Induction of anaesthesia with sevoflurane and isoflurane in the rabbit

The effects of induction of anaesthesia with sevoflurane and isoflurane were studied in rabbits. All rabbits had periods of apnoea (ranging from 30-180 s) during induction which resulted in moderate hypercapnia and acidosis. Arterial pCO2 rose from 4.1 +/- 0.3 kPa to a peak of 7.6 +/- 0.4 kPa (mean +/- SD) (both agents). All animals showed a significant reduction in heart rate (P < 0.05). Heart rate (HR) fell from 226 +/- 33 to a minimum during induction of 57 +/- 32 (sevoflurane) and 199 +/- 41 to 45 +/- 11 (isoflurane). Most animals struggled violently during induction. Use of sevoflurane did not prevent the breath-holding response seen during induction of anaesthesia with other volatile anaesthetics in this species, and the severe apnoea which occurs may represent a significant hazard. The behaviour of the animals indicated that both sevoflurane and isoflurane are aversive, suggesting that this technique should be avoided whenever possible.     

Comparative effects of halothane, isoflurane, sevoflurane and desflurane on the electroencephalogram of the rat

Inhalant anaesthetic agents are commonly used in studies investigating the electroencephalographic (EEG) effects of noxious stimuli in animals. Halothane causes less EEG depression than isoflurane, however, the EEG effects of halothane, isoflurane, sevoflurane and desflurane have not been compared in the same model. This study aimed to compare the EEG effects of these inhalational agents in the rat. Forty male Sprague-Dawley rats were assigned to four groups and anaesthetized with halothane, isoflurane, sevoflurane or desflurane. EEG was recorded from the left and right somatosensory cortices for 5 min at three different multiples of minimal alveolar concentration (MAC) (1.25, 1.5 and 1.75). Median, 95% spectral edge frequency and total power were derived and a single mean value for each was calculated for the first 60 s of each recording period. When the raw EEG contained burst suppression (BS), the BS ratio (BSR) over 60 s was calculated. No BS was found in EEG recorded from the halothane group at any concentration. BS was present at all concentrations with the other anaesthetic agents. BS was almost complete at all concentrations of isoflurane, whereas BSR increased significantly with increasing concentrations of sevoflurane and desflurane. No significant differences were found between the BSR due to the 1.75 MAC multiple of isoflurane, sevoflurane or desflurane. Halothane causes significantly less depression of cortical activity than the newer inhalant agents at equivalent multiples of MAC. These data support the hypothesis that halothane has a fundamentally different mechanism of action than the other inhalant agents.     

乙醇加安定对家兔全身麻醉的实验研究

目的观察应用32%乙醇 安定对家兔的麻醉效果。方法对60只家兔随机分3组,分别静脉注射25%氨基甲酸乙酯、32%乙醇、32%乙醇 安定,观察麻醉起效时间、维持时间、全麻过程中动脉血压、心率和呼吸的变化。结果乙醇加安定的麻醉效果满意,成功率高。结论乙醇价廉,毒副作用小,乙醇加安定麻醉简单易行,安全可靠,适用于家兔手术实验。     

Long-term anaesthesia using inhalatory isoflurane in different strains of mice-the haemodynamic effects

The aim of this study was to establish a simple and safe method of anaesthesia for intravital microcirculatory observations in small laboratory animals. The usefulness of isoflurane inhalation anaesthesia has been investigated in different strains of mice commonly used in experimental medicine. These were the hairless (hr/hr, n = 12), the BALB/c (n = 12) and the nude mouse (nu/nu, n = 3). Anaesthesia was maintained by mask inhalation of isoflurane vaporized at concentrations of up to 4% in the induction phase, at 1.5% during acute surgical procedures and at 0.8-1.3% during prolonged experimental observations. Isoflurane was vapoured in a N(2)O/O(2) mixture and saturated with 32-36% F(i)O(2). During observations the body temperature was kept constant at 37 degrees C. The tail artery was cannulated for monitoring of mean arterial blood pressure (MAP) and heart rate (HR). To maintain the body fluid balance, isotonic saline was administered at a constant rate of 0.2 ml/h. Arterial blood samples were drawn for blood-gas analysis at the end of the experiments. All animals survived the anaesthesia protocol lasting between 3 and 6.5 h. During isoflurane inhalation, no breathing complications or changes in systemic circulatory parameters were observed. Mean values of MAP and HR were 79+/- 3 mmHg and 486+/- 13 min(-1), respectively, over the entire observation period. A moderate acidosis was recorded in animals under isoflurane anaesthesia, with alterations of arterial blood pH, p(a)O(2) and pCO(2) values (7.29+/- 0.06, 130+/- 19 mmHg and 35.6+/- 4.7 mmHg, respectively). In conclusion, inhalation anaesthesia with isoflurane is useful for experimental studies in the mouse due to (1) the simplicity of administration of the anaesthetic, (2) the rapid induction of anaesthesia, (3) easy control of the depth of anaesthesia, (4) the low percentage of complications, and (5) stable MAP and HR during observations lasting several hours. The proposed technique is especially suitable for observations of the microcirculation under intravital fluorescence microscopy.     

Effects of halothane, isoflurane, sevoflurane and desflurane on contraction of ventricular myocytes from streptozotocin-induced diabetic rats

Various clinically used volatile general anaesthetics (e.g. sevoflurane, halothane, isoflurane and desflurane) have been shown to have significant negative inotropic effects on normal ventricular muscle. However, little is known about their effects in ventricular tissue from diabetic animals. Streptozotocin (STZ)-induced diabetes is known to induce changes in the amplitude and time course of shortening and one report suggests that the inotropic effects of anaesthetics are ameliorated in papillary muscles from diabetic animals. The aim of these studies was to investigate this further in electrically stimulated (1 Hz) ventricular myocytes. Cells were superfused with either normal Tyrode (NT) solution or NT containing anaesthetic (1 mM) for a period of 2 min (at 30-32 degrees C). Myocytes from STZ rats were shown to have a significantly longer time to peak shortening (p > 0.001, n = 50) and the amplitude of shortening tended to be greater but this was not significant (p = 0.13, n = 50). Halothane, isoflurane, desflurane and sevoflurane significantly (p < 0.05) reduced the magnitude of shortening of control cells by 72.5 +/- 3.2%, 46.5 +/- 9.7%, 28.9 +/- 4.3% and 22.8 +/- 5.6%, respectively (n > 11 per group) but their steady-state negative inotropic effect was found to be no different in cells from STZ-treated rats (73.0 +/- 4.8%, 40.7 +/- 4.7%, 25.0 +/- 5.2% and 19.8 +/- 5.2%, respectively, n > 10 per group). Therefore, we conclude that the inotropic effects of volatile anaesthetics were not altered by STZ treatment.     

Effects of halothane,isoflurane, sevoflurane and desflurane on contraction of ventricular myocytes from streptozotocin-induced diabetic rats

Various clinically used volatile general anaesthetics (e.g. sevoflurane, halothane, isoflurane and desflurane) have been shown to have significant negative inotropic effects on normal ventricular muscle. However, little is known about their effects in ventricular tissue from diabetic animals. Streptozotocin (STZ)-induced diabetes is known to induce changes in the amplitude and time course of shortening and one report suggests that the inotropic effects of anaesthetics are ameliorated in papillary muscles from diabetic animals. The aim of these studies was to investigate this further in electrically stimulated (1 Hz) ventricular myocytes. Cells were superfused with either normal Tyrode (NT) solution or NT containing anaesthetic (1 mM) for a period of 2 min (at 30–32°C). Myocytes from STZ rats were shown to have a significantly longer time to peak shortening (p > 0.001, n= 50) and the amplitude of shortening tended to be greater but this was not significant (p= 0.13, n= 50). Halothane, isoflurane, desflurane and sevoflurane significantly (p < 0.05) reduced the magnitude of shortening of control cells by 72.5 ± 3.2%, 46.5 ± 9.7%, 28.9 ± 4.3% and 22.8 ± 5.6%, respectively (n > 11 per group) but their steady-state negative inotropic effect was found to be no different in cells from STZ-treated rats (73.0 ± 4.8%, 40.7 ± 4.7%, 25.0 ± 5.2% and 19.8 ± 5.2%, respectively, n > 10 per group). Therefore, we conclude that the inotropic effects of volatile anaesthetics were not altered by STZ treatment. (Mol Cell Biochem 261: 209–215, 2004)     

Effects of isoflurane on voltage-dependent calcium fluxes in rabbit T-tubule membranes: comparison with alcohols

The effects of racemic (+/-) and (+)- and (-)-stereoisomers of isoflurane on depolarization-induced (45)Ca(2+) fluxes mediated by voltage-dependent Ca(2+) channels were investigated in transverse tubule membrane vesicles from rabbit skeletal muscle. In the concentration range 0.5 to 2 mM, (+/-)-isoflurane inhibited (45)Ca(2+) fluxes and functionally modulated the effects of the Ca(2+) channel antagonist nifedipine (1-10 microM). Isoflurane-induced inhibition of (45)Ca(2+) fluxes was not significantly affected by pretreatment with either pertussis toxin (5 microg/ml) or phorbol 12-myristate 13-acetate (50 nM). Further experiments indicated that there were no significant differences between (+)- and (-)-stereoisomers of isoflurane with respect to the extent of inhibition of (45)Ca(2+) fluxes. Radioligand binding studies indicated that racemic and (+)- and (-)-isoflurane were equally effective in displacing the specific binding of [(3)H]PN 200-110 to transverse tubule membranes. There were no apparent differences between the effects of (+)- and (-)-isoflurane on the characteristics of [(3)H]PN 200-110 binding. Although the concentrations of isoflurane for the inhibitions of (45)Ca(2+) fluxes and radioligand bindings were similar, the concentrations of n-alcohols required for the inhibition of (45)Ca(2+) fluxes were lower than those for the displacement of radioligand. Comparison of the data for the displacement of [(3)H]PN 200-110 binding and the inhibition of (45)Ca(2+) fluxes by isoflurane and by n-alcohols suggested that both isoflurane and n-alcohols may have more than a single binding site. In conclusion, results indicate that isoflurane, independent of intracellular Ca(2+) levels, nonstereospecifically inhibits the function of voltage-dependent Ca(2+) channels and this effect is mediated through multiple binding sites.     

Occupational exposure to isoflurane during anaesthesia induction with standard and scavenging double masks in dogs, pigs and ponies

Induction of anaesthesia using a face mask may cause workplace pollution with anaesthetics. The aim of this study was to compare the effect of the use of a standard versus a scavenging double face mask on isoflurane pollution during induction of anaesthesia in experimental animals: six dogs, 12 pigs and five ponies. Pigs were anaesthetized only once using either mask type randomly (n = 6). Dogs and ponies were anaesthetized twice, using different mask types for each occasion in a random order with at least 14 days between experiments. The masks were attached to a Bain breathing system (dogs and pigs) or to a circle system (ponies) using a fresh gas flow of 300 or 50 mL/kg/min, respectively, with 5% vaporizer dial setting. Isoflurane concentrations were measured in the anaesthetist's breathing zone using an infrared photoacoustic spectrometer. The peak isoflurane concentrations (pollution) during baseline and induction periods were compared with Wilcoxon test in all species, and values between the mask types were compared with either Wilcoxon (ponies and dogs) or Mann-Whitney tests (pigs) (P < 0.05). Pollution was higher during induction when compared with baseline regardless of the mask type used but it was only statistically significant in dogs and pigs. Pollution was lower during induction with double versus single masks but it was only significant in pigs. Despite the lack of statistical significance, large and consistent differences were noted in all species, hence using scavenging masks is recommended to reduce isoflurane workplace pollution.     

Pituitary-adrenocortical axis, serum serotonin and biochemical response after halothane or isoflurane anaesthesia in rabbits

To document the changes in serum serotonin, adrenocorticotrophic hormone (ACTH), corticosterone levels and select biochemical parameters in response to inhalant anaesthesia, 20 New Zealand White (NZW) rabbits were assigned to two treatment groups: halothane and isoflurane. Induction of anaesthesia was achieved using a face mask (3.5% halothane and 4.5% isoflurane in oxygen) followed by endotracheal intubation and maintenance of anaesthesia for 30 min (1.5% halothane and 2.5% isoflurane in oxygen). Blood samples were obtained before anaesthetic induction, and at 1, 10, 30, 60, 120 min and 24, 48 and 72 h after endotracheal intubation. Serum serotonin and corticosterone levels were measured by competitive enzyme immunoassay, ACTH by radioimmunoassay. Serum glucose, alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), blood urea nitrogen (BUN) and creatinine levels were measured using an automated analyser. Significant increases in serum ACTH and corticosterone levels occurred after halothane administration while serum serotonin levels did not change. An increase in serum corticosterone and serotonin levels occurred in the isoflurane group but no changes in ACTH concentrations were detected. Administration of halothane significantly increased serum glucose, ALT, AST, BUN and creatinine levels. After isoflurane administration, there was a significant increase in serum glucose, AST, BUN and creatinine levels. Based on these results, halothane stimulates the hypothalamic-pituitary-adrenal axis to a greater extent than isoflurane, but isoflurane increases serum serotonin levels. Both anaesthetic agents alter select biochemical parameters. These results should be taken into account when blood samples are evaluated in treated isoflurane or halothane anaesthetized rabbits.     

Dynamic causal models and physiological inference: a validation study using isoflurane anaesthesia in rodents

Generative models of neuroimaging and electrophysiological data present new opportunities for accessing hidden or latent brain states. Dynamic causal modeling (DCM) uses Bayesian model inversion and selection to infer the synaptic mechanisms underlying empirically observed brain responses. DCM for electrophysiological data, in particular, aims to estimate the relative strength of synaptic transmission at different cell types and via specific neurotransmitters. Here, we report a DCM validation study concerning inference on excitatory and inhibitory synaptic transmission, using different doses of a volatile anaesthetic agent (isoflurane) to parametrically modify excitatory and inhibitory synaptic processing while recording local field potentials (LFPs) from primary auditory cortex (A1) and the posterior auditory field (PAF) in the auditory belt region in rodents. We test whether DCM can infer, from the LFP measurements, the expected drug-induced changes in synaptic transmission mediated via fast ionotropic receptors; i.e., excitatory (glutamatergic) AMPA and inhibitory GABA(A) receptors. Cross- and auto-spectra from the two regions were used to optimise three DCMs based on biologically plausible neural mass models and specific network architectures. Consistent with known extrinsic connectivity patterns in sensory hierarchies, we found that a model comprising forward connections from A1 to PAF and backward connections from PAF to A1 outperformed a model with forward connections from PAF to A1 and backward connections from A1 to PAF and a model with reciprocal lateral connections. The parameter estimates from the most plausible model indicated that the amplitude of fast glutamatergic excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) behaved as predicted by previous neurophysiological studies. Specifically, with increasing levels of anaesthesia, glutamatergic EPSPs decreased linearly, whereas fast GABAergic IPSPs displayed a nonlinear (saturating) increase. The consistency of our model-based in vivo results with experimental in vitro results lends further validity to the capacity of DCM to infer on synaptic processes using macroscopic neurophysiological data.     

Four methods for general anaesthesia in the rabbit: a comparative study

The efficacy and safety of pentobarbitone, ketamine/xylazine, fentanyl/fluanisone/diazepam, and halothane/nitrous oxide anaesthesia were compared in 4 groups of six New Zealand White rabbits. Heart and respiratory rates, body temperature, reflexes, blood pressure and blood gases were measured. Pentobarbitone appeared to be unsuitable for anaesthesia in rabbits, as 5 of the 6 rabbits to whom it was administered, required artificial respiration or died. The combinations of ketamine/xylazine and fentanyl-fluanisone/diazepam both produced unpredictable levels of anaesthesia together with a substantial decline in arterial blood pressure and PO2. Despite a severe drop in blood pressure (up to 37.5%), anaesthesia with halothane and nitrous oxide was found to be superior to the other anaesthetic agents.     

Repeated anaesthesia with isoflurane and xylazine/levomethadone/fenpipramide premedication in female Beagle dogs: influence on general health and wellbeing

Beagle dogs continue to be used in experimental studies and preclinical and clinical trials, many of which address the usage of anaesthesia. In order to reduce the number of animals, researchers tend to conduct several experiments on a single animal. The question arises, however, as to whether or not this frequent usage involves more than simply additional stress and discomfort for the individual animal. Within the framework of an existing study involving six female Beagle dogs, we investigated the effects of repeated (5) isoflurane anaesthesia with xylazine/levomethadone/fenpipramide premedication carried out at short intervals (2 weeks) and compared these with the effects of two treatments intermitted by a longer resting period (8 weeks). To verify our hypothesis that frequent anaesthesia affects the dog's wellbeing more than the occasional anaesthesia, the following parameters were measured at regular intervals: body weight, body temperature, respiratory rate, blood pressure, reflexes and heart rate, both at rest and during a treadmill exercise. In addition, recovery behaviour subsequent to anaesthesia was monitored for one hour. Our observations indicate that the anaesthetic effects are most prominent 24 h after the anaesthetic treatment. However, crossover analysis of our data cannot show that there is no statistical difference of whether dogs were anaesthetized occasionally or frequently. In our study, it appears that frequent anaesthesia within a two-week period did not affect the wellbeing and general health of Beagle dogs in a super-additive manner and that a minimum of two-week testing-free period is sufficient to ensure complete recovery from the unwanted effects induced by anaesthesia.     

MRS glucose mapping and PET joining forces: re‐evaluation of the lumped constant in the rat brain under isoflurane anaesthesia

Although numerous positron emission tomography (PET) studies with ¹⁸F‐fluoro‐deoxyglucose (FDG) have reported quantitative results on cerebral glucose kinetics and consumption, there is a large variation between the absolute values found in the literature. One of the underlying causes is the inconsistent use of the lumped constants (LCs), the derivation of which is often based on multiple assumptions that render absolute numbers imprecise and errors hard to quantify. We combined a kinetic FDG‐PET study with magnetic resonance spectroscopic imaging (MRSI) of glucose dynamics in Sprague–Dawley rats to obtain a more comprehensive view of brain glucose kinetics and determine a reliable value for the LC under isoflurane anaesthesia. Maps of T_max/CMR_glc derived from MRSI data and T_max determined from PET kinetic modelling allowed to obtain an LC‐independent CMR_glc. The LC was estimated to range from 0.33 ± 0.07 in retrosplenial cortex to 0.44 ± 0.05 in hippocampus, yielding CMR_glc between 62 ± 14 and 54 ± 11 μmol/min/100 g, respectively. These newly determined LCs for four distinct areas in the rat brain under isoflurane anaesthesia provide means of comparing the growing amount of FDG‐PET data available from translational studies.