Is PEEP detrimental to splanchnic perfusion in mechanically ventilated patients?

Objective

Disturbances in splanchnic perfusion leads to insufficiency of the gut mucosal barrier. As a consequence it causes bacterial translocation that might be a trigger to septic shock and multiorgan failure. The present study was designed to assess whether mechanical ventilation with positive end-expiratory pressure (PEEP) is a factor disturbing cardiac output and splanchnic perfusion. Gastric intramucosal PCO₂ (PiCO₂) and pH (pHi) are currently used as indices of the accuracy of splanchnic perfusion and as end points to guide therapeutic intervention. The definition of the ideal PEEP does not include improvement in oxygen delivery and its accessibility in the splanchnic region.

Design

A prospective study.

Setting

Department of Anesthesiology and Intensive Care of Medical Postgraduate Education Center, Warsaw, Poland.

Patients

Twenty adult ICU patients after laparotomy (hemicolec-tomy, colectomy) (group A) and five nonsurgical ICU patients (group B). All of them did not have serious respiratory and circulatory abnormalities, and did not need adrenergic or any circulatory support. All were mechanically ventilated under sedation with PEEP 0, PEEP 5, PEEP 10, PEEP 15. Each patient ventilated with PEEP 0 was a control for himself/herself. Each ventilation setting period lasted 1 hour. All the measurements were performed twice during that time.

Measurements and results

PiCO₂-PaCO₂, pH-pHi, CI, CVP, ITBVI, EVLWI were measured using gastric tonometry and the PiCCO method (pulse contour cardiac output) after each change of PEEP value. No differences in pH-pHi and PiCO₂-PaCO₂ were observed between groups A and B. PEEP does not compromise gastric mucosal perfusion, as assessed by tonometry. Even the patient's age was not essential. A decrease in cardiac output did not result in necessity of adrenergic support. Only in one case there was a need to use it for more than 1 hour after setting PEEP 10. Mean values of CI were higher in group A compared with nonoperated group B. CI depends on the age and PEEP level. CVP was increased by PEEP in both groups, but ITBVI was almost untouched, the right ventricle preload did not decrease, and EVLWI was slightly lowered under PEEP 15. IAP did not exceed 10 mmHg in any case.

Conclusion

PEEP up to 15 cmH₂O is well tolerated by the majority of ICU patients. The results of the present study indicate that incremental increases in PEEP do not impact on splanchnic perfusion as assessed by gastric tonometry in patients with adequate fluid loading. In some cases a necessity for adrenergic support might appear. Facing the fact of nonaffecting splanchnic perfusion, we cannot recommend any PEEP value as ideal for perfusing that region. More studies are needed in this area, particularly in patients receiving adrenergic support.