Improved tissue perfusion (Po2 histograms) in extracorporeal circulation using membrane instead of bubble oxygenators

Abstract

We made an experimental study of dogs undergoing extracorporeal circulation and used bubble oxygenators (BOs) (N = 8) or membrane oxygenators (MOs) (N = 7). Hematologic changes were related with alterations in tissue oxygen supply, which reflect microcirculatory changes. The tissue oxygen supply was measured with an eight-wire P o 2 electrode on the surface of the sartorius muscle. From 104 P o 2 values a frequency distribution curve (P o 2 histogram) was computed. Hematologic studies, in particular platelet numbers and function (adenosine diphosphate-induced aggregation), were performed. The extracorporeal circuit was primed with about 1 L of homologous blood. A momentary fall of platelet numbers and function occurred after the start of partial bypass (400 ml/min). Arterial pressures frequently showed an initial rise followed by a severe but transient drop in pressure, while the continuously monitored muscle surface P o 2 dropped to zero for a longer period. During total bypass, tissue oxygen supply was restored and was sufficient in both the BO and MO groups, as indicated by the improved P o 2 histograms (means between 3.45 and 4.50 kPa). After extracorporeal circulation a clear distinction appeared between the BO and the MO groups. In the BO group impaired P o 2 histograms (mean 1.83 ± 0.53 kPa) were observed, which coincided with a high systemic vascular resistance (mean 0.69 ± 0.14 kPa min/L/kg), low cardiac output (71 ± 9 ml/min/kg), and decreased platelet numbers (33.10 9 /L ± 16) and function (11% ± 6%). In comparison, the MO group had normal histograms (mean 5.45 ± 0.82 kPa, p < 0.05), normal systemic vascular resistance values (0.42 ± 0.07 kPa min/L/kg, N.S.), normal cardiac output (101 ± 12 L/min/kg, p < 0.05), and better maintained platelet numbers (128.10 9 /L ±23, p < 0.0005) and function (30% ± 11, p < 0.01). In this study, advantages of MO over BO perfusion could be quantitated in terms of better tissue oxygen supply after extracorporeal circulation, correlating with a better hemocompatibility. P o 2 muscle surface histograms appeared to be a reliable method to evaluate tissue oxygen supply, which reflects tissue perfusion.