Evaluation of urine specific gravity as a predictor of hypotension during anaesthesia in healthy dogs premedicated with dexmedetomidine.

OBJECTIVE: To investigate the relationship between urine specific gravity (USG) and the risk of arterial hypotension during general anaesthesia (GA) in healthy dogs premedicated with dexmedetomidine and methadone. STUDY DESIGN: Prospective clinical cohort study. ANIMALS: A total of 75 healthy client-owned dogs undergoing GA for elective tibial plateau levelling osteotomy. METHODS: 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 GA with alfaxalone to effect, the bladder was expressed and USG measured. An arterial catheter was placed, and residual blood was used to measure packed cell volume (PCV) and total protein (TP). GA 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. RESULTS: Data from 14 dogs were excluded. Of the 61 dogs, 16 (26%) were hypotensive during GA, 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 GA. CONCLUSIONS AND CLINICAL RELEVANCE: In healthy dogs premedicated with dexmedetomidine and methadone and maintained under GA 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.

Use of midazolam in combination with medetomidine for premedication in healthy dogs.

OBJECTIVE: To assess the sedative effects, propofol sparing properties and impact on quality of induction and intubation of intravenous (IV) medetomidine and midazolam administered consecutively at different doses compared to medetomidine alone in healthy dogs for premedication. STUDY DESIGN: Prospective, randomized, blinded, clinical study. ANIMALS: A total of 40 adult healthy client owned dogs, weighing 18 ± 7 kg (mean ± standard deviation). METHODS: Dogs were assigned to four groups: medetomidine 15 µg kg-1 (positive control group), medetomidine 10 µg kg-1 and midazolam 0.2 mg kg-1, medetomidine 5 µg kg-1 and midazolam 0.3 mg kg-1, and medetomidine 5 µg kg-1 and midazolam 0.2 µg kg-1. The same clinician assessed sedation after administration at T2.5 minutes and T5 minutes using a composite simple descriptive sedation scale ranging between 0 and 15 (0 = no sedation; 15 = profound sedation). The dose of propofol for induction, quality of induction, ease of intubation and any adverse events were recorded. RESULTS: There was no significant difference in sedation scores between treatment groups at T2.5 minutes or T5 minutes (p = 0.82 and p = 0.63, respectively). Administration of midazolam in combination with medetomidine resulted in 71% of dogs displaying paradoxical behaviours (p < 0.0001) such as agitation, excitation, restlessness, aggression and vocalization, which was different from pre-sedation. Propofol requirement was not different between groups. Induction and tracheal intubation quality was smooth in all groups. CONCLUSION: In healthy dogs, at the doses studied, the combination of medetomidine-midazolam administered IV for premedication provided moderate sedation but was associated with a high incidence of paradoxical behaviours. This drug combination IV is not recommended for premedication in healthy dogs.