Effect of oxygen on postoperative cardiovascular response to exercise.

OBJECTIVE: To evaluate the effect of supplemental oxygen on postoperative cardiovascular response to submaximal exercise. DESIGN: Randomised, controlled study. SETTING: University hospital, Denmark. SUBJECTS: 16 patients having major abdominal operations. INTERVENTIONS: A submaximal exercise test (heart rate up to 120 min(-1)) done twice on the third day after operation. Patients were given either 100% oxygen (4 L min(-1)) or air (21% oxygen, 4 L min(-1)) 30 minutes before and during the test in randomised order. During the tests they were monitored with a Holter tape recorder and a pulse oximeter. MAIN OUTCOME MEASURES: Heart rate during exercise. RESULTS: At similar workloads there were significantly lower heart rates (median decrease 3 min(-1)) during exercise tests with oxygen compared with air (p < 0.05). Holter monitoring showed signs of myocardial ischaemia in 6 patients in relation to exercise testing, 4 of them related to both tests, 2 of them only when breathing air. Signs of myocardial ischaemia disappeared when the exercise ended. CONCLUSION: During the late postoperative period supplementary oxygen reduced heart rate in response to exercise to the same degree as observed previously in non-surgical patients and surgical patients not taking exercise. These findings do not suggest that decreased peripheral tissue oxygenation is responsible for the impaired cardiovascular response to exercise in postoperative patients.