Effects of an intravenous bolus of alfaxalone versus propofol on intraocular pressure in sheep

Effects of propofol on intraocular pressure in premedicated and nonpremedicated dogs with and without glaucoma

OBJECTIVE To establish a study cutoff for evidence of glaucoma on the basis of IOP measurements from a large population of healthy dogs and to assess the effects of IV propofol administration on IOPs in premedicated and nonpremedicated dogs with and without glaucoma defined by this method. DESIGN Prospective, descriptive study. ANIMALS 234 client-owned dogs. PROCEDURES IOPs measured in 113 healthy dogs (226 eyes) were used to calculate an IOP value indicative of glaucoma. The IOPs were measured in an additional 121 dogs (237 eyes) undergoing ophthalmic surgery. Midazolam-butorphanol was administered IV as preanesthetic medication to 15 and 87 dogs with and without glaucoma, respectively. A placebo (lactated Ringer solution) was administered IV to 8 and 11 dogs with and without glaucoma, respectively. Anesthesia of surgical patients was induced with propofol IV to effect. The IOPs and physiologic variables of interest were recorded before (baseline) and after preanesthetic medication or placebo administration and after propofol administration. RESULTS An IOP > 25 mm Hg was deemed indicative of glaucoma. Compared with baseline measurements, mean IOP was increased after propofol administration in nonpremedicated dogs without glaucoma and unchanged in nonpremedicated dogs with glaucoma. Propofol-associated increases in IOP were blunted in premedicated dogs without glaucoma; IOP in affected eyes of premedicated dogs with glaucoma was decreased after preanesthetic medication and after propofol administration. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that preexisting IOP influences the response to anesthetic drugs, and administration of preanesthetic medication with muscle-relaxing properties may blunt or reduce propofol-induced increases in IOP. Further research with a larger number of dogs is needed to confirm our results in dogs with glaucoma.

Non-continuous measurement of intraocular pressure in laboratory animals

Glaucoma is a leading cause of blindness, which is treatable but currently incurable. Numerous animal models therefore have both been and continue to be utilized in the study of numerous aspects of this condition. One important facet associated with the use of such models is the ability to accurately and reproducibly measure (by cannulation) or estimate (by tonometry) intraocular pressure (IOP). At this juncture there are several different approaches to IOP measurement in different experimental animal species, and the list continues to grow. We feel therefore that a review of this subject matter is timely and should prove useful to others who wish to perform similar measurements. The general principles underlying various types of tonometric and non-tonometric techniques for non-continuous determination of IOP are considered. There follows discussion of specific details as to how these techniques are applied to experimental animal species involved in the research of this disease. Specific comments regarding anesthesia, circadian rhythm, and animal handling are also included, especially in the case of rodents. Brief consideration is also given to possible future developments.

Evaluation of intravenous administration of alfaxalone, propofol, and ketamine-diazepam for anesthesia in alpacas

OBJECTIVE

To evaluate the effects of induction of anesthesia with alfaxalone in alpacas.

STUDY DESIGN

Prospective, randomized, crossover design.

ANIMALS

Five healthy alpacas (96.7 ± 19.9 kg, 9.6 ± 3.1 years old).

METHODS

The alpacas were anesthetized on three occasions with alfaxalone, propofol, or ketamine-diazepam by intravenous injection. Quality of induction and intubation was assessed using a simple descriptive scale, and quality of recovery was scored: 1 (very poor)-5 (excellent). The auricular artery was catheterized for measurement of systolic (SAP), mean (MAP), and diastolic (DAP) arterial pressures and collection of blood. Variables measured were hemoglobin oxygen saturation (SpO2 ), respiratory rate, and end-tidal carbon dioxide partial pressure (Pe'CO2 ), and ECG. Repeated measures anova was used to assess effects of drug and time. Significance was set at p < 0.05.

RESULTS

Mean dose of alfaxalone sufficient to allow intubation was 2.1 mg kg(-1) . Induction was excellent with all protocols. Heart rate (HR), SAP and MAP were significantly higher following alfaxalone compared to ketamine-diazepam. Blood lactate concentration when standing following alfaxalone was higher compared to minutes 1 and 6, and to propofol (p < 0.05). All alpacas required oxygen supplementation and mechanical ventilation to treat SpO2  < 90% or Pe'CO2  > 60 mmHg. Time from induction to standing was longer with alfaxalone (34.1 ± 3.2 minutes) than propofol (19.0 ±4.3 minutes) or ketamine-diazepam (24.9 ±1.7 minutes). Recovery quality median scores were clinically and statistically different: 2 (alfaxalone), 4 (ketamine-diazepam), and 5 (propofol). Tremors, paddling, rolling, seizure-like activity and thrashing characterized recovery from alfaxalone.

CONCLUSION

Recovery quality was worst with alfaxalone. HR, SAP, MAP were increased at minute 1 in all protocols. Transient hypercapnia and hypoxia was observed with all protocols.

CLINICAL RELEVANCE

All protocols were adequate for induction of anesthesia. Alfaxalone alone in unpremedicated alpacas is not recommended.

Determination of the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to a standardised noxious stimulus in goats

OBJECTIVE

To determine the minimum infusion rate (MIR) of alfaxalone required to prevent purposeful movement of the extremities in response to noxious stimulation.

STUDY DESIGN

Prospective, experimental.

ANIMALS

Eight healthy goats; four does and four wethers.

METHODS

Anaesthesia was induced with alfaxalone 3 mg kg(-1) intravenously (IV). A continuous IV infusion of alfaxalone, initially at 0.2 mg kg(-1)  minute(-1) , was initiated. Following endotracheal intubation the goats breathed spontaneously via a circle breathing circuit delivering supplementary oxygen. The initial infusion rate was maintained for 30 minutes before testing for responses. The stimulus was clamping on the proximal (soft) part of one digit of the hoof with Vulsellum forceps for 60 seconds. In the absence or presence of purposeful movement of the extremities, the infusion rate was reduced or increased by 0.02 mg kg(-1)  minute(-1) and held constant for 30 minutes before claw-clamping again. Alfaxalone MIR was calculated as the mean of the infusion rates that allowed and abolished movement. Cardio-respiratory parameters were measured. Recovery from general anaesthesia was timed and quality scored. Results are presented as median (range).

RESULTS

The MIR of alfaxalone was 0.16 (0.14-0.18) mg kg(-1)  minute(-1) or 9.6 (8.4-10.8) mg kg(-1)  hour(-1) . Induction of and recovery from anaesthesia were excitement-free. Cardio-respiratory changes were minimal, although compared to baseline HR increased, and at 2 minutes post-induction, (prior to oxygen supplementation), PaO2 decreased significantly from 84 (80-88) to 70 (51-72) mmHg [11.2 (10.7-11.7) to 9.3 (6.8-9.6) kPa]. Sporadic muscle twitches, unrelated to depth of anaesthesia, were observed during the period of general anaesthesia. Time (minutes) to sternal recumbency and standing were 4.0 (3.0-10.0) and 41.5 (25.0-57.0) respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Alfaxalone can be used for total intravenous anaesthesia (TIVA) in goats and is associated with minimal adverse effects. Oxygen supplementation is advised, especially when working at higher altitudes.

The effects of midazolam and butorphanol, administered alone or combined, on the dose and quality of anaesthetic induction with alfaxalone in goats

Goats are rarely anaesthetised; consequently, scant information is available on the efficacy of anaesthetic drugs in this species. Alfaxalone is a relatively new anaesthetic agent, of which the efficacy in goats has not yet been studied. In this study, the sedative and alfaxalonesparing effects of midazolam and butorphanol, administered alone or concomitantly, in goats were assessed. Eight clinically healthy goats, four does and four wethers, were enlisted in a randomised crossover manner to receive intramuscular sedative treatments consisting of saline 0.05 mL/kg, or midazolam 0.30 mg/kg, or butorphanol 0.10 mg/kg, or a combination ofmidazolam 0.30 mg/kg with butorphanol 0.10 mg/kg before intravenous induction of general anaesthesia with alfaxalone. Following induction, the goats were immediately intubated and the quality of anaesthesia and basic physiological cardiorespiratory and blood-gas parameters were assessed until the goats had recovered from anaesthesia. The degree of sedation, quality of induction and recovery were scored. When compared with saline (3.00 mg/kg), midazolam,administered alone or with butorphanol, caused a statistically significant increased level of sedation and a reduction in the amount of alfaxalone required for induction (2.00 mg/kg and 1.70 mg/kg, respectively). Butorphanol alone (2.30 mg/kg) did not cause significant changes in level of sedation or alfaxalone-induction dose. During induction and recovery, the goats were calm following all treatments, including the control group. Cardiorespiratory and blood gasparameters were maintained within clinically acceptable limits. The present study showed that midazolam, administered alone or combined with butorphanol, produces a degree of sedation that significantly reduces the dose of alfaxalone required for induction of general anaesthesia in goats, without causing any major adverse cardiorespiratory effects.