Use of transcutaneous oxygen sensors to titrate PEEP

The relationship of transcutaneous oxygen tension (PtcO2) to arterial oxygen tension (PaO2), pulmonary shunt (Qsp/Qt), mixed venous oxygen tension (PVO2), and O2 delivery was determined in patients with respiratory failure in order to explore the possible usefulness of PtcO2 to titrate the level of positive end expiratory pressure (PEEP). Transcutaneous oxygen sensors were applied to the chest of surgical ICU adult patients who were in acute postoperative respiratory failure. The patients had mechanical ventilation with volume ventilators and an intermittent mandatory ventilation (IMV) rate, which allowed normal pH and arterial CO2 tension ventilation (PacO2). Swan-Ganz and arterial catheters were inserted. The blood volume was measured by iodinated I-125-serum albumin and brought into the normal range, before the study began, with appropriate volume therapy. Serial cardiorespiratory data were taken before and after PEEP was increased from zero to 20 cm H2O, in 5 cm increments. PtcO2 correlated well with PaO2 and PV-O2; it was inversely correlated with Qsp/Qt. PtcO2 correlated with O2 delivery in only seven severely ill patients mean alveolar-arterial oxygen tension difference [A-aDO2] was 380 mmHg and the pulmonary shunt was 37%). For the eight other patients, variations in the greatly elevated cardiac output associated with hypoxemia led to poor correlations between PtcO2 and O2 delivery. There was no significant depression of cardiac output in any of the studies. We conclude that the continuous noninvasive nature of PtcO2 monitoring greatly increased the safety and simplicity of PEEP optimization and respiratory management of adult patients with respiratory failure.