Intraosseous access — branching viva

Branching viva — intraosseous access

The examiner releases the stem and then branches into four probes. A strong candidate answers the decision first, defends the physiology, demonstrates the technique, and names the complications without prompting. [1] [3]

Opening (examiner)

"A two-year-old arrives cold, mottled, and barely rousable with septic shock. Heart rate 180, capillary refill 6 seconds, blood pressure 60/35. Two peripheral cannulation attempts over 75 seconds have failed. What is your next move?" [1]

Branch 1 — The decision (expected answer)

State the rule and act on it: if intravenous access cannot be secured within 60 to 90 seconds in a child with shock, arrest, status epilepticus, or peri-arrest, place an intraosseous needle now rather than attempting a third cannula. Name the operator, state the decision aloud, and run the clock. Central lines and cut-downs take too long in an unstable child. [1] [3]

Probe. "Why IO and not a central line?" — A central line takes many minutes and interrupts resuscitation; an IO is placed in under a minute, does not interrupt compressions, and delivers drugs to the heart in seconds at intravenous doses. [1] [2]

Branch 2 — Physiology (expected answer)

The medullary cavity holds thin-walled venous sinusoids held open by the rigid cortex, so they do not collapse in shock when peripheral veins have shut down. Fluid and drugs drain through the central venous canal and the nutrient vein into the systemic circulation and reach the heart in seconds, with pharmacokinetics close to a central line. Every drug that can be given intravenously can be given intraosseously at the same dose. [9] [12]

Probe. "Why is gravity flow too slow?" — The rigid cavity resists flow, so rapid resuscitation needs a pressure bag at 300 mmHg or a syringe bolus. [9]

Branch 3 — Technique and confirmation (expected answer)

Site: proximal tibia, flat anteromedial surface, one to two centimetres below and medial to the tibial tuberosity. Needle: EZ-IO 15 mm pink for 3 to 39 kilograms; 25 mm blue for 40 kilograms and over; 45 mm yellow for the adolescent or oedematous child. Drill perpendicular until a give is felt, stop, remove the stylet. Confirm: needle firm, aspirate if possible (failure does not exclude placement), easy flush with no swelling, distal limb soft and perfused. [1]

Probe. "You cannot aspirate marrow — is the line failed?" — No. Aspiration often fails even with a good line; an easy flush with no swelling is the better confirmation. [1] [12]

Probe. "The child is conscious and cries with each bolus." — Give preservative-free, epinephrine-free lidocaine 0.5 milligram per kilogram, maximum 40 milligrams, slowly IO over about two minutes, dwell 60 seconds, then flush. Half the dose may be repeated. [1]

Branch 4 — Complications and disposition (expected answer)

Name and prevent them: extravasation (swollen firm limb) leading to compartment syndrome — stop, remove, choose another site; through-and-through penetration; fracture and growth-plate injury (correct landmark, perpendicular angle); infection (cellulitis, osteomyelitis, septic arthritis) which rises with dwell time — remove within 24 hours; fat and marrow micro-embolism — avoid repeated and prolonged use. After removal, observe the limb for 24 hours for swelling, pain, or infection. [3] [11]

Probe. "A paramedic suggests the proximal humerus in an adolescent arrest — what is the advantage?" — Faster central drug return than the tibia, with comparable first-attempt success; the trade-off is a harder landmark, so the tibia remains the taught first site. [8]

Examiner's wrap

Outcome is driven by the underlying illness, not the access route. A 2025 JAMA Network Open study of paediatric out-of-hospital cardiac arrest found intraosseous access was faster than intravenous but did not by itself improve survival to discharge — IO buys speed of treatment, which is exactly what it is for. [2]