Quantifying recirculation in extracorporeal membrane oxygenation: a new technique validated.

RATIONALE: The efficacy of veno-venous extracorporeal membrane oxygenation is limited by the phenomenon of recirculation, which is difficult to quantify. Existing measurement techniques using readily available equipment are unsatisfactory. OBJECTIVES: 1) To compare the accuracy of measurements of recirculation made using equations comparing blood oxygen content or saturation alone at different points in an ex vivo circuit; 2) to validate a new step-change technique for quantifying recirculation in vivo. METHODS: anesthetized greyhound dogs cannulated for veno-arterial support were connected to a circuit that allowed the creation of a known level of recirculation ex vivo and blood oxygen content/saturation monitoring. In two dogs, the accuracy of measurements derived from oxygen content and oxygen saturation were compared. The potential of a new technique for measuring recirculation in vivo by comparing the oxygen content of blood sampled during oxygenator bypass to that following a step-change in circuit oxygenation was demonstrated in a veno-venous pilot study and validated in a three-dog veno-arterial study. RESULTS: Measurements made using oxygen content versus oxygen saturation showed superior correlation with true recirculation (r(2)=0.87 vs. 0.64, p<0.0001) and less proportional measurement bias (10.3% vs. 49.8%, p=0.0045). Measurements of recirculation made using a step-change in circuit oxygenation and comparing oxygen content as is required for measuring in vivo recirculation overestimated by only 18.6% (95% Cl: 3.9-33.2%) and had excellent correlation with true values (r(2)=0.89). CONCLUSIONS: 1) Measurement of recirculation using oxygen content is superior to that using oxygen saturation alone, which demonstrates significant measurement bias; 2) the novel step-change technique is a sufficiently accurate technique for the measurement of recirculation in animal models.

Extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is a technique that involves oxygenation of blood outside the body, and provides support to selected patients with severe respiratory or cardiac failure. The two major ECMO modalities are venoarterial and venovenous. Data from several randomised trials support the use of ECMO in neonatal respiratory failure, and a recent randomised controlled trial of ECMO in adults has produced encouraging results. The evidence base for ECMO use in cardiac disease is developing, but progress has been slowed by considerations of clinical equipoise and evolving indications for ECMO. Advancing ECMO technology and increasing experience with ECMO techniques have improved patient outcomes, reduced complications and expanded the potential applications of ECMO. Awareness of the indications and implications of ECMO among doctors managing patients with severe but potentially reversible respiratory or cardiac failure may help facilitate better communication between health care teams and improve patient recovery.