INTRODUCTION: Humidification of inspiratory gases is essential during mechanical ventilation. Heat and moisture exchangers are commonly used to aide humidification but malfunctions can occur. We report a case of ventilator circuit obstruction by a heat and moisture exchanger with a review of prior literature.
CASE PRESENTATION: A 24 year-old woman with a past medical history of asthma was admitted to the ICU in status asthmaticus. She was intubated in the emergency department. A heat and moisture exchanger (HME) was inline in the breathing circuit. Continuous nebulizer treatments were begun with albuterol 0.083% and ipratropium 0.02%. Her ventilator was set to assist volume control with a set rate of 16, tidal volume (TV) 400 mL with positive end-expiratory pressure 5 cm Water with FiO2 0.40. Her initial peak inspiratory pressures (PIP) varied between 25 and 40 cm Water. At 24 hours, the TVs were noted to drop to 150-200 mL with inspiratory pressure alarm limits reached reducing the maximal ventilator delivered TV. No leak was found in the ventilator circuit. Decreased bilateral breath sounds were noted on physical exam, vitals were stable and trachea was mid-line. The suction catheter passed easily, the patient was not biting the endotracheal tube, and there were no secretions in the patient circuit nor in the HME. The patient was disconnected and was easily ventilated with the bag-valve mask. It was noted that the ventilator was still sensing high-pressure. The HME was removed from the circuit and the ventilator immediately reported low pressures. The patient was reconnected to the ventilator and TVs of 400ml were restored. We believe continuous administration of albuterol and ipratropium in saturation of the HME leading to resistance to airflow. Our patient was extubated by the 6th hospital day and left the hospital on the 9th day. She remained well five months after admission.
DISCUSSIONS: Heat and moisture exchangers (HMEs) are passive devices that provide 60-80% of the necessary humidity by capturing exhaled moisture and allowing it to be used in subsequent breaths. HMEs are simple, cheap and require little maintenance. The central component of HMEs is hygroscopic material which readily absorbs moisture. When an HME possesses bacteria filtering properties it can be designated as a HMEF. Various critical occlusions of HMEs have been reported, primarily in the anesthesiology literature. Several of the reports describe defects or loose components in the HME itself. Prados reported a case of obstruction by a plastic plug in a defective HME that acted as one way ball valve that caused air trapping. Prasad reported a partial separation between two interconnecting parts of the plastic housing resulting in a significant leak. Casta reported acute airway obstruction due to a dislodged paper component of an HME. Several reports describe obstruction of the HMEF by contaminants causing pore occlusion of the filter membrane. Contaminants described include condensed water, hemoptysis, and proteinaceous fluid associated with pulmonary edema. McEwan and associates described a case of obstruction of a bacterial filter in the expiratory limb of a breathing circuit that resulted in bilateral tension pneumothorax. The filter was clogged with sputum, ciliary epithelium, and inflammatory cells. Several cases describe obstruction with nebulised medications: albuterol, ipratropium and acetylcysteine. Walton and associates described two cases of obstruction using nebulized albuterol with a breathing circuit where both filters were coated with a powdery white film. Nebulization of normal saline, the diluent for albuterol, did not reproduce this obstructive coating.
CONCLUSION: Obstruction of the heat and moisture exchanger should be considered in the differential diagnosis of airway obstruction and insufficient tidal volumes. Heat and moisture exchangers should be removed prior to the administration of aerosol or metered dose inhaler treatments.
DISCLOSURE: Jeffrey Williams, No Financial Disclosure Information; No Product/Research Disclosure Information