Assessment of Waste Anesthetic Gas Scavenging System Efficiency in Oral Surgery Operatories Using Infrared Video and Real-time Air Concentration Analysis

Abstract

Chronic exposure to waste nitrous oxide can cause adverse health effects which are well documented. Quantitative measurements are routinely used but the utilization of qualitative evaluation has been limited. Refining a qualitative method and combining both evaluation techniques can result in improved control of waste nitrous oxide gases. This study seeks to combine both types of evaluation. The objectives of this study are (1) to evaluate the efficacy of two scavenging systems of divergent designs that are currently used in oral surgery practice and (2) to evaluate the effect of work practices on the efficacy of one of these systems. Equipment used in this study includes: an infrared video camera for visualization of nitrous oxide gas, a digital video camera, and a real-time, datalogging gas detection instrument capable of detecting nitrous oxide. The two scavenging systems used in this study are denoted as System A and System B. Three data sets were collected in order to meet the study objectives. Each data set included a minimum of 13 surgeries and controllable variables were minimized, including type of surgery and concentration of anesthetic gas administered. Each data set included both types of video imaging and real-time air sampling for the duration of the surgery. The first and second data sets were collected from a single oral surgeon and utilized System A and System B, respectively. The first data set was designed to represent a highly motivated office with extensive experience with both systems. Together, these data sets allow a comparison of two systems with regard to exposure control efficacy. The third data set was collected in a second practice and utilized System A. This data set is representative of the system’s performance in an office with little experience with this specific system. The sampling, observation methods, and infrared imaging allow the data to be both qualitatively and quantitatively evaluated. Infrared video is utilized to qualitatively assess both the amount and movement of nitrous oxide emissions during surgeries and the effect of work practices and surgical elements on nitrous oxide emissions. Real-time air concentration data is used for quantitative evaluation of the system efficacy and can be correlated to notable events identified by infrared or digital video imagery. Initial comparison of data sets utilized descriptive statistics. Digital video is used primarily to aid in analysis by clarifying work practices and surgery events. Generally, patient and surgical variables affect visible waste gas emissions from both systems (eg level of sedation, patient anxiety level and respiratory patterns, and degree of manual manipulation during surgery). Increased visibility of emissions on IR images correlates to elevated air concentrations. Qualitative evaluation of the infrared video demonstrates that System A results in emissions that produce a smaller, less intense, and less diffuse stream than System B. This is supported by quantitative real-time air data concentrations that were below the ACGIH TLV of 50 ppm TWA on two sampling days when System A was used. The 8 hr TWA was above 50 ppm on the two sampling days when System B was used in the same office under conditions comparable to those in which System A was used. The refined work practices of the experienced user resulted in decreased 8 hr TWA values compared to a practitioner with no previous experience with system A. The inexperienced user still had an 8hr TWA that was lower than the experienced user System B values. Quantitative comparison was complicated on some data collection days in the inexperienced user’s office due to nitrous oxide use in adjacent operatories by other practitioners which may have overwhelmed the office HVAC system. Control of nitrous oxide emissions below established guidelines is possible. Compliance is dependent on the scavenging system design, the practitioner’s motivation for proper system utilization and maintenance, and less easily controlled patient and surgical variables. This study suggests that infrared video imaging is a useful tool for assessing both the amount and behavior of waste gas emissions and for determining appropriate work practice modifications aimed at maximizing system performance.