Voltage changes in the lithium dilution cardiac output sensor after exposure to blood from horses given xylazine.

BACKGROUND In a previous in vitro study using saline medium, the authors showed that certain drugs changed the voltages of lithium dilution cardiac output (LiDCO) sensors and also influenced their accuracy in measuring lithium concentrations. These two parameters correlated and so we examined whether such drug-sensor interaction exists when LiDCO sensor was exposed to xylazine in blood. METHODS Five healthy adult warm-blood horses were injected with 0.5 mg kg(-1) xylazine i.v. Physiological saline solution and venous blood were consecutively sampled through the same LiDCO sensor at 60, 45, 30, 15, and 0 min before and then 5, 15, 30, 45, and 60 min after xylazine injection. Sensor voltages were recorded and the differences between saline- and blood-exposed sensor voltages were compared at each time point. RESULTS Saline-exposed sensor voltages continuously increased in a non-linear pattern during the experiment. Blood-exposed sensor voltages also increased in a similar pattern, but it was interrupted by an abrupt increase in voltage after xylazine injection. The differences between saline- and blood-exposed sensor voltages were 7 (6.1-8) mV [median (range)] before xylazine but decreased significantly at 5 and 15 min after xylazine treatment. The highest drug-induced voltage change was 3.4 (1.6-7) mV. CONCLUSIONS This study showed that exposure of a LiDCO sensor to blood after a single clinically relevant dose of xylazine in horses changed the voltages of the sensors for 15 min. Comparison of saline- and blood-exposed sensor voltages could become a tool to detect drug-sensor interactions.