Field application of SPME as a novel tool for occupational exposure assessment with inhalational anesthetics

Occupational exposure to inhalational anesthetics occurs routinely in operating rooms. It could induce serious health hazards and diseases. This exposure assessment is a crucial step in determining risks. In this study, a pen-shaped holder for solid-phase microextraction (SPME) sampler was successfully applied as a time-weighted average sampling tool for workshift exposure assessment of operation room staff to halothane. It proved to be very convenient for use in occupational environments such as operation rooms. Samples were analyzed by a gas chromatography-mass spectrometry. The validity of the SPME method was checked in real-world conditions with Occupational Safety and Health Administration (OSHA) 103 standard method for the determination of inhalational anesthetics. A good agreement between OSHA 103 and SPME methods was obtained and results demonstrated no statistically significant differences in anesthetic concentrations determined by the two analytical methods (p ≥ 0.05). It is concluded that SPME in retracted mode could successfully be applied in occupational exposure assessment purposes.

Apparent ‘electrocatalytic’ activity of multiwalled carbon nanotubes in the detection of the anaesthetic halothane: occluded copper nanoparticles

The electrocatalytic detection of the anaesthetic halothane on a multiwalled carbon nanotube modified glassy carbon electrode is reported with a low limit of detection of 4.6 microM. A thorough investigation of the underlying cause of this apparent catalytic effect is undertaken by comparing the response of various carbon electrodes including glassy carbon, basal- and edge-plane pyrolytic graphite electrodes (bppg and eppg respectively) to increasing additions of halothane. The reduction of halothane is shifted by 250-300 mV to more negative potentials at an eppg electrode than that observed at the GC-CNT electrode. Therefore the results of this investigation show that, surprisingly, the electrocatalysis is not solely due to the introduction of edge-plane-like defect sites on the carbon nanotubes as is commonly found for many other substrates showing favourable voltammetry at nanotube modified electrodes. Instead, we reveal that in this unusual case the electroactive sites for the reduction of halothane are due to the presence of copper nanoparticles occluded within the carbon nanotubes during their production, which are never completely removed by standard purification techniques such as acid washing. This is only the third known case where apparent electrocatalysis by carbon nanotube modified electrodes is due to occluded metal-related nanoparticles within the nanotube structure, rather than the active sites being the edge-plane-like defect sites on the nanotubes. Furthermore this is the first case where the active sites are nanoparticles of copper metal, rather than metal oxide nanoparticles (namely oxides of iron(II)/(III)) as was found to be the case in the previous examples.

Effect of halothane on lung carcinoma cells A 549

The halogenated hydrocarbons, such as halothane, are widely used as anesthetics in clinical practice; however their application is often accompanied with metabolic, cardiovascular and respiratory complications. One of the possible factors for this negative outcome might be the severe toxicity of these agents. In this paper, we investigate in vitro effects of halothane on human lung carcinoma A 549 cells, namely on their cytotoxicity, adhesive properties and metabolic activity. The cytotoxicity response of lung carcinoma A 549 cells to halothane was determined by lactate dehydrogenase (LDH) assay (for cytotoxicity), by detachment assay after adhesion to type IV collagen (for cell adhesive properties) and by surface tension measurements of culture medium (for cell metabolic activity). Regarding the cytotoxicity, the determined maximal non-toxic concentration of halothane on A 549 cells, given here as volume percentages (vol.%) was 0.7 vol.% expressed as aqueous concentration in the culture medium. Direct measurement of the actual halothane concentration in the culture medium showed that 0.7 vol.% corresponds to 1.05 mM and 5.25 aqueous-phase minimum alveolar concentration (MAC). Concentrations equal or higher than 1.4 vol.% (2.1 mM; 10.5 MAC) of halothane provoked complete detachment (cell death), or reduction of initial adhesion to collagen IV in half of the cell population. Surfactant production of A 549 cells, registered up to 48 h after halothane treatment, was inhibited by halothane concentrations as low as 0.6 vol.% (0.9 mM; 4.5 MAC). Our results demonstrate that sub toxic halothane concentrations of 0.6 vol.% inhibits surfactant production; concentrations in the range 0.8-1.4 vol.% induce membrane damages and concentrations equal and higher than 1.4 vol.%--cell death of approximately 50% of the cells.

Low-affinity analytical chromatography for measuring inhaled anesthetic binding to isolated proteins

The direct measure of volatile anesthetic binding to protein is complicated by weak affinity and therefore rapid kinetics. Consequently, several puted targets for these clinically important drugs have only functional data to support a direct mode of action. While several methods for measuring some aspects of binding are available, all have significant limitations. We introduce the use of analytical chromatography for the purpose of directly measuring volatile anesthetic binding to protein, and show that it can provide estimates of both affinity and stoichiometry for proteins that can be obtained in fairly high purity and mass. Using this approach we characterize halothane binding to serum albumin as low affinity and multisite, and to myoglobin or cytochrome C as strictly nonspecific. This approach will be useful in directly characterizing equilibrium, solution binding to isolated proteins in preparation for more time-consuming methods with structural resolution.

Bioactivation and cytotoxicity of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) in isolated rat hepatocytes

The bioactivation and cytotoxicity of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123), a replacement for some ozone-depleting chlorofluorocarbons, were investigated using freshly isolated hepatocytes from non-induced male rats. A time- and concentration-dependent increase in the leakage of lactate dehydrogenase and a concentration-dependent loss of total cellular glutathione were observed in cells incubated with 1, 5 and 10 mM HCFC-123 under normoxic or hypoxic (about 4% O2) conditions. Lactate dehydrogenase leakage was completely prevented by pretreating the cell suspension with the free radical trapper N-t-butyl-alpha-phenylnitrone. The aspecific cytochrome P450 (P450) inhibitor, metyrapone, totally prevented the lactate dehydrogenase leakage from hepatocytes, while two isoform-specific P450 inhibitors, 4-methylpyrazole and troleandomycin (a P450 2E1 and a P450 3A inhibitor, respectively), provided a partial protection against HCFC-123 cytotoxicity. Interestingly, pretreatment of cells with glutathione depletors, such as phorone and diethylmaleate, did not enhance the HCFC-123-dependent lactate dehydrogenase leakage. Two stable metabolites of HCFC-123, 1-chloro-2,2,2-trifluoroethane and 1-chloro-2,2-difluoroethene, were detected by gas chromatography/mass spectrometry analysis of the head space of the hepatocyte incubations carried out under hypoxic and, although at a lower level, also normoxic conditions, indicating that reductive metabolism of HCFC-123 by hepatocytes had occurred. The results overall indicate that HCFC-123 is cytotoxic to rat hepatocytes under both normoxic and hypoxic conditions, due to its bioactivation to reactive metabolites, probably free radicals, and that P450 2E1 and, to a lower extent, P450 3A, are involved in the process.

Concentrations of anaesthetic gases in hospital operating theatres

Occupational exposure to anaesthetic gases (halothane, forane and nitrous oxide) was assessed in hospitals located in Lódź and its satellite towns. Individual dosimetry and stationary sampling methods were employed. The samples of air from workplaces were analysed by gas chromatography with mass detection or flow ionisation (halothane, forane) and by infra-red spectroscopy method (nitrous oxide). The concentrations of halothane and accompanying substances (ethanol, isopropanol and diethyl ether) indicate that Polish OELs were met in the majority of the hospitals. As Polish hygiene standards for forane and nitrous oxide are no available, the concentration values were compared with Swedish and German OELs. The comparison revealed that forane concentrations did not exceed Swedish OEL but nitrous oxide did exceed German maximum allowable levels.

Occupational exposure to inhaled anaesthetics: a follow-up study on anaesthetists of an eastern European university hospital

BACKGROUND

Although no dose-response relationship for the health risks associated with the occupational exposure to inhaled anaesthetics exists, public health authorities recommend threshold values. The aim of the present study was to assess if and to what extent these threshold values are exceeded in an eastern European university hospital before and after measures had been taken to reduce occupational exposure.

METHODS

At nine workplaces occupational exposure of anaesthetists to nitrous oxide and halothane or isoflurane was measured by means of photoacoustic infrared spectrometry. The measurements were carried out in 1996 and were repeated in 1997 after the installation of active scavenging devices at five workplaces and an air-conditioning system at one workplace.

RESULTS

Occupational exposure to nitrous oxide and halothane or isoflurane was lower in 1997 compared to 1996. In 1997 most of the nitrous oxide values still exceeded the threshold value of 100 ppm, whereas most of the halothane and isoflurane values were already below the threshold values of 5 ppm and 10 ppm in 1996.

CONCLUSION

The measures taken were effective in reducing waste gas exposure. Nevertheless, further efforts are necessary, especially for nitrous oxide, to reach western European standards. These efforts comprise structural measures such as active scavenging devices and air-conditioning systems at all workplaces, the use of total intravenous anaesthesia, low-flow anaesthesia and an appropriate working technique.

Rapid analysis of halothane in biological samples using headspace solid-phase microextraction and gas chromatography-mass spectrometry--a case of a double homicide

A simple, rapid, and sensitive method for the analysis of halothane in biological samples was developed. The procedure describes the extraction of halothane from blood, liver, kidney, brain, urine, bile, and stomach contents by headspace solid-phase microextraction (HS-SPME) followed by capillary gas chromatography coupled with mass spectrometry (GC-MS). The recovery in blood samples after addition of ammonium sulfate and sulfuric acid was 72% compared to a sample prepared in water (100%). Linearity was established over a concentration range of 0.1-100 mg/kg of spiked blood samples with an excellent coefficient of correlation (0.996) and a limit of detection of 0.004 mg/kg. The time for analysis was approximately 40 min per sample including the extraction step. The procedure was used for quantitation of halothane in various samples in a case of a double homicide. HS-SPME in combination with GC-MS was an effective method for the determination and quantitation of halothane in biological material.

Staff exposure to anaesthetic gases in theatre and non theatre areas

Environmental monitoring of anaesthetic gases was carried out in theatre areas in eight hospitals as well as in Delivery suites, radiology, radiotherapy and Dental suites. High staff exposures occurred in nontheatre areas although exposures in theatres were generally satisfactory. Environmental control measures are required where staff exposures exceed legal standards.

Homicidal poisoning with halothane

A double homicide by smothering with halothane-moistened towels is described and the blood and tissue concentrations of halothane are discussed in comparison to the literature.

Human halothane metabolism, lipid peroxidation, and cytochromes P(450)2A6 and P(450)3A4

OBJECTIVE

Halothane undergoes both oxidative and reductive metabolism by cytochrome P450 (CYP), respectively causing rare immune-mediated hepatic necrosis and common, mild subclinical hepatic toxicity. Halothane also causes lipid peroxidation in rodents in vitro and in vivo, but in vivo effects in humans are unknown. In vitro investigations have identified a role for human CYPs 2E1 and 2A6 in oxidation and CYPs 2A6 and 3A4 in reduction. The mechanism-based CYP2E1 inhibitor disulfiram diminished human halothane oxidation in vivo. This investigation tested the hypotheses that halothane causes lipid peroxidation in humans in vivo, and that CYP2A6 or CYP3A4 inhibition can diminish halothane metabolism.

METHODS

Patients (n = 9 each group) received single doses of the mechanism-based inhibitors troleandomycin (CYP3A4), methoxsalen (CYP2A6) or nothing (controls) before a standard halothane anaesthetic. Reductive halothane metabolites chlorotrifluoroethane and chlorodifluoroethylene in exhaled breath, fluoride in urine, and oxidative metabolites trifluoroacetic acid and bromide in urine were measured for 48 h postoperatively. Lipid peroxidation was assessed by plasma F2-isoprostane concentrations.

RESULTS

The halothane dose was similar in all groups. Methoxsalen decreased 0- to 8-h trifluoroacetic acid (23 +/- 20 micromol vs 116 +/- 78 micromol) and bromide (17 +/- 11 micromol vs 53 +/- 49 micromol) excretion (P < 0.05), but not thereafter. Plasma F2-isoprostanes in controls were increased from 8.5 +/- 4.5 pg/ml to 12.5 +/- 5.0 pg/ml postoperatively (P < 0.05). Neither methoxsalen nor troleandomycin diminished reductive halothane metabolite or F2-isoprostane concentrations.

CONCLUSIONS

These results provide the first evidence for halothane-dependent lipid peroxidation in humans. Methoxsalen effects on halothane oxidation confirm in vitro results and suggest limited CYP2A6 participation in vivo. CYP2A6-mediated, like CYP2E1-mediated human halothane oxidation, can be inhibited in vivo by mechanism-based CYP inhibitors. In contrast, clinical halothane reduction and lipid peroxidation were not amenable to suppression by CYP inhibitors.

Factitious halothane detection during trigger-free anesthesia in a malignant hyperthermia susceptible patient

PURPOSE

To discuss the problems encountered when halothane was detected in a presumed 'clean' patient circuit during the 'trigger-free' anesthetic management of a known Malignant Hyperthermia Susceptible (MHS) patient for routine orthopedic surgery.

CLINICAL FEATURES

A 29-yr-old MHS woman had a wrist arthroscopy/exploration/fusion under general anesthesia. During the course of the 'trigger-free' anesthetic the respiratory gas analyser detected end-tidal halothane in the patient circuit. The patient was disconnected from the circuit as attempts to identify the source of the readings were undertaken. After ruling out the presence of halothane by various clinical manoeuvre the patient was reconnected to the circuit without sequelae.

CONCLUSION

By exclusion the problem was presumed to be a factitious reading resulting from the respiratory gas analyser incorrectly identifying patient-expired methane as halothane.

[Levels of "waste" halothane in operating rooms at gynecologic and obstetrical clinics--preliminary results]

INTRODUCTION

Medical staff working in surgical wards of hospitals, people that work on transport or storaging of gases and liquids, employees working on gas tanks and gas installations, mechanics for anesthetic devices and employees in the process of production of these substances are professionally exposed to anesthetic gases or and fumes that are released in their working environment. It has been confirmed that there were some deviations of indicators of the liver function after a long term exposure of the medical staff (surgeons, anesthesiologists, instrument nurses and anesthetists) to halothane and it has been notified that the level of wasted-halothane in the indoor air of the surgical theaters should be measured in order to get a correct and complete evaluation of the professional risk. The term "wasted-halothane" in this research means fumes of halothane that leave a closed circle: anesthetic device--respiratory organs (patient)--indoor air of the workplace (operating room).

MATERIALS AND METHODS

Tests were done in the theaters of the surgical wards of the Department of Gynecology and Obstetrics of Novi Sad. During the testing period no ventilation system was used in any of the theaters. Tested groups included anesthesiologists, instrument nurses and anesthetists who were the members of the surgical team. Tests have not been done on same individuals, but the same workplace. Samples were taken using the "individual sample" method from the breathing zone of the tested person using a rubber pipe fixed on the shoulder. Pumps (personal samplers--"Casella") were set to absorb 0.2 liters of air per minute. Laboratory analyses of these samples were done using a method of desorption of the halothane fumes from the active coal with benzyl-alcohol, and their evaluation on gaschromatograph (Electron-Capture-Detector). The threshold Limit Value (TLV) of halothane fumes at the workplace is 40 mg/m3.

RESULTS

During three days of sampling 32 samples of indoor air were taken from the surgical wards of the Department. 30 samples were taken in the surgical theaters, one in the hall between surgical theaters, and one in the room for rest of the staff. Concentration of halothane fumes in the theatre No 1 was between 6.9 mg/m3 and 27.31 mg/m3 in anesthetists, between 33.08 mg/m3 and 37.62 mg/m3 in anesthesiologists and between 6.9 mg/m3 and 27.31 mg/m3 in instrument nurses. At the theatre No 2 concentration of halothane fumes was between 31.27 mg/m3 and 37.9 mg/m3 in anesthetists, between 3.56 mg/m3 and 91.7 mg/m3 in anesthesiologists and up to 95.5 mg/m3 in instrumenting nurses. Concentration of halothane fumes in the theatre No 3 were between 4.19 mg/m3 and 17.18 mg/m3 in anesthetics, between 6.23 mg/m3 and 37.62 mg/m3 in anesthesiologists and between 8.27 mg/m3 and 12.33 mg/m3 in instrument nurses. In the hall between these surgical theaters the concentration was 3.02 mg/m3 and 0.28 mg/m3 in the room for rest.

DISCUSSION

Halothane fumes were present in the atmosphere of the working environment in significant quantities at all tested places Especially indicative were the results that showed that the concentration of halothane fumes in the theatre No 1, at the end of surgical operational program, was much higher than at the beginning, and what is even more important it was much higher than those in TLV in anesthesiologists and instrument nurses (more than twice higher). The differences of concentrations between specific occupations within the surgical team were also significant. Our results show that the most exposed were anesthesiologists and instrument nurses, who spent most time nearby the operation table. The anesthetists were much less exposed, due to the fact that they are assistants that often leave the surgical theater during the surgical interventions. Indicators illustrate that the increase of the concentration of halothane fumes depends on the length the surgical theaters were used. It shows an increase of halothane fumes co

[Evaluation of exposure to halothane and ethyl alcohol among technicians responsible for maintenance of anesthesia equipment]

The authors discuss the measurements of exposure to halotane and ethyl alcohol among technicians responsible for maintenance of anaesthesiological instruments that occurs at various stages of maintenance work and in an operating room.

Effect of intravenous lidocaine on halothane minimum alveolar concentration in ponies

This study investigated the effect of lidocaine i.v. on halothane minimum alveolar concentration (MAC) in ponies. Six ponies were anaesthetised with thiopentone and succinylcholine, intubated and anaesthesia maintained with halothane. Ventilation was controlled and blood pressure maintained within clinically acceptable limits. Following a 2 h equilibration period, baseline halothane MAC was determined. The ponies were then given a loading dose of lidocaine (2.5 or 5 mg/kg bwt) or saline over 5 min, followed by a constant infusion of lidocaine (50 or 100 microg/kg/min, or saline, respectively). The halothane MAC was redetermined after a 60 min infusion of lidocaine or saline. The baseline halothane MAC for the control group was mean +/- s.d. 0.94 +/- 0.03%, and no significant decrease occurred following saline infusion. Lidocaine decreased halothane MAC in a dose-dependent fashion (r = 0.86; P < 0.0003). The results indicate that i.v. lidocaine may have a role in equine anaesthesia.

End tidal halothane concentration and postoperative analgesia requirements in dogs: a comparison between intravenous oxymorphone and epidural bupivacaine alone and in combination with oxymorphone

The purpose of this study was to compare the effects of epidural bupivacaine (BUP) and oxymorphone/bupivacaine (O/B) and intravenous (i.v.) oxymorphone (IVO) on halothane requirements during hind end surgery and postoperative analgesia in 24 dogs. Dogs were randomly assigned to treatment groups: O/B--oxymorphone (0.1 mg/kg) in 0.75% bupivacaine (1 mg/kg for a total volume of 0.2 ml/kg); BUP--0.5% bupivacaine (1 mg/kg for a total volume of 0.2 ml/kg) with i.v. oxymorphone (0.05 mg/kg) postoperatively; and IVO--oxymorphone (0.05 mg/kg) pre- and postoperatively. Heart rate (HR), respiratory rate, arterial blood pressure, end-tidal carbon dioxide and halothane, and arterial blood gases were recorded prior to treatment and every 15 minutes thereafter. Once surgery had begun, end-tidal halothane concentrations were decreased as low as possible while still maintaining a stable anesthetic plane. Data were analyzed using ANOVA with P < 0.05 considered significant. End-tidal halothane requirements did not differ significantly among treatments. Respiratory depression was increased and HR was decreased in the O/B and IVO groups. Postoperative analgesic requirements were significantly less in dogs receiving O/B.

Concentration measures of volatile anesthetics in the aqueous phase using calcium sensitive electrodes

Volatile anesthetic concentrations have been difficult to measure, but are an important experimental parameter for in vitro studies of anesthetic actions. Calcium sensitive electrodes were investigated as a means of continuously monitoring anesthetic concentrations in artificial cerebrospinal fluids (ACSF). Anesthetic-induced Ca2+ electrode signals were compared at room (22 degrees C) and physiological (35 degrees C) temperatures. Electrophysiological measures of anesthetic effects on synaptic potentials provided a bioassay. Halothane and isoflurane produced negative changes in calcium electrode potentials which were linearly related to concentrations over a clinically useful range (0.5-1.5 MAC). Anesthetic-induced voltages persisted in nominally zero Ca2+ ACSF and even in deionized water. A good correlation (r>0.9) was found for calcium electrode measures of anesthetic concentration and synaptic response depression produced by halothane, at both 22 and 35 degrees C. These results support three conclusions: (1) calcium sensitive electrodes provide a useful measure of volatile anesthetic concentrations in aqueous solution. (2) Care must be taken when using these electrodes for Ca2+ concentration measurements, if a volatile anesthetic is also to be used, since the anesthetic could introduce an appreciable error (>50%). (3) A temperature change of 13 degrees C had surprisingly little effect on Ca2+ electrode responses or on synaptic depression produced by anesthetics.

Effects of gas flow management on postintubation end-tidal anesthetic concentration and operating room pollution

STUDY OBJECTIVE

To study how different anesthetic practices during the transition from anesthetic delivery by mask to endotracheal intubation affect end-tidal postintubation anesthetic concentration and operating room (OR) pollution.

DESIGN

Prospective study.

SETTING

Anesthesia research laboratory.

MEASUREMENTS AND MAIN RESULTS

We studied four gas flow management practices: practice vaporizer off, only the anesthetic vaporizer was turned off; all off, oxygen (O2), nitrous oxide (N2O), and the vaporizer were turned off; gas off: O2 and N2O were turned off; and all on: neither the gas flows nor the vaporizer were turned off. A model of inhalational anesthetic induction was simulated by using an adult circle system attached to a reservoir bag ("artificial lung"). By using a fixed gas flow, we achieved an end-tidal N2O (ETN2O) concentration of 70% and end-tidal halothane (ETHal) concentration of 3%, then stopped mechanical ventilation and performed the four practices for a 30-second "intubation" period. During this time, the reservoir bag was disconnected from the circuit, and the gas volume exiting the circuit (pollution volume) was measured. After this 30-second disconnect period, the bag was reconnected to the anesthetic circuit, and the original ventilation, gas flows, and vaporizer setting were resumed. The anesthetic concentrations were measured at 10, 20, and 30 seconds after reconnection. For the vaporizer off practice, ETHal was low and did not return to equilibrium within 30 seconds (p < 0.05); ETN2O clinically was unaltered. In the all off practice, anesthetic concentrations were below equilibrium at 10, 20, and 30 seconds (p < 0.05). For the gas off practice, ETHal was slightly below equilibrium at all times; ETN2O was below equilibrium at 10, 20, and 30 seconds (p < 0.05). In the all on practice, end-tidal anesthetic concentrations were unchanged when compared with equilibrium (p > 0.05). Pollution volumes in the vaporizer off and all on practices were ten-fold higher than in the all off and gas off practices (p < 0.05).

CONCLUSION

In a mechanical model of anesthetic induction, turning the gas flows off before "intubation" and leaving the vaporizer on (the gas off practice) maintained "postintubation" end-tidal drug concentrations close to "preintubation" equilibrium and minimized OR pollution.

Focal heat stimulation for the determination of the minimum alveolar concentration of halothane in the rabbit

A focal heat stimulus of 54.37 +/- 0.07 (SD) degrees C was applied for 30 s to the inner aspect of the pinna of the ear for the determination of the minimum alveolar concentration (MAC) of halothane in New Zealand White rabbits. The latency before head movement was measured electromanometrically. The MAC value was 1.05 +/- 0.09 (SD)%. Other physiological responses occurred inconsistently and could not be used as reliable end points for the determination of the MAC in the rabbit.

[Room air contamination with halothane during pediatric bronchoscopy]

Halothane anesthesia is frequently used for pediatric bronchoscopy. A disadvantage of the equipment used, a rigid bronchoscope together with inhalation anesthesia is the contamination of the working environment. The aim of this study was to determine the exposure of anesthetist and endoscopist during pediatric bronchoscopy under halothane anesthesia in a worst-case working environment and to compare these measurements with the currently valid international threshold values. Ten children (ASA I-III) scheduled for diagnostic bronchoscopy were included in the study. After induction with thiopentone and relaxation with atracurium all children were intubated with a rigid bronchoscope and manually ventilated through a bypass of the bronchoscope. Anesthesia was maintained by means halothane (0.5-2.0 vol%) in 100% oxygen with a flow of 10 l/min. The investigation was done in an operating room without air conditioning and scavenging system. Trace concentrations were measured every 2 minutes in the breathing zones of the anesthetist and the endoscopist by means of a highly sensitive direct reading instrument. Lower detection limit was 0.02 ppm. The mean age (+/- SD) of the children was 29.9 +/- 15.9 months (range: 4 weeks-48 months). Ventilation and oxygenation were stable throughout the bronchoscopic procedure. Mean exposure (+/- SEM) to halothane was 57.7 +/- 18.9 ppm for the anesthetist and 96.3 +/- 22.9 ppm for the endoscopist. The difference was statistically significant (ANOVA, P < 0.05). All international threshold values (2-50 ppm) were exceeded by far. Peak concentrations higher than 200 ppm halothane could be detected several times. The main result of the present study is that under the given situation in the operating room with insufficient room ventilation and no scavenging system halothane anesthesia for rigid bronchoscopy in children results in an occupational exposure that is higher than all known health regulation guidelines. Therefore, in case of insufficient working conditions total intravenous anesthesia might be a better alternative also in very small infants.

Occupational exposure to sevoflurane, halothane and nitrous oxide during paediatric anaesthesia. Waste gas exposure during paediatric anaesthesia

We report the findings of a study on exposure of operating room staff to sevoflurane, halothane and nitrous oxide during induction and maintenance of anaesthesia in children. Concentrations of anaesthetic agents in the operating theatre were measured directly by highly sensitive, photoacoustic infrared spectrometer during 20 anaesthetics. Samples were taken from the breathing zones of the anaesthetist and the circulating nurse. The operating theatre was of modern design with an air conditioning system providing 20 changes of air each hour. The threshold values of 100 ppm N2O, 50 ppm isoflurane and 10 ppm halothane recommended by the United Kingdom Committee for Occupational Safety and Health (COSH) were exceeded in several cases for a short time during mask induction. After tracheal intubation, trace concentrations of sevoflurane, halothane and N2O were mostly under the recommended levels and comparable to levels measured during adult anaesthesia.

Intermittent positive ventilation through a laryngeal mask in children: does it cause gastric dilatation?

After obtaining Ethics Committee approval and informed consent, sixty children, ASA Grade 1 or 2 and aged six months to ten years, were randomly allocated to receive intermittent positive pressure ventilation through either a laryngeal mask or a tracheal tube. Inflation pressures were maintained below 20 cm H2O, and gas aspirated from the stomach via an orogastric tube over a one h period. No large volumes were aspirated and no differences were detected between the groups. We conclude that healthy children over the age of six months can be safely ventilated through the laryngeal mask airway without gastric distension.

Simple method for simultaneous determination of halothane, enflurane, and isoflurane in Krebs solution using capillary gas chromatography

A simple gas chromatography (GC) method for the simultaneous determination of halothane, enflurane, and isoflurane in Krebs buffer solution has been developed. The method utilizes methylene chloride as the internal standard and liquid-liquid extraction using chloroform as the solvent. The method demonstrated excellent recovery (100%) of each component and a linear calibration range of 100-700, 100-800, and 300-1,400 micrograms/mL for halothane, isoflurane, and enflurane, respectively. Intra-day accuracy and precision had an error and coefficient of variation of less than 5.1% and 2.7%, respectively.

Human reductive halothane metabolism in vitro is catalyzed by cytochrome P450 2A6 and 3A4

The anesthetic halothane undergoes extensive oxidative and reductive biotransformation, resulting in metabolites that cause hepatotoxicity. Halothane is reduced anaerobically by cytochrome P450 (P450) to the volatile metabolites 2-chloro-1,1-difluoroethene (CDE) and 2-chloro-1,1,1-trifluoroethane (CTE). The purpose of this investigation was to identify the human P450 isoform(s) responsible for reductive halothane metabolism. CDE and CTE formation from halothane metabolism by human liver microsomes was determined by GC/MS analysis. Halothane metabolism to CDE and CTE under reductive conditions was completely inhibited by carbon monoxide, which implicates exclusively P450 in this reaction. Eadie-Hofstee plots of both CDE and CTE formation were nonlinear, suggesting multiple P450 isoform involvement. Microsomal CDE and CTE formation were each inhibited 40-50% by P450 2A6-selective inhibitors (coumarin and 8-methoxypsoralen) and 55-60% by P450 3A4-selective inhibitors (ketoconazole and troleandomycin). P450 1A-, 2B6-, 2C9/10-, and 2D6-selective inhibitors (7,8-benzoflavone, furafylline, orphenadrine, sulfaphenazole, and quinidine) had no significant effect on reductive halothane metabolism. Measurement of product formation catalyzed by a panel of cDNA-expressed P450 isoforms revealed that maximal rates of CDE formation occurred with P450 2A6, followed by P450 3A4. P450 3A4 was the most effective catalyst of CTE formation. Among a panel of 11 different human livers, there were significant linear correlations between the rate of CDE formation and both 2A6 activity (r = 0.64, p < 0.04) and 3A4 activity (r = 0.64, p < 0.03). Similarly, there were significant linear correlations between CTE formation and both 2A6 activity (r = 0.55, p < 0.08) and 3A4 activity (r = 0.77, p < 0.005). The P450 2E1 inhibitors 4-methylpyrazole and diethyldithiocarbamate inhibited CDE and CTE formation by 20-45% and 40-50%, respectively; however, cDNA-expressed P450 2E1 did not catalyze significant amounts of CDE or CTE production, and microsomal metabolite formation was not correlated with P450 2E1 activity. This investigation demonstrated that human liver microsomal reductive halothane metabolism is catalyzed predominantly by P450 2A6 and 3A4. This isoform selectivity for anaerobic halothane metabolism contrasts with that for oxidative human halothane metabolism, which is catalyzed predominantly by P450 2E1.

Accumulation of foreign gases during closed-system anaesthesia

In a previous study, accumulation of methane was found at the end of closed-system ventilation. As on-line analysis of gas concentrations is now available, we examined the progressive increase in concentrations of methane, carbon monoxide and acetone during modern, closed-system conditions, and their influence on infrared halothane analysis, in 26 non-pregnant, gynaecological patients. A computer-controlled closed-system anaesthesia apparatus (PhysioFlex) was used for ventilation during total i.v. anaesthesia (excluding nitrous oxide or potent inhalation anaesthetics) for gynaecological laparoscopy. Methane, carbon monoxide and acetone concentrations were analysed every 15 min in a photoacoustic infrared monitor and halothane concentrations by built-in infrared spectrometry. Mean methane concentrations increased progressively after 105 min to 941 (SD 1094) ppm, but concentrations of carbon monoxide and acetone did not increase significantly. In 18 patients, the infrared measurement falsely indicated 0.79 (0.52)% "halothane" after 60 min, but no reading appeared in the other eight patients. We conclude that methane accumulated progressively under strict closed-system conditions in higher concentrations than reported previously. In two-thirds of patients it induced false "halothane" readings.

Effects of 3 MAC of halothane, enflurane and isoflurane on cilia beat frequency of human nasal epithelium in vitro

We have measured the effects of three times the minimum alveolar concentration (MAC) of halothane, enflurane and isoflurane on cilia beat frequency of human nasal epithelial brushings from 18 healthy adult patients. Using the transmitted light technique and paired perfusion chambers, the cilia were exposed to 2.25% halothane, 5% enflurane or 3.6% isoflurane in air, or air alone, in a controlled and blinded manner. Over a 4-h observation period, cilia beat frequency of the samples exposed to inhalation anaesthetic agents demonstrated a significant reduction in frequency compared with controls exposed to air alone. Mean cilia beat frequency for the samples exposed to halothane was 9.3 (SEM 1.3) compared with its controls of 11.4 (1.0); for the samples exposed to enflurane, 10.9 (1.3) compared with its controls of 11.6 (1.2); and for the samples exposed to isoflurane, 10.8 (1.1) compared with its controls of 11.6 (1.2). There was a statistically significant difference between the samples exposed to all three volatile agents and their associated controls (halothane, P = 0.01; enflurane, P = 0.03; isoflurane, P = 0.01; nested repeated measures analysis of variance utilizing polynomial contrasts).

A lower solubility recommends the use of desflurane more than isoflurane, halothane, and enflurane under low-flow conditions

STUDY OBJECTIVE

To determine whether the lower solubility of desflurane, over that of isoflurane, enflurane, and halothane, favors its use in low-flow anesthesia.

DESIGN

Prospective clinical study.

SETTING

Technical University of Munich.

PATIENTS

40 elderly (> or = 65 yrs), ASA physical status II and III surgical patients.

INTERVENTIONS

All patients were anesthetized and received delivered concentrations (FD) of 4% desflurane, 1.5% isoflurane, 1.8% enflurane, or 0.9% halothane (n = 10 patients for each anesthetic) in a fresh gas inflow of 3 L/min (high-flow), until end-tidal target concentrations (FA) of 2% desflurane, 0.5% isoflurane, 0.6% enflurane, and 0.3% halothane were obtained. After 30 minutes, the inflow was decreased to 1 L/min (low-flow), and the FD and the inspired concentration (FI) were adjusted to maintain the target concentration.

MEASUREMENTS AND MAIN RESULTS

The concentrations of the halogenated anesthetics, as well as nitrous oxide, oxygen (O2), and carbon dioxide, were measured in delivered gas at the common gas outlet and at the endotracheal tube connector. Transcutaneous O2 saturation, noninvasive blood pressure, and heart rate were also measured. During the first 30 minutes of high-flow administration, the target concentration was attained sooner with desflurane than with isoflurane, enflurane, or halothane (median levels: 4 min vs. 6 min, 8 min, or 10 min; p < 0.01). After the reduction of inflow to 1 L/min, FD had to be materially increased to maintain F1 and FA for the more soluble anesthetics, but not for desflurane.

CONCLUSIONS

At low flows, FD provides a reasonable surrogate of F1 and FA for desflurane, but not for isoflurane, enflurane, or halothane. The rapid and predictable titrability of desflurane favors its safe use in low-flow technique.

Determination of anaesthetic agent concentration by refractometry

Reference refractivity values have been derived for the anaesthetic agents halothane, isoflurane, enflurane, sevoflurane and desflurane which are traceable to national measurement standards. A simple method and equation have been derived for the application of these data to the measurement of agent concentration by refractometry. The main instrumental sources of uncertainty associated with this method are discussed and their respective contributions quantified. Agent concentration can be measured routinely at the +/- 1% level of uncertainty using this approach.

A comparison of sevoflurane with halothane, enflurane, and isoflurane on bronchoconstriction caused by histamine

This study was conducted to assess the effect of sevoflurane on lung resistance and compliance, and its responsiveness to histamine. We studied eight dogs to compare the effect of sevoflurane, isoflurane, enflurane, and halothane on bronchoconstriction caused by histamine. Baseline values of pulmonary resistance (RL) and dynamic pulmonary compliance (Cdyn) were measured prior to administration of histamine. Histamine (2, 4, and 8 micrograms.kg-1) were administered iv, and the values of RL and Cdyn at the time of peak effect were recorded. Under 1 or 2 MAC anaesthesia, sevoflurane as well as the other three anaesthetics had no bronchoactive effects. The four anaesthetics, including sevoflurane, demonstrated inhibitory effect on increases in RL and decreases in Cdyn caused by histamine. At 1 MAC anaesthesia, % changes in RL caused by 2, 4, or 8 micrograms.kg-1 of histamine were 38 +/- 11, 85 +/- 21, or 132 +/- 24% (mean +/- SE) for halothane, and 65 +/- 11, 132 +/- 15, or 172 +/- 19% for sevoflurane, respectively. Sevoflurane was less effective than halothane in preventing increases in RL. In preventing decreases in Cdyn, sevoflurane was less effective than halothane only at 8 micrograms.kg-1 of histamine under 1 and 2 MAC anaesthesia. There was no difference in attenuating effect on changes in RL and Cdyn between sevoflurane and isoflurane or enflurane. We concluded that sevoflurane was less potent than halothane in attenuating changes in RL and Cdyn in response to iv histamine.

[Pollution of operating room air by anesthetic gases in relation to the air conditioning method and anesthesia techniques]

Volatile anesthetics are suspected to cause various health risks even in subnarcotic concentrations (hepatotoxicity, mutagenicity, teratogenicity). Yet only for halothane a limit (MAK-value = 5 ppm) has been established for the entire FRG. In addition, in 1991 Hamburg and Schleswig-Holstein defined preliminary limits for isoflurane, enflurane and nitrous oxide. We analysed the pollution of operating-room air by narcotic gases in 20 hospitals of Niedersachsen. In several cases limits have been exceeded evidently. Reasons for high concentrations were: insufficient room ventilation, defective air-conditioning plants, technical defects (leakage) and high gas emission due to special techniques in anesthesia (bronchoscopy). In order to take care of personnel-health air concentration of anesthetic gases should be kept as low as possible by the help of sufficient room ventilation avoiding unnecessary emissions.

In vivo fluorine-19 magnetic resonance spectroscopy of cerebral halothane in postoperative patients: preliminary results

This study reports the use of 19F MRS to study halothane in the brain of eight patients recovering from halothane anesthesia of short duration. Resonances attributable to halothane were observed up to 90 min after withdrawal of the anesthetic agent. The signal-to-noise ratio for an unlocalized spectrum acquired using a 6 cm surface coil was typically 20 with data collection times of 2 min. In seven patients a single resonance was seen with a mean (+/- SD) chemical shift of +43.3 (+/- 1.8) ppm, referenced to NaF at 0 ppm. This resonance exhibited a T1 value of between 0.5 and 1 s, and a T2* (estimated from the linewidth of the resonance) between 3.5 and 10 ms. In one patient two resonances were observed with chemical shifts of +38 and +41 ppm. Because we cannot exclude the possibility that this was due to field inhomogeneity, the significance of the last finding is uncertain. However, phantom studies show that the chemical shift of halothane in different environments (such as water, olive oil, methanol, and lecithin) can vary to an extent that accounts for the two resonances seen in our patient. These results demonstrate the feasibility of in vivo 19F MRS studies of fluorinated volatile agents in humans. The potential for clinical 19F MRS of fluorinated anesthetics is discussed.

Accuracy and cross-sensitivity of 10 different anesthetic gas monitors

OBJECTIVE

The objective of this study was to test the accuracy and cross-sensitivity of commercially available anesthetic gas monitors.

METHODS

Using gas chromatography (GC) as a reference method, the accuracy, cross-sensitivity, and ability to recognize an erroneously selected agent were determined in the following 10 monitors for volatile anesthetics: Datex Capnomac Ultima-S, Datex Capnomac, Ohmeda 5330 agent monitor, Iris Dräger, Andros Dräger PM 8020 (all monochromatic, infrared analyzers), Nellcor N-2500E, Criticare POET II, Irina Dräger (all polychromatic, infrared analyzers), Siemens Servo Gas Monitor 120 (a piezoelectric analyzer), and Brüel & Kajer Type 1304 (a photoacoustic analyzer). Accuracy was determined at 0.5, 1, 2, and 4 times the minimal alveolar concentration (MAC) of either halothane or isoflurane in oxygen (O2). The cross-sensitivity tests were performed with 70 vol% nitrous oxide in O2, 5 vol% carbon dioxide in O2, 0.032 vol% alcohol in O2, and 70% water vapor in O2. The photoacoustic analyzer showed a higher accuracy for isoflurane than the polychromatic infrared monitors. The greatest inaccuracy with isoflurane was found in the Iris Dräger monitor, which had a maximal bias percentage by volume (vol%) of 0.09 at 0.5 MAC. (This bias was within the manufacturer's specified tolerance of +/- 0.1 vol% or 10% relative difference of reading, whichever is greater.) Irina Dräger was the most accurate analyzer with halothane (mean % bias [relative %] +/- SD, 0.9 +/- 2.0%). The greatest bias with halothane was found in the monochromatic infrared analyzers, with a maximal % bias at 0.5 MAC of 50.3% of the GC reading (12.4% with a new inner Nafion tube) found in the Datex Ultima monitor. The Siemens gas monitor showed a cross-sensitivity for water vapor (-0.248 vol%). The monochromatic infrared analyzers showed a small sensitivity to alcohol (additional deviation of 0.011 to 0.147 vol% at 2 MAC isoflurane) but no sensitivity to nitrous oxide. No cross-sensitivity was found in the polychromatic infrared and photoacoustic analyzers. An incorrect selection of anesthetic agent when using a monochromatic infrared analyzer can be fatal; for example, when using halothane and selecting isoflurane the values measured by the Datex Capnomac monitor were nearly 6 times: below the actual value (i.e., 1 vol% "isoflurane" on the display = 6 vol% halothane in reality).

CONCLUSIONS

The photoacoustic measurement principle is more accurate than the other methods, although the polychromatic infrared analyzers are safer because they detect erroneously selected agents.

Minimum alveolar concentration of halothane: an ethnic comparison

The minimum alveolar concentration (estimate of spread) of halothane which was determined in 42 Chinese, Nepalese or European patients was found to be 0.70% (0.66-0.74%) in Chinese and 0.70% (0.65-0.76%) in Nepalese and 0.68% (0.65-0.72%) in Europeans, using the Spearman Kärber method of analysis. This preliminary trial suggests that there is no ethnic difference in the minimum alveolar concentration of halothane between Asians and Europeans.

A focal cryogenic brain lesion does not reduce the minimum alveolar concentration for halothane in rats

BACKGROUND

A focal cortical cryogenic brain injury has been reported to reduce the brain pentobarbital concentrations needed to prevent movement in response to pain in rats. This occurred despite any apparent behavioral changes in the awake animals. To determine whether this was true with other anesthetics, the authors determined the minimum alveolar concentration (MAC) for halothane in normothermic, normocarbic ventilated Sprague-Dawley rats previously subjected to a freezing injury of the parietal cortex.

METHODS

Injury was produced in halothane-anesthetized rats by applying a cold (-70 degrees C), 4-mm-diameter brass rod to the exposed dura for 5 or 15 s. Animals then were studied 3 days after injury, a time when cerebral metabolism in the ipsilateral hemisphere reaches a minimum. Minimum alveolar concentration was determined using a tail-clamp stimulus, combined with end-tidal anesthetic sampling. In addition, exploratory activity was measured by the open field test just before MAC determination, and spontaneous nocturnal motility was monitored by an electronic motion sensor during the night before testing.

RESULTS

In normal animals subjected only to preparatory surgery, MAC was 1.10 +/- 0.07% (mean +/- SD). Almost identical values were found in rats subjected to 5- and 15-s cryogenic injuries (1.11 +/- 0.07% and 1.08 +/- 0.06%, respectively). There were no intergroup differences in open field test results or in spontaneous nocturnal activity.

CONCLUSIONS

These results indicate that a focal cortical brain injury that has no obvious neurologic or behavioral effects in the awake rat does not alter halothane requirements.

Evaluation of three transportable multigas anesthetic monitors: the Bruel & Kjaer Anesthetic Gas Monitor 1304, the Datex Capnomac Ultima, and the Nellcor N-2500

We compared the performance of three newly developed anesthetic agent (AA) monitors: the Bruel & Kjaer Anesthetic Agent Monitor 1304 (BK 1304), the Datex Capnomac Ultima (ULTIMA), and the Nellcor N-2500 (N-2500). The following were investigated: the linearity and accuracy in measuring AAs, oxygen, carbon dioxide, and nitrous oxide; the linearity and accuracy during warm-up time; the effect of increasing respiratory rate on the accuracy; the consequences of a difference between monitored and delivered AA and of delivering a mixture of AAs; and, finally, the effect of water vapor and alcohol. For all three monitors we found that the accuracy in determining the respiratory and anesthetic gases was sufficient for clinical use (the N-2500 does not measure oxygen). Because of the calibration mixture supplied with the device, however, the ULTIMA recorded values that were 10 to 12% (relative) less than the AA that was present. The BK 1304 had greater accuracy at higher respiratory rates than did the other two monitors, probably favoring its use in pediatric anesthesia. The N-2500 will detect which agent (isoflurane, enflurane, or halothane) is being used, alone or in a mixture. With the two other monitors the user must define which agent is given. In some situations a difference between this and the one actually delivered can theoretically lead to an overdose of AA, with the ULTIMA up to a 14.9 minimal alveolar concentration (MAC) overdose. No interference from alcohol or water vapor in the expired air was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Test-tube equilibration of volatile anaesthetic concentrations

We have measured concentrations of volatile anaesthetics after injection into test-tube assay solutions. In non-agitated tubes, aqueous anaesthetic concentrations decreased significantly throughout 40 min of incubation. Agitation (20-s vortex) of the tubes decreased the aqueous anaesthetic concentration by approximately 80% from concentrations in non-agitated tubes and resulted in more stable liquid anaesthetic concentrations over time. A decrease of less than 15% occurred between 10 and 50 min of incubation.

Halothane concentrations required to block the cardiovascular responses to incision (MAC CVR) in infants and children

The purpose of this study was to determine the halothane concentration in N2O required to block the cardiovascular responses to skin incision (MAC CVR) in infants and children. We studied 64 unpremedicated ASA 1 infants and children (one month to seven years). In each infant or child, anaesthesia was induced slowly with halothane and N2O, and an endotracheal tube was placed. The MAC CVR was assessed, after a steady state end-tidal halothane concentration had been established for ten minutes, by the "up and down technique" of Dixon. Positive responses were defined as an increase in MAP or HR > 10%. The MAC CVR50 values of halothane with 60% N2O were 1.16 +/- 0.23% at 1-6 mo, 1.17 +/- 0.18% at 7-12 mo, 0.95 +/- 0.26% at 1-3 yr, and 1.12 +/- 0.16% at 4-7 yr. The value at 1-3 years children was less than those in the other age groups (P < 0.05). The changes of MAP were correlated with changes of both HR and pupillary diameter. These results indicate that the values of MAC CVR50 of halothane in infants and children are higher than those required to block motor responses (MAC). The halothane requirement to block cardiovascular responses is lowest in the children aged one to three years.

Fast-responding, fibre-optic based sensing system for the volatile anaesthetic halothane, using an ultraviolet absorption technique and a fluorescent film

An improved version of a fast-responding sensing system for the widely used volatile anaesthetic halothane (2-bromo-2-iodo-1,1,1-trifluoroethane) is described. The concentration of halothane is determined using an ultraviolet radiation (UV) absorption technique. Ultraviolet radiation at 230 nm is conveyed by a silica optical fibre to a gas flow-through cell containing the halothane, and the intensity of the UV reaching the other side of the cell is measured using a fluorescent polymer film. This paper describes the development of an efficient fluorescent polymer film for the sensor based on poly(ethylene glycol) containing two fluorophores (2,5-diphenyloxazole and tris[4,4,4-trifluoro-1-(2-thienyl)butane- 1,3-diono]europium(III)). The film fluoresces strongly with a red line spectrum when excited in the range from about 200 to 380 nm. There is evidence of direct energy transfer between the two fluorophores. A similar effect is observed in films prepared from Carbowax 20M and the europium chelate. An advantage of this approach is that the fluorescent radiation can be transmitted back to a silicon photo-detector using an inexpensive polymer optical fibre bundle. Two experimental sensor systems for halothane are described and the results show that, although the response does not obey the Beer-Lambert law, a reliable system for determining halothane can be constructed, which operates over the medically important range 0-3%. This paper also describes how the signal-to-noise ratio of the system can be improved by using the long fluorescence lifetime of the film.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidural morphine reduces halothane MAC in humans

The effect of epidural morphine sulphate (4 mg in 10 ml saline) on the minimum alveolar concentration of halothane was investigated in a double-blind, randomized fashion in ten adult patients undergoing abdominal surgery, and compared with the minimum alveolar concentration of halothane after epidural administration of 10 ml saline in a similar group of patients. Morphine sulphate, administered through the epidural catheter 98 +/- 33 min before to skin incision reduced the minimum alveolar concentration of halothane by 28% (0.57% vs 0.78%, P < 0.05).

Continuous infusions of atracurium and vecuronium, compared with intermittent boluses of pancuronium: dose requirements and reversal

This study was designed to determine the effect of prolonged infusion on the ease of reversal of atracurium and vecuronium, and whether factors which potentiate the block delayed reversal. In phase one, 40 patients were randomized (double blind) to determine the steady state conditions for atracurium and vecuronium. Fourteen atracurium patients and 17 vecuronium patients were evaluable. The unblinded second phase involved the steady state conditions using halothane or isoflurane and atracurium infusions. The infusion required for 95% twitch depression (TD95) for atracurium was 7.6 +/- 1.1 micrograms.kg-1 x min-1. The requirement for vecuronium changes with time: TD95 at 30 min was 1.01 +/- 0.16, at 60 min 0.89 +/- 0.12 and after 90 min 0.85 +/- 0.17 micrograms.kg-1 x min-1 (P < 0.05). The mean TD95 was 0.94 +/- 0.23 micrograms.kg-1 x min-1. Multivariate regression analysis of the infusion data revealed a vecuronium model predicting TD95 by the duration of infusion (P < 0.05) and weight (P = 0.05). Atracurium TD95 was predicted by age (P = 0.05). The addition of an inhalation agent to atracurium reduced the infusion rate by 2.01 +/- 0.28 micrograms.kg-1 x min-1 (P = 0.0001) for each increase in MAC. The mean reversal times for atracurium with three different anaesthetics and for vecuronium were not different. Reversal of pancuronium blockade, from less profound twitch depression (86.4 vs 95%) took twice as long as for atracurium and vecuronium for which the following predictors were identified: age, weight, duration of infusion, level of blockade, and type of anaesthetic, using a stepwise regression model.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaesthetic uptake and washout characteristics of patient circuit tubing with special regard to current decontamination techniques

The amounts of halothane and isoflurane trapped after exposure for up to 3 h at 2 MAC in commonly used anaesthesia circuit tubing were quantitated by gas chromatography. The decontaminating effects of procedures such as flushing with oxygen, thermal disinfection and/or routine storage were assessed in a similar way. After halothane exposure, anaesthetic content was highest in silicone (398 +/- 55 mg 100 g-1). Lower quantities were found in all other tubings investigated (electrically conductive latex: 64 +/- 4, conductive rubber: 62 +/- 4, polyethylene-vinyl-acetate (PEVA): 293 +/- 10 and 149 +/- 17 for non-conductive corrugated and spiral tubes, respectively, polysulfone (Hytrel): 155 +/- 10 mg 100 g-1). The isoflurane contents were substantially lower (silicone: 278 +/- 23; others: 55 +/- 7, 61 +/- 6, 163 +/- 9 and 86 +/- 8, 74 +/- 4 mg 100 g-1). The tubings' content did not correlate with the material's partition coefficient as full saturation was not achieved during exposure. Decontamination procedures reduced the content of volatile anaesthetics to a variable extent. Conductive latex and rubber showed the highest residual content, even after thermal disinfection and subsequent storage. Twenty-minute flushing with oxygen (8 l min-1) decreased effluent gas concentrations below 5 p.p.m. in all tubings. With silicone, after 1 h flushing, halothane concentrations still exceeded 10 p.p.m. (isoflurane: 8 p.p.m.). It is concluded that urgent decontamination by a 20-min flush warrants the safe re-use of previously 'contaminated' conductive rubber and latex as well as polysulfone tubings in critical situations, e.g. in malignant hyperthermia patients if disposable tubing is not immediately available.(ABSTRACT TRUNCATED AT 250 WORDS)

Methods to produce calibration mixtures for anesthetic gas monitors and how to perform volumetric calculations on anesthetic gases

A simple procedure for making calibration mixtures of oxygen and the anesthetic gases isoflurane, enflurane, and halothane is described. One to ten grams of the anesthetic substance is evaporated in a closed, 11,361-cc glass bottle filled with oxygen gas at atmospheric pressure. The carefully mixed gas is used to calibrate anesthetic gas monitors. By comparison of calculated and measured volumetric results it is shown that at atmospheric conditions the volumetric behavior of anesthetic gas mixtures can be described with reasonable accuracy using the ideal gas law. A procedure is described for calculating the deviation from ideal gas behavior in cases in which this is needed.

Instrumentation for the breath-by-breath determination of oxygen and carbon dioxide based on nondispersive absorption measurements

This paper describes the development and evaluation of instrumentation for the breath-by-breath determination of oxygen and carbon dioxide in respiratory gases. The method is based on nondispersive absorption and uses the 145-nm absorption band for detection of oxygen and the 4.3-micron band for detection of carbon dioxide. A xenon discharge lamp with a sharp band at 147 nm was chosen as the source for the determination of oxygen, and a carbon dioxide discharge lamp with a sharp band at 4.3 micron was chosen for determination of carbon dioxide. A vacuum photodiode was used as the detector for oxygen, and a photoconductive cell with a built-in interference filter was used for detection of carbon dioxide. Plots of absorbance (A) vs concentration (C, %) were linear for oxygen and were nonlinear for carbon dioxide. Typical least-squares calibration equations were A = 0.020C + 0.02 for oxygen (0-100%) and A = 0.0012C2 + 0.050C + 0.008 for carbon dioxide (0-8%). Comparisons of computed (y) vs prepared (x) values for the concentrations given above were linear for both gases, yielding y = (1.00 +/- 0.01)x - 0.13 +/- 0.73 for oxygen and y = (1.07 +/- 0.02)x - 0.04 +/- 0.06 for carbon dioxide. The standard deviations were 1.2% at 50% oxygen and 1.5% at 4% carbon dioxide. Records are presented to illustrate breath-by-breath monitoring of these gases in a healthy subject.

MAC-awake of isoflurane, enflurane and halothane evaluated by slow and fast alveolar washout

End-tidal anaesthetic concentrations at first eye opening in response to a verbal command during recovery from anaesthesia (MAC-awake), were measured for isoflurane (n = 16), enflurane (n = 16) and halothane (n = 14). MAC-awake was measured during either slow or fast alveolar washout. Slow washout was obtained by decreasing anaesthetic concentrations in predetermined steps of 15 min, assuming equilibration between brain and alveolar partial pressures. Fast alveolar washout was obtained by discontinuation of the inhalation anaesthetic, which had been maintained at 1 MAC for at least 15 min. Mean MAC-awake obtained with slow alveolar washout was similar for isoflurane (0.25 (SD 0.03) MAC), and enflurane (0.27 (0.04) MAC) and significantly greater than values obtained by fast alveolar washout (isoflurane: 0.19 (0.03) MAC; enflurane: 0.20 (0.03) MAC). The MAC-awake of isoflurane and enflurane was significantly less than that of halothane, which was 0.59 (0.10) MAC as evaluated by the slow and 0.50 (0.05) MAC as evaluated by the fast alveolar washout method. Recovery time from anaesthesia with fast alveolar washout was 8.8 (4.0) min for halothane, which was not different from isoflurane (15 (2.5) min), but significantly shorter than for enflurane (22 (10) min), reflecting differences in the anaesthetic concentration gradient between MAC and MAC-awake values. These data do not support the hypothesis of a uniform ratio between MAC and MAC-awake values.