Assessing ProSeal laryngeal mask positioning: the suprasternal notch test.

Abstract

To the Editor: Brimacombe, Keller, and Berry recently described a case of gastric insufflation occurring during positive pressure ventilation (PPV) with the ProSeal™ laryngeal mask airway (PLMA) (1). During insertion the PLMA tip folded backward, pinching off the drain tube (DT), preventing it from acting as an esophageal vent. The tip of the mask was folded backward behind the bowl against the posterior pharyngeal wall instead of being located behind the cricoid cartilage. This case dramatizes the lack of a reliable and easy maneuver for determining whether the leading edge of the PLMA lies behind the cricoid cartilage. We propose such a simple test, the suprasternal notch (SSN) test. A nontoxic soap solution (such as used by children to blow bubbles) is placed across the proximal end of the DT, creating a membrane (2). Gently tapping the SSN causes the soap membrane to pulsate, confirming PLMA tip location behind the cricoid cartilage. Fiberoptically, tapping the SSN compresses the distal tip of the PLMA and distorts the DT where it passes through the cuff tip. This very slight DT deformation is sufficient to cause the extremely sensitive soap membrane to visibly bulge with tapping. Another useful sign, cardiac pulsation of the soap membrane (3), occasionally occurs because the esophageal mucosa abutting the DT is itself pulsating. We recently had a case with the exact PLMA malposition described by Brimacombe, Keller, and Berry (1). After PLMA insertion we suspected a malposition because the integral bite block was mostly outside of the mouth and incisors. Also, the oropharyngeal leak occurred at only 24 cm H2O. Fiberoptic examination via the airway tube showed that the PLMA tip was folded posteriorly backwards, in essence truncating the distal 50% of the mask. With this malposition the SSN test was negative—the soap membrane did not pulsate when the SSN was tapped. Because we believe that the PLMA is considerably more complex than the Classic LMA, and because we usually use the PLMA with PPV, we utilize the following steps to assess PLMA positioning (Table 1). First, we inflate the cuff to 60 cm H2O pressure (4). Second, we assess for adequate insertion depth by examining the relation of the integral bite block with respect to the incisors. Usually most of the bite block is within the mouth. Third, we assess for unobstructed inspiratory and expiratory flow. We hand ventilate the patient and observe chest rise and fall, examine the capnograph, and evaluate the feel of the anesthesia bag. If we suspect partial obstruction, as can occur with infolding of the PLMA cuff (5), we reinsert the PLMA. Fourth, we evaluate the seal. We perform a “soap bubble DT test” to verify zero leak at the mask/esophageal seal (3). If we detect a small leak from the DT we try to advance the PLMA further. We confirm that the maximum seal pressure is limited by an oropharyngeal leak, not a breech of the mask/esophageal seal (3). Fifth, we perform a SSN notch test. If this test is negative we reinsert the PLMA.Table 1: Steps to Assess ProSeal™ Laryngeal Mask Airway (PLMA) PositioningWe have evaluated the SSN test in 50 consecutive patients. We have placed the PLMA and, if necessary, reinserted it until satisfactory positioning has been achieved based on the first four of the five criteria listed above (Table 1). In all 50 patients the SSN test has been positive—membrane pulsation has been easily elicited by gently tapping the SSN. We believe that a positive SSN test reliably indicates the presence of the PLMA tip behind the cricoid cartilage. Cornelius J. O’Connor Jr, MD Carl J. Borromeo, MD Michael S. Stix, MD, PhD