use of iso-shunt lines and calculation of venous admixture for controlled oxygen therapy in the post-operative period

ABSTRACT

Thirty patients undergoing elective abdominal and thoracic surgery were studied. Parameters of hypoxemia [PaQ2, [P[A-a]O2, Qs/Qt] were measured mixture preoperative, postoperative and after oxygen therapy. All the patients showed postoperative hypoxemia, which was more evident in cases of thoracic surgery. The iso-shunt lines graph was used to determine the optimal F1 O2 to be administered for correction of postoperative hypoxemia. The graph assumption of virtual shunt lead to underestimation of venous admixture. Application of the iso-shunt lines graph proved to be a useful practical method for prediction of the optimal F1 O2 required for correction of postoperative hypoxemia. The iso-shunt lines graph is inaccurate in the range of 25% venous admixture