To investigate the relationship between urine specific gravity (USG) and the risk
of arterial hypotension during general anaesthesia in healthy dogs that received a
dexmedetomidine & methadone premedication.
Prospective clinical cohort study.
A total of 75 healthy client owned dogs undergoing general anaesthesia for elective
After placing an intravenous catheter, dogs were premedicated with dexmedetomidine
(5 μg kg-1) and methadone (0.3 mg kg-1) intravenously. After induction of general anaesthesia with alfaxalone given to effect,
the bladder was expressed, and USG was measured. An arterial catheter was placed,
and residual blood was used to measure packed cell volume (PCV) and total protein
(TP). General anaesthesia was maintained with isoflurane vaporised in oxygen and a
femoral and sciatic nerve block were performed. Arterial blood pressure < 60 mmHg
was defined as hypotension and recorded by the anaesthetist. Treatment for hypotension
was performed in a stepwise manner following a flow chart. Frequency of hypotension,
treatment, and response to treatment were recorded. Logistic regression modelling
was used to assess the association between USG, TP, and PCV and incidence of perioperative
hypotension. p < 0.05.
Data from 14 dogs were excluded. Of the 61 dogs 16 (26 %) were hypotensive during
general anaesthesia, 15 dogs needed treatment of which 12 were responsive to a decrease
in inhalant vaporiser setting. The logistic regression model was not statistically
significant (p = 0.8). There was no significant association between USG (p = 0.6), TP (p = 0.4), PCV (p = 0.8) and arterial hypotension during general anaesthesia.
Conclusion and clinical relevance
In, healthy dogs premedicated with dexmedetomidine and methadone and maintained under
general anaesthesia with isoflurane and a femoral and sciatic nerve block, there was
no relationship between the specific gravity of urine collected after premedication
and intraoperative arterial hypotension.