A retrospective comparison of induction with thiopental/guaifenesin and propofol/ketamine in Thoroughbred racehorses anesthetized with sevoflurane and medetomidine during arthroscopic surgery.

This study compares clinical characteristics between induction with thiopental/guaifenesin and propofol/ketamine in Thoroughbred racehorses anesthetized with sevoflurane and medetomidine. Clinical records of 214 horses that underwent arthroscopic surgery between 2015 and 2016 were retrospectively retrieved. Horses were premedicated with medetomidine and midazolam to sedate at the adequate level for smooth induction, and then induced with either thiopental (4.0 mg/kg) and guaifenesin (100 mg/kg) in Group TG (n=91) or propofol (1.0 mg/kg) and ketamine (1.0 mg/kg) in Group PK (n=123). Anesthesia was maintained using sevoflurane with constant rate infusion of medetomidine. Quality of induction/recovery, sevoflurane requirement, cardiovascular function and recovery characteristics were evaluated. Anesthetic induction scores (median, range) for Group TG (5, 2-5) and Group PK (5, 2-5) were not significantly different. There were no significant differences in end-tidal sevoflurane concentration (mean ± standard deviation) between Group TG and Group PK (both 2.4 ± 0.2%). Dobutamine infusion rate (µg/kg/min) required for keeping mean arterial blood pressure (MAP) above 70 mmHg in Group PK (0.43, 0.10-1.40) was significantly lower than in Group TG (0.67, 0.08-1.56). Recovery score in Group PK (5, 2-5) was significantly higher than in Group TG (4, 2-5). Both propofol/ketamine and thiopental/guaifenesin provided a smooth induction of anesthesia. Moreover, induction with propofol/ketamine resulted in lower dobutamine requirements for keeping MAP above 70 mmHg during maintenance, and better quality of recovery. Induction with propofol/ketamine would be preferable to thiopental/guaifenesin in Thoroughbred racehorses anesthetized with sevoflurane and medetomidine during arthroscopic surgery.

Clinical effects of constant rate infusions of medetomidine-propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery.

BACKGROUND: The aim of the present study was to evaluate clinical efficacy of constant rate infusions (CRIs) of medetomidine-propofol combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery. Thirty horses were sedated intravenously (IV) with medetomidine (6.0 µg/kg) and midazolam (0.02 mg/kg) and induced IV with ketamine (1.0 mg/kg) and propofol (1.0 mg/kg). These horses were randomly allocated to three groups and maintained with sevoflurane and CRI of either medetomidine (3.0 µg/kg/h) (Group M; n = 10); or medetomidine (3.0 µg/kg/h) and propofol (3.0 mg/kg/h) (Group MP3; n = 10); or medetomidine (3.0 µg/kg/h) and propofol (6.0 mg/kg/h) (Group MP6; n = 10). End-tidal sevoflurane concentration (ETSEVO), cardiovascular parameters, plasma propofol concentration, and recovery time and quality were compared among groups. Data were analyzed by using ANOVA with Tukey's multiple comparison test, considering P < 0.05 significant. RESULTS: ETSEVO (%) was 2.4 ± 0.1 in Group M, 1.7 ± 0.2 in Group MP3, and 1.4 ± 0.2 in Group MP6; ETSEVO declined significantly in a propofol-dose-dependent manner. The rates of dobutamine infusion (µg/kg/min) required to keep the mean arterial blood pressure over 70 mmHg were significantly lower in Group MP3 (0.20 ± 0.10) and Group MP6 (0.15 ± 0.06) than in Group M (0.37 ± 0.18). Recovery time and quality did not differ among groups. All horses in Group MP3 required only one attempt to stand, and recovery quality was excellent. Plasma propofol concentrations were stable throughout maintenance of anesthesia in Group MP3, whereas those in Group MP6 increased significantly with increasing duration of maintenance. CONCLUSIONS: CRIs of medetomidine-propofol reduced the sevoflurane requirement for surgical anesthesia as the propofol dose increased, compared with a CRI of medetomidine alone. Additionally, the two propofol protocols provided good maintenance of cardiovascular function. CRIs of medetomidine (3.0 µg/kg/h) and propofol (3.0 mg/kg/h) resulted in excellent-quality recovery. This protocol could therefore be an especially useful additive to sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery.

Clinical evaluation of constant rate infusion of alfaxalone-medetomidine combined with sevoflurane anesthesia in Thoroughbred racehorses undergoing arthroscopic surgery.

BACKGROUND: Alfaxalone has a number of pharmacological properties which are desirable for constant rate infusion (CRI). Previously, the co-administration of alfaxalone and medetomidine is shown to be suitable for short-term anesthesia in horses. However, the use of alfaxalone-medetomidine CRI with inhalational anesthesia under surgical procedures have not been investigated in clinical cases. The aim of the present study was to evaluate the clinical efficacy of alfaxalone-medetomidine CRI in sevoflurane-anesthetized Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane requirement, cardiovascular function, and induction/recovery quality were compared between horses maintained with sevoflurane in combination with medetomidine CRI (3 µg/kg/h) (Group M; n = 25) and those maintained with sevoflurane in combination with alfaxalone-medetomidine CRI (0.5 mg/kg/h and 3 µg/kg/h, respectively) (Group AM; n = 25). RESULTS: The mean end-tidal sevoflurane concentrations were significantly lower in Group AM (1.8 ± 0.2%) than in Group M (2.4 ± 0.1%). The mean dobutamine infusion rate required for maintaining mean arterial blood pressure within the target values (60-80 mmHg) was significantly lower in Group AM (0.53 ± 0.20 µg/kg/min) than in Group M (0.85 ± 0.32 µg/kg/min). Induction and recovery scores were not significantly different between two groups. However, excitatory response during recovery were observed in five horses in Group AM. The mean plasma alfaxalone concentrations were stable throughout the maintenance period (0.77 ± 0.12 to 0.85 ± 0.13 µg/mL), and decreased significantly immediately after standing (0.32 ± 0.07 µg/mL). CONCLUSIONS: Alfaxalone-medetomidine CRI reduced sevoflurane requirement by approximately 26% with good maintenance of cardiopulmonary function in Thoroughbred racehorses undergoing arthroscopic surgery. Sevoflurane in combination with alfaxalone-medetomidine CRI may be a clinically effective anesthetic technique for Thoroughbred racehorses. However, 20% of horses administered alfaxalone showed remarkable excitatory response during recovery. Greater attention to excitatory response may be advisable if alfaxalone is used for induction or maintenance of anesthesia. A larger study is needed to explore the clinical relevance of these findings.

Comparison of oxidative stress under different propofol administration protocols in Thoroughbred racehorses by bOS and bAP assessment.

It is desirable to reduce surgery-induced oxidative stress (OS) because it can cause immune suppression and delayed wound healing. Propofol is known to have antioxidant potential and to reduce OS in humans, but there have been no studies of this issue in horses. This study was conducted to evaluate OS under three different propofol administration protocols in Thoroughbred racehorses undergoing arthroscopic surgery with sevoflurane anesthesia. Blood oxidative stress (bOS) and blood antioxidant power (bAP) were used as OS biomarkers. Both bOS and bAP significantly decreased after surgery in all groups, but no differences in these reductions were found among them. Different propofol administration protocols with sevoflurane anesthesia did not cause a difference in OS in Thoroughbred racehorses that underwent arthroscopic surgery.

Experience of using water-dispersed paper bedding for equine scintigraphy.

Equine scintigraphy has been legally permitted in Japan since 2009; however, it has not yet been a routine modality for horses. One reason is the legal regulations concerning the disposal of contaminated bedding. However, overseas, the bedding after scintigraphy can be disposed following radioactivity decay, but this is not allowed in Japan. Therefore, beddings are required to stored permanently in a controlled area, implying that large amounts of beddings such as straw would be kept untreated, which is quite unpractical. This may cause a hospital owner to hesitate to construct an equine scintigraphy facility. Therefore, it is proposed that water-dispersed paper bedding is disposed as aqueous waste after radioactivity decay. The purpose of this study was to check the availability of bedding, thus radioisotopes were not used in this study. Three horses were housed individually in stalls covered with water-dispersed paper bedding for 48 hr. Physical condition, including body weight, was monitored, and a complete blood cell count and biochemical analysis were conducted. The results revealed that physical conditions and results of blood analysis were all stable within the normal range, and the veterinarian did not find any specific abnormality in any of the three horses. No marked changes in the levels of blood cortisol were observed before and after stalling, suggesting almost no stress for the horses. Because the water-dispersed paper bedding did not negatively affect the horses, it can be used as a substitute for conventional straw bedding.

Validation of the bispectral index as an indicator of anesthetic depth in Thoroughbred horses anesthetized with sevoflurane.

To evaluate the bispectral index (BIS) as an indicator of anesthetic depth in Thoroughbred horses, BIS values were measured at multiple stages of sevoflurane anesthesia in five horses anesthetized with guaifenesin and thiopental following premedication with xylazine. There was no significant difference between the BIS values recorded at end-tidal sevoflurane concentrations of 2.8% (median 60 ranging from 47 to 68) and 3.5% (median 71 ranging from 49 to 82) in anesthetized horses. These BIS values during anesthesia were significantly lower (P<0.01) than those in awake horses (median 98 ranging from 98 to 98) or sedated horses (median 92 ranging from 80 to 93). During the recovery phase, the BIS values gradually increased over time but did not significantly increase until the horses showed movement. In conclusion, the BIS value could be useful as an indicator of awakening during the recovery period in horses, as previous reported.

Cardiovascular effects of dobutamine and phenylephrine infusion in sevoflurane-anesthetized Thoroughbred horses.

To determine dose-dependent cardiovascular effects of dobutamine and phenylephrine during anesthesia in horses, increasing doses of dobutamine and phenylephrine were infused to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and infused 3 increasing doses of dobutamine (0.5, 1.0 and 2.0 µg/kg/min) for 15 min each dose. Following to 30 min of reversal period, 3 increasing doses of phenylephrine (0.25, 0.5 and 1.0 µg/kg/min) were infused. Cardiovascular parameters were measured before and at the end of each 15-min infusion period for each drug. Blood samples were collected every 5 min during phenylephrine infusion period. There were no significant changes in heart rate throughout the infusion period. Both dobutamine and phenylephrine reversed sevoflurane-induced hypotension. Dobutamine increased both mean arterial blood pressure (MAP) and cardiac output (CO) as the result of the increase in stroke volume, whereas phenylephrine increased MAP but decreased CO as the result of the increase in systemic vascular resistance. Plasma phenylephrine concentration increased dose-dependently, and these values at 15, 30 and 45 min were 6.2 ± 1.2, 17.0 ± 4.8 and 37.9 ± 7.3 ng/ml, respectively.

Hemodynamic effects of 6% hydroxyethyl starch infusion in sevoflurane-anesthetized thoroughbred horses.

To determine hemodynamic effects of hydroxyethyl starch (HES) infusion during anesthesia in horses, incremental doses of 6% HES were administered to 6 healthy Thoroughbred horses. Anesthesia was induced with xylazine, guaifenesin and thiopental and maintained with sevoflurane at 2.8% of end-tidal concentration in all horses. The horses were positioned in right lateral recumbency and administered 3 intravenous dose of 6% HES (5 ml/kg) over 15 min with 15-min intervals in addition to constant infusion of lactated Ringer's solution at 10 ml/kg/hr. Hemodynamic parameters were measured before and every 15 min until 90 min after the administration of 6% HES. There was no significant change in heart rate and arterial blood pressures throughout the experiment. The HES administration produced significant increases in mean right atrial pressure, stroke volume, cardiac output (CO) and decrease in systemic vascular resistance (SVR) in a dose-dependent manner. There was no significant change in electrolytes (Na(+), K(+), Cl(-)) throughout the experiment, however, packed cell volume, hemoglobin concentration, and total protein and albumin concentrations decreased in a dose-dependent manner following the HES administration. In conclusion, the HES administration provides a dose-dependent increase in CO, but has no impact upon arterial blood pressures due to a simultaneous decrease in SVR.