Lower Esophageal Sphincter Pressure During Prolonged Cardiac Arrest and Resuscitation,☆☆,,★★

Presented in abstract form at the Society for Academic Emergency Medicine Annual Meeting, Washington DC, May 1994.
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Abstract

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 H 2O. 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. [Bowman FP, Menegazzi JJ, Check BD, Duckett TM: Lower esophageal sphincter pressure during prolonged cardiac arrest and resuscitation.Ann Emerg Med August 1995;26:216-219.]

Section snippets

INTRODUCTION

Prompt establishment of adequate ventilation is a primary concern in the management of cardiac arrest. In the unprotected airway, the delivered tidal volume depends on several factors, including lung compliance, adequacy of mask seals, flow rate, and gastric distension. Gastric insufflation occurs when air enters the stomach and can lead to regurgitation and pulmonary aspiration1. The lower esophageal sphincter (LES) is a pressure-sensitive valve that limits gastric insufflation and reflux in

MATERIALS AND METHODS

Our protocol was approved by the University of Pittsburgh Animal Care and Use Committee. Eighteen female mixed-breed domestic swine were used; their mean mass was 21.9±1.7 kg. The animals were sedated with IM ketamine (10 mg/kg) and xylazine (1 mg/kg). Each was then anesthetized intravenously with a loading dose of 40 mg/kg a-chl oralose followed by a maintenance infusion of 10 mg/kg/hour. Each animal was then orotracheally intubated with a 5-0 cuffed endotracheal tube and mechanically

RESULTS

The mean baseline LES tone was 20.6±2.8 cm H 2O. This baseline value resembles the values found in human beings under general anesthesia, indicating that ours may be an appropriate model. LES pressure values during the arrest and after ROSC are given in Table 1.LES pressure decreased steadily during the 7 minutes of VF but was significantly reduced during minutes 2 through 7 compared with the baseline value (all comparisons, P<.01). ROSC occurred in 10 of the 18 trials. After ROSC, LES pressure

DISCUSSION

Lung compliance in human beings is poor during cardiac arrest.4 This fact is important in that air introduced by means of positive-pressure ventilation tends to bypass the lungs and take the path of least resistance. With an LES pressure lower than that previously reported during cardiac arrest, it is likely that larger volumes of air than previously reported would enter the stomach rather than ventilate the lungs.

The American Heart Association Guidelines for Cardio-pulmonary Resuscitation

CONCLUSION

In this swine model, we found the baseline value of LES pressure to be comparable to the 20 cm H 2O found in human beings under general anesthesia. However, LES tone decreased rapidly when VF was induced. Even after ROSC occurred, LES tone reached a plateau at a level about half that at baseline during the observation period. Further studies of the decay of LES tone during human cardiac arrest and its effects on mask ventilation and gastric insufflation are warranted.

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From the Center for Emergency Medicine of Western Pennsylvania* and the Division of Medicine, School of Medicine, University of Pittsburgh, Pittsburgh Pennsylvania.

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Funded by the Pittsburgh Emergency Medicine Foundation and the Center for Emergency Medicine of Western Pennsylvania.

Address for reprints: James J Menegazzi, PhD, Center for Emergency Medicine, 230 McKee Place, Suite 500, Pittsburgh, Pennsylvania 15213, 412-578-3235, Fax 412-578-3241

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Reprint no. 47/1/66265

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