[Effects of positive end expiratory pressure on oxygen transport]

Fifteen patients admitted at the ICU of our hospital suffering from respiratory failure and submitted to mechanical ventilation were included in a study upon the influence of positive end expiratory pressure (PEEP) on oxygen transport. When the PaO2/FiO2 index was less than 300, 200, and 150, PEEP of +5, +10, and +15 cmH2O respectively was introduced. A Swan-Ganz catheter in the pulmonary artery and a catheter in a radial artery were inserted with the aim to obtain mixed venous blood samples and determine cardiac output, and vascular pulmonary resistances for each PEEP value. When PEEP increased from 5 cmH2O to 15 cmH2O, oxygen supply decreased a 12.4% (p less than 0.05), oxygen extraction from the tissues increased a 21.4% (p less than 0.025) and cardiac output decreased a 7.9% (p less than 0.02) while vascular pulmonary resistances increased a 6.6% (p = NS). We conclude that a PEEP of 5 cmH2O impairs tissue oxygenation when compared with PEEP of 5 cmH2O and that oxygen supply decrease with cardiac output.