Negative end-expiratory versus zero end-expiratory pressure flow-controlled ventilation in a porcine hemorrhagic shock model

Abstract

Background

Hemorrhagic shock is a life-threatening event whereby low flow may lead to end-organ dysfunction. This is aggravated by mechanical ventilation, where a positive intrathoracic pressure further deteriorates venous filling of the heart. The aim of this study was to evaluate the effects of a mild negative end-expiratory pressure (NEEP) on mean arterial pressure compared to zero end-expiratory pressure (ZEEP) in a porcine hemorrhagic shock model.

Methods

In anesthetized pigs, hemorrhagic shock was induced by a standardized lesion in the common femoral artery. After achieving half of baseline arterial pressure, hemorrhage was stopped. Ventilation was then switched to either flow-controlled ventilation with ZEEP (0 cmH₂O, n = 6) or NEEP (−5 cmH₂O, n = 6). After 5 min, fluid resuscitation was initiated (30 ml/kg) over 60 min and the observation period ended after 120 min.

Results

The primary outcome parameter mean arterial pressure was significantly improved within the first 15 min with NEEP compared to ZEEP (49 vs 40 mmHg, MD 9 (95% CI 2 to 15); p = 0.031), but this effect diminished throughout fluid resuscitation. The cardiac index was similar in both groups. Evaluation of lung mechanics revealed a decrease in dynamic compliance (29 vs 44 ml/cmH₂O, MD −14 (95% CI −20 to −9); p < 0.001) in the NEEP group without differences in gas exchange.

Conclusions

Application of −5 cmH₂O NEEP improved mean arterial pressure but not cardiac index during hemorrhagic shock and the first 15 min of fluid resuscitation compared to ZEEP. Thereby gas exchange performance was similar.