Effects of positive end-expiratory pressure on tissue gas tensions and oxygen transport.

To determine whether positive end-expiratory pressure (PEEP) impairs peripheral tissue oxygenation, hemodynamic variables including blood and subcutaneous tissue gas tensions were measured at 0, 5, 10, 15, and 20 cm H2O of PEEP, in 9 patients who were being mechanically ventilated for acute pulmonary failure. Increasing the level of PEEP produced parallel decreases in cardiac output and oxygen delivery (DO2 = cardiac output X arterial oxygen content); however, there were no significant changes in mean arterial blood pressure (MAP), oxygen consumption (VO2), mixed-venous oxygen tension (PvO2), pH, or base excess. Subcutaneous tissue oxygen (PtO2) and carbon dioxide (PtCO2) tensions, which were directly measured in the femoral region by a mass spectrometer, also remained at their baseline levels (zero end-expiratory pressure). We concluded that peripheral tissue oxygenation is not impaired up to the level of 20 cm H2O of PEEP, even though DO2 significantly decreases.