The influence of body mass and thoracic dimensions on arterial oxygenation in anaesthetized horses and ponies

ObjectiveTo examine the relationship between body mass and thoracic dimensions on arterial oxygen tensions (PaO₂) in anaesthetized horses and ponies positioned in dorsal recumbency.Study designProspective clinical study.AnimalsThirty six client-owned horses and ponies, mean [±SD (range)] age 8.1 ± 4.8 (1.5–20) years and mean body mass 467 ± 115 (203–656) kg.MethodsBefore general anaesthesia, food and water were withheld for 12 and 1 hours respectively. Body mass (kg), height at the withers (H), thoracic circumference (C), thoracic depth (length between dorsal spinous process and sternum; D), thoracic width (between point of shoulders; W), and thoracic diagonal length (point of shoulder to last rib; L) were measured. Pre-anaesthetic medication was with intravenous (IV) romifidine (0.1 mg kg⁻¹). Anaesthesia was induced with an IV ketamine (2.2 mg kg⁻¹) and diazepam (0.05 mg kg⁻¹) combination and maintained with halothane in 1:1 oxygen:nitrous oxide (N₂O) mixture. Animals were positioned in dorsal recumbency and allowed to breathe spontaneously. Nitrous oxide was discontinued after 10 minutes, and arterial blood samples obtained and analysed for gas tensions at 15, 30 and 60 minutes after connection to the anaesthetic breathing circuit. Data were analysed using anova and Pearson's correlation co-efficient.ResultsThe height per unit body mass (H kg⁻¹) and thoracic circumference per unit body mass (C kg⁻¹) correlated strongly (r = 0.85, p < 0.001 and r = 0.82, p < 0.001 respectively) with arterial oxygen tensions (PaO₂) at 15 minutes.ConclusionsThere is a strong positive correlation between H kg⁻¹ and C kg⁻¹ and PaO₂ after 15 minutes of anaesthesia in halothane-anaesthetized horses positioned in dorsal recumbency.Clinical relevanceReadily obtained linear measurements (height and thoracic circumference) and body mass may be used to predict the ability of horses to oxygenate during anaesthesia.     

Assessment of cardiac troponin I and C-reactive protein concentrations associated with anesthetic protocols using sevoflurane or a combination of fentanyl, midazolam, and sevoflurane in dogs

ObjectiveTo report serum cardiac troponin I (cTnI) and C-reactive protein (CRP) concentrations in dogs anesthetized for elective surgery using two anesthetic protocols.Study designProspective, randomized clinical study.AnimalsTwenty client-owned dogs presenting for elective ovariohysterectomy or castration.MethodsThe dogs were randomized into two groups. All dogs were premedicated with glycopyrrolate (0.011 mg kg^?1) and hydromorphone (0.1 mg kg^?1) IM approximately 30 minutes prior to induction of anesthesia. Anesthesia in dogs in group 1 was induced with propofol (6 mg kg^?1) IV to effect and in dogs in group 2 with diazepam (0.2 mg kg^?1) IV followed by etomidate (2 mg kg^?1) IV to effect. For maintenance of anesthesia, group 1 received sevoflurane (adjustable vaporizer setting 0.5–4%) and group 2 received a combination of fentanyl (0.8 μg kg^?1 minute^?1) and midazolam (8.0 μg kg^?1 minute^?1) IV plus sevoflurane (adjustable vaporizer setting 0.5–4%) to maintain anesthesia. Serum cTnI and CRP concentrations were measured at baseline and 6, 18, and 24 hours post-anesthetic induction. Biochemical analysis was performed at baseline. Lactate was obtained at baseline and 6 hours post-anesthetic induction. Heart rate and mean arterial blood pressure were measured intra-operatively.ResultsBaseline serum cTnI and CRP concentrations were comparable between groups. A significant difference in serum cTnI or CRP concentrations was not detected post-operatively between groups at any time point. Serum CRP concentrations were significantly increased post-anesthetic induction in both groups, which was attributed to surgical trauma.Conclusions and clinical relevanceThere was no significant difference in serum cTnI and CRP concentrations between anesthetic protocols. Further investigation in a larger number of dogs is necessary to confirm the current findings.     

Electroencephalographic Responses to a Noxious Surgical Stimulus in Mules,Horses, and Ponies

The aim of this study was to investigate the electroencephalographic (EEG) response of equidae to a castration stimulus. Study 1 included 11 mules (2½–8 years; 230–315 kg) and 11 horses (1½–3½ years; 315–480 kg); study 2 included four ponies (15–17 months; 176–229 kg). They were castrated under halothane anesthesia after acepromazine premedication (IV [study 1] and intramuscular [study 2]) and thiopental anesthetic induction. Animals were castrated using a semiclosed technique (study 1) and a closed technique (study 2). Raw EEG data were analyzed and the EEG variables, median frequency (F50), total power (Ptot), and spectral edge frequency (F95), were derived using standard techniques at skin incision (skin) and emasculation (emasc) time points. Baseline values of F50, Ptot, and F95 for each animal were used to calculate percentage change from baseline at skin incision and emasculation. Differences were observed in Ptot and F50 data between hemispheres in horses but not mules (study 1) and in one pony (study 2). A response to castration (>10% change relative to baseline) was observed in eight horses (73% of animals) and four mules (36% of animals) for F50 and nine horses (82%) and four mules (36%) for Ptot. No changes in F95 data were observed in any animal in study 1. Responses to castration were observed in three ponies (75% of animals) for F50, one pony (25%) for F95, and all ponies for Ptot. Alteration of acepromazine administration and castration technique produced a protocol that identified changes in EEG frequency and power in response to castration.     

Effects of general anesthesia on myoelectric activity of the intestine in horses.

Myoelectric activity was monitored from the terminal ileum, cecum, and colonic pelvic flexure by use of AgpAgCl bipolar electrodes in 4 adult horses before, during, and after general anesthesia. Horses were anesthetized by way of 3 commonly used regimens, including xylazine (1.1 mg/kg of body weight) and ketamine hydrochloride (2.2 mg/kg); thiopental sodium (7.7 mg/kg), followed by halothane vaporized in oxygen; and thiopental sodium (2.5 g) in guaifenesin (100 mg/ml) solution given to effect, followed by halothane in oxygen. All 3 anesthetic regimens decreased intestinal spike-burst activity in the areas monitored. The slowest return to preanesthetic myoelectric activity was observed after xylazine and ketamine administration. After both of the barbiturate/halothane anesthetic regimens, there was a rebound increase in spike-burst frequency, without alteration in the proportion of propagative myoelectric events. All 3 anesthetic regimens appeared to reset the timing of the small and large intestinal migrating myoelectric complexes. By 9 hours after recovery from anesthesia, the effects of anesthesia, irrespective of regimen, had disappeared. Although anesthesia significantly (P less than 0.05) altered intestinal myoelectric activity, no particular anesthetic regimen had a prolonged effect. Results of our study indicate that the particular chosen regimen of general anesthesia is unimportant in development of motility disturbances in horses after anesthesia.     

The effect of general anesthesia and abdominal surgery upon plasma thromboxane B concentrations in horses

OBJECTIVE: To compare the effect of anesthesia alone with anesthesia and abdominal surgery on plasma thromboxane B(2) concentrations in horses. STUDY DESIGN: Non-randomized experimental study. ANIMALS: Six male mixed-bred horses (5-12 years, 350 +/- 18 kg). METHODS: All horses were anesthetized for 2.5 hours using halothane, and a month later abdominal surgery was performed using the same anesthetic technique with a similar duration. The schedule of anesthesia included pre-medication with diazepam (0.1 mg kg(-1) IM), followed by xylazine (2.2 mg kg(-1) IV), and 10 minutes later anesthesia was induced with ketamine hydrochloride (2.2 mg kg(-1) IV). After orotracheal intubation, anesthesia was maintained with halothane. Blood samples for the determination of thromboxane B(2) (TXB(2)) were obtained before, at induction, at 60 minutes after halothane was first inspired, and at recovery from anesthesia as well as at the corresponding stages of the experimental abdominal surgery (before induction, prior to laparotomy, enterectomy, enteroanastomosis, abdominal wall closure). RESULTS: Baseline value for the anesthesia group was 76 +/- 12 pg mL(-1) and increased (p < 0.001) after 1 hour of anesthesia to 265 +/- 40 pg mL(-1). With surgery, the corresponding value was 285 +/- 21 pg mL(-1) (hour 1, p < 0.001) and 210 +/- 28 pg mL(-1) (hour 2, p < 0.001), respectively. These were not different from anesthesia alone. CONCLUSION: The increased concentrations of thromboxane B(2) between 1 and 2.5 hours of halothane anesthesia and during the corresponding stages of the surgical intervention suggested that the anesthetic technique caused a significant increase in thromboxane B(2) and that surgery did not appear to contribute to this response.     

The effect of four anesthetic protocols on splenic size in dogs

Objective To characterize the effects of four anesthetic protocols on the size of the spleen during surgery in dogs. Study design Prospective experimental trial. Animals Twenty‐four beagle dogs, 1.1 ± 0.3 years of age and weighing 10.9 ± 2.7 kg. Methods Dogs were allocated to receive one of four anesthetic protocols: 1 – pre‐medication with acepromazine and butorphanol, induction with thiopental; 2 – pre‐medication with acepromazine and butorphanol, induction with propofol; 3 – pre‐medication with medetomidine and butorphanol, induction with propofol; and 4 – pre‐medication with medetomidine and butorphanol, induction with ketamine and diazepam. Anesthesia was then maintained with halothane. At laparotomy, the spleen length, width, and height were measured, these were measured again just prior to closure of the abdomen. Splenic area and volume were calculated. Hematocrit and total serum protein (TSP) were measured before and after induction and during laparotomy. Results Splenic volume was greatest after protocol 4 (161.2 ± 40.2 cm³; p < 0.05) and was least after protocol 2. The differences in volume were because of differences in length, width, and height between groups. There was no significant change in area, length, or width over the study period. Hematocrit decreased significantly in all dogs but at different times. The decrease occurred after pre‐medication if acepromazine was administered, at induction following protocol 3 and during surgery following protocol 4. Conclusions If splenic volume is to be minimized during surgery, then acepromazine and propofol should be used in the anesthetic protocol. The administration of medetomidine, diazepam, and ketamine will produce a greater splenic volume. Lack of correlation between hematocrit and spleen size following the anesthetic protocols studied suggests sequestration of red blood cells in nonsplenic sites.     

Cardiopulmonary effects of diazepam/ketamine/isoflurane or xylazine/ketamine/isoflurane in foals undergoing abdominal surgery

The purpose of this study was to evaluate the cardiopulmonary effects of anesthetic induction with diazepam/ketamine or xylazine/ketamine with subsequent maintenance of anesthesia using isoflurane in foals undergoing abdominal surgery. Seventeen foals underwent laparotomy at 7–10 days of age and a laparoscopy 7–10 days later. Foals were randomly assigned to receive xylazine (0.8 mg kg^?1)/ketamine (2 mg kg^?1) (X/K)(n = 9) or diazepam (0.2 mg kg^?1)/ketamine (2 mg kg^?1) (D/K)(n = 8) for induction of anesthesia for both procedures. In all foals, anesthesia was maintained with isoflurane in oxygen with the inspired concentration adjusted to achieve adequate depth of anesthesia as assessed by an individual blinded to the treatments. IPPV was employed throughout using a tidal volume of 10 mL kg^?1 adjusting the frequency to maintain eucapnia (PaCO₂ 35–45 mm Hg, 4.7–6.0 kPa). Cardiopulmonary variables were measured after induction of anesthesia prior to, during, and following surgery. To compare the measured cardiopulmonary variables between the two anesthetic regimes for both surgical procedures, results were analyzed using a three‐way factorial anova for repeated measures (p < 0.05). During anesthesia for laparotomy, mean CI and MAP ranged from 110 to 180 mL kg^?1 minute^?1 and 57–81 mm Hg, respectively, in the D/K foals and 98–171 mL kg^?1 minute^?1 and 50–66 mm Hg in the X/K foals. Overall, CI, HR, SAP, DAP, and MAP were significantly higher in foals in the D/K group versus the X/K group during this anesthetic period. During anesthesia for laparoscopy, mean CI and MBP ranged from 85 to 165 mL kg^?1 minute^?1 and 67–83 mm Hg, respectively, in the D/K group, and 98–171 mL kg^?1 minute^?1 and 48–67 mm Hg in the X/K group. Only HR, SAP, DAP, and MAP were significantly higher in the D/K group versus X/K group during this latter anesthetic period. There were no significant differences between groups during either surgical procedure for end‐tidal isoflurane, PaO₂, PaCO₂, or pH. In conclusion, anesthesia of foals for laparotomy and laparoscopy with diazepam/ketamine/isoflurane is associated with less hemodynamic depression than with xylazine/ketamine/isoflurane.     

Anesthetic, cardiorespiratory, and metabolic effects of four intravenous anesthetic regimens induced in horses immediately after maximal exercise

OBJECTIVE: To determine the anesthetic, cardiorespiratory, and metabolic effects of 4 IV anesthetic regimens in Thoroughbred horses recuperating from a brief period of maximal exercise. ANIMALS: 6 adult Thoroughbreds. PROCEDURE: Horses were preconditioned by exercising them on a treadmill. Each horse ran 4 simulated races, with a minimum of 14 days between races. Races were run at a treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until fatigued or for a maximum of 2 minutes. Two minutes after exercise, horses received a combination of xylazine hydrochloride (2.2 mg/kg of body weight) and acepromazine maleate (0.04 mg/kg) IV. Five minutes after exercise, horses received 1 of the following 4 IV anesthetic regimens: ketamine hydrochloride (2.2 mg/kg); ketamine (2.2 mg/kg) and diazepam (0.1 mg/kg); tiletamine hydrochloride-zolazepam hydrochloride (1 mg/kg); and guaifenesin (50 mg/kg) and thiopental sodium (5 mg/kg). Treatments were randomized. Cardiopulmonary indices were measured, and samples of blood were collected before and at specific times for 90 minutes after each race. RESULTS: Each regimen induced lateral recumbency. The quality of induction and anesthesia after ketamine administration was significantly worse than after other regimens, and the duration of anesthesia was significantly shorter. Time to lateral recumbency was significantly longer after ketamine or guaifenesin-thiopental administration than after ketaminediazepam or tilet-amine-zolazepam administration. Arterial blood pressures after guaifenesin-thiopental administration were significantly lower than after the other regimens. CONCLUSIONS AND CLINICAL RELEVANCE: Anesthesia can be safely induced in sedated horses immediately after maximal exercise. Ketamine-diazepam and tilet-amine-zolazepam induced good quality anesthesia with acceptable perturbations in cardiopulmonary and metabolic indices. Ketamine alone and guaifenesin-thiopental regimens are not recommended.     

Blood pressure and electrocardiographic effects of acepromazine in anaesthetized horses

Acepromazine, a phenothiazine tranquilizer, causes hypotension in standing horses ( Parry et al. 1982 ). However, a retrospective study ( Taylor & Young 1993 ) showed that acepromazine pre‐anesthetic medication did not affect arterial blood pressure (MAP) in anaesthetized horses. This study examined the effects of acepromazine on MAP during romifidine–ketamine–halothane anaesthesia in horses anaesthetized for various surgical procedures. Forty‐four horses were allocated by block randomization to groups A and B. Group A received acepromazine 0.05 mg kg^?1 IM 30 minutes before induction of anaesthesia, group B did not. All horses received romifidine 0.1 mg kg^?1 IV 5 minutes before anaesthesia was induced with diazepam 0.05 mg kg^?1 and 2.2 mg kg^?1 ketamine IV. The horses' trachea were intubated and horses breathed 50% oxygen and 50% nitrous oxide plus halothane (concentration adjusted as required clinically) from a circle breathing system. Nitrous oxide was discontinued after 10 minutes and analgesics, flunixin 1.1 mg kg^?1 and either morphine 0.1 mg kg^?1 or butorphanol 0.05 mg kg^?1 (matched for horses undergoing the same procedure) administered IV. The facial or dorsal metatarsal artery was catheterized for direct measurement of MAP (every 10 min) and withdrawal of blood for gas analysis (every 30 min). The electrocardiogram (ECG) was monitored continuously with a 10 seconds printout obtained every 10 minutes. Intermittent positive pressure ventilation (IPPV) was instigated if PaCO₂ exceeded 9.3 kPa (70 mm Hg). Dobutamine was infused (1.0–5.0 kg^?1minute^?1) if MAP < 58 mm Hg and was continued until MAP > 70 mm Hg. Mean age, weight and duration of anaesthesia were compared between the groups using a t‐test for independent samples. Gender distribution and numbers of horses requiring IPPV or dobutamine were compared between groups using a chi‐squared test (with Yates correction). To compare MAP over time, the area under the curve (MAPAUC) was calculated and compared between groups using a t‐test. Horses receiving dobutamine were excluded from MAPAUC and MAP comparisons. The ECG printouts were examined for arrhythmias. There were no significant differences between groups (p > 0.05). Group A contained three stallions, 10 geldings and nine mares, aged 6.3 years (range 0.75–18). Group B comprised eight stallions, 11 geldings and three mares aged 7.3(1–16) years. Duration of anaesthesia was group A 97 (50–140) minutes, group B 99 (50–160) minutes. Eight horses in group A and three in group B required IPPV. Nine horses in group A and four in group B received dobutamine. Mean arterial pressure ranged from 60 to 128 mm Hg in group A and 58–96 mm Hg in group B. Mean MAPAUC was 5941 mm Hg minute^?1 in group A, in B 6000 mm Hg minute^?1. Atrial pre‐mature complexes were recorded from one horse in group B. No other arrhythmias were detected. Although MAP was lower in the acepromazine group, this appeared unlikely to cause a clinical problem. The incidence of arrhythmias was too low to determine the influence of acepromazine in this study.     

The effects of lactated Ringer's solution (LRS) or LRS and 6% hetastarch on the colloid osmotic pressure, total protein and osmolality in healthy horses under general anesthesia

ObjectiveTo investigate changes in colloid osmotic pressure (COP), total protein (TP) and osmolality (OSM) during anesthesia in horses given intravenous lactated Ringer’s solution (LRS) or LRS and hetastarch (HES).Study designProspective, clinical trial.AnimalsFourteen horses presented for surgery. Mean age 8.3 ± 1.9 years; mean weight 452 ± 25 kg.MethodsHorses were premedicated with xylazine intravenously (IV); anesthesia was induced with ketamine and diazepam IV, and maintained with sevoflurane. Butorphanol was administered IV with pre-medications or immediately after induction. Xylazine was administered IV for recovery if necessary. LRS was administered IV to all horses with a target rate of 5–10 mL kg^?1 hour^?1. Half of the horses also received 6% HES, 2.5 mL kg^?1 over 1 hour in addition to LRS. Horses that received LRS only were considered the LRS group. Horses that received both LRS and HES were considered the LRS/HES group. Blood was drawn pre- and post-anesthesia, immediately following induction, and every 30 minutes throughout anesthesia. COP, TP and OSM were measured.ResultsCOP and TP significantly decreased at similar rates for both treatment groups from pre-anesthetic values. Pre-anesthetic COP was significantly greater in the LRS group when compared to the LRS/HES group pre-, post- and throughout anesthesia. In the LRS group post-anesthetic OSM was significantly different than the pre-anesthesia value and that for the LRS/HES group.Conclusions and clinical relevanceAdministration of IV HES (2.5 mL kg^?1, over 1 hour) in combination with LRS does not attenuate the decrease in COP typically seen during anesthesia with crystalloid administration alone. Based on these results, administration of HES at this rate and total volume would not be expected to prevent fluid shifts into the interstitium through its effects on COP.     

β-endorphin immunoreactivity during anaesthesia in equidae

Objective To determine the effects of surgery, hypoxia, hypercapnia and flunixin administration on plasma β‐endorphin immunoreactivity (BEI) in anaesthetized horses. Study design Prospective crossover study. Animals Six healthy adult Welsh Mountain ponies and seven healthy adult Thoroughbreds. Methods Ponies were anaesthetized with thiopentone and halothane or with pentobarbitone and the horses with guaiphenesin, thiopentone and halothane. Ponies were anaesthetized for 2 hours and on separate occasions underwent a period of hypoxia, hypercapnia, anaesthesia only, or were given flunixin at induction. The horses were anaesthetized for 2 hours and on separate occasions underwent surgery to relocate one carotid artery subcutaneously or anaesthesia only. Plasma samples were taken pre‐anaesthesia, at 20 minute intervals during, and after anaesthesia for BEI assay using radio‐immunoassay. Analysis of variance of the concentration‐time curve was used for statistical analysis. Results Pre‐anaesthetic β‐endorphin immunoreactivity (BEI) values ranged between 5.7 and 20.4 pmol L^?1. Induction of anaesthesia caused a five to 10 fold increase in mean plasma BEI in all cases except the hypercapnia group. Halothane anaesthesia increased BEI in ponies and horses but there were no significant changes during pentobarbitone anaesthesia. The increase in BEI in the hypoxic group was greater (peak value 136.8 ± 32.2 pmol L^?1) and sustained for a longer period compared with levels in those given halothane alone or in those which became hypercapnic. There was marked individual variation in the flunixin group and changes were not significant. Surgery in the horses resulted in the highest peak values in the study (182.5 ± 153.0 pmol L^?1) but the AUC was not significantly higher than in the same animals without surgery, where the peak value was 102.9 ± 42.1 pmol L^?1. Conclusions Beta‐endorphin appeared to be a sensitive marker of an endocrine stress response but its physiological role during equine anaesthesia is unknown. Clinical relevance Unknown.     

Evaluation of analgesic and physiologic effects of epidural morphine administered at a thoracic or lumbar level in dogs undergoing thoracotomy

ObjectiveTo evaluate the analgesic and physiological effects of epidural morphine administered at the sixth and seventh lumbar or the fifth and sixth thoracic vertebrae in dogs undergoing thoracotomy.Study designProspective, randomized, blinded trial.AnimalsFourteen mixed-breed dogs, weighing 8.6 ± 1.4 kg.MethodsThe animals received acepromazine (0.1 mg kg^?1) IM and anesthesia was induced with propofol (4 mg kg^?1) IV. The lumbosacral space was punctured and an epidural catheter was inserted up to the region between the sixth and seventh lumbar vertebrae (L, n = 6) or up to the fifth or sixth intercostal space (T, n = 8). The dogs were allowed to recover and after radiographic confirmation of correct catheter position, anesthesia was reinduced with propofol IV and maintained with 1.7% isoflurane. Following stabilization of monitored parameters, animals received morphine (0.1 mg kg^?1) diluted in 0.9% NaCl to a final volume of 0.25 mL kg^?1 via the epidural catheter, and after 40 minutes, thoracotomy was initiated. Heart rate and rhythm, systolic, mean and diastolic arterial pressures, respiratory rate, arterial hemoglobin oxygen saturation, partial pressure of expired CO₂ and body temperature were measured immediately before the epidural administration of morphine (0 minute) and every 10 minutes during the anesthetic period. The Melbourne pain scale and the visual analog scale were used to assess post-operative pain. The evaluation began 3 hours after the epidural administration of morphine and occurred each hour until rescue analgesia.ResultsThere were no important variations in the physiological parameters during the anesthetic period. The post-operative analgesic period differed between the groups, being longer in T (9.9 ± 1.6 hours) compared with L (5.8 ± 0.8 hours).ConclusionsThe use of morphine, at a volume of 0.25 mL kg^?1, administered epidurally over the thoracic vertebrae provided longer lasting analgesia than when deposited over the lumbar vertebrae.Clinical relevanceThe deposition of epidural morphine provided longer lasting analgesia when administered near to the innervation of the injured tissue without increasing side effects.     

Glomerular filtration rate after tramadol, parecoxib and pindolol following anaesthesia and analgesia in comparison with morphine in dogs

ObjectiveTo compare the effects of morphine, parecoxib, tramadol and a combination of parecoxib, tramadol and pindolol on nociceptive thresholds in awake animals and their effect on glomerular filtration rate (GFR) in dogs subjected to 30 minutes of anesthesia.AnimalsEight adult mixed breed experimental dogs.Study designRandomized, controlled trial.MethodsDogs received 0.05 mg kg^?1 acepromazine subcutaneously (SC) as anaesthetic pre-medication. Thirty to sixty minutes later, they received either tramadol 3 mg kg^?1 intravenously, (IV), parecoxib (1 mg kg^?1 IV), a combination of tramadol 3 mg kg^?1 (IV), parecoxib 1 mg kg^?1 (IV) and pindolol 5 μg kg^?1 (SC), morphine (0.1 mg kg^?1 (IV) or 0.9% saline (2 mL). Anaesthesia was then induced with IV propofol to effect (2.9 ± 0.8 mg kg^?1) and maintained with halothane in oxygen for 30 minutes. Systolic arterial blood pressure was maintained above 90 mmHg with IV fluids and by adjusting the inspired halothane concentration. Post-treatment nociceptive thresholds to mechanical stimuli, expressed as percent of pre-treatment values, were compared between the treatments to assess the analgesic efficacy of the drugs. Plasma iohexol clearance (ICL), a measure of GFR, was estimated both before and 24 hours after induction of anaesthesia to study the drugs’ effects on renal perfusion. Nociceptive threshold and GFR data were compared using mixed model analysis in sas^®9.1.ResultsBoth tramadol and parecoxib produced similar analgesia, which was less than that of morphine. Their combination with pindolol produced analgesia comparable with morphine. None of the test drugs, either alone or in combination, reduced GFR.ConclusionTramadol and parecoxib (either alone or in combination) can increase nociceptive thresholds in awake dogs and have minimal effects on renal perfusion in normotensive dogs subjected to anaesthesia.     

Recovery of horses from general anesthesia in a darkened or illuminated recovery stall

ObjectiveTo assess whether recovery from general anesthesia, in an illuminated or a darkened stall, has an effect on time to first movement, time to standing, and recovery score.Study designProspective randomized clinical study.AnimalsTwenty-nine healthy, 2- to 5-year-old horses undergoing surgical correction of dorsal displacement of the soft palate.MethodsEach horse was assigned randomly to recover in either an illuminated (n = 15) or a darkened stall (n = 14). For pre-anesthetic medication, all horses received intravenous (IV) xylazine (0.4 mg kg⁻¹) and butorphanol (0.02 mg kg⁻¹). Anesthesia was induced with midazolam (0.1 mg kg⁻¹) and ketamine (2.2 mg kg⁻¹) IV and maintained on isoflurane in oxygen. Vital parameters, end-tidal CO₂ and isoflurane were recorded at 5-minute intervals. At the conclusion of anesthesia, horses were placed in either an illuminated or a darkened stall and xylazine (0.2 mg kg⁻¹) IV was administered at extubation. Video cameras were used to record the horses while they were allowed to recover undisturbed. Video recordings were later viewed and recoveries were evaluated on a 100-point scale by three graders.ResultsHorses in illuminated and darkened recovery stalls were evaluated on total anesthesia time, minimum alveolar concentration hours of isoflurane, time to first movement, time to standing, and total recovery score. There were no significant differences between the two groups in any of the measured parameters.ConclusionRecovering horses in a darkened versus an illuminated recovery stall may provide no benefit.Clinical relevanceDarkening the recovery stalls for horses recovering from general anesthesia may be unnecessary.     

Effects of pre‐operative administration of medetomidine on plasma insulin and glucose concentrations in healthy dogs and dogs with insulinoma

ObjectiveTo investigate the effect of medetomidine on plasma glucose and insulin concentrations in dogs with insulinoma and in healthy dogs undergoing anesthesia and surgery.AnimalsTwenty–five dogs with insulinoma and 26 healthy dogs.MethodsIn dogs with insulinoma, medetomidine (5 μg kg^?1) was randomly included (n = 12) or omitted (n = 13) from the pre–anesthetic medication protocol, which typically contained an opioid and an anticholinergic. Healthy dogs received medetomidine (5 μg kg^?1; n = 13) or acepromazine (0.04 mg kg^?1; n = 13) plus an opioid (morphine 0.5 mg kg^?1) and an anticholinergic (atropine 0.04 mg kg^?1) as pre–anesthetic medications. Pre–anesthetic medications were given intramuscularly. Plasma glucose and insulin concentrations were measured before (sample 1) and 30 minutes after pre–anesthetic medication (sample 2), and at the end of surgery in dogs with insulinoma or at 2 hours of anesthesia in healthy dogs (sample 3). Glucose requirement to maintain intra–operative normoglycemia in dogs with insulinoma was quantified and compared. Data were analyzed with anova and Bonferroni post–test, t–tests or chi–square tests as appropriate with p < 0.05 considered significant. Data are shown as mean ± SD.ResultsMedetomidine significantly decreased plasma insulin concentrations and increased plasma glucose concentrations in healthy dogs and those with insulinoma. These variables did not change significantly in the dogs not receiving medetomidine. In the dogs with insulinoma, intra–operative glucose administration rate was significantly less in the animals that received medetomidine compared to those that did not.ConclusionsPre–anesthetic administration of medetomidine significantly suppressed insulin secretion and increased plasma glucose concentration in dogs with insulinoma and in healthy dogs undergoing anesthesia and surgery.Clinical relevanceThese findings support the judicious use of medetomidine at low doses as an adjunct to the anesthetic management of dogs with insulinoma.     

Comparison of tramadol and morphine for pre-medication of dogs undergoing general anesthesia for orthopedic surgery

Tramadol is a centrally acting analgesic with opioid and monoaminergic actions. Its clinical effects have been well characterized in humans, where it has been in use for many years, but little is known for veterinary species. This study evaluated the sedative, emetic, thiopental‐sparing and intraoperative respiratory and hemodynamic effects of tramadol in comparison to morphine for pre‐medication of dogs undergoing orthopedic surgery under halothane anesthesia. Sixteen adult, healthy, mixed breed dogs (8.0 ± 2.6 kg) were studied. Eight dogs were pre‐medicated with tramadol (1.0 mg kg^‐1 IM) and the other eight with morphine (1.0 mg kg^–1 IM). After 20 minutes, anesthesia was induced with thiopental and subsequently maintained with halothane in oxygen using a Bain system, with spontaneous respiration. Degree of sedation and occurrence of emesis were evaluated after pre‐anesthetic medication. Dose of thiopental necessary for tracheal intubation was compared between the two groups. Arterial blood gas analyzes were done before pre‐medication and at 60 minutes of anesthesia. Heart rate and noninvasive arterial blood pressure were recorded before pre‐medication and every 10 minutes during anesthesia. Observer was blinded of the treatment given for each dog. Tramadol produced no visible sedation and no vomiting, while morphine induced a moderate degree of sedation in all dogs and vomiting in 62% of them. Dogs pre‐medicated with tramadol required significantly more thiopental (17 ± 3.8 mg kg^–1) for induction of anesthesia than those pre‐medicated with morphine (12 ± 1.8 mg kg^–1). Pre‐medication with morphine was associated with significantly higher PaCO₂ and lower pH at 60 minutes of anesthesia. The remaining respiratory parameters and the hemodynamic variables were similar between the two groups. In conclusion, dogs pre‐medicated with tramadol at 1 mg kg^–1 IM do not become visibly sedated and require a greater amount of thiopental for induction of anesthesia than pre‐medication with morphine. As intraoperative respiratory function is better preserved with tramadol, it may be useful for pre‐medication of respiratory compromised patients.     

Metabolic acidosis in healthy mules under general anaesthesia with halothane

ObjectiveTo report the severe metabolic acidosis identified in a group of 11 healthy mules anaesthetized with halothane for castration.Study designData generated from a prospective study.AnimalsEleven mules aged 2.5–8 years, weighing 230–315 kg and 11 horses aged 1.5–3.5 years, weighing 315–480 kg.MethodsAnimals were anaesthetized for castration as part of an electroencephalographic study. Preanaesthetic medication was acepromazine (0.03 mg kg^?1) administered through a preplaced jugular venous catheter. Anaesthesia was induced 30–90 minutes later with intravenous thiopental (10 mg kg^?1). After orotracheal intubation, anaesthesia was maintained with halothane vaporised in oxygen. The animals’ lungs were ventilated to maintain the end-tidal CO₂ concentration between 3.9 and 4.5 kPa (29–34 mmHg). Anaesthetic monitoring included invasive blood pressure measurement via the auricular artery (mules) and submandibular branch of the facial artery (horses). Arterial blood gas samples were drawn from these catheters at three time points during surgery and pH, PaCO₂, base excess (ecf) and HCO₃^? were measured. Values were compared between groups using a Mann–Whitney test. p was taken as <0.05. Results are reported as median (range).ResultsPaCO₂ did not differ between groups but pH was significantly lower in mules [7.178 (7.00–7.29)] compared to horses [7.367 (7.24–7.43)] (p = 0.0002). HCO₃^? values were significantly lower in the mules [16.6 (13.0–22.3) mM] compared to horses [23.7 (20.9–23.7) mM] (p = 0.0001), whilst base excess (ecf) was significantly more negative in the mules [?11.4 (?1.27 to ?16) mM] compared to horses [?1.3 (?5.8 to +2.4) mM] (p = 0.0004).Conclusion and clinical relevanceThis study demonstrated severe metabolic acidosis in healthy mules, which may have prompted intervention with drug therapies in a clinical arena. It is probable that the acidosis existed prior to anaesthesia and caused by diet, but other possible causes are considered.     

Observations of the potency and duration of vecuronium in isoflurane-anesthetized horses

ObjectiveTo evaluate the potency and duration of three subparalyzing doses of vecuronium (VEC) in isoflurane-anesthetized horses.Study designProspective experimental study.AnimalsThirteen healthy adult horses undergoing arthroscopic surgery.MethodsDuring isoflurane anesthesia, horses received one of three doses of vecuronium (25, 50, or 100 μg kg^?1). Neuromuscular transmission was monitored with acceleromyography (AMG) with train-of-four (TOF) stimulation of the radial nerve. Maximal depression of the first twitch (T1), and onset time were recorded for each dose. Recovery time to a TOF ratio >90% was also evaluated.ResultsVecuronium 25 μg kg^?1 produced no observable T1 depression in four horses. VEC 50 μg kg^?1 (n = 5) produced a maximal T1 depression of [median (min, max)] 41 (20, 71) % in four horses, and no neuromuscular block was seen in the fifth. VEC 100 μg kg^?1 was given to four horses and produced a T1 depression of 73 (64, 78) %. Of the four horses in which VEC 50 μg kg^?1 produced a measurable neuromuscular block, three recovered spontaneously 43 (40, 52) minutes after VEC administration; a fourth subject received edrophonium to reverse residual block at the end of the surgery. Spontaneous recovery after VEC 100 μg kg^?1 occurred by 112 minutes in one horse, and had to be facilitated by edrophonium in the remaining three horses, more than 2 hours after VEC had been given.Conclusions and clinical relevanceA dose of 100 μg kg^?1 VEC in isoflurane anesthetized horses failed to produce complete paralysis. The partial neuromuscular block lasted at least 2 hours after this dose had been administered. Edrophonium was required to reverse the neuromuscular block in three of four horses. It is likely that more than 100 μg kg^?1 VEC would be necessary for complete neuromuscular blockade in horses, and that this dose will last >2 hours.     

The effect of volatile anaesthetics on the relative sensitivity of facial and distal thoracic limb muscles to vecuronium in dogs

ObjectiveTo compare n. facialis-m. nasolabialis (nF-mNL) and n. ulnar-mm. carpi flexorii (nU-mCF) sensitivity to vecuronium during halothane or isoflurane anaesthesia.Study designRandomized, prospective, experimental study.AnimalsForty-four client-owned dogs (19 male, 25 female) undergoing surgery; mean age: 5.0 years; mean body mass: 24.7 kg.MethodsThirty minutes after acepromazine (0.05 mg kg^?1) and morphine (0.5 mg kg^?1), anaesthesia was induced with intravenous (IV) thiopental and maintained with either halothane (n = 22) or isoflurane (randomly allocated) in oxygen. The lungs were mechanically ventilated and end-tidal inhaled anaesthetic (Fe’_IAA) maintained at 1.2 × MAC values. Neuromuscular transmission at nF-uNL and nU-mCF was monitored using the train of four count. Vecuronium (50 μg kg^?1 IV) was injected (t = 0) after 15 trains, 50-60 minutes after inhalational anaesthesia began, when Fe’_IAA had been constant for >15 minutes. Times of the disappearance (-) and reappearance (+) of the fourth (T4) and first twitch (T1) were recorded allowing the calculation of: latent (t = 0 to T4-) and manifest onset times (t = 0 to T1-) duration of blockade (T1- to T1+) and drug effect (T4- to T4+) and recovery time (T1+-T4+). Student’s paired t-test was used to compare simultaneous responses at nF-uNL and nU-mCF. An unpaired t-test was used to compare anaesthetic effects.ResultsLatent and manifest onset times were significantly (p < 0.05) briefer, blockade and drug effects were significantly longer and recovery from blockade were significantly slower in the nF-mNL unit in both halothane and isoflurane recipients. Profound block duration and drug action were significantly longer and recovery from blockade were significantly slower in halothane recipients at both nerve-muscle units.Conclusion and clinical relevanceThe nF-mNL was more sensitive than nU-mCF to vecuronium, particularly in halothane-anaesthetized dogs.