Cardiorespiratory changes following cardiopulmonary bypass in patients with normal and abnormal preoperative cardiorespiratory function

We studied cardiorespiratory function following cardiopulmonary bypass for aorto-coronary bypass (six patients) and for mitral valve replacement (five patients). Our investigations were carried out within six hours of bypass. We used inspired oxygen concentrations of 21%, 40% and 100%. We measured mean pulmonary artery (PPA) and wedge (PPW) pressures, cardiac output and arterial blood gas tensions. The first group of patients had normal preoperative hemodynamic studies. Following bypass (mean duration 62 minutes) PPA and pulmonary vascular resistance remained normal despite the presence of hypoxemia (mean PaO2 61 mmHg) secondary to pulmonary shunting (mean 22%). The second group of patients had abnormal preoperative and postoperative hemodynamic studies. Following mitral valve replacement hyperoxemia (mean PaO2 330 mmHg) was associated with an abnormally elevated PPW (mean 20 mmHg) while hypoxemia (mean PaO2 59 mmHg) was associated with an almost normal PPW (mean 13 mmHg). Cardiac output decreased and systemic vascular resistance increased with hyperoxemia