Circulation 107,515 • Volume 29, No. 1 • June 2014   Issue PDF

Which System Should be Used for Waste Anesthetic Gas Disposal?

Robert Welninski

A Dear Q&A,

Is there any literature or documentation that speaks about the benefits or hazards of a waste anesthetic gas disposal (WAGD) outlet versus a vacuum outlet for scavenging? The manufacturer of our anesthesia machines states that it does not matter which source we use.

Robert Welninski
Chicago, Illinois

A Dear Mr. Welninski,

BeaconMedaes has produced a paper on waste anesthetic gas disposal (WAGD). There is a reference to NFPA-99 that carries a warning about mixing of WAGD and medical vacuum, primarily focused on high oxygen concentrations from WAGD in the oil based suction pumps. There is no proof, however, that this has created any real problems in actual use.

Figure 1 illustrates the ideal system where there are separate main lines for WAGD and vacuum. In this case all suction comes from the main vacuum line and the waste anesthetic gas goes into the WAGD main line. In this case all suction devices and the WAGD system are operating at full capacity.

Figure 1.

Figure 2 illustrates the case where there is no main WAGD line, and the anesthesia machine scavenging interface connects to a main vacuum line. When all of these lines have separate pipelines from the gas outlets in the utility column to the main Vacuum lines, there is again no degradation of performance in any of the suction systems or the WAGD interface.

Figure 2.

Figure 3 illustrates a scenario where the WAGD is plugged into the same pipeline as the anesthesia suction because the gas outlets are connected together in the gas utility column. In this case if the WADG flow were high the anesthesia suction would be compromised. Ideally, the scavenging flow would be equal to the total fresh gas flow set on the anesthesia machine plus the excess drive gas from the bellows plus the waste gas from the respiratory gas analyzer. This flow will have limited impact on suction flow of 140 liters/minute. However, if the WAGD flow was half of the total suction flow, the suction would drop from 140 liters/minute to 70 liters/minute.

Figure 4 illustrates the case where the surgical suction, anesthesia suction, and the WAGD flows are all connected together in the gas utility column. A single pipe from the outlets in the gas utility column to the main vacuum line will cause all suction to be degraded. Imagine at the end of the case when the surgical suction is running full open, the scavenging system is running and the patient begins active regurgitation and your suction flows which are supposed to be at 140 liters/minute, are below 45 liters/minute with concomitant decreases in pressure.

When a manufacturer tells you that you can use either a WAGD outlet or a vacuum outlet, they are referring to Figure 1 or Figure 2. Avoiding Figures 3 and 4 would be advantageous and permit full suction capabilities through soft tip or Yankauer suctions tips.

The APSF Committee on Technology

Numerous questions to the Committee on Technology are individually and quickly answered each quarter by knowledgeable committee members or designated consultants. Many of those responses would be of value to the general readership, but are not suitable for the Dear SIRS column. Therefore, we have created this simple column to address the needs of our readership.

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