[Hypoxemia after heart surgery. An exception or a normal development?]

The course of respiratory exchange through arterial blood gas analysis after coronary bypass-grafting and valvular replacement has been investigated in a cohort of 62 patients. Arterial blood gases were measured at baseline (the day before surgery), and then 1, 2, 3 and 9 days after surgery; in a subset of 18 patients, randomly selected from the same population, pulmonary function tests were also performed at baseline and repeated on day 9. Arterial blood gases showed a remarkable prevalence of hypoxaemia (as defined as arterial PaO2 less than 60 mmHg): 31% on the first, 50% on the second, and 40% on the third post-operative day; anemia and desaturated mixed venous blood were also prominent findings during the first two days. Arterial PO2 resulted higher afterward, although its mean value then was significantly lower than baseline (81.5 +/- 8.8 vs 93.1 +/- 9 mmHg, p less than 0.005). Pulmonary function tests evidenced widespread restrictive changes, with alterated thoraco-pulmonary mechanics (loss of more than 40% of vital capacity and one second forced expiratory flow) and parenchimal lung damage (residual volume and CO diffusion capacity decrease). Some differences in PaO2 course between coronary patients and valvular patients have been releaved; the mean basal PaO2 value of valvular was significantly lower then the other one (86.7 +/- 10.8 vs 94.7 +/- 10.9, p less than 0.05).