Isoflurane Anesthesia In Horses Research Articles

Clinical and Hematological Effect of Constant Rate Infusion of Ketamine Alone and Ketamine-dexmedetomidine Combination on Isoflurane Anesthesia in Horses

Background: Anaesthetic management of horses for a successful surgery is of utmost importance but a risky procedure than other companion animals. Peri-aneasthetic morbidity and mortality in horses could be alarming if proper combinations of drugs were not used. Balanced anaesthetic combinations are being explored by various authors to find safer combinations.Therefore current study was planned to evaluate the effect of CRI of ketamine alone and ketamine-dexmedetomidine combination for isoflurane anesthesia in horses. Methods: Twenty four clinical cases of horses were randomly divided into three groups S, D and DK, having eight animals in each. Xylazine (1 mg/kg) and butorphanol (0.05 mg/kg) were given intravenously for premedication and ketamine (2 mg/kg) and midazolam (0.2 mg/kg) were used for induction of anesthesia. Normal saline (1000 ml/hour), ketamine alone (2 mg/kg/hr), ketamine (2 mg/kg/hr) and dexmedetomidine (2 µg/kg/hr) combination were given as CRI in groups S, K and KD, respectively. Thiopentone sodium (200 mg bolus, 5%) was given as fast intravenous to facilitate endotracheal intubation in some of the cases. Anesthesia was maintained with isoflurane in oxygen and anesthetic efficacy was evaluated based on clinical and haematological parameters. Result: Overall quality of sedation, muscle relaxation, response to surgical stimuli, quality of intubation, anesthetic depth and quality of recovery was significantly (p less than 0.05) better in group KD. Down-time (min) and duration of anesthesia were non significantly less in group KD. CRI of ketamine and dexmedetomidine combination was having significant (p less than 0.05) thiopentone sodium and isoflurane sparing effect. Heart rateand RR, did not show any significant variation among groups but rectal temperature was significantly low in KD group than groups S and K. CRI of ketamine-Dexmedetomidine combination produced a better quality of anesthesia and significant thiopentone sodium and isoflurane sparing effect thus was found suitable for anesthesia of horses.

Effects of detomidine or romifidine during maintenance and recovery from isoflurane anaesthesia in horses

ObjectiveTo evaluate the effects of detomidine or romifidine on cardiovascular function, isoflurane requirements and recovery quality in horses undergoing isoflurane anaesthesia. Study designProspective, randomized, blinded, clinical study. AnimalsA total of 63 healthy horses undergoing elective surgery during general anaesthesia. MethodsHorses were randomly allocated to three groups of 21 animals each. In group R, horses were given romifidine intravenously (IV) for premedication (80 μg kg–1), maintenance (40 μg kg–1 hour–1) and before recovery (20 μg kg–1). In group D2.5, horses were given detomidine IV for premedication (15 μg kg–1), maintenance (5 μg kg–1 hour–1) and before recovery (2.5 μg kg–1). In group D5, horses were given the same doses of detomidine IV for premedication and maintenance but 5 μg kg–1 prior to recovery. Premedication was combined with morphine IV (0.1 mg kg–1) in all groups. Cardiovascular and blood gas variables, expired fraction of isoflurane (Fe′Iso), dobutamine or ketamine requirements, recovery times, recovery events scores (from sternal to standing position) and visual analogue scale (VAS) were compared between groups using either anova followed by Tukey, Kruskal-Wallis followed by Bonferroni or chi-square tests, as appropriate (p < 0.05). ResultsNo significant differences were observed between groups for Fe′Iso, dobutamine or ketamine requirements and recovery times. Cardiovascular and blood gas measurements remained within physiological ranges for all groups. Group D5 horses had significantly worse scores for balance and coordination (p = 0.002), overall impression (p = 0.021) and final score (p = 0.008) than group R horses and significantly worse mean scores for VAS than the other groups (p = 0.002). Conclusions and clinical relevanceDetomidine or romifidine constant rate infusion provided similar conditions for maintenance of anaesthesia. Higher doses of detomidine at the end of anaesthesia might decrease the recovery quality.

Effect of 15° Reverse Trendelenburg Position on Arterial Oxygen Tension during Isoflurane Anesthesia in Horses.

Simple SummaryHorses commonly develop low blood oxygen levels during anesthesia, especially when they are placed on their backs. This study investigated whether a 15° head-up tilt, in a homogenous group of anesthetized horses positioned on their backs, would result in better blood oxygen levels as compared to no tilt. The results showed significantly greater blood oxygen levels with tilt compared to no tilt in five out of six horses tested. In one horse the effect was the opposite. The concurrent effect on cardiovascular function remains to be tested in detail. Further studies are needed to confirm these findings in a larger group of horses and to determine the effects on blood pressure and treatment options.Lower than expected arterial oxygen tension (PaO2) continues to be an unresolved problem in equine anesthesia. The aim of this randomized, crossover, and prospective study using six adult horses is to determine if a 15° reverse Trendelenburg position (RTP) increases PaO2 during inhalation anesthesia. Under constant-dose isoflurane anesthesia, dorsally recumbent horses were positioned either horizontally (HP) or in a 15° RTP for 2 h. Lungs were mechanically ventilated (15 mL/kg, 6 breaths/min). Arterial carbon dioxide tension (PaCO2), PaO2, inspired oxygen fraction (FiO2), and end-tidal carbon dioxide tension (EtCO2) were determined every 30 min during anesthesia. Indices of dead-space ventilation (Vd/Vt), oxygenation (P–F ratio), and perfusion (F–shunt) were calculated. Dobutamine and phenylephrine were used to support mean arterial pressure (MAP). Data are presented as median and range. In one horse, which was deemed an outlier due to its thoracic dimensions and body conformation, indices of oxygenation worsened in RTP compared to HP (median PaO2 438 vs. 568 mmHg; P–F ratio 454 vs. 586 mmHg, and F–shunt 13.0 vs. 5.7 mmHg). This horse was excluded from calculations. In the remaining five horses they were significantly better with RTP compared to HP. Results in remaining five horses showed that PaO2 (502, 467–575 vs. 437, 395–445 mmHg), P-F ratio (518, 484–598 vs. 455, 407–458 mmHg), and F-shunt (10.1, 4.2–11.7 vs. 14.2, 13.8–16.0 mmHg) were significantly different between RTP and HP (p = 0.03). Other variables were not significantly different. In conclusion, the 15° RTP resulted in better oxygenation than HP in dorsally recumbent, isoflurane-anesthetized horses, although worsening of oxygenation may occur in individual horses. A study detailing the cardiovascular consequences of RTP is necessary before it can be recommended for clinical practice.

Evaluation of the Effects of Doxapram in Combination with Xylazine on Recovery of Horses Isoflurane-Anesthetized

This randomized double-blinded study evaluated the recovery from isoflurane anesthesia in horses receiving doxapram and xylazine. 6 horses were anesthetized 4 times (minimum of 2-week washout period). Anesthesia was performed with xylazine (0.6 mg/kg), ketamine (2.2 mg/kg), midazolam (0.1 mg/kg), and maintained with isoflurane for 90 minutes. At recovery, horses received one of the following randomized treatments: RX: xylazine (0.2 mg/kg), RXD1: xylazine (0.2 mg/kg) and doxapram (0.1 mg/kg), RXD2: xylazine (0.2 mg/kg) and doxapram (0.2 mg/kg), or RS: saline. Recoveries were rope-assisted and evaluated with a descriptive qualitative scale. Heart rate, respiratory frequency (fR), and blood gas analysis were evaluated at 5 minutes intervals while the horse allowed. Data were analyzed with ANOVA or Friedman test (P < .05). Times to sternal (minutes) were RX: 40.5 ± 12.3, RXD1: 25.8 ± 11.5, RXD2: 31.4 ± 7.0, and RS: 33.4 ± 5.3, and were not different. Times to standing (minutes) were RX: 41.0 ± 9.9, RXD1: 33.5 ± 6.2, RXD2: 40.0 ± 11.3, and RS: 36.3 ± 9.9, and were not different. Heart rate decrease over time within RXD1 and RXD2 (T0 = 47 ± 15 and 47 ± 15, T5 = 38 ± 8 and 38 ± 8, T10 = 39 ± 4 and 36 ± 6, respectively), but was not different among groups. There was no difference in fR among groups or over time. There was no difference in recovery scores among groups. In conclusion, administration of doxapram to isoflurane-anesthetized horses did not change recovery time or quality.

Comparison of Recovery Quality Following Medetomidine versus Xylazine Balanced Isoflurane Anaesthesia in Horses: A Retrospective Analysis.

Simple SummaryRecovery from general anaesthesia poses the most critical phase of equine anaesthesia and is the main cause for the relatively high anaesthetic mortality rate compared to other species. It is, therefore, essential to identify anaesthetic protocols that promote safe recoveries. This retrospective study compared the quality of 470 recoveries following general anaesthesia with the anaesthetic gas isoflurane combined with a constant rate infusion of two different alpha-2 adrenergic agonists (xylazine or medetomidine). On the basis of video recordings, recovery quality was scored by two observers unaware of animal details, procedure, or drugs used. Additionally, factors that may affect recovery (e.g., breed, age, procedure, duration of anaesthesia, and intraoperative complications) were taken into consideration. Horses needing higher doses of xylazine to sedate prior to anaesthesia, the intraoperative use of tetrastarch for cardiovascular support, and the use of salbutamol to improve inadequate blood oxygenation during general anaesthesia were related to poorer recovery scores. Whilst recoveries of horses treated with medetomidine took significantly longer compared to xylazine, the attempts to stand and the overall quality of recovery were similar for both groups, indicating that both anaesthetic protocols promote similarly safe recoveries.Medetomidine partial intravenous anaesthesia (PIVA) has not been compared to xylazine PIVA regarding quality of recovery. This clinical retrospective study compared recoveries following isoflurane anaesthesia balanced with medetomidine or xylazine. The following standard protocol was used: sedation with 7 µg·kg−1 medetomidine or 1.1 mg·kg−1 xylazine, anaesthesia induction with ketamine/diazepam, maintenance with isoflurane and 3.5 µg·kg−1·h−1 medetomidine or 0.7 mg·kg−1·h−1 xylazine, and sedation after anaesthesia with 2 µg·kg−1 medetomidine or 0.3 mg·kg−1 xylazine. Recovery was timed and, using video recordings, numerically scored by two blinded observers. Influence of demographics, procedure, peri-anaesthetic drugs, and intraoperative complications (hypotension, hypoxemia, and tachycardia) on recovery were analysed using regression analysis (p < 0.05). A total of 470 recoveries (medetomidine 279, xylazine 191) were finally included. Following medetomidine, recoveries were significantly longer (median (interquartile range): 57 (43–71) min) than xylazine (43 (32–59) min) (p < 0.001). However, the number of attempts to stand was similar (medetomidine and xylazine: 2 (1–3)). Poorer scores were seen with increased pre-anaesthetic dose of xylazine, intraoperative tetrastarch, or salbutamol. However, use of medetomidine or xylazine did not influence recovery score, concluding that, following medetomidine–isoflurane PIVA, recovery is longer, but of similar quality compared to xylazine.

Studies to Evaluate the Safety of Constant Rate Infusions of Dexmedetomidine, Ketamine and Lidocaine Alone or in Combination during Isoflurane Anesthesia in Horses

Background: Horses mount a huge stress response to anesthesia when compared to other animals, hence are risky candidates for anesthesia. Inhalant anesthetic agents offer more control to anesthetic depth and facilitate rapid recovery, hence are considered to be safer than intravenous agents for surgical procedures requiring more than an hour, however, newer drug combinations are being explored to minimize the undesired consequences and dose rate of inhalant agents. The present study explored the safety of dexmedetomidine, ketamine and lidocaine constant rate infusion alone or as a combination along with Isoflurane for safer anesthesia in horses.Methods: The study was conducted on 28 horses divided into S, D, DK and DKL groups having 7 animals in each. Xylazine (1 mg/kg) and butorphanol (0.05mg/kg) were given intravenously for premedication. Ketamine (2 mg/kg) and midazolam (0.2 mg/kg) were used for induction and anesthesia was maintained with isoflurane. Normal saline (1000ml/hour), Dexmedetomidine (2µg/kg/hr), Dexmedetomidine and ketamine (2 µg/kg/hr and 2 mg/kg/hr) and Dexmedetomidine, ketamine and lidocaine (2 µg/kg/hr, 2 mg/kg/hr and 2 mg/kg/h) were given as CRI in groups S, D, DK and DKL, respectively. Thiopentone sodium (250mg bolus, 5%) was given as a fast intravenous bolus whenever required. Anesthetic efficacy was evaluated based on clinical, haemato-biochemical, hemodynamic, and endocrine variables.Result: A significant decline in mean arterial pressure was noticed in group DKL but changes in CVP and SpO2 in different groups were non-significant. Higher Blood glucose and low Insulin levels were seen in group DK during 45-60 min. Constant rate infusions of Dexmedetomidine, Ketamine and Lidocaine alone or in combination produced a significant sparing effect on Isoflurane and thiopentone while they improved peri-operative quality of anesthesia in horses.

Recovery Quality After Romifidine Versus Detomidine Infusion During Isoflurane Anesthesia in Horses

To examine the influence of detomidine or romifidine on recovery quality from isoflurane anesthesia, 78 anesthetic records were reviewed, from horses that had received romifidine (group R) during premedication [80–120 μg kg−1 IV], anesthetic maintenance (40 μg kg−1 hour−1 IV), and recovery (20 μg kg−1 IV) or detomidine (group D), at doses of 10–20 μg kg−1 IV, 5 μg kg−1 hour−1 IV, and 2.5 μg kg−1 IV, respectively. Duration of the different recovery phases, the number of attempts to sternal and standing, scores for transition to standing (TrSta), balance and coordination once standing (BC), and final recovery score (FS) were compared between groups using a Mann–Whitney U-test, independent t-test, or chi-squared test, as appropriate (alpha 0.05). Parametric data are represented as the mean ± standard deviation, and nonparametric data as the median (interquartile range). Compared with group D (25 horses), horses in group R (53 horses) needed significantly fewer attempts to achieve sternal recumbency [R 1 (1–1) vs. D 1 (1–2)], remained significantly longer in sternal recumbency [R 10 (3–14,5) vs. D 5 (1–9,5) minutes], needed significantly less attempts to stand [R 1 (1–1) vs. D 2 (1–4)], and a significantly shorter time to stand after making their first attempt [R 0 (0–0) vs. D 3 (0–6) minutes], with significantly better scores for TrSta, BC, and FS in group R. The results suggest that, at the doses used, romifidine provides a better recovery quality.

Pharmacokinetics and recovery effects of postanesthetic administration of xylazine and dexmedetomidine following isoflurane anesthesia in horses

Introduction: Understanding the pharmacokinetics of α2-adrenergic agonists during anesthetic recovery and their effect on inhalant anesthetic washout could be useful in managing equine anesthesia.

Effects of xylazine and doxapram on recovery of isoflurane anesthesia in horses

Introduction: Doxapram could potentially increase respiratory rate and cardiac output. This study aimed to evaluate if the administration of doxapram with xylazine would promote a faster and better recovery quality in horses isoflurane-anesthetized.

Effect of detomidine or romifidine constant rate infusion on plasma lactate concentration and inhalant requirements during isoflurane anaesthesia in horses

ObjectiveInfluence of detomidine or romifidine constant rate infusion (CRI) on plasma lactate concentration and isoflurane requirements in horses undergoing elective surgery. Study designProspective, randomised, blinded, clinical trial. AnimalsA total of 24 adult healthy horses. MethodsAll horses were administered intramuscular acepromazine (0.02 mg kg−1) and either intravenous detomidine (0.02 mg kg−1) (group D), romifidine (0.08 mg kg−1) (group R) or xylazine (1.0 mg kg−1) (group C) prior to anaesthesia. Group D was administered detomidine CRI (10 μg kg−1 hour−1) in lactated Ringer's solution (LRS), group R romifidine CRI (40 μg kg−1 hour−1) in LRS and group C an equivalent amount of LRS intraoperatively. Anaesthesia was induced with ketamine and diazepam and maintained with isoflurane in oxygen. Plasma lactate samples were taken prior to anaesthesia (baseline), intraoperatively (three samples at 30 minute intervals) and in recovery (at 10 minutes, once standing and 3 hours after end of anaesthesia). End-tidal isoflurane percentage (Fe′Iso) was analysed by allocating values into three periods: Prep (15 minutes after the start anaesthesia–start surgery); Surgery 1 (start surgery–30 minutes later); and Surgery 2 (end Surgery 1–end anaesthesia). A linear mixed model was used to analyse the data. A value of p<0.05 was considered significant. ResultsThere was a difference in plasma lactate between ‘baseline’ and ‘once standing’ in all three groups (p<0.01); values did not differ significantly between groups. In groups D and R, Fe′Iso decreased significantly by 18% (to 1.03%) and by 15% (to 1.07%), respectively, during Surgery 2 compared with group C (1.26%); p<0.006, p<0.02, respectively. Conclusions and clinical relevanceIntraoperative detomidine or romifidine CRI in horses did not result in a clinically significant increase in plasma lactate compared with control group. Detomidine and romifidine infusions decreased isoflurane requirements during surgery.

Effects of positive end-expiratory pressure titration on intestinal oxygenation and perfusion in isoflurane anaesthetised horses.

High airway pressures, necessary to keep equine lungs open, can have a detrimental impact on central and peripheral perfusion. The aim of this study was to assess the effects of stepwise increasing airway pressure recruitment on central and intestinal perfusion and oxygenation during isoflurane anaesthesia in horses. In vivo experimental study. Ten anaesthetised horses were ventilated using intermittent positive pressure ventilation immediately after induction. After 90 min, end-expiratory pressure (PEEP) was increased by steps of 5 cmH2 O every 10 min up to a PEEP of 30 cmH2 O and decreased back to zero maintaining a constant airway pressure difference of 20 cmH2 O. Mean arterial blood pressure (MAP), heart rate, central venous pressure, pulmonary artery pressure, expiratory isoflurane concentration and cardiac output (thermodilution method) were measured. Cardiac index (CI) was calculated. Arterial blood gases were taken to measure arterial partial oxygen pressure (PaO2 ) and calculate arterial oxygen saturation (SaO2 ). Intestinal microperfusion and oxygenation were measured by laser Doppler flowmetry and white-light spectrophotometry. After ventral median laparotomy, a probe was placed on the stomach, jejunum and pelvic flexion of the colon. An ANOVA for repeated measurements and Tukey's post hoc test were used for statistical analysis (α = 5%). Recruitment of the lungs resulted in a significant increase in PaO2 from 201 ± 58 mmHg (baseline) to a maximum of 495 ± 75 mmHg. The CI and MAP decreased continuously with increasing airway pressures. When CI and MAP were 37 ± 9 ml/kg/min and 52 ± 8 mmHg (at PEEP of 25 cmH2 O), respectively, a sudden decrease in intestinal perfusion followed by a delayed decrease in oxygenation occurred. There was linear correlation between airway pressures and CI and MAP but not between central and gastrointestinal perfusion. Despite improvement of arterial oxygenation the decrease in CI and, therefore, in oxygen delivery PEEP resulted in a decrease in gastrointestinal oxygenation.

Cardiopulmonary Effects and Recovery Quality of Remifentanil–Isoflurane Anesthesia in Horses

Remifentanil is a potent opioid with minimum alveolar concentration–sparing effects in humans and dogs, but its effects in horses have not been reported. We proposed to evaluate the cardiopulmonary effects, the duration, and recovery quality of remifentanil in isoflurane-anesthetized horses. Ten horses were premedicated with xylazine (1 mg/kg IV), induced with ketamine and diazepam (2.2 mg/kg/0.1 mg/kg IV), and maintained with isoflurane in oxygen delivered by a mechanical ventilator. Each horse was anaesthetized twice in a randomized order, with 1 week between treatments. In both treatment groups, a bolus of 0.5 μg/kg and a 120-minute infusion of remifentanil (0.375 μg/kg/min) or sterile water (delivered at the same rate per volume as the remifentanil) commenced when an end-tidal isoflurane concentration of 1.2%–1.4% was reached. Cardiopulmonary variables, arterial blood gas variables, time to extubation, and recovery scores were not significantly different between groups. The time to first movement was significantly different, which is longer for the placebo group (25.6 ± 17.7 minutes) than that for the remifentanil group (11.33 ± 5.38 minutes). The time to standing was significantly different; in the placebo group, it was 47 ± 20 minutes, and in the remifentanil group, it was 30.7 ± 9.3 minutes.

Effect of postoperative xylazine administration on cardiopulmonary function and recovery quality after isoflurane anesthesia in horses

To evaluate equine cardiopulmonary function and recovery quality after administration of 0.25 or 0.50 mg/kg xylazine intravenously (IV) during recovery. Randomized, blinded, prospective, clinical study. Horses (n = 20). During recovery after 3 hours of isoflurane anesthesia for arthroscopic surgery, horses were administered either 0.25 mg/kg (G25, n = 10) or 0.50 mg/kg (G50, n = 10) xylazine intravenously. Vital signs and arterial blood samples were obtained during recovery before sedation (baseline), 5, 10, 20, 30, and 45 minutes after xylazine and 30 minutes after standing. The quality of recovery scores ranged from 10 to 72 (10 = best, 72 = worst). G25 horses recovered faster (mean ± SD, 33 ± 5 min) than G50 horses (50 ± 7 min, P < .0001). Mean maximal decrease in arterial oxygen tension was 55 ± 11 mmHg in G25 (at 10 minutes; P < .05) and 54 ± 7 mmHg in G50 (at 20 minutes; P < .01). G25 group had a total recovery score (23 [range 18-29]) and number of attempts to stand (4 ± 2) greater than the G50 group (18 [10-23] and 1 ± 1, respectively; P < .001). Both doses of xylazine promoted a moderate and transient hypoxemia during recovery; however, the 0.5 mg/kg dose produced a longer and improved quality of recovery from anesthesia.

Effects of postanesthetic sedation with romifidine or xylazine on quality of recovery from isoflurane anesthesia in horses

To test the hypothesis that postanesthetic sedation with romifidine would dose-dependently improve recovery quality of recovery from isoflurane anesthesia in horses more than postanesthetic sedation with xylazine. Prospective, randomized, blinded clinical trial. 101 healthy adult horses examined at the University of California-Davis Veterinary Medical Teaching Hospital from 2007 to 2009. Horses were sedated with xylazine, and anesthesia was induced with guaifenesin, diazepam, and ketamine via a standardized drug protocol. Anesthesia for surgical or diagnostic procedures was maintained with isoflurane in oxygen for 1 to 4 hours. At the end of anesthesia, horses were moved to a padded stall for recovery. Once the breathing circuit was disconnected and the patient was spontaneously breathing, either xylazine (100 or 200 μg/kg [45 or 91 μg/lb]) or romifidine (10 or 20 μg/kg [4.5 or 9.1 μg/lb]) was administered i.v.. Objective patient, surgical, and anesthesia data were recorded. Subjective visual analog scale (VAS) scores of recovery quality were assigned by a single individual who was unaware of the treatment received. A stepwise linear regression model was used to correlate patient and procedure factors with the VAS score. Painful procedures, longer anesthesia times, and the Arabian horse breed were associated with poorer VAS scores. Adjustment for these factors revealed an improved VAS recovery score associated with the use of a romifidine dose of 20 μg/kg. In healthy adult horses anesthetized with isoflurane for > 1 hour, the results of this study supported the use of 20 μg of romifidine/kg, i.v., rather than lower romifidine doses or xylazine, for postanesthetic sedation to improve recovery quality.

Assessment of unassisted recovery from repeated general isoflurane anesthesia in horses following post-anesthetic administration of xylazine or acepromazine or a combination of xylazine and ketamine

ObjectivesTo compare the effects of sedative doses of acepromazine, xylazine or xylazine/ketamine administered to horses after isoflurane anesthesia on the quality of recovery and anesthesia recovery times. To determine if recovery scores improve after repeated consecutive anesthetic episodes. Study designProspective, randomized, crossover study. AnimalsFifteen adult research horses, 6.5 ± 3.4years old and weighing 499 ± 40 kg. MethodsHorses undergoing three anesthetic episodes with isoflurane for magnetic resonance of the forelimbs were administered acepromazine (0.02 mg kg−1 IV) or xylazine (0.3 mg kg−1 IV) or xylazine (0.15 mg kg−1 IV) combined with ketamine (0.3 mg kg−1 IV) in random order upon arrival in recovery. The quality of recovery was compared between the three treatments using a composite numerical rating and a general descriptive scoring system. ResultsHorses administered xylazine had better recovery scores than horses administered xylazine/ketamine, associated with better scores during their move to sternal, strength and number of attempts to standing. Horses administered acepromazine had similar recovery scores to horses administered xylazine and to horses administered xylazine/ketamine. Time to sternal recumbency and time to extubation were statistically longer for the xylazine treatment. Time to standing was similar between treatments. Horses had better recovery scores during the third anesthetic episode, regardless of the sedative drug administered, associated with better scores for strength and number of attempts to standing. ConclusionsXylazine administration was superior to xylazine/ketamine but similar to acepromazine. This study also indicates that horses improve the quality of recovery during consecutive anesthetics associated with longer time to sternal and to standing, regardless of the sedative used. Clinical relevanceAll treatments provided good quality recoveries. The experience of the individual horse gained during recent previous anesthetic episodes may have a positive effect in facilitating a better recovery.

Continuous intravenous lidocaine infusion during isoflurane anaesthesia in horses undergoing surgical procedures

The aim of the present study was to evaluate the adjunction of lidocaine as a continuous intravenous (IV) infusion during general anaesthesia with isoflurane in a clinical setting. For this purpose sixty horses (ASA I-III) undergoing elective surgery were assigned to a prospective, blinded, randomized clinical trial. After induction of anaesthesia, isoflurane end-tidal concentration was set at 1.3% and subsequently adjusted to maintain surgical plane of anaesthesia. Horses assigned to the group ISO-L (n=40) received IV lidocaine (1.5 mg kg-1, followed by 2.4 mg kg-1 hr-1, reduced later to 2 mg kg-1 hr-1) until 15 minutes before the end of the anaesthesia, while the control group ISO (n=20) received physiologic saline solution. All horses were ventilated mechanically. Mean arterial pressure (MAP) was maintained over 70 mmHg by IV infusion of dobutamine when necessary. Recovery quality was scored from one (very good) to five (very poor). The isoflurane concentration required in ISO-L group decreased down to 24% less (1.2% vs. 1.57%, P<0.05) than in the ISO group with time. Physiological parameters were similar in both groups. Recovery phases were scored of slight, but significant poorer quality (P=0.034) in horses receiving lidocaine (2, IQR 1-3) than in the control group (1, IQR 1-2), although the quality was still acceptable. The use of a continuous IV infusion of lidocaine at 2-2.4 mg kg-1 hr-1 during general anaesthesia allowed for 24% reduction of the isoflurane requirement, without relevant difference in clinical cardiovascular parameters. Under the condition of the present study, the administration of lidocaine tended to reduce moderately the quality of recovery from anaesthesia.

Effects of high and low inspired fractions of oxygen on horse erythrocyte membrane properties, blood viscosity and muscle oxygenation during anaesthesia

ObjectivesTo evaluate whether a period of hyperoxia or after a period of hypoxia produced changes attributable to reactive oxygen species in anaesthetized horses. Study designProspective randomized experimental study. AnimalsSix healthy (ASA I) geldings, aged 4.5–9.5 years and weighing 510–640 kg−1. MethodsAfter 30 minutes breathing air as carrier gas for isoflurane, horses were assigned randomly to breathe air as carrier gas (CG0.21) or oxygen as carrier gas (CG1.00) for a further 90 minutes. After an interval of 1 month each horse was re-anaesthetized with the other carrier gas for the 90 minute test period. Ventilation was controlled throughout anaesthesia. Arterial blood was sampled to measure gas tensions, lactate, cholesterol, vitamin E, 4-hydroxy-alkenals, 8-epi-PGF2α, half haemolysis time, half erythrolysis time, and erythrocyte membrane fluidity. Muscle blood flow and oxygenation were evaluated by near infrared spectroscopy and coloured Doppler. ResultsAfter the first 30 minutes horses were hypoxemic. Subsequently the CG1.00 group became hyperoxaemic (PaO2∼240 mmHg) whereas the CG0.21 group remained hypoxaemic (PaO2∼60 mmHg) and had increased lactate concentration. No significant changes in vitamin E, 4-hydroxy-alkenals, or 8-epi-PGF2α concentrations were detected. During the 90 minute test period the CG0.21 group had increased resistance to free-radical-mediated lysis in erythrocytes, whereas the CG1.00 group had slightly decreased resistance of whole blood to haemolysis. CG0.21 induced a progressive muscle deoxygenation whereas CG1.00 induced an increase in muscle oxygen saturation followed by progressive deoxygenation towards baseline. Conclusions and clinical relevanceDuring isoflurane anaesthesia in horses, the hyperoxia induced by changing from air to oxygen induced minimal damage from reactive oxygen species. Using air as the carrier gas decreased skeletal muscle oxygenation compared with using oxygen.

Evaluation of anesthesia recovery quality after low-dose racemic or S-ketamine infusions during anesthesia with isoflurane in horses

To compare anesthesia recovery quality after racemic (R-/S-) or S-ketamine infusions during isoflurane anesthesia in horses. 10 horses undergoing arthroscopy. After administration of xylazine for sedation, horses (n = 5/group) received R-/S-ketamine (2.2 mg/kg) or S-ketamine (1.1 mg/kg), IV, for anesthesia induction. Anesthesia was maintained with isoflurane in oxygen and R-/S-ketamine (1 mg/kg/h) or S-ketamine (0.5 mg/kg/h). Heart rate, invasive mean arterial pressure, and end-tidal isoflurane concentration were recorded before and during surgical stimulation. Arterial blood gases were evaluated every 30 minutes. Arterial ketamine and norketamine enantiomer plasma concentrations were quantified at 60 and 120 minutes. After surgery, horses were kept in a padded recovery box, sedated with xylazine, and video-recorded for evaluation of recovery quality by use of a visual analogue scale (VAS) and a numeric rating scale. Horses in the S-ketamine group had better numeric rating scale and VAS values than those in the R-/S-ketamine group. In the R-/S-ketamine group, duration of infusion was positively correlated with VAS value. Both groups had significant increases in heart rate and mean arterial pressure during surgical stimulation; values in the R-/S-ketamine group were significantly higher than those of the S-ketamine group. Horses in the R-/S-ketamine group required slightly higher end-tidal isoflurane concentration to maintain a surgical plane of anesthesia. Moderate respiratory acidosis and reduced oxygenation were evident. The R-norketamine concentrations were significantly lower than S-norketamine concentrations in the R-/S-ketamine group. Compared with R-/S-ketamine, anesthesia recovery was better with S-ketamine infusions in horses.

A comparison of recovery times and characteristics with sevoflurane and isoflurane anaesthesia in horses undergoing magnetic resonance imaging

ObjectiveTo compare recovery times and quality following maintenance of anaesthesia with sevoflurane or isoflurane after a standard intravenous induction technique in horses undergoing magnetic resonance imaging (MRI). Study designProspective, randomised, blinded clinical study. AnimalsOne hundred ASA I/II horses undergoing MRI.Materials and methods Pre-anaesthetic medication with intravenous acepromazine and romifidine was followed by induction of anaesthesia with diazepam and ketamine. The animals were randomised into two groups to receive either sevoflurane or isoflurane in oxygen. Horses were subjectively scored (0–5) for temperament before sedation, for quality of sedation, induction and maintenance and anaesthetic depth on entering the recovery area. Recoveries were videotaped and scored by an observer, unaware of the treatment, using two scoring systems. Times to the first movement, head lift, sternal recumbency and standing were recorded along with the number of attempts to achieve sternal and standing positions. Variables were compared using a Student t-test or Mann–Whitney U-test (p < 0.05), while the correlation between subjective recovery score and other relevant variables was tested calculating the Spearman Rank correlation coefficient and linear regression modelling performed when significant. ResultsSeventy-seven horses entered the final analysis, 38 received isoflurane and 39 sevoflurane. Body mass, age and duration of anaesthesia were similar for both groups. There were no differences in recovery times, scoring or number of attempts to achieve sternal recumbency and standing between groups. Weak, but significant, correlations were found between the subjective recovery score for the pooled data from both groups and both temperament and time in sternal recumbency. ConclusionsNo differences in recovery times or quality were detected following isoflurane or sevoflurane anaesthesia after intravenous induction. Clinical relevanceSevoflurane affords no obvious advantage in recovery over isoflurane following a standard intravenous induction technique in horses not undergoing surgery.

A comparison of equine recovery characteristics after isoflurane or isoflurane followed by a xylazine–ketamine infusion

ObjectiveTo determine whether infusion of xylazine (XYL) and ketamine (KET) for 30 minutes after isoflurane administration in horses would result in improved quality of recovery from anesthesia, without detrimental cardiopulmonary changes. Study designRandomized, blinded experimental trial. AnimalsSeven healthy adult horses aged 6.4 ± 1.9 years and weighing 506 ± 30 kg. MethodsHorses were anesthetized twice, at least 1 week apart. On both occasions, anesthesia was induced by the administration of XYL, diazepam, and KET, and maintained with isoflurane for approximately 90 minutes, the last 60 minutes of which were under steady-state conditions (1.2 times the minimum alveolar concentration isoflurane). On one occasion, horses were allowed to recover from isoflurane anesthesia, while on the other, XYL and KET were infused for 30 minutes after termination of isoflurane administration. Heart rate, respiratory rate, arterial blood pressure, pH, and blood-gases were measured and recorded at set intervals during steady-state isoflurane anesthesia and XYL–KET infusion. Recovery events were timed and subjectively scored by one nonblinded and two blinded observers. Data were analyzed using a restricted maximum likelihood-based mixed effect model repeated measures analysis. ResultsInfusion of XYL and KET resulted in longer recovery times, but there was no significant improvement in recovery quality score. ConclusionsUnder the conditions of this study, infusion of XYL and KET does not positively influence recovery from isoflurane anesthesia in horses. Clinical relevanceThis study does not support the routine use of XYL and KET infusions in horses during the transition from isoflurane anesthesia to recovery.