Transpulmonary thermodilution (TPTD) using the injection of ice-cold saline is a reliable technique for measuring cardiac output in adults and children. We describe two cases in which these measurements were erroneously influenced by diffusion of the temperature indicator. If the thermistor-tipped arterial catheter is in close proximity to the central venous catheter, the injection of an ice- cold indicator might lead to an early temperature drop in the arterial catheter thus producing a biphasic dilution curve. This is called the “cross-talk phenomenon”. In the first case, concerning a child undergoing congenital cardiac surgery, we show that this phenomenon is dependent on blood flow. In the second case we demonstrate an animal experiment in which the cross-talk phenomenon occurred during a very low flow state. However in this case the venous catheter was positioned in the inferior caval vein and not in close proximity to the arterial catheter. The cross-talk phenomenon can also occur when the arterial catheter is not in close position to the central ve- nous catheter. We conclude that when using TPTD measurements with arterial and venous catheters both positioned in the lower body, the cross-talk phenomenon may occur. Therefore the thermodilution curve should always be closely monitored for a biphasic shape, especially when the cardiac output is low.
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