Relationship between postoperative hypoxemia and the operative site.

The effect of the site of operation on postoperative hypoxemia was studied in 104 patients undergoing thoraco-abdominal, thoracic, upper abdominal, lower abdominal, extra-abdominal and non-thoracic operations. The degree of postoperative hypoxemia was the most extensive in patients undergoing thoraco-abdominal, moderate in thoracic and upper abdominal operations, and minimal in lower abdominal and other operations. On the other hand, the duration of hypoxemia also differed with the surgical procedures. Arterial oxygen tension returned to almost control values by the 3rd postoperative day in cases of lower abdominal and extremity operations and by the 7th postoperative day in those undergoing thoracic and upper abdominal surgery. Postoperative hypoxemia, however, remained throughout the fourteen day study period, in patients undergoing thoraco-abdominal operation. True shunt was measured in 27 patients with thoraco-abdominal, thoracic and upper abdominal operations. An increase in true shunt was evident postoperatively in the entire group of patients. The increase was significantly larger and longer lasting in cases of thoraco-abdominal incision than that in cases of thoracic and upper abdominal incision alone. Differences in postoperative true shunt between cases of thoracic and upper abdominal incisions were nil.