Abstract 59: The Incidence Of Pulmonary Aspiration With Laryngeal Mask Airway Use During Cardiopulmonary Resuscitation And Positive Pressure Ventilation In Swine.
Objective: Pulmonary aspiration of gastric contents occurs 20 –30% of the time during cardiopulmonary resuscitation (CPR) of cardiac arrest. This is due to loss of protective airway reflexes, pressure changes generated during CPR, and positive pressure ventilation (PPV). Even though the American Heart Association (AHA) has recommended the laryngeal mask airway (LMA) as an acceptable alternative airway for use by EMS personnel, concerns over the capacity of the device to protect from pulmonary aspiration remain. We sought to determine the incidence of aspiration after LMA placement, CPR and PPV.
Methods: We conducted a prospective study on 16 consecutive post-experimental mixed-breed domestic swine of either sex (mean mass 25.7 ±1.4 kgs). A standard size-4 LMA was modified so that a vacuum catheter could be advanced into and past the LMA diaphragm. The LMA was placed into the hypopharynx and its position confirmed using End-tidal CO2 and direct visualization of lung expansion. Fifteen milliliters of heparinized blood were instilled into the pharynx. After 5 PPVs with a mechanical ventilator, chest compressions were performed for 60s with asynchronous ventilations continuing at a rate of 12 per minute. After chest compressions, a suction catheter was inserted through the cuff and suction applied for approximately 1 minute. The catheter was removed and inspected for signs of blood. The LMA cuff was deflated and the LMA removed. The intima of the LMA diaphragm was inspected for signs of blood. In a validation cohort of 4 animals, the LMA was reinserted, a cricothyrotomy performed and 5 mL of blood instilled directly into the trachea.
Results: There were 0/16 (95% CI=0 –17%) with a positive tests for the presence of blood in both the vacuum catheter and the intima of the LMA diaphragm. In the validation cohort, all four were positive for blood in both the vacuum catheter and the intima of the LMA diaphragm.
Conclusions: In this simple model of regurgitation of after LMA placement, there was no sign of pulmonary aspiration, and no evidence that blood had passed beyond the seal created by the LMA cuff. Concerns over aspiration with LMA use may be unfounded. Future studies should determine the frequency of pulmonary aspiration after LMA placement in the clinical setting.