An evaluation of anaesthetic induction in healthy dogs using rapid intravenous injection of propofol or alfaxalone

ObjectiveTo evaluate quality of anaesthetic induction and cardiorespiratory effects following rapid intravenous (IV) injection of propofol or alfaxalone.Study designProspective, randomised, blinded clinical study.AnimalsSixty healthy dogs (ASA I/II) anaesthetized for elective surgery or diagnostic procedures.MethodsPremedication was intramuscular acepromazine (0.03 mg kg^?1) and meperidine (pethidine) (3 mg kg^?1). For anaesthetic induction dogs received either 3 mg kg^?1 propofol (Group P) or 1.5 mg kg^?1 alfaxalone (Group A) by rapid IV injection. Heart rate (HR), respiratory rate (f_R) and oscillometric arterial pressures were recorded prior to induction, at endotracheal intubation and at 3 and 5 minutes post-intubation. The occurrence of post-induction apnoea or hypotension was recorded. Pre-induction sedation and aspects of induction quality were scored using 4 point scales. Data were analysed using Chi-squared tests, two sample t-tests and general linear model mixed effect anova (p < 0.05).ResultsThere were no significant differences between groups with respect to sex, age, body weight, f_R, post-induction apnoea, arterial pressures, hypotension, SpO₂, sedation score or quality of induction scores. Groups behaved differently over time with respect to HR. On induction HR decreased in Group P (?2 ± 28 beats minute^?1) but increased in Group A (14 ± 33 beats minute^?1) the difference being significant (p = 0.047). However HR change following premedication also differed between groups (p = 0.006). Arterial pressures decreased significantly over time in both groups and transient hypotension occurred in eight dogs (five in Group P, three in Group A). Post-induction apnoea occurred in 31 dogs (17 in Group P, 14 in Group A). Additional drug was required to achieve endotracheal intubation in two dogs.Conclusions and Clinical relevanceRapid IV injection of propofol or alfaxalone provided suitable conditions for endotracheal intubation in healthy dogs but post-induction apnoea was observed commonly.     

A comparison of induction of anaesthesia using a target-controlled infusion device in dogs with propofol or a propofol and alfentanil admixture

ObjectiveTo compare induction targets, and the haemodynamic and respiratory effects, of propofol, or as an admixture with two different concentrations of alfentanil, delivered via a propofol target-controlled infusion (TCI) system.Study designProspective blinded randomized clinical study.Animals Sixty client-owned dogs scheduled for elective surgery under general anaesthesia. Mean body mass (SD) 28.5 kg (8.7) and mean age (SD) 3.5 years (2.4).MethodsDogs received pre-anaesthetic medication of acepromazine (0.03 mg kg⁻¹) and morphine (0.2 mg kg⁻¹) administered intramuscularly. Animals were randomly assigned to receive one of three induction protocols: propofol alone (group 1), a propofol/alfentanil (11.9 μg mL⁻¹) admixture (group 2), or a propofol/alfentanil (23.8 μg mL⁻¹) admixture (group 3), via a TCI system. Blood target concentrations were increased until endotracheal intubation was achieved, and induction targets were recorded. Heart rate (HR), respiratory rate (f_r) and non-invasive arterial blood pressure were recorded pre-induction, at endotracheal intubation (time 0) and at 3 and 5 minutes post-intubation (times 3 and 5, respectively). Data were analysed using anova for normally distributed data or Kruskal–Wallis test, with significance assumed at p < 0.05.ResultsThere were no significant differences between groups with respect to age, body mass, HR, f_r, systolic and diastolic blood pressure. The blood propofol targets to achieve endotracheal intubation were significantly higher in group 1 compared with groups 2 and 3. Mean arterial blood pressure (MAP) was significantly higher in group 1 at time 0 when compared with groups 2 and 3.Conclusions and clinical relevanceInduction of anaesthesia with a TCI system can be achieved at lower blood propofol targets when using a propofol/alfentanil admixture compared with using propofol alone. However, despite reduced targets with both propofol/alfentanil admixture groups, MAP was lower immediately following endotracheal intubation than when using propofol alone.     

Effect of fentanyl on the induction dose and minimum infusion rate of propofol preventing movement in dogs

Objective

To determine the effect of fentanyl on the induction dose of propofol and minimum infusion rate required to prevent movement in response to noxious stimulation (MIR_NM) in dogs.

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.     

A comparison of the effects of two different doses of ketamine used for co-induction of anaesthesia with a target-controlled infusion of propofol in dogs

ObjectiveTo assess the cardiorespiratory and hypnotic-sparing effects of ketamine co-induction with target-controlled infusion of propofol in dogs.Study designProspective, randomized, blinded clinical study.AnimalsNinety healthy dogs (ASA grades I/II). Mean body mass 30.5 ± SD 8.6 kg and mean age 4.2 ± 2.6 years.MethodsAll dogs received pre-anaesthetic medication with acepromazine (0.03 mg kg^?1) and morphine (0.2 mg kg^?1) administered intramuscularly 30 minutes prior to induction of anaesthesia. Heart rate and respiratory rate were recorded prior to pre-medication. Animals were allocated into three different groups: Group 1 (control) received 0.9% NaCl, group 2, 0.25 mg kg^?1 ketamine and group 3, 0.5 mg kg^?1 ketamine, intravenously 1 minute prior to induction of anaesthesia, which was accomplished using a propofol target-controlled infusion system. The target propofol concentration was gradually increased until endotracheal intubation was possible and the target concentration at intubation was recorded. Heart rate, respiratory rate and noninvasive blood pressure were recorded immediately prior to induction, at successful intubation and at 3 and 5 minutes post-intubation. The quality of induction was graded according to the amount of muscle twitching and paddling observed. Data were analysed using a combination of chi-squared tests, Fisher's exact tests, Kruskal–Wallis, and anova with significance assumed at p< 0.05.ResultsThere were no significant differences between groups in the blood propofol targets required to achieve endotracheal intubation, nor with respect to heart rate, noninvasive blood pressure or quality of induction. Compared with the other groups, the incidence of post-induction apnoea was significantly higher in group 3, but despite this dogs in this group had higher respiratory rates overall.Conclusions and clinical relevanceUnder the conditions of this study, ketamine does not seem to be a useful agent for co-induction of anaesthesia with propofol in dogs.     

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.     

Chronotropic effect of propofol or alfaxalone following fentanyl administration in healthy dogs

ObjectiveTo compare the effect of alfaxalone and propofol on heart rate (HR) and blood pressure (BP) after fentanyl administration in healthy dogs.Study designProspective, randomised clinical study.AnimalsFifty healthy client owned dogs (ASA I/II) requiring general anaesthesia for elective magnetic resonance imaging for neurological conditions.MethodsAll dogs received fentanyl 7 μg kg⁻¹ IV and were allocated randomly to receive either alfaxalone (n = 25) or propofol (n = 25) to effect until endotracheal (ET) intubation was possible. Heart rate and oscillometric BP were measured before fentanyl (baseline), after fentanyl (Time F) and after ET intubation (Time GA). Post-induction apnoea were recorded. Data were analysed using Fisher’s exact test, Mann Whitney U test and one-way anova for repeated measures as appropriate; p value <0.05 was considered significant.ResultsDogs receiving propofol showed a greater decrease in HR (-14 beat minute⁻¹, range -47 to 10) compared to alfaxalone (1 beat minute⁻¹, range -33 to 26) (p = 0.0116). Blood pressure decreased over the three time periods with no difference between groups. Incidence of post-induction apnoea was not different between groups.ConclusionFollowing fentanyl administration, anaesthetic induction with propofol resulted in a greater negative chronotropic effect while alfaxalone preserved or increased HR.Clinical relevanceFollowing fentanyl administration, HR decreases more frequently when propofol rather than alfaxalone is used as induction agent. However, given the high individual variability and the small change in predicted HR (-7.7 beats per minute after propofol), the clinical impact arising from choosing propofol or alfaxalone is likely to be small in healthy animals. Further studies in dogs with myocardial disease and altered haemodynamics are warranted.     

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.     

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.     

A comparison of cardiopulmonary function,recovery quality,and total dosages required for induction and total intravenous anesthesia with propofol versus a propofol‐ketamine combination in healthy Beagle dogs

ObjectiveTo compare cardiopulmonary function, recovery quality, and total dosages required for induction and 60 minutes of total intravenous anesthesia (TIVA) with propofol (P) or a 1:1 mg mL⁻¹ combination of propofol and ketamine (KP).Study designRandomized crossover study.AnimalsTen female Beagles weighing 9.4 ± 1.8 kg.MethodsDogs were randomized for administration of P or KP in a 1:1 mg mL⁻¹ ratio for induction and maintenance of TIVA. Baseline temperature, pulse, respiratory rate (f_R), noninvasive mean blood pressure (MAP), and hemoglobin oxygen saturation (SpO₂) were recorded. Dogs were intubated and spontaneously breathed room air. Heart rate (HR), f_R, MAP, SpO₂, end tidal carbon dioxide tension (Pe’CO₂), temperature, and salivation score were recorded every 5 minutes. Arterial blood gas analysis was performed at 10, 30, and 60 minutes, and after recovery. At 60 minutes the infusion was discontinued and total drug administered, time to extubation, and recovery score were recorded. The other treatment was performed 1 week later.ResultsKP required significantly less propofol for induction (4.0 ± 1.0 mg kg⁻¹ KP versus 5.3 ±1.1 mg kg⁻¹ P, p = 0.0285) and maintenance (0.3 ± 0.1 mg kg⁻¹ minute⁻¹ KP versus 0.6 ±0.1 mg kg⁻¹ minute⁻¹ P, p = 0.0018). Significantly higher HR occurred with KP. Both P and KP caused significantly lower MAP compared to baseline. MAP was significantly higher with KP at several time points. P had minimal effects on respiratory variables, while KP resulted in significant respiratory depression. There were no significant differences in salivation scores, time to extubation, or recovery scores.Conclusions and clinical relevanceTotal intravenous anesthesia in healthy dogs with ketamine and propofol in a 1:1 mg mL⁻¹ combination resulted in significant propofol dose reduction, higher HR, improved MAP, no difference in recovery quality, but more significant respiratory depression compared to propofol alone.     

Effect of benzodiazepines on the dose of alfaxalone needed for endotracheal intubation in healthy dogs

Objective

To evaluate the dose-sparing effect of midazolam or diazepam on the dose of alfaxalone required to achieve endotracheal intubation in premedicated dogs.

Effects of propofol administration rates on cardiopulmonary function and anaesthetic depth during anaesthetic induction in rats

Objective  To compare the effect of three different administration rates of one dose of propofol on the depth and duration of anaesthesia and cardiopulmonary function during induction of anaesthesia in rats using electroencephalogram (EEG) and clinical signs.
Study design  Prospective, randomized experimental trial.
Animals  Twenty-one, adult, male Sprague-Dawley rats weighing 341 ± 26 g (mean ± SD) (325 to 480 g).
Methods  Animals were randomly divided into three groups to receive 20 mg kg⁻¹ propofol as a bolus injection over 1, 2 or 3 minutes (groups P1, P2 and P3 respectively) intravenously (IV). The total duration and number of burst suppression (BS) episodes in the EEG, the time to loss of righting reflex, reflex score from electrical stimulation, respiratory rate, mean arterial pressure and pulse rate were measured from the beginning of propofol injection.
Results  While loss of reflex to electrical stimulus and time to loss of righting reflex in group P3 were slower than in other groups, the total duration and number of BS episodes in group P3 were significantly higher than in groups P1 and P2 and cardiopulmonary depression was less prominent in group P3 than in groups P1 and P2 up to 2 minutes after the start of administration.
Conclusions  Twenty milligram per kg propofol administration IV for 3 minutes increased the duration of anaesthesia and decreased cardiopulmonary depression in rats.
Clinical relevance  Slower infusion of propofol produced surgical anaesthesia with less cardiopulmonary depression in rats.     

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.     

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

ObjectiveTo determine whether the administration of trazodone to dogs 2 hours prior to radiotherapy treatment reduced the dose of propofol required to induce anaesthesia.Study designRetrospective, crossover, case-matched study.AnimalsRecords of 30 client-owned dogs.MethodsAnaesthetic 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.ResultsIn 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 relevancePreanaesthetic trazodone administration reduced the induction dose of propofol compared to when it was not administered to dogs following premedication with IV atropine and alfentanil.     

Determining an optimum propofol infusion rate for induction of anaesthesia in healthy dogs: a randomized clinical trial

ObjectiveTo determine an optimum infusion rate of propofol that permitted rapid tracheal intubation while minimizing the duration of postinduction apnoea.Study designProspective, randomized, blinded clinical trial.AnimalsA total of 60 client-owned dogs presented for elective neutering and radiography.MethodsDogs were randomly allocated to one of five groups (groups A–E) to have propofol at an infusion rate of 0.5, 1, 2, 3, or 4 mg kg^–1 minute^–1, respectively, following intramuscular premedication with methadone 0.5 mg kg^–1 and dexmedetomidine 5 μg kg^–1. Propofol administration was stopped when adequate conditions for tracheal intubation were identified. Time to tracheal intubation and duration of apnoea were recorded. If oxygen haemoglobin saturation decreased to < 90%, manual ventilation was initiated. A one-way analysis of covariance was conducted to compare the effect of propofol infusion rate on duration of apnoea and intubation time whilst controlling for covariates, followed by post hoc tests. The significance level was set at p < 0.05.ResultsPropofol infusion rate had a significant effect on duration of apnoea (p = 0.004) and intubation time (p < 0.001) after controlling for bodyweight and sedation scores, respectively. The adjusted means (± standard error) of duration of apnoea were significantly shorter in groups A and B (49 ± 39 and 67 ± 37 seconds, respectively) than in groups C, D and E (207 ± 34, 192 ± 36 and 196 ± 34 seconds, respectively). Group B (115 ± 10 seconds) had a significantly shorter intubation time than group A (201 ± 10 seconds, p < 0.001).Conclusions and clinical relevanceAn infusion rate of 1.0 mg kg^–1 minute^–1 (group B) appears to offer the optimal compromise between speed of induction and duration of postinduction apnoea.     

Dose requirement and cardiopulmonary effects of diluted and undiluted propofol for induction of anaesthesia in dogs

ObjectiveTo compare the dose, cardiopulmonary effects and quality of anaesthetic induction in dogs using propofol (10 mg mL^–1) and diluted propofol (5 mg mL^–1).Study designRandomized, blinded, clinical study.AnimalsA total of 28 client-owned dogs (12 males/16 females).MethodsFollowing intramuscular acepromazine (0.02 mg kg^–1) and methadone (0.2 mg kg^–1), propofol (UP, 10 mg mL^–1) or diluted propofol (DP, 5 mg mL^–1) was administered intravenously (0.2 mL kg^–1 minute^–1) by an anaesthetist unaware of the allocated group to achieve tracheal intubation. Sedation, intubation and induction quality were scored from 0 to 3. Pre- and post-induction pulse rate (PR), respiratory rate (f_R) and systolic (SAP), mean (MAP) and diastolic (DAP) arterial blood pressure were compared. Time to first breath and induction dose were recorded. Data were analysed for normality and Mann–Whitney U or Student t tests were performed where appropriate. Significance was set at p < 0.05. Data are presented as mean ± standard deviation or median (range).ResultsThe propofol dose administered to achieve induction was lower in the DP group (2.62 ± 0.48 mg kg^–1) than in the UP group (3.48 ± 1.17 mg kg^–1) (p = 0.021). No difference was observed in pre- and post-induction PR, SAP, MAP, DAP and f_R between groups. The differences between post-induction and pre-induction values of these variables were also similar between groups. Time to first breath did not differ between groups. Sedation scores were similar between groups. Quality of tracheal intubation was marginally better with UP 0 (0–1) than with DP 1 (0–2) (p = 0.036), but overall quality of induction was similar between groups [UP 0 (0–1) and DP 0 (0–1), p = 0.549].Conclusion and clinical relevanceDiluting propofol reduced the dose to induce anaesthesia without significantly altering the cardiopulmonary variables.     

Effects of different doses of dexmedetomidine on anaesthetic induction with alfaxalone – a clinical trial

ObjectiveTo document the effects of two doses of dexmedetomidine on the induction characteristics and dose requirements of alfaxalone.Study designRandomized controlled clinical trial.AnimalsSixty one client owned dogs, status ASA I-II.MethodsDogs were allocated randomly into three groups, receiving as pre-anaesthetic medication, no dexmedetomidine (D₀), 1 μg kg^?1 dexmedetomidine (D₁) intramuscularly (IM) or 3 μg kg^?1 dexmedetomidine IM (D₃). All dogs also received 0.2 mg kg^?1 methadone IM. Level of sedation was assessed prior to induction of anaesthesia. Induction of general anaesthesia was performed with alfaxalone administered intravenously to effect at a rate of 1 mg kg^?1 minute^?1; the required dose to achieve tracheal intubation was recorded. Anaesthesia was maintained with isoflurane in oxygen. Cardiopulmonary parameters were recorded throughout the anaesthetic period. Quality of intubation, induction and recovery of anaesthesia were recorded. Quantitative data were compared with one-way anova or Kruskal-Wallis test. Repeated measures were log-transformed and analysed with repeated measures anova (p < 0.05).ResultsTreatment groups were similar for categorical data, with exception of sedation level (p < 0.001). The doses (mean ± SD) of alfaxalone required for intubation were D₀ 1.68 ± 0.24, D₁ 1.60 ± 0.36 and D₃ 1.41 ± 0.43, the difference between D₀ and D₃ being statistically significant (p = 0.036). Heart and respiratory rates during the anaesthetic period were significantly different over time and between groups (p < 0.001); systolic arterial blood pressure was significantly different over time (p < 0.001) but not between groups (p = 0.833). Induction quality and recovery scores were similar between groups (p = 1.000 and p = 0.414, respectively).Conclusions and clinical relevanceThe administration of alfaxalone resulted in a good quality anaesthetic induction which was not affected by the dose of dexmedetomidine. Dexmedetomidine at 3 μg kg^?1 IM combined with methadone provides good sedation and enables a reduction of alfaxalone requirements.     

Effects of graded doses of propofol for anesthesia induction on cardiovascular parameters and intraocular pressures in normal dogs

ObjectiveTo determine the effects of graded doses of propofol on cardiovascular parameters and intraocular pressures (IOP) in normal dogs.Study designProspective, randomized, modified Latin square, cross-over experimental study.AnimalsEleven adult random-source dogs weighing 20.2 ± 5.7 kg.MethodsThere were three treatment groups: propofol 8 mg kg^?1 intravenous (IV) until loss of jaw tone (Group P), propofol until loss of jaw tone +20% (Group P20), and propofol until loss of jaw tone +50% (Group P50). Atracurium 0.1 mg kg^?1 IV was administered in all treatments immediately after the propofol. All dogs received the three treatments in a randomized order, with at least a one week interval between treatments. Direct arterial blood pressure and IOP by applanation tonometry were obtained at baseline, after 5 minutes of pre-oxygenation (before induction), before, and after intubation. Blood gas samples were obtained at baseline, after pre-oxygenation, and before intubation.ResultsThere was no significant difference in IOP readings at any time point among groups. The IOP was significantly higher before intubation versus before induction in all three groups. There was a significantly smaller change in systolic, mean (MAP), and diastolic (DAP) arterial pressures in the P50 group compared with the P group after intubation. There was a significantly smaller change in MAP and DAP in the P50 group compared with the P20 group after intubation. The increase in CO₂ from before induction to before intubation was significantly greater in the P50 group than in the P or P20 groups.Conclusions and clinical relevanceGraded doses of propofol did not affect the increase in IOP observed with propofol induction in normal dogs. Higher doses of propofol are of no apparent additional benefit in animals who cannot tolerate an abrupt increase in IOP but may be of benefit in dogs who cannot tolerate an abrupt increase in blood pressure accompanying orotracheal intubation.