Anesthetic and cardiovascular effects of balanced anesthesia using constant rate infusion of midazolam-ketamine-medetomidine with inhalation of oxygen-sevoflurane (MKM-OS anesthesia) in horses

The anesthetic sparring and cardiovascular effects produced by midazolam 0.8 mg/ml-ketamine 40 mg/ml-medetomidine 0.05 mg/ml (0.025 ml/kg/hr) drug infusion during sevoflurane in oxygen (MKM-OS) anesthesia was determined in healthy horses. The anesthetic sparring effects of MKM-OS were assessed in 6 healthy thoroughbred horses in which the right carotid artery was surgically relocated to a subcutaneous position. All horses were intubated and ventilated with oxygen using intermittent positive pressure ventilation (IPPV). The end-tidal concentration of sevoflurane (ET(SEV)) required to maintain surgical anesthesia was approximately 1.7%. Heart rate and mean arterial blood pressure averaged 23-41 beats/min and 70-112 mmHg, respectively. All horses stood between 23-44 min after the cessation of all anesthetic drugs. The cardiovascular effects of MKM-OS anesthesia were evaluated in 5 healthy thoroughbred horses ventilated using IPPV. Anesthesia was maintained for 4 hr at an ET(SEV) of 1.7%. Each horse was studied during left lateral (LR) and dorsal recumbency (DR) with a minimum interval between evaluations of 1 month. Cardiac output and cardiac index were maintained between 70-80% of baseline values during LR and 65-70% of baseline values during DR. Stroke volume was maintained between 75-85% of baseline values during LR and 60-70% of baseline values during DR. Systemic vascular resistance was not different from baseline values regardless of position. MKM-OS anesthesia may be useful for prolonged equine surgery because of its minimal cardiovascular depression in both of lateral and dorsal recumbency.     

Differences in need for hemodynamic support in horses anesthetized with sevoflurane as compared to isoflurane

OBJECTIVE: To study whether hemodynamic function in horses, particularly mean arterial blood pressure (MAP), is better maintained with sevoflurane than isoflurane, thus requiring less pharmacological support. STUDY DESIGN: Prospective randomized clinical investigation. Animals Thirty-nine racehorses undergoing arthroscopy in lateral recumbency. METHODS: Horses were assigned to receive either isoflurane (n = 20) or sevoflurane (n = 19) at 0.9-1.0 minimum alveolar concentration (MAC) for maintenance of anesthesia. Besides routine clinical monitoring, cardiac output (CO) was measured by lithium dilution. Hemodynamic support was prescribed as follows: when MAP decreased to <70 mmHg, patients were to receive infusion of 0.1% dobutamine, which was to be discontinued at MAP >85 mmHg or heart rate >60 beats minute(-1). Statistical analysis of results, given as mean +/- SD, included a clustered regression approach. RESULTS: Average inhalant anesthetic time [91 +/- 35 (isoflurane group) versus 97 +/- 26 minutes (sevoflurane group)] and dose (in MAC multiples), volume of crystalloid solution infused, and cardiopulmonary parameters including CO were similar in the two groups, except heart rate was 8% higher in isoflurane than sevoflurane horses (p < 0.05). To maintain MAP >70 mmHg, isoflurane horses received dobutamine over a significantly longer period (55 +/- 26 versus 28 +/- 21% of total anesthetic time, p < 0.01) and at a 51% higher dose than sevoflurane horses (41 +/- 19 versus 27 +/- 23 microg kg(-1) MAC hour(-1); p = 0.058), with 14/20 isoflurane animals and only 9/19 sevoflurane horses being infused with dobutamine at >30 microg kg(-1) MAC hour(-1) (p < 0.05). Dobutamine infusion rates were consistently lower in the sevoflurane as compared to the isoflurane group, with differences reaching significance level during the 0-30 minutes (p < 0.01) and 61-90 minutes periods (p < 0.05). CONCLUSIONS AND CLINICAL RELEVANCE: Horses under sevoflurane anesthesia may require less pharmacological support in the form of dobutamine than isoflurane-anesthetized horses. This could be due to less suppression of vasomotor tone.     

Combination of continuous intravenous infusion using a mixture of guaifenesin-ketamine-medetomidine and sevoflurane anesthesia in horses

The anesthetic and cardiovascular effects of a combination of continuous intravenous infusion using a mixture of 100 g/L guaifenesin-4 g/L ketamine-5 mg/L medetomidine (0.25 ml/kg/hr) and oxygen-sevoflurane (OS) anesthesia (GKM-OS anesthesia) in horses were evaluated. The right carotid artery of each of 12 horses was raised surgically into a subcutaneous position under GKM-OS anesthesia (n=6) or OS anesthesia (n=6). The end-tidal concentration of sevoflurane (EtSEV) required to maintain surgical anesthesia was around 1.5% in GKM-OS and 3.0% in OS anesthesia. Mean arterial blood pressure (MABP) was maintained at around 80 mmHg under GKM-OS anesthesia, while infusion of dobutamine (0.39+/-0.10 microg/kg/min) was necessary to maintain MABP at 60 mmHg under OS anesthesia. The horses were able to stand at 36+/-26 min after cessation of GKM-OS anesthesia and at 48+/-19 minutes after OS anesthesia. The cardiovascular effects were evaluated in 12 horses anesthetized with GKM-OS anesthesia using 1.5% of EtSEV (n=6) or OS anesthesia using 3.0% of EtSEV (n=6). During GKM-OS anesthesia, cardiac output and peripheral vascular resistance was maintained at about 70% of the baseline value before anesthesia, and MABP was maintained over 70 mmHg. During OS anesthesia, infusion of dobutamine (0.59+/-0.24 microg/kg/min) was necessary to maintain MABP at 70 mmHg. Infusion of dobutamine enabled to maintaine cardiac output at about 80% of the baseline value; however, it induced the development of severe tachycardia in a horse anesthetized with sevoflurane. GKM-OS anesthesia may be useful for prolonged equine surgery because of its minimal cardiovascular effect and good recovery.     

Infusion of guaifenesin,ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses

OBJECTIVE: To evaluate effects of infusion of guaifenesin, ketamine, and medetomidine in combination with inhalation of sevoflurane versus inhalation of sevoflurane alone for anesthesia of horses. DESIGN: Randomized clinical trial. ANIMALS: 40 horses. PROCEDURE: Horses were premedicated with xylazine and anesthetized with diazepam and ketamine. Anesthesia was maintained by infusion of guaifenesin, ketamine, and medetomidine and inhalation of sevoflurane (20 horses) or by inhalation of sevoflurane (20 horses). A surgical plane of anesthesia was maintained by controlling the inhaled concentration of sevoflurane. Sodium pentothal was administered as necessary to prevent movement in response to surgical stimulation. Hypotension was treated with dobutamine; hypoxemia and hypercarbia were treated with intermittent positive-pressure ventilation. The quality of anesthetic induction, maintenance, and recovery and the quality of the transition to inhalation anesthesia were scored. RESULTS: The delivered concentration of sevoflurane (ie, the vaporizer dial setting) was significantly lower and the quality of transition to inhalation anesthesia and of anesthetic maintenance were significantly better in horses that received the guaifenesin-ketamine-medetomidine infusion than in horses that did not. Five horses, all of which received sevoflurane alone, required administration of pentothal. Recovery time and quality of recovery were not significantly different between groups, but horses that received the guaifenesin-ketamine-medetomidine infusion required fewer attempts to stand. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that in horses, the combination of a guaifenesin-ketamine-medetomidine infusion and inhalation of sevoflurane resulted in better transition and maintenance phases while improving cardiovascular function and reducing the number of attempts needed to stand after the completion of anesthesia, compared with inhalation of sevoflurane.     

Propofol-ketamine anesthesia for internal fixation of fractures in racehorses

To assess the clinical usability of propofol-ketamine anesthesia for internal fixation of fractures in racehorses, hemodynamics, blood pH and gases, and vital responses to the continuous intravenous anesthesia in 7 surgical cases were analyzed. The quality of induction with propofol was variable for individual horses. The vital signs reflecting circulation, breath, and anesthetic depth were kept good without any troubles throughout the surgery. Mean time from the end of anesthesia to standing up was prolonged, however recovery from anesthesia was calm and smooth in all cases. Propofol-ketamine anesthesia may be a clinically usable technique for internal fixation of fractures in racehorses, however induction with propofol alone is not recommended.     

Use of sevoflurane for anesthetic management of horses during thoracotomy

OBJECTIVE: To evaluate sevoflurane as an inhalation anesthetic for thoracotomy in horses. ANIMALS: 18 horses between 2 and 15 years old. PROCEDURE: 4 horses were used to develop surgical techniques and were euthanatized at the end of the procedure. The remaining 14 horses were selected, because they had an episode of bleeding from their lungs during strenuous exercise. General anesthesia was induced with xylazine (1.0 mg/kg of body weight, IV) followed by ketamine (2.0 mg/kg, IV). Anesthesia was maintained with sevoflurane in oxygen delivered via a circle anesthetic breathing circuit. Ventilation was controlled to maintain PaCO2 at approximately 45 mm Hg. Neuromuscular blocking drugs (succinylcholine or atracurium) were administered to eliminate spontaneous breathing efforts and to facilitate surgery. Cardiovascular performance was monitored and supported as indicated. RESULTS: 2 of the 14 horses not euthanatized died as a result of ventricular fibrillation. Mean (+/- SD) duration of anesthesia was 304.9 +/- 64.1 minutes for horses that survived and 216.7 +/- 85.5 minutes for horses that were euthanatized or died. Our subjective opinion was that sevoflurane afforded good control of anesthetic depth during induction, maintenance, and recovery. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of sevoflurane together with neuromuscular blocking drugs provides stable and easily controllable anesthetic management of horses for elective thoracotomy and cardiac manipulation.     

Plasma colloid osmotic pressure and total protein in horses during colic surgery

OBJECTIVE: To assess the changes in colloid osmotic pressure (COP) in horses undergoing surgery for colic. STUDY DESIGN: Prospective clinical evaluation. ANIMALS: Twenty-nine adult horses presented for emergency laparotomy. METHODS: Horses were premedicated with intravenous (IV) xylazine and anesthesia was induced with ketamine, diazepam and guaifenesin and was maintained with isoflurane as required. Lactated Ringer's solution (LRS) was given to all horses during anesthesia. Blood was collected in heparin before, and every 30 minutes during, anesthesia to measure COP, total protein concentration (TP), osmolality, packed cell volume, electrolytes, glucose and lactate. In addition, COP was estimated using different formulas previously described for horses. RESULTS: Before anesthesia, COP and TP were 18.7 +/- 2.2 mmHg (2.49 +/- 0.29 kPa) and 6.3 +/- 0.7 g dL(-1), respectively. The horses received a mean +/- SD of 19.5 +/- 3.9 mL kg(-1) hour(-1) (range 15-25 mL kg(-1)hour(-1)) of LRS during anesthesia. The COP and TP decreased linearly (R(2) = 0.99, p < 0.01) during anesthesia and reached the lowest point at the end of anesthesia with a COP of 11.6 +/- 1.6 mmHg (1.55 +/- 0.21 kPa) and TP of 4.4 +/- 0.4 g dL(-1). The Pearson correlation coefficient for COP versus TP was r(2) = 0.78. Calculation of COP from TP concentrations showed that two formulas could predict COP to within 1 mmHg (0.13 kPa) (Thomas & Brown 1992; Boscan et al. 2007). CONCLUSIONS AND CLINICAL RELEVANCE: Colloid osmotic pressure, like TP, decreased greatly over the course of crystalloid fluid infusion during anesthesia for laparotomy in horses with colic. This change may predispose the animal to tissue edema with subsequent morbidity.     

Clinical evaluation of balanced anesthesia using infusion of midazolam–ketamine–medetomidine in combination with inhalation of sevoflurane (MKM–OS anesthesia) in horses

MKM–OS anesthesia provides general anesthesia with minimum cardiovascular depression in experimental horses. The purpose of this study was to evaluate the effect of MKM–OS anesthesia in clinical cases. Sixty‐eight horses were anesthetized with MKM–OS anesthesia for selective or emergency surgery. The horse physical status was categorized based upon the American Society of Anesthesiologists (ASA) classification scheme. Forty‐four horses were classified as ASA I or II (low‐risk; 30 soft tissue, eight ophthalmic, and six orthopedic surgeries) and 24 horses were classified as ASA III to V (high‐risk; 24 emergency colic surgeries). All horses were administered medetomidine (0.005 mg kg^–1 IV) as premedication and anesthetized with ketamine (2.5 mg kg^–1 IV) and midazolam (0.04 mg kg^–1 IV). The horses were orotracheally intubated and connected to a large animal breathing circuit that delivered oxygen‐sevoflurane and administered the midazolam (0.8 mg mL^–1)‐ketamine (40 mg mL^–1)‐medetomidine (0.05 mg mL^–1) drug combination at a rate of 0.025 mL kg^–1 hour^–1. Surgical anesthesia was maintained by controlling the dial setting of the sevoflurane vaporizer and achieved by delivering 1.6–1.8% of end‐tidal sevoflurane concentration. All horses were mechanically ventilated during anesthesia. Hypercapnia and hypoxia were not sufficiently improved in high‐risk horses (PaCO₂; low‐risk 45–53 mm Hg versus high‐risk 56–60 mm Hg, p < 0.01: PaO₂ low‐risk 248–388 mm Hg versus high‐risk 95–180 mm Hg, p < 0.01). Heart rate was significantly higher in high‐risk horses (low‐risk 37–42 bpm versus high‐risk 44–73 bpm, p < 0.01). Dobutamine infusion was required in five low‐risk (11%) and 17 high‐risk horses (68%) to maintain mean arterial blood pressure >70 mm Hg. Eleven high‐risk horses died during the perioperative period (three euthanized during surgery, two died during recovery, six died after recovery). The quality of recovery was good in low‐risk horses and good to satisfactory in high‐risk horses. MKM–OS anesthesia provided excellent surgical anesthesia with minimal to mild cardiovascular depression in low risk‐horses and mild to moderate cardiovascular depression in high risk‐horses. The possibility of preserve cardiovascular function could be the advantage of MKM–OS anesthesia in high‐risk horses.     

Recovery From Sevoflurane Anesthesia in Horses: Comparison to Isoflurane and Effect of Postmedication With Xylazine

Objective—To compare recovery from sevoflurane or isoflurane anesthesia in horses. Study Design—Prospective, randomized cross-over design. Animals—Nine Arabian horses (3 mares, 3 geldings, and 3 stallions) weighing 318 to 409 kg, 4 to 20 years old. Methods—Horses were anesthetized on three occasions with xylazine (1.1 mg/kg), Diazepam (0.03 mg/kg intravenously [IV]), and ketamine (2.2 mg/kg IV). After intubation, they were maintained with isoflurane or sevoflurane for 90 minutes. On a third occasion, horses were maintained with sevoflurane and given xylazine (0.1 mg/kg IV) when the vaporizer was turned off. Horses were not assisted in recovery and all recoveries were videotaped. Time to extubation, first movement, sternal, and standing were recorded as was the number of attempts required to stand. Recoveries were scored on a 1 to 6 scoring system (1 = best, 6 = worst) by the investigators, and by three evaluators who were blinded to the treatments the horses received. These blinded evaluators assessed the degree of ataxia present at 10 minutes after each horse stood, and recorded the time at which they judged the horse to be ready to leave the recovery stall. Results—Mean times (± SD) to extubation, first movement, sternal, and standing were 4.1 (1.7), 6.7 (1.9), 12.6 (4.6), and 17.4 (7.2) minutes with isoflurane; 3.4 (0.8), 6.6 (3.1), 10.3 (3.1), and 13.9 (3.0) minutes with sevoflurane; and 4.0 (1.2), 9.1 (3.3), 13.8 (6.5), and 18.0 (7.1) with sevoflurane followed by xylazine. Horses required a mean number of 4 (2.3), 2 (0.9), and 2 (1.6) attempts to stand with isoflurane, sevoflurane, and sevoflurane followed by xylazine respectively. The mean recovery score (SD) for isoflurane was 2.9 (1.2) from investigators and 2.4 (1.1) from blinded evaluators. For sevoflurane, the mean recovery score was 1.7 (0.9) from investigators and 1.9 (1.1) from evaluators, whereas the recoveries from sevoflurane with xylazine treatment were scored as 1.7 (1.2) from investigators and 1.7 (1.0) from blinded evaluators. Conclusions—Recoveries appeared to vary widely from horse to horse, but were significantly shorter with sevoflurane than isoflurane, although sevoflurane followed by xylazine was no different from isoflurane. Under the conditions of the study, recoveries from sevoflurane and sevoflurane followed by xylazine were of better quality than those from isoflurane. Clinical Relevance—Sevoflurane anesthesia in horses may contribute to a shorter, safer recovery from anesthesia.     

Clinical observations during induction and recovery of xylazine-midazolam- propofol anesthesia in horses

To evaluate clinical usefulness of xylazine (1.0 mg/kg)-midazolam (20 microg/kg)-propofol (3.0 mg/kg) anesthesia in horses, 6 adult Thoroughbred horses were examined. The quality of induction varied from poor to excellent and 5 out of 6 horses presented myotonus in the front half of the body. However, paddling immediately after induction observed in other reports of equine propofol anesthesia was not observed. Recovery time was 35.3 +/- 9.3 min and the quality of recovery was calm and smooth in all horses. Respiration rate decreased after induction and hypoxemia was observed during lateral recumbency. Heart rate also decreased after induction, however mean arterial blood pressure was maintained above approximately 100 mmHg.     

Excision of Intralaryngeal Granulation Tissue in 25 Horses Using a Neodymium:YAG Laser (1986 to 1991)

Granulation tissue masses arising from the axial surface of the arytenoid cartilage in 25 horses were excised using a contact neodymium:yttrium aluminum garnet laser. A technique that eliminated the need for general anesthesia or laryngotomy was developed for transen-doscopic removal of the masses in standing horses. Nineteen racehorses made abnormal upper respiratory tract noises or their performance was decreased, whereas six horses not used for racing had a history of stertor (five horses) or epistaxis after nasogastric intubation (one horse). Thoroughbreds were significantly (p = .0126) overrepresented compared with the hospital population. The granulation tissue masses were successfully excised and the defect healed in all 25 horses, although a second excision of granulation tissue regrowth was necessary in four horses. In 21 horses, the underlying chondrosis did not progress appreciably. In four horses with preexisting moderate arytenoid cartilage thickening and concurrent laryn-geal abnormalities, the surgery site healed but the underlying chondrosis progressed substantially. Twelve of 19 (63%) racehorses returned to race at least three times after the surgery. Of the 19 racehorses, five had only slight arytenoid cartilage involvement whereas 14 had moderate cartilage thickening or concurrent laryngeal pathology. All five horses with slight apparent arytenoid cartilage involvement and no concurrent laryngeal pathology returned to racing. Seven of the 14 horses (50%) with moderate underlying cartilage thickening or concurrent laryngeal pathology returned to racing. The six horses not used for racing returned to their previous activity without further respiratory problems.     

Transendoscopic contact neodymium:yttrium aluminum garnet laser correction of epiglottic entrapment in standing horses

Fifty-seven Standardbred and 44 Thoroughbred racehorses and 1 Thoroughbred polo mare with primary clinical signs of exercise intolerance or respiratory tract noise or combined exercise intolerance and respiratory tract noise were referred for laser correction of epiglottic entrapment. Significantly (P less than 0.001) more Standardbred than Thoroughbred racehorses were affected, compared with the observed hospital population during the same period. At referral, 14 horses did not have evident epiglottic entrapment and were returned to exercise without development of entrapment after treatment, which consisted of 1 week of rest and administration of anti-inflammatory medication. In 88 standing horses under sedation and topical anesthesia, epiglottic entrapment was corrected transendoscopically by use of a contact neodymium:yttrium aluminum garnet laser. In these 88 horses, 98% of entrapments were persistent, 92% were thick, 97% were wide, and 45% were ulcerated. Thirty-one percent of the horses had endoscopic evidence of epiglottic hypoplasia, and 8% had deviated epiglottic axis. Complete correction was achieved in 97% of the horses, Persistent dorsal displacement of the soft palate in 1 horse and severe epiglottic hypoplasia with thick, chronic entrapping membranes in 2 horses precluded successful transendoscopic correction with the horses in standing position. Most horses were treated on an outpatient basis, and all were able to be returned to exercise after 7 to 14 days of rest and treatment with anti-inflammatory medication. Entrapment recurred in 4 horses (5%), 3 of which had hypoplastic epiglottis. Dorsal displacement of the soft palate developed after surgery in 9 horses (10%) and continued in 4 horses (5%) that had displaced soft palate before surgery. All these horses had epiglottic hypoplasia. Laser correction of epiglottic entrapment in standing horses was safe, well tolerated, and effective. Laser surgery was an alternative to conventional surgery, and eliminated the need for general anesthesia and laryngotomy. It also reduced convalescence and postoperative complications.     

Arterial hypotension and the development of postanesthetic myopathy in halothane-anesthetized horses

The effect of halothane-induced hypotension on the development of postanesthetic myopathy was studied, using 6 healthy adult horses. Horses were anesthetized with halothane in oxygen for 3.5 hours on each of 2 occasions. Intermittent positive-pressure ventilation was used to maintain PaCO2 of 45 to 55 mm of Hg throughout both anesthetic exposures. By regulating the inspired halothane concentration, a mean arterial blood pressure of 85 to 95 mm of Hg (normotension) was maintained throughout the 1st anesthetic exposure, and a mean arterial blood pressure of 55 to 65 mm of Hg (hypotension) was maintained during the 2nd anesthetic exposure. All horses recovered uneventfully from normotensive anesthesia, but all had some muscle dysfunction after prolonged hypotensive anesthesia. Because of apparent animal discomfort and lameness involving more than 1 limb, 3 horses were euthanatized soon after they recovered from hypotensive anesthesia. The 3 other horses showed a degree of lameness. In addition, 1 horse had raised, swollen plaques over the hip, rib, and facial areas which were in contact with the surgical table, and another had evidence of facial nerve paralysis. One hour after the 6 horses stood after hypotensive anesthesia was completed, values obtained for aspartate transaminase and creatinine were significantly (P less than 0.05) greater than those obtained after normotensive anesthesia was completed. Aspartate transaminase, total bilirubin, and creatinine values were significantly (P less than 0.05) increased when compared with those obtained before horses were anesthetized. A large increase was measured in creatine kinase. Twenty-four hours after hypotensive anesthesia was completed, creatine kinase and lactate dehydrogenase in the 3 surviving horses were significantly (P less than 0.05) greater than those values after normotensive anesthesia was completed.     

Evaluation of cardiovascular effects of total intravenous anesthesia with propofol or a combination of ketamine-medetomidine-propofol in horses

OBJECTIVE: To evaluate the cardiovascular effects of total IV anesthesia with propofol (P-TIVA) or ketamine-medetomidine-propofol (KMP-TIVA) in horses. ANIMALS: 5 Thoroughbreds. PROCEDURES: Horses were anesthetized twice for 4 hours, once with P-TIVA and once with KMP-TIVA. Horses were medicated with medetomidine (0.005 mg/kg, IV) and anesthetized with ketamine (2.5 mg/kg, IV) and midazolam (0.04 mg/kg, IV). After receiving a loading dose of propofol (0.5 mg/kg, IV), anesthesia was maintained with a constant rate infusion of propofol (0.22 mg/kg/min) for P-TIVA or with a constant rate infusion of propofol (0.14 mg/kg/min), ketamine (1 mg/kg/h), and medetomidine (0.00125 mg/kg/h) for KMP-TIVA. Ventilation was artificially controlled throughout anesthesia. Cardiovascular measurements were determined before medication and every 30 minutes during anesthesia, and recovery from anesthesia was scored. RESULTS: Cardiovascular function was maintained within acceptable limits during P-TIVA and KMP-TIVA. Heart rate ranged from 30 to 40 beats/min, and mean arterial blood pressure was > 90 mm Hg in all horses during anesthesia. Heart rate was lower in horses anesthetized with KMP-TIVA, compared with P-TIVA. Cardiac index decreased significantly, reaching minimum values (65% of baseline values) at 90 minutes during KMP-TIVA, whereas cardiac index was maintained between 80% and 90% of baseline values during P-TIVA. Stroke volume and systemic vascular resistance were similarly maintained during both methods of anesthesia. With P-TIVA, some spontaneous limb movements occurred, whereas with KMP-TIVA, no movements were observed. CONCLUSIONS AND CLINICAL RELEVANCE: Cardiovascular measurements remained within acceptable values in artificially ventilated horses during P-TIVA or KMP-TIVA. Decreased cardiac output associated with KMP-TIVA was primarily the result of decreases in heart rate.     

Long-term study of partial arytenoidectomy with primary mucosal closure in 76 Thoroughbred racehorses (1992-2006)

REASON FOR PERFORMING STUDY: The effectiveness and best method to perform a partial arytenoidectomy in racehorses is unclear. This study was performed to evaluate the success of and complications that can occur after a unilateral partial arytenoidectomy with primary mucosal closure in Thoroughbred racehorses. HYPOTHESIS: Partial arytenoidectomy is an effective surgical procedure to return Thoroughbred racehorses, afflicted by arytenoid chondropathy or a failed laryngoplasty, to preoperative levels of performance. METHODS: Seventy-six Thoroughbred racehorses admitted to the New Bolton Centre between 1992 and 2006 were assessed. Information was obtained from the medical records about the horse, laryngeal abnormalities, surgery and other findings during hospitalisation. Racing information was evaluated relative to those independent variables by an analysis of variance with a level of significance of P<0.05. RESULTS: Arytenoid chondropathy was the presenting complaint in 54 horses and failed laryngoplasty in 22 horses. Thirteen horses (17%) underwent a second surgery for laser excision of intralaryngeal granulation tissue at the arytenoidectomy site. Seventy-three horses were discharged from the hospital and racing outcome was evaluated. Sixty horses (82%) raced after surgery and 46 horses (63%) raced 5 or more times after surgery. The median time from surgery to the first start was 6 months. The average earnings/start was not significantly different before and after surgery. There was no association between earnings after surgery and age, gender, location of lesion, type of lesion, duration of tracheal intubation or undergoing a second surgery. CONCLUSIONS AND POTENTIAL RELEVANCE: A Thoroughbred racehorse is likely to race after a unilateral partial arytenoidectomy with primary mucosal closure and return to a preoperative level of performance.     

Influence of halothane, isoflurane, and sevoflurane on gastroesophageal reflux during anesthesia in dogs

OBJECTIVE: To determine whether maintenance of anesthesia with halothane or sevoflurane is associated with a lower incidence of gastroesophageal reflux (GER) than the use of isoflurane in dogs undergoing orthopedic surgery. ANIMALS: 90 dogs. PROCEDURES: Dogs were evaluated during elective orthopedic surgery. Dogs with a history of vomiting or that had received any drugs that would alter gastrointestinal tract function were excluded from the study. The anesthetic protocol used was standardized to include administration of acepromazine maleate and morphine prior to induction of anesthesia with thiopental. Dogs were allocated to receive halothane, isoflurane, or sevoflurane to maintain anesthesia. A sensor-tipped catheter was placed to measure esophageal pH during anesthesia. Gastroesophageal reflux was defined as an esophageal pH < 4 or > 7.5. RESULTS: 51 dogs had 1 or more episodes of acidic GER during anesthesia. Reflux was detected in 14 dogs receiving isoflurane, 19 dogs receiving halothane, and 18 dogs receiving sevoflurane. In dogs with GER, mean +/- SD time from probe placement to onset of GER was 36 +/- 65 minutes and esophageal pH remained < 4 for a mean of 64% of the measurement period. There was no significant association between GER and start of surgery or moving a dog on or off the surgery table. Dogs that developed GER soon after induction of anesthesia were more likely to regurgitate. CONCLUSIONS AND CLINICAL RELEVANCE: Maintenance of anesthesia with any of the 3 commonly used inhalant agents is associated with a similar risk for development of GER in dogs.     

Sevoflurane anaesthesia in clinical equine cases: maintenance and recovery

A new inhalant anaesthetic, sevoflurane, was used to maintain anaesthesia in 40 animals (2 mules and 38 horses of 9 breeds) presented for various surgical procedures. Eighteen mares, 11 stallions and 11 geldings underwent 6 orthopaedic and 34 soft tissue operations. Induction of anaesthesia was achieved with combinations of xylazine (0.5–1.1 mg/kg), diazepam (0.03–0.1 mg/kg), butorphanol (0.02 mg/kg), guaifenesin (50–84 mg/kg) and ketamine (1.1 mg/kg). Following tracheal intubation, a surgical plane of anaesthesia was maintained with sevoflurane in oxygen delivered from a precision vaporiser. Temperature, ECG, arterial blood pressure and expired gas composition were monitored. Mechanical ventilation was used in most animals (n=37) because of hypoventilation (P_aCO₂ > 7.31 kPa [55 mmHg]). Following surgery, horses were moved to a recovery room and allowed to recover alone (n=36) or with assistance (n=4). Time to sternal recumbency, standing, the time when satisfactory coordination was present (after standing) and the number of attempts to stand were recorded. The quality of recovery was scored on a 1 (best) to 6 (worst) scale. Mean blood pressures at 30, 60, 90, 120 and 150 min of anaesthesia were 72, 73, 74, 75 and 72 mmHg, respectively. Systolic and diastolic pressures at 30, 60, 90, 120 and 150 min of anaesthesia were 97, 97, 94, 96, 93 and 59, 63, 64, 68, 67 mmHg, respectively. Dobutamine was used in 23 horses to maintain mean arterial blood pressure > 60 mmHg. Mean heart and respiratory rates at 30, 60, 90, 120 and 150 min of anaesthesia were 36, 38, 39, 38 and 38 beats/min, and 9, 8, 8, 8 and 8 breaths/min. Mean duration of anaesthesia was 121 rnin (sd: 56 min), mean time to sternal recumbency was 27 min (sd: 13 min), average time to standing (all horses) was 33 min (sd: 12 min) and time to satisfactory coordination was 44 min (sd: 13 min). Most horses (n=37) received xylazine during recovery (mean dose 0.18 mg/kg iv). The median number of attempts to sternal recumbency and standing were 1.0 (range; 1–7) and 2.0 (range; 1–20), respectively, while the median recovery score was 1.5 (range; 14). The ‘depth’ of anaesthesia was easy to control and recoveries were generally very satisfactory.     

The recovery of horses from inhalant anesthesia: a comparison of halothane and isoflurane

Objective— Recovery is one of the more precarious phases of equine general anesthesia. The quality and rate of recovery of horses from halothane and isoflurane anesthesia were compared to determine differences in the characteristics of emergence from these commonly used inhalant anesthetics. Experimental Design— Prospective, randomized blinded clinical trial. Sample Population— A total of 96 Thoroughbred and 3 Standardbred racehorses admitted for elective distal forelimb arthroscopy. Methods— All horses were premedicated with intravenous xylazine, induced with guaifenesin and ketamine, and maintained on a large animal circle system fitted with an out of the circle, agent specific vaporizer. Recoveries were managed by a blinded scorer with a standardized protocol. A 10 category scoring system was used to assess each horse's overall attitude, purposeful activity, muscle coordination, strength and balance from the time of arrival in recovery to standing. Times to extubation, sternal recumbency and standing were recorded. Median recovery scores and mean times to extubation, sternal and standing were compared using the Mann‐Whitney U test and student's t test, respectively. Results— The median score for horses recovering from halothane was lower (20.0; range, 10 to 57) than that for horses recovering from isoflurane (27.5; range, 10 to 55). Horses in the two groups were extubated at similar mean times (halothane, 11.3 ± 5.5 and isoflurane, 9.5 ± 5.2 minutes ) but horses recovering from isoflurane achieved sternal recumbency (halothane, 37.7 ± 12.1 and isoflurane, 24.7 ± 8.8 minutes ) and stood (halothane, 40.6 ± 12.9 and isoflurane, 27.6 ± 9.6 minutes ) sooner than those recovering from halothane. Conclusions— The recovery of horses from isoflurane anesthesia was more rapid but less composed than that from halothane. Clinical Relevance— The quality of recovery following isoflurane was worse than after halothane anesthesia using the criteria chosen for this study. However, the range of recovery scores was similar for both groups and all horses recovered without significant injury.     

Cardiovascular effects of continuous propofol infusion in horses

We examined the influence of propofol infusion on cardiovascular system at the rate of 0.14, 0.20 and 0.30 mg/kg/min in six adult Thoroughbred horses. The cardiovascular parameters were heart rate (HR), mean arterial pressure (MAP), mean right atrial pressure (MRAP), stroke volume (SV), cardiac output (CO), systemic vascular resistance (SVR), pre-ejection period (PEP) and ejection time (ET). In order to keep the ventilation conditions constantly, intermittent positive pressure ventilation was performed, and the partial arterial CO(2) pressure was maintained at 45 to 55 mmHg during maintenance anesthesia. SV showed a significant dose-dependent decrease however, CO did not show significant change. SVR decreased significantly at higher dose. PEP was prolonged and PEP/ET increased significantly at the highest dose. From these results, it became clear that SV decreases dose-dependently due to decrease of cardiac contractility during anesthesia with continuous propofol infusion in horses. On the other hand, since MAP and CO did not show significant changes, total intravenous anesthesia with propofol was suggested to be suitable for long-term anesthesia in horses.     

Evaluation of intraocular pressure in association with cardiovascular parameters in normocapnic dogs anesthetized with sevoflurane and desflurane

The objective of this study was to determine intraocular pressure (IOP) and cardiac changes in normocapnic dogs maintained under controlled ventilation and anesthetized using sevoflurane or desflurane. Sixteen healthy adult mixed-breed dogs, seven males and nine females, weighing 10-15 kg were used. The dogs were randomly assigned to one of two groups composed of eight animals anesthetized with sevoflurane (SEVO) or desflurane (DESF). In both groups, anesthesia was induced with propofol (10 mg/kg), and neuromuscular blockade was achieved with rocuronium (0.6 mg/kg/h i.v.). No premedication was given. Ventilation was adjusted to maintain end-tidal carbon dioxide partial pressure at 35 mmHg. Anesthesia was maintained with 1.5 minimum alveolar concentration (MAC) of sevoflurane or desflurane. In both groups IOP was measured by applanation tonometry (Tono-Pen) before induction of anesthesia. IOP, mean arterial pressure (MAP), heart rate (HR), cardiac index (CI) and central venous pressure (CVP) were also measured 45 min after the beginning of inhalant anesthesia and then every 20 min for 60 min. A one-way repeated measures anova was used to compare data within the same group and Student's t-test was used to assess differences between groups. P < 0.05 was considered statistically significant. Measurements showed normal IOP values in both groups, even though IOP increased significantly from baseline during the use of desflurane. IOP did not differ between groups. CI in the desflurane group was significantly greater than in the sevoflurane group. Sevoflurane and desflurane have no clinically significant effects on IOP, MAP, HR, CI or VCP in the dog.