Ventilatory failure following active humidification of a retained HMEF in an intubated infant: a case report

Heat and moisture exchanger filters (HMEFs) provide passive humidification and microbial filtration during pediatric anesthesia, but their apparatus dead space and flow resistance-trivial in adults-may represent a clinically important fraction of tidal volume in infants. Progressive moisture saturation further increases resistance, and simultaneous use with an active heated humidifier can precipitate circuit occlusion.

A 13-month-old boy undergoing ophthalmologic surgery developed wheezing, progressively rising peak inspiratory pressure (PIP), and hypercapnia (PaCO₂ 81.5 mmHg) after a difficult intubation. Presumed bronchospasm was treated with salbutamol, sevoflurane escalation, epinephrine, hydrocortisone, and magnesium, producing only partial improvement. He was transferred intubated to the ICU with the same breathing circuit and HMEF in situ. Within approximately 10 min of connection to a ventilator equipped with active heated humidification, PIP rose to 40 cmH₂O, delivered tidal volume fell from 90 mL to 50 mL, and PaCO₂ rose to 119.5 mmHg. The HMEF was visibly saturated; its immediate removal produced prompt resolution of pressure, volume, wheeze, and blood gases.

An unremoved HMEF exposed to active heated humidification can cause fulminant ventilatory failure in infants. HMEF dead space, saturation status, and humidifier compatibility must be explicitly verified before and during every pediatric perioperative transfer.