Monitoring of optimal oxygen Transport by the transcutaneous oxygen tension method in the pig.

The validity of the transcutaneous oxygen tension (PaO2) method as opposed to measurement of arterial oxygen tension (PaO2) and mixed venous oxygen saturation (SVO2), for monitoring optimal oxygen transport, was studied in six mechanically ventilated pigs with an oleic acid lung injury. With stepwise increments in positive end-expiratory pressure (PEEP) from zero to 20 cmH2O maximum oxygen flux was found at a PEEP of 8 cmH2O and named "optimal PEEP". With increasing PEEP, cardiac output (CO) was maintained up to a PEEP of 8 cmH2O, when it began to decline, while venous admixture decreased at all respiratory settings up to a PEEP of 16, when it was about one-fourth of the value (38.7%) at a PEEP of zero. PaO2 increased with rising PEEP and reached a steady level at a PEEP of 16 cmH2O. PtCO2 and SVO2 parallelled each other and rose steeply up to a PEEP of 8 cmH2O. They showed a further slight increase up to a PEEP of 12 and after that a tendency to decrease. It is concluded that PtCO2 and SVO2 both seem to distinguish the optimal PEEP and give more adequate information than does PaO2. The PtCO2 method has the advantage of being non-invasive.