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.     

The effect of nitrous oxide on halothane, isoflurane and sevoflurane requirements in ventilated dogs undergoing ovariohysterectomy

OBJECTIVE: To examine the effect of 64% nitrous oxide (N2O) on halothane (HAL), isoflurane (ISO) or sevoflurane (SEV) requirements in dogs undergoing ovariohysterectomy. STUDY DESIGN: Prospective, randomized, clinical trial. ANIMALS: Ninety, healthy dogs of (mean +/- SD) body weight 21.2 +/- 10.0 kg and age 17.8 +/- 22.8 months. MATERIALS AND METHODS: After premedication with acepromazine, hydromorphone and glycopyrrolate, anesthesia was induced with thiopental administered to effect. Dogs received one of six inhalant protocols (n = 15 group): HAL; HAL/N2O; ISO; ISO/N2O; SEV; or SEV/N2O. End-tidal CO2 was maintained at 40 +/- 2 mmHg with intermittent positive pressure ventilation (IPPV). Body temperature, heart rate, indirect systemic arterial blood pressures, inspired and end-tidal CO2, volatile agent, N2O and O2 were recorded every 5 minutes. The vaporizer setting was decreased in 0.25-0.5% decrements to elicit a palpebral reflex, and this level maintained. Statistical analysis included two-way anova for repeated measures with Bonferroni's correction factor and statistical significance assumed when p < 0.05. Percentage reduction in end-tidal volatile agent was calculated at 60 minutes after starting study. RESULTS: End-tidal HAL, ISO and SEV decreased when N2O was administered. Percentage reduction: HAL (12.4%); ISO (37.1%) and SEV (21.4%). Diastolic, mean and systolic blood pressures increased in ISO/N2O compared with ISO. Heart rate increased in ISO/N2O and SEV/N2O compared with ISO and SEV, respectively. Systolic, mean and diastolic blood pressures increased in SEV compared with HAL and ISO. Systolic, mean, diastolic blood pressures and heart rate increased in SEV/N2O and ISO/N2O compared with HAL/N2O. CONCLUSIONS: N2O reduces HAL, ISO and SEV requirements in dogs undergoing ovariohysterectomy. Cardiovascular stimulation occurred when N2O was used with ISO, less so with SEV and not with HAL     

Anesthetic effects of ketamine or isoflurane induction prior to isoflurane anesthesia in medetomidine-premedicated dogs

Dogs were given medetomidine (10 microg/kg body weight, intramuscularly) followed in 10 minutes by either ketamine (4 mg/kg body weight, intravenously) or isoflurane mask induction and maintained on isoflurane for 30 minutes. Medetomidine induced lateral recumbency in all dogs. Endotracheal intubation was faster and smoother when dogs were given ketamine than when induced with isoflurane. Analgesia was excellent in all groups. Respiratory depression was more profound when dogs were given ketamine. Recovery quality was smooth and similar among all groups. Medetomidine-premedicated dogs could be induced with either ketamine or isoflurane and maintained on 1.3% isoflurane to achieve good analgesia with smooth recovery from anesthesia.     

Inhalation anesthesia in Dumeril's monitor (Varanus dumerili) with isoflurane, sevoflurane, and nitrous oxide: effects of inspired gases on induction and recovery.

Induction and recovery from inhalation anesthesia of Dumeril's monitors (Varanus dumerili) using isoflurane, sevoflurane, and nitrous oxide (N2O) were characterized using a randomized crossover design. Mean times to induction for isoflurane in 100% oxygen (O2), sevoflurane in 100% O2, sevoflurane in 21% O2:79% nitrogen (N2; room air), and sevoflurane in 66% N2O:34% O2 were 13.00 +/- 4.55, 11.20 +/- 3.77, 10.40 +/- 2.50, and 9.40 +/- 2.80 min, respectively, at 26 degrees C (n = 10). Mask induction with sevoflurane was significantly faster than with isoflurane. There was no significant difference between the induction time for sevoflurane in O2 or in room air, but sevoflurane combined with N2O resulted in significantly faster inductions than were obtained with sevoflurane in 100% O2. All treatments resulted in a significantly higher respiratory rate than in undisturbed animals. There were no significant differences in respiratory rate among lizards receiving O2, isoflurane in 100% O2, sevoflurane in room air, and sevoflurane combined with N2O, but animals receiving sevoflurane in O2 had a lower respiratory rate than those receiving pure O2. The sequence of complete muscle relaxation during induction was consistent and not significantly different among the four treatments: front limbs lost tone first, followed by the neck and the hind limbs; then the righting reflex was lost and finally tail tone. There were no significant differences in recovery times between isoflurane and sevoflurane or between sevoflurane in 100% O2 and sevoflurane combined with N2O. Similar recovery times were observed in animals recovering in 100 and 21% O2.     

Effects of hypercapnic hyperpnea on recovery from isoflurane or sevoflurane anesthesia in horses

Objective To test the hypothesis that hypercapnic hyperpnea produced using endotracheal insufflation with 5–10% CO₂ in oxygen could be used to shorten anesthetic recovery time in horses, and that recovery from sevoflurane would be faster than from isoflurane. Study design Randomized crossover study design. Animals Eight healthy adult horses. Methods After 2 hours’ administration of constant 1.2 times MAC isoflurane or sevoflurane, horses were disconnected from the anesthetic circuit and administered 0, 5, or 10% CO₂ in balance O₂ via endotracheal tube insufflation. End‐tidal gas samples were collected to measure anesthetic washout kinetics, and arterial and venous blood samples were collected to measure respiratory gas partial pressures. Horses recovered in padded stalls without assistance, and each recovery was videotaped and evaluated by reviewers who were blinded to the anesthetic agent and insufflation treatment used. Results Compared to isoflurane, sevoflurane caused greater hypoventilation and was associated with longer times until standing recovery. CO₂ insufflation significantly decreased anesthetic recovery time compared to insufflation with O₂ alone without significantly increasing PaCO₂. Pharmacokinetic parameters during recovery from isoflurane with CO₂ insufflation were statistically indistinguishable from sevoflurane recovery without CO₂. Neither anesthetic agent nor insufflation treatment affected recovery quality from anesthesia. Conclusions and clinical relevance Hypercapnic hyperpnea decreases time to standing without influencing anesthetic recovery quality. Although the lower blood gas solubility of sevoflurane should favor a shorter recovery time compared to isoflurane, this advantage is negated by the greater respiratory depression from sevoflurane in horses.     

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.     

Mask induction of anaesthesia with isoflurane or sevoflurane in premedicated cats

A comparison was made of the time to and quality of induction of anaesthesia when sevoflurane (n=14) or isoflurane (n=14) was delivered by mask in premedicated healthy adult cats presented for elective surgery. Times to induction and intubation were significantly shorter with sevoflurane (210 +/- 57 seconds and 236 +/- 60 seconds, respectively) than with isoflurane (264 +/- 75 seconds and 292 +/- 73 seconds). The quality of induction was similar for both agents. Two cats in each group developed opisthotonus of less than 45 seconds' duration. Both sevoflurane and isoflurane produced mask induction of anaesthesia of a similar quality in this species. Sevoflurane provided more rapid induction of anaesthesia and establishment of a controlled airway than isoflurane.     

The effects of nitrous oxide on recovery from isoflurane anaesthesia in dogs

O bjectives : To assess rate and quality of recovery from anaesthesia where isoflurane was delivered in oxygen or oxygen/nitrous oxide.
M ethods : Dogs anaesthetised with propofol were randomly allocated to receive isoflurane maintenance in either 100 per cent oxygen (group 1) or 66 per cent nitrous oxide (N₂O)/34 per cent oxygen (group 2). Time from end of anaesthesia to achieving sternal recumbency was recorded. Incidence of adverse behaviours (vocalisation, uncontrolled head movement and restlessness) were assessed. Recovery quality was recorded on a visual analogue scale (VAS) (anchored at 0 with "best possible" recovery and "did not recover" at 100 mm). Age, weight, gender, anaesthetic duration, mean vaporiser setting, VAS scores, recovery times, postoperative temperature and behavioural scores were compared (chi-squared test, Mann-Whitney U test or t -test as appropriate, significance P≤0·05).
R esults : Objective data from 54 dogs were analysed, only VAS data where the observer was unaware of treatment group were used (n=33). Recovery was faster in group 2 dogs (median 10 min [range 4 to 31] compared with 14 minutes [3 to 43] in group 1, P=0·049) with less restlessness (0 [0 to 4] compared with 2 [0 to 4] in group 1, P=0·013) and uncontrolled head movement (0 [0 to 4] compared with 1 [0 to 3] in group 1, P<0·001). However, VAS scores were not statistically different between groups (group 1: mean 39·4 mm [s.d. 24·0)]; group 2: 30·1 mm [25·9]; P=0·303).
C linical S ignificance : Addition of N₂O to isoflurane anaesthesia results in a lower incidence of adverse behaviour (for example restlessness) and marginally faster recovery.     

Hepatic effects of halothane, isoflurane or sevoflurane anaesthesia in dogs

The effects of halothane, isoflurane and sevoflurane anaesthesia on hepatic function and hepatocellular damage were investigated in dogs, comparing the activity of hepatic enzymes and bilirubin concentration in serum. An experimental study was designed. Twenty-one clinically normal mongrel dogs were divided into three groups and accordingly anaesthetized with halothane (n = 7), isoflurane (n = 7) and sevoflurane (n = 7). The dogs were 1-4 years old, and weighed between 13.5 and 27 kg (18.4 +/- 3.9). Xylazine HCI (1-2 mg/kg) i.m. was used as pre-anaesthetic medication. Anaesthesia was induced with propofol 2 mg/kg i.v. The trachea was intubated and anaesthesia maintained with halothane, isoflurane or sevoflurane in oxygen at concentrations of 1.35, 2 and 3%, respectively. Intermittent positive pressure ventilation (tidal volume, 15 ml/kg; respiration rate, 12-14/min) was started immediately after intubation and the anaesthesia lasted for 60 min. Venous blood samples were collected before pre-medication, 24 and 48 h, and 7 and 14 days after anaesthesia. Serum level of aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP) and gamma-glutamyltransferase (GGT), lactate dehydrogenase (LDH GGT) activities and bilirubin concentration were measured. Serum AST, ALT and GGT activities increased after anaesthesia in all groups. In the halothane group, serum AST and ALT activities significantly increased all the time after anaesthesia compared with baseline activities. But in the isoflurane group AST and ALT activities increased only between 2 and 7 days, and in the sevoflurane group 7 days after anaesthesia. GGT activity was increased in the halothane group between 2 and 7 days, and in the isoflurane and sevoflurane groups 7 days after anaesthesia. All dogs recovered from anaesthesia without complications and none developed clinical signs of hepatic damage within 14 days. The results suggest that the use of halothane anaesthesia induces an elevation of serum activities of liver enzymes more frequently than isoflurane or sevoflurane from 2 to 14 days after anaesthesia in dogs. The effects of isoflurane or sevoflurane anaesthesia on the liver in dogs is safer than halothane anaesthesia in dogs.     

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

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

Recovery characteristics following maintenance of anaesthesia with sevoflurane or isoflurane in dogs premedicated with acepromazine

A standard anaesthetic protocol was used to anaesthetise 40 dogs for intravenous urography and a retrograde urethrogram or vaginourethrogram. The dogs were allocated by blocked randomisation to receive either isoflurane or sevoflurane for maintenance of anaesthesia after they had been premedicated with acepromazine and pethidine, and anaesthesia induced with propofol. An observer who was unaware of which agent had been used assessed ataxia 30 and 60 minutes after discontinuation of administration of the anaesthetic and assigned an overall recovery score. No complications occurred during anaesthesia of either group of dogs. The scores for ataxia were significantly lower after 60 minutes than after 30 minutes, but there was no significant difference between the groups. The quality of recovery was significantly better in the dogs that received sevoflurane than in those that received isoflurane, but the recovery times were similar.     

Speed of induction of anaesthesia in dogs administered halothane, isoflurane, sevoflurane or propofol in a clinical setting

OBJECTIVE: To compare the speed and quality of induction of general anaesthesia using three different inhalant agents and one intravenous agent, in healthy dogs undergoing desexing surgery. MATERIALS AND METHODS: Less excitable dogs were not premedicated; others were premedicated with intramuscular acepromazine and morphine. Anaesthesia induction protocol was randomly assigned, with halothane, isoflurane or sevoflurane delivered by mask, or propofol delivered intravenously. Maximum vaporiser settings were used for inhalant inductions. Induction of anaesthesia was considered complete at the time of endotracheal intubation. Quality of induction was scored by the administering veterinarian. RESULTS: Seventy-one dogs were enrolled. Twenty-four received no premedication and 47 received premedication. Isoflurane inductions were significantly faster than halothane inductions (2.86 +/- 0.25 vs 3.71 +/- 0.22 min; mean +/- SE, P = 0.013). Sevoflurane inductions (3.29 +/- 0.24 min) were not significantly different from either halothane (3.71 +/- 0.22 min, P = 0.202) or isoflurane inductions (2.86 +/- 0.25 min, P = 0.217). Induction with propofol (1.43 +/- 0.13 min) was significantly faster than inhalant induction (P < 0.001 in each case). Premedication decreased the dose requirement and time to induction for dogs induced with propofol, but did not significantly change the time to intubation for inhalant inductions. Dogs administered propofol and/or premedication were significantly more likely to have an excellent quality of induction, but there was no difference between inhalant agents in terms of induction quality. CONCLUSION: Sevoflurane possesses chemical properties that should produce a more rapid induction of anaesthesia in comparison to halothane or isoflurane. However, in clinical practice patient related factors outweigh this improvement.     

Desaturation times between dogs preoxygenated via face mask or flow-by technique before induction of anesthesia

Objective

To compare time to desaturation after induction of anesthesia following administration of oxygen via face mask or flow-by for 3 minutes.

Evaluation of induction characteristics and hypnotic potency of isoflurane and sevoflurane in healthy dogs

OBJECTIVE: To determine induction characteristics and the minimum alveolar concentration (MAC) at which consciousness returned (MACawake) in dogs anesthetized with isoflurane or sevoflurane. ANIMALS: 20 sexually intact male Beagles. PROCEDURES: In experiment 1, 20 dogs were randomly assigned to have anesthesia induced and maintained with isoflurane or sevoflurane. The MAC at which each dog awoke in response to auditory stimulation (MACawake-noise) was determined by decreasing the end-tidal concentration by 0.1 volume (vol %) every 15 minutes and delivering a standard audible stimulus at each concentration until the dog awoke. In experiment 2, 12 dogs received the same anesthetic agent they were administered in experiment 1. After duplicate MAC determination, the end-tidal concentration was continually decreased by 10% every 15 minutes until the dog awoke from anesthesia (MACawake). RESULTS: Mean induction time was significantly greater for isoflurane-anesthetized dogs (212 seconds), compared with the sevoflurane-anesthetized dogs (154 seconds). Mean+/-SD MACawake-noise was 1.1+/-0.1 vol % for isoflurane and 2.0+/-0.2 vol % for sevoflurane. Mean MAC was 1.3+/-0.2 vol % for isoflurane and 2.1+/-0.6 vol % for sevoflurane, and mean MACawake was 1.0+/-0.1 vol % for isoflurane and 1.3+/-0.3 vol % for sevoflurane. CONCLUSIONS AND CLINICAL RELEVANCE: Sevoflurane resulted in a more rapid induction than did isoflurane. The MACawake for dogs was higher than values reported for both agents in humans. Care should be taken to ensure that dogs are at an appropriate anesthetic depth to prevent consciousness, particularly when single-agent inhalant anesthesia is used.     

The use of sevoflurane in a 2:1 mixture of nitrous oxide and oxygen for rapid mask induction of anaesthesia in the cat.

An inhalational technique for rapid induction of anaesthesia in unsedated cats using sevoflurane and nitrous oxide is described. Using a pliable, tight-fitting, face mask, sevoflurane (7.5-8%) was delivered from an out-of-circuit precision vaporiser connected to a coaxial non-rebreathing system using a fresh gas flow of 1 l oxygen and 2 l nitrous oxide per min. Cats were restrained with gentle but firm pressure applied by scruffing the dorsal cervical skin until the righting reflex was lost and the patient could be positioned in lateral recumbency. Typically, cats could be positioned on their side in a light plane of anaesthesia within 1 min of applying the mask, at which time the sevoflurane concentration was reduced to 5% or less. A similar protocol, using a lower initial concentration of sevoflurane, is recommended for old or debilitated patients. Maintenance of light sevoflurane (2-4%) anaesthesia by mask permitted minor interventions to be performed readily, including blood collection, intravenous chemotherapy, abdominal palpation, radiography and ultrasonography. More painful procedures, such as bone marrow aspiration, required a deeper plane of anaesthesia. Cats were sufficiently deep to be intubated, if this was required, about 3 min after commencing the induction. Recovery from sevoflurane/nitrous oxide anaesthesia was smooth and rapid, with most cats being able to right within 5 min of discontinuing the agents. This protocol for rapid inhalational induction and recovery is particularly suited to feline practice, where rendering an uncooperative patient unconscious greatly facilitates the completion of many minor diagnostic and therapeutic procedures, especially when these must be performed on successive days or when peripheral vascular access is limited. For longer procedures, isoflurane may be substituted for sevoflurane for maintenance of anaesthesia in order to minimise cost.     

Serum biochemical indicators of hepatobiliary function in dogs following prolonged anaesthesia with sevoflurane or isoflurane

Objective To investigate the changes in serum enzymes considered as biochemical indicators of hepatobiliary function in dogs following 5 hours of anaesthesia with isoflurane (ISO) or sevoflurane (SEVO). Study design Experimental randomized crossover study, with intervals of at least 15 days between successive treatments. Animals Eight healthy adult mongrel dogs, four male, four female, weight 13.6–21.6 kg. Methods Treatments consisted of anaesthesia with ISO or SEVO at 1 or 1.5 minimum alveolar concentration (MAC) delivered in oxygen. MAC was taken as 1.39% for ISO and 2.36% for SEVO. Anaesthesia was induced by mask then, after endotracheal intubation, maintained according to the treatment protocol using a small animal circle system. Cardiopulmonary monitoring was carried out. Venous blood samples, obtained by needle puncture, were taken at 24 hours and 2, 7 and 14 days post anaesthesia. Serum concentrations of total protein, aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactate dehydrogenase, (LDH), alkaline phosphatase (ALP), gamma‐glutamyltransferese and total bilirubin were measured. Changes with time and with treatment were compared by Friedman analysis, Wilcoxon Signed test and Kruskal‐Wallis test as relevant. p‐ value < 0.05 was considered significant. Results Compared to base‐line values, at 24 hours post‐anaesthesia there were significant increases in AST, ALT, ALP and LDH following one or more of the treatments, but by 2 days residual changes were not significant. At 24 hours, AST for treatment 1.5 MAC ISO was higher than 1 MAC ISO (p < 0.002), and LDH higher for 1.5 MAC SEVO than 1 MAC SEVO. Conclusion and clinical relevance Both ISO and SEVO, at concentrations used for clinical anaesthesia, produce transient moderate effects on some hepatobiliary enzyme concentrations in dogs.