A dose titration study into the effects of diazepam or midazolam on the propofol dose requirements for induction of general anaesthesia in client owned dogs,premedicated with methadone and acepromazine

ObjectiveTo assess the effect of a benzodiazepine co–induction on propofol dose requirement for induction of anaesthesia in healthy dogs, to describe any differences between midazolam and diazepam and to determine an optimal benzodiazepine dose for co–induction.Study designProspective, randomised, blinded placebo controlled clinical trial.AnimalsNinety client owned dogs (ASA I–III, median body mass 21.5kg (IQR 10–33)) presented for anaesthesia for a variety of procedures.MethodsDogs were randomised to receive saline 0.1 mL kg^?1, midazolam or diazepam at 0.2, 0.3, 0.4 or 0.5 mg kg^?1. All dogs received 0.01 mg kg^?1 acepromazine and 0.2 mg kg^?1 methadone intravenously (IV). Fifteen minutes later, sedation was assessed and scored prior to anaesthetic induction. Propofol, 1 mg kg^?1, was administered IV, followed by the treatment drug. Further propofol was administered until endotracheal intubation was possible. Recorded data included patient signalment, sedation score, propofol dosage and any adverse reactions.ResultsMidazolam (all groups combined) significantly reduced propofol dose requirement compared to saline (p < 0.001) and diazepam (p = 0.008). Midazolam (0.4 mg kg^?1) significantly reduced propofol dose requirement (p = 0.014) compared to saline, however other doses failed to reach statistical significance. Diazepam did not significantly reduce propofol dose requirement compared to saline (p = 0.089). Dogs weighing <5 kg, regardless of treatment group, required a greater propofol dose than those weighing 5–40 kg (p = 0.002) and those >40 kg (p = 0.008). Dogs which were profoundly sedated required less propofol than those which were mildly sedated (p < 0.001) and adequately sedated (p = 0.003).Conclusions and clinical relevanceMidazolam (0.4 mg kg^?1) given IV after 1 mg kg^?1 of propofol significantly reduced the further propofol dose required for intubation compared to saline. At the investigated doses, diazepam did not have significant propofol dose sparing effects.     

The effects of diazepam or midazolam on the dose of propofol required to induce anaesthesia in cats

ObjectivesAssess effects of benzodiazepine administration on the propofol dose required to induce anaesthesia in healthy cats, investigate differences between midazolam and diazepam, and determine an optimal benzodiazepine dose for co-induction.Study designProspective, randomised, blinded, placebo-controlled clinical trial.AnimalsNinety client-owned cats (ASA I and II) with a median (interquartile range) body mass of 4.0 (3.4–4.9) kg.MethodsAll cats received 0.01 mg kg⁻¹ acepromazine and 0.2 mg kg⁻¹ methadone intravenously (IV). Fifteen minutes later, sedation was scored on a scale of 1–5, with 5 indicating greatest sedation. Propofol, 2 mg kg⁻¹, administered IV, was followed by either midazolam or diazepam at 0.2, 0.3, 0.4 or 0.5 mg kg⁻¹ or saline 0.1 mL kg⁻¹. Further propofol was administered until endotracheal intubation was possible. Patient signalment, sedation score, propofol dosage and adverse reactions were recorded.ResultsMidazolam and diazepam (all doses) significantly reduced the propofol dose required compared with saline (p < 0.001). There was no difference between midazolam and diazepam in propofol dose reduction (p = 0.488). All individual doses of midazolam reduced propofol requirement compared with saline (0.2 mg kg⁻¹, p = 0.028; 0.3 mg kg⁻¹, p = 0.006; 0.4 mg kg⁻¹, p < 0.001; 0.5 mg kg⁻¹, p = 0.009). Diazepam 0.2 mg kg⁻¹ did not reduce the propofol dose compared with saline (p = 0.087), but the remaining doses did (0.3 mg kg⁻¹, p = 0.001; 0.4 mg kg⁻¹, p = 0.032; 0.5 mg kg⁻¹, p = 0.041). Cats with sedation scores of 3 required less propofol than cats with scores of 2 (p = 0.008). There was no difference between groups in adverse events.Conclusions and clinical relevanceMidazolam (0.2–0.5 mg kg⁻¹) and diazepam (0.3–0.5 mg kg⁻¹) administered IV after 2 mg kg⁻¹ propofol significantly reduced the propofol dose required for tracheal intubation.     

Fentanyl or midazolam for co-induction of anaesthesia with propofol in dogs

ObjectivePropofol may cause adverse effects (e.g. apnoea, hypotension) at induction of anaesthesia. Co-induction of anaesthesia may reduce propofol requirements. The effect of fentanyl or midazolam on propofol dose requirements and cardiorespiratory parameters was studied.Study designRandomized, controlled, blinded clinical study.AnimalsSixty-six client owned dogs (35 male, 31 female, ASA I-II, age 6–120 months, body mass 4.7–48.0 kg) were selected.MethodsPre-medication with acepromazine (0.025 mg kg⁻¹) and morphine (0.25 mg kg⁻¹) was administered by intramuscular injection. After 30 minutes group fentanyl-propofol (FP) received fentanyl (2 μg kg⁻¹), group midazolam-propofol (MP) midazolam (0.2 mg kg⁻¹) injected over 30 seconds via a cephalic catheter and in a third group, control-propofol (CP), the IV catheter was flushed with an equivalent volume of heparinized saline. Anaesthesia was induced 2 minutes later, with propofol (4 mg kg⁻¹minute⁻¹) administered to effect. After endotracheal intubation anaesthesia was maintained with a standardized anaesthetic protocol. Pulse rate, respiratory rate (RR) and mean arterial pressure (MAP) were recorded before the co-induction agent, before induction, and 0, 2 and 5 minutes after intubation. Apnoea ≥30 seconds was recorded and treated. Sedation after pre-medication, activity after the co-induction agent, quality of anaesthetic induction and endotracheal intubation were scored.ResultsPropofol dose requirement was significantly reduced in FP [2.90 mg kg⁻¹(0.57)] compared to CP [3.51 mg kg⁻¹ (0.74)] and MP [3.58 mg kg⁻¹(0.49)]. Mean pulse rate was higher in MP than in CP or FP (p = 0.003). No statistically significant difference was found between groups in mean RR, MAP or incidence of apnoea. Activity score was significantly higher (i.e. more excited) (p = 0.0001), and quality of induction score was significantly poorer (p = 0.0001) in MP compared to CP or FP. Intubation score was similar in all groups.Conclusions and clinical relevanceFentanyl decreased propofol requirement but did not significantly alter cardiovascular parameters. Midazolam did not reduce propofol requirements and caused excitement in some animals.     

Alfaxalone in cyclodextrin for induction and maintenance of anaesthesia in ponies undergoing field castration

Objective  To evaluate the induction and maintenance of anaesthesia using alfaxalone following pre-anaesthetic medication with romifidine and butorphanol in ponies undergoing castration in the field.
Study design  Prospective clinical study.
Animals  Seventeen male ponies weighing 169 ± 29 kg.
Methods  The ponies were sedated with romifidine and butorphanol intravenously (IV). Induction time was recorded following administration of alfaxalone 1 mg kg⁻¹ and diazepam 0.02 mg kg⁻¹ IV. If movement during surgery occurred, alfaxalone 0.2 mg kg⁻¹ was administered IV. The quality of anaesthetic induction, and recovery were scored on a subjective scale of 1 (good) to 5 (poor). The number of attempts to attain sternal recumbency and standing, quality of recovery and times from induction to end of surgery, first head lift, sternal recumbency and standing were recorded.
Results  Induction quality was good [median score (range) 1 (1–3)] with a mean ± SD time of 29 ± 6 seconds taken to achieve lateral recumbency. Ten ponies required incremental doses of alfaxalone during surgery. Mean times to the end of surgery, first head lift, sternal recumbency and standing were 26 ± 9 minutes, 31 ± 9 minutes, 33 ± 9 minutes and 34 ± 9 minutes respectively. The number of attempts to attain sternal recumbency was 1(1–1) and to attain standing was 1(1–2). Quality of recovery was good, with a recovery score of 1(1–2).
Conclusions and clinical relevance  Alfaxalone provided smooth induction and recovery characteristics and was considered suitable for maintenance of anaesthesia for castration in ponies.     

Effects of altering the sequence of midazolam and propofol during co‐induction of anaesthesia

ObjectiveTo assess the effects of varying the sequence of midazolam and propofol administration on the quality of induction, cardiorespiratory parameters and propofol requirements in dogs.Study designRandomized, controlled, clinical study.AnimalsThirty‐three client owned dogs (ASA I‐III, 0.5–10 years, 5–30 kg).MethodsDogs were premedicated with acepromazine (0.02 mg kg^?1) and morphine (0.4 mg kg^?1) intramuscularly. After 30 minutes, group midazolam‐propofol (MP) received midazolam (0.25 mg kg^?1) intravenously (IV) before propofol (1 mg kg^?1) IV, group propofol‐midazolam (PM) received propofol before midazolam IV at the same doses, and control group (CP) received saline IV, instead of midazolam, before propofol. Supplementary boluses of propofol (0.5 mg kg^?1) were administered to effect to all groups until orotracheal intubation was completed. Behaviour after midazolam administration, quality of sedation and induction, and ease of intubation were scored. Heart rate (HR), respiratory rate, and systolic arterial blood pressure were recorded before premedication, post‐premedication, after midazolam or saline administration, and at 0, 2, 5, and 10 minutes post‐intubation. End‐tidal CO₂ and arterial oxygen haemoglobin saturation were recorded at 2, 5 and 10 minutes post‐intubation.ResultsQuality of sedation and induction, and ease of intubation were similar in all groups. Incidence of excitement was higher in the MP compared to CP (p = 0.014) and PM (p = 0.026) groups. Propofol requirements were decreased in MP and PM groups with respect to CP (p < 0.001), and in PM compared to MP (p = 0.022). The HR decreased after premedication in all groups, and increased after midazolam and subsequent times in MP (p = 0.019) and PM (p = 0.001) groups. Incidence of apnoea and paddling was higher in CP (p = 0.005) and MP (p = 0.031) groups than in PM.Conclusions and clinical relevanceAdministration of midazolam before propofol reduced propofol requirements although caused mild excitement in some dogs. Administration of propofol before midazolam resulted in less excitatory phenomena and greater reduction of propofol requirements.     

Intravenous sufentanil‐midazolam versus sevoflurane anaesthesia in medetomidine pre‐medicated Himalayan rabbits undergoing ovariohysterectomy

ObjectiveTo compare physiological effects of sufentanil-midazolam with sevoflurane for surgical anaesthesia in medetomidine premedicated rabbits.Study designProspective, randomized controlled experimental study.AnimalsEighteen female Himalayan rabbits, weight 2.1 ± 0.1 kg.MethodsPremedication with 0.1 mg kg⁻¹ medetomidine and 5 mg kg⁻¹ carprofen subcutaneously, was followed by intravenous anaesthetic induction with sufentanil (2.3 μg mL⁻¹) and midazolam (0.45 mg mL⁻¹). After endotracheal intubation, anaesthesia was maintained with sufentanil-midazolam (n = 9) or sevoflurane (n = 9). Ovariohysterectomy was performed. Intermittent positive pressure ventilation was performed as required. Physiological variables were studied perioperatively. Group means of physiologic data were generated for different anaesthetic periods. Data were compared for changes from sedation, and between groups by anova. Post-operatively, 0.05 mg kg⁻¹ buprenorphine was administered once and 5 mg kg⁻¹ carprofen once daily for 2–3 days. Rabbits were examined and weighed daily until one week after surgery.ResultsSmooth induction of anaesthesia was achieved within 5 minutes. Sufentanil and midazolam doses were 0.5 μg kg⁻¹ and 0.1 mg kg⁻¹, during induction and 3.9 μg kg⁻¹ hour⁻¹ and 0.8 mg kg⁻¹ hour⁻¹ during surgery, respectively. End-tidal sevoflurane concentration was 2.1% during surgery. Assisted ventilation was required in nine rabbits receiving sufentanil-midazolam and four receiving sevoflurane. There were no differences between groups in physiologic data other than arterial carbon dioxide. In rabbits receiving sevoflurane, mean arterial pressure decreased pre-surgical intervention, heart rate increased 25% during and after surgery and body weight decreased 4% post-operatively. Post-operative problems sometimes resulted from catheterization of the ear artery.ConclusionSevoflurane and sufentanil-midazolam provided surgical anaesthesia of similar quality. Arterial blood pressure was sustained during sufentanil-midazolam anaesthesia and rabbits receiving sevoflurane lost body weight following ovariohysterectomy. Mechanical ventilation was required with both anaesthetic regimens.Clinical relevanceAnaesthesia with sufentanil-midazolam in medetomidine premedicated healthy rabbits is useful in the clinical and the research setting, as an alternative to sevoflurane.     

Comparison of racemic ketamine and S-ketamine as agents for the induction of anaesthesia in goats

ObjectiveTo compare racemic ketamine and S-ketamine as induction agents prior to isoflurane anaesthesia.Study designProspective, blinded, randomized experimental study.AnimalsThirty-one healthy adult goats weighing 39-86 kg.MethodsGoats were premedicated with xylazine (0.1 mg kg^?1) intravenously (IV) given over 5 minutes. Each goat was assigned randomly to one of two treatments for IV anaesthetic induction: group RK (15 goats) racemic ketamine (3 mg kg^?1) and group SK (16 goats) S-ketamine (1.5 mg kg^?1). Time from end-injection to recumbency was measured and quality of anaesthetic induction and condition for endotracheal intubation were scored. Anaesthesia was maintained with isoflurane in oxygen for 90 minutes. Heart rate, invasive arterial blood pressure, oxygen saturation, temperature, end-tidal carbon dioxide and isoflurane were recorded every 5 minutes. Arterial blood samples were taken for analysis every 30 minutes. Recovery time to recurrence of swallowing reflex, to first head movement and to standing were recorded and recovery quality was scored. Two-way repeated measures anova, Mann-Whitney and a Mantel-Cox tests were used for statistical analysis as relevant with a significance level set at p < 0.05.ResultsInduction of anaesthesia was smooth and uneventful in all goats. There was no statistical difference between groups in any measured parameter. Side effects following anaesthetic induction included slight head or limb twitching, moving forward and backward, salivation and nystagmus but were minimal. Endotracheal intubation was achieved in all goats at first or second attempt. Recovery was uneventful on all occasions. All goats were quiet and needed only one or two attempts to stand.Conclusions and clinical relevanceS-ketamine at half the dose rate of racemic ketamine in goats sedated with xylazine and thereafter anaesthetised with isoflurane induces the same clinically measurable effects.     

Alfaxalone compared with ketamine for induction of anaesthesia in horses following xylazine and guaifenesin

ObjectiveTo compare anaesthesia induced with either alfaxalone or ketamine in horses following premedication with xylazine and guaifenesin.Study designRandomized blinded cross-over experimental study.AnimalsSix adult horses, five Standardbreds and one Thoroughbred; two mares and four geldings.MethodsEach horse received, on separate occasions, induction of anaesthesia with either ketamine 2.2 mg kg^?1 or alfaxalone 1 mg kg^?1. Premedication was with xylazine 0.5 mg kg^?1 and guaifenesin 35 mg kg^?1. Incidence of tremors/shaking after induction, recovery and ataxia on recovery were scored. Time to recovery was recorded. Partial pressure of arterial blood oxygen (PaO₂) and carbon dioxide (PaO₂), arterial blood pressures, heart rate (HR) and respiratory rates were recorded before premedication and at intervals during anaesthesia. Data were analyzed using Wilcoxon matched pairs signed rank test and are expressed as median (range).ResultsThere was no difference in the quality of recovery or in ataxia scores. Horses receiving alfaxalone exhibited a higher incidence of tremors/shaking on induction compared with those receiving ketamine (five and one of six horses respectively). Horses recovered to standing similarly [28 (24–47) minutes for alfaxalone; 22 (18–35) for ketamine] but took longer to recover adequately to return to the paddock after alfaxalone [44 (38–67) minutes] compared with ketamine [35 (30–47)]. There was no statistical difference between treatments in effect on HR, PaO₂ or PaCO₂ although for both regimens, PaO₂ decreased with respect to before premedication values. There was no difference between treatments in effect on blood pressure.Conclusions and clinical relevanceBoth alfaxalone and ketamine were effective at inducing anaesthesia, although at induction there were more muscle tremors after alfaxalone. As there were no differences between treatments in relation to cardiopulmonary responses or quality of recovery, and only minor differences in recovery times, both agents appear suitable for this purpose following the premedication regimen used in this study.     

Midazolam,as a co‐induction agent,has propofol sparing effects but also decreases systolic blood pressure in healthy dogs

ObjectiveTo evaluate the effects of the co-administration of midazolam on the dose requirement for propofol anesthesia induction, heart rate (HR), systolic arterial pressure (SAP) and the incidence of excitement.Study designProspective, randomized, controlled and blinded clinical study, with owner consent.AnimalsSeventeen healthy, client owned dogs weighing 28 ± 18 kg and aged 4.9 ± 3.9 years old.MethodsDogs were sedated with acepromazine 0.025 mg kg^?1 and morphine 0.25 mg kg^?1 intramuscularly (IM), 30 minutes prior to induction of anesthesia. Patients were randomly allocated to receive midazolam (MP; 0.2 mg kg^?1) or sterile normal saline (CP; 0.04 mL kg^?1) intravenously (IV) over 15 seconds. Propofol was administered IV immediately following test drug and delivered at 3 mg kg^?1 minute^?1 until intubation was possible. Scoring of pre-induction sedation, ease of intubation, quality of induction, and presence or absence of excitement following co-induction agent, was recorded. HR, SAP and respiratory rate (f_R) were obtained immediately prior to, immediately following, and 5 minutes following induction of anesthesia.ResultsThere were no significant differences between groups with regard to weight, age, gender, or sedation. Excitement occurred in 5/9 dogs following midazolam administration, with none noted in the control group. The dose of propofol administered to the midazolam group was significantly less than in the control group. Differences in HR were not significant between groups. SAP was significantly lower in the midazolam group compared with baseline values 5 minutes after its administration. However, values remained clinically acceptable.Conclusions and clinical relevanceThe co-administration of midazolam with propofol decreased the total dose of propofol needed for induction of anesthesia in sedated healthy dogs, caused some excitement and a clinically unimportant decrease in SAP.     

Short‐term anaesthesia with xylazine,diazepam/ketamine for castration in horses under field conditions: Use of intravenous lidocaine

Reasons for performing study: Lidocaine single boluses and/or constant rate infusions are commonly administered intraoperatively during inhalant anaesthesia to lower inhalant concentrations, promote or maintain gastrointestinal motility, and potentially supplement analgesia. The benefits of using lidocaine with injectable anaesthesia for field surgeries has not been fully explored to determine advantages and disadvantages of lidocaine as an anaesthetic and analgesic adjunct in these conditions and impact on recovery quality. Objectives: To evaluate the use of systemic lidocaine with a standard field injectable anaesthetic protocol related to the need for additional drug administration as well as overall recovery score and quality. Hypothesis: The administration of systemic lidocaine with xylazine‐diazepam/ketamine anaesthesia for castration in the field decreases the need for additional injectable doses required for maintenance, but prolong and potentially impact the overall recovery score and quality in horses. Methods: Thirty client‐owned horses underwent standard injectable anaesthesia for field castration. Fifteen horses received lidocaine 3 mg/kg bwt, i.v. as a single bolus, and 15 received saline equal volume. The horses were monitored for the need for additional injectable anaesthetics and scored for overall recovery and quality by a blinded anaesthetist. Results: There were no statistically significant differences in the overall recovery score and quality, or need for additional injectable anaesthetic between horses receiving lidocaine and those receiving saline. There was a significantly longer time for the horses to stand after induction in the lidocaine group (mean 30.7 min) vs. saline group (mean 22.5 min) (P<0.04). Conclusions: Lidocaine, 3 mg/kg bwt i.v., does not adversely affect recovery using injectable field regimes, but the overall recovery period was longer. Lidocaine does not appear to reduce the need for additional injectable administration during surgery. Potential relevance: Further research is warranted to define the benefit of systemic lidocaine with field anaesthesia in horses by exploring the ideal dose and plasma level of lidocaine with injectable anaesthesia.     

Comparison of propofol with ketofol,a propofol‐ketamine admixture,for induction of anaesthesia in healthy dogs

ObjectiveTo compare anaesthetic induction in healthy dogs using propofol or ketofol (a propofol-ketamine mixture).Study designProspective, randomized, controlled, ‘blinded’ study.AnimalsSeventy healthy dogs (33 males and 37 females), aged 6–157 months and weighing 4–48 kg.MethodsFollowing premedication, either propofol (10 mg mL^?1) or ketofol (9 mg propofol and 9 mg ketamine mL^?1) was titrated intravenously until laryngoscopy and tracheal intubation were possible. Pulse rate (PR), respiratory rate (f_R) and arterial blood pressure (ABP) were compared to post-premedication values and time to first breath (TTFB) recorded. Sedation quality, tracheal intubation and anaesthetic induction were scored by an observer who was unaware of treatment group. Mann–Whitney or t-tests were performed and significance set at p = 0.05.ResultsInduction mixture volume (mean ± SD) was lower for ketofol (0.2 ± 0.1 mL kg^?1) than propofol (0.4 ± 0.1 mL kg^?1) (p < 0.001). PR increased following ketofol (by 35 ± 20 beats minute^?1) but not consistently following propofol (4 ± 16 beats minute^?1) (p < 0.001). Ketofol administration was associated with a higher mean arterial blood pressure (MAP) (82 ± 10 mmHg) than propofol (77 ± 11) (p = 0.05). TTFB was similar, but ketofol use resulted in a greater decrease in f_R (median (range): ketofol -32 (-158 to 0) propofol -24 (-187 to 2) breaths minute^?1) (p < 0.001). Sedation was similar between groups. Tracheal intubation and induction qualities were better with ketofol than propofol (p = 0.04 and 0.02 respectively).Conclusion and clinical relevanceInduction of anaesthesia with ketofol resulted in higher PR and MAP than when propofol was used, but lower f_R. Quality of induction and tracheal intubation were consistently good with ketofol, but more variable when using propofol.     

S‐ketamine versus racemic ketamine in dogs: their relative potency as induction agents

ObjectiveTo determine the potency ratio between S-ketamine and racemic ketamine as inductive agents for achieving tracheal intubation in dogs.Study designProspective, randomized, ‘blinded’, clinical trial conducted in two consecutive phases.Animals112 client-owned dogs (ASA I or II).MethodsAll animals were premedicated with intramuscular acepromazine (0.02 mg kg⁻¹) and methadone (0.2 mg kg⁻¹). In phase 1, midazolam (0.2 mg kg⁻¹) with either 3 mg kg⁻¹ of racemic ketamine (group K) or 1.5 mg kg⁻¹ of S-ketamine (group S) was administered IV, for induction of anaesthesia and intubation. Up to two additional doses of racemic (1.5 mg kg⁻¹) or S-ketamine (0.75 mg kg⁻¹) were administered if required. In phase 2, midazolam (0.2 mg kg⁻¹) with 1 mg kg⁻¹ of either racemic ketamine (group K) or S-ketamine (group S) was injected and followed by a continuous infusion (1 mg kg minute⁻¹) of each respective drug. Differences between groups were statistically analyzed via t-test, Fisher exact test and ANOVA for repeated measures.ResultsDemographics and quality and duration of premedication, induction and intubation were comparable among groups. During phase 1 it was possible to achieve tracheal intubation after a single dose in more dogs in group K (n = 25) than in group S (n = 16) (p = 0.046). A dose of 3 mg kg⁻¹ S-ketamine allowed tracheal intubation in the same number of dogs as 4.5 mg kg⁻¹ of racemic ketamine. The estimated potency ratio was 1.5:1. During phase 2, the total dose (mean ± SD) of S-ketamine (4.02 ±1.56 mg kg⁻¹) and racemic ketamine (4.01 ± 1.42) required for tracheal intubation was similar.Conclusion and clinical relevanceRacemic and S-ketamine provide a similar quality of anaesthetic induction and intubation. S-ketamine is not twice as potent as racemic ketamine and, if infused, the potency ratio is 1:1.     

Comparison of diazepam–ketamine and thiopentone for induction of anaesthesia in healthy dogs

Objective To compare the anaesthetic and cardiopulmonary effects of a diazepam–ketamine combination with thiopentone for induction of anaesthesia in dogs. Animal population Twenty healthy dogs of various breeds weighing between 3.8 and 42.6 kg undergoing major orthopaedic or soft tissue surgery. Materials and methods Pre‐anaesthetic medication in all cases was intramuscular acepromazine and methadone given 30 minutes before induction of anaesthesia. Each animal was then randomly assigned to receive either thiopentone or diazepam and ketamine. Quality of conditions for, and time to tracheal intubation were recorded. Anaesthesia was maintained with halothane in oxygen and nitrous oxide. Heart rate, respiratory rate, systolic blood pressure, end tidal carbon dioxide tensions and oxygen saturation were recorded at 10 minute intervals throughout surgery. The quality of recovery from anaesthesia was assessed. Results The quality of induction in both groups was satisfactory. The total mean time (± SD) to tracheal intubation (162 ± 84 seconds) was significantly longer in dogs receiving diazepam and ketamine compared to dogs receiving thiopentone (62 ± 28 seconds). Heart rate, systolic blood pressure and end tidal carbon dioxide concentration were not significantly different between groups. Respiratory rate was significantly higher in the diazepam–ketamine group between 0 and 30 minutes. The quality of recovery was similar in each group. Conclusions There appear to be fewer differences between the induction agents examined in this study than was previously believed. No pressor, or other cardiovascular stimulating effects were detected in the dogs that received diazepam and ketamine. Clinical relevance The absence of obvious differences between groups suggests that pre‐anaesthetic medication, inhaled anaesthetics and the physiological effects of surgery itself probably had a greater effect on the variables studied than the induction agent used. Further studies are required to determine whether diazepam and ketamine offers significant advantages over other induction agents in the unhealthy dog.