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October 24, 2015
10:00:00 AM - 12:00:00 PM
Room Hall B2-Area B
Evaluation of Methods for Preparation of an Anesthesia Machine for Pediatric Malignant Hyperthermia Susceptible Patients
Joseph Orr, Ph.D., Kyle M. Burk, B.S., Derek J. Sakata, M.D.
University of Utah, Salt Lake City, Utah , United States
Disclosures: J. Orr: B. Ownership; Self; Dynasthetics LLC. C. Royalties; Self; Dynasthetics LLC. K.M. Burk: F. Funded Research; Self; Dynasthetics LLC. D.J. Sakata: B. Ownership; Self; Dynasthetics LLC. C. Royalties; Self; Dynasthetics.
Susceptible Patients

Introduction: Safe delivery of fresh gases from anesthesia workstations for Malignant Hyperthermia Susceptible (MHS) patients requires concentrations of residual anesthetic vapor within the fresh gas to be below 5 parts per million (ppm). Preparing the workstation can be done either by flushing the machine with high fresh gas flows for an extended period or by using activated charcoal filters to capture any residual vapor. A recently published paper found that patient Minute Ventilation (MV) affects flush time. Flushing a workstation with typical adult MV settings and then decreasing MV to pediatric settings causes vapor concentrations to rebound. The same paper stated that charcoal filters had not been tested under decreased MVs typical with pediatric anesthesia. We replicated the published additional flush time experiment and found a similar rebound effect. We also tested the activated charcoal filters using typical pediatric ventilation settings.

Methods: An anesthesia machine (Apollo, Draeger) was contaminated by delivering 1 MAC of anesthetic vapor to a mock patient followed by a simulated emergence in which the vaporizer was turned off and the Fresh Gas Flow (FGF) was increased to 10 L/min for 3 minutes. The breathing circuit and bag were replaced and then the concentration of residual vapor was measured using a trace gas analyzer (MIRAN SaphIRe, Thermo Electron Environmental Instruments, Franklin MA). The time needed to flush the residual anesthetic from the contaminated machine, using adult ventilation settings (TV = 600 ml, rate = 10/min) and FGF of 10 L/min, was evaluated. After the residual vapor concentration fell below the safe limit of 5 ppm, the ventilation was reduced to settings appropriate for a small pediatric patient (TV = 50 ml, rate = 30/min). Since reducing MV caused the vapor concentration to rise above 5 ppm, the additional time needed to flush the machine at the pediatric settings was also measured.

We also tested the effectiveness of the activated charcoal filters (VaporClean, Dynasthetics, Salt Lake City, UT) when used with pediatric ventilation settings (TV = 50 ml, rate = 30/min). To do this the machine was contaminated as described above and filters were placed on each limb of the breathing circuit for 90 minutes. The FGF was set at 10 L/min for the first 45 minutes and at 3 L/min for the following last 45 minutes. At 90 minutes the filters were removed and the concentration of residual vapor in the circuit was measured.

Results: The table below shows the washout times for each gas using the adult ventilation settings and the additional time needed above the initial flush that was needed after reducing ventilation to the pediatric settings.

When using the activated charcoal filters, the maximum observed concentration in ppm was 0.14 when testing with isoflurane, 0.30 when testing with sevoflurane and 0.28 when testing with desflurane. After removing the filters, the maximum observed concentration in ppm was 7.61 for isoflurane, 7.07 for

sevoflurane and 6.18 for desflurane. Fresh gas flow was set at 3 L/min when testing using the activated charcoal filters.

Discussion: These results show that when preparing an anesthesia machine for a pediatric MHS patient, additional flush time is needed. In addition, we have shown that activated charcoal filters are effective when used with decreased MV, typical in pediatric anesthesia.

References: 1. Cottron N et al, The sevoflurane washout profile of seven recent anesthesia workstations for MH-susceptible adults and infants: a bench test study, Anesth Analg. 2014 July; 119(1):67-75.

Figure 1

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