Study objective: Unprotected airway ventilation models have been based on a lower esophageal sphincter (LES) pressure found in human beings under general anesthesia. Whether this assumption is applicable during cardiac arrest in human beings is unknown. We attempted to determine the effects of prolonged ventricular fibrillation (VF) on the tension of the LES in a swine model of cardiac arrest.
Design: Prospective experimental trial using 18 female mixed-breed domestic swine (mean weight, 21.9 +/- 2.0 kg).
Results: Animals were anesthetized, intubated, and fitted with instruments for the monitoring of LES pressure. LES tone was measured with a LECTRON 302 esophageal monitor (American Antec, Incorporated). VF was induced with a 3-second, 100 mA transthoracic shock and left untreated for 8 minutes; then resuscitation was attempted. LES tension was measured during the first 7 minutes of the arrest. If return of spontaneous circulation (ROSC) occurred, LES pressure was measured for 7 more minutes. The mean baseline LES pressure was 20.6 +/- 2.8 cm H2O. During minutes 1 through 7 of the arrest the LES tone (mean +/- SD) decreased from 18.0 +/- 3.0 to 3.3 +/- 4.2. ROSC occurred in 10 of the 18 trials. In the 7 minutes after ROSC, LES pressure increased from 4.7 +/- 3.8 to 9.8 +/- 3.0.
Conclusion: This study demonstrated a rapid and severe decrease in LES tone during prolonged cardiac arrest. When ROSC occurred, LES tension increased quickly but did not return to baseline.