Use of blood oxygen partial pressure in the right atrium in the calculation of intrapulmonary shunt

: In order to assess the usefulness of blood samples taken from the right atrium (RA) in the calculation of intrapulmonary shunt (Qs/Qt), we correlated the values of Qs/Qt obtained through RA sampling with those obtained form a simultaneous sample of blood from the pulmonary artery (PA). The study was done in six mongrel dogs (15 to 23 Kg) who were anesthetized and artificially ventilated. The Qs/Qt measurements were repeated at different levels of cardiac output (CO). Changes in CO were elicited by both mechanical (A-V fistula) and pharmacological (Hydralazine) means. Besides the Qs/Qt correlation we also correlated the oxygen-hemoglobin saturation (Sat %) and oxygen tension (PvO2) values between the two sites of mixed venous sampling. The correlations of the different parameters between RA and PA samples we obtained were as follows: Qs/Qt r = 0.93 (p less than 0.001); Sat % r = 0.87 (p less than 0.001); and for PvO2 r = 0.91 (p less than 0.001). The significant correlations of these parameters were maintained independent of the CO level. We conclude that in our model a sample of blood obtained from the RA is useful for the calculation of Qs/Qt.