Gastroesophageal reflux during spontaneous respiration with the laryngeal mask airway.

PURPOSE: To determine the incidence of gastroesophageal reflux during general anesthesia with the Laryngeal Mask Airway (LMA).

METHODS

Twenty unpremedicated patients with no risk factors for reflux having day case anesthesia were included. Type of surgery was Orthopedic (n=8), General (n=7) and Gynecological (n=5). The average duration of anesthesia was 38.1 min, range 12 - 71 min. Anesthesia was induced with 1-2 microg x kg(-1) fentanyl and 2-3 mg x kg(-1) propofol and maintained with oxygen 33%, nitrous oxide 66% and isoflurane 1% (end-tidal). Ventilation by hand was performed until spontaneous respiration resumed. To facilitate surgery, 13 patients were placed in the supine and seven in the lithotomy positions. Two pH-sensitive electrodes were used to identify reflux. One was placed in the oesophagus 20 cm from the anterior nares to detect esophageal reflux and the other was placed through the bars of the LMA to detect refluxing material around the LMA.

RESULTS

Esophageal reflux occurred in 12 patients (60%), in five of the 13 in the supine position and in all patients in the lithotomy position. The LMA electrode detected a decrease in pH in four cases (20%), all in the lithotomy position. The incidence reflux in the lithotomy and supine positions was different (Exact Probability test; P = 0.01).

CONCLUSION

This study suggests that the lithotomy position predisposes patients to a higher risk of aspiration than the supine position when using a LMA.