There are a few reports of the application of high PEEP (PEEP greater than or equal to 15 cm H2O) infants and children. Data concerning cardiac index (CI), pulmonary venous admixture (Qsp/Qt), and arterial mixed venous oxygen content difference (avDO2) during mechanical ventilation with high PEEP have not been reported. Fourteen infants and children were treated with high levels of PEEP; 8 of these patients were monitored with pulmonary artery catheters. Cardiopulmonary data were obtained from these 8 patients and pulmonary barotrauma data were tabulated from all 14 patients. At highest PEEP, CI = 3.6 +/- 0.6 L/min x M2, avDO2 = 4,45 +/- 0.83 ml/dl and Qsp/Qt = 16.7 +/- 2.1%. One patient experienced severe cardiac depression unresponsive to therapy; it resolved when PEEP was lowered. Pulmonary barotrauma was a frequent complication. Pneumothroax occurred in 6 patients. No patient died from pulmonary barotrauma. We conclude that PEEP greater than or equal to 15 cm H2O can be used in infants and children to decrease Qsp/Qt toward normal; CI and avDO2 can usually be maintained in an acceptable range. Patients should be frequently monitored for pulmonary barotrauma.