The ventilation-perfusion relation and gas exchange in mitral valve disease and coronary artery disease - Implications for anesthesia, extracorporeal circulation, and cardiac surgery

Background: Patients with mitral valve disease (MVD) are at greater risk for respiratory complications after cardiac surgery compared with patients with coronary artery disease (CAD). The authors hypothesized that ventilation-perfusion (V) over circle(A)/(Q) over circle) inequality is more pronounced in patients with MM) before and after induction of anesthesia and during and after surgery when extracorporeal circulation (ECC) is used. Methods: In patients with MVD (n = 12) or with CAD (n = 12), (V) over circle(A) (Q) over circle distribution was determined using the multiple inert gas elimination technique. Intrapulmonary shunt ((Q) under circle(s) (Q) under circle(r) defined as regions with (V) over circle(A) (Q) over circle < 0.005 [% of total perfusion ((Q) over circle(T))], perfusion of ''low'' (V) over circle(A) (Q) over circle areas (0.005 less than or equal to (V) over circle(A) (Q) over circle < 0.1, [% of (Q) over circle(T))], ventilation of ''high'' (V) over circle(A)<(Q<over circle> regions (10 less than or equal to (V) over circle(A) (Q) over circle less than or equal to 100 [% of total ventilation (V) over circle(E)]), and dead space ((V) over circle(A) (Q) over circle > 100 [% of (V) over circle(E)])) were calculated from the retention/excretion data of the inert gases. Recordings were obtained while patients spontaneously breathed air in the awake state, during mechanical ventilation after induction of anesthesia, after separation of patients from ECC, and 4 h after operation. Results: (Q) over circle(s) (Q) over circle(T) was low in the awake state (MVD group, 3% +/- 3%; CAD group, 3% +/- 4%) and increased after induction of anesthesia to 10% +/- 8% (MVD group, P < 0.05) and 11% +/- 7% (CAD group, P < 0.01). (Q) over circle(s) (Q) over circle(T) increased further after separation from ECC (MVD group 24% +/- 9%, P < 0.01; CAD group, 23% +/- 7%, P < 0.01). Similarly, alveolar-arterial oxygen tension difference (PA-aO2) increased from 168 +/- 54 mmHg (anesthetized state) to 427 +/- 138 mmHg after ECC (MVD group, P < 0.01) and from 153 +/- 65 mmHg to 377 +/- 1201 mmHg (CAD group, P < 0.01). In both groups. Conclusions: (Q) over circle(s) (Q) over circle(r) is the main pathophysiologic mechanism of gas exchange impairment during cardiac surgery for MVD or CAD. Impairment of pulmonary gas exchange secondary to general anesthesia, cardiac surgery, and ECC are comparable for patients undergoing myocardial revascularization or mitral valve surgery.