Impact of haemodynamic alterations on arterial blood gases during off-pump coronary revascularization

ABSTRACT

Cardiac stabilization during “off-pump” coronary revascularization (OPCAB) has been implicated in causing intraoperative hemodynamic disturbances. Stroke volume and cardiac output reductions may alter the ventilation/perfusion ratio in the lungs and compromise the gas exchange. This study was conducted to determine the impact of heart’s stabilization on arterial blood-gas profile in patients undergoing OPCAB surgery. After institutional approval and informed consent, 57 patients undergoing OPCAB procedures were studied. LIMA was anastomosed to LAD in all patients. In 20 patients a second coronary vessel received a graft, while in 5 patients a third vessel was also anastomosed under propofol-remifentanil (TIVA) anesthetic technique. FiO₂ was equal to 1. Compression fork-type stabilizer was used. Full hemodynamic profile, mixed venous oxygen saturation, acid base status, end-tidal partial pressure of carbon dioxide and ST-segment changes were monitored before heart’s stabilization (T1 values-baseline), 5 minutes after stabilization (T2 values), before stabilizer’s removal (T3 values) and 10 minutes after stabilizer’s removal (T4 values). Oxygen delivery and consumption, VD/VT and Qs/Qt were calculated. Ventilation was kept unchanged during data collection. Statistical analysis for pairwise comparisons with baseline values (T1) was performed with Dunnett’s two-sided multiple-comparison procedure. Statistical analysis was performed using the t-paired test. A value of p<0.05 was considered statistically significant. During LIMA→LAD grafting (n=57) cardiac stabilization and anastomotic maneuvering caused significant hemodynamic changes. Cardiac output, stroke volume and mixed venous oxygen saturation decreased significantly (4.44 ± 1.0 → 3.43 ± 0.8 L/min, 70.6 ± 15.5 → 52.6 ± 14.2 ml, 83.5 ± 4.7 → 76.5 ± 8.0 % respectively; p<0.001 for all) while systolic, diastolic and mean pulmonary pressure, central venous pressure and capillary wedge pressure increased significantly during stabilizer’s application (T2, T3 values). Calculated O₂ delivery and consumption were decreased. PH, bicarbonate and base excess decreased significantly at all times compared to baseline (7.45 ± 0.03 → 7.43 ± 0.03, 23.9 ± 1.44 → 22.9 ± 1.98 mEq/L, 0.06 ± 1.6 → -0.98 ± 1.9 respectively; p<0.001 for all) while arterial partial pressure and end-tidal partial pressure of carbon dioxide decreased at T2, T3 interval and increased at T4. Arterial partial pressure of oxygen increased significantly after stabilizer’s placement (T2, T3 interval) and decreased in stage T4. Qs/Qt was decreased during anastomotic maneuvering. IN OPCAB SURGERY, THE HEMODYNAMIC CHANGES DUE TO the heart’s stabilization caused significant changes in the arterial blood gas profile. The reduction of systemic flow and tissue perfusion led to increased plasma hydrogen ion concentration. Restoration of flow was followed by “wash-out” phenomena. Arterial tension and exhalation of CO₂ were primarily influenced by the decreased O₂ consumption, the increased VD/VT and the buffering of protons after the stabilizer’s removal. In this study population, the deterioration in gas exchange was minor. Although these changes are not persistent, they may have implications in the intraoperative management of patients with compromised alveolar gas-exchange.