Iatrogenic puncture of the laryngeal mask airway cuff.

Abstract

A 30-year-old male, intravenous drug user presented for drainge of a forearm abscess. Due to problems with veins anaesthesia was induced with sevoflurane in oxygen; a size 4 laryngeal mask airway (LMA) was easily inserted. The cuff was inflated with 25 ml of air and correct placement confirmed. Peripheral venous access was initially unsuccessful and cannulation of the left internal jugular vein was attempted using an 18G abbocath cannula with a 10-ml syringe attached; the right internal jugular vein was sclerosed. Advancing the cannula, 5 ml of air under pressure entered the syringe unexpectedly and the cannula was withdrawn. The patient was breathing spontaneously and there was no suggestion or evidence of a tension pneumothorax. It was obvious the LMA cuff had been punctured and a further 10 ml of air was introduced into the cuff. Despite the puncture of the LMA cuff, the pilot balloon remained inflated and no obvious air leak was present. The capnograph trace and reservoir bag movements remained unchanged, with normal breath sounds heard on auscultation of the lungs and side of the neck. The pressure in the cuff was measured through the pilot balloon and found to be 22 cmH2O. Throughout the 25-min procedure no signs of cuff deflation appeared. The pressure in the cuff remained at 22 cmH2O. Intravenous access in a dorsal foot vein was established and anaesthesia maintained with isoflurane in a N2O/O2 mixture. The remaining procedure was uneventful. Examination of the LMA cuff in a beaker of water and inflated with 45 ml of air resulted in a stream of bubbles from the puncture site (figure top of next page). Whatever volume of air was introduced, the leak always stopped with a residual volume of 24 ml in the cuff and a cuff pressure of 22 cmH2O. Interestingly, the deflation test with the mask cuff to a high vacuum did not result in gradual re-inflation as might be expected. The silicone cuff of the LMA is permeable to a variety of gases, with CO2 and N2O rapidly diffusing through the membrane [1], causing a rise in pressure within the air-filled cuff [2]. The diffusion of gas into the LMA cuff may have compensated for any leak, but more likely, as gas diffused into the cuff and the pressure increased, the hole in the silicone rubber opened, acting as a pressure limiting leak at 22 cmH2O. Dental damage to the LMA cuff has been reported [3, 4]. In the first report the LMA was used in a ‘can't intubate, can't ventilate’ scenario and a 0.5-cm tear noted. The second report during elective use described the replacement of the LMA on three occasions due to a leak. We are not aware of any reports of iatrogenic puncture of the LMA cuff and its subsequent use. Three points arise from this incident. First, neck vein cannulation may be difficult due to distortion of the oropharynx by the LMA. Second, the importance of performing all pre-use tests is highlighted [5]. In this case the puncture of the LMA was obvious, but if the device had been sterilised for re-use, the leak would have been detected by the inflation test only (50% overinflation with the device under water). Finally, inadvertent puncture of the LMA cuff may not result in complete cuff deflation and the device may continue to function normally.