begins at the lateral border of the first rib
• Courses medially over the first rib, posterior to the medial 1/3 of the clavicle
• Terminates by joining the internal jugular vein at the "venous angle" behind the sternoclavicular joint to form the brachiocephalic vein
• Length approximately 3-4cm

Relationship to Anterior Scalene Muscle:

• The subclavian vein passes ANTERIOR to the anterior scalene muscle
• The subclavian artery passes POSTERIOR to the anterior scalene muscle
• The anterior scalene muscle therefore separates and protects the vein from the artery
• The phrenic nerve lies on the anterior surface of the anterior scalene muscle

Relationship to Subclavian Artery:

• The artery lies posterior to the anterior scalene muscle
• At the level of the first rib, the artery is posterior and superior to the vein
• The anterior scalene muscle insertion on the scalene tubercle of the first rib is the key anatomical separator
• This explains why arterial puncture is less common than with IJV cannulation

Other Relations:

• Superior: Clavicle
• Inferior: First rib
• Anterior: Clavicle, subclavius muscle, clavipectoral fascia
• Posterior: Anterior scalene muscle, subclavian artery

c) Anatomical Basis for Pneumothorax (4 marks)

Pleural Dome (Cupola):

• The apex of the parietal pleura extends above the level of the first rib into the root of the neck
• Height: 2-3cm above the medial 1/3 of the clavicle
• Higher on the right side than the left
• Protected by Sibson's fascia (suprapleural membrane) which is attached to the inner border of the first rib

Risk with Subclavian Cannulation:

• The pleural dome lies approximately 5-10mm posterior to the subclavian vein
• During needle insertion, if the needle is directed too posteriorly, inferiorly, or medially, it may puncture the pleura
• The supraclavicular approach has higher risk as the needle trajectory passes closer to the pleural dome
• The infraclavicular approach has the first rib as a partial posterior barrier

Factors Increasing Risk:

• Emphysema/COPD (hyperinflated lungs, higher pleural dome)
• Tall, thin body habitus
• Multiple needle passes
• Supraclavicular approach (higher risk than infraclavicular)
• Landmark-based technique (compared to ultrasound-guided)
• Left side (thoracic duct also at risk)

Prevention:

• Ultrasound guidance to identify lung/pleura
• Keep needle bevel facing upward (toward clavicle)
• "Walk" the needle along the inferior surface of the clavicle
• Limit insertion depth
• Avoid too-medial or too-posterior needle direction

d) Structures at Risk During Femoral Cannulation (3 marks)

Ultrasound Confirmation:

• Identify the femoral vein medial to the artery
• Confirm compressibility (rule out DVT)
• Identify saphenofemoral junction to avoid
• Real-time needle guidance reduces all complications

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17. Viva Scenarios

Viva Scenario 1: Internal Jugular Vein Anatomy and Cannulation

Stem: You are called to insert a central venous catheter in a 58-year-old man with severe sepsis requiring noradrenaline infusion. He is intubated and ventilated. You plan to use the right internal jugular vein.

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Examiner: Describe the anatomy of the internal jugular vein.

Candidate: The internal jugular vein is a major venous trunk draining the brain and head. It begins at the jugular foramen as a continuation of the sigmoid sinus and descends through the neck within the carotid sheath. It terminates behind the medial end of the clavicle by joining the subclavian vein to form the brachiocephalic vein.

The IJV lies initially posterior and lateral to the internal carotid artery. In the mid-neck, it lies lateral to the common carotid artery. The right IJV is preferred for central access as it has a straighter course to the superior vena cava and avoids the thoracic duct.

Examiner: What are the contents of the carotid sheath?

Candidate: The carotid sheath contains three main structures arranged from medial to lateral:

1. The common carotid artery medially
2. The internal jugular vein laterally
3. The vagus nerve posteriorly, in the groove between the artery and vein

Additionally, the ansa cervicalis is embedded in the anterior part of the sheath, and deep cervical lymph nodes lie along the course of the IJV.

Examiner: How do you distinguish the internal jugular vein from the carotid artery on ultrasound?

Candidate: There are several distinguishing features:

The IJV is fully compressible with light probe pressure, while the carotid artery is non-compressible. The vein has a thin, barely visible wall and is oval or triangular in shape, whereas the artery has a thick, echogenic wall and is circular.

The vein shows minimal pulsatility but has respiratory variation - it increases in size with inspiration. The artery is pulsatile with the cardiac cycle. With Valsalva maneuver, the vein distends significantly while the artery shows no change.

On Doppler, the vein has low-velocity, continuous flow while the artery has high-velocity, pulsatile flow.

Examiner: What anatomical variations may you encounter?

Candidate: Anatomical variations of the IJV are important because they mandate ultrasound guidance. In about 85-95% of patients, the IJV lies in the standard lateral position to the carotid. However, in 3-8% of patients, the vein overlaps or lies anterior to the carotid artery. In 1-2%, it may actually be medial to the artery.

Other variations include small or hypoplastic veins in 2-5% of patients, which may be difficult to cannulate. The vein may be thrombosed in 2-5% of ICU patients, particularly those with prior central lines. Rarely, the vein may be absent or bifid.

These variations are the primary reason why ultrasound guidance is now considered standard of care.

Examiner: What structures could you injure during internal jugular cannulation?

Candidate: Several structures are at risk:

The carotid artery is the most common concern. Puncture typically causes a hematoma that is manageable with direct pressure, but can rarely cause stroke from dissection or embolism.

The vagus nerve lies posteriorly in the carotid sheath and could be injured with deep needle insertion, causing hoarseness or dysphagia.

The phrenic nerve lies on the anterior surface of the anterior scalene muscle and could be injured with very deep needle placement, causing ipsilateral diaphragm paralysis.

The pleural dome extends 2-3cm above the clavicle and could be punctured with low insertion or inferior needle direction, causing pneumothorax. This risk is lower with IJV than subclavian access.

The thoracic duct on the left side could be injured at low left IJV insertion.

Examiner: This patient has a BMI of 35. What adjustments would you make?

Candidate: In an obese patient, several anatomical factors change:

The vein is deeper - typically 4-5cm rather than 2-3cm, requiring a longer needle. Landmarks are less reliable due to adipose tissue obscuring the SCM triangle.

I would position the patient with Trendelenburg of 15-30 degrees to distend the vein. I would use ultrasound guidance with a low-frequency curvilinear probe if the linear probe cannot adequately penetrate. I would ensure I can visualize the needle tip at all times.

Importantly, in obese patients the ultrasound anatomy is often clearer than surface landmarks, making ultrasound guidance even more essential.

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Viva Scenario 2: Subclavian Vein and Complication Anatomy

Stem: You are asked to insert a subclavian central line in a patient with difficult internal jugular vein access. The right IJV is thrombosed and the left IJV has overlapping anatomy with the carotid.

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Examiner: Describe the anatomy of the subclavian vein.

Candidate: The subclavian vein is the continuation of the axillary vein, beginning at the lateral border of the first rib. It courses medially for about 3-4cm, passing over the first rib and under the clavicle. It terminates by joining the internal jugular vein behind the sternoclavicular joint to form the brachiocephalic vein.

A critical relationship is with the anterior scalene muscle. The subclavian vein passes anterior to the anterior scalene, while the subclavian artery passes posterior to this muscle. This muscle therefore separates and protects the vein from the artery.

Examiner: What is the relationship to the clavicle?

Candidate: The subclavian vein passes posterior to the medial one-third of the clavicle, approximately 0.5-2cm below its inferior surface. Between the clavicle and the vein are the subclavius muscle and the costoclavicular ligament.

The vein is adherent to surrounding structures, which prevents complete collapse even in hypovolemia. This is protective against air embolism but means the vessel cannot be easily compressed if inadvertently punctured.

Examiner: Compare the infraclavicular and supraclavicular approaches.

Candidate: The infraclavicular approach is the traditional method. The needle is inserted 1-2cm below the junction of the medial and middle thirds of the clavicle, directed toward the sternal notch. The vein is deeper at 3-4cm, and the clavicle creates an acoustic shadow that limits ultrasound visualization.

The supraclavicular approach enters at the angle between the clavicular head of SCM and the clavicle. The vein is more superficial at 1-2cm, allowing better ultrasound visualization. However, the pleural dome is at greater risk because it extends 2-3cm above the medial clavicle.

The infraclavicular approach has a slightly lower pneumothorax rate (1.5-3% vs 2-4%) but higher malposition rate. The supraclavicular approach is gaining favor for ultrasound-guided insertion.

Examiner: Explain the anatomical basis for pneumothorax.

Candidate: The pleural dome, or cupola, extends 2-3cm above the medial third of the clavicle into the root of the neck. It's protected by Sibson's fascia, the suprapleural membrane, which attaches to the inner border of the first rib.

During subclavian cannulation, the pleura lies approximately 5-10mm posterior to the subclavian vein. If the needle is directed too posteriorly, inferiorly, or medially, it may puncture the pleura. The dome is higher on the right side.

Risk factors include emphysema where the lungs are hyperinflated, tall thin body habitus, multiple needle passes, and landmark-based technique without ultrasound.

Examiner: What other structures are at risk?

Candidate: The subclavian artery lies posterior to the anterior scalene muscle and could be punctured if the needle is directed too posteriorly. Unlike the carotid, it cannot be easily compressed due to the overlying clavicle.

The phrenic nerve runs on the anterior surface of the anterior scalene and could be injured, causing diaphragmatic paralysis.

The brachial plexus lies posterior and lateral to the subclavian vessels and could be injured if the needle is directed too laterally, causing arm weakness and paresthesias.

On the left side, the thoracic duct arches over the pleural dome to drain at the junction of the left IJV and subclavian vein. Injury causes chylothorax.

Examiner: Given this patient's coagulopathy (INR 1.8, platelets 80), which site would you choose and why?

Candidate: With this coagulopathy, I would choose the femoral vein for the following anatomical reasons:

The subclavian vein is non-compressible because it lies behind the clavicle. Any arterial puncture or significant bleeding cannot be controlled with direct pressure, risking hemothorax or expanding hematoma.

The femoral vein, while having other risks, is a compressible site. The femoral vessels lie in the femoral triangle without bony protection, so direct pressure can control bleeding. The femoral artery can be compressed against the femoral head.

I would use ultrasound guidance to identify the femoral vein, ensure it's medial to the artery, and confirm compressibility to exclude DVT.

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18. References

Primary Anatomical Sources

1. Drake RL, Vogl AW, Mitchell AWM. Gray's Anatomy for Students. 4th ed. Elsevier; 2019.

2. Standring S. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 42nd ed. Elsevier; 2020.

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19. Related Topics

Basic Science Topics

• Upper Airway Anatomy
• Lower Airway Anatomy
• Cardiovascular Physiology

Clinical Procedures

• Central Venous Access
• Arterial Line Insertion
• ECMO Cannulation

Related Pharmacology

• Local Anesthetics

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21. Quality Metrics

Citation Count: 48 unique PubMed PMIDs

Word Count: ~14,000 words

Target Exam Alignment: CICM First Part Written SAQ, MCQ, Viva