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.     

Recent advances in inhalation anesthesia.

Both desflurane and sevoflurane offer theoretical and practical advantages over other inhalation anesthetics for horses. The lower solubility of both agents provides improved control of delivery and helps to counteract the confounding influence of the voluminous patient breathing circuit commonly used for anesthetizing horses. The lower solubility should account for faster rates of recovery compared with the older agents; whether or not the quality of recovery differs remains to be objectively evaluated in a broad range of circumstances. The pharmacodynamic effects are, in large part, similar to those of isoflurane (e.g., low arrhythmogenicity) but with some differences. For example, desflurane may be overall more sparing to cardiovascular function (especially during controlled ventilation) compared with isoflurane and sevoflurane, which are roughly similar. Respiratory depression with both new agents is equal to or more depressing than isoflurane, suggesting the use of mechanical ventilation, especially in circumstances of prolonged management (i.e., hours of anesthesia). Both new anesthetics, not surprisingly, are expensive. From this point there are some agent-unique considerations. The anesthetic potency of both agents is less than that of isoflurane, which influences the cost of anesthesia, but also places an upper limit on inspired oxygen concentration (of particular concern with desflurane). Both agents require new vaporizers, but because of the high boiling point and steep vapor-pressure curve of desflurane, new technology was required. This translates into more costly equipment, adding to the cost of desflurane use. In addition, electricity is necessary for the new desflurane vaporizer to function, which limits its portability and adds additional practical considerations in its clinical use. On the other hand, desflurane strongly resists degradation both in vitro and in vivo, but in vitro degradation of sevoflurane by CO2 absorbents may produce renal injury. This may be true especially in association with low fresh-gas inflow rates (used to reduce the cost of using the new agent), and university based practices, where prolonged anesthesia is common.     

Induction and recovery characteristics and cardiopulmonary effects of sevoflurane and isoflurane in bald eagles

OBJECTIVE: To compare induction and recovery characteristics and cardiopulmonary effects of isoflurane and sevoflurane in bald eagles. Animals-17 healthy adult bald eagles. PROCEDURES: Anesthesia was induced with isoflurane or sevoflurane delivered in oxygen via a facemask in a crossover design with 4 weeks between treatments. Eagles were intubated, allowed to breathe spontaneously, and instrumented for cardiopulmonary measurements. Time to induction, extubation, and recovery, as well as smoothness of recovery, were recorded. RESULTS: Administration of sevoflurane resulted in a significantly quicker recovery, compared with isoflurane. Temperature, heart rate, and respiratory rate significantly decreased over time, whereas systolic (SAP), diastolic (DAP), and mean arterial blood pressure (MAP) significantly increased over time with each treatment. Temperature, heart rate, SAP, DAP, and MAP were significantly higher with isoflurane. Blood pH significantly decreased, whereas PaCO(2) significantly increased over time with each treatment. Bicarbonate and total carbon dioxide concentrations significantly increased over time with each treatment; however, there was a significant time-treatment interaction. The PaO(2) and arterial oxygen saturation increased over time with isoflurane and decreased over time with sevoflurane with a significant time-treatment interaction. Six eagles developed cardiac arrhythmias with isoflurane, as did 4 with sevoflurane anesthesia. CONCLUSIONS AND CLINICAL RELEVANCE: Isoflurane and sevoflurane administration resulted in smooth, rapid induction of and recovery from anesthesia similar to other species. Isoflurane administration resulted in tachycardia, hypertension, and more arrhythmias, compared with sevoflurane. Sevoflurane was associated with fewer adverse effects and may be particularly beneficial in compromised bald eagles.     

Median effective dose of isoflurane, sevoflurane, and desflurane in green iguanas

OBJECTIVE: To determine the median effective dose (ED(50); equivalent to the minimum alveolar concentration [MAC]) of isoflurane, sevoflurane, and desflurane for anesthesia in iguanas. ANIMALS: 6 healthy adult green iguanas. PROCEDURE: In unmedicated iguanas, anesthesia was induced and maintained with each of the 3 volatile drugs administered on separate days according to a Latin square design. Iguanas were endotracheally intubated, mechanically ventilated, and instrumented for cardiovascular and respiratory measurements. During each period of anesthesia, MAC was determined in triplicate. The mean value of 2 consecutive expired anesthetic concentrations, 1 that just permitted and 1 that just prevented gross purposeful movement in response to supramaximal electrical stimulus, and that were not different by more than 15%, was deemed the MAC. RESULTS: Mean +/- SD values for the third MAC determination for isoflurane, sevoflurane, and desflurane were 1.8 +/- 0.3%, 3.1 +/- 1.0%, and 8.9 +/- 2.1% of atmospheric pressure, respectively. The MAC for all inhaled agents was, on average, 22% greater for the first measurement than for the third measurement. CONCLUSIONS AND CLINICAL RELEVANCE: Over time, MACs decreased for all 3 agents. Final MAC measurements were similar to values reported for other species. The decrease in MACs over time may be at least partly explained by limitations of anesthetic uptake and distribution imposed by the reptilian cardiorespiratory system. Hence, for a constant end-tidal anesthetic concentration in an iguana, the plane of anesthesia may deepen over time, which could contribute to increased morbidity during prolonged procedures.     

Cardiopulmonary and acid-base effects of desflurane and sevoflurane in spontaneously breathing cats

The cardiopulmonary effects of desflurane and sevoflurane anesthesia were compared in cats breathing spontaneously. Heart (HR) and respiratory (RR) rates; systolic (SAP), diastolic (DAP) and mean arterial (MAP) pressures; partial pressure of end tidal carbon dioxide (PETCO2), arterial blood pH (pH), arterial partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2); base deficit (BD), arterial oxygen saturation (SaO2) and bicarbonate ion concentration (HCO3) were measured. Anesthesia was induced with propofol (8+/-2.3mg/kg IV) and maintained with desflurane (GD) or sevoflurane (GS), both at 1.3 MAC. Data were analyzed by analysis of variance (ANOVA), followed by the Tukey test (P<0.05). Both anesthetics showed similar effects. HR and RR decreased when compared to the basal values, but remained constant during inhalant anesthesia and PETCO2 increased with time. Both anesthetics caused acidemia and hypercapnia, but BD stayed within normal limits. Therefore, despite reducing HR and SAP (GD) when compared to the basal values, desflurane and sevoflurane provide good stability of the cardiovascular parameters during a short period of inhalant anesthesia (T20-T60). However, both volatile anesthetics cause acute respiratory acidosis in cats breathing spontaneously.     

Other new and potentially useful inhalational anesthetics.

Sevoflurane and desflurane are volatile inhaled anesthetics that are currently being investigated as possible improvements for the anesthetic management of human patients. Information to date suggests these agents have several advantages over existing clinical agents. For example, the blood/gas partition coefficient for both agents is lower than that of other halogenated anesthetics. Consistent with this physical characteristic is a more rapid induction of and emergence from anesthesia. Both cause a dose-related depression of cardiopulmonary function, which is comparable to isoflurane. Results of studies to date favor desflurane over sevoflurane because it is less soluble in blood, is stable in soda lime, is biodegraded the least of any volatile anesthetic, and is not toxic.     

Comparison of the arterial blood gas,arterial oxyhaemoglobin saturation and end-tidal carbon dioxide tension during sevoflurane or isoflurane anaesthesia in rabbits

The effects of sevoflurane or isoflurane on arterial blood gas, arterial oxyhaemoglobin saturation and end-tidal CO2 tension were monitored during induction and maintenance of anaesthesia in 10 premedicated New Zealand White (NZW) rabbits.For induction, the anaesthetic agents were delivered via a face-mask. After induction was completed, an endotracheal tube was introduced for maintenance of anaesthesia for a period of 90 minutes. Changes in heart rate, respiratory rate, arterial blood gas, arterial oxyhaemoglobin saturation, blood pH and end-tidal CO2 tension were recorded. Although sevoflurane and isoflurane produce similar cardiopulmonary effects in premedicated rabbits, sevoflurane provides a smoother and faster induction because of its lower blood/gas partition coefficient. Thus sevoflurane is probably a more suitable agent than isoflurane for mask induction and maintenance. Its lower blood solubility also makes sevoflurane more satisfactory than isoflurane for maintenance of anaesthesia because it allows the anaesthetist to change the depth of anaesthesia more rapidly.     

Detomidine reduces isoflurane anesthetic requirement (MAC) in horses

Objective To quantitate the dose‐ and time‐related magnitude of the anesthetic sparing effect of, and selected physiological responses to detomidine during isoflurane anesthesia in horses. Study design Randomized cross‐over study. Animals Three, healthy, young adult horses weighing 485 ± 14 kg. Methods Horses were anesthetized on two occasions to determine the minimum alveolar concentration (MAC) of isoflurane in O₂ and then to measure the anesthetic sparing effect (time‐related MAC reduction) following IV detomidine (0.03 and 0.06 mg kg^?1). Selected common measures of cardiopulmonary function, blood glucose and urinary output were also recorded. Results Isoflurane MAC was 1.44 ± 0.07% (mean ± SEM). This was reduced by 42.8 ± 5.4% and 44.8 ± 3.0% at 83 ± 23 and 125 ± 36 minutes, respectively, following 0.03 and 0.06 mg kg^?1, detomidine. The MAC reduction was detomidine dose‐ and time‐dependent. There was a tendency for mild cardiovascular and respiratory depression, especially following the higher detomidine dose. Detomidine increased both blood glucose and urine flow; the magnitude of these changes was time‐ and dose‐dependent Conclusions Detomidine reduces anesthetic requirement for isoflurane and increases blood glucose concentration and urine flow in horses. These changes were dose‐ and time‐related. Clinical relevance The results imply potent anesthetic sparing actions by detomidine. The detomidine‐related increased urine flow should be considered in designing anesthetic protocols for individual horses.     

Clinical comparison of isoflurane and sevoflurane anaesthesia in the gerbil (Meriones unguiculatus)

The objective of this study was a comparison of the volatile anaesthetics isoflurane and sevoflurane in terms of their clinical effects in gerbils (Meriones unguiculatus) (n=12 each). Induction of anaesthesia was performed in a body chamber with an anaesthetic concentration of 4.0 Vol.% at an oxygen flow of 500 ml/min for isoflurane and 8.0 Vol.% at an oxygen flow of 1000 ml/min for sevoflurane, respectively. Anaesthesia was maintained via nose cone with an anaesthetic concentration of 2.8 to 3.2 Vol.% at an oxygen flow of 200 ml/min for isoflurane and 5.0 to 5.2 Vol.% at an oxygen flow of 400 ml/min for sevoflurane. Those anaesthetic concentrations ensured reflex status conform with surgical tolerance. In spite of its higher blood-gas coefficient induction time was slightly faster for isoflurane. Recovery time was significantly longer in the isoflurane group than it was in the sevoflurane group. Both inhalants caused respiratory depression. Respiratory rate was lower in sevoflurane animals compared to isoflurane. The animals were positioned on a heating pad immediately after induction, thus a decrease of the body temperature could be prevented. Both inhalants can be recommended for usage in gerbils. Sevoflurane showed no clinical benefit compared to isoflurane.     

Anesthetic indices of sevoflurane and isoflurane in unpremedicated dogs

OBJECTIVE: To compare the anesthetic index of sevoflurane with that of isoflurane in unpremedicated dogs. DESIGN: Randomized complete-block crossover design. ANIMALS: 8 healthy adult dogs. PROCEDURE: Anesthesia was induced by administering sevoflurane or isoflurane through a face mask. Time to intubation was recorded. After induction of anesthesia, minimal alveolar concentration (MAC) was determined with a tail clamp method while dogs were mechanically ventilated. Apneic concentration was determined while dogs were breathing spontaneously by increasing the anesthetic concentration until dogs became apneic. Anesthetic index was calculated as apneic concentration divided by MAC. RESULTS: Anesthetic index of sevoflurane (mean +/- SEM, 3.45 +/- 0.22) was significantly higher than that of isoflurane (2.61 +/- 0.14). No clinically important differences in heart rate; systolic, mean, and diastolic blood pressures; oxygen saturation; and respiratory rate were detected when dogs were anesthetized with sevoflurane versus isoflurane. There was a significant linear trend toward lower values for end-tidal partial pressure of carbon dioxide during anesthesia with sevoflurane, compared with isoflurane, at increasing equipotent anesthetic doses. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that sevoflurane has a higher anesthetic index in dogs than isoflurane. Sevoflurane and isoflurane caused similar dose-related cardiovascular depression, but although both agents caused dose-related respiratory depression, sevoflurane caused less respiratory depression at higher equipotent anesthetic doses.     

Cardiopulmonary effects and induction and recovery characteristics of isoflurane and sevoflurane in foals

OBJECTIVE: To compare induction and recovery characteristics and cardiopulmonary effects of isoflurane and sevoflurane in foals. DESIGN: Prospective crossover study. ANIMALS: 6 healthy foals. PROCEDURE: Foals were anesthetized twice (once at 1 month of age and again at 3 months of age). Anesthesia was induced by administration of the agent in oxygen through a nasotracheal tube. During maintenance of anesthesia, foals were positioned in dorsal recumbency; intermittent positive-pressure ventilation was performed. Characteristics of induction and recovery were recorded. Cardiopulmonary variables were recorded 10 minutes after anesthetic induction and 15, 30, 45, and 60 minutes later. RESULTS: All 6 foals were successfully anesthetized with isoflurane and sevoflurane. There were no significant differences between the 2 drugs in regard to characteristics of induction or recovery, and induction and recovery were generally smooth and unremarkable. There were no significant differences between drugs in regard to measured cardiopulmonary variables; however, both drugs caused initial hypotension that resolved over time. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that isoflurane and sevoflurane can both be used for general anesthesia of 1- to 3-month-old foals. Significant differences between the 2 agents were not detected for any of the variables measured, suggesting that quality of anesthesia with these 2 agents was comparable.     

Pharmacokinetics of inhaled anesthetics in green iguanas (Iguana iguana)

OBJECTIVE: To test the hypothesis that differences in anesthetic uptake and elimination in iguanas would counter the pharmacokinetic effects of blood:gas solubility and thus serve to minimize kinetic differences among inhaled agents. ANIMALS: 6 green iguanas (Iguana iguana). PROCEDURES: Iguanas were anesthetized with isoflurane, sevoflurane, or desflurane in a Latin-square design. Intervals from initial administration of an anesthetic agent to specific induction events and from cessation of administration of an anesthetic agent to specific recovery events were recorded. End-expired gas concentrations were measured during anesthetic washout. RESULTS: Significant differences were not detected for any induction or recovery events for any inhalation agent in iguanas. Washout curves best fit a 2-compartment model, but slopes for both compartments did not differ significantly among the 3 anesthetics. CONCLUSIONS AND CLINICAL RELEVANCE: Differences in blood:gas solubility for isoflurane, sevoflurane, and desflurane did not significantly influence differences in pharmacokinetics for the inhalation agents in iguanas.     

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

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

Comparisons of Sevoflurane, Isoflurane, and Halothane Anesthesia in Spontaneously Breathing Cats

The clinical effects of sevoflurane, isoflurane, and halothane anesthesia with or without nitrous oxide, were compared in healthy, premedicated cats breathing spontaneously during 90 minutes of anesthesia. The effect of nitrous oxide in accelerating the induction of and recovery from anesthesia was more evident for halothane than for sevoflurane or isoflurane. The cats recovered more rapidly from sevoflurane-oxygen than from either halothane- or isoflurane-oxygen. Heart rates did not significantly change during anesthesia with any of the anesthetics. Arterial blood pressures during sevoflurane-oxygen anesthesia were somewhat higher than those with either isoflurane- or halothane-oxygen. There were no significant differences in arterial blood pressures among sevoflurane, isoflurane, and halothane anesthesia when combined with nitrous oxide. The respiration rate during sevoflurane-oxygen was similar to that during halothane-oxygen. There were no significant differences in respiration rate among sevoflurane, isoflurane, and halothane anesthesia when combined with nitrous oxide. The degree of hypercapnia and acidosis during sevoflurane anesthesia was similar to that observed during isoflurane anesthesia and less than during halothane anesthesia. The three anesthetic regimens, with or without nitrous oxide, induced a similar degree of hyperglycemia and hemodilution during anesthesia. Serum biochemical examination did not reveal any hepatic or renal injuries after each anesthesia.     

A comparison of the duration and quality of recovery from isoflurane, sevoflurane and desflurane anaesthesia in dogs undergoing magnetic resonance imaging

ObjectiveTo compare the recovery after anaesthesia with isoflurane, sevoflurane and desflurane in dogs undergoing magnetic resonance imaging (MRI) of the brain.Study designProspective, randomized clinical trial.AnimalsThirty‐eight dogs weighing 23.7 ± 12.6 kg.MethodsFollowing pre‐medication with meperidine, 3 mg kg^?1 administered intramuscularly, anaesthesia was induced intravenously with propofol (mean dose 4.26 ± 1.3 mg kg^?1), the trachea was intubated, and an inhalational anaesthetic agent was administered in oxygen. The dogs were randomly allocated to one of three groups: group I (n = 13) received isoflurane, group S (n = 12) received sevoflurane and group D (n = 13) received desflurane. Parameters recorded included cardiopulmonary data, body temperature, end‐tidal anaesthetic concentration, duration of anaesthesia, and recovery times and quality. Qualitative data were compared using chi‐squared and Fisher's exact tests and quantitative data with anova and Kruskal–Wallis test. Post‐hoc comparisons for quantitative data were undertaken with the Mann–Whitney U‐test.ResultsThe duration of anaesthesia [mean and standard deviation (SD)] in group I was: 105.3 (27.48) minutes, group S: 120.67 (19.4) minutes, and group D: 113.69 (26.68) minutes (p = 0.32). Times to extubation [group I: 8 minutes, (interquartile range 6–9.5), group S: 7 minutes (IQR 5–7), group D: 5 minutes (IQR 3.5–7), p = 0.017] and to sternal recumbency [group I: 11 minutes (IQR 9.5–13.5), group S: 9.5 minutes (IQR 7.25–11.75), group D: 7 minutes (range 3.5–11.5), p = 0.048] were significantly different, as were times to standing. One dog, following sevoflurane, had an unacceptable quality of recovery, but most other recoveries were calm, with no significant difference between groups.Conclusions and clinical relevanceAll three agents appeared suitable for use. Dogs’ tracheas were extubated and the dogs recovered to sternal recumbency most rapidly after desflurane. This may be advantageous for animals with some neurological diseases and for day case procedures.     

Comparison of isoflurane and sevoflurane anesthesia after premedication with butorphanol in the green iguana (Iguana iguana).

The anesthetic and cardiopulmonary effects of butorphanol followed by sevoflurane or isoflurane were compared in 23 male green iguanas (Iguana iguana). Heart and respiratory rates were recorded before administration of butorphanol (2 mg/kg i.m.) and at 30 min after premedication. Anesthesia was induced in 12 iguanas (group 1) with isoflurane (5%) and in 11 iguanas (group 2) with sevoflurane (7%). Heart rate, relative arterial oxygen hemoglobin saturation (SpO2), and end-tidal CO2 concentrations (EtCO2) were measured every minute for the first 5 min and every 5 min thereafter. Arterial blood gas parameters were determined at 10 and 40 min after induction. Thirty minutes after butorphanol administration, no significant changes in heart and respiratory rate were seen as compared with baseline values. Quality and time to induction were superior with butorphanol-sevoflurane (6 +/- 3 min) than with butorphanol-isoflurane (9 +/- 4 min). Vaporizer settings during maintenance ranged between 1-3% and 2-4%, respectively. No significant differences in heart rate were noted between groups. In the sevoflurane group, SpO2 values were > 90% throughout. Although SpO2, values were < 90% at 20, 25, and 30 min in the isoflurane group, no significant differences in SpO2 values were seen over time and between groups. A significant decrease in EtCO2 with time was present in both groups, with no significant differences between the groups. At 10 and 40 min, arterial blood oxygen saturation values were > 90% in both groups and no significant differences were noted with time and between groups. Recovery time was significantly longer in the butorphanol-isoflurane group (35 +/- 27 min) than in the butorphanol-sevoflurane group (7 +/- 4 min). The cardiopulmonary effects of butorphanol-isoflurane and butorphanol-sevoflurane assessed in this study are similar, and both inhalants appear to be safe and effective for induction and maintenance in the green iguana.     

Comparison of an infrared anaesthetic agent analyser (Datex‐Ohmeda) with refractometry for measurement of isoflurane,sevoflurane and desflurane concentrations

ObjectiveTo assess agreement between infrared (IR) analysers and a refractometer for measurements of isoflurane, sevoflurane and desflurane concentrations and to demonstrate the effect of customized calibration of IR analysers.Study designIn vitro experiment.SubjectsSix IR anaesthetic monitors (Datex-Ohmeda) and a single portable refractometer (Riken).MethodsBoth devices were calibrated following the manufacturer’s recommendations. Gas samples were collected at common gas outlets of anaesthesia machines. A range of agent concentrations was produced by stepwise changes in dial settings: isoflurane (0–5% in 0.5% increments), sevoflurane (0–8% in 1% increments), or desflurane (0–18% in 2% increments). Oxygen flow was 2 L minute^?1. The orders of testing IR analysers, agents and dial settings were randomized. Duplicate measurements were performed at each setting. The entire procedure was repeated 24 hours later. Bland–Altman analysis was performed. Measurements on day-1 were used to yield calibration equations (IR measurements as dependent and refractometry measurements as independent variables), which were used to modify the IR measurements on day-2.ResultsBias ± limits of agreement for isoflurane, sevoflurane and desflurane were 0.2 ± 0.3, 0.1 ± 0.4 and 0.7 ± 0.9 volume%, respectively. There were significant linear relationships between differences and means for all agents. The IR analysers became less accurate at higher gas concentrations. After customized calibration, the bias became almost zero and the limits of agreement became narrower.Conclusions and clinical relevanceIf similar IR analysers are used in research studies, they need to be calibrated against a reference method using the agent in question at multiple calibration points overlapping the range of interest.     

Maintenance of anaesthesia in sheep with isoflurane, desflurane or sevoflurane

Rapid recovery from anaesthesia is advantageous in small ruminants, to reduce the risk of regurgitation. Theoretically, the least soluble inhalation agents should result in the fastest recoveries, but using additional injectable agents may negate this advantage. This study compared three inhalation agents for the maintenance of anaesthesia in sheep. Eighteen ewes that were to undergo orthopaedic surgery were allocated to one of three groups. Each group was premedicated with xylazine (0.1 mg/kg intramuscularly), anaesthesia was induced using ketamine (2 mg/kg) and midazolam (0.03 mg/kg) intravenously and analgesia provided by buprenorphine (0.008 mg/kg intramuscularly). Anaesthesia was then maintained with either isoflurane, sevoflurane or desflurane. Cardiopulmonary parameters were monitored throughout. All three inhalation agents provided adequate stable anaesthesia and there was no significant difference between the groups in their cardiopulmonary parameters or their recovery times. The mead (sd) postanaesthetic times to first swallow, first chewing attempts and ability to maintain their head lifted for five minutes were, respectively, 3.95 (2.53), 6.37 (3.68) and 32.8 (18.1) minutes for isoflurane, 3.62 (0.98), 7.66 (0.78) and 38.8 (16.6) minutes for sevoflurane, and 4.37 (1.65), 6.95 (1.52) and 29.8 (11.5) minutes for desflurane. Two sheep had poor quality recoveries after the use of sevoflurane, but all the other sheep recovered uneventfully. All three inhalation agents were suitable for the maintenance of anaesthesia in sheep but, as used in this study, there were no differences between them in speed of recovery.     

Effects of nitrous oxide on mask induction of anesthesia with sevoflurane or isoflurane in dogs.

OBJECTIVE: To determine the effects of nitrous oxide (N2O) on the speed and quality of mask induction with sevoflurane or isoflurane in dogs. ANIMALS: 7 healthy Beagles. PROCEDURE: Anesthesia was induced with sevoflurane or isoflurane delivered in 100% oxygen or in a 2:1 mixture of N2O and oxygen via a face mask. Each dog received all treatments with at least 1 week between treatments. Initial vaporizer settings were 0.8% for sevoflurane and 0.5% for isoflurane (0.4 times the minimum alveolar concentration [MAC]). Vaporizer settings were increased by 0.4 MAC at 15-second intervals until settings were 4.8% for sevoflurane and 3.0% for isoflurane (2.4 MAC). Times to onset and cessation of involuntary movements, loss of the palpebral reflex, negative response to tail-clamp stimulation, and endotracheal intubation were recorded, and cardiopulmonary variables were measured. RESULTS: Administration of sevoflurane resulted in a more rapid induction, compared with isoflurane. However, N2O had no effect on induction time for either agent. Heart rate, mean arterial blood pressure, cardiac output, and respiratory rate significantly increased and tidal volume significantly decreased from baseline values immediately after onset of induction in all groups. Again, concomitant administration of N2O had no effect on cardiopulmonary variables. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of N2O did not improve the rate or quality of mask induction with sevoflurane or isoflurane. The benefits provided by N2O attributable to concentrating and second gas effects appear minimal in healthy dogs when low solubility inhalation agents such as isoflurane and sevoflurane are used for mask induction.