Airway Obstruction Caused by Sputa in Heat and Moisture Exchange Filter During Ventilation Using Supra-Laryngeal Mask Airway: A Case Report

Abstract

Introduction: Supra-laryngeal mask airway (LMA) is widely accepted as an alternative to the tracheal tube. However, compared to the use of a tracheal tube, it may take longer to identify the many different causes of sudden respiratory distress. In particular, heat and moisture exchange filters are one of the most overlooked causes. Case presentation: The case was that of a 76-year-old male Japanese patient (161.9 cm, 66.5 kg) who underwent an open renal biopsy. He presented with chronic obstructive pulmonary disease, with a Hugh–Jones dyspnea score of 2. The patient did not discontinue smoking prior to the operation. Anesthesia was induced using propofol (100 mg), fentanyl (100 ?g), and remifentanil (0.3 ?g/kg/min). I-gel™ #4 was inserted following neuromuscular blockade with rocuronium (40 mg). Anesthesia was maintained with 3–6% desflurane under positive pressure ventilation. After induction in the left lateral and jackknife positions, the following ventilator settings were used: volume-controlled ventilation with tidal volumes of 450 mL, respiratory rate of 12 breaths per minute, an inspiratory: expiratory ratio of 1:2, and a positive end expiratory pressure of 5 cmH2O. With these settings, the peak inspiratory pressure was 16 cmH2O. Five minutes after initiating the operation, the peak inspiratory pressure steadily increased to 30 cmH2O. Although we administered rocuronium, the peak inspiratory pressure and end-tidal carbon dioxide concentration increased over time. When we disconnected the heat and moisture exchange filter and LMA, we noticed a large quantity of sputa. A suction catheter was passed down the LMA and the sputa was removed, but the LMA was not obstructed. The peak inspiratory pressure continued to increase with tidal volumes of only 20–30 mL. Despite a normal external appearance of the heat and moisture exchange filter, we replaced it with a new one. The ability to ventilate improved immediately and the SpO2 recovered from 92% to 100%. Conclusions