Halothane hepatitis without halothane: role of inapparent circuit contamination and its prevention

Halothane and other halogenated anesthetic agents are liquids which are highly soluble in rubber and plastic materials widely used as components of anesthesia machines. These agents must be administered using machines equipped with vaporizers. We report a patient with a past history of halothane hepatitis in whom recurrence was suspected despite the fact that halothane had been avoided purposely during the subsequent operation. Circumstances led us to believe that inapparent circuit contamination of vaporizer-equipped anesthesia machine with halothane may be responsible for the inadvertant rechallenge and recurrence of halothane hepatitis. Vaporizer-equipped machines were tested for inapparent contamination with halothane and enflurane using Perkin-Elmer mass spectrometer. Oxygen alone was passed through the anesthesia circuits, and gas in the efferent limbs of the machines was tested for halothane (in eight machines) and enflurane (in two machines) which were found in various concentrations in all machines so tested. Our findings suggest that inapparent contamination may be widely prevalent in vaporizer-equipped anesthesia machines. The validity of this conclusion was confirmed in five patients with previous diagnosis of halothane hepatitis who subsequently underwent operations under general anesthesia during which machines never equipped with vaporizers were successful in preventing recurrence of hepatitis. We conclude that patients with a prior history of halothane hepatitis are at risk of inapparent circuit contamination-induced recurrent hepatitis. Unless such contamination can be confidently excluded, vaporizer-equipped machines should not be used to administer general anesthesia in these susceptible patients.

[Accuracy of halothane vaporizers with respect to temperature, carrier gas composition and gas flow rate]

Since the precise measurement of halothane-concentration in the patients gas support during routine anesthesia still requires much effort, the accuracy of the vaporizers halothane output remains important for the safety of anesthesia and the education of younger anesthesiologists. In the present study 30 halothane vaporizers (14 Fluotec Mark 3/Cyprane Ltd., 12 Vapor 19/Dräger, 4 Abingdon/Penlon) were removed from the operating rooms in the University Hospital Göttingen to test their accuracy. The measurements were performed with a masspectrometer under standardized laboratory conditions with varied temperatures (10 degrees, 21 degrees, 35 degrees C), gasflows (3, 5, 8 l/min) and compositions of carrier gas (100% O2, N2O/O2 = 2/1). All vaporizers in this study showed a light tendency to higher halothane outputs for low concentration adjustments and to distinct lower outputs for higher concentration adjustments. The Vapor 19 vaporizers compensated well with changes of temperatures and gasflows but had a distinct dependency on carriers gas compositions. The Fluotec Mark 3 vaporizers output depended on the temperature and gasflow but was almost unaffected by the carrier gas composition. Tremendous deviations appeared with the Abingdon vaporizers, which seamed to be without any temperature compensation and which were highly gas flow dependent. It can be concluded from our results that vaporizers according to their construction tend to be imprecise.

Anesthetic potency of nitrous oxide in young swine (Sus scrofa)

Determination of nitrous oxide (N2O) potency was accomplished by extrapolation using the concepts of minimum alveolar concentration (MAC) and additivity among inhalation anesthetics. Halothane and isoflurane anesthetic requirement (alveolar concentration) necessary to achieve MAC in 9 pigs decreased with each successive increase in the percentage of inspired N2O (25%, 50%, 75%). Halothane and isoflurane MAC was determined to be 0.94 +/- 0.03 and 1.75 +/- 0.01 volumes percent, respectively. Halothane and isoflurane requirements decreased to 0.74 +/- 0.02, 0.66 +/- 0.02, and 0.58 +/- 0.02; and to 1.56 +/- 0.02, 1.38 +/- 0.02, and 1.08 +/- 0.03 volumes percent with 25%, 50%, and 75% N2O, respectively. The line of best fit derived from regression analysis of the combined data (isoflurane and halothane MAC values) had a correlation coefficient of 0.987 and an X intercept equivalent to 195% N2O. The potency of N2O in pigs was similar to that of other domesticated mammals and reduced halothane and isoflurane anesthetic requirements by approximately 50% of the reduction observed in human beings.

[Testing of an ultraviolet Halothane Meter]

The object of Halothane Meter (HM) study is to estimate its reliability (accuracy and stability) and its possible effect on the degradation of the molecule by the action of the UV (254 nm). The zero instability of the apparatus, clinically evident, is due to the constructor who undertakes to modify it. The molecule analysis, treated in vivo (4 hours of anesthesia) and in vitro by irradiation respectively by the HM (cathodeon 254 nm) and a source of some wavelength UV is realised by UV spectrophotometry, IR spectrophotometry, RMN spectrometry. The results of all analysis allow to exclude the molecule degradation which could impede the recirculation of treated gas in a closed circle.

Automatic control in anesthesia: a comparison in performance between the anesthetist and the machine

This report is divided into two parts. First, we developed two new servo control systems by modifying an existing one. The original system was designed to control inspired halothane concentration using mean arterial pressure; the two new systems were designed to control inspired halothane concentration using end-tidal concentration or to control mean arterial pressure using the automated infusion of nitroprusside. Second, we compared the performance of experienced physician and nurse anesthetists (nine, six, and six experiments, respectively). The experiments incorporated a standardized testing sequence of two changes in desired blood pressure (set point) and two pharmacologically induced disturbances in blood pressure (perturbations). The scoring was designed to examine how fast blood pressure changed (90% response time), how far past the set point it went (overshoot), how long it took to eliminate most of the fluctuations in blood pressure (settling time), and the degree of fluctuation of blood pressure after settling (stability). Given three systems to be tested, there were (3 X 14) 42 possible mean scores for the machine and 42 for the anesthetists. The machine scored better than the anesthetists in 38 out of 42 of the mean scores; the differences were statistically significant in 19 out of 42 scores. The wide scatter in performances of the anesthetists prevented the achievement of significance in nine cases with large differences between means. Thus when the scores from the three systems were combined to achieve a larger n value, the machine outperformed the anesthetist in 12 out of 14 scores.(ABSTRACT TRUNCATED AT 250 WORDS)

Gas scavenging during bronchoscopy under general anesthesia

Prevention of exposure of the endoscopist to high levels of anesthetic gases during bronchoscopy was attempted experimentally in dogs by a scavenging system. Results were compared with exposure during the conventional technique of anesthetic gas administration for clinical bronchoscopy using the rigid open ventilating bronchoscope. The scavenging system consisted of a vacuum pump applied to the open ventilating rigid bronchoscope sidearm connection during intratracheal administration of nitrous oxide, , oxygen, and halothane gas mixture. Gas samples were taken from the trachea, the proximal end of the bronchoscope, and the endoscopist's breathing zone, and analyzed by gas chromatography. Findings indicate that halothane anesthesia for bronchoscopy administered by conventional techniques is a source of air pollution in the operating room and exposes the endoscopist to subanesthetic levels of halothane that may affect psychomotor functioning. The use of the gas scavenging system lowered the concentrations of halothane and nitrous oxide at the endoscopist's breathing zone to a level at which inhalation for short periods has no clinical effects, while the concentrations of the anesthetics and oxygen in the trachea were maintained at a satisfactory level.

Anaesthetic vapour concentrations in the EMO system

Measurements of the vapour concentrations delivered by the EMO and Oxford Miniature Vaporizers (OMV) were made with both continuous (plenum mode) and intermittent (drawover mode) air flows. Leakage of ether, halothane and trichloroethylene vapours through the corrugated elephant tubing was also measured. Both vaporizers performed most consistently with the intermittent flows for which they were designed. Outputs were minimal at very low carrier gas flows, reached their greatest at the higher settings in the middle flow range and tended to be low at the highest flows. These effects were far more notable with continuous than with intermittent flows. Minimal amounts of ether were lost through the tubing but halothane losses were appreciable, while losses of trichloroethylene were enough to reduce the concentrations available to the patient. The EMO is not suitable for plenum use with carrier gas flows below about 10 litres/min. The OMV is a useful plenum vaporizer although the outputs are generally lower than indicated at higher flows.

Cross-sensitivity in water vapor in the Engström EMMA

Halothane, enflurane, and isoflurane vapor concentrations (0-3%) were simultaneously measured by a calibrated Engström EMMA and Beckman LB-2 gas analyzer, and were heated and/or humidified by an inline Bird humidifier. Data were treated by regression analysis for lines of best fit. Water vapor produced increasing cross-sensitivity as a function of temperature in all vapors measured by the Engström EMMA but not in the Beckman LB-2. At 38 degrees C cross-sensitivity by water vapor was 0.97, 0.92, and 1.12 volumes percent reading for halothane, enflurane, and isoflurane, respectively. Water vapor cross-sensitivity with the EMMA in the isoflurane selector position was statistically higher (P less than 0.05) than in the other two positions. We conclude that water vapor cross-sensitivity in the Engström EMMA is in excess of the manufacturer's specifications (0.3 volumes percent at 37 degrees C) and different with respect to the anesthetic gas being measured.

Controlled anaesthesia: a clinical evaluation of an approach using patient characteristics identified during uptake

The performance of a system to control the alveolar concentration of halothane in patients undergoing halothane and nitrous oxide or halothane anaesthesia with controlled ventilation has been evaluated. The method involved the identification and quantification of the uptake characteristics of patients from their early response to the anaesthetic and implements the vaporizer control necessary to achieve and maintain a desired alveolar halothane concentration. Initial targets are based on the concept of MAC, but modifications to the desired alveolar concentration may be effected readily by the anaesthetist at any time during the procedure if evaluation of the normal clinical signs indicates inappropriate depth of anaesthesia. The results obtained during anaesthesia for routine surgery in 80 patients demonstrated that the system was accurate, stable, robust and able to adapt for variability between patients in the uptake of halothane.

Monitoring anesthetic vapor concentrations using a piezoelectric detector: evaluation of the Engstrom EMMA

The Engstrom anesthetic gas analyzer (EMMA) was evaluated to determine the reproducibility, response time, gas interference, water vapor dependence, and sensitivity. The analyzer also was evaluated clinically in 20 children undergoing orthopedic surgery. Difference between the analyzer output and anesthetic gas standard (reproducibility) ranged from 0.013 +/- 0.008 vol % to 0.018 +/- 0.018 vol %. Response times decreased from 710 ms at 5 l X min-1 to 149 ms at 30 l X min-1. Nitrous oxide caused an offset of +0.11 +/- 0.007 vol %. Water vapor caused positive offsets of 0.25 +/- 0.044 vol %, 0.51 +/- 0.027 vol %, and 0.80 +/- 0.037 vol % at 25 degrees C, 30 degrees C, and 34 degrees C, respectively. The analyzer reproducibly measured dry gas concentrations, but compensation had to be made for water vapor when measuring wet gases. The analyzer's usefulness for end-tidal monitoring was questioned because of its slow response time and its sensitivity to water vapor.

Verapamil decreases MAC for halothane in dogs

Verapamil hydrochloride is a calcium entry blocking drug that is being prescribed with increasing frequency for cardiovascular disorders in the perioperative setting. Verapamil's calcium channel blocking effect is not selective, because it also exerts activity on the sodium channel. Because of the well-described effects of sodium channel blockers on anesthetic requirements, the authors studied the MAC for halothane in dogs before and after a therapeutic dose of verapamil 0.5 mg . kg-1. There was a 25% reduction in halothane MAC from 0.97-0.72% (P less than 0.01) when a therapeutic plasma level of verapamil (64 ng . ml-1) was present. Anesthetic requirements for halothane are reduced by dl-verapamil possibly on the basis of its local anesthetic-like sodium channel blocking properties. Adjustments in anesthetic dosage may be necessary in patients receiving verapamil.

Minimal alveolar concentrations for halothane, enflurane, and isoflurane in the cat

The minimal alveolar concentrations for halothane, enflurane, and isoflurane in the domestic cat were found to be 1.19 +/- 0.05 (SEM)%, 2.37 +/- 0.06%, and 1.61 +/- 0.04%, respectively. During the potency studies, it was observed that enflurane and isoflurane resulted in shorter wake-up times, compared with halothane. However, enflurane and isoflurane produced electroencephalographic (EEG) and clinical signs of CNS irritability (EEG spiking, myoclonus) in normocapnic or mildly hypocapnic cats. In addition, enflurane and isoflurane caused greater airway irritability (coughing, salivation) than did halothane.

Uptake and distribution of halothane in infants: in vivo measurements and computer simulations

We measured uptake of halothane (the fraction of halothane in expired gas divided by the fraction of halothane in inspired gas, FE/FI) with a mass spectrometer over time in 7 infants less than 3 months of age. FE/FI for halothane in these infants increased more rapidly than has been described in adults by others. In addition, we developed a mathematical model for halothane uptake and distribution that incorporates age-dependent anatomic and physiologic parameters (alveolar ventilation, functional residual capacity, cardiac output, brain volume, etc). The model closely predicts FE/FI for halothane measured in the infants. At 5 min observed FE/FI was 0.67, at 15 min observed FE/FI was 0.80, while the predicted FE/FI values were 0.65 and 0.82, respectively. The model predicts that the myocardial and brain halothane concentrations will increase more rapidly in the infant than in the adult. Achievement of high myocardial halothane concentrations early in the anesthetic induction may cause the hypotension and bradycardia commonly seen in infants. Sensitivity of the infant myocardium to halothane would further exacerbate the effect of more rapid myocardial uptake.

Leakage of volatile anaesthetics from agent-specific keyed vapourizer filling devices

Agent-specific keyed vapourizer filling devices were designed to ensure that an anaesthetic vapourizer is filled with the correct agent. Since there appear to be no reports of possible loss of volatile agent or operating room pollution resulting from either the design or patterns of use of these devices, measurements were made with three anaesthetic agents and two methods of use. First, two bottles each of methoxyflurane, enflurane and halothane were fitted with a suitable filling device and the weight of agent lost from each bottle over six weeks was measured. Bottle #1 of each agent remained without agitation between weighings; bottle #2 was tipped to mimic filling of a vapourizer. Weight loss over the six week period was 2.76 and 3.15 per cent of the halothane, 2.22 and 2.43 per cent of the enflurane, and 0.58 and 0.96 per cent of the methoxyflurane, for bottles #1 and #2, respectively. Second, pollution was measured with an infra-red analyser for halothane, using bottles #1 and #2, as described above, and a third bottle on which the filling device was replaced by the screw-on cap after each filling of the vapourizer. Vapour loss was undetectable for bottle #1, between 25 and 30 ppm for bottle #2, and between 350 and 400 ppm for bottle #3. Thus, although the design of the filling devices results in loss of the anaesthetic agent, this loss represents potential pollution only when the device is replaced by the screw-on cap between use. Therefore, when using filling devices, these should be left on the bottle of volatile agent between fillings to decrease operating room pollution.

A sandwich electrode for multi-gas analysis: a prototype

A prototype composite electrode consisting of a metallized membrane "outer" cathode, and a conventional "inner" silver disc cathode, both sharing the same electrolyte, is described. Preliminary results indicate that the metallized membrane will act as an oxygen filter, allowing anaesthetic gases such as nitrous oxide, to pass through to the second (inner) cathode, where they may be reduced. Linear relationships exist for oxygen concentration and metallized membrane current; and for nitrous oxide concentration and the second cathodic current. Extension of this technique to measure both halothane and nitrous oxide on the second cathode, simultaneously with oxygen on the metallized membrane, is discussed.

A laboratory investigation of a multigas monitor for anaesthesia (EMMA)

A new volatile anaesthetic gas analyser (EMMA) was tested in the laboratory. It was shown to have an accurate, linear response, with minimal zero drift and to be almost unaffected by carrier gases. It is a versatile and sensitive machine with a fast response time indicating that it might be used for breath-by-breath monitoring. The EMMA is a useful new anaesthetic gas analyser than should find widespread clinical usage.

Remote monitoring by mass spectrometry during anaesthesia. Evaluation of a suitable inlet system

We describe a three-stage mass spectrometer inlet system suitable for use in operating theatres and evidence of its performance in delay and response times to step changes in oxygen and halothane concentrations. At 55 m and a sampled gas flow of 100mlmin-1, the inlet imposed a delay of 21s and prolonged the 10-90% response to 310ms for oxygen and 510ms for halothane. A linear relationship between inlet length and 10-90% response time at constant sampled gas flow was demonstrated for halothane but not for oxygen. Our results compared with those of other workers support the chosen compromise between practical flexibility and convenience versus maximum speed of response that was adopted in this system design.

Closed-circuit halothane and enflurane using an in-circle Goldman vaporizer

A closed-circle absorber system incorporating an in-circle Goldman vaporizer was used to administer halothane or enflurane in oxygen to adult patients. The attained inspired and end-tidal concentrations of volatile agent after a period of stabilization at each vaporizer setting were measured by mass spectrometry. During spontaneous respiration under halothane the ranges of inspired concentrations at settings 1, 11/2 and 2 were respectively 0.5-0.9%, 1.4-2.4% and 3.3-4.5%. corresponding inspired enflurane concentrations at the same settings were 0.8-1.4%, 1.9-2.8% and 3.7-5.0%. IPPV to 5% end-tidal carbon dioxide, although increasing the inspired concentrations slightly, produced considerable increases in end-tidal concentrations. Minimal pre-oxygenation was used to assess the problem of nitrogen accumulation within the circuit. The maximum nitrogen concentration was 56%.

Controller anaesthesia: an approach using patient characteristics identified during uptake

A system to control the alveolar anaesthetic concentration of patients undergoing halothane anaesthesia with controlled ventilation is described. Parameters characterizing the alveolar concentration response are determined on-line from breath-by-breath measurement of the inspired and end-tidal concentrations and the mixed venous anaesthetic partial pressure is estimated throughout the procedure. The method does not depend on the use of reference models or pre-programming and the inspired concentration required to control the alveolar concentration is determined as induction proceeds. Results using both computer simulations and data from patients undergoing routine clinical anaesthesia are analysed. Off-line verification results illustrate the operation of the technique and in 20 cases the inspired concentration, as controlled by the anaesthetist, was compared with that predicted by the automated system. These results indicate the feasibility of the system as a method for the control of anaesthesia.

Anaesthetic gases and health risks to laboratory personnel: a review

The evidence that chronic exposure to inhalational anaesthetic agents may be associated with psychomotor, hepatic and renal dysfunction, to increased susceptibility to infections and neoplastic disease, and to an increased incidence of miscarriages and foetal abnormalities, is discussed. The risk to pregnant women seems greatest after exposure to rather high concentrations of nitrous oxide. Although it is not suggested that all laboratory premises will be equally at risk, such levels as 400 ppm halothane and 8000 ppm nitrous oxide can build up in small poorly ventilated rooms when these agents are used for several hours at a time. A strong plea is entered for all to be aware of the hazard and to ensure that good ventilation and preferably, purpose-built scavenging equipment are installed wherever inhalational agents are used.

Thermocamera studies of enflurane and halothane vapours

The ability of enflurane and halothane to absorb infra-red (IR) energy was used to visualize their vapours; IR radiation was emitted by a heated screen and the absorption was studied with an IR camera. Even small concentrations of enflurane (0.2 vol %) and halothane (0.5 vol %) could be detected when released into the operating room atmosphere. Enflurane and nitrous oxide were dispersed in a similar way when they leaked from the face mask. Thus when anaesthetic pollution is monitored in the operating room, measurements of the concentration of nitrous oxide are sufficient for routine purposes. The IR method has added a new dimension to the study of occupational exposure to otherwise invisible gases.

Genetic differences in reductive metabolism and hepatotoxicity of halothane in three rat strains

The relationship between the reductive metabolism of halothane and hepatotoxicity was examined in three rat strains (Fischer 344, Sprague-Dawley, and black hooded Wistar) to determine if there were genetic differences in 1) the reductive metabolism of halothane under identical exposure conditions, and 2) the susceptibility to the hepatotoxic effects of halothane. Halothane hepatotoxic was produced in all rat strains by exposing phenobarbital-pretreated rats to 1 per cent halothane under mild hypoxia (14 per cent oxygen, inspired) for 2 h. Generally the levels of both 2-chloro-1,1,1-trifluoroethane (CTF) and 2-chloro-1,1-difluoroethylene (CDF), two volatile metabolites of halothane, increased from the onset of anesthetic exposure and reached a plateau after approximately 60 min. The exception to this trend were phenobarbital-pretreated Wistar rats (exposed to 1 per cent halothane with 14 per cent oxygen) where the levels of either CDF or CTF were high initially (10-min sample) and decreased in subsequent samples to reach a plateau after 80 min. The plateau levels of both CDF (approximately 6 ppm) and CTF (approximately 20 ppm) were not significantly different among the three rat strains exposed to halothane (1 per cent) and hypoxia with prior enzyme induction. There were, however, significant differences in both biochemical and pathological changes among the three strains exposed under the above identical conditions when the rats were killed 24 h after anesthetic exposure. For example, serum alanine aminotransferase (ALT) was increased fourfold in the Fischer strain but only doubled for the other two strains. Moreover, while all three strains had various amounts of hepatocyte damage in the vicinity of the central veins when the rats were exposed to halothane, hypoxia, and enzyme induction, only the Fischer strain showed hepatocyte damage under the exposure conditions of halothane (1 per cent) and normoxia (21 per cent oxygen, inspired) with prior enzyme induction. The results support the role of reductive metabolism of halothane in the etiology of halothane hepatotoxicity. Furthermore, they suggest that genetic variations in the susceptibility of the liver to the reactive intermediates or metabolites formed during reductive metabolism of halothane may be a significant factor in halothane hepatotoxicity.

The polarographic measurement of halothane

The polarographic reduction of halothane on silver cathodes was studied. Silver catalyses the reduction of halothane: two electrons are exchanged in the reduction process. Experiments using a rotating disc electrode showed a linear relationship between observed current and halothane concentration. A Silastic membrane-covered polarographic electrode was constructed using a silver cathode which gave a good linear response to changes in halothane concentration over the range 0.5% v/v halothane in nitrogen. Oxygen interferes with the measurement of halothane, but can be removed from a gas sample before analysis.

Trace anesthetic vapors in hospital operating-room environments

This study investigated concentrations of halothane anesthetic vapors in the operating rooms of two hospitals in the Ottawa, Ontario, Canada, area. Air samples, taken by active charcoal tubes and dosimeter badges, were analyzed by a gas chromatographic technique. Readings of 71 samples taken from hospital A and 65 samples from hospital B ranged from 1.0 to 29.4 parts per billion (ppb) for the active period and 0.1 to 3.8 ppb for the inactive period. All samples showed trace concentrations of halothane, but were well below the recommended maximal level.

Evaluation of the efficacy of an active scavenger for controlling air contamination in an operating theatre

Contamination of the air with halothane in a poorly ventilated ENT theatre was found to be very great (median concentration 449 micrograms litre-1, 177 samples), but was reduced significantly (P less than 0.005) by the use of an active scavenger of patients' expired gases (median concentration 159 micrograms litre-1, 168 samples). For about 18% of the time when the theatre was in use, the halothane concentration in the air was greater than 1000 micrograms litre-1, whether or not the patients' expired gases were being scavenged. Although not measured quantitatively, this appeared to correspond approximately to the period of time in theatre when patients were not connected to the anaesthetic circuit.

Waste anesthetic gas exposures to veterinarians and animal technicians

A survey of veterinarians was conducted in an 11-county region of eastern Colorado to determine the extent of usage of inhalation anesthetics and to measure exposures of veterinarians and their assistants to waste anesthetic gases. The survey indicated that inhalation anesthetics were used in 80.8% of the 210 practices. Exposures to waste anesthetics in veterinary practices were far less than reported in human hospitals. Waste anesthetic concentrations were affected by size of the patient, type of breathing system, and use of scavenging systems. Dilution ventilation had no effect on breathing zone concentrations. The endotracheal tube and occasionally the anesthetic machine were the major sources of leakage of anesthetic gases.

An improved ultra-violet halothane meter

The development of an ultra-violet absorption meter, suitable for the measurement of concentrations of halothane (0-5%) under clinical conditions, is described. The scale is accurate to 0.05% and the zero draft did not exceed 0.25% halothane over 15 h after a 5-min warm-up period. The inherent time of response is about 2 s.

Evaluation of infrared analysers used for monitoring waste anaesthetic gas levels in operating theatres

Several commercially available infrared analysers used to monitor levels of waste anaesthetic agent levels in operating theatres have been evaluated with respect to their specified accuracy, linearity and level of sensitivity.