Summary of results
Of the 99 dogs enrolled on to the study, two dogs maintained the same body temperature throughout the procedure, two had an increase in body temperature( 0.1 ° C and 0.3 ° C) and the other 95 had a decrease in body temperature of between 0.2 ° C and 3.4 ° C( mean = 1.35, SD = 0.794).
The study found that the BCS of the dog and the duration of the MRI scan had a statistically significant effect on the decrease in the patient ' s body temperature.
A patient ' s age, the type of recumbency in the scanner and the premedication combination had no statistically significant effect on the patient ' s body temperature.
See Appendix 1( via link on page 49) for full results.
Discussion
Effect of BCS on body temperature
This study identified a significant negative correlation between BCSs and perianaesthetic temperature reduction, with higher BCS being associated with smaller temperature decreases( Table 1).
Table 1. Average decrease in body temperature in dogs grouped by body condition score( BCS).
BCS
1 – 3 2 ° C 4 – 5 1.4 ° C 6 – 9 1.2 ° C
Mean temperature decrease
Effect of patient age on body temperature
No significant correlation was observed between age and perianaesthetic temperature changes. This supports the findings of Clark-Price et al. [ 18 ], who similarly identified no age-related association during anaesthesia. However, this differs from studies reporting lower core body temperatures in older dogs and humans [ 19, 20 ].
These discrepancies may reflect differences in patient populations. Unlike studies focused on healthy dogs, the present cohort comprised patients with neurological disorders, some of which may alter thermoregulation, such as steroid-responsive meningitis-arteritis [ 21 ] and discospondylitis [ 22 ]. Furthermore, Zanghi et al. [ 19 ] suggested that cognitive status, rather than age per se, is more strongly linked to changes in core body temperature. As this was not evaluated here, future studies should investigate the influence of cognitive dysfunction on perianaesthetic thermoregulation.
Effect of recumbency on body temperature
No association was found between the type of recumbency and perianaesthetic temperature decrease. Interpretation is limited by the uneven group distribution: 67( 67.7 %) of the dogs were in dorsal recumbency, 30( 30.3 %) in sternal recumbency, and only 2( 2 %) changed recumbency mid-procedure. Similarly, Redondo et al. [ 3 ] observed that dogs in sternal or dorsal recumbency were more likely to develop hypothermia than those in lateral recumbency; however, their study also suffered from uneven group sizes, with 63 % in lateral, 27 % in dorsal and 8 % in sternal recumbency. Together, these findings emphasise the need for a more standardised study design with evenly distributed groups to determine whether recumbency plays a direct role in thermoregulation under anaesthesia.
These findings are consistent with those of Davis et al. [ 12 ], who reported a positive association between BCS and resting body temperature and suggested that subcutaneous fat provides insulation, which limits heat dissipation. Accordingly, dogs with a higher BCS may retain heat more effectively while anaesthetised.
However, the uneven distribution of dogs among the BCS groups weakened comparisons: of the 99 dogs, 55( 55.6 %) were overweight( BCS 6 – 9), 39( 39.4 %) were of ideal weight( BCS 4 – 5) and only five( 5.1 %) were underweight( BCS 1 – 3). Recruitment of larger and more balanced groups would have strengthened the analysis.
In addition, BCS is inherently subjective [ 9 ]. Unlike Piccione et al. [ 17 ], who used dual independent assessment with consensus scoring, this study relied on single-observer scoring, increasing the likelihood of bias.
Effect of premedication on body temperature
Only opioid, α2-adrenergic receptor agonist and acepromazine premedication protocols were evaluated in this study, due to small numbers in other groups. No significant correlation was observed between premedication type and temperature decrease, although sedative and anaesthetic agents are well known to influence thermoregulation. Previous research has shown that premedication may cause reductions in temperature via sedation, reduced activity and muscle relaxation [ 23, 24 ].
Clark-Price et al. [ 18 ] reported greater decreases in rectal temperature in dogs receiving α2-agonists, most likely due to vasoconstriction and peripheral cooling [ 25, 26 ]. They also found the opioid class to be important, with methadone( a full μ-agonist) being associated with greater temperature decreases than
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