Cardiopulmonary effects of titrating positive end-expiratory pressure to match abdominal pressure on an experimental model of abdominal hypertension and acute lung injury

Objective

There is some controversy in the literature on how patients with concomitant intra-abdominal hypertension (IAH) and acute lung injury (ALI) should be ventilated. It has been suggested that application of external positive end-expiratory pressure (PEEP) matching abdominal pressure could improve ventilatory performance during ALI and IAH [1]. Our purpose with the present study was to evaluate the cardiopulmonary effects of PEEP matching abdominal pressure (AP) in an experimental model of IAH and ALI.

Methods

Eight anesthetized pigs were instrumented and then submitted to IAH of 20 mmHg for 30 minutes with a CO₂ insufflator. Respiratory and hemodynamic parameters were measured and then also after ALI was induced by lung lavage with saline (3 ml/kg) and Tween (2.5%). Pressure × volume curves of the respiratory system were performed by a quasi-static low flow method during IAH and ALI, and PEEP was then adjusted to 27 cmH₂O for 30 minutes.

Results

IAH decreased pulmonary and respiratory system static compliances and increased airway resistance, alveolar–arterial oxygen gradient and respiratory dead space. The presence of concomitant ALI exacerbates these findings. Thirty minutes of mechanical ventilation with PEEP identical to AP moderately improved oxygenation and respiratory mechanics. Even though cardiac output was maintained through an increased heart rate, this short course of increased PEEP caused an important decline in the stroke index and right ventricle ejection fraction.

Conclusion

Concomitant IAH and ALI produce important impairments in the respiratory physiology. PEEP equalization to AP may improve the respiratory performance, but with a secondary hemodynamic derangement.