- Meeting abstract
The use of lithium dilution for measuring cardiac output and shunt fraction in patients during venovenous extracorporeal membrane oxygenation: a feasibility study in a flow model
Critical Care volume 2, Article number: P076 (1998)
Increasing numbers of adult and pediatric patients are being treated with venovenous ECMO using double lumen catheters. One of the major limitations of these catheters is the recirculation of arterialised blood back into the ECMO circuit, rather than passing through the right heart and pulmonary circulation. This shunt fraction may amount to 50% of the total flow of the ECMO circuit and the management of these patients has been hindered by the absence of a simple clinical method for measuring cardiac output and this shunt fraction. We have previously described a method of measuring cardiac output in which lithium chloride is injected intravenously and its plasma concentration-time curve measured in arterial blood using a lithium-selective electrode .
The patient circulation and ECMO circuit were represented by a flow model (Fig. 1). Pump C was set at 3 1/min throughout. Pump E (ECMO) and S (shunt) were varied to provide 3 shunt fractions, (approximately 12, 25, 50%) at each of 3 ECMO flow rates (approximately 0.5, 1.0 and 2.0 l/min). Following a bolus injection of lithium chloride (0.15 mmol), its dilution curves were recorded simultaneously by sensors A and B (see Fig. 1). The flows through pump S and pump C were calculated from the 9 pairs of lithium dilution curves and compared to the actual flows delivered.
This method would be suitable for adult and pediatric patients (in whom a smaller dose of lithium would be given). Although cardiac output could be measured during ECMO if the lithium was injected into the pulmonary artery, the proposed method avoids pulmonary artery catheterisation and allows shunt flows to be calculated.
Linton , et al: . Crit Care Med. 1997, 25: 1796-1800. 10.1097/00003246-199711000-00015.
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Jonas, M., Linton, R., Band, D. et al. The use of lithium dilution for measuring cardiac output and shunt fraction in patients during venovenous extracorporeal membrane oxygenation: a feasibility study in a flow model. Crit Care 2 (Suppl 1), P076 (1998). https://doi.org/10.1186/cc206