Induction dose and recovery quality of propofol and alfaxalone with or without midazolam coinduction followed by total intravenous anesthesia in dogs

Anesthesia, pain management and surgical approach of ovariectomy or orchiectomy in six Egyptian fruit bats (Rousettus aegyptiacus): A case report

The purpose of this report is to describe the anesthetic and analgesic management and the surgical procedures of gonadectomy in six (four females and two males) healthy adult Egyptian fruit bats (Rousettus aegyptiacus). Bats were anesthetized with a combination of alfaxalone, midazolam, and morphine administered subcutaneously. Incisional line infiltration using bupivacaine was administered in all bats, and additional bilateral intratesticular injection was administered in the males. Ovariectomy was performed via a dorsal approach, by bilateral midline skin incisions at the paralumbar fossa level. Orchiectomy was performed via a ventral approach, by bilateral midline incisions of scrotal skin above the testes. Following surgery, all bats were administered flumazenil for midazolam reversal, and meloxicam for postoperative analgesia, subcutaneously. All bats recovered from anesthesia uneventfully. Bats were monitored for complications up to 10 days following surgery, when skin sutures were removed. No morbidities or mortalities occurred during this period in any of the bats. In conclusion, ventral approach orchiectomy and dorsal approach ovariectomy using the injectable combination alfaxalone-midazolam-morphine in conjunction with local anesthesia and meloxicam are feasible procedures in Egyptian fruit bats and can be performed with relative ease. However, further studies using these techniques in a larger group of bats should be performed to establish their safety.

Effects of Cisatracurium in Sevoflurane and Propofol Requirements in Dog-Undergoing-Mastectomy Surgery

The purpose of the present study was to test whether the addition of cisatracurium in combination with propofol and sevoflurane would result in a change in doses of used anesthetic drugs. Ten dogs (Group A) undergoing elective unilateral mastectomy surgery were included in the study. To induce and maintain anesthesia, subjects received propofol and sevoflurane at varying doses; analgesia was performed with remifentanil. After three months, the same subjects (Group B) underwent contralateral mastectomy and received the same anesthetic protocol with the addition of cisatracurium at a dosage of 0.2 mg/kg−1. The following parameters were monitored during anesthesia: heart rate, systolic blood pressure, end-tidal CO2, oxygen saturation, halogenate requirement, and rectal temperature at baseline (T0), induction (T1), 5 (T5), 10 (T10), 15 (T15), 20 (T20), 25 (T25), 30 (T30), and 35 (T35) time points. In Group A, halogenate requirement was reduced at all the time points other than T1 (p < 0.001); in Group B, the percentage of halogenate requirement was already reduced at T1 and remained constant during the experimental period, showing no significant intragroup differences. The dose requirements of sevoflurane and propofol varied significantly between the two groups, with significantly lower dosages in the Group B (the cisatracurium-treated group). Moreover, patients treated with cisatracurium showed a stable anesthetic plan. The nondepolarizing-muscle-relaxant cisatracurium besylate could be considered a useful adjunct to anesthetic protocols.

Thoracic epidural anaesthesia vs intrathecal morphine in dogs undergoing major thoracic and abdominal surgery: clinical study

BACKGROUND

There is scant clinical research on neuraxial analgesia in dogs undergoing major surgery. With this study we compared the perioperative analgesic effects of thoracic epidural anaesthesia (TEA) and intrathecal morphine (ITM) in dogs scheduled for thoracic or cranial abdominal surgery. The dogs received methadone and dexmedetomidine, were anaesthetized with propofol maintained with sevoflurane, and randomly assigned to receive either TEA (ropivacaine 0.5% at 0.2 mg/kg and morphine 0.1 mg/kg administered at T₁₂-T₁₃) or ITM (morphine 30 μg/kg administered at L₆-L₇). Intraoperative rescue analgesia (iRA) was fentanyl 1 μg/kg administered if heart rate or mean arterial pressure increased by 30% above the pre-stimulation level. Glasgow Pain Composite Scale score (GPCS) dictated the use of postoperative rescue analgesia (pRA) with methadone 0.2 mg/kg.

RESULTS

There was a statistically significant difference in iRA, median time to first fentanyl bolus, median fentanyl dose after surgical opening, and median GPCS score at 30 minutes (min), 1 ,2, 4, 6, and 8 hours (h) between the two groups (p<0.001; p<0.001; p<0.001; p<0.01; p<0.01; p<0.001; p<0.01; p=0.01; p=0.01, respectively). Fewer TEA than ITM group dogs required iRA during surgical opening and pRA: 5% (1/18) and 2/18 (11%), respectively, in the TEA and 83% (16/18) and 10/18 (55%), respectively, in the ITM group. Side effects were urinary retention in 3/18 (16%) TEA group dogs and 2/18 (11%) ITM group dogs and prolonged sedation in 2/18 (11%) in ITM group dogs. TEA and ITM were effective in managing perioperative pain in dogs undergoing thoracic or cranial abdominal surgery.

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.

Sedative effects of alfaxalone and hydromorphone with or without midazolam in cats: a pilot study

OBJECTIVES

The aim of this pilot study was to compare the quality of sedation and ease of intravenous (IV) catheter placement following sedation using two intramuscular (IM) sedation protocols in cats: hydromorphone, alfaxalone and midazolam vs hydromorphone and alfaxalone.

METHODS

This was a prospective, randomized and blinded study. Cats were randomly assigned to receive an IM injection of hydromorphone (0.1 mg/kg), alfaxalone (1.5 mg/kg) and midazolam (0.2 mg/kg; HAM group), or hydromorphone (0.1 mg/kg) and alfaxalone (1.5 mg/kg; HA group). Sedation scoring (0-9, where 9 indicated maximum sedation) was performed at 0, 5, 10, 15 and 20 mins from the time of injection. At 20 mins, an IV catheter placement score (0-10, where 10 indicated least resistance) was performed.

RESULTS

Twenty-one client-owned adult cats were included in this study. Sedation and IV catheter placement scores were compared between groups using Wilcoxon rank sum tests. Peak sedation was significantly higher (P = 0.002) in the HAM group (median 9; range 7-9) than in the HA group (median 7; range 3-9), and IV catheter placement scores were significantly higher (P = 0.001) in the HAM group (median 9.5; range 7-10) compared with the HA group (median 7; range 4-9). Spearman correlations were calculated between IV catheter placement score and sedation scores. There was a significant positive correlation of average sedation over time (correlation 0.83; P <0.001) and sedation at 20 mins (correlation 0.76; P <0.001) with a higher, more favorable IV catheter placement score.

CONCLUSIONS AND RELEVANCE

These preliminary results suggest that the addition of midazolam to IM alfaxalone and hydromorphone produced more profound sedation and greater ease of IV catheter placement than IM alfaxalone and hydromorphone alone.

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.

Evaluation of the analgesic effect of fentanyl-ketamine and fentanyl-lidocaine constant rate infusions in isoflurane-anesthetized dogs undergoing thoracolumbar hemilaminectomy

OBJECTIVE

To evaluate anesthetic conditions and postoperative analgesia with the use of intraoperative constant rate infusions (CRIs) of fentanyl-lidocaine or fentanyl-ketamine in dogs undergoing thoracolumbar hemilaminectomy.

STUDY DESIGN

Prospective, randomized, blinded, clinical study.

ANIMALS

A total of 32 client-owned dogs.

METHODS

Dogs were premedicated with fentanyl (5 μg kg^-1) administered intravenously (IV), anesthesia was induced with IV alfaxalone and maintained with isoflurane. Fentanyl (0.083 μg kg^-1 minute^-1) was infused IV with either ketamine (0.5 mg kg^-1; then 40 μg kg^-1 minute^-1; group KF) or lidocaine (2 mg kg^-1; then 200 μg kg^-1 minute^-1; group LF) assigned randomly. Heart rate, noninvasive arterial pressures, respiratory rate, esophageal temperature, end-tidal partial pressure of carbon dioxide and isoflurane concentration were recorded throughout anesthesia. Maintenance of anesthesia, recovery and postoperative pain (Glasgow Composite Pain Scale) were scored. Cardiopulmonary data were analyzed using a two-way anova with repeated measures, demographics of the two groups with a t test, and scores with Mann-Whitney U test, with p < 0.05.

RESULTS

All dogs recovered from anesthesia without complications. No significant difference was found between groups for cardiopulmonary variables, total anesthesia time, sedation score and requirement for postoperative sedation or for rescue analgesia. Anesthetic maintenance score was of lower quality in KF than in LF [median (interquartile range): 0 (0-0.5) versus 0 (0-0); p = 0.032)], but still considered ideal. Recovery score was higher and indicative of less sedation in LF than in KF [1 (1-1.5) versus 0.5 (0-1); p < 0.0001]. Pain score was higher in KF than in LF [2 (1-3) versus 1 (1-2); p = 0.0009].

CONCLUSIONS AND CLINICAL RELEVANCE

Both CRIs of KF and LF provided adequate anesthetic conditions in dogs undergoing thoracolumbar hemilaminectomy. Based on requirement for rescue analgesia, postoperative analgesia was adequate in both groups.

Use of intravenous lidocaine to treat dexmedetomidine-induced bradycardia in sedated and anesthetized dogs

OBJECTIVE

To assess cardiopulmonary function in sedated and anesthetized dogs administered intravenous (IV) dexmedetomidine and subsequently administered IV lidocaine to treat dexmedetomidine-induced bradycardia.

STUDY DESIGN

Prospective, randomized, crossover experimental trial.

ANIMALS

A total of six purpose-bred female Beagle dogs, weighing 9.1 ± 0.6 kg (mean ± standard deviation).

METHODS

Dogs were randomly assigned to one of three treatments: dexmedetomidine (10 μg kg^-1 IV) administered to conscious (treatments SED1 and SED2) or isoflurane-anesthetized dogs (end-tidal isoflurane concentration 1.19 ± 0.04%; treatment ISO). After 30 minutes, a lidocaine bolus (2 mg kg^-1) IV was administered in treatments SED1 and ISO, followed 20 minutes later by a second bolus (2 mg kg^-1) and a 30 minute lidocaine constant rate infusion (L-CRI) at 50 (SED1) or 100 μg kg^-1 minute^-1 (ISO). In SED2, lidocaine bolus and L-CRI (50 μg kg^-1 minute^-1) were administered 5 minutes after dexmedetomidine. Cardiopulmonary measurements were obtained after dexmedetomidine, after lidocaine bolus, during L-CRI and 30 minutes after discontinuing L-CRI. A mixed linear model was used for comparisons within treatments (p < 0.05).

RESULTS

When administered after a bolus of dexmedetomidine, lidocaine bolus and L-CRI significantly increased heart rate and cardiac index, decreased mean blood pressure, systemic vascular resistance index and oxygen extraction ratio, and did not affect stroke volume index in all treatments.

CONCLUSION AND CLINICAL RELEVANCE

Lidocaine was an effective treatment for dexmedetomidine-induced bradycardia in healthy research dogs.

Evaluation of alfaxalone and midazolam with or without flumazenil reversal in Egyptian fruit bats (Rousettus aegyptiacus)

OBJECTIVES

To evaluate alfaxalone-midazolam anesthesia in Egyptian fruit bats (Rousettus aegyptiacus) and the effect of flumazenil administration on recovery time and quality.

STUDY DESIGN

Randomized, blinded, crossover and controlled, experimental trial.

ANIMALS

A total of 10 male Egyptian fruit bats.

METHODS

Bats were anesthetized with alfaxalone (15 mg kg^-1) and midazolam (2 mg kg^-1) administered subcutaneously. During anesthesia, vital signs, muscle tone and reflexes were monitored every 10 minutes. Flumazenil (0.3 mg kg^-1) or saline at an equal volume was administered subcutaneously 60 minutes after anesthetic administration. Time to induction, time to first movement and recovery time (flying) were measured. Quality of induction, anesthesia and recovery were assessed on a 1-3 scale (1, poor; 2, good; 3, excellent).

RESULTS

Time to induction was 4.2 ± 1.9 minutes (mean ± standard deviation), with median quality score of 2 (range, 1-3). Anesthesia quality score was 3 (1-3). During anesthesia, heart rate and respiratory frequency decreased significantly and penis relaxation, indicating muscle tone, increased significantly. Administration of flumazenil significantly reduced mean recovery time compared with saline (10 ± 5 versus 45 ± 17 minutes, respectively), and significantly improved the quality of recovery [2.5 (2-3) versus 1 (1-2), respectively].

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone-midazolam anesthesia resulted in good induction, muscle relaxation and sufficient anesthesia to perform routine diagnostic and therapeutic procedures for approximately 40 minutes. Reversal of midazolam with flumazenil is recommended, resulting in quicker and better recovery.

Comparison between intravenous lidocaine and fentanyl on cough reflex and sympathetic response during endotracheal intubation in dogs

OBJECTIVE

To compare the effects of intravenous (IV) lidocaine and fentanyl on the cough reflex and autonomic response during endotracheal intubation in dogs.

STUDY DESIGN

Randomized, blinded, superiority clinical trial.

ANIMALS

A total of 46 client-owned dogs undergoing magnetic resonance imaging.

METHODS

After intramuscular methadone (0.2 mg kg^-1), dogs were randomized to be administered either IV lidocaine (2 mg kg^-1; group L) or fentanyl (7 μg kg^-1; group F). After 5 minutes, alfaxalone was administered until endotracheal intubation was possible (1 mg kg^-1 IV over 40 seconds followed by 0.4 mg kg^-1 increments to effect). Total dose of alfaxalone was recorded and cough reflex at endotracheal intubation was scored. Heart rate (HR) was continuously recorded, Doppler systolic arterial blood pressure (SAP) was measured every 20 seconds. Vasovagal tonus index (VVTI) and changes (Δ) in HR, SAP and VVTI between pre-intubation and intubation were calculated. Groups were compared using univariate and multivariate analysis. Statistical significance was set as p < 0.05.

RESULTS

Group F included 22 dogs and group L 24 dogs. The mean (± standard deviation) alfaxalone dose was 1.1 (± 0.2) and 1.35 (± 0.3) mg kg^-1 in groups F and L, respectively (p = 0.0008). At intubation, cough was more likely in group L (odds ratio = 11.3; 95% confidence intervals, 2.1 - 94.2; p = 0.01) and HR increased in 87.5% and 54.5% of groups L and F, respectively (p = 0.02). The median (range) ΔHR between pre-intubation and intubation was higher (13.1%; - 4.3 to + 55.1) in group L (p = 0.0021). Between groups, SAP and VVTI were similar.

CONCLUSION AND CLINICAL RELEVANCE

At the stated doses, whilst reducing the alfaxalone dose, fentanyl is superior to lidocaine in suppressing the cough reflex and blunting the increase in HR at endotracheal intubation in dogs premedicated with methadone.

Dose and cardiopulmonary effects of propofol alone or with midazolam for induction of anesthesia in critically ill dogs

OBJECTIVE

To determine the dose and cardiopulmonary effects of propofol alone or with midazolam for induction of anesthesia in American Society of Anesthesiologists status ≥III dogs requiring emergency abdominal surgery.

STUDY DESIGN

Prospective, randomized, blinded, clinical trial.

ANIMALS

A total of 19 client-owned dogs.

METHODS

Dogs were sedated with fentanyl (2 μg kg^-1) intravenously (IV) for instrumentation for measurement of heart rate, arterial blood pressure, cardiac index, systemic vascular resistance index, arterial blood gases, respiratory rate and rectal temperature. After additional IV fentanyl (3 μg kg^-1), the quality of sedation was scored and cardiopulmonary variables recorded. Induction of anesthesia was with IV propofol (1 mg kg^-1) and saline (0.06 mL kg^-1; group PS; nine dogs) or midazolam (0.3 mg kg^-1; group PM; 10 dogs), with additional propofol (0.25 mg kg^-1) IV every 6 seconds until endotracheal intubation. Induction/intubation quality was scored, and anesthesia was maintained with isoflurane. Variables were recorded for 5 minutes with the dog in lateral recumbency, breathing spontaneously, and then in dorsal recumbency with mechanical ventilation for the next 15 minutes. A general linear mixed model was used with post hoc analysis for multiple comparisons between groups (p < 0.05).

RESULTS

There were no differences in group demographics, temperature and cardiopulmonary variables between groups or within groups before or after induction. The propofol doses for induction of anesthesia were significantly different between groups, 1.9 ± 0.5 and 1.1 ± 0.5 mg kg^-1 for groups PS and PM, respectively, and the induction/intubation score was significantly better for group PM.

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam co-induction reduced the propofol induction dose and improved the quality of induction in critically ill dogs without an improvement in cardiopulmonary variables, when compared with a higher dose of propofol alone.

Effects of ketamine or midazolam continuous rate infusions on alfaxalone total intravenous anaesthesia requirements and recovery quality in healthy dogs: a randomized clinical trial

OBJECTIVE

To determine the alfaxalone dose reduction during total intravenous anaesthesia (TIVA) when combined with ketamine or midazolam constant rate infusions and to assess recovery quality in healthy dogs.

STUDY DESIGN

Prospective, blinded clinical study.

ANIMALS

A group of 33 healthy, client-owned dogs subjected to dental procedures.

METHODS

After premedication with intramuscular acepromazine 0.05 mg kg^-1 and methadone 0.3 mg kg^-1, anaesthetic induction started with intravenous alfaxalone 0.5 mg kg^-1 followed by either lactated Ringer's solution (0.04 mL kg^-1, group A), ketamine (2 mg kg^-1, group AK) or midazolam (0.2 mg kg^-1, group AM) and completed with alfaxalone until endotracheal intubation was achieved. Anaesthesia was maintained with alfaxalone (6 mg kg^-1 hour^-1), adjusted (±20%) every 5 minutes to maintain a suitable level of anaesthesia. Ketamine (0.6 mg kg^-1 hour^-1) or midazolam (0.4 mg kg^-1 hour^-1) were employed for anaesthetic maintenance in groups AK and AM, respectively. Physiological variables were monitored during anaesthesia. Times from alfaxalone discontinuation to extubation, sternal recumbency and standing position were calculated. Recovery quality and incidence of adverse events were recorded. Groups were compared using parametric analysis of variance and nonparametric (Kruskal-Wallis, Chi-square, Fisher's exact) tests as appropriate, p < 0.05.

RESULTS

Midazolam significantly reduced alfaxalone induction and maintenance doses (46%; p = 0.034 and 32%, p = 0.012, respectively), whereas ketamine only reduced the alfaxalone induction dose (30%; p = 0.010). Recovery quality was unacceptable in nine dogs in group A, three dogs in group AK and three dogs in group AM.

CONCLUSIONS AND CLINICAL RELEVANCE

Midazolam, but not ketamine, reduced the alfaxalone infusion rate, and both co-adjuvant drugs reduced the alfaxalone induction dose. Alfaxalone TIVA allowed anaesthetic maintenance for dental procedures in dogs, but the quality of anaesthetic recovery remained unacceptable irrespective of its combination with ketamine or midazolam.

Anesthetic management of a dog with severe subaortic stenosis and mitral valve disease complicated with atrial fibrillation undergoing ovariohysterectomy

The anesthetic management in patients with subaortic stenosis and mitral valve disease should involve intensive monitoring and the anesthesiologist's main concern is to ensure oxygen delivery and tissue perfusion. Since anesthetic procedures in such patients are rare, there is no previous report about the anesthetic management. A 5.5-year old, 32-kg Boxer, suffering a severe heart disease due to a final stage subaortic stenosis and mitral insufficiency, was anesthetized for an ovariohysterectomy to remove an ovarian tumor that was producing high-volume ascites. Methadone (0.3 mg kg^-1) was administered intramuscularly (IM) for pre-anesthetic medication, etomidate (1.3 mg kg^-1) and midazolam (0.2 mg kg^-1) were used for the induction of anesthesia and after endotracheal intubation, anesthesia was maintained with sevoflurane vaporized in oxygen and air. Fentanyl (5-10 μg kg^-1 h^-1) and paracetamol (15 mg kg^-1) were administered to improve analgesia. Previous persistent atrial fibrillation was refractory to medication (digoxin, diltiazem, and pimobendan) and continued during the anesthetic procedure. Dobutamine (1.5-5 μg kg^-1 minute^-1) helped to maintain mean arterial blood pressure above 60 mmHg. Epidural morphine (0.1 mg kg^-1) and incisional bupivacaine (2 mg kg^-1) were administered at the end of surgery to provide postoperative analgesia. Anesthesia was otherwise uneventful, and recovery was considered excellent.

Effect of midazolam on the quality and duration of anaesthetic recovery in healthy dogs undergoing elective ovariohysterectomy or castration

OBJECTIVE

To determine whether the use of a single dose of midazolam affects quality and duration of the recovery period in healthy dogs undergoing elective castration or ovariohysterectomy.

STUDY DESIGN

Prospective, randomized, placebo-controlled, masked clinical trial.

ANIMAL POPULATION

Seventy-four client-owned dogs undergoing neutering.

METHODS

Following cage demeanour scoring using a simple descriptive scale (SDS), dogs were premedicated with acepromazine (0.03 mg kg^-1) and pethidine (3 mg kg^-1) intramuscularly (quadriceps muscle). Twenty minutes later sedation was scored with an SDS. Male dogs were induced with midazolam (0.25 mg kg^-1) (group M) or an equivalent amount of Hartmann's solution (group P) and propofol intravenously (IV). Female dogs were induced with propofol alone and were administered midazolam (group M) or Hartmann's solution (group P) 5 minutes before intraoperative manipulation of the first ovary. Anaesthesia was maintained with isoflurane in oxygen. Intraoperative analgesia was provided with morphine (0.3 mg kg^-1 IV) prior to the start of surgery. Male dogs were administered intratesticular lidocaine (1 mg kg^-1). All dogs were administered meloxicam (0.2 mg kg^-1 IV) at the end of the procedure, and recovery was scored with an SDS following extubation and 30 minutes later. Time to extubation, head lift, sternal position and standing and complications during recovery were recorded. Data are presented as median (range).

RESULTS

Time to standing was significantly longer in animals in group M [56 (13-179) minutes] than in group P [44 (4-137) minutes], and the early recovery score in group M [3 (2-6)] was overall worse than in group P [3 (1-5)]. Significantly more dogs in group M (n = 30) than in group P (n = 22) displayed hypotension.

CONCLUSIONS AND CLINICAL RELEVANCE

The administration of midazolam prolonged time to standing and had a mild negative effect on the quality of recovery in a pooled population of healthy male and female dogs undergoing neutering.

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.

Determination of midazolam dose for co-induction with alfaxalone in sedated cats

OBJECTIVE

To investigate the median effective dose 50 (ED₅₀) of midazolam required for endotracheal intubation when used for co-induction of anesthesia with a low dose of alfaxalone in sedated cats.

STUDY DESIGN

Randomized up-and-down study.

ANIMALS

A group of 14 mixed-breed cats (eight males, six females), aged 5-12 years and weighing 4.4-6.8 kg.

METHODS

The cats were randomly assigned in a sequential allocation numbers from one to 14. Cats were sedated with dexmedetomidine (3 μg kg^-1) and methadone (0.3 mg kg^-1) intramuscularly. After 15 minutes, the quality of sedation was subjectively evaluated. Anesthesia induction was performed by intravenous (IV) administration of alfaxalone (0.25 mg kg^-1) over a 60 second interval, followed by another 60 second interval, and then an IV dose of midazolam was administered over a 5 second interval. The initial midazolam dose was 0.3 mg kg^-1; then, the midazolam dose was adjusted by ±0.1 mg kg^-1 for each consecutive cat based on successful or unsuccessful endotracheal intubation of the previous animal following an up-and-down method. This sequence was followed until six nonsequential crossovers were observed. Crossover was defined as two opposite outcomes in two sequential animals. Data were analyzed using isotonic regression with bootstrapping for determination of midazolam ED₅₀ and logistic regression for correlations (p < 0.05).

RESULTS

Overall, six independent crossovers were found, and ED₅₀ of midazolam was 0.08 ± 0.04 mg kg^-1. Sedation score and successful tracheal intubation had a strong positive correlation (p = 0.02).

CONCLUSIONS AND CLINICAL RELEVANCE

This study determined that 0.08 ± 0.04 mg kg^-1 of midazolam co-administered with 0.25 mg kg^-1 of alfaxalone IV allowed smooth endotracheal intubation in half of the cats sedated with methadone and dexmedetomidine at the doses used in this study.

Alfaxalone-Xylazine Anesthesia in Laboratory Mice (Mus musculus)

Since its recent reformulation, alfaxalone has gained popularity as an injectable veterinary anesthetic, including promising studies demonstrating the use of alfaxalone-xylazine for anesthesia in mice. Here we sought to expand these studies by testing additional dose ranges, elaborating on physiologic monitoring, testing sex- and strain-associated differences, and evaluating efficacy during actual surgical conditions. C57BL/6J mice showed significant sex-associated differences in anesthetic sensitivity, with males requiring higher doses of alfaxalone (80-120 mg/kg IP alfaxalone with 10 mg/kg IP xylazine) than females (40-80 mg/kg IP alfaxalone with 10 mg/kg IP xylazine) to achieve a surgical plane of anesthesia. In addition, female outbred CD1 mice were less sensitive to alfaxalone than female inbred C57BL/6J mice. When used during actual surgery, alfaxalone-xylazine administered intraperitoneally provided adequate anesthesia for a model of orthopedic surgery, whereas the same anesthetic regimen during laparotomy resulted in unacceptably high mortality; survival during laparotomy increased when drugs were administered subcutaneously. These results indicate that alfaxalone-xylazine may be a viable option for injectable surgical anesthesia in mice, although strain- and sex-associated differences and alternative routes of administration should be considered when optimizing the anesthetic regimen for specific experimental conditions.

Comparison of two intravenous anesthetic infusion regimens for alfaxalone in cats

OBJECTIVE

To compare the performance of an alfaxalone constant rate intravenous (IV) infusion versus a 3-step IV infusion, both following a loading dose, for the maintenance of a target plasma alfaxalone concentration of 7.6 mg L^-1 (effective plasma alfaxalone concentration for immobility in 99% of the population) in cats.

STUDY DESIGN

Prospective randomized crossover study.

ANIMALS

A group of six healthy, adult male neutered cats.

METHODS

Catheters were placed in a jugular vein for blood sampling and in a medial saphenous vein for drug administration. An IV bolus of alfaxalone (2 mg kg^-1) was administered, followed by either 0.2 mg kg^-1 minute^-1 for 240 minutes (single infusion; SI) or 0.4 mg kg^-1 minute^-1 for 10 minutes, then 0.3 mg kg^-1 minute^-1 for 30 minutes, and then 0.2 mg kg^-1 minute^-1 for 200 minutes (3-step infusion; 3-step). Plasma alfaxalone concentration was measured at six time points during the infusions. Measures of performance were calculated for each infusion regimen and compared using the paired Wilcoxon signed-rank test.

RESULTS

Median (range) absolute performance error, divergence, median prediction error and wobble were 15 (8-19)%, -8 (-12 to -6)% hour^-1, -12 (-19 to -7)% and 10 (8-19)%, respectively, in the SI treatment, and 6 (2-16)%, 0 (-13 to 2)% hour^-1, 1 (-16 to 4)% and 4 (3-6)% respectively, in the 3-step treatment and were significantly smaller in the 3-step treatment than in the SI treatment.

CONCLUSION AND CLINICAL RELEVANCE

After IV administration of a bolus dose, a 3-step infusion regimen can better maintain stable plasma alfaxalone concentrations close to the target concentration than a single constant rate infusion.