Quantification of recirculation by thermodilution during venovenous extracorporeal membrane oxygenation

Purpose: The aim of this study was to determine whether recirculation could be quantified by a thermodilution technique during venovenous (VV) extraco rporeal membrane oxygenation (ECMO) in a rabbit model. Methods: Five New Zealand white rabbits, mean weight, 4.5 (range, 3.7 to 5. 7) kg, were anesthetized, instrumented, cannulated with a double-lumen cath eter, and placed on VV ECMO. Serial injections of ice-cold saline were perf ormed at the arterial arm of the circuit, and the resultant temperature cha nge at various pump flows was measured at the venous arm of the circuit usi ng a thermistor-tipped catheter and a cardiac output computer. Results were compared with the respective 100% recirculation measured with all the circuit flow passing through the bridge. Results: Using linear regr ession, recirculation percentage could be calculated as: 19 + 0.1 x pump fl ow (R-2 = 0.81,P < .005). Recirculation correlated positively with pump flo w. Variability between results at each flow was less than 10%. Conclusions: Recirculation can be quantified during VV ECMO by measuring th e change in temperature in the venous arm using a cardiac output computer a fter injection of a known quantity of ice-cold saline in the arterial side of the circuit. The effect of interventions to reduce recirculation can be assessed conveniently and reliably. J Pediatr Surg 35:1411-1414. Copyright (C) 2000 by W.B. Saunders Company.