Cardiorespiratory and anaesthetic effects of two continuous rate infusions of dexmedetomidine in alfaxalone anaesthetized dogs

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.

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.

The anesthetic effects of intramuscular alfaxalone in dogs premedicated with low-dose medetomidine and/or butorphanol

We aimed to evaluate the induction, anesthesia, and cardiorespiratory effects of intramuscular (IM) anesthetic protocol with alfaxalone following premedication with low-dose medetomidine, butorphanol, or a combination of both (medetomidine–butorphanol) in dogs. Six healthy beagles were administered 1, 2.5, or 5 mg/kg alfaxalone IM following premedication with low-dose medetomidine (5 µg/kg; MA-IM), butorphanol (0.3 mg/kg; BA-IM), or medetomidine-butorphanol (5 µg/kg and 0.3 mg/kg, respectively; MBA-IM). Each dog received 9 treatments with minimum 7-day washout period between treatments. Dogs were allowed to breath room air during anesthetic induction. We attempted endotracheal intubation after alfaxalone administration. Alfaxalone produced a dose-dependent anesthetic effect in each anesthetic protocol. Intubation was achieved in 4 out of 6 dogs that received MA-IM and BA-IM with 2.5 mg/kg alfaxalone and in all dogs that received MBA-IM with 1, 2.5, and 5 mg/kg alfaxalone. The median durations [minimum–maximum] of accepting intubation were 79 [0–89], 97 [84–120], and 117 [84–217] min, respectively. Hypotension (mean arterial blood pressure <60 mmHg) did not develop, but bradycardia (heart rate <60 beats/min) was observed in all dogs that received the MA-IM and MBA-IM protocols. Severe hypoxemia (percutaneous arterial oxygen saturation <90%) developed in 2 dogs that received MBA-IM with 5 mg/kg alfaxalone. We consider that the MA-IM and BA-IM protocols with ≥2.5 mg/kg alfaxalone and the MBA-IM protocol with 1–2.5 mg/kg alfaxalone could provide clinically useful and effective anesthesia without causing severe cardiorespiratory depression in healthy dogs.

Cardiopulmonary Effects of a Partial Intravenous Anesthesia Technique for Laboratory Swine

Various anesthetic protocols are used in laboratory swine, each with specific advantages and disadvantages. Partial intravenous anesthetic techniques (PIVA) help minimize dose-dependent cardiopulmonary effects of inhalant drugs. The aim of this study was to determine the cardiopulmonary effects of a PIVA in laboratory swine. In a prospective, nonrandomized clinical study, 8 healthy juvenile Landrace-White pigs were premedicated with azaperone (0.20 ± 0.20 mg/kg IM), dexmedetomidine (0.02 ± 0.002 mg/kg IM), and alfaxalone (2.0 ± 0.20 mg/kg IM), and anesthesia was induced with intravenous alfaxalone. Anesthesia was maintained by using constant-rate infusion of dexmedetomidine (2 μg/kg/h) and alfaxalone (25 μg/kg/min) in combination with isoflurane. After the fraction of expired isoflurane was adjusted to 1.1% to 1.5%, respiratory rate, heart rate, systemic and pulmonary arterial pressure, central venous pressure, cardiac output, bispectral index, systemic vascular resistance, and arterial and mixed venous blood gases were recorded every 10 min for 60 min. Statistical analysis consisted of repeated-measures one-way ANOVA. Significant decreases occurred in heart rate, pulmonary mean arterial pressure, pulmonary diastolic pressure, partial pressure of arterial oxygen, partial pressure of venous oxygen; significant increases occurred in respiratory rate, minute volume index, diastolic arterial blood pressure, systemic vascular resistance, and arterial pH over time. We consider that the observed statistically significant cardiopulmonary changes were clinically important and that the PIVA protocol provided hemodynamic and respiratory stability for short-term anesthesia of laboratory swine.

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.

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.

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.

The pharmacological effects of intramuscular administration of alfaxalone combined with medetomidine and butorphanol in dogs

The pharmacological effects of intramuscular (IM) administration of alfaxalone combined with medetomidine and butorphanol were evaluated in 6 healthy beagle dogs. Each dog received three treatments with a minimum 10-day interval between treatments. The dogs received an IM injection of alfaxalone 2.5 mg/kg (ALFX), medetomidine 2.5 µg/kg and butorphanol 0.25 mg/kg (MB), or their combination (MBA) 1 hr after the recovery from their instrumentation. Endotracheal intubation was attempted, and dogs were allowed to breath room air. Neuro-depressive effects (behavior changes and subjective scores) and cardiorespiratory parameters (rectal temperature, heart rate, respiratory rate, direct blood pressure, central venous pressure and blood gases) were evaluated before and at 2 to 120 min after IM treatment. Each dog became lateral recumbency, except for two dogs administered the MB treatment. The duration was longer in the MBA treatment compared with the ALFX treatment (100 ± 48 min vs 46 ± 13 min). Maintenance of the endotracheal tube lasted for 60 ± 24 min in five dogs administered the MBA treatment and for 20 min in one dog administered the ALFX treatment. Cardiorespiratory variables were maintained within clinically acceptable ranges, although decreases in heart and respiratory rates, and increases in central venous pressure occurred after the MBA and MB treatments. The MBA treatment provided an anesthetic effect that permitted endotracheal intubation without severe cardiorespiratory depression in healthy dogs.

The pharmacological effects of the anesthetic alfaxalone after intramuscular administration to dogs

The pharmacological effects of the anesthetic alfaxalone were evaluated after intramuscular (IM) administration to 6 healthy beagle dogs. The dogs received three IM doses each of alfaxalone at increasing dose rates of 5 mg/kg (IM5), 7.5 mg/kg (IM7.5) and 10 mg/kg (IM10) every other day. Anesthetic effect was subjectively evaluated by using an ordinal scoring system to determine the degree of neuro-depression and the quality of anesthetic induction and recovery from anesthesia. Cardiorespiratory variables were measured using noninvasive methods. Alfaxalone administered IM produced dose-dependent neuro-depression and lateral recumbency (i.e., 36 ± 28 min, 87 ± 26 min and 115 ± 29 min after the IM5, IM7.5 and IM10 treatments, respectively). The endotracheal tube was tolerated in all dogs for 46 ± 20 and 58 ± 21 min after the IM7.5 and IM10 treatments, respectively. It was not possible to place endotracheal tubes in 5 of the 6 dogs after the IM5 treatment. Most cardiorespiratory variables remained within clinically acceptable ranges, but hypoxemia was observed by pulse oximetry for 5 to 10 min in 2 dogs receiving the IM10 treatment. Dose-dependent decreases in rectal temperature, respiratory rate and arterial blood pressure also occurred. The quality of recovery was considered satisfactory in all dogs receiving each treatment; all the dog exhibited transient muscular tremors and staggering gait. In conclusion, IM alfaxalone produced a dose-dependent anesthetic effect with relatively mild cardiorespiratory depression in dogs. However, hypoxemia may occur at higher IM doses of alfaxalone.