Effect of rate of administration of propofol or alfaxalone on induction dose requirements and occurrence of apnea in dogs

OBJECTIVE

To evaluate the effect of rate of administration of propofol or alfaxalone on induction dose requirements and incidence of postinduction apnea (PIA) in dogs following premedication with methadone and dexmedetomidine.

STUDY DESIGN

Prospective, randomized clinical trial.

ANIMALS

Thirty-two healthy American Society of Anesthesiologists class I client-owned dogs (seven females, 25 males), aged between 5 and 54 months, weighing between 2.0 and 48.2 kg.

METHODS

Dogs were premedicated intramuscularly with 0.5 mg kg^-1 methadone and 5 μg kg^-1 dexmedetomidine. Thirty minutes after premedication, dogs were preoxygenated for 5 minutes before the induction agent was administered intravenously via a syringe driver until orotracheal intubation was achieved. Dogs were randomized to receive alfaxalone 0.5 mg kg^-1 minute^-1 (A-Slow), alfaxalone 2 mg kg^-1 minute^-1 (A-Fast), propofol 1 mg kg^-1 minute^-1 (P-Slow), or propofol 4 mg kg^-1 minute^-1 (P-Fast). Oxygen saturation of hemoglobin (SpO₂), end-tidal carbon dioxide and respiratory rate were monitored. If PIA (≥30 seconds without a breath) occurred, the time to the first spontaneous breath was measured. If SpO₂ decreased below 90%, the experiment was stopped and manual ventilation initiated.

RESULTS

The mean±standard deviation induction doses of alfaxalone and propofol were lower in the A-Slow [A-Slow 0.9±0.3 mg kg^-1, A-Fast 2.2±0.5 mg kg^-1 (p≤0.001)] and P-Slow [P-Slow 1.8±0.6 mg kg^-1, P-Fast 4.1±0.7 mg kg^-1 (p≤0.001)] groups, respectively. The incidence of PIA was 25% for the A-Slow and P-Slow groups and 100% for the A-Fast and P-Fast groups (p = 0.007).

CONCLUSIONS AND CLINICAL RELEVANCE

Both propofol and alfaxalone following methadone and dexmedetomidine premedication caused PIA. Induction dose requirement and incidence of PIA were affected by the rate of administration of both drugs. When possible, propofol and alfaxalone doses should be reduced and administered slowly to reduce PIA.

[Clinical usability and practicability of Alfaxalone for short-term anaesthesia in the cat after premedication with Buprenorphine]

Objective of this clinical study was to assess the anaesthetic quality (induction and recovery) and utility of short term alfaxalone anaesthesia in healthy and diseased cats. Cardiopulmonary effects and the influence on haematological and biochemical blood parameters were evaluated.

MATERIAL AND METHODS

Twenty feline patients (ASA1-4) were anaesthetized with alfaxalone for various short surgical or diagnostic procedures. Heart rate, breathing rate, end-tidal CO2 partial pressure, arterial oxygen saturation, mean arterial blood pressure and the body temperature were measured and recorded every 10 minutes. Before, after and 6 hours after anaesthesia venous blood samples were taken and haematologic and blood chemistry parameters were determined. Recovery time and quality were assessed by a numerical rating scale.

RESULTS

Anaesthetic induction was rapid and smooth in all cats. Spontaneous respiration was maintained in all cats. Cardiopulmonary parameters mostly remained within a clinically tolerable range. Noticeable was a high heart rate (mean >190 bpm) at the beginning of anaesthesia lasting up to 10 minutes. Statistically significant changes (p<0.05) occurred in some haematologic parameters (RBC, haemoglobin, haematocrit and MCV decreased), electrolytes and venous acid-base-status (bicarbonate, chloride and base excess increased, sodium and potassium decreased) and blood chemistry parameters (alanine aminotransferase, glutamate dehydrogenase and creatinine decreased). None of these changes appeared to have clinical relevance. Recovery was smooth in the majority of cats. Mild signs of hyperexcitability (muscle tremor, short term opisthotonus and hyperacusis) occurred in individual animals. The duration of recovery varied between 21 and 93 minutes.

CONCLUSION AND CLINICAL RELEVANCE

Alfaxalone by repeated intravenous injection is suitable for short-term diagnostic and surgical procedures in cats. Because of its minor cardiovascular effects and slight respiratory depression, it is also well tolerated by patients with increased anaesthetic risk (ASA 3 and 4).

Efficacy of preanesthetic intramuscular administration of ephedrine for prevention of anesthesia-induced hypotension in cats and dogs

To determine if the preanesthetic administration of ephedrine would prevent anesthesia-induced hypotension in dogs and cats, 10 cats were anesthetized with acepromazine, butorphanol, ketamine, and isoflurane, and 8 dogs were anesthetized with acepromazine, morphine, propofol, and halothane. Cats received ephedrine or saline 10 minutes after premedication. Dogs received ephedrine or saline at the time of premedication. Systolic arterial blood pressure, respiratory rate, heart rate, end-tidal CO2, O2 saturation, cardiac rhythm, and rectal temperature were recorded.The systolic arterial pressure in cats receiving saline was significantly lower than baseline at 10 minutes after premedication, and systolic arterial pressure was < 80 mmHg for the duration of anesthesia. In cats receiving ephedrine, the systolic arterial pressure was significantly lower than baseline for the duration of anesthesia, but systolic arterial pressure was not < 80 mmHg until 25 min after induction. In dogs, systolic arterial pressure was significantly lower than baseline by 5 and 40 min after pre-medication in dogs receiving saline and ephedrine, respectively. There was no difference in heart rate, respiratory rate, end-tidal CO2, rectal temperature, O2 saturation, or cardiac rhythm among treatment groups. Prophylactic ephedrine delayed, but did not prevent, the onset of hypotension.

Comparison between analgesic effects of buprenorphine, carprofen, and buprenorphine with carprofen for canine ovariohysterectomy

OBJECTIVE

To compare the analgesic effects of buprenorphine, carprofen, and their combination in dogs undergoing ovariohysterectomy.

STUDY DESIGN

Prospective, randomized blinded clinical study.

ANIMALS

60 dogs.

METHODS

Treatments were buprenorphine 0.02 mg kg(-1), intramuscularly (IM) (group B); carprofen 4 mg kg(-1), subcutaneously (SC) (group C); or a combination of both (group CB). Anesthesia was induced with propofol and maintained with isoflurane. A Dynamic Interactive Visual Analog Scale (DIVAS, 0-100 mm) and the Glasgow Composite Pain Scale (GCMPS, 0-24) were used to evaluate comfort and sedation at baseline, 2, 4, 6, and 24 hours after extubation. Rescue analgesia was provided with buprenorphine (0.02 mg kg(-1)). Wound swelling measurements (WM) and a visual inflammation score (VIS) of the incision were made after surgery and 2, 4, 6, and 24 hours later. p < 0.05 was considered significant.

RESULTS

Group C required more propofol (5.0 +/- 1.4 mg kg(-1)) compared with B (3.3 +/- 1.1 mg kg(-1)) and CB (3.2 +/- 0.7 mg kg(-1)); respectively, p = 0.0002 and 0.0001. Rescue analgesia was required in nine dogs. B had a higher GCMPS and DIVAS III score at 6 hours (2.6 +/- 2.5) and (23 +/- 22.5 mm) compared with C (1.0 +/- 1.3, 6 +/- 7.3 mm) and CB (1.5 +/- 1.4, 8 +/- 10.7 mm); respectively, p = 0.02 and 0.006. Group C had a lower sedation score at 2 hours (43 +/- 23.6 mm) compared with B (68 +/- 32.1 mm) and BC (69 +/- 22.1 mm); respectively, p = 0.03 and 0.004. Group B had a higher WM score at 2 hours (3 +/- 0.8 mm) compared with C (2 +/- 0.6 mm) p = 0.01 and at 6 hours (3 +/- 1 mm) compared with C (2 +/- 0.8 mm) and CB (2 +/- 0.8 mm); respectively, p = 0.01 and 0.008. VIS was not different between groups.

CONCLUSION AND CLINICAL RELEVANCE

All treatments provided satisfactory analgesia for the first 6 hours and at 24 hours. C and CB pain score and WS were superior to B at 6 hours. No superior analgesic effect was noted when the drugs were combined.

Effects of premedication with fentanyl and midazolam on mask induction of anaesthesia of dogs with sevoflurane

Fourteen beagles were used to determine the effects of fentanyl and midazolam as a premedicant for mask induction of anaesthesia with sevoflurane. The drugs were administered to each dog in a randomised cross-over design with a seven-day washout period between experiments. After a 15-minute equilibration period, a treatment consisting of fentanyl (10 mug/kg bodyweight) and midazolam (0.2 mg/kg) was given either intravenously or intramuscularly. Anaesthesia was then induced by the use of a facemask with sevoflurane in 100 per cent oxygen at a flow rate of 4 l/minute. Vaporiser settings were increased by 0.8 per cent at 15-second intervals until the value corresponding to 4.8 per cent sevoflurane was achieved. The time to the onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation and cardiopulmonary variables were measured. Both the treatments with tentanyl and midazolam resulted in a shorter and smoother induction of anaesthesia than treatment with saline, and the cardiopulmonary changes were smaller and milder.

Total intravenous anaesthesia with propofol or propofol/ketamine in spontaneously breathing dogs premedicated with medetomidine

The cardiorespiratory parameters, the depth of anaesthesia and the quality of recovery were evaluated in six spontaneously breathing dogs that had been premedicated with medetomidine (40 microg/kg, supplemented with 20 microg/kg an hour later), administered with either propofol (1 mg/kg followed by 0.15 mg/kg/minute, intravenously), or with ketamine (1 mg/kg followed by 2 mg/kg/hour, intravenously) and propofol (0.5 mg/kg followed by 0.075 mg/kg/minute, intravenously). The dogs' heart rate and mean arterial blood pressure were higher and their minute volume of respiration and temperature were lower when they were anaesthetised with propofol plus ketamine, and a progressive hypercapnia leading to respiratory acidosis was more pronounced. When the dogs were anaesthetised with propofol/ketamine they recovered more quickly, but suffered some unwanted side effects. When the dogs were anaesthetised with propofol alone they recovered more slowly but uneventfully.

The effects of two dosages of midazolam on short-duration anesthesia in the harp seal (Phoca groenlandica)

The purpose of this study was to provide safe anesthesia for bronchoalveolar lavage and assess the utility of premedication with i.m. midazolam for short-duration anesthesia with isoflurane in harp seals (Phoca groenlandica). Fourteen yearling harp seal pups were anesthetized three times each as part of a prospective, cross-over, blinded study. Each animal received i.m. premedication with saline, low-dose, or high-dose midazolam (respectively 0.1 and 0.2 mg/ kg). Following premedication, anesthesia was induced with 4% isoflurane in oxygen delivered through a mask and connected to a Bain non-rebreathing system. A significantly longer time was taken from the end of general anesthesia to head movement in the high-dose group compared with the saline group (P = 0.002). A significantly longer time was taken from the end of general anesthesia to ambulation in the high-dose group compared with the saline group (P = 0.006). There were no significant differences between groups in the subjective assessment of anesthetic quality or ease of intubation. Premedication with i.m. midazolam at the dosages used did prolong recovery from anesthesia, although to a degree unlikely to be significant clinically.

Effect of 1- and 10-day administration of tepoxalin on minimum alveolar concentration of isoflurane and sevoflurane in dogs

Analgesics given preoperatively have the potential to decrease the amount of inhalant anesthetics required intraoperatively (i.e., to decrease the minimum alveolar concentration, or MAC, for the inhalant). Tepoxalin is an NSAID approved for the treatment of arthritis in dogs in the United States and, hence, could be administered to patients undergoing anesthesia. In this study, administration of a single dose or a 10-day course of tepoxalin did not affect the MAC for isoflurane or sevoflurane.

Effect of preoperative administration of tepoxalin on induction dose of injectable anesthetics in dogs

Medications given preoperatively have the potential to affect the induction dose of injectable anesthetics, which could result in an anesthetic overdose. Tepoxalin is an NSAID approved for the treatment of arthritis in dogs in the United States and hence could be administered in patients requiring anesthesia. In this study, administration of a single dose or a 10-day course of tepoxalin did not affect the induction dose (dose that allowed intubation) of propofol, thiopental, or ketamine-diazepam and also did not affect the time required for dogs to recover from anesthesia.

A synthetic fraction of feline facial pheromones calms but does not reduce struggling in cats before venous catheterization

OBJECTIVE

To evaluate whether a synthetic analogue of feline facial pheromone (FFP) calms cats before, and reduces struggling during intravenous catheterization.

DESIGN

Block-randomized, 'blinded' clinical trial.

ANIMALS

Seventy-seven healthy cats presented for elective surgery.

PROCEDURE

Cats given glycopyrrolate and oxymorphone were assigned to one of four treatments: acepromazine and exposure to FFP (aceFFP); acepromazine and exposure to a placebo (acePlac); exposure to FFP only (FFP) and exposure to placebo only (Plac). The behaviour of cats was recorded on videotape for evaluation by assessors unaware of treatment group. Cats' veins were then catheterized by veterinary students unaware of the study protocol. Based on each cat's response to catheterization, the student independently decided whether intramuscular ketamine was required.

RESULTS

Cats in the aceFFP group appeared to be calmer than acePlac cats on the basis of head position and their location in the cage (suggesting benefit from FFP among cats receiving acepromazine) but appeared to be less sedated. Cats in the aceFFP group also appeared to be calmer than FFP cats on the basis of head position and location in the cage. Feline facial pheromone cats were also calmer than Plac cats when compared using body and leg position. Exposure to FFP did not significantly reduce struggling at catheterization, nevertheless, the students were able to catheterize the veins in all cats.

CONCLUSION AND CLINICAL RELEVANCE

There were no detrimental behavioural effects associated with either FFP or acepromazine. The FFP had additional calming effects in cats given acepromazine and, to a lesser degree, helped to calm cats that were not given acepromazine. Feline facial pheromone helps to calm cats in unfamiliar surroundings.

Dexmedetomidine or medetomidine premedication before propofol-desflurane anaesthesia in dogs

The objective of this study was to evaluate dexmedetomidine as a premedicant in dogs prior to propofol-desflurane anaesthesia, and to compare it with medetomidine. Six healthy dogs were anaesthetized. Each dog received intravenously (i.v.) five preanaesthetic protocols: D1 (dexmedetomidine, 1 microg/kg, i.v.), D2 (dexmedetomidine, 2 microg/kg, i.v.), M1 (medetomidine, 1 microg/kg, i.v.), M2 (medetomidine, 2 microg/kg, i.v.), or M4 (medetomidine, 4 microg/kg, i.v.). Anaesthesia was induced with propofol (2.3-3.3 mg/kg) and maintained with desflurane. The following variables were studied: heart rate (HR), mean arterial pressure, systolic arterial pressure, diastolic arterial pressure, respiratory rate (RR), arterial oxygen saturation, end-tidal CO2, end-tidal concentration of desflurane (EtDES) required for maintenance of anaesthesia and tidal volume. Arterial blood pH (pHa) and arterial blood gas tensions (PaO2, PaCO2) were measured during anaesthesia. Time to extubation, time to sternal recumbency and time to standing were also recorded. HR and RR decreased significantly during sedation in all protocols. Cardiorespiratory variables during anaesthesia were statistically similar for all protocols. EtDES was significantly different between D1 (8.1%) and D2 (7.5%), and between all doses of medetomidine. Desflurane requirements were similar for D1 and M2, and for D2 and M4 protocols. No statistical differences were observed in recovery times. The combination of dexmedetomidine, propofol and desflurane appears to be effective for induction and maintenance of general anaesthesia in healthy dogs.

Effects of preoperative epidural administration of racemic ketamine for analgesia in sheep undergoing surgery

OBJECTIVE

To investigate the effects of preoperative epidural administration of racemic ketamine to provide analgesia in sheep undergoing experimental hind limb orthopedic surgery.

ANIMALS

12 adult sheep (weight range, 51.4 to 67.2 kg).

PROCEDURE

Sheep were anesthetized with guaifenesin, thiopental, and isoflurane; after induction of anesthesia, sheep received a lumbosacral epidural injection of ketamine (1 mg/kg; n = 6) or saline (0.9% NaCl) solution (1 mL/7 kg; 6 [control group]). Respiratory and cardiovascular variables were recorded before and at intervals during and for 6 hours after anesthesia. During that 6-hour postoperative period, analgesia was evaluated subjectively with a numeric ranking scale that included assessments of comfort, posture, movement, and response to wound palpation; buprenorphine was administered when a score > 3 (maximum score, 10) was achieved. Rectal temperature, heart and respiratory rates, and lameness were evaluated daily for 2 weeks after surgery.

RESULTS

At all evaluations, cardiovascular and respiratory variables were comparable between the 2 groups. Compared with control sheep, time to first administration of rescue analgesic was significantly longer and total dose of buprenorphine administered during the 6- hour postoperative period was significantly decreased for ketamine-treated sheep. During the second week following surgery, ketamine-treated sheep had significantly less lameness than control sheep.

CONCLUSIONS AND CLINICAL RELEVANCE

In sheep undergoing hind limb surgery, preoperative epidural administration of ketamine appears to provide analgesia in the immediate postoperative period and has residual analgesic effects, which may contribute to more rapid return of normal function in surgically treated limbs.

Comparison of two pre-anaesthetic medetomidine doses in isoflurane anaesthetized sheep

OBJECTIVE

To compare the sedative, anaesthetic-sparing and arterial blood-gas effects of two medetomidine (MED) doses used as pre-anaesthetic medication in sheep undergoing experimental orthopaedic surgery.

STUDY DESIGN

Randomized, prospective, controlled experimental trial.

ANIMALS

Twenty-four adult, non-pregnant, female sheep of various breeds, weighing 53.9 +/- 7.3 kg (mean +/- SD).

METHODS

All animals underwent experimental tibial osteotomy. Group 0 (n = 8) received 0.9% NaCl, group L (low dose) (n = 8) received 5 microg kg(-1) MED and group H (high dose) (n = 8) received 10 microg kg(-1) MED by intramuscular (IM) injection 30 minutes before induction of anaesthesia with intravenous (IV) propofol 1% and maintenance with isoflurane delivered in oxygen. The propofol doses required for induction and endtidal isoflurane concentrations (F(E')ISO) required to maintain anaesthesia were recorded. Heart and respiratory rates and rectal temperature were determined before and 30 minutes after administration of the test substance. The degree of sedation before induction of anaesthesia was assessed using a numerical rating scale. Arterial blood pressure, heart rate, respiratory rate, FE'ISO, end-tidal CO2 (FE'CO2) and inspired O2 (FIO2) concentration were recorded every 10 minutes during anaesthesia. Arterial blood gas values were determined 10 minutes after induction of anaesthesia and every 30 minutes thereafter. Changes over time and differences between groups were examined by analysis of variance (anova) for repeated measures followed by Bonferroni-adjusted t-tests for effects over time.

RESULTS

Both MED doses produced mild sedation. The dose of propofol for induction of anaesthesia decreased in a dose-dependent manner: mean (+/-SE) values for group 0 were 4.7 (+/-0.4) mg kg(-1), for group L, 3.2 (+/-0.4) mg kg(-1) and for group H, 2.3 (+/-0.3) mg kg(-1)). The mean (+/-SE) FE'ISO required to maintain anaesthesia was 30% lower in both MED groups [group L: 0.96 (+/-0.07) %; group H: 1.06 (+/-0.09) %] compared with control group values [(1.54 +/- 0.17) %]. Heart rates were constantly higher in the control group with a tendency towards lower arterial blood pressures when compared with the MED groups. Respiratory rates and PaCO2 were similar in all groups while PaO2 increased during anaesthesia with no significant difference between groups. In group H, one animal developed a transient hypoxaemia: PaO2 was 7.4 kPa (55.7 mmHg) 40 minutes after induction of anaesthesia. Arterial pH values and bicarbonate concentrations were higher in the MED groups at all time points.

CONCLUSION AND CLINICAL RELEVANCE

Intramuscular MED doses of 5 and 10 microg kg(-1) reduced the propofol and isoflurane requirements for induction and maintenance of anaesthesia respectively. Cardiovascular variables and blood gas measurements remained stable over the course of anaesthesia but hypoxaemia developed in one of 16 sheep receiving MED.

Comparison of xylazine and medetomidine as premedicants for cats being anaesthetised with propofol-sevoflurane

The effects of premedicating cats with saline, xylazine or medetomidine before anaesthetising them with propofol-sevoflurane were compared. Twenty-four cats were randomly assigned to three groups of eight to receive either 0.25 ml of saline, 0.50 mg/kg of xylazine or 0.02 mg/kg of medetomidine intravenously, and anaesthesia was induced with propofol and maintained with sevoflurane. Medetomidine produced a greater reduction in the induction dose of propofol and fewer adverse postoperative effects than saline or xylazine. Hypoxaemia was observed after induction with propofol in the cats premedicated with saline and xylazine, but not in the cats given medetomidine. The cats treated with medetomidine and xylazine developed profound bradycardia. The blood pressure of the cats premedicated with saline and xylazine decreased, but the blood pressure of the cats premedicated with medetomidine was maintained. The cats premedicated with saline took longer to recover from anaesthesia than the other two groups.

Four preanesthetic oral sedation protocols for rhesus macaques (Macaca mulatta)

The efficacies and ease of administration of four oral preanesthetic sedation protocols were compared in 18 adult, male rhesus macaques (Macaca mulatta) to achieve heavy sedation and alleviate anxiety, agitation, and potential trauma associated with remote anesthesia induction. The macaques, with average age and weight of 10 yr and 12.5 kg, respectively, were randomly assigned to one of four groups. Group 1 was given 10 mg/kg tiletaminezolazepam and 0.05 mg/kg medetomidine p.o., group 2 was given 1 mg/kg midazolam and 20 mg/kg ketamine p.o., group 3 was given 20 mg/kg ketamine and 0.05 mg/kg medetomidine p.o., and group 4 was given 3 mg/kg midazolam p.o. All protocols produced effects ranging from mild sedation to no response to noxious stimuli, depending on the success of administration. The mean interval to peak effect was 27-43 min in all groups. Ketamine and medetomidine provided significantly better sedation than midazolam alone; there were no other statistically significant differences among the four protocols. Oral tiletamine-zolazepam and medetomidine provided smooth, mild to moderate sedation with few side effects. The midazolam and ketamine combination resulted in severe ataxia. Orally administered ketamine and medetomidine provided smooth, easily reversible, heavy sedation leading to no response to noxious stimuli. Midazolam alone provided only mild sedation. No statistically significant differences in palatability of the four protocols were identified. Orally administered ketamine and medetomidine (group 3) provided the most consistently heavy sedation. A compounding pharmacy may be able to increase the palatability and level of acceptance of these combinations. Alternatively, oral midazolam syrup is well accepted by some animals and provides a mild sedative and calming effect, which may decrease stress associated with the induction of anesthesia via darting, pole syringes, etc.

Results of 24-hour ambulatory electrocardiography in dogs undergoing ovariohysterectomy following premedication with medetomidine or acepromazine

OBJECTIVE

To investigate heart rate characteristics in dogs undergoing ovariohysterectomy following premedication with medetomidine or acepromazine.

DESIGN

Clinical trial.

ANIMALS

43 client-owned dogs.

PROCEDURE

24-hour ambulatory electrocardiography was performed beginning approximately 1 hour prior to administration of premedications. Dogs were premedicated with medetomidine and butorphanol (n = 21) or acepromazine and butorphanol (22) and, approximately 85 minutes later, were anesthetized with propofol and isoflurane. Electrocardiographic recordings were examined to determine heart rate, cardiac conduction disturbances (ventricular premature complexes and atrioventricular block), and indices of heart rate variability (HRV).

RESULTS

Minimum heart rate during the 24-hour recording period was significantly lower among dogs given medetomidine than among dogs given acepromazine, but during the postoperative period, heart rate increased in all dogs as they became physically active. Intraoperative time domain HRV indices were lower and the low frequency-to-high frequency ratio was higher among dogs given acepromazine than among dogs given medetomidine; however, significant differences between groups were no longer seen by 6 hours after surgery. There was no significant difference between groups with regard to the number of ventricular premature complexes or to values of scaling exponent alpha2 (a nonlinear measure of HRV).

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that there are greater enhancements in vagally related heart rate indices in medetomidine-treated dogs that may persist until 6 hours after surgery. Despite the low heart rates, dogs given medetomidine showed expected responses to surgery and positional stimuli, and the 2 preanesthetic protocols may not result in different prevalences of ventricular premature complexes.

Effects of preanesthetic administration of morphine on gastroesophageal reflux and regurgitation during anesthesia in dogs

OBJECTIVE

To determine the effect of morphine administered prior to anesthesia on the incidence of gastroesophageal reflux (GER) in dogs during the subsequent anesthetic episode.

ANIMALS

90 dogs (30 dogs/group).

PROCEDURE

The randomized prospective clinical study included healthy dogs with no history of vomiting. Dogs were scheduled to undergo elective orthopedic surgery. Food was withheld for (mean+/-SD) 17.8+/-4.1 hours prior to induction of anesthesia. The anesthetic protocol included acepromazine maleate, thiopental, and isoflurane. Dogs were randomly selected to receive morphine at various dosages (0, 0.22, or 1.10 mg/kg, IM) concurrent with acepromazine administration prior to induction of anesthesia. A sensor-tipped catheter was used to measure esophageal pH, and GER was defined as a decrease in pH to < 4 or an increase to > 7.5.

RESULTS

40 dogs had acidic reflux, and 1 had biliary reflux. Proportions of dogs with GER were 8 of 30 (27%), 15 of 30 (50%), and 18 of 30 (60%) for morphine dosages of 0, 0.22, and 1.10 mg/kg, respectively. Mean duration of GER was 91.4+/-56.8 minutes. There was no significant association between GER and age, weight, vomiting after preanesthetic medication, administration of antimicrobials, or start of surgery.

CONCLUSIONS AND CLINICAL RELEVANCE

Most healthy dogs vomit after a large dose of morphine, but vomiting does not increase the likelihood of GER during the subsequent anesthetic episode. Administration of morphine prior to anesthesia substantially increases the incidence of GER during the subsequent anesthetic episode.

Romifidine-Ketamine Anaesthesia in Atropine and Triflupromazine Pre-medicated Buffalo Calves

The study was conducted on 10 buffalo calves with a weight of 98.5 +/- 3.9 kg and age 9.7 +/- 1.3 months. Ten trials of two treatments were carried out using a randomized block design. Atropine at the dose of 0.02 mg/kg bodyweight was administered in both the groups. The animals of group I received romifidine at the dose of 10 microg/kg i.v., 10 min after atropine administration, whereas, animals of group II received triflupromazine at the dose of 0.3 mg/kg i.m. and 10 min later romifidine at the dose of 10 microg/kg i.v. immediately followed by ketamine at the dose of 5 mg/kg i.v. The onset of action of romifidine in group I occurred within 2 min and the animals remained under mild sedation for 31 +/- 4.8 min. In group II, the triflupromazine-romifidine-ketamine combination induced anaesthesia for 14 +/- 2.3 min. Hypothermia, significant bradycardia and respiratory depression was noticed in both groups at different time intervals.

Effects of ovariohysterectomy on canine blood neutrophil respiratory burst: a chemiluminescence study

OBJECTIVE

To examine blood neutrophil counts and luminol-enhanced chemiluminescence (CL) responses in dogs undergoing ovariohysterectomy (OH), premedicated with 2 different drugs.

STUDY DESIGN

Randomized clinical study.

ANIMALS

Forty-two healthy client-owned bitches.

METHODS

Dogs had OH under isoflurane anesthesia with either acepromazine or medetomidine, both in combination with butorphanol, administered as preanesthetic medication. Blood samples were collected when the dog was admitted, at the end of surgery, and the next day (approximately 20 hours after surgery). Blood neutrophils were counted automatically, and neutrophil oxidative activity was assessed by measuring blood CL responses (induced by opsonized zymosan and enhanced by luminol) at 37 degrees C for 40 minutes.

RESULTS

Number of circulating neutrophils was significantly increased the day after surgery reflected by enhanced blood CL responses. Neutrophil CL, however, was not significantly altered. No significant differences were detected for perioperative Polymorphonuclear neutrophil (PMN) characteristics between the 2 preanesthetic regimens.

CONCLUSIONS

In conclusion, despite clearly increasing the number of circulating neutrophils, OH did not significantly affect neutrophil respiratory burst, as measured by whole-blood CL responses.

CLINICAL RELEVANCE

Surgical operation of moderate intensity (e.g., OH) did not significantly alter one of the important immune functions, neutrophil oxidative activity. Further studies are warranted to confirm the significance of this finding, and to assess the value of following this variable in different animal patient populations.

Evaluation of the effects of premedication on gastroduodenoscopy in cats

OBJECTIVE

To evaluate the effects of hydromorphone, hydromorphone and glycopyrrolate, medetomidine, and butorphanol premedication on the difficulty and time required to pass an endoscope into the stomach and duodenum of cats anesthetized with ketamine and isoflurane.

DESIGN

Randomized complete block crossover study.

ANIMALS

8 purpose-bred adult female cats.

PROCEDURES

Each cat was premedicated and anesthetized 4 times with an interval of at least 7 days between procedures. Cats were premedicated with hydromorphone, hydromorphone and glycopyrrolate, medetomidine, or butorphanol administered IM. Twenty minutes after premedication, sedation was assessed by use of a subjective ordinal scale. Cats received ketamine administered IM, and 10 minutes later a cuffed orotracheal tube was placed and anesthesia maintained with isoflurane. Cats breathed spontaneously throughout the procedure. When end-tidal isoflurane concentration was stable at 1.4% for 15 minutes, endoscopy was begun. The times required to pass the endoscope through the cardiac and pyloric sphincters were recorded, and the difficulty of endoscope passage was scored by use of a subjective ordinal scale.

RESULTS

No significant differences in difficulty or time required to pass the endoscope through the cardiac and pyloric sphincters were found among premedicant groups. Premedication with medetomidine resulted in the greatest degree of sedation and longest time to return to sternal recumbency.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that hydromorphone, hydromorphone and glycopyrrolate, medetomidine, and butorphanol at the doses tested can be used satisfactorily to premedicate cats prior to general anesthesia for gastroduodenoscopy.

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 cm(3); 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.

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 inhalant anesthetic and body temperature on peri-anesthetic serum concentrations of transdermally administered fentanyl in dogs

OBJECTIVES

To determine whether moderate hypothermia during anesthesia significantly affects the serum concentration of transdermally delivered fentanyl and whether halothane or isoflurane affect these concentrations.

STUDY DESIGN

Randomized cross-over experimental trial.

ANIMALS

Six mature, healthy Beagles (three males, three females) weighing 10.6 +/- 0.43 kg.

METHODS

A 50-microg hour(-1) fentanyl patch was applied 36 hours prior to anesthesia. Anesthesia was induced at time 0 (t = 0). Each dog received four treatments: isoflurane + normothermia (ISO-NORM), isoflurane + hypothermia (ISO-HYPO), halothane + normothermia (HAL-NORM), and halothane + hypothermia (HAL-HYPO). Dogs were intubated and maintained at 1.5 times MAC. Animals in the hypothermia treatments were cooled to 35 degrees C during anesthesia. Serum fentanyl analysis was performed at -36, -24, -12, 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 18, and 26 hours. Direct arterial blood pressures and arterial blood gases were monitored.

RESULTS

The mean body temperatures (+/-SEM) during the anesthetic period for the four treatments were: ISO-NORM = 37.7 +/- 0.07 degrees C, ISO-HYPO = 35.8 +/- 0.1 degrees C, HAL-NORM = 37.7 +/- 0.06 degrees C, and HAL-HYPO = 35.8 +/- 0.13 degrees C. The mean (+/-SEM) serum fentanyl concentrations (SFC) for both hypothermia treatments were significantly lower than baseline concentrations at t = 1 hour and persisted for the duration of anesthesia for the ISO-HYPO treatment but only from t = 1 to 2 hours for the HAL-HYPO treatment. Serum fentanyl concentrations returned to baseline within one hour of the end of anesthesia, regardless of body temperature. There were no significant differences between treatments for systolic or diastolic blood pressure but mean blood pressures were higher during normothermia versus hypothermia during the last hour of anesthesia.

CONCLUSIONS AND CLINICAL RELEVANCE

Hypothermia during inhalation anesthesia produced a significant reduction in SFC using transdermal administration and was more protracted with isoflurane than halothane anesthesia. While significant reductions in SFC occurred, the SFC were still within the range believed to confer analgesia.

Cardiopulmonary effects of medetomidine, oxymorphone, or butorphanol in selegiline-treated dogs

OBJECTIVES

To determine if chronic selegiline HCl administration affects the cardiopulmonary response to medetomidine, oxymorphone, or butorphanol in dogs.

STUDY DESIGN

Prospective randomized experimental study.

ANIMALS

Twenty-eight adult, random source, hound dogs weighing 21-33 kg.

METHODS

Dogs were assigned to the following treatment groups: selegiline + medetomidine (MED; n = 6); placebo + MED (n = 6), selegiline + oxymorphone (OXY; n = 6); placebo + OXY (n = 6); selegiline + butorphanol (BUT; n = 7) or placebo + BUT (n = 6). Nine dogs were treated with two of the three pre-medicants. Dogs were treated with selegiline (1 mg kg(-1) PO, q 24 hours) or placebo for at least 44 days prior to pre-medicant administration. On the day of the experiment, arterial blood for blood gas analysis, blood pressure measurements, ECG, cardiac ultrasound (mM-mode, 2-D, and continuous wave Doppler), and behavioral observations were obtained by blinded observers. An IV injection of MED (750 micro g m(-2)), OXY (0.1 mg kg(-1)) or BUT (0.4 mg kg(-1)) was given. Cardiopulmonary and behavioral data were collected at 1, 2, 5, 15, 30, and 60 minutes after injection.

RESULTS

Selegiline did not modify responses to any of the pre-medicant drugs. Medetomidine caused a significant decrease in heart rate (HR), cardiac output (CO), and fractional shortening (FS). Mean arterial pressure (MAP), systemic vascular resistance (SVR), and central venous pressure (CVP) were increased. Level of consciousness and resistance to restraint were both decreased. Oxymorphone did not affect MAP, CO, CVP, or SVR, but RR and PaCO(2) were increased. Level of consciousness and resistance to restraint were decreased. BUT decreased heart rate at 1 and 5 minutes. All other cardiovascular parameters were unchanged. BUT administration was associated with decreased arterial pH and increased PaCO(2). BUT decreased level of consciousness and resistance to restraint.

CONCLUSIONS AND CLINICAL RELEVANCE

Although pre-medicants themselves altered cardiopulmonary and behavioral function, selegiline did not affect the response to medetomidine, oxymorphone, or butorphanol in this group of normal dogs.

Evaluation of the use of anesthesia and analgesia in reptiles

OBJECTIVE

To determine anesthetic techniques and the drugs used to provide anesthesia and analgesia to reptiles.

DESIGN

Mail-out questionnaire.

SAMPLE POPULATION

367 members of the Association of Reptile and Amphibian Veterinarians.

PROCEDURE

1,091 members listed in the 2002 directory of the Association of Reptile and Amphibian Veterinarians were asked to complete a questionnaire regarding anesthesia and analgesia.

RESULTS

367 of 1,091 (33.6%) individuals completed the questionnaire; 88.8% used inhalants (particularly isoflurane) for anesthesia, and ketamine, propofol, and butorphanol were the most commonly used injectable agents. Intubation, fluids, and having a dedicated anesthetist were most commonly used for patient support, and pulse oximetry and Doppler ultrasonography were most commonly used for monitoring. Respiratory depression, difficulty monitoring anesthetic depth, prolonged recovery, and hypothermia were the most frequent complications. Nearly all respondents believed that reptiles feel pain, but analgesics were used infrequently for many reasons.

CONCLUSIONS AND CLINICAL RELEVANCE

Providing anesthesia in reptiles is difficult, especially regarding anesthetic depth and vital parameters, and methods of support are used less frequently than in domestic species. Provision of analgesia is uncommon. Research regarding pain and its assessment, response to analgesics, and drug pharmacokinetics is needed. Dissemination of this information to practitioners needs to be improved for enhancement of the standard of care for reptiles.

Effect of preoperative administration of tepoxalin on hemostasis and hepatic and renal function in dogs

Preemptive analgesia is an important part of surgical management, but some NSAIDs can adversely affect platelet function or renal or hepatic status. Tepoxalin is approved in the United States for control of pain and inflammation associated with arthritis and in Europe for relief of pain caused by musculoskeletal disorders. In this study, no significant effects on indices of hemostasis or renal or hepatic function were detected when a single preoperative oral dose of tepoxalin was administered to young healthy dogs undergoing anesthesia and surgery.

Effects of acepromazine on the incidence of vomiting associated with opioid administration in dogs

OBJECTIVE

To evaluate the anti-emetic properties of acepromazine in dogs receiving opioids as pre-anesthetic medication.

STUDY DESIGN

Randomized prospective clinical study.

ANIMALS

One hundred and sixteen dogs (ASA I or II), admitted for elective surgical procedures. The dogs were a mixed population of males and females, purebreds and mixed breeds, 0.25-13.4 years of age, weighing 1.8-57.7 kg.

METHODS

A prospective clinical trial in which the dogs were randomly assigned to one of three groups. All groups received acepromazine (0.05 mg kg(-1) intramuscularly (i.m.)). Group I received acepromazine 15 minutes prior to opioid administration. Group II received acepromazine in combination with the opioid. Group III received acepromazine 15 minutes after opioid administration. One of three different opioids was administered i.m. to each dog: morphine sulfate at 0.5 mg kg(-1); hydromorphone hydrochloride at 0.1 mg kg(-1); or oxymorphone hydrochloride at 0.075 mg kg(-1).

RESULTS

Dogs receiving acepromazine before the opioid (group I) had a significantly lower incidence of vomiting (18%) than dogs in groups II (45%) and III (55%). The degree of sedation was significantly lower in the dogs receiving the combination of acepromazine and the opioid (group II) than in dogs receiving the opioid as the first drug (group III).

CONCLUSIONS AND CLINICAL RELEVANCE

Acepromazine administered 15 minutes before the opioid lowers the incidence of vomiting induced by opioids.

A comparison of the analgesic effects of butorphanol with those of meloxicam after elective ovariohysterectomy in dogs

This study was designed to compare the analgesic effects of butorphanol with those of meloxicam following ovariohysterectomy. Fifteen dogs were premedicated with 0.05 mg/kg body weight (BW) of acepromazine by intramuscular (IM) injection, plus 0.2 mg/kg BW of meloxicam by subcutaneous (SC) injection. Fifteen dogs were premedicated with 0.05 mg/kg BW of Acepromazine, IM, plus 0.2 mg/kg BW of butorphanol, IM. Anesthesia was induced with thiopental, and dogs were maintained on halothane. All pain measurements were performed by 1 experienced individual, blinded to treatment. Pain scores and visual analogue scales (VAS) were performed at 2, 3, 4, 6, 8, 12, and 24 hours postpremedication. An analgesiometer was used to determine the pressure required to produce an active avoidance response to pressure applied at the incision line. Pain scores, VAS, and analgesiometer scores were analyzed by using a generalized estimating equations method. A significance level of P < 0.05 was considered significant. Animals that received meloxicam demonstrated significantly lower pain scores and VAS than did animals that received butorphanol in the first 12 hours after surgery. Results of this study suggest that meloxicam will produce better postoperative analgesia than will butorphanol. Mucosal bleeding times were performed on cooperative animals in the study group (11 butorphanol, 13 meloxicam). Bleeding times were performed prior to premedication, 6 hours following premedication, and 24 hours after premedication. The 6- and 24-hour readings were compared with baseline bleeding times by using a paired t-test with a Bonferroni correction (a significance level of P < 0.025). Bleeding times did not change significantly over time.

Clinical usefulness of propofol as an anesthetic induction agent in dogs and cats

Propofol was used as an induction agent of general anesthesia in 77 dogs and 64 cats, all client owned, for a variety of surgeries/treatments or diagnostic procedures. The mean intravenous doses of propofol required to achieve endotracheal intubation in dogs and cats were 6.5 +/- 1.4 mg/kg and 10.1 +/- 2.8 mg /kg, respectively. Most of the animals could be induced to anesthesia smoothly by the administration of propofol with a high incidence of apnea. Propofol is a clinically valuable anesthetic induction agent in both dogs and cats, however, care must be taken for apnea.

A comparison of thiopental, propofol, and diazepam-ketamine anesthesia for evaluation of laryngeal function in dogs premedicated with butorphanol-glycopyrrolate

Thiopental, propofol, and diazepam-ketamine were compared for evaluation of laryngeal function in dogs. There was no significant difference among the three protocols in time to observation of normal function after drug administration or in the occurrence of swallowing, laryngospasm, or breathing. Jaw tone was significantly greater with diazepam-ketamine. Exposure of the larynx was excellent in five dogs and moderate in three dogs, each receiving thiopental or propofol. Exposure was excellent in one dog, moderate in six dogs, and poor in one dog receiving diazepam-ketamine. Exposure of the larynx for laryngeal function evaluation is more readily accomplished with thiopental or propofol than with diazepam-ketamine.

[Anesthesia and analgesia of ornamental birds]

Pet birds are frequently viewed as difficult patients for anaesthesia. The present paper revises the current anaesthetic procedures for injectable and inhalant anaesthetics. Currently the method of choice for the anaesthesia of pet birds is the isoflurane inhalation anaesthesia. Special emphasis is given to the preanaesthetic preparations. Fasting is shorter for pet birds than for mammals. Anaesthetized birds are at special risk for hypothermia. Methods for the prevention of heat loss are given. The use of analgesics are recommended both for welfare reasons but also because of the possibility to reduce the concentration of inhalation anaesthetics and therefore the amount of possible exposure of personnel to waste gases.

24-hour Holter-monitoring in the perianaesthetic period in dogs premedicated with dexmedetomidine

Baseline and perianaesthetic 24-hour Holter recordings were carried out in six healthy beagles. After dexmedetomidine premedication anaesthesia was induced with propofol and maintained with propofol infusion or isoflurane for one hour. Dexmedetomidine alone was used as control. The recordings were analysed for ventricular premature complexes (VPC), atrioventricular (AV) blocks and mean heart rate/hour (HR). In most recordings, no ventricular arrhythmias were detected, the maximum frequency being two VPCs/24 h. VPCs were not seen during anaesthesia or during the recovery period. The development of second-degree AV-blocks varied from dog to dog. Most of the heart blocks were seen during the premedication period when bradycardia was most prominent. During the subsequent night, HR was similar between treatments and did not differ from that seen on the baseline recordings. In beagles treated with dexmedetomidine alone or combined with propofol or propofol/isoflurane, ventricular arrhythmias were not detected more frequently than those reported in healthy non-anaesthetised dogs.

Effects of preoperative administration of ketoprofen on anesthetic requirements and signs of postoperative pain in dogs undergoing elective ovariohysterectomy

OBJECTIVE

To determine the effects of preoperative administration of ketoprofen on anesthetic requirements and signs of postoperative pain in dogs undergoing elective ovariohysterectomy.

DESIGN

Randomized, controlled clinical trial.

ANIMALS

22 clinically normal client-owned dogs.

PROCEDURE

60 minutes before induction of anesthesia, 11 dogs were given ketoprofen (2 mg/kg [0.9 mg/lb], i.m.), and the other 11 were given saline (0.9% NaCl) solution. Dogs were premedicated with glycopyrrolate, acepromazine, and butorphanol and anesthetized with thiopental; anesthesia was maintained with isoflurane. Ovariohysterectomy was performed by an experienced surgeon, and butorphanol was given 15 minutes before completion of the procedure. Objective behavioral scores and numerical pain scores at rest and with movement were recorded every 2 hours for 12 hours after surgery and then every 4 hours for an additional 12 hours.

RESULTS

Preoperative administration of ketoprofen did not reduce the dose of thiopental required to induce anesthesia or the end-tidal concentration of isoflurane required to maintain anesthesia. Activity levels and median objective behavioral scores were significantly higher 4 and 6 hours after surgery in dogs given ketoprofen than in dogs given saline solution. However, mean numerical pain scores in dogs given ketoprofen were not significantly different from scores for dogs given saline solution at any time.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that preoperative administration of ketoprofen does not reduce anesthetic requirements in dogs undergoing elective ovariohysterectomy but may reduce signs of pain after surgery. Results also suggest that the objective behavioral score may be a more sensitive measure of acute postoperative pain than traditional numerical pain scores.

Clinical comparison of xylazine and medetomidine for premedication of horses

OBJECTIVE

To compare the analgesic and cardiopulmonary effects of medetomidine and xylazine when used for premedication of horses undergoing general anesthesia.

DESIGN

Randomized clinical trial.

ANIMALS

40 horses.

PROCEDURE

Twenty horses were premedicated with medetomidine (10 microg/kg [4.5 microg/lb], i.m.) and the other 20 were premedicated with xylazine (2 mg/kg [0.9 mg/kg], i.m.). Horses were then anesthetized with a combination of guaifenesin and ketamine; anesthesia was maintained with halothane. Additional doses of medetomidine or xylazine were given if horses were not sufficiently sedated at the time of anesthetic induction. After induction of anesthesia, sodium pentothal was administered as necessary to prevent limb movements. Hypotension was treated with dobutamine; hypoventilation and hypoxemia 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

Scores for the quality of the transition to inhalation anesthesia were significantly higher for horses premedicated with medetomidine than for horses premedicated with xylazine. However, other scores, recovery times, and numbers of attempts needed to achieve sternal recumbency and to stand were not significantly different between groups.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that medetomidine is suitable for premedication of horses undergoing general anesthesia. Analgesic and cardiopulmonary effects of medetomidine were similar to those of xylazine, except that the transition to inhalation anesthesia was smoother when horses were premedicated with medetomidine, rather than xylazine.

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.

Evaluation of the perioperative stress response in dogs administered medetomidine or acepromazine as part of the preanesthetic medication

OBJECTIVE

To compare the perioperative stress response in dogs administered medetomidine or acepromazine as part of the preanesthetic medication.

ANIMALS

42 client-owned dogs that underwent elective ovariohysterectomy.

PROCEDURE

Each dog was randomly allocated to receive medetomidine and butorphanol tartrate (20 microgram/kg and 0.2 mg/kg, respectively, IM) or acepromazine maleate and butorphanol (0.05 and 0.2 mg/kg, respectively, IM) for preanesthetic medication. Approximately 80 minutes later, anesthesia was induced by administration of propofol and maintained by use of isoflurane in oxygen. Each dog was also given carprofen before surgery and buprenorphine after surgery. Plasma concentrations of epinephrine, norepinephrine, cortisol, and beta-endorphin were measured at various stages during the perioperative period. In addition, cardiovascular and clinical variables were monitored.

RESULTS

Concentrations of epinephrine, norepinephrine, and cortisol were significantly lower for dogs administered medetomidine. Concentrations of beta-endorphin did not differ between the 2 groups. Heart rate was significantly lower and mean arterial blood pressure significantly higher in dogs administered medetomidine, compared with values for dogs administered acepromazine.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicate that for preanesthetic medications, medetomidine may offer some advantages over acepromazine with respect to the ability to decrease perioperative concentrations of stress-related hormones. In particular, the ability to provide stable plasma catecholamine concentrations may help to attenuate perioperative activation of the sympathetic nervous system.

Effects of medetomidine-midazolam, midazolambutorphanol, or acepromazine-butorphanol as premedicants for mask induction of anesthesia with sevoflurane in dogs

OBJECTIVE

To characterize the effects of medetomidine-midazolam, midazolam-butorphanol, or acepromazine-butorphanol as premedicants for mask induction of anesthesia with sevoflurane in dogs.

ANIMALS

10 healthy Beagles.

PROCEDURE

The following premedicants were administered intramuscularly: medetomidine-midazolam (20 microg/kg and 0.3 mg/kg, respectively), midazolam-butorphanol (0.1 and 0.2 mg/kg, respectively), and acepromazine-butorphanol (0.05 and 0.2 mg/kg, respectively). Saline (0.9% NaCI) solution (0.1 ml/kg) was administered intramuscularly as a control. Anesthesia was induced in each dog with sevoflurane in a 100% O2 at a flow rate of 4 L/min developed by a facemask. Vaporizer settings were increased by 0.8% at 15-second intervals until the value corresponding to 4.8% sevoflurane was achieved. Time to onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation were recorded, and the cardiopulmonary variables were measured.

RESULTS

Mask induction with sevoflurane in dogs that received each premedicant resulted in a shorter induction time and milder changes in heart rate, mean arterial blood pressure, cardiac output, and respiratory rate, compared with mask induction without premedicants. Treatment with medetomidine-midazolam resulted in a shorter and smoother induction, compared with acepromazine-butorphanol or midazolam-butorphanol treatment, whereas the cardiovascular changes were greater. Cardiopulmonary variables of dogs during induction following treatment with acepromazine-butorphanol or midazolam-butorphanol were maintained close to the anesthetic maintenance values for sevoflurane, with the exception of mild hypotension that was observed in dogs following acepromazine-butorphanol treatment.

CONCLUSION AND CLINICAL RELEVANCE

In dogs use of premedicants provides a smoother and better quality mask induction with sevoflurane.

Effects of two preanesthetic regimens for ophthalmic surgery on intraocular pressure and cardiovascular measurements in dogs

The effects of different preanesthetic medications (acepromazine plus either meperidine or butorphanol) given before the induction of anesthesia with midazolam and ketamine on intraocular pressure, heart rate, and arterial blood pressure were investigated in 20 dogs. Following administration of preanesthetics and induction of anesthesia, dogs were intubated and anesthesia was maintained with halothane for 10 minutes. Intraocular pressure was significantly higher (P <.05) at several evaluations for dogs premedicated with acepromazine/meperidine than for those premedicated with acepromazine/butorphanol. Mean heart rate and diastolic arterial blood pressure were significantly (P <.05) higher 5 minutes after administration of acepromazine/meperidine than after acepromazine/butorphanol. Results of this study suggest that acepromazine/butorphanol is a satisfactory preanesthetic combination to use before induction of anesthesia with midazolam and ketamine for ophthalmic surgery in dogs.

Some clinical effects of midazolam premedication in propofol-induced and isoflurane-maintained anaesthesia in dogs during ovariohysterectomy

In a randomised, placebo-controlled clinical trial, anaesthesia was induced with propofol (4 mg/kg) after intravenous premedication with or without midazolam (0.1 mg/kg), in a group of 8 dogs scheduled for ovariohysterectomy. Midazolam administration induced acute behavioural changes, and increased reflex suppression after propofol induction. Compared to the control group, the dose required to obtain loss of the pedal reflex was significantly reduced by 37%, and the end-tidal isoflurane concentration during maintenance, reduced by 23%.

Clinical comparison of preanaesthetic intramuscular medetomidine and dexmedetomidine in domestic sheep

Medetomidine and its active d-enantiomer, dexmedetomidine, are highly selective alpha-2 agonists with potent sedative, anaesthetic-sparing and analgesic effects. These properties make them an ideal pre-anaesthetic medication for noxious surgical procedures. However, sheep can develop adverse hypoxaemic effects after intravenous alpha-2 agonists. Objective of the present study was to compare intramuscular injection of medetomidine or dexmedetomidine at equipotent doses as preanaesthetic medication prior to isoflurane anaesthesia in sheep. Nineteen healthy, adult, non-pregnant, female sheep of various breeds were used. The study was carried out as a randomised, blind trial. Group A received 15 micrograms/kg bwt dexmedetomidine and group B received 30 micrograms/kg bwt medetomidine intramuscularly (i.m.) 30 minutes prior to induction of anaesthesia. Anaesthesia was induced with ketamine (2.0 mg/kg bwt i.v.) and maintained with isoflurane in 100% oxygen. End expired anaesthetic concentration (FEiso), respiratory frequency (fR), direct arterial blood pressures and heart rates (HR) were measured. Arterial blood samples were taken at intervals. Data were averaged over time (sum of measurements/number of measurements) and tested for differences between groups by independent t-tests, and ANOVA for repeated measures followed by Bonferroni corrected t-tests. There were no differences in demographic data between the groups. Duration of anaesthesia [A: 170 (42) minutes, B: 144 (33) minutes] and duration of surgery [A: 92 (32) minutes, B: 85 (31) minutes] were similar in both groups. Average FEiso concentrations required to maintain a surgical plane of anaesthesia were not significantly different between groups [A: 0.82 (0.14)%; B: 1.00 (0.25)%]. Mean average fR, did not differ between groups [A: 31 (14), B: 37 (15)]. Heart rates were significantly lower in group B over the course of the anaesthesia. Mean arterial blood pressures (MAP) were not significantly different between the groups. The PaO2 was less variable in group A than in group B. Individual minimum values were 19.1 kPa and 7.9 kPa in group A and B, respectively. There were no significant differences in PaCO2 and paH between the groups and over time. In conclusion, intramuscular application of dexmedetomidine at 15 micrograms/kg bwt and medetomidine at 30 micrograms/kg bwt prior to isoflurane anaesthesia induced similar changes in clinically monitored cardiorespiratory parameters. The observed differences (heart rates, PaO2) between dexmedetomidine and medetomidine at the chosen dose relationship can be considered clinically not significant. At the chosen dose rates individual animals responded with a transient drop in blood oxygenation, therefore careful monitoring is required. In addition, in compromised sheep medetomidine and dexmedetomidine should be used carefully.

Survey on small animal anaesthesia

OBJECTIVE

To ascertain anaesthetic practices currently for dogs and cats in Australia.

METHODS

A questionnaire was distributed to 4,800 veterinarians throughout Australia, seeking data on numbers of dogs and cats anaesthetised per week; drug preferences for anaesthetic premedication, induction and maintenance; use of tracheal intubation, supplemental nitrous oxide and anaesthetic antagonists; and types of vaporisers, breathing systems and anaesthetic monitoring devices used or available. Additional questions concerned proportions of different animal types seen in the practice, and the respondent's university and year of graduation.

RESULTS

The response rate was 19%; 95% of respondents graduated from Australian universities, about half since 1985. Most responses (79%) came from mainly small animal practices. On average 16 dogs and 12 cats were anaesthetised each week. Premedication was used more often in dogs than cats, with acepromazine and atropine most favoured in both species. For anaesthetic induction, thiopentone was most preferred in dogs and alphaxalone/alphadolone in cats. Inhaled agents, especially halothane, were preferred for maintenance in both species. Most respondents usually employed tracheal intubation when using inhalational anaesthetic maintenance, but intubation rates were lower during injectable anaesthetic maintenance and a minority of respondents provided supplemental O2. Nitrous oxide was administered regularly by 13% of respondents. The agents most frequently used to speed recovery from anaesthesia were doxapram and yohimbine. The most widely used vaporisers were the Fluotec Mark III and the Stephens machine. Most (95%) respondents used a rebreathing circuit for large dogs and a non-rebreathing system was used for small dogs by 68% of respondents. Most respondents (93%) indicated some form of aid was available to monitor general anaesthesia: the three most mentioned were an apnoea alarm, oesophageal stethoscope and electrocardiogram.

CONCLUSION

Diverse approaches were evident, but there appeared to be less variation in anaesthetising dogs: premedication was more frequent and less varied in type, while thiobarbituates dominated for induction and inhalants for maintenance. Injectable maintenance techniques had substantial use in cats, but little in dogs. Evident disparity between vaporisers available and circuits used suggested either confusion in terminology or incorrect use of some vaporisers in-circuit. While most respondents used monitoring equipment or a dedicated observer to invigilate anaesthesia, the common reliance on apnoea alarms is of concern, because of unproven reliability and accuracy.

Comparison of medetomidine and dexmedetomidine as premedicants in dogs undergoing propofol-isoflurane anesthesia

OBJECTIVE

To compare 3 dose levels of medetomidine and dexmedetomidine for use as premedicants in dogs undergoing propofol-isoflurane anesthesia.

ANIMALS

6 healthy Beagles.

PROCEDURE

Dogs received medetomidine or dexmedetomidine intravenously at the following dose levels: 0.4 microg of medetomidine or 0.2 microg of dexmedetomidine/kg of body weight (M0.4/D0.2), 4.0 microg of medetomidine or 2.0 microg of dexmedetomidine/kg (M4/D2), and 40 microg of medetomidine or 20 microg of dexmedetomidine/kg (M40/D20). Sedation and analgesia were scored before induction. Anesthesia was induced with propofol and maintained with isoflurane. End-tidal isoflurane concentration, heart rate, and arterial blood pressures and gases were measured.

RESULTS

Degrees of sedation and analgesia were significantly affected by dose level but not drug. Combined mean end-tidal isoflurane concentration for all dose levels was higher in dogs that received medetomidine, compared with dexmedetomidine. Recovery time was significantly prolonged in dogs treated at the M40/D20 dose level, compared with the other dose levels. After induction, blood pressure decreased below reference range and heart rate increased in dogs treated at the M0.4/D0.2 dose level, whereas blood pressure was preserved in dogs treated at the M40/D20 dose level. However, dogs in these latter groups developed profound bradycardia and mild metabolic acidosis during anesthesia. Treatment at the M4/D2 dose level resulted in more stable cardiovascular effects, compared with the other dose levels. In addition, PaCO2 was similar among dose levels.

CONCLUSIONS AND CLINICAL RELEVANCE

Dexmedetomidine is at least as safe and effective as medetomidine for use as a premedicant in dogs undergoing propofol-isoflurane anesthesia.

Preanaesthetic use of atropine in small animals

Although it is unwise to recommend any preanaesthetic drug or regimen to be used routinely without consideration for the individual patient, the procedure being undertaken or the other drugs that will be used during the anaesthetic, of all anaesthetic-related drugs that might be under review, atropine is probably one of the least 'toxic' and least likely to cause life-threatening complications when used correctly. In most small veterinary practices there isn't the luxury of a dedicated anaesthetist available to monitor and manage each anaesthetised patient and the best form of cardiac monitor available may be an audible rate monitor. In this situation the advantages combined with the usual indications probably far outweigh the disadvantages of using atropine prophylactically. If a choice must be made, a sinus tachycardia under anaesthesia is probably preferable to a profound bradyarrhythmia. Absolute contraindications for using atropine are rare; the drug, when used alone, has low incidence of toxicity at clinically recommended doses in dogs and cats. Further, the new inhalation agents available to veterinarians (enflurane and isoflurane) do not sensitise the heart to the effect of catecholamines, so that the predominance of sympathetic tone produced when atropine is used is unlikely to precipitate dysarrthythmias during gaseous anaesthesia. Rhythm disturbances that occur under halothane anaesthesia when atropine is used, suggest there is some other cause, or agent, that is arrhythmogenic, such as an alpha 2 agonist, excessively deep level of anaesthesia, hypercapnia or hypoxaemia. Notwithstanding the above arguments, my preference, as a specialist anaesthetist, is that a drug is given only as required (not before) and that when, for example, any unusual heart rhythm occurs, all possible reasons for the occurrence (such as excessively deep anaesthesia or hypoventilation) are eliminated before other drugs like atropine or antiarrhythmics are administered.

Avian anesthesia

Providing a safe anesthetic environment is the key to successful avian anesthesia. Knowledge and understanding the anatomic and physiologic differences between birds and mammals help to prevent most emergency situations and guide responses in critical situations. Thorough preanesthetic history and examination, correction of underlying conditions, and use of simple anesthetic protocols all optimize the outcome of the procedure. Finally, critical monitoring helps to anticipate most crises and reduces incidences of mortality and morbidity in avian anesthesia.

Primate anesthesia

This article provides an update on some of the recent advances in primate anesthesia. It focuses in particular on some of the newest information available regarding the effects of opioids and alpha-2 agonists in primates, and how these effects are different from what we might expect in other companion animals. It reviews the important properties of the latest induction and inhalation agents, and stresses the need for continuous monitoring of the anesthetized patient.