Obesity hypoventilation with acute decompensation — FFICM MCQ

Correct answer: C — Start bilevel NIV with controlled oxygen

D (Start bilevel NIV with controlled oxygen) is correct. This man has acute-on-chronic obesity hypoventilation syndrome (OHS) with acidaemic hypercapnic respiratory failure (pH 7.27, PaCO2 10.1 kPa) precipitated by a lower respiratory/inflammatory insult, and the clear lung field excludes a primary parenchymal process needing higher FiO2. As he remains rousable, protects his airway and is haemodynamically stable, first-line management per BTS/ICS guidance is bilevel NIV, using the same threshold criteria as for AECOPD, delivered with titrated (controlled) oxygen to avoid worsening CO2 retention via loss of hypoxic drive and V/Q mismatch. Bilevel pressure support actively augments alveolar ventilation and offloads the respiratory muscles against the high impedance of severe obesity, which CPAP alone cannot achieve. Why the other options are wrong: A CPAP without pressure support: CPAP recruits alveoli and improves oxygenation and upper airway patency but provides no inspiratory pressure support, so it does not correct alveolar hypoventilation or acidaemic hypercapnia. B Intubate immediately for normal PaCO2: intubation is reserved for those failing NIV, an unprotected airway, or haemodynamic compromise, none of which apply here, and immediate invasive ventilation in morbid obesity carries higher procedural and weaning risk that should be avoided if NIV is feasible. C Doxapram and avoid ventilatory support: doxapram is an obsolete respiratory stimulant with a poor safety profile and is not recommended over NIV in acidaemic acute hypercapnic respiratory failure. E High-flow nasal oxygen alone: HFNO improves oxygenation and dead-space washout but does not reliably deliver the pressure support required to reverse significant hypercapnic acidosis in OHS. Key point: In acidaemic hypercapnic OHS with a protected airway, bilevel NIV with controlled oxygen is first-line, reserving intubation for NIV failure or airway/haemodynamic compromise.

Reference: British Thoracic Society/Intensive Care Society Guideline for the ventilatory management of acute hypercapnic respiratory failure in adults, Thorax 2016 (recommendations on obesity hypoventilation syndrome and controlled oxygen therapy), https://pmc.ncbi.nlm.nih.gov/articles/PMC4800170/