Anesthetic Gas Levels with Use of the Double Mask
All levels of N2O (Fig. 2) decreased, and 0% of offices exceeded the limit of 25 ppm (95% upper confidence limit of 34%) using the double mask (median N2O level with double mask: 3.0 ppm, IQR = 2.3–4.7 ppm, n = 9, P = 0.0055) and all levels of sevoflurane (Fig. 3) decreased and 0% of offices exceeded the limit of 2 ppm (95% upper confidence limit of 34%) using the double mask (median sevoflurane level: 0 ppm, IQR = 0–0.39 ppm, n = 9, P =0.0024).
Currently, many small surgical interventions continue to migrate from hospitals into office-based facilities, and this trend will likely increase in the years to come. There are a number of reasons for this trend, including greater patient and provider satisfaction, but it is ultimately perceived cost savings that has led to such an acceleration. It is simply more cost efficient to operate a small office-based facility compared with a large, full-scale hospital (with its attached emergency room, intensive care unit etc.), and several studies have now demonstrated that the risks of adverse events tend to be comparable between hospital-based ambulatory surgery and cases performed in freestanding ambulatory surgicenters and office-based facilities.7–10
The provision of dental care for very young children, especially with developmental disabilities or special needs often requires GA. Although it is possible to do an IV induction followed by total IV anesthesia after sedation with oral midazolam, this is not popular among many anesthesiologists because of associated delays in recovery and the increase in arousal distress.11 For this reason, a mask induction with inhaled anesthetics without oral premedication is frequently chosen for young pediatric patients.
When contemplating pediatric GA in dental office buildings, the practitioner has to be aware of the structural differences, because most of these facilities are not built as designated “anesthetizing locations.” One of the differences, for example, is a lack of hospital OR grade HVAC systems, designed to provide augmented air exchanges, and this may, especially during mask inductions for GA in pediatric patients, lead to significant exposure to inhaled anesthetic waste gas levels.
The retrofitting of dental offices with OR grade HVAC systems is likely not economically feasible (and in many cases probably structurally not possible) and may not be sufficient to reduce anesthetic waste gas exposure during mask use to acceptable levels without installation of additional scavenging.6 Dr. Reiz’s group in Sweden had previously experimented with augmented scavenging devices at the head of the operating bed, ultimately leading to the development of the double mask, however, applying significant suction flows to the outer mask (35 m3/h). Although a scavenging fan to supply this suction flow is commercially available together with the double mask, the unit is large and heavy, making it a less than ideal solution for small offices (and even less so for mobile office-based anesthesia).
An alternative suction, uniformly present in dental offices, is the high-volume evacuator used by the dentist themselves, of which there are usually 2 to 3 in each operatory (in addition to a low-volume suction). These high-volume suctions provide approximately 200 L/min (approximately 12 m3/h) and are vented outside the office. As they are only used by the dentist during the case (when the patient is already tracheally intubated), these suctions are readily available for the mask induction. Although the total flow provided by these suctions is lower than the flow of the commercial scavenging fan, it appeared to be sufficient to decrease anesthetic waste gas levels below threshold in our study.
The disadvantages of the double-mask system is its slightly more bulky setup, along with audible noise from the attached suction, both of which can be explained to the parents and the child and which did not present a problem in the authors’ experience. The masks can be reused with proper sterilization (as per instructions by the manufacturer) and are recommended to be changed after 5 years of use.c
In summary, we demonstrated in our study that the double-mask system, when used with dental high-volume suction in freestanding dental offices, was sufficient to decrease the exposure to anesthetic waste gas levels during pediatric mask induction in at least two thirds of offices when compared with the traditional mask, although the suction flow was lower than what was originally published.6 Larger studies are needed to demonstrate that this decrease in exposure to anesthetic waste gases would be true across all anesthetizing sites. This system may be useful for in-hospital ORs where, despite augmented air exchanges, the anesthetic waste gas levels may still exceed the recommended levels during pediatric mask inductions.
Name: Matt M. Kurrek, MD.
Contribution: This author helped design and conduct the study, collect the data, analyze the data, and prepare the manuscript. This author attests to the integrity of the original data and the analysis.
Attestation: Matt M. Kurrek approved the final manuscript and attests to the integrity of the original data and the analysis reported in this manuscript. Matt M. Kurrek is the archival author.
Name: Steven L. Dain, MD.
Contribution: This author helped design the study and prepare the manuscript.
Attestation: Steven L. Dain approved the final manuscript.
Name: Alexander Kiss, PhD.
Contribution: This author helped design the study, analyze the data, and prepare the manuscript. This author attests to the integrity of the original data and the analysis.
Attestation: Alexander Kiss approved the final manuscript.
This manuscript was handled by: Peter S. A. Glass, MB, ChB.
aOccupational Safety & Health Administration/United States Department of Labor. Anesthetic Gases: Guidelines for Workplace Exposure. http://www.osha.gov/dts/osta/anestheticgases/index.html. Accessed August 13, 2012.
bPersonal communication, Mitch Beckwith, Air Techniques Inc, Melville, NY, 2012.
cMedicvent AB Pendelgatan 3 SE-904 22 Umea Sweden Double Mask Instruction Manual. Available at: www.medicvent.se/Gismo/Bildarkiv/org/980/210000%20manual%20_eng_%202010-11-02.pdf. Accessed August 13, 2012
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© 2013 International Anesthesia Research Society
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