The laryngeal mask airway: Anesthetic gas leakage and fiberoptic control of positioning

Abstract

Study Objective: To examine the anesthetic gas leakage and prelaryngeal position of the laryngeal mask airway (LMA). Design: Clinical trial evaluating LMA ventilation conditions. Setting: Lithotripsy room of a urology clinic at a university hospital. Patients: 100 adult ASA physical status I and II patients undergoing general anesthesia for kidney stone lithotripsy. Interventions: Anesthesia was induced with propofol 1.5 to 2.5 mglkg intravenously (IV) and fentanyl 1 to 1.5 μg/kg IV and maintained with isofurane plus nitrous oxide in oxygen. Measurements and Main Results: Waste anesthetic gas concentration, an indicator of mask tightness during intermittent positive-pressure ventilation, was measured using an infrared oxide analyzer. LMA position in relation to laryngeal skeleton was assessed using fiberoptic laryngoscopy. The LMA was found to be gastight in 62% of patients, with a peak airway pressure up to 25 cmH 2O. During peak airway pressure ventilation less than 10 cmH 2O and during spontaneous ventilation, waste anesthetic gas contamination in the anesthesiologist's breathing zone was within legal limits in every case. During peak airway pressure ventilation up to 30 cmH 2O, contamination was found within legal limits in 78% of all cases. Fiberoptic control showed a central position in 59% of cases, lateral deviations to the left or right in 29%, dorsal positions in 8%, and ventral positions in 4%. Incorrect ventral or dorsal positioning was related to forced reclining or forced f exion of the patient's head. There was no correlation between LMA position and tightness. The esophageal entrance was visible in 15 patients using high peak airway pressure greater than 25 CMH 2O. Conclusions: The LMA is a new airway management technique with good qualities of tightness and ventilation conditions. However, contraindications such as patients with a full stomach, intra-abdominal surgery, high peak airway pressure, prolonged operation, and an inexperienced anesthesiologist apply.