PaO2 during anaesthesia and years of smoking predict late postoperative hypoxaemia and complications after upper abdominal surgery in patients without preoperative cardiopulmonary dysfunction

Background: The incidence of late postoperative hypoxaemia and complication s after upper abdominal surgery is 20-50% among cardiopulmonary healthy pat ients. Atelectasis development during anaesthesia and surgery is the main h ypothesis to explain postoperative hypoxaemia. This study tested the predic tive value of PaO2<19 kPa during combined general and thoracic epidural ana esthesia and the preoperative functional residual capacity (FRC) reduction in the 30 degrees head tilt-down position for the development of late prolo nged postoperative hypoxaemia, PaO2<8.5 kPa for a minimum of 3 out of 4 day s, and other complications. Methods: Forty patients without cardiopulmonary morbidity, assessed by EGG, spirometry, FRC and diffusion capacity preoperatively, underwent upper abd ominal surgery. PaO2 during anaesthesia and preoperative FRC reduction were compared to known risk factors for the development of hypoxaemia and compl ications: age, pack-years of smoking and duration of operation. The effect of optimizing pulmonary compliance with peroperative positive end-expirator y pressure (PEEP) on postoperative hypoxaemia and complications was evaluat ed in a blinded and randomized manner. Results: Late prolonged postoperative hypoxaemia and other complications we re found in 37% and 38% of the patients, respectively. Patients with PaO2>1 9 kPa during anaesthesia with FIO2=0.33 exhibited a risk, irrespective of P EEP status, of suffering late prolonged hypoxaemia of 0% (0;23) and patient s with PaO2<19 kPa a risk of 52% (32;71), P<0.005. Having smoked more than 20 pack-years was associated with a 47% (19;75) higher incidence of postope rative complications than having smoked less than 20 pack-years, P<0.006. Conclusions: PaO2 during anaesthesia and smoked pack-years provide new tool s evaluating patients undergoing upper abdominal surgery in order to predic t the patients who develop late postoperative hypoxaemia and complications.