Anesthetic potency and cardiopulmonary effects of sevoflurane in goats: comparison with isoflurane and halothane.

The anesthetic potency and cardiopulmonary effects of sevoflurane were compared with those of isoflurane and halothane in goats. The (mean +/- SD) minimal alveolar concentration (MAC) was 0.96 +/- 0.12% for halothane, 1.29 +/- 0.11% for isoflurane, and 2.33 +/- 0.15% for sevoflurane. Cardiopulmonary effects of sevoflurane, halothane and isoflurane were examined at end-tidal concentrations equivalent to 1, 1.5 and 2 MAC during either spontaneous or controlled ventilation (SV or CV). During SV, there were no significant differences in respiration rate, tidal volume and minute ventilation between anesthetics. Dose-dependent decreases in both tidal volume and minute ventilation induced by halothane were greater than those by either sevoflurane or isoflurane. Hypercapnia and acidosis induced by sevoflurane were not significantly different from those by either isoflurane or halothane at 1 and 1.5 MAC, but were less than those by halothane at 2 MAC. There was no significant difference in heart rate between anesthetics during SV and CV. During SV, all anesthetics induced dose-dependent decreases in arterial pressure, rate pressure product, systemic vascular resistance, left ventricular minute work index and left ventricular stroke work index. Systemic vascular resistance with isoflurane at 2 MAC was lower than that with sevoflurane. During CV, sevoflurane induced dose-dependent circulatory depression (decreases in arterial pressure, cardiac index, rate pressure product, systemic vascular resistance, left ventricular minute work index and right ventricular minute work index), similar to isoflurane. Halothane did not significantly alter systemic vascular resistance from 1 to 2 MAC.     

Assessment of halothane and sevoflurane anesthesia in spontaneously breathing rats

OBJECTIVE: To characterize halothane and sevoflurane anesthesia in spontaneously breathing rats. ANIMALS: 16 healthy male Sprague-Dawley rats. PROCEDURE: 8 rats were anesthetized with halothane and 8 with sevoflurane. Minimum alveolar concentration (MAC) was determined. Variables were recorded at anesthetic concentrations of 0.8, 1.0, 1.25, and 1.5 times the MAC of halothane and 1.0, 1.25, 1.5, and 1.75 times the MAC of sevoflurane. RESULTS: Mean (+/- SEM) MAC for halothane was 1.02 +/- 0.02% and for sevoflurane was 2.99 +/- 0.19%. As sevoflurane dose increased from 1.0 to 1.75 MAC, mean arterial pressure (MAP) decreased from 103.1 +/- 5.3 to 67.9 +/- 4.6 mm Hg, and PaCO2 increased from 58.8 +/- 3.1 to 92.2 +/- 9.2 mm Hg. As halothane dose increased from 0.8 to 1.5 MAC, MAP decreased from 99 +/- 6.2 to 69.8 +/- 4.5 mm Hg, and PaCO2 increased from 59.1 +/- 2.1 to 75.9 +/- 5.2 mm Hg. Respiratory rate decreased in a dose-dependent fashion from 88.5 +/- 4.5 to 58.5 +/- 2.7 breaths/min during halothane anesthesia and from 42.3 +/- 1.8 to 30.5 +/- 4.5 breaths/min during sevoflurane anesthesia. Both groups of rats had an increase in eyelid and pupillary aperture with an increase in anesthetic dose. CONCLUSIONS AND CLINICAL RELEVANCE: An increase in PaCO2 and a decrease in MAP are clinical indicators of an increasing halothane and sevoflurane dose in unstimulated spontaneously breathing rats. Increases in eyelid aperture and pupil diameter are reliable signs of increasing depth of halothane and sevoflurane anesthesia. Decreasing respiratory rate is a clinical indicator of an increasing dose of halothane.     

Effects of isoflurane,sevoflurane and methoxyflurane on the electroencephalogram of the chicken

ObjectiveAnaesthetics have differing effects on mammalian electroencephalogram (EEG) but little is known about the effects on avian EEG. This study explored how inhalant anaesthetics affect chicken EEG.Study designExperimental study.AnimalsTwelve female Hyline Brown chickens aged 6–11 weeks.MethodsEach chicken was anaesthetized with isoflurane, sevoflurane, and methoxyflurane. For each, anaesthesia was adjusted to 1, 1.5 and 2 times Minimum Anaesthetic Concentration (MAC). Total Power (Ptot), Median Frequency (F50), Spectral Edge Frequency (F95) and Burst Suppression Ratio (BSR) were calculated at each volume concentration. BSR data were analyzed using doubly repeated measures anova. Neither isoflurane nor sevoflurane could be included in analysis of F50, F95 and Ptot because of extensive burst suppression; Methoxyflurane data were analyzed using RM anova.ResultsThere was a significant interaction between anaesthetic and concentration on BSR [F(4,22) = 10.65, p < 0.0001]. For both isoflurane and sevoflurane, BSR increased with concentration. Isoflurane caused less suppression than sevoflurane at 1.5 MAC and at final 1 MAC while methoxyflurane caused virtually no burst suppression. Methoxyflurane concentration had a significant effect on F50 [F(2,20) = 3.83, p = 0.04], F95 [F(2,20) = 4.03, p = 0.03] and Ptot [F(2,20) = 5.22, p = 0.02]. Decreasing methoxyflurane from 2 to 1 MAC increased F50 and F95. Ptot increased when concentration decreased from 1.5 to 1 MAC and tended to be higher at 1 MAC than at 2 MAC.Conclusions and Clinical relevanceIsoflurane and sevoflurane suppressed chicken EEG in a dose-dependent manner. Higher concentrations of methoxyflurane caused an increasing degree of synchronization of EEG. Isoflurane and sevoflurane suppressed EEG activity to a greater extent than did methoxyflurane at equivalent MAC multiples. Isoflurane caused less suppression than sevoflurane at intermediate concentrations. These results indicate the similarity between avian and mammalian EEG responses to inhalant anaesthetics and reinforce the difference between MAC and anaesthetic effects on brain activity in birds.     

The influence of ventilation mode (spontaneous ventilation, IPPV and PEEP) on cardiopulmonary parameters in sevoflurane anaesthetized dogs

The purpose of this study was to investigate the cardiopulmonary influences of sevoflurane in oxygen at two anaesthetic concentrations (1.5 and 2 MAC) during spontaneous and controlled ventilation in dogs. After premedication with fentany-droperidol (5 microg/kg and 0.25 mg/kg intramuscularly) and induction with propofol (6 mg/kg intravenously) six dogs were anaesthetized for 3 h. Three types of ventilation were compared: spontaneous ventilation (SpV), intermittent positive pressure ventilation (IPPV), and positive end expiratory pressure ventilation (PEEP, 5 cm H2O). Heart rate, haemoglobin oxygen saturation, arterial blood pressures, right atrial and pulmonary arterial pressures, pulmonary capillary wedge pressure and cardiac output were measured. End tidal CO2%, inspiratory oxygen fraction, respiration rate and tidal volume were recorded using a multi-gas analyser and a respirometer. Acid-base and blood gas analyses were performed. Cardiac index, stroke volume, stroke index, systemic and pulmonary vascular resistance, left and right ventricular stroke work index were calculated. Increasing the MAC value during sevoflurane anaesthesia with spontaneous ventilation induced a marked cardiopulmonary depression; on the other hand, heart rate increased significantly, but the increases were not clinically relevant. The influences of artificial respiration on cardiopulmonary parameters during 1.5 MAC sevoflurane anaesthesia were minimal. In contrast, PEEP ventilation during 2 MAC concentration had more pronounced negative influences, especially on right cardiac parameters. In conclusion, at 1.5 MAC, a surgical anaesthesia level, sevoflurane can be used safely in healthy dogs during spontaneous and controlled ventilation (IPPV and PEEP of 5 cm H2O).     

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.     

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.     

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.     

Comparison of isoflurane and halothane as inhalation anaesthetics in the dog

Summary

A number of clinically important features of isoflurane anaesthesia were studied in comparison to those of halothane. Two groups of dogs were used. After light premedication, anaesthesia was induced by mask, and both groups of dogs were maintained for 30 minutes at 1.5 × MAC value of either halothane or isoflurane in a combination of oxygen and nitrous oxide (50:50). All animals were ventilating spontaneously.

There was no difference in the speed of induction of the halothane and isoflurane groups. Blood pressure in both groups dropped to approximately 7.5 kPa (56 mm Hg) during maintenance anesthesia (1.5 MAC), while the heart rate was significantly higher in the isoflurane group. Individual respiratory variables were not significantly different between the two groups, however the differences between the trends of the mean values were significant (Sign‐test). In general, with isoflurane, respiration rates were lower, with the tidal volume and end tidal CO₂ being greater.

The trends in pH and arterial pCO₂ showed a slightly more severe respiratory acidosis in the isoflurane group. However, neither group showed values corresponding to any expected clinical problems. Speed of recovery (determined by times to head‐lift and righting‐reflex) was greater in the isoflurane group. Previously known important features of isoflurane are low biodegradability, low blood: gas partition coefficient, and decreased myocardial sensitivity to catecholamines. It is concluded from this study that isoflurane deserves a place in canine anesthesia whenever these specific pharmacologic properties are desired.     

Effects of Halothane, Enflurane, and Isoflurane on Supraventricular and Ventricular Rate in Dogs With Complete Atrioventricular Block

Complete atrioventricular (AV) block was produced in 32 chloralose-anesthetized autonomically intact dogs to determine the effects of halothane, enflurane, and isoflurane on supraventricular and ventricular rate. Halothane (n = 17), enflurane (n = 6), and isoflurane (n = 9) were administered in three separate experiments in sequential minimum alveolar concentration (MAC) multiples of 0.5, 1.0, 1.5, 2.0, 1.5, and 1.0. Supraventricular rate, ventricular rate, and mean arterial blood pressure (MAP) were measured and recorded at baseline and after a 20-minute equilibration period of each inhalation anesthetic at each MAC multiple. Increasing concentrations of enflurane and isoflurane significantly decreased supraventricular rate ( P < .05). Ventricular rate was not significantly changed by sequential MAC multiples of halothane, enflurane, and isoflurane. Increasing concentrations of halothane, enflurane, and isoflurane significantly decreased MAP with enflurane producing the most significant decrease ( P < .05). Ventricular arrhythmias occurred in 5 of 17 dogs anesthetized with halothane and 1 of 9 dogs anesthetized with isoflurane. Inhalation anesthesia can significantly decrease supraventricular rate and MAP, does not alter ventricular rate, and can produce ventricular arrhythmias in dogs with complete AV block.     

Halothane-sparing effect of xylazine in dogs and subsequent reversal with tolazoline

Halothane MAC (the minimum alveolar concentration of halothane to produce anaesthesia in 50% of the animals tested) was determined to be 0.92 ± 0.16 volumes % in eight English Pointer dogs. Alterations in halothane MAC induced by an intravenous bolus of xylazine (1.1 mg/kg) and then tolazoline (5 mg/kg) was determined in each dog following control (halothane MAC) measurement. Following xylazine administration, MAC significantly decreased to 0.57 ± 0.023%. Immediately following determination of the xylazine-halothane MAC value in each dog, tolazoline was administered and the halothane requirement (MAC) was again assessed. Halothane MAC significantly increased to 1.24 ± 0.036%. Tolazoline administration induced immediate arousal in the xylazine-halothane anaesthetized dogs requiring a rapid increase in halothane concentration to maintain anaesthesia. Thus, the administration of tolazoline, an alpha adrenergic antagonist, following xylazine administration significantly increased the anaesthetic requirement (MAC) of halothane. Xylazine, an alpha 2 adrenergic agonist, decreased halothane anaesthetic requirement (MAC) in the eight dogs studied. These results are consistent with the hypotheses that stimulation of central alpha 2 receptors is the mechanism by which xylazine produces sedation and that inhibition of CNS excitatory neurotransmitter release decreases halothane anaesthetic requirement. In contrast, the increase in halothane requirement and arousal from xylazine-halothane anaesthesia that occurred following i.v. tolazoline administration indicates an increase in CNS excitatory neurotransmitter activity.     

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.     

Sevoflurane anesthesia in psittacines.

Duration of anesthesia onset (time to intubation) and recovery (time to extubation, sternal and standing) and quality of recovery were compared for sevoflurane and isoflurane in 10 adult psittacines. Both agents were initially administered at an equal volume percentage (2%) rather than at equal minimum alveolar concentrations (MACs), therefore the initial concentration was above the isoflurane MAC for dogs and birds (1.3%) but below the sevoflurane MAC for dogs (2.3%). The time to intubation was significantly longer with sevoflurane because of initially delivering the sevoflurane below suspected MAC for birds. Although recovery times (time to extubation, sternal, and standing) were not significantly different, birds recovering from sevoflurane were less ataxic. Sevoflurane is a suitable inhalant agent for use in these psittacines and merits further study.     

Comparison of electroencephalogram activity and auditory evoked responses during isoflurane and halothane anaesthesia in the rat

Objectives To compare the second differential index (SDI) calculated from the auditory evoked potential (AEP) and electroencephalogram (EEG) parameters: median frequency (MF), spectral edge frequency (SEF) and burst suppression rate (BSR) determined at four equivalent minimum alveolar concentrations (MAC) of isoflurane or halothane. Animals Twelve male Wistar rats weighing 418 g (SD ± 18.4 g). Methods Auditory evoked potentials and EEG responses were recorded in animals implanted with electrodes at established anaesthetic concentrations. Depth of anaesthesia was assessed using the strength of the pedal withdrawal reflex (PWR), and data were analysed using repeated measures anova and paired t‐tests. Results The SEF tended to decrease with increasing depth of halothane anaesthesia (F = 4.198, p = 0.05), but not with isoflurane. The MF and SDI were significantly higher during halothane than with isoflurane (F = 5.82, p = 0.036 and F = 5.263, p = 0.045, respectively) at equivalent depths of anaesthesia, and EEG burst suppression occurred at deeper planes of isoflurane but not halothane anaesthesia. Conclusions The study demonstrated that EEG and AEP characteristics recorded at MAC equivalent concentrations were suppressed to a greater degree by isoflurane than by halothane. These findings have strong implications for research projects where EEG recordings are collected, and also cast more general doubts upon the value of such parameters for evaluating depth of isoflurane anaesthesia in rats.     

Electroencephalography of Detomidine-Ketamine-Halothane and Detomidine-Ketamine-lsoflurane Anesthetized Horses During Orthopedic Surgery A Comparison

This study was done to compare the electroencephalographic (EEG) response evoked by orthopedic surgery in halothane- and isoflurane-anesthetized horses. Eight horses scheduled for bilateral arthroscopic surgery of the stifle were premedicated with detomidine (20 μg/kg) intravenously and five minutes later induced to anesthesia with ketamine (2.2 mg/kg) intravenously. Anesthesia was maintained with either halothane or isoflurane. Assignment of inhalation anesthetic was done randomly. The multiple of minimal alveolar concentration (MAC) of halothane required for anesthesia was significantly higher than the multiple of MAC of isoflurane (p < .05) required. Total amplitude of the EEG with halothane was smaller than with isoflurane (p < .05), but 13.0 to 32.0 Hz high frequency/0.0 to 3.9 Hz low frequency (|3/A) ratio was greater for halothane (p < .05). Arterial partial pressure of oxygen (PaO₂) was significantly (p < .05) higher with isoflurane than with halothane. The differences in EEG frequency shift observed suggest that isoflurane provided better analgesia than halothane for this group of horses.     

Comparison of isoflurane and halothane as inhalation anaesthetics in the dog

A number of clinically important features of isoflurane anaesthesia were studied in comparison to those of halothane. Two groups of dogs were used. After light premedication, anaesthesia was induced by mask, and both groups of dogs were maintained for 30 minutes at 1.5 X MAC value of either halothane or isoflurane in a combination of oxygen and nitrous oxide (50:50). All animals were ventilating spontaneously. There was no difference in the speed of induction of the halothane and isoflurane groups. Blood pressure in both groups dropped to approximately 7.5 kPa (56 mm Hg) during maintenance anesthesia (1.5 MAC), while the heart rate was significantly higher in the isoflurane group. Individual respiratory variables were not significantly different between the two groups, however the differences between the trends of the mean values were significant (Sign-test). In general, with isoflurane, respiration rates were lower, with the tidal volume and end tidal CO2 being greater. The trends in pH and arterial pCO2 showed a slightly more severe respiratory acidosis in the isoflurane group. However, neither group showed values corresponding to any expected clinical problems. Speed of recovery (determined by times to head-lift and righting-reflex) was greater in the isoflurane group. Previously known important features of isoflurane are low biodegradability, low blood: gas partition coefficient, and decreased myocardial sensitivity to catecholamines. It is concluded from this study that isoflurane deserves a place in canine anesthesia whenever these specific pharmacologic properties are desired.     

Portable mass spectrometry for measurement of anaesthetic agents and methane in respiratory gases

Monitoring the composition of gases breathed by anaesthetised patients requires measurement methods with fast responses, high accuracy and good reliability. There is also an increasing demand for systems to be able to monitor more than one target analyte simultaneously, but some gas analysers can be sensitive to the presence of methane gas in exhaled breath, consequently leading to inaccurate measurements of the anaesthetic agent. This study investigated the feasibility of employing portable quadrupole mass spectrometry to monitor volatile anaesthetic agents (halothane, isoflurane and sevoflurane), methane accumulation in anaesthetic rebreathing systems, and inspired and exhaled carbon dioxide and oxygen concentrations during equine anaesthesia in a clinical setting. The volatile anaesthetic agents were easily measurable and methane was detectable. The instrument had an advantage over short wavelength infrared absorption spectrometry analysers because it could monitor anaesthetic agents and other respiratory gases simultaneously and at extremely low concentrations, although further optimisation is required.     

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.     

Effect of medetomidine on respiration and minimum alveolar concentration in halothane- and isoflurane-anesthetized dogs

OBJECTIVE: To evaluate the effect of medetomidine on minimum alveolar concentration (MAC), respiratory rate, tidal volume, minute volume (V(M)), and maximum inspiratory occlusion pressure (IOCP(max)) in halothane- and isoflurane-anesthetized dogs. ANIMALS: 6 healthy adult dogs (3 males and 3 females). PROCEDURE: The MAC of both inhalants was determined before and 5, 30, and 60 minutes after administration of medetomidine (5 microg/kg, IV). Dogs were subsequently anesthetized by administration of halothane or isoflurane and administered saline (0.9% NaCl) solution IV or medetomidine (5 microg/kg, IV). Respiratory variables and IOCP(max) were measured at specific MAC values 15 minutes before and 5, 30, and 60 minutes after IV administration of medetomidine while dogs breathed 0% and 10% fractional inspired carbon dioxide (FICO2). Slopes of the lines for VM/FICO2 and IOCP(max)/FICO2 were then calculated. RESULTS: Administration of medetomidine decreased MAC of both inhalants. Slope of V(M)/FICO2 increased in dogs anesthetized with halothane after administration of medetomidine, compared with corresponding values in dogs anesthetized with isoflurane. Administration of medetomidine with a simultaneous decrease in inhalant concentration significantly increased the slope for V(M)/FICO2, compared with values after administration of saline solution in dogs anesthetized with halothane but not isoflurane. Values for IOCP(max) did not differ significantly between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Equipotent doses of halothane and isoflurane have differing effects on respiration that are most likely attributable to differences in drug effects on central respiratory centers. Relatively low doses of medetomidine decrease the MAC of halothane and isoflurane in dogs.     

Effect of inhalation anaesthetics on total respiratory resistance in conscious ponies

Total respiratory resistance was measured rapidly and non-invasively in 6 conscious ponies before and after they inhaled approximately 25% of the minimal anaesthetic concentration (0.25 MAC) of either enflurane, halothane, or isoflurane, over a 10 min period. The forced random noise (FRN) method was used to measure the impedance over the frequency range of 5 to 40 Hz and its real part, the resistance, was extracted from these impedance measurements. At the concentrations used, halothane appeared to have no effect on the total respiratory resistance; enflurane and isoflurane seemed to increase it but the changes were not statistically significant.     

Effects of halothane and isoflurane on baroreflex sensitivity in horses

Baroreflex sensitivity (BS) was used to quantitatively assess the effects of halothane and isoflurane on the heart rate/arterial pressure relationship during steady-state (10 minutes) and dynamic pressure changes in adult horses. Arterial pressure was decreased in response to nitroglycerin or sodium nitroprusside and increased in response to phenylephrine HCl. Mean (+/- SEM) BS in awake horses was 28.9 +/- 2.6 and 13.2 +/- 2.0 ms/mm of Hg during steady-state decreases and increases in systolic arterial pressure (SAP), respectively. Halothane and isoflurane either significantly (P less than 0.05) decreased or eliminated BS during steady-state decreases in SAP, with no significant differences detected between anesthetic agents. During steady-state decreases in SAP, significant (P less than 0.05) correlation between R-R interval and arterial pressure was not observed for 6 of 10 and 4 of 11 halothane and isoflurane anesthesia periods, respectively. Halothane significantly (P less than 0.05) decreased BS during steady-state increases in SAP to 7.9 +/- 0.6 and 6.5 +/- 1.1 ms/mm of Hg during low and high minimal alveolar concentration (MAC) multiples, respectively. Isoflurane decreased BS during steady-state increases in SAP to 9.6 +/- 1.5 and 6.6 +/- 1.1 ms/mm of Hg during low and high MAC anesthesia, respectively, with high MAC of isoflurane decreasing BS significantly (P less than 0.05), compared with awake and low MAC values. Plasma catecholamine (epinephrine and norepinephrine) concentrations increased significantly (P less than 0.05), compared with baseline values during steady-state vasodilator infusions in halothane- and isoflurane-anesthetized horses.(ABSTRACT TRUNCATED AT 250 WORDS)