Halothane MAC in dogs unchanged by phenobarbital

Halothane MAC in dogs was not significantly changed by phenobarbital (PB) therapy. Following 10 consecutive days of oral PB (10 mg/kg), halothane MAC was 0.95 +/- 0.05 vol/dl (mean +/- SE) compared with a halothane MAC of 1.05 +/- 0.03 vol/dl in another group not given PB. The absence of change in MAC may reflect either the development of tolerance to CNS sedative effects of PB or the masking of antanalgesia effects of the barbiturate by associated sedation and/or analgesia.

Halothane 0.2-4% analysis by gas chromatography

The katharometer detector is better suited to the analysis of gaseous halothane (0.2-4%) than is the flame ionization detector, since the peak heights are directly proportional to concentration, and are more reproducible.

Exposure to anesthetic gases and ethanol during work in operating rooms

The concentration of halothane and ethanol in operating rooms was measured during 37 routine operations performed in nine different departments of surgery at six different hospitals. The time-weighted halothane concentrations in the respiratory zones of anesthetic and surgical nurses were 0.3--34.0 ppm (time-weighted average 7.2 ppm) and 0.1--9.2 ppm (time-weighted average 2.5 ppm), respectively, in the different operating departments. The corresponding ethanol concentrations were 0.3--36.5 ppm (time-weighted average 12.5 ppm) for anesthetic nurses and 1.5--46.6 ppm (time-weighted average 15.3 ppm) for surgical nurses. The anesthetic technique influences the exposure of the operating staff to anesthetic gases, but it does not affect exposure to ethanol. In controlled experiments volunteers were exposed to low concentrations of halothane or ethanol. About 60% of both substances was retained. The content of ethanol in the end-expired air approached zero within a few minutes after the end of exposure, while low residual concentrations of halothane were demonstrable for more than 1 h. Although exposure to ethanol is insignificant in relation to the metabolic capacity of the body, ethanol indicates the presence of volatile disinfectant components, and its spread through the room atmosphere should be kept in mind when the ventilation of operating rooms is designed. The effective elimination of airborne pollutants in operating rooms calls for good general ventilation in conjunction with local exhaust close to the sources of anesthetic gas leakage. General ventilation mainly affects the concentration of substances well-mixed with the room atmosphere, such as volatile disinfectant components and anesthetic vapor that has spread beyond the actual work zones of the medical staff. For a significant reduction in the concentration of anesthetic gases in the respiratory zones of the medical staff, the gases must be vented at the source of leakage. Since airborne anesthetics occur not only in operating rooms, general ventilation has to meet certain minimum requirements also in anesthetic induction rooms and recovery rooms. Operating rooms and anesthetic induction rooms must also be supplied with local exhaust systems.

Trace concentrations of halothane in human breast milk

Halothane concentrations of 2 p.p.m. have been found in the breast milk of a lactating, practising anaesthetist. This concentration was consistent with the operating theatre environment. The authors fell that, in spite of the limited scope of the study, this is an additional reason for the elimination of waste anaesthetic agents from the operating theatre.

Closed circuit halothane anaesthesia. Use of the Narkotest as an in-line monitor in a nonpolluting technique

Theoretical considerations of closed circuit anaesthesia using oxygen and halothane are examined. Clinical experience has confirmed the value of the Narcotest as a reliable in-line monitor of inspired halothane concentration, while the use of an oxygen analyser is a desirable adjunct. The advantages of economy and elimination of theatre pollution are discussed.

An occupational health approach to anaesthetic air pollution

The principles of occupational health practice as applicable to operating theatre staff are stated. Operating theatre air was samples for halothane at three Sydney hospitals--one in which a scavenging system was in operation and two without such a system. A method giving time-weighted average concentrations over the period of sampling was used. Anaesthetic techniques varied for adults and children. The scavenging system was found to be highly efficient. Less than 0.1 ppm of halothane was found in the air of one theatre in which a flow rate of 4 litres per minute with 0.5% halothane and controlled ventilation were being used for routine anaesthetics in adults. In another theatre in which paediatric surgery was being performed, the anaesthetic technique utilized a flow rate of 6 litres per minute with 0.5% halothane and a T-piece, and the air was found to contain 0.8 ppm of halothane. Concentrations of up to 8 ppm were found in unscavenged theatres. Other possible occupational hazards of the environment, such as exposure to X-rays, viral infection and aerosol sprays, are mentioned. These may be significant.

[The concentrations of halothane in the operating theatre and its dependance on various methods of removal (author's transl)]

Measurement of halothane concentrations by means of gas chromatography was used to compare the efficiency of 1) a filtration system and 2) ducting of gases into the exhaust of the ventilation system of our operating threatre. The concentrations were found to be lower when the latter method was used. Measurements made subsequently provided data on halothane concentrations occurring during routine service when different methods of anaesthesia were used, with and without ducting of gases into the ventilation exhaust system.

Adsorption of anaesthetic vapours on charcoal beds

The adsorptive properties of four charcoals have been examined in relation to their value as adsorbents in filters attached to an anaesthetic trolley. Data for four anaesthetics have been obtained. The test conditions (flow rate, concentration, humidity) were those relevant to the application, and the effect of variation of these conditions was also studied. The air flow resistance of the charcoals was measured. Basic data are thus provided for the design of suitable adsorbers. The performance of two prototype anaesthetic adsorbers has been measured.

An instrument for the accurate and continuous measurement of halothane concentrations in nitrous oxide-oxygen mixtures

An instrument is described which measures continuously both the halothane concentration and the composition of the carrier gas when the vaporizer is situated outside the breathing circuit. The instrument is an adapted katharometer in which the out-of-balance voltage is used to measure the concentration of one compound in a three-component mixture, and the total voltage reduction across the constant-current-supplied bridge is used to indicate the proportions of the other two components. Halothane concentrations can be determined with an inaccuracy of 0.1% for concentrations up to 6%. Nitrous oxide (N2O) concentration in the nitrous oxide-oxygen mixture, serving as carrier gas, can be determined with an accuracy of 1% over the whole range up to 100% N2O. The 99% response time of the instrument is approximately 1 min.

An expired gas collection and disposal system

An expired gas collection and disposal system based on an independent suction pump is described. The halothane concentration in the atmosphere was measured, with and without the system. The increase of halothane concentration was limited to 1 p.p.m. above the theatre basal value with the system in use, and 5 p.p.m. when no venting was used.

The uptake and elimination of halothane in dogs: a two- or multicompartment system? I: Gas chromatographic determination of halothane in blood and in inspired and end-tidal gases

The gas chromatographic determination of volatile organic anaesthetic agents in blood and in respiratory gases is described. The analysis in blood is based on a head space technique. Sampling of inspired and end-tidal gases is carried out by means of a system including a gas sampling valve.

Minimum blood concentration--a universal concept of anaesthetic potency

Although brain concentration of anaesthetic agents is attractive as a method of expressing anaesthetic potency, both theoretical and practical considerations limit the usefulness of this index. Therefore, the MAC concept has been utilized to develop another expression of potency: the minimum blood concentration. This takes into account the blood/gas solubility coefficient, and the fact that at equilibrium the amount of anaesthetic agent present in brain is reflected in the blood concentration, and it is applicable to both parenteral and to inhalation anaesthetic agents.

Residual halothane: Patient and personnel exposure

In addition to offering further data on the exposure of surgical and recovery-room personnel to low levels of halothane in room air, the authors demonstrate the presence of halothane levels in the blood of some surgical patients managed by other inhalation agents from machines previously used for halothane. The authors concluded that these levels, while low, may be of clinical significance in selected patients.

Operating room air pollution: influence of anaesthetic circuit, vapour concentration, gas flow and ventilation

Atmospheric halothane was sampled from three selected operating theatres and anaesthetic rooms during the middle of operating sessions. Two of the operating theatres studied were ventilated with total air exchange once every six minutes; the third operating theatre had no ventilation. End-tidal samples were obtained from anaesthetists. Halothane vapour concentrations were analysed by gas-liquid chromatography. The effect of commonly used anaesthetic circuits on the level of contamination in the ambient atmosphere was studied. Concentrations of halothane vapour in the theatre atmosphere were found to vary with sampling site, anaesthetic circuit used, total gas flow and vapour concentration, the scavenging system employed and the efficiency of ventilation system. Although the ventilation system considerably reduced the level of halothane in the operating room atmosphere, it did not totally eliminate the contaminating vapour. A significant reduction in operating-room pollution was obtained by use of simple scavenging equipment. Scavenging of anaesthetic vapours outside the operating room led to 97.3 per cent reduction of overall mean concentration of halothane in the operating room atmosphere and reduction of 72 per cent in end-tidal samples of anaesthetists, with the Magill semiclosed circuit. The implications of these findings are discussed.

Use of refractometry to determine nitrogen accumulation in close d circuits

We have described a technique by which a portable interference refractometer may be used to determine the accumulation of nitrogen in a totally closed anaesthetic circuit. The inspired mixture contained halothane, oxygen, nitrous oxide and nitrogen. The concentrations of the first two were controlled with u.v. paramagnetic analysers respectively. It was then possible to determine the percentage of nitrous oxide replaced by nitrogen by measuring the refractive power of the mixture.

Determination of the minimum alveolar concentration (MAC) of halothane in the white New Zealand rabbit

The minimum alveolar concentration (MAC) was determined in rabbits as the mean of the lowest alveolar halothane concentration preventing and the highest permitting a response to stimulus. MAC for the rabbit was 0.8 plus or minus 0.3 per cent. The measurement of MAC in the rabbit appears to reflect the arterial and brain anaesthetic concentrations.

Totally closed circuit nitrous oxide/oxygen anaesthesia

Totally closed circuit anaesthesia has been used with nitrous oxide/oxygen gas mixtures, supplemented by halothane for spontaneous breathing, or by opiates for artificial ventilation. Oxygen expenditure averaged 227 ml/min, while nitrous oxide expenditure declined exponentially from an initial value of 462 ml/min to 110 ml/min after 2 hr. These flow rated included gas sampled for analysis. Inspired oxygen concentration was maintained at 30 per cent by monitoring with a paramagnetic analyser. Halothane expenditure average 3.5 ml (liquid) per hr. Halothane concentrations in the operating theatre atmosphere did not increase above 0.03 p.p.m.

Atmospheric pollution with halothane in operating theatres. A clinical study using activated charcoal

Considerable reductions of halothane pollution in the operating theatre environment can be achieved with canisters containing activated charcoal attached to the expiratory limb of the anaesthetic circuit. This study indicates that the efficiency is greatest with cases requiring endotracheal intubation. If the facemask is employed, it is essential to achieve a tight seal with the contours of the face to eliminate unnecessary pollution.

Anaesthetic pollution and its prevention

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