Halothane: how should it be used in a developing country?

The anaesthetic agent halothane is still widely used in developing countries including the Islamic Republic of Iran because of its low price. Because of halothane-induced hepatitis, a rare complication, it has been replaced by other inhalation anaesthetics in Western countries; it has been suggested by some Iranian professionals that the Islamic Republic of Iran should do the same. We evaluated various dimensions of this replacement through a literature review to assess the incidence of halothane-induced hepatitis and costs of anaesthetics in the country. We also conducted a questionnaire survey of 30 anaesthesiology/gastroenterology experts about their views on the subject. The results indicate that the incidence of halothane hepatitis in the Islamic Republic of Iran is very low and could mostly be avoided by strict adherence to guidelines. Complete withdrawal of halothane in the Islamic Republic of Iran might not be appropriate at present. Comprehensive cost-effectiveness studies are needed before a decision is made on complete replacement of halothane with other anaesthetics.

[Low flow anaesthesia with isoflurane and sevoflurane in the dog]. / Low-flow-Anästhesie mit Isofluran und Sevofluran beim Hund.

The aim of the present study was to compare the safety and efficacy of sevoflurane and isoflurane during low flow anaesthesia (fresh gas flow (FGF) 14 ml/kg/min) as well as to compare the consumption of both anaesthetics. Data were gathered from 60 dogs assigned for surgery under general anaesthesia with an expected duration of 75 minutes or longer. All dogs were induced with 0.6 mg/kg (maximum 25 mg) l-methadone and 1 mg/kg (maximum 25 mg) diazepam i.v.. Anaesthesia was maintained with isoflurane (group 1) or sevoflurane (group 2) in a mixture with 50% O2 and 50% N2O as carrier gases, under controlled ventilation. Monitoring included electrocardiogram, body temperature, the temperature of in- and exspired gases, arterial oxygen saturation, arterial blood pressure as well as a continuous monitoring of inhaled and exhaled gas concentrations (O2, N2O, CO2, isoflurane, sevoflurane). The consumption of isoflurane and sevoflurane as well as the dogs' recovery times were evaluated for both groups. In all groups the inspired oxygen concentrations ranged above the minimum value of 30 Vol% during low flow anaesthesia, with an arterial oxygen saturation above 97%. End tidal concentration of CO2, heart rate and arterial blood pressure were within the physiological ranges and showed no differences between the two groups. Recovery time was significantly shorter after sevoflurane compared to isoflurane anaesthesia, whilst the consumption of sevoflurane was higher than that of isoflurane. Sevoflurane appears to be as clinically safe as isoflurane in low flow anaesthesia. Even considering that sevoflurane is more expensive than isoflurane, the use of the low flow technique decreases the cost of anaesthesia due to the reduced volatile anaesthetic consumption.

Isoflurane is an effective alternative to ketamine/xylazine/acepromazine as an anesthetic agent for the mouse electroretinogram.

The electroretinogram (ERG) is an essential measure of retinal function for studying mouse models of retinal disease. Ketamine, in combination with xylazine and/or acepromazine, is the most commonly used anesthetic agent. Although it works well in most situations, some fragile mouse strains have high mortality rates with this ketamine cocktail. We compared isoflurane with the ketamine cocktail in a longitudinal study of light-adapted and dark-adapted ERGs in C57BL/6J mice. Waveforms were averaged, oscillatory potentials (OPs) were extracted by digital filtration, and key ERG parameters were analyzed. The ERG waveforms were qualitatively similar with both anesthetics, and the male and female ERG parameters did not show significant differences. For light-adapted ERGs, b-wave amplitude and implicit time, and wavelet index were decreased under isoflurane anesthesia, whereas for dark-adapted ERGs, a- and b-wave implicit times were decreased and wavelet index was increased. The dark-adapted b-wave amplitude showed a significant inverse correlation with animal weight and age. Rod phototransduction gain and the Naka-Rushton n and R (max) parameters were the same for both anesthetics, and only the Naka-Rushton log k parameter was significantly elevated for isoflurane anesthesia. We propose that isoflurane is a satisfactory alternative to the ketamine cocktail for anesthesia in the mouse ERG. Precise quantitative comparisons, however, should only employ study designs using isoflurane versus isoflurane, or ketamine versus ketamine. Moreover, in light of the effects of both isoflurane and the ketamine cocktail on blood glucose levels, it would be prudent to control the fasting state of the animals in quantitative ERG studies.

Minimum alveolar concentration of isoflurane in mechanically ventilated Dumeril monitors.

OBJECTIVE: To determine minimum alveolar concentration (MAC) of isoflurane in mechanically ventilated Dumeril monitors (Varanus dumerili). DESIGN: Prospective study. ANIMALS: 10 healthy adult Dumeril monitors. PROCEDURE: Anesthesia was induced with isoflurane in oxygen delivered through a face mask. Monitors were endotracheally intubated, and end-tidal and inspired isoflurane concentrations were continuously measured. After equilibration at an end-tidal-to-inspired isoflurane concentration ratio of >0.9 for 20 minutes, an electrical stimulus (50 Hz, 50 V) was delivered to the ventral aspect of the tail for up to 1 minute and the monitor was observed for purposeful movement. End-tidal isoflurane concentration was then decreased by 10%, and equilibration and stimulation were repeated. The MAC was calculated as the mean of the lowest end-tidal isoflurane concentration that prevented positive response and the highest concentration that allowed response. A blood sample for blood gas analysis was collected from the tail vein at the beginning and end of the anesthetic period. RESULTS: Mean +/- SD MAC of isoflurane was 1.54 +/- 0.17%. Mean heart rates at the upper and lower MAC values were 32.4 +/- 3 beats/min and 34 +/- 4.5 beats/min, respectively. During the experiment, PaCo2 decreased significantly from 43.1 mm Hg to 279 mm Hg and blood pH and HCO3 concentration increased significantly from 7.33 to 7.64 and from 25.3 to 32.9 mmol/L, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The MAC of isoflurane in Dumeril monitors was similar to that reported in mammals but lower than values reported in other reptiles. This difference may be reflective of the more advanced cardiovascular physiologic features of monitor lizards.

Use of propofol-isoflurane as an anesthetic regimen for cesarean section in dogs.

OBJECTIVE: To evaluate use of propofol-isoflurane as an anesthetic regimen for cesarean section in dogs and to compare this protocol with epidural analgesia and anesthesia induced with thiopental sodium. DESIGN: Prospective study. ANIMALS: 141 bitches admitted for cesarean section. PROCEDURE: General anesthesia was induced with propofol in 141 dogs undergoing cesarean section. After intubation, anesthesia was maintained by means of inhalation of isoflurane (0.5 to 2.0%), administered in a 65:35 mixture of oxygen:nitrous oxide. After induction, 20 minutes were allowed to elapse before delivery of puppies was begun. Viability of neonates was ascertained immediately after surgery. Owners were interviewed by telephone to determine survival of puppies during the postoperative period. Survival rates from this study were compared with those from cesarean section performed on dogs under epidural analgesia or under general anesthesia induced with thiopental sodium. RESULTS: Induction, maintenance, and recovery were problem free in all bitches. Of 412 puppies delivered by cesarean section, 293 (71%) survived, 13 (3%) were born alive but died within 20 minutes of delivery, and 106 (26%) were stillborn. Survival rate for puppies from dams induced with propofol-isoflurane was similar to that for puppies from dams receiving epidural analgesia. Survival rate for puppies delivered by cesarean section performed on dams under general anesthesia was higher for dams induced with propofol than for dams induced with thiopental sodium. CLINICAL IMPLICATIONS: General anesthesia induced with propofol and maintained with isoflurane is acceptable for performing cesarean section in dogs.

The clinical use of desflurane.

Desflurane, a newly introduced potent, inhaled anesthetic, differs from its predecessors in having a lower solubility in blood and tissues. The lower solubility imparts a greater control to the maintenance of anesthesia and a more rapid elimination and recovery from anesthesia. In other respects, the pharmacological properties of desflurane resemble those of its sister anesthetic, isoflurane, currently the most widely-used potent anesthetic in this and other countries. The qualitative exceptions to this resemblence are that desflurane is more pungent and produces a greater increase in heart rate, particularly at deeper levels of anesthesia.

The nonlinear potency of sub-MAC concentrations of nitrous oxide in decreasing the anesthetic requirement of enflurane, halothane, and isoflurane in rats.

The effect of nitrous oxide (N2O) on the MAC of enflurane, halothane, and isoflurane was determined in male rats. Each rat received either enflurane, halothane, or isoflurane, along with 0%, 15%, or 75% N2O. Anesthetic equilibration was verified by mass spectrometry sampling of end-tidal gases. MAC was determined at each N2O concentration by the standard tail clamp method. The N2O dose-response data for each animal were fit by a second-order polynomial equation to estimate the value of a second-order coefficient. A linear dose-response would result in a value of zero, whereas the extent to which the data deviate from nonlinearity would be reflected by an increase in the value of this coefficient. The null hypothesis, that the second-order coefficient should be zero, was tested by a one-sample two-tailed t test. The volatile anesthetic requirement decreased as the N2O concentration increased; however, it did not do so linearly. For each of the three volatile anesthetic groups, the second-order coefficients were consistently greater than zero (P less than 0.05). These data are not consistent with the accepted presumption that the summation of N2O with volatile anesthetics is linear.