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Preparing the Anesthesia Machine for MHS Patients

Ensure that anesthetic vaporizers are disabled by removing, or taping in the “OFF” position. Most vaporizers have a significant reservoir of anesthetic agent that cannot be drained, thus draining is not an acceptable choice.  During preparation of the machine, attach a new breathing circuit and reservoir bag to the Y-piece of the circle system and set the ventilator to inflate the bag periodically.  For newer anesthesia workstations, this may require flowing 10 L/min of fresh gas for up to 104 minutes. For older machines, flow 10 L/min of fresh gas for 20 minutes. Also, changing the COabsorbent is recommended. Consult the manufacturer of the machine for specific instructions on preparation of the machine for an MH patient.

For both new and older machines, adding commercially available activated charcoal filters to the circuit will remove anesthetic gases and obviate the need for purging the system as described. However, the anesthesia machine will still need to be flushed with high fresh gas flows (≥ 10 L/min) for 90 seconds prior to placing the activated charcoal filters on both the inspiratory and expiratory ports. These filters are effective in keeping gas concentration below 5 ppm for up to 12 hours with fresh gas flows of at least 3 L/min.


  • Shanahan H, O’Donoghue R, O’Kelly P, Synnott A, O’Rourke J. Preparation of the Drager Fabius CE and Drager Zeus anaesthetic machines for patients susceptible to malignant hyperthermia. Eur J Anaesthesiol. 2012;29 (5): 229-34.
  • Jones C, Bennett K, Kim T, Bulger T, Pollock N. Preparation of Datex-Ohmeda Aestiva and Aisys anaesthetic machines for use in malignant hyperthermia susceptible patients. Anaesth Intensive Care. 2012;40 (3): 490-7.
  • Kim TW, Nemergut ME. Preparation of modern anesthesia workstations for malignant hyperthermia-susceptible patients: a review of past and present practice. Anesthesiology. 2011: 114(1): 205-12.
The mission of MHAUS is to promote optimum care and
scientific understanding of MH and related disorders.