Preliminary investigation into change in packed cell volume (PCV) after administration of two premedication protocols followed by induction and maintenance of anaesthesia in goats

Administration of certain sedative and anaesthetic agents can cause a reduction in circulating packed cell volume (PCV) probably due to sequestration of red cells in the spleen, increasing its size.

The effect on PCV after intravenous (IV) administration of butorphanol then diazepam, five minutes apart, or, these premedicants administered in reverse order, followed by propofol and isoflurane anaesthesia have not been investigated in goats.

Two cohorts of Saanen goats, one for castration (males, 5 months, 13 goats) and one for experimental orthopaedic surgery for another study (females, 3 to 5 years, 12 goats) were included in this research. Goats were randomized to receive either butorphanol or diazepam first followed by the other agent IV five minutes apart prior to anaesthesia. Four blood samples to analyse PCV were taken per goat (baseline, after the first and second premedicant administration, and after propofol induction). A between and within-subjects design ANOVA was applied to determine the difference in PCV over time between treatment groups.

Baseline PCV across all goats had a mean of 0.42 L/L (range 0.28 – 0.78 L/L). Both combinations of butorphanol and diazepam followed by induction of anaesthesia with propofol caused a clinically and statistically significant reduction in PCV (p < 0.001), with values dropping by 29.0 % (diazepam-first) and 29.1 % (butorphanol-first) from baseline values to the last sample (an overall decrease in PCV of 0.12 L/L for both groups). However, there was no statistical difference between groups (p = 0.696).

Results demonstrate that clinicians need to be aware of the magnitude of reduction in PCV that can occur when butorphanol and diazepam are used as premedicants prior to propofol administration.