The effect of preanaesthetic oral trazodone hydrochloride on the induction dose of propofol: a preliminary retrospective study.

OBJECTIVE: To determine whether the administration of trazodone to dogs 2 hours prior to radiotherapy treatment reduced the dose of propofol required to induce anaesthesia. STUDY DESIGN: Retrospective, crossover, case-matched study. ANIMALS: Records of 30 client-owned dogs. METHODS: Anaesthetic records from all dogs undergoing weekly radiotherapy treatment between January 2020 and December 2020 were retrospectively assessed. All dogs were premedicated with 10 µg kg-1 alfentanil and 12 µg kg-1 atropine intravenously (IV) and anaesthesia was induced with IV propofol. In part 1, the propofol induction dose was compared between anaesthetics when trazodone was administered prior to the anaesthetic (T) versus not (NT). For part 2, control dogs not administered trazodone during the treatment course were case-matched based on bodyweight and tumour location and type. The propofol induction dose was compared between the first (C1) and last (C2) anaesthetic to identify the effects of confounding factors. A Wilcoxon signed-rank test for repeated measurements was performed to identify any significant differences in the propofol induction dose between NT and T in the study dogs and between C1 and C2 in the control dogs. RESULTS: In part 1, 15 study dogs that were administered trazodone prior to at least one anaesthetic were identified. A significant difference in propofol induction dose between groups NT and T was identified [3.3 (2.1-7.4) and 2.0 (1.5-5.0) mg kg-1, respectively; p = 0.003]. In part 2, 15 dogs were case-matched to the study cohort. The dose of propofol administered did not differ between the first and last anaesthetic [2.5 (1.6-6.4) and 2.6 (1.9-8.9) mg kg-1, respectively; p = 0.638]. CONCLUSIONS AND CLINICAL RELEVANCE: Preanaesthetic trazodone administration reduced the induction dose of propofol compared to when it was not administered to dogs following premedication with IV atropine and alfentanil.

The effect of body condition on propofol requirement in dogs.

OBJECTIVE: To determine if body condition score (BCS) influences the sedative effect of intramuscular (IM) premedication or the dose of intravenous (IV) propofol required to achieve endotracheal intubation in dogs. STUDY DESIGN: Prospective clinical study. ANIMALS: Forty-six client-owned dogs undergoing general anaesthesia. METHODS: Dogs were allocated to groups according to their BCS (BCS, 1 [emaciated] to 9 [obese]): Normal-weight Group (NG, n = 25) if BCS 4-5 or Over-weight Group (OG, n = 21) if BCS over 6. Dogs were scored for sedation prior to IM injection of medetomidine (5 µg kg(-1) ) and butorphanol (0.2 mg kg(-1) ) and twenty minutes later anaesthesia was induced by a slow infusion of propofol at 1.5 mg kg(-1)  minute(-1) until endotracheal intubation could be achieved. The total dose of propofol administered was recorded. Data were tested for normality then analyzed using Student t-tests, Mann-Whitney U tests, chi-square tests or linear regression as appropriate. RESULTS: Mean ( ± SD) propofol requirement in NG was 2.24 ± 0.53 mg kg(-1) and in OG was 1.83 ± 0.36 mg kg(-1) . The difference between the groups was statistically significant (p = 0.005). The degree of sedation was not different between the groups (p = 0.7). Post-induction apnoea occurred in 11 of 25 animals in the NG and three of 21 in OG (p = 0.052). CONCLUSIONS: Overweight dogs required a lower IV propofol dose per kg of total body mass to allow tracheal intubation than did normal body condition score animals suggesting that IV anaesthetic doses should be calculated according to lean body mass. The lower dose per kg of total body mass may have resulted in less post-induction apnoea in overweight/obese dogs. The effect of IM premedication was not significantly affected by the BCS. CLINICAL RELEVANCE: Induction of general anaesthesia with propofol in overweight dogs may be expected at lower doses than normal-weight animals.

Diabetes mellitus affects the duration of action of vecuronium in dogs.

OBJECTIVE: To compare the duration of action of vecuronium in diabetic dogs with a control group. STUDY DESIGN: Prospective clinical study. ANIMALS: Forty client-owned diabetic (n = 20) and non-diabetic dogs. METHODS: Dogs were considered free from other concurrent disease based on clinical examination and laboratory data. After pre-anaesthetic medication with acepromazine and methadone, anaesthesia was induced with intravenous (IV) propofol and maintained with isoflurane-nitrous oxide in oxygen. Neuromuscular blockade (NMB) was achieved with vecuronium, 0.1 mg kg(-1) IV and its effects recorded by palpation (pelvic limb digital extension) and electromyography (m. tibialis cranialis) of responses (twitches; T) to repeated train-of-four (TOF) nerve stimulation. Time to onset of NMB was the period between vecuronium injection and loss of fourth twitch (T4) in the TOF pattern recorded by EMG and palpation. Duration of NMB was defined as the time from drug administration to return of T1 by palpation (T1(tactile) ) and EMG (T1(EMG) ). Times to return of T2-4 were also recorded. Time from induction of anaesthesia to vecuronium injection was recorded. Heart rate, non-invasive mean arterial pressure, body temperature, end-tidal isoflurane and end-tidal CO(2) concentrations were recorded at onset of NMB and when T1(EMG) returned. Loss and return of palpable and EMG responses for diabetic and non-diabetic dogs were compared using t-tests and Mann Whitney U-tests. RESULTS: There were significant (p < 0.05) differences between diabetic and non-diabetic dogs for the return of all four palpable and EMG responses. Times (mean ± SD) for return of T1(tactile) were 13.2 ± 3.5 and 16.9 ± 4.2 minutes in diabetic and non-diabetic dogs respectively. There were no differences between diabetic and non-diabetic dogs in the time to onset of vecuronium with EMG or tactile monitoring. CONCLUSIONS AND CLINICAL RELEVANCE: The duration of action of vecuronium was shorter in diabetic dogs as indicated by both tactile and EMG monitoring.

Comparison of pain on injection during induction of anaesthesia with alfaxalone and two formulations of propofol in dogs.

OBJECTIVE: To compare the incidence of pain during injection of three intravenous induction agents in dogs. STUDY DESIGN: Prospective, crossover, randomized, blinded, clinical study. ANIMALS: Thirty dogs requiring anaesthesia for radiotherapy. METHODS: Dogs were anaesthetized on three occasions at weekly intervals. An IV cephalic catheter was placed, flushed with saline and alfentanil 0.01 mg kg(-1) and atropine 0.02 mg kg(-1) administered. After 30 seconds either: propofol lipid macroemulsion (Drug(P) ), propofol lipid-free microemulsion (Drug(PC) ) or alfaxalone (Drug(A)) was administered over 60 seconds. Each induction agent was administered once to each dog. Induction was recorded by video and reviewed by an assessor, unaware of treatment. Catheter placement (number of attempts, site, size and recent vein use) were recorded. Behavioural changes associated with pain or excitation, were recorded. Severity of pain on injection was recorded (mild, moderate or severe pain). Incidence of pain was analysed using logistic regression, excitation using McNemar's test (p < 0.05) and association of pain with induction agent and catheter placement using the Akaike Information Criterion (AIC). RESULTS: No dogs reacted to saline or Drug(A,) thus Drug(A) was excluded from analysis. Pain on injection occurred in six dogs (20%) with Drug(PC) and one dog (3.3%) with Drug(P). Pain was severe in four dogs with Drug(PC). Drug(P) resulted in a trend for reduced risk of pain compared to Drug(PC) (p = 0.076, odds ratio [confidence intervals] 0.14 [0.027-0.86]). Both propofol formulations resulted in greater risk of excitation than Drug(A) (p = 0.0003, odds ratio 4.5 [1.86-10.90]). Induction agent was associated with pain, whilst catheter placement was not. One dog developed facial oedema and one other dog skin necrosis adjacent to the catheter site following Drug(PC.) The study was terminated early due to ethical concerns about the severity of reactions with Drug(PC). conclusions and clinical relevance: Drug(PC) was associated with clinically relevant moderate to severe pain behaviour whilst Drug(A) and Drug(P) were not.

The sedative effects of low-dose medetomidine and butorphanol alone and in combination intravenously in dogs.

OBJECTIVE: To evaluate the sedative effects of intravenous (IV) medetomidine (1 microg kg(-1)) and butorphanol (0.1 mg kg(-1)) alone and in combination in dogs. STUDY DESIGN: Prospective, blinded, randomized clinical trial. ANIMALS: Sixty healthy (American Society of Anesthesiologists I) dogs, aged 6.2 +/- 3.2 years and body mass 26 +/- 12.5 kg. METHODS: Dogs were assigned to four groups: Group S (sodium chloride 0.9% IV), Group B (butorphanol IV), Group M (medetomidine IV) and Group MB (medetomidine and butorphanol IV). The same clinician assessed sedation before and 12 minutes after administration using a numerical scoring system in which 19 represented maximum sedation. Heart rate (HR), respiratory rate, pulse quality, capillary refill time and rectal temperature were recorded after each sedation score assessment. Sedation scores, sedation score difference (score after minus score before administration) and patient variables were compared using one-way anova for normally distributed variables and Kruskal-Wallis test for variables with skewed distributions and/or unequal variances. Where significance was found, further evaluation used Bonferroni multiple comparisons for pair-wise testing. RESULTS: Breed, sex, neuter status, age and body mass did not differ between groups. Sedation scores before substance administration were similar between groups (p = 0.2). Sedation scores after sedation were significantly higher in Group MB (mean 9.5 +/- SD 5.5) than in group S (2.5 +/- 1.8) (p < 0.001), group M (3.1 +/- 2.5) (p < 0.001) and group B (3.7 +/- 2.0) (p = 0.003). Sedation score difference was significantly higher in Group MB [7 (0-13)] than in Group S [0 (-1 to 4)] (p < 0.001) and Group M [0 (0-6)] (p < 0.001). HR decreased significantly in Groups M and MB compared with Group S (p < 0.05). CONCLUSION AND CLINICAL RELEVANCE: Low-dose medetomidine 1 microg kg(-1) IV combined with butorphanol 0.1 mg kg(-1) IV produced more sedation than medetomidine or butorphanol alone. HR was significantly decreased in both medetomidine groups.

A comparison of recovery times and characteristics with sevoflurane and isoflurane anaesthesia in horses undergoing magnetic resonance imaging.

OBJECTIVE: To compare recovery times and quality following maintenance of anaesthesia with sevoflurane or isoflurane after a standard intravenous induction technique in horses undergoing magnetic resonance imaging (MRI). STUDY DESIGN: Prospective, randomised, blinded clinical study. Animals One hundred ASA I/II horses undergoing MRI. MATERIALS AND METHODS: Pre-anaesthetic medication with intravenous acepromazine and romifidine was followed by induction of anaesthesia with diazepam and ketamine. The animals were randomised into two groups to receive either sevoflurane or isoflurane in oxygen. Horses were subjectively scored (0-5) for temperament before sedation, for quality of sedation, induction and maintenance and anaesthetic depth on entering the recovery area. Recoveries were videotaped and scored by an observer, unaware of the treatment, using two scoring systems. Times to the first movement, head lift, sternal recumbency and standing were recorded along with the number of attempts to achieve sternal and standing positions. Variables were compared using a Student t-test or Mann-Whitney U-test (p < 0.05), while the correlation between subjective recovery score and other relevant variables was tested calculating the Spearman Rank correlation coefficient and linear regression modelling performed when significant. RESULTS: Seventy-seven horses entered the final analysis, 38 received isoflurane and 39 sevoflurane. Body mass, age and duration of anaesthesia were similar for both groups. There were no differences in recovery times, scoring or number of attempts to achieve sternal recumbency and standing between groups. Weak, but significant, correlations were found between the subjective recovery score for the pooled data from both groups and both temperament and time in sternal recumbency. CONCLUSIONS: No differences in recovery times or quality were detected following isoflurane or sevoflurane anaesthesia after intravenous induction. Clinical relevance Sevoflurane affords no obvious advantage in recovery over isoflurane following a standard intravenous induction technique in horses not undergoing surgery.

Comparison of carprofen and meloxicam for 72 hours following ovariohysterectomy in dogs.

OBJECTIVE: To compare the peri- and post-operative (72 hours) analgesic effects of injectable and orally administered carprofen and meloxicam for ovariohysterectomy in dogs. STUDY DESIGN: Prospective, randomized clinical study. ANIMALS: Forty-three dogs undergoing elective ovariohysterectomy. MATERIALS AND METHODS: Dogs were randomly assigned to receive pre-operative carprofen, meloxicam or sterile saline by subcutaneous injection. Pre-anaesthetic medication was intramuscular acepromazine (0.02 mg kg(-1)) and methadone (0.2 mg kg(-1)). Anaesthesia was induced with either thiopentone or propofol injected to effect, and maintained with isoflurane in oxygen. Visual analogue scores (VAS) for pain and sedation were recorded at 1, 2, 3, 4 and 6 hours following tracheal extubation. Oral medication with the same treatment was continued post-operatively for 3 days, with VAS scores for pain being recorded before, and 2 hours after treatment on each day. Differences between group age, body mass, duration of general anaesthesia, time from treatment injection to tracheal extubation and time from treatment injection to first oral treatment were analysed using one-way analysis of variance and Kruskal-Wallis test. Visual analogue scores for pain and sedation were analysed using a re-randomization method. The significance level was set at p < 0.05. RESULTS: Meloxicam-treated subjects had lower mean VAS than the control group at 2 and 6 hours following tracheal extubation. Control group VAS were more varied than meloxicam scores (at 6 hours) and carprofen scores (at 3 and 6 hours). On the first post-operative day, pre- to post-treatment VAS scores decreased significantly after meloxicam. On day 3, scores in the meloxicam-treated group were significantly lower than control values after treatment. Changes in pre- to post-treatment VAS were greater in animals receiving either meloxicam or carprofen compared with those given saline. CONCLUSIONS AND CLINICAL RELEVANCE: Both carprofen and meloxicam provided satisfactory analgesia for 72 hours following ovariohysterectomy in dogs.