Oxygen, high-flow and non-invasive respiratory support — formative SAQs

SAQ 1 (10 marks, 15 minutes)

A 5-month-old infant presents with bronchiolitis, marked recession, grunting and SpO2 of 88 per cent in room air. After 30 minutes of standard low-flow nasal cannula oxygen at 2 L/min, there is no improvement. Outline your approach to escalating respiratory support, including device selection, starting parameters, reassessment plan and failure criteria. ^[7]

Model answer

Immediate assessment and threat gate (2 marks) — Assess airway patency, breathing and circulation. Clear the threat gate: confirm the infant is not in extremis — no apnoea, bradycardia, silent chest or altered conscious state — which would mandate immediate bag-mask ventilation and intubation. This infant is failing standard oxygen but still has a drive to breathe and is therefore a candidate for escalation to non-invasive support. ^[7]

Device selection and rationale (2 marks) — The problem is moderate bronchiolitis with high work of breathing and hypoxaemia that has failed standard low-flow oxygen. The appropriate next step is high-flow nasal cannula (HFNC), which provides precise FiO2, dead-space washout, reduced work of breathing and a modest PEEP effect. CPAP or BiPAP would be alternatives if HFNC fails or if the problem demands reliable set pressure, but HFNC is the evidence-supported first escalation step in moderate bronchiolitis. ^{[1] [7]}

Starting parameters (2 marks) — Initiate HFNC with a flow of 2 L/kg/min, titrated between 1 and 2 L/kg/min, with FiO2 set to the minimum achieving the target saturation of 92 to 95 per cent. Use correctly sized nasal prongs. Ensure the gas is heated and humidified. ^{[1] [7]}

Reassessment plan (2 marks) — Reassess within 30 to 60 minutes of starting, assessing work of breathing (rate, recession, grunting), efficacy (air entry, breath sounds) and effect (SpO2, colour, conscious state). If improving, continue and wean FiO2 first. If not improving, check the interface for leak and consider escalating to CPAP (5 to 7 cmH2O) or BiPAP (IPAP 10 to 15, EPAP 4 to 6 cmH2O). ^[7]

Failure criteria and escalation (2 marks) — Define failure at the outset: persistent or worsening hypoxaemia, rising PaCO2 on blood gas, worsening acidosis, exhaustion (falling rate with quieting chest), haemodynamic instability, or apnoea. If any criterion is met, proceed to intubation without delay — the cardinal error is persisting with a failing non-invasive trial. ^[7]