Heat and moisture exchangers (HMEs) are commonly used to minimize temperature loss and to protect mucosa from drying (thus preserving ciliary activity and lung mechanics). These devices are known to increase dead space and airway resistance (l-4). Two studies have indicated that resistance is increased after the HME becomes wet (3,4). One case report implicated a blood-soaked HME in an acute increase in airway pressure that resolved after removal of the HME (5). We recently managed a case where a HME contributed to ventilatory difficulties in a small infant presenting for repair of tetralogy of Fallot. A HME was placed at the beginning of the procedure. Just prior to weaning from cardiopulmonary bypass, an active heated humidifier was added and the HME was inadvertently left in place. During attempts at hand ventilation, there was a stiff, noncompliant feel to the ventilator bag (airway pressure 30-40 cm H,O). Direct visualization of the lungs revealed full inflation, with no significant deflation. The endotracheal tube was irrigated with 3 mL of normal saline and suctioned, but no secretions were aspirated. At this time, the HME was discovered and removed. Thereafter, the lungs were easily inflated with airway pressure 25-30 cm H,O and ready deflation was observed. The HME was noted to be warm and the filter material saturated with liquid. We were fortunate that our patient was supported by cardiopulmonary bypass and we had direct visualization of the lungs, alerting us to the possible etiology of this problem. Active humidification is a contraindication to the use of the HME. In addition, any situation that may lead to the saturation of the HME (irrigation fluid, secretions, bleeding, nebulized mediations) may represent a risk of complete airway obstruction.
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