Lithium dilution, pulse power analysis, and continuous thermodilution cardiac output measurements compared with bolus thermodilution in anaesthetized ponies.

This research evaluates different techniques for measuring cardiac output in anaesthetized ponies and finds that lithium dilution, continuous thermodilution, and pulse power analysis methods do not align accurately with the standard bolus thermodilution method.

Objective of the Study

• This study was conducted to compare the accuracy of different cardiac output (CO) measurement techniques against the standard bolus thermodilution (BTD) method on isoflurane-anaesthetized Shetland ponies.

Methods Employed in the Study

• Eight anaesthetized ponies were the subjects of this study. The ponies received infusions of xylazine, ketamine, and midazolam in specified quantities.
• The CO of these ponies was then measured using BTD, continuous thermodilution (CTD), lithium dilution (LiDCO), and pulse power analysis (PulseCO) methods.
• Lithium was injected into the jugular vein and blood was sampled from the facial artery for the detection of lithium, and this artery was also used for PulseCO.
• The measurements were recorded during four different haemodynamic conditions, which are regulated by the anaesthetic isoflurane and cardiovascular medication dobutamine.

Results Derived from the Study

• The study found a significant bias in the LiDCO-BTD and CTD-BTD comparisons, implying a deviation of the readings between these methods and the standard BTD.
• Due to the wide limits of agreement, the researchers concluded that the methods were not interchangeable.
• The research revealed a possible error in LiDCO that might explain the observed bias as the comparison between CTD and BTD showed less bias.
• Furthermore, changes in PulseCO did not correlate with those of BTD, and there was weak correlation and concordance between CTD and BTD.

Conclusions of the Study

• This study is the first to exhibit a significant bias between the LiDCO-BTD comparison in animals receiving xylazine, ketamine, and midazolam infusions.
• The discrepancy in readings reinforces the conclusion that neither PulseCO nor CTD have reliable trending abilities.
• The research concludes that further studies are necessary to understand the potential influences of different drugs on the precision of the LiDCOplus system.