Atmospheric pollution in operating theatres. A review and a report on the use of reuseable activated charcoal canisters

Effect of charcoal filter on the emergence from sevoflurane anesthesia in a semi-closed rebreathing circuit

PURPOSE

A charcoal filter attached within the anesthetic circuit has been shown to efficiently adsorb halothane or isoflurane, thus hastening anesthetic recovery in low or minimal flow system. This study was intended to demonstrate whether the charcoal filter enhances the recovery time from sevoflurane anesthesia using a semi-closed circuit system.

MATERIALS AND METHODS

Thirty healthy patients scheduled for elective surgery under sevoflurane anesthesia were randomly assigned to the charcoal filter or control group. Upon completion of surgery, the end-tidal concentration of sevoflurane was maintained at 2.0 vol%. A charcoal filter was attached to the expiratory limb of the breathing circuit of charcoal filter group subjects. After sevoflurane was discontinued, ventilation was controlled with the same minute volume as the intra-operative period at a fresh gas flow rate of 5 L·min⁻¹ with 100% O₂. The elimination kinetics of sevoflurane from end-tidal concentration, Bispectral index and times of eye opening and extubation were obtained.

RESULTS

The exponential time constant (τ) of alveolar sevoflurane concentration in the charcoal filter group was significantly shorter than that in the control group (1.7±0.5 vs. 2.5±1.1 min, p=0.008). The charcoal filter hastened rapid eye opening (11.1±3.8 vs. 14.8±3.0 min, p=0.007) and extubation (11.9±3.9 vs. 15.3±3.2 min, p=0.014), compared to the control group.

CONCLUSION

A charcoal filter enhances the recovery from sevoflurane anesthesia with a semi-closed rebreathing circuit.

Adsorption of halothane from a paediatric T-piece circuit by activated charcoal

Experiments were conducted to compare the efficacy of six commonly available charcoals in adsorbing halothane in a paediatric T-piece system. Tests were also done to compare the effect of mass of charcoal and canister shape and size on adsorption and airways resistance. It was found that charcoals vary in their adsorptive capacity and that the size and shape of cannisters is important.

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.

Intravenous anaesthesia by infusion. A technique using alphaxolone/alphadolone (althesin)

Two hundred and seventy-three patients were anaesthetised using aphaxolone/alphadolone as a sole anaesthetic agent, administered in either a 10% solution or in increments of neat drug. Analgesics were given where necessary. This technique was instituted to provide a method of anaesthesia that avoided pollution of the atmosphere, with its possible harmful effects. As experience was gained, better results were obtained. Overall, 86% of the anaesthetics administered were without problems, 12% presented some difficulty, usually minor movement of the patient, and in 2% this technique was abandoned.

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.

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.