Minimum infusion rate of alfaxalone for total intravenous anaesthesia after sedation with acepromazine or medetomidine in cats undergoing ovariohysterectomy

Comparison of the effect of three intramuscular sedation protocols on packed cell volume and total protein in cats

OBJECTIVES

The aim of this study was to evaluate the change in packed cell volume (PCV) and total protein following intramuscular preanesthetic sedation with one of three drug combinations in cats.

METHODS

Thirty client-owned cats were enrolled in this prospective, randomized, blinded, clinical study. A venous blood sample was obtained prior to administration of any sedation and PCV, total protein, electrolytes (Na+, K+, Cl-, iCa2+), glucose and lactate were measured. Cats were randomly assigned to receive one of three intramuscular sedation protocols (n = 10 cats/protocol): methadone 0.2 mg/kg + acepromazine 0.02 mg/kg (MA), methadone 0.2 mg/kg + dexmedetomidine 5 µg/kg (MD) or methadone 0.2 mg/kg + midazolam 0.2 mg/kg + alfaxalone 2 mg/kg (MMA). Twenty-five minutes later, cats were assessed for level of sedation followed by another venous blood sampling to evaluate the same variables as above.

RESULTS

There were no significant differences in demographics (age, weight, sex) between groups. Level of sedation was significantly higher in MMA cats. Within groups, after premedication, PCV and hemoglobin significantly decreased in all groups, total protein significantly decreased in the MA and MMA groups and glucose significantly increased in the MD group. For electrolytes, statistical changes were not clinically relevant; Cl- mean difference was significantly different between MA and MD; in the MD group Na+ and Cl- significantly decreased and in the MMA group Cl- significantly increased.

CONCLUSIONS AND RELEVANCE

All three sedation protocols caused significant decreases in PCV and hemoglobin in healthy cats.

Intramuscular alfaxalone and methadone with or without ketamine in healthy cats: effects on sedation and echocardiographic measurements

OBJECTIVE

To evaluate the effect of alfaxalone and methadone administered intramuscularly (IM), with or without ketamine, on sedation and echocardiographic measurements in healthy cats.

STUDY DESIGN

A randomized, blinded, clinical study.

ANIMALS

A group of 24 client-owned cats.

METHODS

Baseline echocardiographic evaluation (bEchoCG) was performed. Cats were given IM alfaxalone (2 mg kg^-1) and methadone (0.3 mg kg^-1) with (AMK group) or without (AM group) ketamine (1 mg kg^-1). A sedation score (0-5, indicating none to good sedation) was assigned at 5 (T5), 10 (T10) and 15 (T15) minutes after IM injection. At T15, a second echocardiographic evaluation (sEchoCG) was performed. Data are shown as median (range). Significance was p < 0.05.

RESULTS

Finally, 21 cats were included. Sedation score was significantly higher in the AMK (11 cats) than in the AM group (10 cats): 4 (1-5) versus 0.5 (0-4) at T5 (p = 0.003); 4 (1-5) versus 1.5 (0-5) at T10 (p = 0.043); and 4 (1-5) versus 2 (0-5) at T15 (p = 0.024). All echocardiographic measurements obtained were within reference ranges. Between the groups, aortic root area (p = 0.009) and end-diastolic aortic dimension (p = 0.011) were significantly higher in the AM group at bEchoCG and sEchoCG, respectively. Within each group, values at bEchoCG and sEchoCG showed no significant differences, except for pulmonary peak velocity (0.85 m second^-1; p = 0.028) in the AMK group and ejection time (154 m second; p = 0.03) in the AM group; both variables decreased after sedation.

CONCLUSIONS AND CLINICAL RELEVANCE

In this population of healthy cats, neither protocol produced clinically meaningful effects on the echocardiographic variables evaluated. Alfaxalone with methadone produced mild sedation, whereas the addition of 1 mg kg^-1 ketamine induced adequate sedation for diagnostic procedures.

Hemodynamic effects of subclinical, clinical and supraclinical plasma alfaxalone concentrations in cats

OBJECTIVE

To characterize the hemodynamic effects of subclinical, clinical and supraclinical plasma alfaxalone concentrations in cats.

STUDY DESIGN

Experimental study.

ANIMALS

A group of six adult healthy male neutered cats.

METHODS

Cats were anesthetized with desflurane in oxygen for instrumentation. Catheters were placed in a medial saphenous vein for drug administration and in a carotid artery for arterial blood pressure measurement and blood collection. A thermodilution catheter was placed in the pulmonary artery via an introducer placed in a jugular vein for measurement of central venous pressure, pulmonary artery pressure, pulmonary artery occlusion pressure, cardiac output and core body temperature, and for sampling mixed venous blood. A lead II electrocardiogram was connected. Desflurane administration was discontinued and a target-controlled infusion system was used to administer alfaxalone to reach six plasma alfaxalone concentrations ranging from 1.0 to 30.4 mg L^-1, with 7.6 mg L^-1 considered a clinical concentration for anesthesia. Cardiovascular measurements were recorded, and arterial and mixed-venous blood samples were collected for blood-gas analysis and plasma alfaxalone concentration measurement at each target concentration. Data were analyzed using a repeated-measures analysis of variance and Dunnett's test for comparisons to the lowest target concentration. Significance was set at p < 0.05.

RESULTS

Mean ± standard deviation plasma alfaxalone concentrations were 0.73 ± 0.32, 1.42 ± 0.41, 3.44 ± 0.40, 6.56 ± 0.43, 18.88 ± 6.81 and 49.47 ± 5.50 mg L^-1 for the 1, 1.9, 3.8, 7.6, 15.2, and 30.4 mg L^-1 target concentrations, respectively. PaCO₂ increased with increasing target plasma alfaxalone concentrations and was 69.4 ± 14.2 mmHg (9.3 ± 1.9 kPa) at the 30.4 mg L^-1 target. Some cardiovascular variables were statistically significantly affected by increasing target plasma alfaxalone concentrations.

CONCLUSION AND CLINICAL RELEVANCE

Within the plasma concentration range studied, alfaxalone caused hypoventilation, but the cardiovascular effects were of small clinical significance.

AAFP Feline Anesthesia Guidelines

AIM

The overarching purpose of the AAFP Anesthesia Guidelines (hereafter referred to as the 'Guidelines') is to make anesthesia and sedation safer for the feline patient. Scope and accessibility: It is noteworthy that these are the first exclusively feline anesthesia guidelines authored by an expert panel, making them particularly useful as an extensively referenced, practical resource for veterinary practice teams. Because much of the key content is presented in tabular or visual format, the Guidelines have a high level of accessibility and convenience that invites regular usage. While the recommendations in the Guidelines focus primarily on client-owned cats, the content is also applicable to community-sourced animals with an unknown medical history.

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.

Anesthetic and cardiorespiratory effects of single-bolus intravenous alfaxalone with or without intramuscular xylazine-premedication in calves

The anesthetic and cardiorespiratory effects of xylazine-alfaxalone combination were evaluated in calves. Six calves (age: 6–9 months old; weight: 114–310 kg) were anesthetized with intravenous alfaxalone 15 min after administration of intramuscular saline (0.5 ml/100 kg) or xylazine (0.1 mg/kg; 0.5 ml/100 kg of a 2% xylazine solution). Anesthesia induction was smooth and orotracheal intubation was achieved in all calves. The calves anesthetized with xylazine-alfaxalone required a smaller induction dose of alfaxalone (1.23 ± 0.17 mg/kg, P=0.010) and accepted endotracheal intubation for a significantly longer period (16.8 ± 7.2 min, P=0.022) than the calves anesthetized with alfaxalone alone (2.28 ± 0.65 mg/kg 7.3 ± 1.6 min). At 5 min after induction, tachycardia (heart rate: 166 ± 47 beats/min of heart rate), hypertension (mean arterial blood pressure: 147 ± 81 mmHg) and hypoxemia (partial pressure of arterial blood oxygen [PaO₂]: 43 ± 10 mmHg) were observed in the calves anesthetized with alfaxalone alone, whereas hypoxemia (PaO₂: 47 ± 7 mmHg) and mild hypercapnia (partial pressure of arterial blood carbon dioxide: 54 ± 5 mmHg) were observed in the calves anesthetized with xylazine-alfaxalone. Premedication with xylazine provided a sparing effect on the induction dose of alfaxalone and a prolongation of anesthetic effect. Oxygen supplementation should be considered to prevent hypoxemia during anesthesia.

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.

Dexmedetomidine-methadone-ketamine versus dexmedetomidine-methadone-alfaxalone for cats undergoing ovariectomy

OBJECTIVE

To compare the duration, quality of anaesthesia and analgesia, and quality of recovery of dexmedetomidine and methadone combined with either ketamine or alfaxalone.

STUDY DESIGN

Randomized, prospective clinical trial.

ANIMALS

A group of 44 healthy client-owned cats presenting for ovariectomy.

METHODS

Cats were randomly assigned to one of the two treatment groups: DAM (n=22), which was administered intramuscularly (IM) dexmedetomidine (15 μg kg^-1), methadone (0.3 mg kg^-1) and alfaxalone (3 mg kg^-1), and DKM (n=22), which was administered IM dexmedetomidine (15 μg kg^-1), methadone (0.3 mg kg^-1) and ketamine (3 mg kg^-1). During anaesthesia, heart rate, respiratory rate and systolic arterial pressure were measured every 5 minutes. Cats that moved or had poor muscle relaxation were administered an additional 1 mg kg^-1 of either alfaxalone (DAM) or ketamine (DKM) intravenously (IV). In cases of increased autonomic responses to surgical stimulation, fentanyl (2 μg kg^-1) was administered IV. At the end of the surgery, atipamezole (75 μg kg^-1) was administered IM, and the times to both sternal recumbency and active interaction were recorded. Quality of recovery was evaluated with a simple descriptive scale. The UNESP-Botucatu multidimensional composite pain scale and a visual analogue scale were used to evaluate postoperative analgesia at the return of active interaction and 1, 2 and 3 hours later.

RESULTS

The additional anaesthesia and rescue fentanyl requirements were similar between groups. The quality of recovery was better in the DAM group than in the DKM group [simple descriptive scale scores: 0 (0-1) and 1 (0-3), respectively; p=0.002]. Postoperative pain scores decreased progressively over time in both groups, with no significant differences (p=0.08) between them.

CONCLUSIONS AND CLINICAL RELEVANCE

Both protocols provided comparable quality of anaesthesia and analgesia and were suitable for cats undergoing ovariectomy. In combination with methadone and dexmedetomidine, alfaxalone and ketamine showed comfortable and reliable recoveries.

A comparison of cardiopulmonary effects and anaesthetic requirements of two dexmedetomidine continuous rate infusions in alfaxalone-anaesthetized Greyhounds

OBJECTIVE

To determine the effects of two dexmedetomidine continuous rate infusions on the minimum infusion rate of alfaxalone for total intravenous anaesthesia (TIVA), and subsequent haemodynamic and recovery effects in Greyhounds undergoing laparoscopic ovariohysterectomy.

STUDY DESIGN

Prospective, randomized and blinded clinical study.

ANIMALS

Twenty-four female Greyhounds.

METHODS

Dogs were premedicated with dexmedetomidine 3 μg kg^-1 and methadone 0.3 mg kg^-1 intramuscularly. Anaesthesia was induced with IV alfaxalone to effect and maintained with a TIVA mixture of alfaxalone in combination with two different doses of dexmedetomidine (0.5 μg kg^-1 hour^-1 or 1 μg kg^-1 hour^-1; groups DEX0.5 and DEX1, respectively). The alfaxalone starting dose rate was 0.07 mg kg^-1 minute^-1 and was adjusted (± 0.02 mg kg^-1 minute^-1) every 5 minutes to maintain a suitable depth of anaesthesia. A rescue alfaxalone bolus (0.5 mg kg^-1 IV) was administered if dogs moved or swallowed. The number of rescue boluses was recorded. Heart rate, arterial blood pressure and arterial blood gas were monitored. Qualities of sedation, induction and recovery were scored. Differences between groups were tested for statistical significance using a Student's t test or Mann-Whitney U test as appropriate.

RESULTS

There were no differences between groups in sedation, induction and recovery quality, the median (range) induction dose of alfaxalone [DEX0.5: 2.2 (1.9-2.5) mg kg^-1; DEX1: 1.8 (1.2-2.9) mg kg^-1], total dose of alfaxalone rescue boluses [DEX0.5: 21.0 (12.5-38.8) mg; DEX1: 22.5 (15.5-30.6) mg] or rate of alfaxalone (DEX0.5: 0.12±0.04 mg kg^-1 minute^-1; DEX1: 0.12±0.03 mg kg^-1 minute^-1).

CONCLUSIONS AND CLINICAL RELEVANCE

Co-administration of dexmedetomidine 1 μg kg^-1 hour^-1 failed to reduce the dose rate of alfaxalone compared with dexmedetomidine 0.5 μg kg^-1 hour^-1 in Greyhounds undergoing laparoscopic ovariohysterectomy. The authors recommend an alfaxalone starting dose rate of 0.1 mg kg^-1 minute^-1. Recovery quality was good in the majority of dogs.

Cardiorespiratory and anesthetic effects of combined alfaxalone, butorphanol, and medetomidine in Thoroughbred horses

This study evaluated induction of anesthesia and cardiorespiratory and anesthetic effects during maintained anesthesia with the combination of alfaxalone, medetomidine, and butorphanol. Alfaxalone (1.0 mg/kg) was administered to induce anesthesia after premedication with medetomidine (7.0 µg/kg), butorphanol (25 µg/kg), and midazolam (50 µg/kg) in six Thoroughbred horses. Intravenous general anesthesia was maintained with alfaxalone (2.0 mg/(kg∙hr)), medetomidine (5.0 µg/(kg∙hr)), and butorphanol (30 µg/(kg∙hr)) for 60 min. Electrical stimulation of the upper oral mucosa was used to assess anesthetic depth at 10 min intervals during anesthesia. Heart rate (HR), respiratory rate (RR), and mean arterial pressure (MAP) were measured. All horses became recumbent within 1 min after alfaxalone administration. Induction scores were 5 (best) in five horses and 4 in one horse. During the 60-min anesthesia, average HR, RR, and MAP were 35.8 ± 2.6 beat/min, 4.7 ± 0.6 breath/min, and 129 ± 3 mmHg, respectively. No horse moved with electrical stimulation; however, two horses experienced apnea (no respiration for 1 to 3 min). Recovery scores were 5 (best) in two horses and 3 in four horses. These results suggest that alfaxalone is effective for induction and maintenance of anesthesia and analgesia when combined with butorphanol and medetomidine for 60 min in Thoroughbreds. However, respiratory depression might require support.

Alfaxalone for total intravenous anaesthesia in bitches undergoing elective caesarean section and its effects on puppies: a randomized clinical trial

OBJECTIVE

To evaluate the effects and reliability of alfaxalone constant rate infusion (CRI) in comparison to isoflurane to maintain anaesthesia in bitches undergoing elective caesarean section.

STUDY DESIGN

Prospective, randomized, 'blinded' clinical trial.

ANIMALS

Twenty-two client-owned bitches and 94 puppies.

METHODS

Bitches were randomly assigned to receive an alfaxalone CRI [0.2 mg kg(-1)  minute(-1) intravenously (IV), and once the last puppy was delivered, the dose was halved; n = 11] or 2% (vaporizer dial setting) isoflurane (n = 11) for maintenance of anaesthesia. All dogs were induced with alfaxalone (3 mg kg(-1) ) IV. Additional alfaxalone (0.3 mg kg(-1) IV) was administered if the depth of anaesthesia was inadequate and the total dose was calculated. Bitches were mechanically ventilated. Analgesia was administered after the delivery of puppies. Physiological variables were recorded every 5 minutes. The bitches' recovery times were also recorded. Quality of induction and recovery were evaluated. Puppies' vigour was evaluated with a modified Apgar score at 5 and 60 minutes after birth. Puppies' survival rates at 24 and 48 hours and at 15 days were recorded. Data were analysed using an anova, Student's t-test or Wilcoxon rank-sum test.

RESULTS

The rescue dose of alfaxalone was higher (p = 0.01); bitches' recoveries were longer (p < 0.001) and puppies' Apgar scores were significantly lower at 5 and 60 minutes (p < 0.001 and p = 0.003, respectively) with alfaxalone than with isoflurane. However, no significant differences were found for puppies' survival between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone CRI seems to be a possible protocol for puppies and bitches undergoing elective caesarean sections. However, bitches recovered more slowly and puppy Apgar scores were lower in comparison to isoflurane.