A comparison of end-tidal halothane concentrations measured at proximal and distal ends of the endotracheal tube in the horse

Measurements (n = 126) of end-tidal halothane concentrations were taken from 21 horses anesthetized for routine and emergency surgery. One hundred five paired values allowed comparison of gas samples taken near the oral end of the endotracheal tube (Y1) to samples obtained at the cuffed end of the endotracheal tube (Y2). Twenty-one paired readings were assessed to compare samples taken 25 cm beyond the cuffed end of the tube (Y3) to samples from Y1. Measurements were made at all locations at 15-minute intervals starting 30 minutes after beginning halothane. All measurements were made in triplicate at end-expiration, and both sites were sampled within 1 minute of each other. Halothane concentration was measured by rapid infrared analysis with a gas sampling rate of 150 ml/min and displayed as a digital reading. Calibration of the machine was checked regularly. The difference between readings (Y1-Y2 or Y1-Y3 = Sdif) was tested using general linear models and a significance level of p less than 0.05 was used. The variable Sdif was analyzed with respect to time, mode of ventilation, and type of recumbency; no effects of these variables were detected. The mean values (+/- SD) of 105 readings for Y1 and Y2 were 2.41 vol% (+/- 0.49) and 2.39 vol% (+/- 0.49) respectively, and the Pearson's correlation coefficient (Y1 vs Y2) was 0.96. The mean values (+/- SD) of 21 measurements for Y1 and Y3 were 2.31 vol% (+/- 0.27) and 2.32 vol% (+/- 0.28) respectively and the Pearson's correlation coefficient (Y1 vs Y3) was 0.98.

Determination of contamination of a chemical warfare-proof operating theatre with volatile anaesthetic agents and assessment of anaesthetic gas scavenging systems

Three types of anaesthetic waste scavenging systems (active antipollution system, Papworth Block passive system and activated charcoal absorber system) were compared with a non-scavenging control to assess their effectiveness in reducing waste halothane concentrations in a chemical warfare-proof operating theatre. All three systems were found to reduce the level of pollution significantly.

Visceral losses of desflurane, isoflurane, and halothane in swine

Percutaneous loss of inhaled anesthetics is small relative to their uptake. The minor nature of this loss results in part from the substantial barrier to diffusion posed by the skin. Pleural and peritoneal surfaces pose less effective barriers because diffusion distances are smaller than in the skin. Accordingly, we measured visceral loss to air of desflurane, isoflurane, and halothane from pleural and peritoneal surfaces in five juvenile swine. Pleural and peritoneal losses per percent end-tidal anesthetic correlated directly with the solubility of the anesthetic in blood or tissues. The total pleural losses for the first 30 min of anesthetic administration were desflurane, 1.22 +/- 0.22 mL (mean +/- standard deviation for the 30-min period); isoflurane, 2.34 +/- 0.52 mL; and halothane, 4.69 +/- 0.98 mL; respective peritoneal losses were 0.64 +/- 0.12 mL, 1.23 +/- 0.25 mL, and 2.69 +/- 0.57 mL. Pleural loss per unit time did not change with increasing duration of anesthesia, whereas peritoneal loss increased for all anesthetics. These visceral losses are greater than total percutaneous losses in humans given these anesthetics for the same period of time, but the loss of anesthetic by either route is too small to affect measurements of anesthetic kinetics or recovery.

N-Trifluoroacetyl-ethanolamine: a proposed urinary metabolite of halothane: validation and measurement in children

It has been postulated that trifluoroacetyl chloride, a halothane metabolite, can bind covalently with the phosphatidylethanolamine component of the hepatic cell membrane and cause cell necrosis. Breakdown of the necrotic hepatocyte would release N-trifluoroacetyl-ethanolamine (TFAE) into the serum with subsequent urinary excretion. An original High Performance Liquid Chromatography (HPLC) method for the measurement of TFAE is described. In six children 1% halothane was administered for one hour and the halothane uptake measured. Urinary excretion of TFAE was measured for up to eight days and found to be 0.09 +/- 0.07% or less of the absorbed halothane. In children TFAE is not a major urinary metabolite of halothane.

Performance of BOC Ohmeda Tec 3 and Tec 4 vaporisers following tipping

The introduction of systems to facilitate the changing of vaporisers on the back bar of the anaesthetic machine has increased the risk of a vaporiser being tipped or inverted prior to attachment. The performance of three Ohmeda Tec 3 and three Ohmeda Tec 4 vaporisers following tipping to 30 degrees, 90 degrees and inversion to 180 degrees was measured using a calibrated Datex Capnomac AGM-103 analyser. Both types of vaporiser when switched off tolerated tipping and inversion without alteration of the anaesthetic concentration subsequently delivered. The same was true for the Tec 3 after tipping to 30 degrees and 90 degrees with the dial set at zero or above. However, after inversion of the Tec 3 vaporiser with the dial at zero or higher, the anaesthetic concentration delivered was much greater than shown on the dial, initially exceeding 12% for all agents. Should a Tec 3 vaporiser be inverted with the dial at any setting other than OFF, it is necessary to adequately flush it with fresh gas and check its output prior to use.

Immunological disturbances in anaesthetic personnel chronically exposed to high occupational concentrations of nitrous oxide and halothane

Immunological changes in anaesthetic personnel exposed to occupational concentrations of holothane and nitrous oxide 10-60 times greater than the advised maximum were studied during routine work and after 3-4 weeks holiday. Red cell count, haemoglobin concentration and haematocrit decreased during exposure although not significantly, in comparison with a control group, but all had increased significantly after the holidays. Other changes were altered neutrophils and lymphocyte counts. Basophils disappeared from the blood during the exposure. Monocytes were not affected during the exposure, but increased after its cessation. Percentages of CD2 and CD4 lymphocytes increased significantly, but numbers of cells in T lymphocyte subpopulations (total, helper and cytotoxic/suppressor lymphocytes) were not significantly altered. B lymphocytes were most strongly affected: they decreased during working periods and did not recover after holidays. Natural killer (NK) cells, on the other hand, decreased significantly during exposure, but fully recovered during holidays. After stimulation with mitogens, phytohaemaglutin, concanavalin A, and pokeweed, lymphocytes from exposed personnel incorporated significantly more 3H-thymidine than those from control subjects, but stimulation indices did not differ. The natural killer-cell activity, serum Ig concentrations and phagocytosis by granulocytes were not altered.

Evaluation of the Lamtec anaesthetic agent monitor

The Lamtec agent monitor is a compact anaesthetic analyser designed to measure halothane, isoflurane and enflurane. It shows good linearity and stability. The faster model can be used for end-tidal measurements up to 25 breaths per minute. Calibration using a standard of the gas to be measured is recommended.

Safety and efficacy of alfentanil and halothane in paediatric surgical patients

Alfentanil, a congener of the opioid fentanyl, possesses properties that make it an attractive choice for use during short operative procedures. Since the pharmacodynamic aspects of alfentanil have not been well documented in children, this study was undertaken to evaluate the safety, efficacy, and dose requirements of alfentanil when used with nitrous oxide or halothane in paediatric patients. Eighty unpremedicated patients, ASA physical status I or II and aged 2-12 yr were studied. Patients were randomly assigned to one of four groups. After induction of anaesthesia with nitrous oxide, oxygen, and halothane, the groups were treated as follows. In Group 1 (n = 19), after halothane was discontinued, alfentanil 50 micrograms.kg-1 was infused over 30 sec. In Group 2 (n = 20), the end-tidal halothan was maintained at 0.5% and alfentanil 25 micrograms.kg-1 was infused. In Group 3 (n = 20), the end-tidal halothane concentration was maintained at 1% and alfentanil 12.5 micrograms.kg-1 was infused. In Group 4 (n = 21), the end-tidal halothane concentration was maintained at 1.5% and no alfentanil was administered. Patients in Groups 1, 2, and 3 received bolus doses of alfentanil 12.5 micrograms.kg-1 as needed to maintain haemodynamic stability. After alfentanil administration, there were transient decreases in systolic blood pressure in Groups 1 and 2, and in heart rate in Group 2. With surgical stimulation, haemodynamic stability was well maintained except in patients in Group 1, who had an increase in systolic blood pressure. Children Group 1 were alert sooner and their tracheas were extubated earlier than those in Groups 2, 3, and 4.(ABSTRACT TRUNCATED AT 250 WORDS)

Laboratory evaluation of the vital signs (ICOR) piezoelectric anesthetic agent analyzer

The Vital Signs (ICOR) anesthetic agent analyzer, which measures anesthetic vapor concentration by a piezoelectric crystal technique, was evaluated by using standard-calibration gases to measure the accuracy, response time, gas interference, and water vapor dependence of the analyzer. The accuracy for the measurement of vapor concentration was better than 0.08 vol%. The reproducibility of repeated measures averaged 0.003 vol%. The offsets caused by other gases were 0.02 vol% for water vapor, 0.08 vol% for 70% nitrous oxide, and less than 0.01 vol% for oxygen and carbon dioxide. Response time (10 to 90%) was 475 ms. The agent analyzer may be well suited for monitoring volatile agent concentrations during anesthesia.

Biological monitoring of the occupational exposure to halothane (fluothane) in operating room personnel

The concentration of halothane (fluothane) in the ambient atmosphere was determined in five operating theaters of two hospitals in Italy. The concentrations of halothane in the ambient air exceeded the NIOSH recommended time-weighted average exposure levels (median value: 10.38 mg/m3). Halothane was detected in the urine of 58 exposed subjects (anesthetists, surgeons, and nurses). A significant correlation was found between the halothane concentration in urine produced during the shift (Cu, micrograms/L) and halothane environmental concentration (CI, mg/m3) (Cu = 0.242 x CI + 3.51) (N = 58; r = 0.92; p less than 0.0001). The results show that the urinary halothane concentration can be used as an appropriate biological exposure index. The biological values proposed are: 92 micrograms/L, corresponding to a 50 ppm of environmental exposure; 6.5 micrograms/L, corresponding to 2 ppm of environmental exposure and 3.9 micrograms/L, corresponding to a 0.5 ppm of environmental exposure.

Current developments in optical biochemical sensors

By combining modern fibre optics and opto-electronic instrumentation with chemical and biochemical reagent systems, it has become possible to fabricate optical biosensors. The current state of the art in this development is reviewed in this paper. Many developments describe selective and sensitive methods for sensing bioanalytes and it is likely that such a development will continue to be a very active area of analytical research. However, these biosensing devices can be regarded as successful only if their practicality and reliability can be demonstrated.

Comparison of inhalation induction with isoflurane or halothane in children

Thirty-six children (mean age 2.4 years) premedicated with oral chloral hydrate 70 mg kg-1 and atropine 0.03 mg kg-1 were anaesthetized with either 3.75% isoflurane or 2.5% halothane in 70% nitrous oxide in oxygen. The eyelash reflex disappeared in 39 +/- 7 s (mean +/- SD) with isoflurane and in 56 +/- 16 s with halothane (P less than 0.001). Tachypnoea was seen with both anaesthetics. Coughing, breath holding, stridorous breathing and respiratory depression were seen during isoflurane but not during halothane induction (P less than 0.01). In nine of 20 children anaesthetized with isoflurane, the ventilation had to be assisted before intubation. Endotracheal intubation was possible in 224 +/- 35 s with isoflurane and in 281 +/- 64 s with halothane (P less than 0.01). Intubating conditions were satisfactory in 80% of the children anaesthetized with either volatile agent. Cardiovascular responses to endotracheal intubation were minimal with both anaesthetics. No cardiac dysrhythmias were noted. Heart rate was higher during isoflurane than during halothane induction. Diastolic arterial pressure was lower during isoflurane than during halothane induction immediately and 5 min after intubation.

Halothane reductive metabolism in an adult surgical population

The reductive metabolism of halothane was studied in 34 adult patients undergoing routine surgery. Reductive biotransformation of halothane was more extensive in females than males and was also enhanced in two patients treated preoperatively with phenytoin, an enzyme-inducing drug. Tobacco, ethanol and the patient's age, body weight and previous exposure to halothane did not influence reductive metabolism of halothane.

Halothane-sparing effect of benzodiazepines in ponies

The halothane-sparing effect of 2 benzodiazepines, diazepam and temazepam, were investigated in ponies by measuring the minimum alveolar concentration (MAC) for halothane before and after drug administration. The MAC value for halothane decreased 29% and 16% when either 0.044 mg/kg of diazepam or 0.044 mg/kg of temazepam, respectively, was administered intravenously. Heart rate, respiratory rate, systolic and mean arterial blood pressure, and expired CO2 were also measured. No differences were present in these variables before and after drug administration nor were differences noted between the benzodiazepines.

Absence of abundant saturable binding sites for halothane or isoflurane in rabbit brain: inhaled anesthetics obey Henry's law

We tested whether the existence of saturable binding sites for anesthetics causes the solubility of halothane or isoflurane in rabbit brain not to obey Henry's law. For each anesthetic, we measured brain/gas partition coefficients (paired samples) at approximately 0.05 MAC and 5 MAC at 38.5 degrees C. In addition, for halothane, brain/gas partition coefficients (paired samples) were determined at 0.05 MAC and 2 MAC. The values for halothane at 0.05 MAC, 2 MAC, and 5 MAC did not differ; values for isoflurane at 0.05 MAC and 5 MAC did not differ. Over the range of anesthetic partial pressures studied, no evidence for saturable binding was found. We conclude that the solubility of halothane and isoflurane in brain is independent of the partial pressure applied; inhaled anesthetics obey Henry's law.

Infrared analysis of volatile anesthetics: impact of monitor agent setting, volatile mixtures, and alcohol

Infrared analysis can determine exhaled concentrations of the three volatile anesthetics in common use because each absorbs infrared light. Many infrared analyzers use a single source of infrared light at a wavelength of 3.3 microns for measurements of all three agents but cannot identify which agent is in use. Organic gases such as ethanol also absorb infrared light. This study determined the effects on the accuracy of a single-wavelength infrared anesthetic monitor (Capnomac, Puritan-Bennett PB254) of (1) incorrect anesthetic agent setting, (2) mixtures of volatile anesthetics, and (3) ethanol vapor in the analyzed gas. Changing the agent setting on the monitor during steady-state delivery of an agent resulted in readings for the halothane setting five times higher than those for the enflurane setting, and six times higher than those for the isoflurane setting. These ratios reflect the monitor's fixed internal gain for each agent setting. Mixtures of anesthetics had a simple additive effect on the monitor's accuracy. With the monitor set for halothane, 0.2 vol% isoflurane mixed with halothane caused readings 1.2 vol% higher than the true halothane concentration. Conversely, with the monitor set for isoflurane, 1 vol% halothane mixed with isoflurane resulted in readings 0.2 vol% too high. In a model simulating alveolar gas, ethanol vapor corresponding to blood alcohol levels of 0.10, 0.30, and 0.50% had a slight but not clinically significant effect on readings for enflurane and isoflurane but increased readings with the halothane setting 3.5 times the corresponding level of blood alcohol. Clinicians can test for an interfering gas such as ethanol before induction by checking the reading in the halothane setting during preoxygenation.

The effect of exhaled alcohol on the performance of the Datex Capnomac

We investigated the response of the Datex Capnomac to alcohol in expired air. The greatest response was seen when the Capnomac was set to monitor halothane. There was an approximately linear correlation with blood alcohol levels. This effect is of sufficient magnitude to introduce inaccuracies in the measured concentration of halothane.

Halothane and isoflurane alter acetylcholine activated ion channel kinetics

The effects of halothane and isoflurane on the acetylcholine activated ion channel were studied in the frog sartorius muscle using the two electrode voltage clamp technique. The miniature end-plate currents (MEPCs) were recorded and evaluated for amplitude, duration of growth phase and time constant of decay (tau). Both halothane and isoflurane decreased tau in a dose dependent manner. Depression of current amplitude was also dose dependent. The ED50 value indicates tau is more affected than the amplitude of MEPC. Biexponential decay phases were seen in a small fraction of cells exposed to a low concentration of halothane but not isoflurane. Biexponential decay, when seen, was more prominent at less negative clamped membrane potential. The normal linear relationship between membrane potential and tau was not altered by anesthetics.

Estimation of minimum alveolar concentration (MAC) for halothane, enflurane and isoflurane in spontaneously breathing guinea pigs

MAC for halothane, enflurane and isoflurane was determined in guinea pigs (Cavia porcellus) exposed to constant anesthetic concentrations (2.5 hours each) in a flow-through glass chamber. The following values were obtained (N = 8 for each anesthetic): 1.01 +/- 0.03 vol% for halothane, 2.17 +/- 0.04 vol% for enflurane, and 1.15 +/- 0.05 vol% for isoflurane. In guinea pigs, MAC for halothane and enflurane are similar to those reported for other rodents, while MAC for isoflurane is lower. The data indicate that guinea pigs possibly are more susceptible to isoflurane's anesthetic actions than other rodents.

Trace anesthetic gases during xenon arc photocoagulation for retinoblastoma

In pediatric ocular examinations, administration of continuous-flow anesthetic gases containing nitrous oxide, halothane, and oxygen enables the physician to do safe, controlled, reproducible examinations. We did a study in which the levels of waste anesthetic gases were measured during xenon arc photocoagulation procedures used for retinoblastoma. Waste nitrous oxide and halothane gases measured during these procedures significantly exceeded the levels recommended by the National Institute of Safety and Health. These high levels are of particular importance because of the physician's proximity to the patient during the procedure. The high levels of waste gases may have immediate deleterious effects on the physician's functioning capacity and may also pose long-term health hazards for the physician and operating room personnel.

Metabolism of halothane in obese Fischer 344 rats

Halothane is metabolized by an oxidative pathway to stable, nonvolatile end products, trifluoroacetic acid (TFAA) and bromide (Br-), and by reductive pathways to Br-and inorganic fluoride (F-). There is evidence that both oxidatively and reductively formed intermediates may produce hepatotoxicity, although the exact etiology of the fulminant hepatic necrosis seen in humans is unproven. Obese patients receiving volatile anesthetics exhibit higher serum anesthetic metabolite concentrations than do normal-weight patients, and thus might be at greater risk of hepatotoxicity because of higher concentrations of reactive intermediates from halothane metabolism. To eliminate the variables inherent in human clinical studies leading to confounding interpretation of data, this study determined the contributions of oxidative and reductive pathways to halothane metabolism in an animal model of human hypertrophic obesity, the most common form of human obesity. Eight pairs of obese (high-fat diet) and normal-weight (standard chow), male Fischer 344 rats were anesthetized with halothane for 4 h at an inspired concentration of 0.78%. Serum and urinary concentrations of TFAA, Br-, and F-were measured. Thirty-six hours following halothane anesthesia, mean serum TFAA concentrations peaked at 7.3 +/- 1.1 mM in obese rats and 4.7 +/- 0.7 mM in nonobese rats. TFAA urinary excretions during the 180-h period postanesthesia were 519 +/- 69 and 336 +/- 22 mumol, respectively. Peak serum Br- concentrations were 9.1 +/- 1.0 and 6.9 +/- 0.6 mM for obese and nonobese rats, respectively, and Br-urinary excretions were 127 +/- 30 and 79 +/- 14 mumol, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Malignant hyperthermia and the clean machine

Following use with halothane, ten anaesthestic machines were sampled using infrared analysis for halothane contamination. Baseline measurements of halothane were made in the room and at the machine's common gas outlet. Five per cent halothane with four litres per minute oxygen flow was delivered for ten minutes into a scavenged breathing circuit. Halothane was then discontinued, an oxygen flow rate of 12 litres per minute was begun, and continuous measurements were made until the halothane concentration became undetectable. Baseline measurements of the rooms and anaesthestic machines ranged from 0 to 0.8 parts per million. Following the oxygen flow, the halothane concentration decreased to undetectable levels within six minutes in all ten machines.

Porous-layer open-tubular gas chromatography in combination with an ion trap detector to assess volatile metabolites in human breath

A method is described for the quantification of major volatile substances in human breath without preconcentration. Methanol, ethanol, acetaldehyde and acetone are well separated by porous-layer open-tubular column gas chromatography. Low-level detection was possible by means of an ion trap detector. Halothane has been used as internal standard.

Ion mobility spectrometry of halothane, enflurane, and isoflurane anesthetics in air and respired gases

Three common gaseous anesthetics, halothane, enflurane, and isoflurane, were characterized by using ion mobility spectrometry (IMS)/mass spectrometry, and the dependence of product ion distributions on temperature and concentration was evaluated. At 40 degrees C and 500 ppb, negative ion mobility spectra in air largely consisted of monomer or dimer adducts with Br- or Cl- formed through dissociative electron capture of molecular neutrals. With increased temperature or decreased vapor concentrations, declustering and dissociation of product ions became pronounced. Ion-molecule reactions in the drift region of the IMS were evident as distortions in peak shape in the mass-resolved mobility spectra and in variable reduced mobilities for the same ions. A portable hand-held IMS was used for convenient, real-time detection of enflurane in respired gases following a controlled inhalation episode.

[Determination of subanesthetic concentrations of halothane in the environment of operating and recovery rooms]

Concentrations of halothane in parts per million (ppm) in the air were determined during 4 days in the operating rooms and the recovery room of pediatric surgery during the course of surgical anesthesia by inhalation. The operating rooms did not have an anesthetic gas scavenging system. Eighteen samples of air were taken by passive diffusion in sampling tubes of activated charcoal (mode Dräger Orsa 5). The samples were analysed by gas chromatography). We found concentrations between 4.7 ppm and 34.2 ppm that exceed those considered as admissible that range from 2 to 5 ppm. Our present recommendations to reduce the atmospheric contaminating anesthetic gases are the use of scavenging equipment, air-conditioned rooms and routine inspection and leak detection of apparatus and anesthetic circuits.

Inhalation anaesthetics--exposure and control: a statistical comparison of personal exposures in operating theatres with and without anaesthetic gas scavenging

Results are reported for air sampling surveys undertaken by the Health and Safety Executive (HSE) from 1980 to 1984 using diffusive samplers in 40 operating theatres and 18 recovery areas at 27 hospitals. For all personnel the geometric mean time-weighted average exposure to nitrous oxide in unscavenged theatres was 94 ppm and in scavenged theatres 32 ppm; the corresponding means for halothane were 1.7 and 0.7 ppm, respectively. Intermittent use of scavenging led to mean exposures between those found in scavenged and unscavenged conditions. Anaesthetists showed higher mean exposures than other staff in all conditions. Statistical analysis of the data demonstrates that mean exposures of operating theatre staff were significantly lower in scavenged than in unscavenged theatres. For most staff, exposure was also significantly lower in theatres using active scavenging systems compared with those using passive systems. The literature on the hazards of chronic exposure to inhalation anaesthetics and previous studies of exposure is also briefly reviewed.

A comparison of the effects of central v peripheral bolus injections of potassium chloride on aortic root potassium concentrations in swine

Clinically relevant doses of potassium chloride (equivalent to 2 mEq/60 kg of body weight) were administered as rapid intravenous (IV) boluses to healthy halothane-anesthetized pigs. Potassium was given either peripherally through a standard IV ear catheter or centrally through the central venous port of a pulmonary artery catheter. Multiple injections were made in each pig, and cardiac output was varied by changing end-tidal halothane concentration. The aortic root potassium concentration was measured every three to six seconds for 90 seconds following potassium administration in each pig. Monitored variables included end-tidal halothane, end-tidal carbon dioxide, pulmonary artery pressure, mean arterial blood pressure, cardiac output, electrocardiogram, and temperature. Following both peripheral and central administration of potassium chloride, aortic root potassium increased significantly. However, the time required to achieve the peak aortic root potassium concentration was significantly less after central administration. In addition, the change in aortic root potassium concentration was greater following central administration compared with peripheral. The change in aortic root potassium concentration correlated inversely with cardiac output only after central, but not peripheral injection. Despite marked transient hyperkalemia in all animals, no electrocardiographic evidence of hyperkalemia could be demonstrated. It is concluded that small bolus doses of potassium chloride (2 mEq/60 kg) can be given safely either peripherally or centrally in normal, hemodynamically stable swine.

[Use of halothane in a semi-closed circuit]

Halothane was administered to 10 ASA or 11 patients undergoing elective peripheral surgery. The vaporizer was included in the delivery gas line of the semiclosed system. Löwe's square root of time model of uptake was used to calculate the required doses of halothane. In order to reach an alveolar concentration corresponding to 1.3 MAC, 0.5 vol % of halothane (1.3 MAC) combined with 60 vol % of nitrous oxide (0.6 MAC) were administered at a fresh of 20 ml.kg-1. The ventilation controlled in order to maintain end-tidal CO2 partial pressure at a 5 vol %. Inspiratory halothane concentration was measured during the inspiratory plateau. The alveolar fraction was defined as being the mean end expiratory concentration. The latter was well above the theoretical values during the first 9 min of anaesthesia (0.85% at the 4 th min). This concentration then decreased progressively, becoming less than the expected value after 15 min (0.4% at the 30 th min). Löwe's model would therefore seem to lead to a gross overestimation of the amount of anaesthetic vapour to be delivered to a patient at the beginning of anaesthesia, and an underestimation thereafter.

Determination of thymol in halothane anaesthetic preparations by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) procedure has been developed for the isolation and quantification of thymol, a stabilizing agent present in halothane anaesthetic preparations. The method offers improvements in specificity and simplicity with respect to a current official procedure for thymol in halothane. Results for commercial preparations obtained by the proposed procedure demonstrate excellent precision and accuracy with RSD values for replicate analysis ranging from 0.11 to 0.74% and recoveries via fortification from 99.6 to 100.1%. The HPLC method was compared to compendial procedures for thymol bulk substance and halothane products. Chromatographic separation of other related phenolic preservatives used in pharmaceuticals suggests a more extensive application of the proposed procedure.

Preparation of anesthesia machines for patients susceptible to malignant hyperthermia

Malignant hyperthermia is a potentially lethal syndrome that can be triggered by inhaled anesthetics. Thus, it may be appropriate to utilize equipment that minimizes exposure of susceptible patients to inhaled anesthetics. The rate of release of anesthetic stored in anesthesia delivery systems is unknown. To determine residual anesthetic concentrations, the washout rates of halothane and isoflurane were compared, and the effects of a 1-l/min and a 10-l/min fresh gas flow were evaluated. Halothane concentrations were also measured in samples taken from the fresh gas outlet and the Y-piece of the circle system during four separate studies in which various components of the anesthesia system were replaced. In each study an Ohio Modulus anesthesia machine equipped with an Air-Shields ventilator was exposed to 2% halothane for 18 h. Anesthetic concentrations were determined by a gas chromatograph having a sensitivity of 0.1 ppm. Isoflurane washed out 3-4 times faster than halothane. Residual halothane concentration was approximately equal to tenfold greater when the fresh gas flow was 1 l/min rather than 10 l/min: 194 versus 19 ppm after 1 h of washout. Using a 10-l/min fresh gas flow, halothane concentrations in samples obtained from the Y-piece were similar with original or fresh soda lime but were more than tenfold lower after the fresh gas outlet hose and circle system were replaced (approximately equal to 50 ppm vs. approximately equal to 5 ppm after 5 min of washout).(ABSTRACT TRUNCATED AT 250 WORDS)

Mass spectrometry for monitoring respiratory and anesthetic gas waveforms in rats

A method is presented for real-time monitoring of airway gas concentration waveforms in rats and other small animals. Gas is drawn from the tracheal tube, analyzed by a mass spectrometer, and presented as concentration vs. time waveforms simultaneously for CO2, halothane, and other respiratory gases and anesthetics. By use of a respiratory simulation device, the accuracy of mass spectrometric end-tidal CO2 analysis was compared with both the actual gas composition and infrared spectrophotometry. The effects of various ventilator rates and inspiration-to-expiration ratios on sampling accuracy were also examined. The technique was validated in male Sprague-Dawley rats being ventilated mechanically. The difference between the arterial PCO2 (PaCO2) and the end-tidal PCO2 (PETCO2) was not significantly different from zero, and the correlation between PETCO2 and PaCO2 was strong (r = 0.97, P less than 0.0001). Continuous gas sampling for periods up to 5 min did not affect PaCO2, PETCO2, or airway pressures. By use of this new method for measuring end-tidal halothane concentrations in rats approximately 6.5 mo of age, the minimum alveolar concentration of halothane that prevented reflex movement in response to tail clamping was 0.97 +/- 0.04% atmospheric (n = 14). This mass spectrometric technique can be used in small laboratory animals, such as rats, weighing as little as 250 g. Gas monitoring did not distort either PETCO2 or PaCO2. Under the defined conditions of this study, accurate and simultaneous measurements of phasic respiratory concentrations of anesthetic and respiratory gases can be achieved.

Halothane interference at an amperometric oxygen electrode: the development of an oxygen/halothane sensor

The role of electrode materials in the reduction of halothane and oxygen mixtures at rotating and stationary electrodes is considered. Halothane is found to be electroactive within the available electrode-potential range on silver and on gold. Double potential step experiments are considered in order to isolate the individual halothane and oxygen signals. A double integration, single potential step technique is evaluated for the quantitative simultaneous measurements of oxygen and halothane on gold. The influence of electrode purity is discussed in terms of a reaction mechanism and electrode output error.

Decontamination of halothane from anaesthetic machines achieved by continuous flushing with oxygen

The contamination of four types of anaesthetic machine with halothane was sequentially sampled by mass spectrometry while the machines were continuously flushed with oxygen 8 litre min-1 for up to 24 h. Contamination decreased in an exponential manner. Machines fitted with Selectatec vaporizer mounting systems and with the vaporizer removed showed contamination less than 0.02 parts per million (p.p.m.) of halothane after 12 h flushing. Machines with cage-mounted vaporizers or with vaporizers left connected to the Selectatec block demonstrated persisting contamination. The Fluotec Mk.4 vaporizer showed an improvement on earlier designs in this respect. Background contamination concentrations of greater than 0.05 p.p.m. were measured in a patient-free recovery area of an operating theatre suite. Concentrations increased to 1 p.p.m. when patients were admitted following halothane anaesthesia. Decontamination of anaesthetic machines to concentrations of halothane below those detected as background contamination within recovery areas may allow such machines to be used safely to anaesthetize patients at risk from halothane.

Relationship between lower oesophageal contractility, clinical signs and halothane concentration during general anaesthesia and surgery in man

The effects of a range of concentrations of halothane upon lower oesophageal contractility (LOC) and on defined clinical signs has been studied in patients undergoing surgery. Changes in clinical signs were assigned a numerical value by means of a scoring system. One hundred and eighty-one sets of measurements were made in 46 patients exposed to concentrations of halothane between 2.0 and 0.5 minimum alveolar concentration (MAC). The results were examined to identify relationships between (i) the clinical signs and alveolar halothane concentration, (ii) the clinical signs and LOC and (iii) the changes in LOC and alveolar concentration; significant correlations were found between these variables. Decreasing alveolar halothane concentration was associated with an increase in LOC and these increases in LOC were also associated with increases in the clinical score.

[NORMAC--a simple instrument to measure the inspiratory and end- expiratory concentrations of halothane, enflurane, and isoflurane. Clinical use and laboratory investigations]

In 47 gas mixtures particularly made for that purpose the concentration of halothane, enflurane, or isoflurane was estimated with Normac; the estimated and measured values were found to be identical on the average. To verify precision, 40 measurements of one specimen were performed; the standard deviation was 0.03 vol-% (ca. 1% relative error). Any influence of the carrier gas components O2, N2, N2O, and H2O proved to be negligible. The practical clinical application of the apparatus was easy and without malfunctions.

Negative inotropic effects of halothane, enflurane, and isoflurane in papillary muscles from diabetic rats

Myocardial contractile responses to halothane, enflurane, and isoflurane were studied in papillary muscles isolated from streptozotocin-induced diabetic rats and in those from age-matched control rats. The developed tension in diabetic papillary muscles electrically paced at a constant rate was not different from that in control muscles, but both the time to peak tension and the relaxation time of the isometric contraction were significantly prolonged in diabetic muscles. Halothane, enflurane, and isoflurane all produced negative inotropic effects in both diabetic and control muscles. However, the negative inotropic effects were significantly less in the muscles from diabetic rats than in the muscles from control rats throughout the range of concentrations. In muscles from both the diabetic and control rats, the negative inotropic effects of these anesthetics were accompanied by decreases in the time to peak tension and in relaxation time. The results suggest that the myocardium from the diabetic rat is less sensitive to the negative inotropic action of volatile anesthetics than is the myocardium of normal hearts.

Spin-echo fluorine magnetic resonance imaging at 2 T: in vivo spatial distribution of halothane in the rabbit head

Spin-echo 19F magnetic resonance imaging was performed at 2.0 T to explore the in vivo spatial distribution of halothane in the rabbit head. Because the halothane concentration is low in vivo, and because the measured relaxation times of the 19F resonance peak for halothane were T1 approximately equal to 1.0 sec and T2 approximately equal to 3.5-65 msec, 1-3-h imaging times were required (TR = 1 sec, TE = 9 msec) in order to obtain adequate images with a 64 X 256 raw data matrix and a 20-mm slice thickness. With this technique, halothane was primarily detected in lipophilic regions of the rabbit head, but little or no halothane was observed in brain tissue. Because T2 was shorter in brain tissue than in surrounding fat, a shorter TE than we could obtain is needed for optimal spin-echo imaging of brain halothane.

An end-tidal sampler for use with slow response analysers during anaesthesia

An end-tidal sampler is described which can be used during anaesthesia with spontaneous respiration at rates of at least 60 b.p.m. It can be used with slow response analysers such as refractometers and fuel cells to indicate end-tidal concentrations. It can also be used to extend the scope of those breath-to-breath analysers which have a response time which is too slow for the respiratory rates which may occur during anaesthesia with spontaneous breathing. Using the device, mean PCO2 of the samples was 0.13 kPa less than the corresponding values for the end-expiratory PCO2 measured by conventional breath-by-breath analysis. Full response was achieved in 12 breaths.

A laboratory investigation of two new portable gas analysers

Two new portable infrared gas analysers, the Irina (Drägerwerke, Lübeck, Germany) and the Normac (Datex Instrumentarium Corporation, Helsinki, Finland), were tested and the results compared to those from such established methods as gaschromatography and the Beckman LB-2 (Beckman, USA) infrared gas analyser using exactly defined gas mixtures from a vaporizer developed in our laboratory. The analysers were evaluated for their accuracy and precision, noise, zero stability, gain stability and the impact of flow, over-pressure, carrier gas and humidity. All three analysers showed good accuracy and precision. The noise level was acceptable except in the older version of the Normac, but this error has now been corrected by the manufacturer. Zero and gain stability are very good; gas flow and over-pressure do not affect the measurement. The influence of carrier gases and humidity is negligible except for the strong N2O effect on the Beckman. We conclude that this new generation of highly sophisticated and reliable but handy analysers will meet the clinical demands.

Pharmacokinetics of inhaled anesthetics in humans: measurements during and after the simultaneous administration of enflurane, halothane, isoflurane, methoxyflurane, and nitrous oxide

To determine the relative washin and washout characteristics of isoflurane, enflurane, halothane, and methoxyflurane, we administered all four anesthetics simultaneously (total = 1.1 MAC) to nine healthy patients for 2 hr. Concentrations of anesthetics in end-tidal gases were measured during washin and for 5-9 days during washout. Multiexponential (multicompartment) models were fit to the washin and washout curves using least-squares analysis. Slowly equilibrating compartments could only be identified during washout. For 27 of the 36 data sets, five-compartment models fit the washout curves significantly better than four-compartment models. The time constant for our first compartment is consistent with that predicted for washout of the lungs. Time constants for the second, third, and fifth compartments were consistent with current data for blood flows and solubilities of vessel-rich, muscle, and fat tissue groups, respectively. The fourth compartment has a time constant that lies between the time constants predicted for muscle and fat.

Recognition of mixed anesthetic agents by mass spectrometer during anesthesia

Anesthetic agents are sometimes added to the wrong vaporizer on an anesthesia machine. As a result, the vaporizer may deliver a mixture of anesthetic agents at concentrations inappropriate for use on a patient. However, untoward clinical complications related to vaporizers can be prevented with a time-shared mass spectrometer. This device accurately and rapidly indicates the gases and gas concentrations present in a vaporizer.

An evaluation of the Datex Normac anaesthetic agent monitor

A new monitor for volatile anaesthetics, the Datex Normac, was assessed in the laboratory and operating theatre. The instrument had a warm up time of 90 minutes from cold, but only 5 minutes from standby. Zero drift was less than 0.01% over 7 hours, and repeated measurements of gain showed a coefficient of variation of less than 1%. However, gain drift of 6% occurred when the instrument was switched off between periods of use. Signal noise was less than 0.02 vol% on a new instrument, but was about six times greater on an instrument that had been in use for a year. The response time of 550 ms is short enough to allow breath by breath monitoring. When the instrument was calibrated on the enflurane setting, measurements made on the enflurane, halothane and isoflurane settings were accurate to within 6% of the reading. This is satisfactory for clinical purposes, but not for more demanding applications. Calibration canisters are available, and two that we tested were accurate to better than 0.1 vol%. Nitrous oxide, carbon dioxide and water vapour have very small effects on the monitor. The instrument provided trouble-free monitoring in theatre.