Carbon dioxide absorbents for rebreather diving.

Firstly I would like to thank SPUMS members for making me a Life Member of SPUMS; I was surprised and greatly honoured by the award. I also want to confirm and expand on the findings on carbon dioxide absorbents reported by David Harvey et al. For about 35 years, I was the main player in deciding which absorbent went into Australian Navy and Army diving sets. On several occasions, suppliers of absorbents to the anaesthesia market tried to supply the Australian military market. On no occasion did they provide absorbent that came close to the minimum absorbent capacity required, generally being 30-40% less efficient than diving-grade absorbents. Because I regard lives as being more important than any likely dollar saving, the best absorbent was always selected unless two suppliers provided samples with the same absorbent capacity. On almost every occasion, there was a clear winner and cost was never considered. I suggest the same argument for the best absorbent should be used by members and their friends who dive using rebreather sets. I make this point because of my findings on a set that was brought to me after the death of its owner. The absorbent was not the type or grain size recommended by the manufacturer of the set and did not resemble any of the diving grade absorbents I knew of. I suspected by its appearance that it was anaesthetic grade absorbent. When I tested the set, the absorbent system failed very quickly so it is likely that carbon dioxide toxicity contributed to his death. The death was not the subject of an inquest and I have no knowledge of how the man obtained the absorbent. Possibly there was someone from an operating theatre staff who unintentionally caused their friend's death by supplying him with 'borrowed absorbent'. I make this point as I would like to discourage members from making a similar error.

Inner-ear decompression sickness in nine trimix recreational divers.

INTRODUCTION: Recreational technical diving, including the use of helium-based mixes (trimix) and the experimentation of new decompression algorithms, has become increasingly popular. Inner-ear decompression sickness (DCS) can occur as an isolated clinical entity or as part of a multi-organ presentation in this population. Physiological characteristics of the inner ear make it selectively vulnerable to DCS. The inner ear has a slower gas washout than the brain thus potentially making it more vulnerable to deleterious effects of any bubbles that cross a persistent foramen ovale (PFO) and enter the basilar artery, whilst the inner ear remains supersaturated but the brain does not. METHODS: A questionnaire was made widely available to divers to analyse the incidence of inner-ear DCS after technical dives. One-hundred-and-twenty-six divers submitted completed questionnaires, and we studied each incident in detail. RESULTS: Nine (7.1%) of the 126 responders reported to have had at least one episode of inner-ear DCS, of which seven occurred without having omitted planned decompression stops. Of these seven, four suffered from DCS affecting just the inner ear, while three also had skin, joint and bladder involvement. Five of the nine divers affected were found to have a PFO. All affected divers suffered from vestibular symptoms, while two also reported cochlear symptoms. Three divers reported to have balance problems long after the accident. CONCLUSIONS: This small study is consistent with a high prevalence of PFO among divers suffering inner-ear DCS after trimix dives, and the pathophysiological characteristics of the inner ear could contribute to this pathology, as described previously. After an episode of DCS, vestibular and cochlear injury should always be examined for.

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 (tau) 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.

Effect of Fresh Gas Flow on the Work of Breathing of Closed Circuit Anesthesia Using Semiclosed Circuit System / 대한마취과학회지

BACKGOUND: The effect of anesthetic techniques, such as closed circuit anesthesia (CCA) using semiclosed circuit system and semiclosed circuit anesthesia (SCCA), on the work of breathing has not been studied yet in detail. This study was purposed to compare the work of breathing according to anesthetic technique (CCA, SCCA). METHODS: Thirty patients were assigned to receive either SCCA group or CCA group (n = 15). Anesthesia was induced with propofol 2 mg/kg with 2% lidocaine 1 ml. Two percents isoflurane with O2 and N2O 2 L/min were given for 10 min to patients initially to wash in functional residual capacity and the breathing circuits. In SCCA group, anesthesia was maintained with 2% isoflurane in O2 2 L/min and N2O 2 L/min throughout the surgery. In CCA group, O2 was reduced to 200 ml/min and N2O to 100 ml/min with isoflurane vaporizer setting adjusted to 4% for anesthesia maintenance. When the operation was ended, the vaporizer setting of isoflurane deceased to zero and then O2 was increased to 4 L/min for the arousal of the patient. We measured the inspiratory/expiratory concentration of isoflurane, end-tidal CO2, the hemodynamic parameters, the change of airway pressure, the work of breathing, and compliance at anesthetic induction and emergence in both groups. RESULTS: There were no significant differences in the inspiratory/expiratory concentrations of isoflurane, the hemodynamic parameters, end-tidal CO2, airway pressure, the work of breathing and compliance between the groups. CONCLUSIONS: CCA using semiclosed circuit system does not increase the work of breathing compared to SCCA.