Strabismus Surgery - Oculocardiac Reflex, PONV, and Suxamethonium Alternatives

Quick Answer

What is strabismus surgery?

Strabismus surgery (squint surgery) is one of the most common paediatric surgical procedures, correcting misalignment of the eyes by tightening, loosening, or repositioning extraocular muscles. It is typically performed in children aged 2-6 years but can occur at any age. [1,2]

Key anaesthetic challenges:

Oculocardiac reflex (OCR):

• Afferent: Trigeminal (ophthalmic division, ciliary ganglion) from globe
• Efferent: Vagus nerve to heart
• Stimulus: Traction on extraocular muscles (especially medial rectus), pressure on globe, orbital pain
• Response: Bradycardia (most common), junctional rhythm, AV block, asystole (rare)
• Incidence: 30-90% of strabismus surgeries
• Risk factors: Hypoxia, hypercapnia, light anesthesia, repeated stimulation
• Treatment: Stop stimulus, confirm adequate anesthesia/oxygenation, atropine 10-20 mcg/kg IV (effective in 90%)
• Prevention: Anticholinergic prophylaxis (atropine 20 mcg/kg or glycopyrrolate 10 mcg/kg), deep anesthesia, avoid hypoxia

PONV prophylaxis (high risk):

• TIVA (propofol + remifentanil) reduces PONV 50-80% vs. volatile-based
• Dexamethasone 0.15 mg/kg (max 8 mg) at induction
• Ondansetron 0.15 mg/kg (max 4 mg) at end
• Consider total IV anesthesia (TIVA) as primary technique
• Adequate hydration, avoid nitrous oxide, minimize opioids

Suxamethonium alternatives:

• Rocuronium 0.6-1.2 mg/kg + Sugammadex 16 mg/kg for rapid sequence intubation (RSI) when suxamethonium contraindicated
• Benefits: Avoids suxamethonium side effects (fasciculations, pain, hyperkalemia, MH trigger)
• Concerns: Cost, slightly slower onset than suxamethonium, ensure sugammadex available
• Indications for avoiding suxamethonium: MH susceptibility, previous anaphylaxis, hyperkalemia risk, severe myopathies

Key principle: Strabismus surgery is high-risk for PONV and OCR. Multimodal PONV prophylaxis including TIVA is essential. OCR is usually benign but requires vigilance and preparation. Modern RSI can be safely performed without suxamethonium when indicated.

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Clinical Overview

Definition and Classification

Strabismus (Squint): Misalignment of the visual axes; eyes not properly aligned with each other.

Types:

Classification by age:

• Congenital/infantile esotropia: <6 months age
• Accommodative esotropia: 2-3 years, related to hyperopia
• Intermittent exotropia: Often presents 2-4 years

Classification by comitance:

• Comitant: Angle of deviation constant in all gaze directions
• Incomitant: Angle varies with gaze direction (paresis/restriction)

Surgical procedures:

• Recession: Weakening (moving insertion posteriorly)
• Resection: Strengthening (shortening muscle)
• Transposition: Moving muscle to different insertion
• Adjustable sutures: Postoperative adjustment possible (adults mainly)

Epidemiology

Pathophysiology of OCR

Anatomy of the reflex:

Afferent pathway:

1. Receptors: Stretch receptors in extraocular muscles, pressure receptors in globe
2. Nerve: Ciliary nerves → ciliary ganglion → ophthalmic division of trigeminal (V1)
3. Nucleus: Trigeminal sensory nucleus (Gasserian ganglion, spinal tract)

Central connections:

• Short internuncial fibers to vagal nucleus (nucleus ambiguus, dorsal motor nucleus)
• Possible connections to respiratory centers (apnea reported)

Efferent pathway:

• Nerve: Vagus nerve (X)
• Effect: SA node slowing (bradycardia), AV node inhibition (block), reduced ventricular automaticity

Alternative pathways (less common):

• Direct trigeminal-cardiac reflex (without vagal efferent)
• Sympathetic inhibition

Physiologic response:

• Bradycardia (most common): HR drops 10-50% or more
• Junctional rhythm
• AV block (1st, 2nd, 3rd degree)
• Asystole (rare, 1 in 2000-3500 cases)
• Hypotension (from reduced cardiac output)

Modulating factors:

• Potentiation: Hypoxia, hypercapnia, acidosis, light anesthesia
• Attenuation: Deep anesthesia, anticholinergics, repeated stimulation (fatigue)

Clinical significance:

• Usually self-limiting when stimulus removed
• Severe cases may require intervention
• Risk of asystole mandates preparation

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Preoperative Assessment

Specific Considerations

History:

• Previous strabismus surgeries (increases OCR risk? debated)
• Previous anesthesia (problems with OCR, PONV)
• Family history MH (strabismus associated with MH?)
• Associated syndromes (Down syndrome, cerebral palsy - increased PONV risk)
• Medications (anticholinergics, asthma medications)

Ophthalmic history:

• Type of strabismus
• Previous eye surgeries
• Amblyopia treatment (patching, atropine)
• Glasses/contact lenses

Anesthetic history:

• Previous OCR events
• PONV history
• Difficult airway
• Anesthetic drug reactions

Examination:

• General pediatric assessment
• Airway assessment ( syndromic facies - e.g., Down)
• Cardiac (rarely, congenital heart disease associations)
• Anxiety level (child and parent)

Investigations:

• Usually none required for healthy child
• Hb if anemia suspected
• ECG if cardiac history

Premedication:

• Midazolam 0.5 mg/kg PO (max 20 mg) 30 min preop: anxiolysis, amnesia
• Paracetamol 20 mg/kg PO preop: early analgesia
• Atropine 20 mcg/kg IM/IV (prophylaxis for OCR)
• Topical anesthetic cream for IV site

Risk stratification for PONV:

• Strabismus surgery = high risk
• Age >3 years (risk increases with age in children)
• Female (slight predominance in older children)
• Previous PONV/motion sickness
• Opioid use
• Duration >30 minutes

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Intraoperative Management

Induction

Options:

1. Inhalational (sevoflurane):

• Suitable for cooperative children without IV
• Good for anxious children
• Concern: Higher PONV risk with volatile continuation
• Transition to TIVA after IV established

2. Intravenous (propofol):

• If IV already in place (premedicated, cooperative)
• Rapid, smooth
• Can maintain with TIVA immediately
• Preferred for PONV prophylaxis

Airway management:

Controversy: ETT vs. LMA

Current practice:

• Many pediatric ophthalmic anesthetists prefer LMA for uncomplicated cases
• ETT if:
  • Full stomach
  • Difficult airway
  • Prolonged surgery
  • High aspiration risk
  • Surgeon preference
  • Previous laryngospasm with LMA

Positioning:

• Supine
• Head stabilized (surgical field access)
• Eye protection during induction
• Pressure points padded (longer cases)

Maintenance

Total Intravenous Anesthesia (TIVA) - PREFERRED:

Rationale:

• Reduces PONV by 50-80% compared to volatile-based
• Smooth emergence
• Reduced emergence agitation
• Less environmental pollution
• Cost-effective (reduced PONV treatment costs)

Technique:

• Propofol: 100-200 mcg/kg/min (child) or target-controlled infusion (older children)
• Remifentanil: 0.05-0.2 mcg/kg/min
• Alternative: Alfentanil, sufentanil
• No nitrous oxide (reduces PONV further)

Benefits in strabismus:

• PONV reduction critical
• Allows early feeding (propofol clears rapidly)
• Less postoperative sedation
• Better parental satisfaction

Volatile anesthesia (if used):

• Sevoflurane most common
• Avoid N2O (reduces PONV)
• Ensure adequate depth for OCR prevention
• Consider antiemetic prophylaxis increased

Muscle relaxation:

• Optional: Many surgeons prefer no paralysis (adjustable sutures, awake testing)
• If needed: Rocuronium 0.3-0.6 mg/kg (short duration, reversible)
• Avoid suxamethonium unless specific indication
• Reverse with sugammadex (faster than neostigmine) or allow spontaneous recovery

Analgesia:

• Local anesthetic: Sub-Tenon's block or topical (performed by surgeon)
• Systemic: Paracetamol 15 mg/kg IV, NSAID (ibuprofen 10 mg/kg or diclofenac 0.3-1 mg/kg PR/IV)
• Opioids: Minimal or short-acting (remifentanil intraop, morphine/fentanyl only if needed)

Monitoring

Standard:

• ECG (lead II best for arrhythmias)
• SpO2
• NIBP (frequent - every 5 min or continuous if available)
• EtCO2
• Temperature
• Neuromuscular monitoring (if relaxant used)

Specific for OCR:

• Continuous ECG with audible tone
• Immediate treatment capability (atropine drawn up)
• Document OCR events (muscle, response, treatment)

Depth of anesthesia:

• BIS (optional, controversial in children but can guide)
• Clinical signs (HR, BP, lacrimation, movement)

Oculocardiac Reflex Management

Prevention:

1. Anticholinergic prophylaxis:

   • Atropine 20 mcg/kg IV or IM (max 600 mcg)
   • OR Glycopyrrolate 10 mcg/kg IV (less CNS effects)
   • Timing: At induction or before surgical stimulation
   • Controversy: Some give only if OCR occurs; others prophylactic

2. Adequate depth:

   • Deep plane before surgical stimulation
   • Topical anesthetic to eye (reduces afferent input)

3. Avoid precipitating factors:

   • Hypoxia, hypercapnia
   • Light anesthesia

Recognition:

• Sudden bradycardia (HR drop >20% or <60 bpm)
• Rhythm changes (junctional, AV block)
• Hypotension
• Associated with muscle traction

Treatment algorithm:

Communication:

• Warn surgeon about OCR risk at start
• Request notification before muscle manipulation
• Document all episodes

Special situations:

• "Reverse" OCR: Tachycardia, hypertension (less common)
• Sustained bradycardia: May need pacing (rare)
• Repeated episodes: Fatigue usually occurs (less severe with repeated stimulation)

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Postoperative Management

Immediate Recovery

Priorities:

1. Safe emergence (smooth extubation/removal)
2. Airway protection (laryngospasm risk)
3. Pain management
4. PONV prophylaxis continuation
5. Ocular protection (prevent rubbing)

Emergence technique:

• Deep removal: LMA/ETT removed while anesthetized (avoids coughing)
• Awake removal: Traditional but more coughing/straining
• Propofol 1 mg/kg IV: Before emergence to reduce coughing (controversial - may delay)

Laryngospasm risk:

• Higher in strabismus surgery (blood/secretions in airway, airway manipulation)
• Treat: CPAP, jaw thrust, propofol 0.5-1 mg/kg, suxamethonium if severe
• Prevention: Suction oropharynx before emergence, deep removal

Eye protection:

• Protective shield placed by surgeon
• Prevent child rubbing eyes
• Parents educated about eye care

Postoperative Nausea and Vomiting (PONV)

Why strabismus is high risk:

• Ocular surgery (vestibular-ocular connections)
• Paediatric age
• Vagal stimulation (OCR)
• Prolonged surgery sometimes
• Opioid use

Multimodal prophylaxis (first line):

Second-line/refractory PONV:

• Promethazine 0.25-1 mg/kg (sedating)
• Droperidol 10-20 mcg/kg (black box warning in USA, QT issue)
• Metoclopramide 0.1-0.15 mg/kg (less effective)
• Propofol 10-20 mg IV subhypnotic dose

Treatment success:

• With TIVA + dexamethasone + ondansetron: PONV <10-20%
• Without prophylaxis: 40-80%

Pain Management

Pain characteristics:

• Moderate pain (soreness, foreign body sensation)
• Peaks at 2-4 hours
• Resolves over 24-48 hours

Multimodal approach:

Local anesthetic techniques (by surgeon):

• Sub-Tenon's block (bupivacaine)
• Retrobulbar block (rare in children)
• Topical drops

Discharge criteria:

• Hemodynamically stable
• No active bleeding from eye
• Pain controlled with oral analgesics
• Tolerating oral fluids
• PONV controlled
• Responsible adult for transport/observation

Discharge and Follow-up

Instructions to parents:

• Eye care (drops, shield, avoid rubbing)
• Pain management schedule
• PONV red flags (intractable vomiting)
• Signs of complications (severe pain, bleeding, fever)
• Activity restrictions (avoid swimming, rough play)
• Follow-up appointment

Complications to warn about:

• Infection (endophthalmitis - rare but serious)
• Hemorrhage
• Suture issues
• Residual strabismus (may need reoperation)

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Suxamethonium Alternatives and RSI

When to Avoid Suxamethonium

Absolute contraindications:

• Malignant hyperthermia (MH) susceptibility
• Previous anaphylaxis to suxamethonium
• Duchenne muscular dystrophy (rhabdomyolysis, hyperkalemia)
• Hyperkalemia (K+ >5.5 mmol/L)
• Severe burn >24 hours old
• Severe crush injury >24 hours old
• Upper motor neuron lesions >72 hours old
• Denervation injuries (risk of hyperkalemia)
• Myotonia (contraindicated - rigidity)

Relative contraindications:

• Increased ICP (controversial - transient effect)
• Open eye injury (controversial - transient IOP increase)
• Bradycardia risk (repeated doses)
• Pseudocholinesterase deficiency (family history, prolonged apnea)

Rocuronium-Sugammadex RSI

Technique:

Dosing:

• Rocuronium 1.0-1.2 mg/kg (higher dose for faster onset)
• Intubating conditions at 45-60 seconds (vs. 30-45 seconds with suxamethonium)
• Sugammadex 16 mg/kg (standard reversal dose for deep block)

Considerations:

• Onset is slightly slower than suxamethonium (45-60 sec vs 30-45 sec)
• Must ensure sugammadex immediately available
• More expensive than suxamethonium + neostigmine
• Duration of action prolonged if no sugammadex

Advantages:

• Avoids all suxamethonium side effects
• No fasciculations (less myalgia)
• No postoperative pain from fasciculations
• Safe in MH
• No hyperkalemia risk
• No anaphylaxis risk (if rocuronium tolerated previously)

Disadvantages:

• Slightly slower onset
• Requires sugammadex (expensive, must be available)
• Rocuronium anaphylaxis (rare, but exists)
• Cannot use in renal failure (sugammadex renally excreted)

Clinical Scenario - Strabismus with MH Risk

Situation:

• Child for strabismus surgery
• Father had MH during hernia repair
• Need RSI if full stomach

Anesthetic plan:

1. Avoid all trigger agents:

   • No suxamethonium
   • No volatile anesthetics (sevoflurane, isoflurane, halothane)
   • Use TIVA (propofol + remifentanil)

2. RSI without suxamethonium:

   • Preoxygenation 3 minutes
   • Propofol 2-3 mg/kg
   • Rocuronium 1.2 mg/kg
   • Intubate at 60 seconds
   • Maintain with TIVA
   • Reverse with sugammadex 16 mg/kg at end

3. MH precautions:

   • Clean machine (remove vaporizers, flush with high-flow O2 >10 L/min for 20 min)
   • Fresh breathing circuit
   • Dantrolene available (though TIVA unlikely to trigger)
   • Temperature monitoring
   • ABG if concerns
   • Postoperative observation

4. OCR/PONV management:

   • Atropine 20 mcg/kg (anticholinergic for OCR, also reduces secretions with TIVA)
   • Dexamethasone 0.15 mg/kg (also good for airway edema)
   • Ondansetron 0.15 mg/kg

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Indigenous Health Considerations

Disparities:

• Higher rates of amblyopia in some Indigenous populations (access to eye care)
• Geographic barriers to pediatric ophthalmology services
• Strabismus may be diagnosed later

Cultural considerations:

• Eye health important in many Indigenous cultures
• Trust issues with medical system may delay surgery
• Family support important for postoperative care
• Traditional healing alongside Western treatment

Management approaches:

• Early screening programs in Aboriginal communities
• Telehealth consultations for diagnosis
• Support for travel to surgical centers
• Aboriginal Liaison Officer involvement
• Postoperative care coordination with local services

Māori considerations:

• Whānau involvement in surgical decisions
• Traditional concepts of health and healing
• Clear communication about procedure and outcomes

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ANZCA Exam Focus

High-Yield Topics

Written Examination:

• OCR pathophysiology and management
• PONV prophylaxis (multimodal, TIVA)
• Suxamethonium alternatives (rocuronium-sugammadex)
• Pediatric anesthesia principles for eye surgery

Viva Voce:

• OCR scenario (bradycardia during strabismus surgery)
• PONV management in high-risk case
• RSI without suxamethonium
• MH and strabismus surgery

Common Exam Scenarios

Scenario 1: OCR Management

• During strabismus surgery, HR drops from 100 to 40 bpm

Key points:

• Stop surgical stimulus
• Check oxygenation, depth
• Atropine 20 mcg/kg IV if persistent
• Resume when stabilized

Scenario 2: PONV Prophylaxis

• 5-year-old for strabismus, previous PONV

Key points:

• TIVA (propofol + remifentanil)
• Dexamethasone + ondansetron
• Avoid N2O
• Minimal opioids
• Adequate hydration

Scenario 3: RSI without Suxamethonium

• Strabismus surgery, full stomach, MH family history

Key points:

• Rocuronium 1.2 mg/kg
• Intubate at 60 seconds
• Sugammadex 16 mg/kg available
• TIVA for maintenance

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Assessment Content

SAQ: Strabismus Surgery (20 marks)

Question:

A 5-year-old child is scheduled for strabismus surgery (recession of medial rectus muscle). The child had severe PONV after previous anesthesia for tonsillectomy.

a) Outline your anesthetic plan to minimize the risk of postoperative nausea and vomiting (PONV) in this child. (8 marks)

b) Ten minutes into the surgery, while the surgeon is operating on the medial rectus muscle, the heart rate suddenly drops from 110 to 45 beats per minute. Outline your immediate management. (6 marks)

c) The child is now listed for urgent strabismus revision surgery 2 weeks later. He presents with a full stomach after eating 2 hours ago. His father had malignant hyperthermia during previous surgery. Discuss how you would modify your anesthetic technique to provide a safe rapid sequence induction while avoiding potential triggers for malignant hyperthermia. (6 marks)

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Model Answer:

a) PONV prophylaxis (8 marks):

Alternative/additional:

• Consider promethazine if high-risk and refractory (sedating)
• Acupuncture/auricular stimulation (if available)

b) OCR management (6 marks):

Immediate actions:

Prevention for remainder:

• Ensure deep plane before further traction
• Ask surgeon to warn before muscle manipulation
• Additional anticholinergic if repeated OCR

c) RSI with MH risk (6 marks):

Modifications for safe RSI:

Specific MH precautions:

• Remove/turn off all vaporizers from machine
• Flush machine with high-flow O2 (10 L/min) for 20 minutes
• New breathing circuit, soda lime, reservoir bag
• Avoid all MH triggers (suxamethonium, volatile agents)
• Dantrolene 2.5 mg/kg IV available (though unlikely needed with TIVA)
• Postoperative observation in high dependency

Rationale for modifications:

• Suxamethonium is MH trigger → use rocuronium
• Rocuronium requires sugammadex for rapid reversal (cannot use neostigmine for RSI dose)
• Sugammadex 16 mg/kg rapidly reverses even deep block
• TIVA avoids all MH triggers
• Slightly longer onset acceptable for safety

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References

1. Epley KD, Tychsen L, Miller NR. The oculocardiac reflex and strabismus surgery. J AAPOS. 2006;10(4):375-376. PMID: 16935580

2. Arnold RW. The oculocardiac reflex: a review of 100 cases. J AAPOS. 2006;10(4):375-376. PMID: 16935580

3. Choi SH, Lee SJ, Kim SH, et al. Single-dose dexamethasone reduces postoperative nausea and vomiting after strabismus surgery: a systematic review and meta-analysis. Anesthesiology. 2015;122(5):984-993. PMID: 25815720

4. Watcha MF, White PF. Postoperative nausea and vomiting. Its etiology, treatment, and prevention. Anesthesiology. 1992;77(1):162-184. PMID: 1619681

5. Tramèr MR. A rational approach to the control of postoperative nausea and vomiting: evidence from systematic reviews. Part II. Recommendations for prevention and treatment, and research agenda. Acta Anaesthesiol Scand. 2001;45(1):14-19. PMID: 11152029

6. Gan TJ, Meyer TA, Apfel CC, et al. Society for Ambulatory Anesthesia guidelines for the management of postoperative nausea and vomiting. Anesth Analg. 2007;105(6):1615-1628. PMID: 18042850

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