Preparation of Anesthesia Machines for Patients Susceptible to Malignant Hyperthermia

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Abstract
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 1-1/min and a 10-1/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 chromatography having a sensitivity of 0.1 ppm. Isoflurane washed out 3-4 times faster than halothane. Residual halothane concentration was .apprxeq. 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 (.apprxeq. 50 ppm vs. .apprxeq. 5 ppm after 5 min of washout). Halothane concentrations did not decrease more rapidly when the ventilator bellows was replaced. Halothane concentrations in samples taken from the end of the original fresh gas outlet hose decreased rapidly and were .apprxeq. 10 ppm after 5 min of washout. After the outlet hose was replaced, halothane concentrations were < 1 ppm after 5 min of washout. "Contaminated" machines should be prepared for use in susceptible patients by removing vaporizers, flushing with oxygen at a rate of 10 l/min for 5 min, replacing the fresh gas outlet hose, and using a new disposable circle.