Heat and Moisture Exchanger Malfunction Causing Dynamic Hyperinflation and Ventilatory Insufficiency Under General Anesthesia: A Case Report.

Heat and moisture exchangers (HMEs) humidify inspired gases and preserve airway moisture and temperature. Although considered safe, they can rarely contribute to intraoperative complications. We report the case of a 26-year-old female undergoing diagnostic hysterolaparoscopy under general anesthesia (GA) who developed sudden ventilatory deterioration shortly after endotracheal intubation and initiation of mechanical ventilation. Alarms for high airway pressure and low minute ventilation were triggered, accompanied by rising positive end-expiratory pressure. Initial evaluation, including confirmation of endotracheal tube placement, bronchodilator administration, assessment of ventilator settings, and endotracheal tube adjustment, did not resolve the issue. Re-auscultation revealed diminished breath sounds bilaterally, without any adventitious sounds; manual ventilation also failed to improve ventilation. Further inspection revealed excessive water accumulation in the HME filter within the expiratory limb, despite the HME filter having been in use for the last three hours in a previous case, leading to dynamic hyperinflation due to impaired expiration. Replacement of the clogged filter immediately restored normal ventilatory parameters. This case highlights a rare but potentially life-threatening complication of HME filter blockage during GA, leading to dynamic hyperinflation. Anesthesia providers should consider circuit-related causes, such as HME malfunction, in the differential diagnosis of acute intraoperative ventilation difficulty. Especially when standard patient and endotracheal tube-related causes are excluded.