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A study by Lobetti and Lambrechts [ 16 ] looked at the effects of anaesthesia, including hypotension, on renal function in 35 healthy dogs, specifically to determine whether fluid therapy was necessary for healthy patients during the perioperative period. They found that, although no clinically relevant renal dysfunction was evident, there were significant increases in urine gamma-glutamyl transpeptidase( uGGT) activity and the ratio of uGGT to urine creatinine concentration 24 hours after surgery, compared with pre-surgery values. This indicated transient renal damage but was found not to be significant enough to warrant pre-emptive perioperative fluid therapy.
A study by Davis et al. [ 17 ] aimed to document changes in the concentration of urinary biomarkers and results of conventional diagnostic tests for acute kidney injury( AKI) following hypotension and fluid resuscitation. The study used six retired greyhounds, which were anaesthetised and had blood removed by phlebotomy to reduce their blood volume sufficiently to maintain a MAP of ≤40 mmHg. Blood samples were collected via a right jugular venous cannula and urine samples were collected from the bladder via an indwelling urinary catheter 1 hour after anaesthetic induction and at four subsequent time points: data were collected immediately before administration of the colloidal volume expander gelofusine following a 1-hour period of induced severe hypotension, and then at three intervals after MAP was restored to > 60 mmHg with gelofusine. Overall, urinary biomarker concentrations were significantly elevated from baseline, suggesting that the proximal renal tubules are damaged in the earliest stage of ischaemia – reperfusion.
In comparison with the study by Lobetti and Lambrechts [ 16 ], the research conducted by Davis et al. [ 17 ] demonstrated greater methodological quality by reporting the statistical significance of its findings, thereby enabling the reader to regard the results as reliable and valid. Nonetheless, both studies highlighted the potential consequences of hypotension under anaesthesia, particularly for renal function, and reinforced the importance of measuring BP in anaesthetised patients to recognise hypotension. This is reinforced in current literature, as Murrell and Ford- Fennah [ 9 ] stated that adequate renal blood flow is essential to maintain normal renal function, and this may be impaired by hypotension during anaesthesia.
Hypotension and anaesthesia
Hypotension is common in the anaesthetic period due to the effects of anaesthetic agents on the cardiovascular system [ 9 ]. A retrospective study by Gordon and Wagner [ 18 ] aimed to investigate the prevalence of hypotension in anaesthetised patients by reviewing the anaesthesia records of 101 healthy patients, comprising 42 cats and 59 dogs, undergoing elective procedures in private practice. During anaesthesia, SAP was measured with an oscillometric BP monitor in 75 % of the animals, and a Doppler ultrasonic flow detector with a sphygmomanometer in 25 % of the animals. Measurements were performed at least every 10 min and a SAP of < 90 mmHg was considered hypotensive. The study determined that 22 % of dogs and 33 % of cats met the criteria for hypotension while under general anaesthesia; however, Gordon and Wagner ' s [ 18 ] results could be questioned, due to the small sample size and lack of a sample size calculation.
A similar study by Costa et al. [ 19 ] investigated the frequency of hypotension in 188 dogs undergoing elective neutering surgeries and found that 87( 46 %) of the dogs were hypotensive and 72( 38 %) were mildly hypotensive. For this study, a MAP of < 60 mmHg was considered hypotensive and 60 – 79 mmHg was considered mildly hypotensive. Normotensive dogs were significantly older than hypotensive and mildly hypotensive dogs. Another notable finding was that dogs with hypotension had a significantly lower bodyweight than dogs with mild hypotension; however, no correlation was found for sex and MAP. Costa et al. [ 19 ] also investigated the opioid agent used alongside acepromazine; 133 dogs received morphine and 55 received methadone. The group that received morphine had a higher frequency of hypotension than the group that received methadone.
Both studies [ 18, 19 ] found hypotension to be a common occurrence in patients under anaesthesia, but each had different criteria for hypotension. Nonetheless, the studies reflect current thinking of the likes of Murrell and Ford- Fennah [ 9 ] on the influence of some anaesthetic drugs on MAP. Limited research was found on other combinations of anaesthetic drugs and their effects on BP.
A subsequent study by Costa et al. [ 20 ] investigated the prevalence of hypotension in young, healthy dogs undergoing neutering, and the potential factors predisposing them to hypotension under anaesthesia. Two cohorts, consisting of 71 and 24 dogs, were investigated. Variables including sex, age, bodyweight, and indices of hydration( such as urine specific gravity( USG), packed cell volume( PCV) and total solids) were measured before surgery. Invasive BP was monitored using a multiparameter device; MAP was plotted against time to allow calculation of the area under the MAP – time curve, which represents the cumulative MAP exposure over the monitoring period. This value was used as a measurement of correlation between different variables and MAP.
The study concluded that subclinical dehydration, indicated by USG, may contribute to hypotension during anaesthesia, and the authors suggested that withholding water before anaesthesia may influence USG. However, it is important to recognise that a complete data set, including bodyweight, sex, age, USG, total solids and PCV, was available for only 60 of the 71 dogs in the first cohort, as the temperament of some patients prohibited blood sampling.
Volume 41( 2) • April 2026
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