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October 11, 2014
1:00 PM - 3:00 PM
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Do Activated Charcoal Filters With Pediatric Ventilator Settings Produce Clean Anesthesia Machines?
Radhamangalam J. Ramamurthi, M.D., F.R.C.A., John G. Brock-Utne, M.D., Ph.D., Christine G. Jette, M.D.
Stanford University Medical Center, Stanford, California, United States

Current evidence from data on animal studies suggests that to avoid triggering malignant hyperthermia in MH susceptible patients, the residual anesthetic vapor concentration must be less than 5 ppm.. Newer anesthesia machines incorporating more plastic and rubber components into their internal breathing systems which act as a volatile anesthetic sink. Recent studies show that the concentration of volatile anesthetic in anesthesia machines can remain well above the 5ppm threshold after a flush far longer than the previous 20 or 30-minute standard.

MHAUS advocates the use of commercially available activated charcoal filters as one option to provide vapor free anesthesia machine for MH susceptible patients.

There filters have been well studied using adult ventilator settings1. The fresh gas de-coupling mechanism of the newer anesthesia machines and the resultant compartmentalizing of gases during different phases of respiratory cycle makes it possible to have different tidal volumes which may have different effects on wash-out from the internal breathing components of these machines2. Hence there may be a difference in the washout needed for adults and pediatric ventilator settings.


We tested the two most common makes of anesthesia machines in use at Stanford University Hospitals. The aim was to evaluate the effectiveness of these charcoal filters at different ventilator settings using neonatal and pediatric tidal volumes


We first contaminated the Drager Apollo machine to deliver 7% Sevoflurane to a test lung for 90 minutes. During that time, we set the fresh gas flow to 3 LPM and ventilated at a tidal volume of 600 mL with a respiratory rate of 10 BPM. Then we turned–off the vaporizers, replaced the breathing circuit, rebreathing bag, test lung and CO2 absorbent. Per Vapor-Clean manufacturer’s recommendation, we flushed the machine at 10 LPM with a TV of 500 ml at 15 bpm for 90 secs. The charcoal filters (Vapor-Clean, Dynasthetics, Salt Lake City, Utah) were then placed both on inspiratory and expiratory limbs of the circuit. We continuously measured the concentrations of sevoflurane in the inspiratory limb between the breathing circuit and the test lung every 30 seconds until the values reached below 5 ppm, using the Miran SapphIRe XL Gas Analyzer (Thermo-Fisher Scientific, Waltham, MA)). This was repeated for lower and higher tidal volume ventilations and for lower and higher fresh gas flow rates.

Then we repeated the entire experiment on the Datex Aestiva machine.



10LTV: 10 LPM flow with Vt = 50 ml and f 32 = bpm

2HTV: 2LPM flow with Vt = 200ml and f = 8bpm

2LTV: 2 LPM flow with Vt = 50 ml and f = 32 bpm

2LTVAB: 2 LPM flow with Vt = 50 ml and f = 32 bpm, with Adult Bag

as the ‘model lung’

The attached graphs shows that, with modern anesthesia machines, even with varying ventilator settings, the charcoal filter is effective in reducing the vapor concentrations well below the safe levels within minutes.

Apart from improving the safety for MH susceptible patients, using the filters most likely will have implications on turnaround times and first case start times.


1.Birgenheier N, Stoker R, Westenskow D, Orr J. Activated charcoal effectively removes inhaled anesthetics from modern anesthesia machines. Anesth Analg. 2011 Jun;112(6):1363-70.  

2.Gunter JB, Ball J, Than-Win S. Preparation of the Dräger Fabius anesthesia machine for the malignant-hyperthermia susceptible patient. Anesth Analg. 2008 Dec;107(6):1936-45 34

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