Intraoperative assessment and quantification of coronary artery graft patency performed on or off cardiopulmonary bypass.

Within the last 10 years, the incorporation of off-pump coronary artery bypass grafting (OPCAB) into many surgical practices has grown. OPCAB requires the surgeon to operate on a beating heart, and it is generally accepted that OPCAB procedures are more technically demanding. Concerns of possible incomplete revascularizations and decreased graft patency have been noted in the literature. The objective of this study was to evaluate and compare on-pump and off-pump intraoperative coronary artery bypass graft (CABG) flow parameters. Intraoperative flow studies conducted with the Butterfly (Medi-Stim Norge AS, Oslo, Norway) flow meter were analyzed retrospectively on 74 patients. Comparisons were completed between patient groups having had their revascularizations performed on or off cardiopulmonary bypass. Our study revealed significant differences in the mean flow rate through saphenous vein grafts (SVG) to the obtuse marginal artery (OM; p = .014), to the diagonal artery (Diag; p = .003), to the right coronary artery (RCA; p = .001), and to the posterior descending artery (PDA; p = .001). Total blood product use showed significantly increased use of both platelets (PLTs) and cryoprecipitate (Cryo) in the on-pump group (p = .027 and .012, respectively). No differences were found for transfusions of red blood cells (RBCs) or fresh frozen plasma (FFP). Additional findings showed a significantly decreased median length of stay (LOS) for the off-pump group. The on-pump patients had a median hospital stay of 7 days (range, 4-24 days), whereas the off-pump patients had a median stay of 6 days (range, 3-22 days; p = .049). Although we were able to show some significance in the mean flow data supporting increased graft flow with the on-pump technique, we were not able to show an overall increase in all recorded flow characteristics to support one method over another.

Quantification of the effect of altering hematocrit and temperature on blood viscosity.

Rheological changes occurring with the conduct of cardiopulmonary bypass affect the distribution of blood throughout the cardiovascular system. The purpose of this study was to evaluate the effects of changing physical characteristics of fluid on the dynamics of blood flow in an in vitro model. An extracorporeal model simulating coronary vessel constriction was designed that consisted of tubing with varying internal diameters. Tubing sizes were selected as percentage reductions (11, 33, 56, and 78%) of a normal sized (3.6 mm) coronary artery. Flow rates were randomly varied between 150 and 300 mL min(-1) temperatures of 6 and 37 degrees C, and hematocrits of 0, 20, and 38%. Endpoints included viscosity, pressure drop, and volume distribution. As temperature fell from 37 to 6 degrees C, viscosity increased with hematocrit as follows: 192% at 0%, 225% at 20%, and 249% at 38%, p < .001. Pressure drop increased significantly across each tubing size ranging from 173-351%, p < .01, as fluid was cooled from 37 to 6 degrees C. However, intraconduit statistical differences in volumetric distribution of flow were not achieved. Although the induced hypothermia resulted in increases in resistance, statistical significance was only seen in the smallest lumen conduit. In conclusion, the effects of changing temperature has profound influence on fluid distribution secondary to changing blood viscosity in an in vitro model for fluid distribution. Knowledge of such flow alterations may aid in determining optimal perfusion strategies where vessel constrictions are encountered.