Influence of xylazine on the function of the LiDCO sensor in isoflurane anaesthetized horses.

The research explores the effect of the drug xylazine on the reading of the LiDCO sensor, a cardiac output measurement device, in isoflurane anaesthetized horses. It found that xylazine introduced a concentration-dependent bias in the readings of the LiDCO sensor, leading to overestimations.

Study Design and Methodology

• The study conducted was prospective and experimental, involving a sample size of eight Warmblood horses.
• All participating horses were premedicated with xylazine. Anaesthesia was then induced using midazolam and ketamine and was maintained using isoflurane in oxygen.
• The effects of xylazine were measured over a six-hour period during which cardiac output (CO) measurements and blood samples were taken before, during, and after a 60-minute infusion of xylazine.
• Simultaneously, sensor voltages exposed to blood and saline were also recorded and compared before, during, and after xylazine infusion using the Bland-Altman method of agreement – a statistical method often used to compare two measurement techniques on the same samples.

Results

• The CO values before xylazine were similar when measured by Bolus Thermodilution (BTD) and LiDCO. However, after introducing the xylazine infusion, CO values decreased for BTD, while the LiDCO measurements increased considerably, indicating a potential overestimation by the LiDCO sensor due to the presence of xylazine.
• The difference between sensor voltages exposed to saline and blood decreased during xylazine infusion. These differences were initially positive, but shifted to negative during the infusion.
• Significant correlations were found between xylazine plasma concentrations, differences in CO measurements, and differences in sensor voltage (saline – blood).

Conclusions and Implications

• This research proves the hypothesis that xylazine infusion can cause a concentration-dependent bias in LiDCO sensor measurements. This bias leads to an overestimation of cardiac output readings.
• The study findings suggest that sensor voltage differences (saline – blood) may potentially be used as a clinical tool to predict drug-sensor interactions, which would be a significant development in the field of clinical anaesthesia and monitoring.

The evidence from this study could potentially inform more accurate reading and calibration methods for LiDCO sensors, particularly when xylazine is involved or in other situations where drug-sensor interactions may impact measurement accuracy.