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

Evaluation of a rapid sequence induction technique in dogs with or without rocuronium

OBJECTIVE

To determine, using a rapid sequence induction (RSI) technique, whether rocuronium improves the quality and speed of endotracheal intubation in healthy dogs.

STUDY DESIGN

Randomized, crossover, experimental study.

ANIMALS

Six adult intact male Beagles (12.3 ± 0.4 kg).

METHODS

Dogs were premedicated with intravenous acepromazine (0.03 mg kg-1) and hydromorphone (0.1 mg kg-1). Ten minutes later, anesthesia was induced with intravenous propofol (2 mg kg-1 over 5 seconds), followed by saline (0.06 mL kg-1, CT group) or rocuronium (0.6 mg kg-1, RT group), with orotracheal intubation attempted after 45 seconds. Intubation time (IT) and conditions (IC) were assessed. PaO2, PaCO2, arterial blood pH and serum cortisol were obtained before and after RSI. After endotracheal intubation, saline (0.04 mL kg-1) or sugammadex (4 mg kg-1) were administered intravenously in CT or RT groups, respectively. Spontaneous ventilation restoration was noted.

RESULTS

The IT was 54.3 ± 6.9 (mean ± SD) and 57.8 ± 5.2 seconds for CT and RT, respectively (p = 0.385). All laryngoscopies indicated good IC in both treatment groups. Heart rate was lower in CT group than in RT group (66 ± 16 versus 103 ± 39 beats minute-1, p = 0.016). PaCO2, pH, PaO2 and cortisol did not differ between treatments. Compared with baseline, PaCO2 increased from 47.7 ± 6.2 to 58.8 ± 5.8 (p < 0.001) and pH decreased from 7.35 ± 0.04 to 7.28 ± 0.04 (p = 0.003), independent of treatment. Dogs in both treatment groups returned to spontaneous ventilation within 30 seconds of RSI.

CONCLUSIONS AND CLINICAL RELEVANCE

RSI resulted in respiratory acidosis without hypoxemia or increased cortisol. Rocuronium did not improve IT or IC. Spontaneous ventilation was observed immediately after administering saline or sugammadex. The co-administration of rocuronium showed no clinical benefits over propofol alone in RSI in healthy dogs.

Comparison between continuous rate infusion and target-controlled infusion of propofol in dogs: a randomized clinical trial

OBJECTIVE

To compare a propofol continuous rate infusion (CRI) with a target-controlled infusion (TCI) in dogs.

STUDY DESIGN

Randomized prospective double-blinded clinical study.

ANIMALS

A total of 38 healthy client-owned dogs.

METHODS

Dogs premedicated intramuscularly with acepromazine (0.03 mg kg^-1) and an opioid (pethidine 3 mg kg^-1, morphine 0.2 mg kg^-1 or methadone 0.2 mg kg^-1) were allocated to P-CRI group (propofol 4 mg kg^-1 intravenously followed by CRI at 0.2 mg kg^-1 minute^-1), or P-TCI group [propofol predicted plasma concentration (Cp) of 3.5 μg mL^-1 for induction and maintenance of anaesthesia via TCI]. Plane of anaesthesia, heart rate, respiratory rate, invasive blood pressure, oxygen haemoglobin saturation, end-tidal carbon dioxide and body temperature were monitored by an anaesthetist blinded to the group. Numerical data were analysed by unpaired t test or Mann-Whitney U test, one-way analysis of variance and Dunnett's post hoc test. Categorical data were analysed with Fisher's exact test. Significance was set for p < 0.005.

RESULTS

Overall, propofol induced a significant incidence of relative hypotension (mean arterial pressure 20% below baseline, 45%), apnoea (71%) and haemoglobin desaturation (65%) at induction of anaesthesia, with a higher incidence of hypotension and apnoea in the P-CRI than P-TCI group (68% versus 21%, p = 0.008; 84% versus 58%, p = 0.0151, respectively). Propofol Cp was significantly higher at intubation in the P-CRI than P-TCI group (4.83 versus 3.5 μg mL^-1, p < 0.0001), but decreased during infusion, while Cp remained steady in the P-TCI group. Total propofol administered was similar between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Both techniques provided a smooth induction of anaesthesia but caused a high incidence of side effects. Titration of anaesthesia with TCI caused fewer fluctuations in Cp and lower risk of hypotension compared with CRI.

Development of the Auburn Induction Scale for evaluating induction quality in dogs

OBJECTIVE

To develop and begin establishing evidence for validity of an instrument to assess the quality of induction in dogs.

STUDY DESIGN

Cross-sectional survey and video scoring.

ANIMALS AND POPULATION

A total of 51 veterinary anesthesia personnel, four board-certified anesthesiologists and videos of induction of anesthesia in 18 dogs.

METHODS

In Part 1, an online survey was sent to veterinary anesthesia personnel to solicit expressions and words that they associate with induction of anesthesia. These expressions were evaluated by four anesthesiologists to create a composite scale (Auburn Induction Scale). In Part 2, 18 videos were reviewed by the same four anesthesiologists on two separate occasions. The videos were scored using the Auburn Induction Scale, a simple descriptive scale (SDS) and a visual analog scale (VAS). Intra-rater and inter-rater reliability was measured using an intraclass correlation coefficient (ICC). Significance was set at p < 0.05.

RESULTS

The survey yielded 51 responses that were condensed into 133 expressions. The four anesthesiologists created 18 items incorporating the 133 expressions. The mean ± standard deviation intra-rater reliability ICC was 0.81 ± 0.08 for the Auburn Induction Scale, 0.71 ± 0.02 for the SDS and 0.71 ± 0.08 for the VAS for all raters. The mean ± standard deviation inter-rater reliability ICC was 0.69 ± 0.04 for the Auburn Induction Scale, 0.61 ± 0.05 for the SDS and 0.60 ± 0.06 for the VAS.

CONCLUSIONS AND CLINICAL RELEVANCE

In a research setting, widespread use of this scale may be helpful in increasing the accuracy of data and improving agreement between studies assessing induction of anesthesia in dogs. The results of this study have yielded a composite scale that is more reliable between and among raters than a unidimensional scale.

Comparison between propofol and alfaxalone anesthesia for the evaluation of laryngeal function in healthy dogs utilizing computerized software

Laryngeal paralysis is a well-documented cause of upper respiratory tract obstruction in canines. Diagnosis of laryngeal paralysis is usually made by visual evaluation of laryngeal motion whilst patients are under a light-plane of anesthesia. However, in human studies of laryngeal function evaluation, it has been shown that subjective scoring can lead to significant interobserver variance, which may cause false diagnosis. In this study, we propose to introduce a more objective method of assessing laryngeal function using GlotAnTools and Tracker software to directly measure laryngeal motion in anaesthetized patients. Additionally, two anesthetic agents, alfaxalone and propofol, were compared in this study to assess their relative effect on laryngeal motion and thus their suitability for use in this diagnostic process. This study was a two-stage, cross-over, 1:1 randomization, with two active treatment arms. Ten beagles (10–18 months, five males and five females) were exposed to both anesthetic agents and laryngeal motion was recorded using videoendoscopy. GlotAnTools and Tracker software were applied to the recorded images to measure glottal gap area (A) and length (L). A normalized measure of laryngeal function–computed as A/L–was created, representing the "elongatedness" of the rima glottidis. The glottal gap area was significantly reduced in dogs receiving alfaxalone. This study objectively establishes that alfaxalone impacted laryngeal motion significantly more than propofol and confirms the capability of these computational methods to detect differences in laryngeal motion.

Clinical review of the pharmacological and anaesthetic effects of alfaxalone in dogs

This clinical review summarises the pharmacological and anaesthetic properties of alfaxalone in the dog. Available pharmacokinetic-pharmacodynamic data and factors affecting the induction dose have been reported. Furthermore, quality of induction and recovery after alfaxalone administration, the use of alfaxalone for total intravenous anaesthesia, and its effects on the cardio-respiratory system, on laryngeal motion, on intraocular pressure and tear production have been evaluated. Finally, the use of alfaxalone in dogs undergoing caesarean section and the effect of intramuscular alfaxalone administration have been considered.

Assessment of intramuscular administration of three doses of alfaxalone combined with hydromorphone and dexmedetomidine for endoscopic-guided orotracheal intubation in domestic rabbits (Oryctolagus cuniculus)

OBJECTIVE

To determine the dose of alfaxalone for IM administration combined with dexmedetomidine and hydromorphone that would allow endoscopic-guided orotracheal intubation in rabbits without causing a decrease in respiratory rate or apnea.

ANIMALS

15 sexually intact (9 females and 6 males) healthy Miniature Lop rabbits weighing a mean ± SD of 2.3 ± 0.3 kg and ranging in age from 4 to 9 months.

PROCEDURES

In a randomized, controlled clinical trial, rabbits received 0.1 mg of hydro-morphone/kg and 0.005 mg of dexmedetomidine/kg, plus alfaxalone at either 2 mg/kg (5 rabbits), 5 mg/kg (5 rabbits), or 7 mg/kg (5 rabbits). Drugs were mixed in a single syringe and administered IM. Semiquantitative rating scales were used to evaluate quality of anesthesia and intubation. Orotracheal intubation was attempted with endoscopy and confirmed by capnography.

RESULTS

The number of successful intubations was 0, 3, and 4 in rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. Median (range) anesthesia quality scores (scale, 0 to 12; 12 = deepest anesthesia) were 3 (2 to 5), 6 (5 to 6), and 6 (4 to 9) for rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. The median (range) intubation quality scores (scale, 0 to 3 [ie, intubation not possible to easiest intubation]) were 0 (0 to 0), 2 (0 to 3), and 2 (0 to 3) for rabbits receiving 2, 5, and 7 mg of alfaxalone/kg, respectively. None of the rabbits experienced a decrease in respiratory rate or apnea.

CONCLUSIONS AND CLINICAL RELEVANCE

Increasing doses of alfaxalone combined with hydromorphone and dexmedetomidine increased the success rate of endoscopic-guided orotracheal intubation. Increasing the dose of alfaxalone had no effect on respiratory rate.

Scoping review of quality of anesthetic induction and recovery scales used for dogs

OBJECTIVE

To compare, describe and assess the level of validation of all instruments measuring quality of induction and recovery from anesthesia in dogs.

DATABASES USED

A search was performed using the electronic database PubMed to find articles containing an induction quality scale, a recovery quality scale or both in dogs. Articles not directly accessible through PubMed were obtained through the Auburn University Library website and Google Scholar. The phrases 'induction scoring systems dogs', 'recovery scoring systems dogs', 'anesthetic induction score dogs', and 'anesthetic recovery score dogs' were used for searches using the 'best match search' function. The time frame searched was from 1980 to May 2020. The search was conducted from March 2020 to May 2020.

CONCLUSIONS

A thoroughly tested and validated scale for measuring the quality of induction and recovery does not exist in the current veterinary literature. A large disagreement exists between studies on the use of induction and recovery scales, and many have reported inconsistent results with current instruments. It is recommended that an induction and recovery scale intended for wide-scale use be constructed and tested extensively for psychometric validation and reliability.

A comparison of the pharmacodynamic effects of intravenous ketamine-xylazine with alfaxalone in mute swans (Cygnus olor) presenting at a wildlife veterinary hospital

OBJECTIVE

To compare effects of intravenous (IV) alfaxalone with ketamine-xylazine combination on anaesthetic induction, recovery and cardiopulmonary variables in mute swans.

STUDY DESIGN

Randomized, controlled, clinical study.

ANIMALS

A group of 58 mute swans.

METHODS

Swans were given either alfaxalone (10 mg kg-1; group A) or a combination of ketamine (12.5 mg kg-1) and xylazine (0.28 mg kg-1) (group KX) IV. Heart and respiratory rates, end-tidal carbon dioxide and peripheral haemoglobin oxygen saturation were recorded at 5 minute intervals during anaesthesia. Time from anaesthetic induction to intubation, from cessation of isoflurane to extubation, to lifting head, sternal recumbency and absence of head/neck ataxia were recorded. Anaesthetic and recovery quality were scored (1 = very poor; 5 = excellent). Data are presented as median (interquartile range). Significance was set at p < 0.05.

RESULTS

In group A, 44% (12/27) of swans required mechanical ventilation for 2-14 minutes versus 3.2% (1/31) of swans in group KX (p = 0.0002). Heart rate was higher in group A than in group KX [146 (127-168) versus 65.5 (56-78) beats minute-1, respectively; p < 0.0001]. The isoflurane concentration required to maintain anaesthesia was higher in group A than in group KX [2.5% (2.0-3.0%) versus 1.5% (1.0-2.0%), respectively; p = 0.0001]. Time from cessation of isoflurane administration to lifting head was significantly longer in group A than in group KX [12 (9-17) versus 6 (4-7.75) minutes, respectively; p < 0.0001]. Anaesthesia quality scores were significantly better in group KX than in group A [4 (4-5) versus 4 (3-4), respectively; p = 0.0011], as were recovery scores [4 (3-5) versus 2 (2-3), respectively; p = 0.0005].

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone is a suitable anaesthetic induction agent for use in mute swans. There is a greater incidence of postinduction apnoea and a higher incidence of agitation on recovery with alfaxalone than with ketamine-xylazine.

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

OBJECTIVE

To 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 DESIGN

Randomized, blinded, clinical study.

ANIMALS

A total of 28 client-owned dogs (12 males/16 females).

METHODS

Following 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).

RESULTS

The 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 RELEVANCE

Diluting propofol reduced the dose to induce anaesthesia without significantly altering the cardiopulmonary variables.

Sedative and cardiorespiratory effects of intramuscular administration of alfaxalone and butorphanol combined with acepromazine, midazolam, or dexmedetomidine in dogs

OBJECTIVE

To evaluate the sedative and cardiorespiratory effects of IM administration of alfaxalone and butorphanol combined with acepromazine, midazolam, or dexmedetomidine in dogs.

ANIMALS

6 young healthy mixed-breed hounds.

PROCEDURES

Dogs received each of 3 treatments (alfaxalone [2 mg/kg] and butorphanol [0.4 mg/kg] combined with acepromazine [0.02 mg/kg; AB-ace], midazolam [0.2 mg/kg; AB-mid], or dexmedetomidine [0.005 mg/kg; AB-dex], IM) in a blinded, randomized crossover-design study with a 1-week washout period between treatments. Sedation scores and cardiorespiratory variables were recorded at predetermined time points. Data were analyzed by use of mixed-model ANOVA and linear generalized estimating equations with post hoc adjustments.

RESULTS

All treatments resulted in moderate to deep sedation (median score, ≥ 15/21) ≤ 5 minutes after injection. Sedation scores did not differ among treatments until the 40-minute time point, when the score was higher for AB-dex than for other treatments. Administration of AB-dex resulted in median scores reflecting deep sedation until 130 minutes, versus 80 and 60 minutes for AB-ace and AB-mid, respectively, after injection. Heart rate, cardiac output, and oxygen delivery decreased significantly after AB-dex, but not AB-ace or AB-mid administration. Respiratory variables remained within clinically acceptable ranges after all treatments. Undesirable recovery characteristics were observed in 4 dogs after AB-mid treatment. Four dogs required atipamezole administration 180 minutes after AB-dex injection.

CONCLUSIONS AND CLINICAL RELEVANCE

All protocols produced reliable sedation. The results indicated that in young, healthy dogs, AB-mid may produce undesirable recovery characteristics; AB-dex treatment caused cardiovascular depression and should be used with caution.

Continuous Rate Infusion of Alfaxalone during Ketamine-Xylazine Anesthesia in Rats

Alfaxalone is an injectable anesthetic agent that is used in veterinary medicine for general anesthesia. We evaluated the safety and efficacy of alfaxalone delivered through continuous rate infusion by comparing ketamine-xylazine-alfaxalone (KXA) anesthesia with ketamine-xylazine (KX) anesthesia in Sprague-Dawley rats. Anesthesia was induced in male and female rats by using subcutaneous KX. After induction, rats in the KXA group received alfaxalone (10 mg/kg/h IV) for 35 min, whereas rats in the KX group did not receive alfaxalone. At the end of the trial, alfaxalone was discontinued, and xylazine was reversed in all rats by using atipamezole. Throughout anesthesia, we assessed forepaw withdrawal reflex (FPWR), hindpaw withdrawal reflex (HPWR), response to surgical stimulation, heart rate, respiratory rate, SpO₂, body temperature, and time to standing. KXA produced a reliable surgical plane of anesthesia, as evidenced by the loss of both FPWR and HPWR and lack of response to surgical stimulation in all 16 rats, whereas only 6 of the 16 rats in the KX group lost HPWR. No rat in the KXA group regained a paw withdrawal reflex during alfaxalone administration, whereas 3 of the 12 rats (25%) in the KX group that reached a surgical plane of anesthesia exited that plane within the 35-min timeframe. Neither heart rate, respiratory rate, SpO₂, body temperature, nor time to standing differed between KXA and KX groups; and there were no sex-associated differences in anesthesia response. These results indicate that alfaxalone (10 mg/kg/h IV) delivered through continuous rate infusion, in combination with ketamine and xylazine, provides a safe, prolonged, and reliable surgical plane of anesthesia in rats.

Laryngeal Disease in Dogs and Cats: An Update

Laryngeal diseases are manifested by obstructive breathing patterns reflecting functional or mechanical upper airway obstruction. Laryngeal paralysis is the most common disease of the larynx. Diagnosis requires close attention to anesthetic plane and coordination of respiratory effort with laryngeal motion. Surgical arytenoid lateralization improves clinical signs and quality of life in dogs; however, aspiration pneumonia is a recognized complication, and generalized neuropathy can progress. Laryngeal collapse can result from any cause of chronic upper airway obstruction but is most often associated with brachycephalic obstructive airway syndrome. Although uncommon, laryngeal neoplasia has a guarded to grave prognosis regardless of treatment.

Comparison of intravenous anesthetic induction doses and physiologic effects of ketamine or alfaxalone in goats undergoing surgery with isoflurane anesthesia

OBJECTIVE

To compare IV doses of alfaxalone and ketamine needed to facilitate orotracheal intubation and assess effects of each treatment on selected physiologic variables in goats undergoing orthopedic surgery with isoflurane anesthesia.

ANIMALS

18 healthy adult goats.

PROCEDURES

Behavior was assessed before and after sedation with midazolam (0.1 mg/kg, IV) for IV catheter placement. Anesthesia was induced with additional midazolam (0.1 mg/kg, IV) and alfaxalone (n = 9) or ketamine (9) at 2 mg/kg, IV, over 30 seconds. An additional dose of alfaxalone or ketamine (1 mg/kg) was given IV if needed for intubation; anesthesia was maintained with isoflurane in oxygen and IV fluids with ketamine (0.5 to 1 mg/kg/h). Direct systolic (SAP), diastolic (DAP), and mean (MAP) arterial blood pressures; heart rate; and respiratory rate were recorded before induction, immediately after intubation, and during surgery. Qualitative anesthetic induction and recovery characteristics were assessed. Variables were compared within and between groups by statistical methods.

RESULTS

No preinduction variables differed significantly between groups. Postintubation and 30-minute intraoperative SAP, DAP, and MAP were higher for the ketamine group than for the alfaxalone group; within the alfaxalone group, postintubation SAP, MAP, and respiratory rate prior to mechanical ventilation were lower than respective preinduction values. All alfaxalone-group goats were intubated after 1 dose of the induction agent; 5 of 9 ketamine-group goats required an additional (1-mg/kg) dose. Postoperative recovery was good to excellent for all animals.

CONCLUSIONS AND CLINICAL RELEVANCE

Both drugs were suitable for induction of anesthesia after sedation with midazolam, but most goats required higher doses of ketamine to allow intubation. For situations in which alfaxalone administration is appropriate, the potential for decreased arterial blood pressures and respiratory rate should be considered.

Alfaxalone total intravenous anaesthesia in dogs: pharmacokinetics, cardiovascular data and recovery characteristics

OBJECTIVE

To evaluate the cardiovascular effects, pharmacokinetic (PK) data and recovery characteristics of an alfaxalone constant rate infusion (CRI) of different duration in dogs at manufacturer's recommended dose rate.

STUDY DESIGN

Experimental, prospective, randomized, crossover study.

ANIMALS

Six intact female Beagles.

METHODS

Following an intravenous alfaxalone bolus (3 mg kg^-1), anaesthesia was maintained using an alfaxalone CRI at 0.15 mg kg^-1 minute^-1 for 90 (short CRI) or 180 minutes (long CRI). Venous blood samples were collected to determine the PK profile. Cardiovascular variables and recovery characteristics were evaluated. Recovery was scored on a scale ranging from 0, excellent to 4, bad. A mixed-model statistical approach was used to compare the cardiovascular parameters (global α = 0.05). An analysis of variance was performed to compare PK parameters and recovery times between treatments.

RESULTS

No significant difference was noted between protocols for any PK parameter. Volume of distribution at steady state (935.74 ± 170.25 versus 1119.15 ± 190.65 mL kg^-1), elimination half-life (12 ± 2 versus 13 ± 3 minutes), clearance from the central compartment (26.02 ± 4.41 versus 27.74 ± 5.65 mL kg^-1 minute^-1) and intercompartmental clearance (8.47 ± 4.06 versus 12.58 ± 7.03 mL kg^-1 minute^-1) were comparable for short CRI and long CRI. Cardiovascular variables remained within physiological limits. Mechanical ventilation was necessary (short CRI: n = 1, long CRI: n = 4). The manufacturer's recommended dose rate resulted in a light plane of anaesthesia. No significant differences in recovery times and scores were observed between treatments. The quality of recovery was scored as very poor with both protocols.

CONCLUSIONS AND CLINICAL RELEVANCE

PK data were similar between long and short infusions of alfaxalone at the manufacturer's recommended dose, with acceptable cardiovascular conditions. Nevertheless, both protocols resulted in a superficial plane of general anaesthesia with poor recovery characteristics.

Co-induction of anaesthesia with alfaxalone and midazolam in dogs: a randomized, blinded clinical trial

OBJECTIVE

To qualitatively assess the co-induction of anaesthesia with midazolam and alfaxalone and to determine cardiovascular or respiratory alterations compared with alfaxalone alone.

STUDY DESIGN

A randomized, blinded, clinical trial.

ANIMALS

A total of 29 American Society of Anesthesiologists grade I or II, client-owned dogs undergoing elective orthopaedic or soft tissue surgery.

METHODS

All dogs received 0.02 mg kg^-1 acepromazine and 0.3 mg kg^-1 methadone intramuscularly 30 minutes prior to anaesthesia. Measurements of heart rate (HR), respiratory frequency and blood pressure (BP) were assessed pre-induction and at 0, 2 and 5 minutes post-induction. Anaesthesia was induced with 0.5 mg kg^-1 alfaxalone followed by either 0.4 mg kg^-1 midazolam intravenously (group M) or an equal volume of saline (group S). Conditions were assessed for intubation and further boluses of 0.25 mg kg^-1 alfaxalone were given as required. Response to co-induction, ease of intubation and quality of induction were scored, and total dose of alfaxalone required for intubation was recorded. Repeated measures one-way analysis of variance with post hoc Tukey's test was used to assess within group changes over time and Student t tests were used to compare between groups. Incidence of apnoea was assessed using a Fisher's exact test. Data are shown as mean ± standard deviation.

RESULTS

Group M included 14 dogs and group S 15 dogs. There was a significant difference in the total dose of alfaxalone required for intubation, 0.65 ± 0.20 mg kg^-1 group M and 0.94 ± 0.26 mg kg^-1 group S (p = 0.002). Apnoea occurred significantly more frequently in group M (p = 0.007). There were no clinically significant differences in HR or BP at the measured time points between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Co-induction with midazolam had significant alfaxalone-sparing effects with no clinically detectable cardiovascular changes. Apnoea is common after co-induction.

Evaluation of anesthesia produced by ketofol in acepromazine- or medetomidine-sedated dogs

Objective

A randomized, blinded clinical study was conducted to evaluate ketofol (Ketamine + Propofol combination) anesthesia in 12 entire male mongrel dogs sedated with either acepromazine (ACP) or medetomidine.

Materials and Methods

Group A (6) dogs were pre-medicated with ACP and Group B (6) dogs with medetomidine. Anesthesia was induced and maintained using ketofol (ketamine and propofol). Routine open pre-scrotal castration was performed. Sedation score and ease of arousal were assessed and recorded. Duration and depth of anesthesia were evaluated using apnea and the absence of palpebral and pedal reflexes, attempts to stand up, and muscle tremors and post-operative pain. Simple statistics were compared using Student t-test and Mann-Whitney test (p < 0.05).

Results

Medetomidine-sedated dogs had higher sedation scores compared to ACP-sedated dogs. Medetomidine-ketofol produced significantly (p < 0.05) longer duration of anesthesia (24.5 ± 3.1 min) compared to ACP-ketofol (10.0 ± 4.4 min). Sixty-seven percent of dogs anesthetized with ACP-ketofol required top up with ketofol to complete the castration. However, none of the Med-ketofol anesthetized dogs required top up. Med-ketofol produced a more profound depth of anesthesia and smoother recovery from anesthesia compared to ACP-ketofol. Med-ketofol (median score 6) attained better overall post-operative analgesia compared to ACP-ketofol (median score 7), though not statistically significant (p = 0.25). Although both protocols provided adequate anesthesia for castration, top up was required to complete the operation in more than half of ACP-ketofol anesthetized dogs, making Med-ketofol a better protocol.

Conclusion

The study recommends the use of Med-ketofol anesthesia for castration in a dog, and post-operative analgesia to be administered with either protocol, but more so in ACP-ketofol anesthetized dogs undergoing castration.

Clinical measurements performed during alfaxalone total intravenous anaesthesia for radiography and neurophysiological investigations in dogs

OBJECTIVE

To describe clinically relevant, physiological measurements collected during a 3 hour duration of alfaxalone total intravenous anaesthesia.

STUDY DESIGN

Case series.

ANIMALS

A total of 112 client-owned middle-aged or older dogs.

METHODS

Dogs were premedicated with intramuscular acepromazine (0.03 mg kg^-1). Anaesthesia was induced and subsequently maintained for up to 3 hours with alfaxalone administered intravenously. Dogs breathed 100% oxygen via an endotracheal tube. Heart rate, respiratory rate and blood pressure were evaluated 30 minutes after administration of acepromazine and used as baseline values for comparisons of intra-anaesthetic data. Blood glucose was measured 1 week prior to anaesthesia and every hour during alfaxalone anaesthesia. Quality and duration of recovery were recorded. Mean data for physiological variables were compared over three time points-before induction of anaesthesia, for the first hour of anaesthesia and from 60 minutes to discontinuation of anaesthesia.

RESULTS

Mean induction dose of alfaxalone was 1.4 mg kg^-1 [95% confidence interval (CI) 1.3-1.5). Post induction apnoea for >60 seconds occurred in 13 (11.6%) dogs. Mean alfaxalone infusion rate during the first 60 minutes of anaesthesia was 0.099 mg kg^-1 minute^-1; mean infusion rate was 0.092 mg kg^-1 minute^-1 from 60 minutes until discontinuation of anaesthesia. Heart rate was well maintained; hypotension (mean arterial blood pressure < 60 mmHg) was encountered in 23 (21%) dogs. Blood glucose levels did not alter during anaesthesia. Median time between discontinuation of alfaxalone infusion and extubation was 17 (7-35 minutes), time to assuming sternal recumbency was 75 (58-110 minutes), and time to standing was 109 (88-140 minutes).

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone infusion provided effective anaesthesia in this population. In a minority of cases, respiratory and haemodynamic support of the patient was required.

Effects of intravenous administration of tiletamine-zolazepam, alfaxalone, ketamine-diazepam, and propofol for induction of anesthesia on cardiorespiratory and metabolic variables in healthy dogs before and during anesthesia maintained with isoflurane

OBJECTIVE To compare effects of tiletamine-zolazepam, alfaxalone, ketamine-diazepam, and propofol for anesthetic induction on cardiorespiratory and acid-base variables before and during isoflurane-maintained anesthesia in healthy dogs. ANIMALS 6 dogs. PROCEDURES Dogs were anesthetized with sevoflurane and instrumented. After dogs recovered from anesthesia, baseline values for cardiorespiratory variables and cardiac output were determined, and arterial and mixed-venous blood samples were obtained. Tiletamine-zolazepam (5 mg/kg), alfaxalone (4 mg/kg), propofol (6 mg/kg), or ketamine-diazepam (7 and 0.3 mg/kg) was administered IV in 25% increments to enable intubation. After induction (M₀) and at 10, 20, 40, and 60 minutes of a light anesthetic plane maintained with isoflurane, measurements and sample collections were repeated. Cardiorespiratory and acid-base variables were compared with a repeated-measures ANOVA and post hoc t test and between time points with a pairwise Tukey test. RESULTS Mean ± SD intubation doses were 3.8 ± 0.8 mg/kg for tiletamine-zolazepam, 2.8 ± 0.3 mg/kg for alfaxalone, 6.1 ± 0.9 mg/kg and 0.26 ± 0.04 mg/kg for ketamine-diazepam, and 5.4 ± 1.1 mg/kg for propofol. Anesthetic depth was similar among regimens. At M₀, heart rate increased by 94.9%, 74.7%, and 54.3% for tiletamine-zolazepam, ketamine-diazepam, and alfaxalone, respectively. Tiletamine-zolazepam caused higher oxygen delivery than propofol. Postinduction apnea occurred in 3 dogs when receiving alfaxalone. Acid-base variables remained within reference limits. CONCLUSIONS AND CLINICAL RELEVANCE In healthy dogs in which a light plane of anesthesia was maintained with isoflurane, cardiovascular and metabolic effects after induction with tiletamine-zolazepam were comparable to those after induction with alfaxalone and ketamine-diazepam.

Dexmedetomidine combined with etomidate or emulsified isoflurane for induction reduced cardiopulmonary response in dogs

To investigate the effects of etomidate, emulsified isoflurane, and their combination with dexmedetomidine on physiological parameters, electrocardiogram (ECG) results, and the quality of induction and recovery during isoflurane maintenance anaesthesia. 5 mixed-breed dogs received each of four treatments: etomidate (E group); emulsified isoflurane (EI group); both dexmedetomidine and etomidate (DE group); or both dexmedetomidine and emulsified isoflurane (DEI group). All drugs were IV injection administered for induction, followed by 1.5 MAC (minimal alveolar concentration) of isoflurane to maintain anaesthesia. Rectal temperature (RT), respiratory rate (RR), heart rate (HR), mean arterial pressure (MAP), and ECG were measured at baseline, 0, 5, 10, 20, 40, and 60 minutes after intubation. The quality of induction and recovery was evaluated for all dogs. All the anaesthetic procedures provided good conditions for induction of anaesthesia. The quality of induction and recovery in the E group was worse than other groups. The decrease of RR in the E and DE groups was stronger than that in the EI and DEI groups. The dogs in the E group had the most significant prolongation of the Q-T interval and changes in the S-T segment. Deviation and extension of the S-T segment were noted in the El group. The dogs in the DE and DEI groups had fewer changes in the ECG results than those in the E and EI groups. The addition of dexmedetomidine caused less effect on cardiopulmonary parameters and the ECG results than either etomidate or emulsified isoflurane alone. Thus, etomidate or emulsified isoflurane in combination with dexmedetomidine may be useful clinically for the induction of anaesthesia.

Comparison of methohexital and propofol as induction agents for evaluation of laryngeal function in healthy dogs

Objective

To determine the influence of propofol or methohexital, with and without doxapram, on the examination of laryngeal function in dogs.

Study design

Experimental study.

Animals

Forty healthy dogs randomly assigned to 4 groups: propofol with saline (n = 10), propofol with doxapram (n = 10), methohexital with saline (n = 10), or methohexital with doxapram (n = 10).

Methods

Propofol and methohexital were administered to effect. Investigators examined laryngeal function (initial) simultaneously with video laryngoscopy. Doxapram or saline was administered, and laryngeal function was reevaluated (second). Laryngeal motion, quality of laryngeal exposure, and the degree of swallowing, laryngospasm, and jaw tone were scored at each evaluation. Adverse events were recorded. Initial and second videos were evaluated by a masked observer, and still images obtained from both evaluations were evaluated for change in rima glottidis size by 2 masked observers.

Results

Administration of doxapram and saline was delayed with propofol (P = .001). Laryngeal function did not differ between dogs receiving propofol or methohexital, irrespective of doxapram administration. Doxapram improved breathing scores in both groups (P < .001). Jaw tone increased with propofol during the second evaluation (P = .049). Swallowing was more prevalent at initial examination (P = .020). Methohexital resulted in an increased heart rate (P < .001) compared with propofol. Twenty‐five percent of dogs receiving methohexital developed seizure‐like activity (n = 5/20).

Conclusion

Evaluation of laryngeal function did not differ between healthy dogs anesthetized with propofol or methohexital. Methohexital provided shorter examination times with less jaw tone but was associated with adverse events.

Clinical significance

This study provides evidence to recommend propofol over methohexital as an induction agent for laryngeal function examination.

Pharmacokinetics of intramuscular alfaxalone and its echocardiographic, cardiopulmonary and sedative effects in healthy dogs

The pharmacokinetics and the effects of a single intramuscular (IM) dose of alfaxalone on sedation and cardiopulmonary and echocardiographic variables was studied in dogs. Twelve healthy adult Beagles (3 females, 9 males) were used in this prospective controlled cross-over trial. Echocardiography was performed with and without 4 mg kg-1 alfaxalone IM with a week wash-out interval. Sedation (19-point scale; 0 = no sedation), cardiopulmonary parameters, blood gas analysis and plasma concentration of alfaxalone were assessed every 5 minutes following the injection (T0). The influence of the alfaxalone plasma concentration and time on physiological variables was tested using a linear model whereas echocardiographic measurements were compared between conscious and alfaxalone-administered dogs using paired t-tests. Compared to baseline, alfaxalone administration was followed by an increase in heart rate (HR) from T5 to T30 and a decrease in mean arterial pressure (MAP) at T10, T25 and T30, in stroke volume (SV; 15 ± 5 to 11 ± 3 ml; P<0.0001), and end-diastolic volume (EDV; 24.7 ± 5.7 to 19.4 ± 4.9 ml). Cardiac output (CO) and blood gas analysis did not change significantly throughout. Mean plasma half-life was 29 ± 8 minutes, volume of distribution was 1.94 ± 0.63 L kg-1, and plasma clearance was 47.7 ± 14.1 ml kg-1 minute-1. Moderate to deep sedation was observed from T5 to T35. Ten dogs showed paddling, trembling, nystagmus and strong reaction to sound during the procedure. Although there were no significant changes in CO and oxygenation, the impact of HR, MAP, SV, EDV alterations requires further investigations in dogs with cardiac disease.

The minimum infusion rate of alfaxalone during its co-administration with lidocaine at three different doses by constant rate infusion in goats

OBJECTIVE

To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement in response to standardized stimulation while co-administered with lidocaine at three different doses by constant infusion rate infusion (CRI) in goats.

STUDY DESIGN

Prospective, blinded, randomized crossover, experimental.

ANIMALS

A total of eight healthy goats: four does and four wethers.

METHODS

Anaesthetic induction was with lidocaine at 1 mg kg^-1 [low dose of lidocaine (L-Lid)], 2 mg kg^-1 [moderate dose (M-Lid)] or 4 mg kg^-1 [high dose (H-Lid)] and alfaxalone at 2 mg kg^-1. Anaesthetic maintenance was with alfaxalone initially at 9.6 mg kg^-1 hour^-1 combined with one of three lidocaine treatments: 3 mg kg^-1 hour^-1 (L-Lid), 6 mg kg^-1 hour^-1 (M-Lid) or 12 mg kg^-1 hour^-1 (H-Lid). The MIR of alfaxalone was determined by testing for responses to a stimulation in the form of clamping on a digit with a Vulsellum forceps every 30 minutes during lidocaine CRI. Basic cardiopulmonary parameters were measured.

RESULTS

The alfaxalone MIRs were 8.64 (6.72-10.56), 6.72 (6.72-8.64) and 6.72 (6.72-6.72) mg kg^-1 hour^-1 during L-Lid, M-Lid and H-Lid, respectively, without any significant differences among treatments. Compared to the initial rate of 9.6 mg kg^-1 hour^-1, these reductions in MIR are equivalent to 10, 30 and 30%, respectively. Significant increases in heart rate (HR) and arterial carbon dioxide partial pressure (PaCO₂) and decreases in arterial haemoglobin saturation (SaO₂), arterial oxygen partial pressure (PaO₂) and respiratory frequency (f_R) immediately after induction were observed during all lidocaine treatments.

CONCLUSIONS AND CLINICAL RELEVANCE

Lidocaine reduces the alfaxalone MIR by up to 30% with a tendency towards a plateauing in this effect at high CRIs. Immediate oxygen supplementation might be required to prevent hypoxaemia.

Avaliação da dexmedetomidina e do tramadol, associados ao midazolam, em gatas anestesiadas com isoflurano e submetidas à ovário-histerectomia

RESUMO Objetivou-se comparar as alterações cardiorrespiratórias e a analgesia pós-operatória promovidas pela dexmedetomidina e pelo tramadol, quando associados ao midazolam, em felinas. Para tal, foram selecionadas 18 gatas hígidas, divididas em dois grupos randomizados: GDM, tratadas com dexmedetomidina (10µg/kg) e GTM, tratadas com tramadol (2mg/kg), ambos associados a midazolam (0,2mg/kg,) IM. Após 15 minutos, procedeu-se à indução anestésica com propofol (1,46±0,79mL), mantendo-se a anestesia com isoflurano. As felinas foram submetidas à ovário-histerectomia, registrando-se as variáveis cardiorrespiratórias 15 minutos após a MPA (M0), 15 minutos após a indução (M15) e sequencialmente a cada cinco minutos, até o término do procedimento cirúrgico (M20, M25, M30, M35 e M40). A avaliação da dor iniciou-se 30 minutos após o término do procedimento cirúrgico (MP30) e sequencialmente em intervalos de 30 minutos (MP60, MP90, MP120). A partir do MP120, as avaliações foram registradas a cada hora (MP180, MP240 e MP360). A associação dexmedetomidina-midazolam infere diminuição inicial de frequência cardíaca (FC) sem significado clínico e está relacionada à sedação mais pronunciada, à analgesia menor e menos duradoura e a episódios de êmese, quando comparada à associação tramadol-midazolam. Ambos os protocolos denotaram estabilidade cardiorrespiratória e podem ser considerados seguros em felinas submetidas à ovário-histectomia.

Postinduction apnoea in dogs premedicated with acepromazine or dexmedetomidine and anaesthetized with alfaxalone or propofol

OBJECTIVE

To compare incidence and duration of postinduction apnoea in dogs after premedication with methadone and acepromazine (MA) or methadone and dexmedetomidine (MD) followed by induction with propofol (P) or alfaxalone (A).

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

A total of 32 American Society of Anesthesiologists class I dogs (15 females, 17 males), aged between 4 months and 4 years, weighing between 3 and 46 kg.

METHODS

Dogs were randomly allocated to be administered MA+P, MA+A, MD+P or MD+A (methadone 0.5 mg kg^-1 and acepromazine 0.05 mg kg^-1 or dexmedetomidine 5 μg kg^-1). Induction agents were administered intravenously via syringe driver (P at 4 mg kg^-1 minute^-1 or A at 2 mg kg^-1 minute^-1) until successful endotracheal intubation and the endotracheal tube connected to a circle system with oxygen flow at 2 L minute^-1. Oxygen saturation of haemoglobin (SpO₂), end tidal partial pressure of carbon dioxide and respiratory rate were monitored continuously. If apnoea (≥ 30 seconds without breathing) occurred, the duration until first spontaneous breath was measured. If SpO₂ decreased below 90% the experiment was stopped and manual ventilation initiated. Data were analysed with general linear models with significance set at p ≤ 0.05.

RESULTS

There was no statistical difference in the incidence (11 of 16 dogs in A groups and 12 of 16 dogs in P groups), or mean ± standard deviation duration (A groups 125 ± 113 seconds, P groups 119 ± 109 seconds) of apnoea. The SpO₂ of one dog in the MD+P group decreased below 90% during the apnoeic period.

CONCLUSIONS AND CLINICAL RELEVANCE

Propofol and alfaxalone both cause postinduction apnoea and the incidence and duration of apnoea is not influenced by the use of acepromazine or dexmedetomidine in premedication. Monitoring of respiration is recommended when using these premedication and induction agent combinations.

Effect of rate of administration of propofol or alfaxalone on induction dose requirements and occurrence of apnea in dogs

OBJECTIVE

To evaluate the effect of rate of administration of propofol or alfaxalone on induction dose requirements and incidence of postinduction apnea (PIA) in dogs following premedication with methadone and dexmedetomidine.

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

Thirty-two healthy American Society of Anesthesiologists class I client-owned dogs (seven females, 25 males), aged between 5 and 54 months, weighing between 2.0 and 48.2 kg.

METHODS

Dogs were premedicated intramuscularly with 0.5 mg kg^-1 methadone and 5 μg kg^-1 dexmedetomidine. Thirty minutes after premedication, dogs were preoxygenated for 5 minutes before the induction agent was administered intravenously via a syringe driver until orotracheal intubation was achieved. Dogs were randomized to receive alfaxalone 0.5 mg kg^-1 minute^-1 (A-Slow), alfaxalone 2 mg kg^-1 minute^-1 (A-Fast), propofol 1 mg kg^-1 minute^-1 (P-Slow), or propofol 4 mg kg^-1 minute^-1 (P-Fast). Oxygen saturation of hemoglobin (SpO₂), end-tidal carbon dioxide and respiratory rate were monitored. If PIA (≥30 seconds without a breath) occurred, the time to the first spontaneous breath was measured. If SpO₂ decreased below 90%, the experiment was stopped and manual ventilation initiated.

RESULTS

The mean±standard deviation induction doses of alfaxalone and propofol were lower in the A-Slow [A-Slow 0.9±0.3 mg kg^-1, A-Fast 2.2±0.5 mg kg^-1 (p≤0.001)] and P-Slow [P-Slow 1.8±0.6 mg kg^-1, P-Fast 4.1±0.7 mg kg^-1 (p≤0.001)] groups, respectively. The incidence of PIA was 25% for the A-Slow and P-Slow groups and 100% for the A-Fast and P-Fast groups (p = 0.007).

CONCLUSIONS AND CLINICAL RELEVANCE

Both propofol and alfaxalone following methadone and dexmedetomidine premedication caused PIA. Induction dose requirement and incidence of PIA were affected by the rate of administration of both drugs. When possible, propofol and alfaxalone doses should be reduced and administered slowly to reduce PIA.

Alfaxalone alone or combined with midazolam or ketamine in dogs: intubation dose and select physiologic effects

OBJECTIVE

To determine the intubation dose and select physiologic effects of alfaxalone alone or in combination with midazolam or ketamine in dogs.

STUDY DESIGN

Prospective, clinical study.

ANIMALS

Fifty-three healthy client-owned dogs [mean±standard deviation (SD)] 5.1±1.8 years, 27±15.4 kg, scheduled for elective orthopedic surgery.

METHODS

After premedication with acepromazine (0.02 mg kg^-1) and hydromorphone (0.1 mg kg^-1) intramuscularly, alfaxalone (0.25 mg kg^-1) was administered intravenously over 15 seconds followed immediately by 0.9% saline (AS), midazolam (0.3 mg kg^-1; AM), ketamine (1 mg kg^-1; AK1), or ketamine (2 mg kg^-1; AK2). Additional alfaxalone (0.25 mg kg^-1 increments) was administered as required to permit endotracheal intubation. The incidence of apnea and the time from intubation until spontaneous movement were recorded. Heart rate (HR) and blood pressure were recorded 15 minutes after premedication, after intubation and 2, 5, 10 and 15 minutes thereafter. Blood was collected for measurement of serum glucose and insulin concentrations before induction, after intubation and at 2, 5, 10 and 50 minutes. Data were analyzed by split-plot anova with Bonferroni adjustment for the number of group comparisons.

RESULTS

Mean±SD alfaxalone mg kg^-1 doses required for endotracheal intubation were AS (1.0±0.4), AM (0.4±0.2), AK1 (0.5±0.3) and AK2 (0.5±0.4) (p=0.0005). Differences in cardiopulmonary variables among groups were minor; HR decreased in AS, while in other groups, HR increased transiently postintubation. Incidence of apnea in AS was 54% with no significant difference among groups. Midazolam significantly prolonged time from intubation until spontaneous movement (p<0.002).

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam and ketamine reduced the alfaxalone dose required for endotracheal intubation. Serum glucose and insulin concentrations were not influenced by administration of alfaxalone alone or when administered with midazolam or ketamine.

Evaluation of the anesthetic efficacy of alfaxalone in oscar fish (Astronotus ocellatus)

OBJECTIVE

To evaluate effects of alfaxalone on heart rate (HR), opercular rate (OpR), results of blood gas analysis, and responses to noxious stimuli in oscar fish (Astronotus ocellatus).

ANIMALS

6 healthy subadult oscar fish.

PROCEDURES

Each fish was immersed in water containing 5 mg of alfaxalone/L. Water temperature was maintained at 25.1°C, and water quality was appropriate for this species. The HR, OpR, response to noxious stimuli, and positioning in the tank were evaluated, and blood samples for blood gas analysis were collected before (baseline), during, and after anesthesia.

RESULTS

Immersion anesthesia of oscar fish with alfaxalone (5 mg/L) was sufficient for collection of diagnostic samples in all fish. Mean ± SD induction time was 11 ± 3.8 minutes (minimum, 5 minutes; maximum, 15 minutes), and mean recovery time was 37.5 ± 13.7 minutes (minimum, 20 minutes; maximum, 55 minutes). There was a significant difference in OpR over time, with respiratory rates significantly decreasing between baseline and anesthesia and then significantly increasing between anesthesia and recovery. There was no significant difference in HR over time. Median lactate concentrations were significantly increased in all anesthetized fish. Other physiologic or blood gas variables did not change significantly.

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone should be considered as a readily available and easy-to-use anesthetic for oscar fish. Because it is more likely to be found in veterinary hospitals than other traditional anesthetics for fish, its value as an anesthetic for other species of fish should also be considered.

Clinical effects of midazolam or lidocaine co-induction with a propofol target-controlled infusion (TCI) in dogs

OBJECTIVE

To evaluate the propofol requirement, cardiovascular and respiratory variables using midazolam or lidocaine with a propofol target-controlled infusion (PTCI) for induction of anaesthesia in healthy dogs.

STUDY DESIGN

Prospective, randomized, controlled blinded clinical trial.

ANIMALS

Sixty client-owned dogs [American Society of Anesthesiologists (ASA) I-II] undergoing surgical procedures.

METHODS

Thirty minutes after premedication with acepromazine (0.03 mg kg(-1) ) and morphine (0.2 mg kg(-1) ), PTCI was started and maintained at a plasma target concentration of 1 μg mL(-1) . Three minutes later, dogs (n = 20 per group) received either 5 mL 0.9% sodium chloride (SG), 2 mg kg(-1) of lidocaine (LG) or 0.2 mg kg(-1) of midazolam (MG) intravenously (IV) as a co-induction agent. Two minutes later, suitability for endotracheal intubation was assessed. If intubation was not possible, the propofol target was increased by 0.5 μg mL(-1) every 60 seconds until it was successfully achieved. Heart rate (HR), respiratory rate (fR ), and oscillometric systolic arterial pressure (SAP), mean arterial pressure (MAP) and diastolic arterial pressure (DAP) were recorded immediately prior to commencing PTCI (B0), prior to intubation (BI), immediately after (T0), and at 3 (T3) and 5 (T5) minutes post-intubation. End-tidal partial pressures of carbon dioxide (PE(') CO2 ) were recorded at T0, T3 and T5. The occurrence of excitement at any time point was noted.

RESULTS

The median (range) propofol target concentration for endotracheal intubation was significantly lower in MG, 1.5 (1.0-4.0) μg mL(-1) compared with LG, 2.5 (1.5-4.5) μg mL(-1) or SG, 3.0 (2.0-5.0) μg mL(-1) . Heart rate, MAP, fR and PE(') CO2 were similar in the three groups at all time points. No excitement was reported in any dog.

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam, but not lidocaine, provided a significant reduction in PTCI requirement for induction of anaesthesia thereby allowing successful intubation. However, cardiovascular and respiratory effects were not different between the groups.

Strategies for the management and prevention of conformation-related respiratory disorders in brachycephalic dogs

Brachycephalic (short-muzzled) dogs are increasingly popular pets worldwide, with marked increases in registrations of breeds such as the Pug and French Bulldog over the past decade in the UK. Despite their popularity, many brachycephalic breeds are affected by an early-onset, lifelong respiratory disorder, brachycephalic obstructive airway syndrome (BOAS). This disorder arises due to a mismatch in the proportions of the skull and the soft tissues held within the nose and pharynx, resulting in obstruction of the airway during respiration. Increased airway resistance encourages secondary changes such as eversion of the laryngeal saccules and collapse of the larynx. Clinical signs of BOAS are often early onset and chronic, including dyspnea, exercise intolerance, heat intolerance, and abnormal and increased respiratory noise. Episodes of severe dyspnea can also occur, leading to cyanosis, syncope, and death. BOAS may have a severe impact upon the welfare of affected dogs, compromising their ability to exercise, play, eat, and sleep. Although a well-described condition, with surgical treatments for the palliation of this disorder published since the 1920s, many dogs still experience airway restrictions postsurgically and a compromised quality of life. In addition, the prevalence of this disorder does not appear to have substantially reduced in this time, and may have increased. Ultimately, strategies to improve the breeding of these dogs to prevent BOAS are required to improve brachycephalic health and welfare. Recent studies have revealed conformational risk factors associated with BOAS, such as short muzzles and thick necks, which should be discouraged to avoid perpetuating this serious disorder. Positive changes to brachycephalic health may be impeded by a perception of BOAS being "normal for the breed". This perception must be avoided by owners, breeders, and vets alike to prevent undertreatment of individuals and the perpetuation of this serious disorder to future generations of dogs.

Anaesthetic induction and recovery characteristics of a diazepam-ketamine combination compared with propofol in dogs

Induction of anaesthesia occasionally has been associated with undesirable behaviour in dogs. High quality of induction of anaesthesia with propofol has been well described while in contrast variable induction and recovery quality has been associated with diazepam-ketamine. In this study, anaesthetic induction and recovery characteristics of diazepam-ketamine combination with propofol alone were compared in dogs undergoing elective orchidectomy. Thirty-six healthy adult male dogs were used. After habitus scoring (simple descriptive scale [SDS]), the dogs were sedated with morphine and acepromazine. Forty minutes later a premedication score (SDS) was allocated and general anaesthesia was induced using a combination of diazepam-ketamine (Group D/K) or propofol (Group P) and maintained with isoflurane. Scores for the quality of induction, intubation and degree of myoclonus were allocated (SDS). Orchidectomy was performed after which recovery from anaesthesia was scored (SDS) and times to extubation and standing were recorded. Data were analysed using descriptive statistics and Kappa Reliability and Kendall Tau B tests. Both groups were associated with acceptable quality of induction and recovery from anaesthesia. Group P, however, was associated with a poorer quality of induction (p = 0.014), prolonged induction period (p = 0.0018) and more pronounced myoclonus (p = 0.003), but had better quality of recovery (p = 0.000002) and shorter recovery times (p = 0.035) compared with Group D/K. Diazepam-ketamine and propofol are associated with acceptable induction and recovery from anaesthesia. Propofol had inferior anaesthetic induction characteristics, but superior and quicker recovery from anaesthesia compared with diazepam-ketamine.

Multivariable analysis of anesthetic factors associated with time to extubation in dogs

The purpose of this study was to identify factors that prolong the time to extubation in dogs. Anesthetic records of 900 dogs at a university teaching hospital were searched. Multiple linear regression was used to compare independent predictors (patient demographics, anesthetic and intraoperative variables) with the dependent variable (time to extubation). Induction with propofol (P < 0.025) was associated with a shorter time to extubation, while premedication with acepromazine (P = 0.000) was associated with a longer time to extubation. Time to extubation was increased by 0.311 minutes for every kilogram increase in body weight (P = 0.000), 5.924 minutes for every 1 °C loss in body temperature (P = 0.0000), and by 0.096 minutes for every 1 minute increase in anesthetic duration (P = 0.000). Anesthetic variables, which can be manipulated by the anesthetist, include choice of premedication and induction drugs, hypothermia, and duration of anesthesia.

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

OBJECTIVE

To compare the effect of alfaxalone and propofol on heart rate (HR) and blood pressure (BP) after fentanyl administration in healthy dogs.

STUDY DESIGN

Prospective, randomised clinical study.

ANIMALS

Fifty healthy client owned dogs (ASA I/II) requiring general anaesthesia for elective magnetic resonance imaging for neurological conditions.

METHODS

All 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.

RESULTS

Dogs 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.

CONCLUSION

Following fentanyl administration, anaesthetic induction with propofol resulted in a greater negative chronotropic effect while alfaxalone preserved or increased HR.

CLINICAL RELEVANCE

Following 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.

Pharmacokinetic study and evaluation of the safety of taurolidine for dogs with osteosarcoma

Background

Osteosarcoma in dogs and humans share many similarities and the dog has been described as an excellent model to study this disease. The median survival in dogs has not improved in the last 25 years. Taurolidine has been shown to be cytotoxic to canine and human osteosarcoma in vitro. The goals of this study were to determine the pharmacokinetics and safety of taurolidine in healthy dogs and the safety of taurolidine in combination with doxorubicin or carboplatin in dogs with osteosarcoma.

Methods

Two percent taurolidine was infused into six healthy dogs (150 mg/kg) over a period of two hours and blood samples were taken periodically. One dog received taurolidine with polyvinylpyrrolidone (PVP) as its carrier and later received PVP-free taurolidine as did all other dogs in this study. Serum taurolidine concentrations were determined using high-performance liquid chromatography (HPLC) online coupled to ESI-MS/MS in the multiple reaction monitoring mode. Subsequently, the same dose of taurolidine was infused to seven dogs with osteosarcoma also treated with doxorubicin or carboplatin.

Results

Taurolidine infusion was safe in 6 healthy dogs and there were no significant side effects. Maximum taurolidine serum concentrations ranged between 229 to 646 μM. The dog that received taurolidine with PVP had an immediate allergic reaction but recovered fully after the infusion was stopped. Three additional dogs with osteosarcoma received doxorubicin and taurolidine without PVP. Toxicities included dilated cardiomyopathy, protein-losing nephropathy, renal insufficiency and vasculopathy at the injection site. One dog was switched to carboplatin instead of doxorubicin and an additional 4 dogs with osteosarcoma received taurolidine-carboplatin combination. One incidence of ototoxicity occurred with the taurolidine- carboplatin combination. Bone marrow and gastro-intestinal toxicity did not appear increased with taurolidine over doxorubicin or carboplatin alone.

Conclusions

Taurolidine did not substantially exacerbate bone marrow or gastro-intestinal toxicity however, it is possible that taurolidine increased other toxicities of doxorubicin and carboplatin. Administering taurolidine in combination with 30 mg/m² doxorubicin in dogs is not recommended but taurolidine in combination with carboplatin (300 mg/m²) appears safe.