Introduction: Extracorporeal life support (ECLS) is used for the support of cardiorespiratory failure. The standard ECLS circuit has a bridge between venous drainage and infusion tubing. This allows temporary dissociation of the patient from the ECLS circuit. The bridge is opened intermittently to prevent clotting (called flashing). Changes in systemic arterial pressure (SAP) due to changes in systemic vascular resistance (SVR) have been reported during flashing of the bridge which can be avoided if the bridge is kept partially open. An in vitro method is developed to study variations in SAP during closed and open-bridge ECLS.

Methods: A standard neonatal ECLS circuit with simulated SAP was established using normal saline as the circulating fluid. A“patient” extracorporeal flow rate (ECFR) of 300 ml/min, SAP of 60 mmHg, and post oxygenator pressure of 150 mmHg was our reference setting. SVR was changed, by changing the degree of occlusion, with the help of a graduated, clamping device, applied on the arterial catheter distal to the bridge. Resultant pressure changes were measured. The experiment was repeated with various ECFRs to the patient (100 to 300 ml/min) and through the bridge(100 to 300 ml/min using a custom-made, Hultquist-Sapp clamp). Variations in SAP (ΔP) per 100 Wood's units of SVR during all ECFRs were compared with repeated measures ANOVA followed by Tukey-Kramer test.

Results: Variations in SAP were significantly decreased by 12 to 40% during open-bridge ECLS compared to closed-bridge ECLS (p<0.001). We also measured a decrease in SAP and transient reverse flows through arterial and venous cannulae during flashing.

Conclusions: We conclude that open-bridge ECLS decreases the fluctuations in SAP that occur due to changes in SVR. It may also avoid possible deleterious effects of flashing of the bridge. Application of prolonged open bridge ECLS needs to be evaluated. Table

Table 1 Table: SAP changes (ΔP) during closed vs. open-bridge ECLS per 100 Wood's units. (Ratios of flows to patient and bridge during open bridge ECLS: a=1:2; b=1:1; c=2:1).
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