Perioperative distribution of pulmonary vascular resistance in patients undergoing coronary artery surgery

This study was undertaken to measure distribution of pulmonary vascular resistance (PVR) perioperatively in patients undergoing coronary artery bypass grafting (CABG) and to examine the effects of cardiopulmonary bypass (CPB) on pulmonary capillary pressure (Pc) relative to wedge pressure (Pw). Pulmonary artery catheters were placed before anesthetic induction in 18 patients scheduled for elective CABG and systemic hemodynamic variables were measured. Pulmonary artery pressure was recorded during balloon inflation and stored for off-line determination of Pc. Data were collected prior to induction (baseline), as well as after induction and intubation, skin incision, sternotomy, protamine administration, and chest closure. At each data point, downstream (capillary plus venous segments) resistance (Rds) contributed approximately 60% of total PVR and did not change significantly during the operation. PVR decreased (P < 0.05) after CPB and protamine administration, primarily due to a decrease in the absolute magnitude of the upstream (arterial) resistance. Administration of large-dose opioid anesthesia had no significant effect (P > 0.05) on total PVR or on segmental distribution of vascular resistance. At all data points, Pc was significantly larger than Pw (P < 0.05). This study demonstrates that perioperative measurement of Pc is feasible, that during CABG under these conditions, relative contribution of arterial and venous resistances remain relatively unchanged, that Pc is always larger than Pw, and that the administration of large-dose opioid anesthesia has a minimal effect on pulmonary vascular hemodynamics.