Alfaxalone versus propofol in dogs: a randomised trial to assess effects on peri-induction tear production, intraocular pressure and globe position

Evaluation of changes in lacrimal canaliculi width depending on temperature and viscosity of eye drops using spectral-domain optical coherence tomography in dogs

OBJECTIVE

To evaluate the changes in the width of the lower lacrimal canaliculi (LC) upon instillation of artificial tears (AT) at different temperatures and viscosities using spectral-domain optical coherence tomography (SD-OCT).

ANIMAL STUDIED

Eight eyes of four client-owned adult dogs.

PROCEDURES

Imaging of lower LC was performed under general anesthesia. AT at temperatures of 2°C, 20°C, and 38°C, and a high-viscosity tear gel of 20°C, were topically instilled in 100 μL volumes. SD-OCT tracked LC width changes following each instillation.

RESULTS

The average baseline width of the LC was 96.38 ± 30.18 μm. The 2°C AT expanded LC width to 183.50 ± 44.11 μm, returning to baseline in 5.00 ± 1.31 min. The 20°C AT resulted in a width of 155.25 ± 35.79 μm, with a 3.88 ± 1.25 min return. The 38°C AT expanded LC width to 131.75 ± 29.49 μm, with a 2.25 ± 0.89 min return. The high-viscosity tear gel expanded LC width to 208.57 ± 56.31 μm, with remained expanded for 10 or more minutes. In temperature comparisons, the 2°C and 20°C AT significantly expanded the LC width more and had longer return times than the 38°C AT (p < .05). Viscosity comparisons showed higher viscosity eye drops significantly expanded LC width more than lower viscosity eye drops (p < .05).

CONCLUSIONS

This study found that lower temperature and higher viscosity of eye drops had tendency to result in a wider expansion of the LC width. Additionally, the return time to baseline for LC width tended to be longer with eye drops of lower temperature and higher viscosity. This finding could be helpful in advancing future research on tear dynamics.

Mydriasis in eastern box turtles (Terrapene carolina carolina) following topical administration of proparacaine, 10% phenylephrine, and rocuronium bromide

OBJECTIVE

To determine the mydriatic effect of topical 10% phenylephrine with 10 mg/mL rocuronium bromide and compare this protocol with and without pretreatment with proparacaine.

ANIMALS STUDIED

Ten client-owned pet adult eastern box turtles (Terrapene carolina carolina).

PROCEDURES

All turtles were sedated with 8 mg/kg alfaxalone intramuscularly. One group of four turtles received four 20 μL drops of 10% phenylephrine and four 20 μL drops of rocuronium bromide in the right eye. Another group of four turtles received one standard drop of proparacaine followed by four 20 μL drops of 10% phenylephrine and four 20 μL drops of rocuronium bromide in the right eye. Two control group turtles received four 20 μL drops of saline in the right eye. The left eye was untreated in all turtles. Drops of the same type were separated by 2 min while drops of different types were separated by 5 min. Pupil size was recorded at 0, 15, 30, 60, 90, 120, 180, 240, and 360 min after administration of the final drop.

RESULTS

Treatment with 10% phenylephrine and rocuronium bromide resulted in pupil diameter changes from baseline that were statistically significant from zero at 60, 90, and 120 min in the non-proparacaine group and 90 min in the proparacaine group. The time to peak effect was 90 min in the proparacaine group and 75 min in the non-proparacaine group. Saline-treated pupils in the control group decreased in diameter over the study period. Overall, the treated eyes of the proparacaine group and non-proparacaine group were not different from each other, but both dilated more than the control group.

CONCLUSIONS

Rocuronium bromide and 10% phenylephrine can produce effective and safe mydriasis in eastern box turtles, but there was wide interindividual variation in effectiveness. Proparacaine did not improve the mydriatic effect.

Effects of propofol alone or in combination with ketamine on intraocular pressure in unpremedicated dogs

OBJECTIVE

To determine the effects of propofol (P) alone and in combination with ketamine (KP) at ratios of 1:1, 1:2, and 1:3 on intraocular pressure (IOP) in unpremedicated dogs.

ANIMALS STUDIED

A total of 28 cross-bred healthy dogs.

PROCEDURES

Dogs were randomly assigned to one of four groups (n = 7 per group) to receive intravenous P or KP at 1:1, 1:2, and 1:3 ratios, respectively. The infusion was administered at 0.6 mg/kg/min for 60 min. IOP, cardiorespiratory variables, rectal temperature (RT), and pedal reflex were recorded every 5 min for 60 min, starting from baseline (BL).

RESULTS

There was a statistically significant increase in IOP in all groups: P (p = .011), KP 1:1 (p = .003), KP 1:2 (p = .023), and KP 1:3 (p = .008). The IOP increase was less pronounced in the KP 1:2 group and was only significant (p = .023) at T45 compared with BL. A significant correlation was observed between IOP and SpO2 in P (r = -.215, p = .02), KP 1:2 (r = -.579, p < .01), and KP 1:3 (r = -.402, p < .01) groups. IOP significantly increased due to decreased SpO2 below 86.5% (p < .05).

CONCLUSIONS

Propofol alone and in combination with ketamine may increase preexisting IOP in unpremedicated dogs. SpO2 levels below 86.5% may trigger an increase in IOP. Administering KP in a 1:2 ratio at an infusion rate of 0.6 mg/kg/min does not significantly alter IOP for under 45 min in unpremedicated dogs with sufficient oxygenation.

Contouring in the optic plane improves the accuracy of computed tomography-based segmentation of the optic pathway

Canine optic pathway structures are often contoured on CT images, despite the difficulty of visualizing the optic pathway with CT using standard planes. The purpose of this prospective, analytical, diagnostic accuracy study was to examine the accuracy of optic pathway contouring by veterinary radiation oncologists (ROs) before and after training on optic plane contouring. Optic pathway contours used as the gold standard for comparison were created based on expert consensus from registered CT and MRI for eight dogs. Twenty-one ROs contoured the optic pathway on CT using their preferred method, and again following atlas and video training demonstrating contouring on the optic plane. The Dice similarity coefficient (DSC) was used to assess contour accuracy. A multilevel mixed model with random effects to account for repeated measures was used to examine DSC differences. The median DSC (5th and 95th percentile) before and after training was 0.31 (0.06, 0.48) and 0.41 (0.18, 0.53), respectively. The mean DSC was significantly higher after training compared with before training (mean difference = 0.10; 95% CI, 0.08-0.12; P < 0.001) across all observers and patients. DSC values were comparable to those reported (0.4-0.5) for segmentation of the optic chiasm and nerves in human patients. Contour accuracy improved after training but remained low, potentially due to the small optic pathway volumes. When registered CT-MRI images are not available, our study supports routine addition of an optic plane with specific window settings to improve segmentation accuracy in mesaticephalic dogs ≥11 kg.

Effect of anesthetic induction with propofol, alfaxalone or ketamine on intraocular pressure in cats: a randomized masked clinical investigation

OBJECTIVE

To compare the effect of propofol, alfaxalone and ketamine on intraocular pressure (IOP) in cats.

STUDY DESIGN

Prospective, masked, randomized clinical trial.

ANIMALS

A total of 43 ophthalmologically normal cats scheduled to undergo general anesthesia for various procedures.

METHODS

Following baseline IOP measurements using applanation tonometry, anesthesia was induced with propofol (n = 15), alfaxalone (n = 14) or ketamine (n = 14) administered intravenously to effect. Then, midazolam (0.3 mg kg^-1) was administered intravenously and endotracheal intubation was performed without application of topical anesthesia. The IOP was measured following each intervention. Data was analyzed using one-way anova and repeated-measures mixed design with post hoc analysis. A p-value <0.05 was considered significant.

RESULTS

Mean ± standard error IOP at baseline was not different among groups (propofol, 18 ± 0.6; alfaxalone, 18 ± 0.7; ketamine, 17 ± 0.5 mmHg). Following induction of anesthesia, IOP increased significantly compared with baseline in the propofol (20 ± 0.7 mmHg), but not in the alfaxalone (19 ± 0.8 mmHg) or ketamine (16 ± 0.7 mmHg) groups. Midazolam administration resulted in significant decrease from the previous measurement in the alfaxalone group (16 ± 0.7 mmHg), but not in the propofol group (19 ± 0.7 mmHg) or the ketamine (16 ± 0.8 mmHg) group. A further decrease was measured after intubation in the alfaxalone group (15 ± 0.9 mmHg).

CONCLUSIONS AND CLINICAL RELEVANCE

Propofol should be used with caution in cats predisposed to perforation or glaucoma, as any increase in IOP should be avoided.

Effects of tiletamine-zolazepam vs. propofol on peri-induction intraocular pressure in dogs: A randomized, masked crossover study

Introduction

Anesthesia induction agents have the potential to cause severe ocular side effects, resulting in lasting damage to the eye.

Objectives

The purpose of this study is to determine the effects of tiletamine-zolazepam on IOP compared to propofol when they are used as an induction agent in normal healthy dogs.

Methods

Twenty healthy adult client owned dogs weighing 22.2 ± 7.6 kg were selected for the study. In a randomized order, all dogs received tiletamine-zolazepam 5 mg/kg IV or propofol 8 mg/kg IV titrated to effect without premedication. Washout between each treatment was at least seven days. IOP measurements were obtained at four time points: baseline, post-induction, post-intubation, and after recovery using applanation tonometry. No additional procedures were performed. After normality of the data was determined, a linear mixed model was built with time, eye, treatment and all interactions of those variables as fixed effects and subject as a random effect.

Results

There was no significant difference for age, body weight, drug dose, baseline IOP, and recovery IOP between treatments. Average IOP measurements remained within the normal range of 15-25 mmHg at these time points. However, IOP was significantly less elevated by the tiletamine-zolazepam treatment vs. propofol at the post-induction (mean difference: -4.7 ± 4.6 [95%CI -6.8 to -2.5]) and the post-intubation (mean difference: -4.4 ± 4.6 [95%CI -6.5 to -2.2]) time points.

Clinical significance

Dogs receiving tiletamine-zolazepam for anesthetic induction had a significantly less elevated IOP at induction and intubation compared to dogs receiving propofol.

A review of diagnostic tests for qualitative and quantitative tear film deficiency in dogs

Dry eye disease (DED) is a complex multifactorial condition caused by loss of ocular surface homeostasis from quantitative and/or qualitative tear film deficiency. Schirmer tear test (STT) is often the only diagnostic test used to assess for DED in veterinary practice. STT is invaluable in the diagnosis and monitoring of quantitative tear film deficiency (i.e., keratoconjunctivitis sicca); however, it is not sufficient to optimize therapy and fully recognize other contributing factors for the disturbance in ocular surface homeostasis. The present work reviews diagnostic tests for assessing aqueous tear production in veterinary medicine, as well as the quality of tears, corneal epithelial barrier integrity, and the lacrimal functional unit.

A prospective, masked, randomized, controlled superiority study comparing the incidence of corneal injury following general anesthesia in dogs with two methods of corneal protection

Objective

To compare the incidence of corneal injury during general anesthesia (GA) and the immediate post‐operative period in eyes protected with topical ocular lubricant alone with eyes protected with topical lubricant followed by complete eyelid closure using tape.

Animals Studied

One hundred client‐owned dogs (200 eyes) undergoing GA for MRI scan.

Methods

Patients had ocular lubricant applied to both eyes upon induction of anesthesia. One eye was taped closed immediately after induction for the duration of anesthesia using Strappal® tape (BSN medical™; treatment group), and the other eye was not taped (control group). Eyes were randomly allocated to a treatment group. Ophthalmic examination was performed before and after anesthesia; the examiner was masked to eye treatment groups. Corneal injury was defined as corneal ulceration or corneal erosion. A McNemar's test was used to compare the incidence of corneal injury between groups. A paired‐samples t‐test was used to compare Schirmer‐1 tear test (STT‐1) readings between groups.

Results

Sixteen eyes (8%) developed corneal erosion. No corneal ulceration occurred. There was no significant difference between incidence of corneal erosion between groups (p = .454). There was a significant decrease in STT‐1 readings following GA in both groups (p < .001), with no significant difference in STT‐1 between groups (p = .687). No adverse effects of taping the eye closed were observed.

Conclusion

Taping the eyes closed during GA had no additional benefit to the lubrication protocol used in this study.

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.

Estimation of planning organ at risk volumes for ocular structures in dogs undergoing three-dimensional image-guided periocular radiotherapy with rigid bite block immobilization

Planning organ at risk volume (PRV) estimates have been reported as methods for sparing organs at risk (OARs) during radiation therapy, especially for hypofractioned and/or dose‐escalated protocols. The objectives of this retrospective, analytical, observational study were to evaluate peri‐ocular OAR shifts and derive PRVs in a sample of dogs undergoing radiation therapy for periocular tumors. Inclusion criteria were as follows: dogs irradiated for periocular tumors, with 3D‐image‐guidance and at least four cone‐beam CTs (CBCTs) used for position verification, and positioning in a rigid bite block immobilization device. Peri‐ocular OARs were contoured on each CBCT and the systematic and random error of the shifts in relation to the planning CT position computed. The formula 1.3×Σ+0.5xσ was used to generate a PRV of each OAR in the dorsoventral, mediolateral, and craniocaudal axis. A total of 30 dogs were sampled, with 450 OARs contoured, and 2145 shifts assessed. The PRV expansion was qualitatively different for each organ (1‐4 mm for the dorsoventral and 1‐2 mm for the mediolateral and craniocaudal axes). Maximal PRV expansion was ≤4 mm and directional for the majority; most pronounced for corneas and retinas. Findings from the current study may help improve awareness of and minimization of radiation dose in peri‐ocular OARs for future canine patients. Because some OARs were difficult to visualize on CBCTs and/ or to delineate on the planning CT, authors recommend that PRV estimates be institution‐specific and applied with caution.

Anesthetic Effects of Intramuscular Alfaxalone-Ketamine in Naked Mole Rats (Heterocephalus glaber)

In this study, adult intact male and female (n = 10) naked mole rats (Heterocephalus glaber) were anesthetized by using a combination of ketamine (20 mg/kg IM), and alfaxalone (4.0 mg/kg IM). Induction and recovery times were recorded. Vital parameters, including heart rate, respiratory rate, and reflexes, were monitored every 5 min during the anesthetic period. Anesthetic induction was smooth and rapid. Induction time was significantly longer in male rats (median, 325 s; range, 180 to 385 s) than in females (median, 145 s; range, 118 to 180 s). In addition, overall duration of loss of righting reflex was shorter in male mole rats (median, 50 min; range, 36 to 65 min) than females (median, 70 min; range, 60 to 85 min). Males largely had intact withdrawal reflexes, whereas females showed variable loss of both forelimb and hindlimb withdrawal reflexes. Neither recovery time (mean ± 1 SD, 16 ± 13 min) nor vital parameters differed between sexes. None of animals showed any anesthesia-related adverse responses. According to these findings, intramuscular AK is a safe and effective protocol that provides brief, light anesthesia in male naked mole rats and deeper anesthesia in females. We recommend adding analgesics when this AK protocol is used for pain-inducing or invasive procedures, and further studies evaluating higher doses and different combinations are indicated.

A systematic review of the effects of injectable sedative and anesthetic drugs and inhalant anesthetics on intraocular pressure in the dog

OBJECTIVE

The purpose of this systematic review was to summarize the results of studies that have determined the effect of injectable and inhalant drugs used in anesthesia on intraocular pressure (IOP) in dogs.

DATABASES USED

A comprehensive search of research literature was performed without language restriction. The search utilized the PubMed, CAB Abstracts and the University of Georgia's Galileo electronic databases using a combination of free text terms 'Ophthalmology', 'Intraocular Pressure', 'Anesthetic', 'Anesthesia', 'Canine' or 'Dog'. The time frame searched was from 1970 to October 2018. Any published research paper that dealt with sedatives or anesthetics administered systemically and the canine eye was evaluated.

CONCLUSIONS

The effects of many anesthetic drugs in dogs with ocular pathology are largely unknown. Many anesthetic drugs do not induce clinically relevant changes in IOP in dogs with normal eyes, although some studies demonstrated results with statistically significant changes. The dose, route of administration, experimental conditions, drug combinations, timing of measurements, measurement technology and setting or individual animal characteristics may all produce some heterogeneity in results from multiple studies.

Effect of intramuscular administration of medetomidine and xylazine on tear flow measured by the Schirmer tear test I in healthy cats

OBJECTIVES

This study aimed to investigate the effects of intramuscular medetomidine and xylazine on tear flow in healthy cats.

METHODS

Five cats each received medetomidine 10, 20, 40 and 80 µg/kg IM; xylazine 1.0, 2.0, 4.0 and 8.0 mg/kg IM; and physiological saline (2.0 ml IM) in a randomised order separated by intervals of at least 1 week. The Schirmer tear test (STT) I was performed in both eyes before and 0.25, 0.5, 0.75, 1, 2, 3, 4, 5, 6, 7, 8 and 24 h after each dose.

RESULTS

The STT I value decreased significantly at 0.5 and 1.0 h and at 0.75 and 1.0 h in both eyes after administration of medetomidine at 10 or 40 µg/kg. After administration of medetomidine 80 µg/kg, there was a significant decrease in the STT I reading at 0.75, 2 and 3 h in the left eye and 0.75, 1, 2 and 3 h in the right eye. The STT I value decreased significantly at: 0.5, 0.75, 1 and 2 h in the left eye and 0.75 h in the right eye after administration of xylazine 1.0 mg/kg; 0.5, 0.75, 1 and 2 h in the left eye and 0.5, 0.75, 1 and 3 h in the right eye after administration of xylazine 2.0 mg/kg; 0.5, 0.75, 1 and 2 h in both eyes after administration of xylazine 4.0 mg/kg; and 0.5, 0.75, 1, 2 and 3 h in the left eye and 0.75, 1, 2, 3 and 4 h in the right eye after administration of xylazine 8.0 mg/kg.

CONCLUSIONS AND RELEVANCE

Both medetomidine and xylazine significantly decreased feline tear flow measured by STT I. Therefore, the ocular surface should be monitored carefully and protected appropriately in cats treated with these sedatives.

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.

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.