Masks for the Reduction of Methyl Methacrylate Vapor Inhalation

Abstract

Background:

Exposure to methyl methacrylate vapor (MMA) presents an occupational risk to orthopedic surgeons and ancillary personnel in the operating room. The purpose of this study was to identify a disposable face mask to reduce MMA organic vapor inhalation in the operative suite.

Methods:

First, the effectiveness of MMA vapor filtration was determined in the laboratory. A section of activated carbon impregnated filter face mask (Model 8514, 3M Inc.) was exposed to 150 ppm MMA vapor and MMA ppm of filtered air was monitored until MMA vapor was detectable. The face mask was then worn as directed in the operating room during routine cement mixing during total knee arthroplasty to determine the exposure to MMA vapors during the procedure both with and without the activated carbon impregnated filter face mask.

Results:

The activated carbon impregnated face mask was effective in reducing MMA vapor inhalation to non-detectable levels for up to 40 minutes in the laboratory at steady-state exposure of 150 ppm MMA vapor as well as throughout cement mixing and curing in the operative suite during routine total knee arthroplasty.

Conclusions:

An activated carbon impregnated face mask offers a solution for the orthopedic surgeon and supporting personnel who wish to limit their exposure to MMA vapors due to health concerns.

Level of Evidence: III

Introduction

Poly-methyl methacrylate bone cements contain methyl methacrylate (MMA), a substance known for its sensitizing and toxic properties. MMA is a volatile organic compound utilized for the production of co-polymer methacrylate-butadiene-styrene in a variety of total joint reconstruction procedures.

Due to its potentially hazardous properties, the US Occupational Safety and Health Administration (OSHA) permissible exposure limit for MMA is 100 parts per million (ppm) over an 8 hour work day. The concentrations of MMA in immediate breathing zones can vary widely in the operative suite.¹ MMA is known to irritate the respiratory system mucosa.² The developmental effects such as skeletal abnormalities and low birth weight have been documented in animal studies.^3,4 However these results are controversial and have not been repeated to examine birth defects at the occupational exposure limit.⁵ Nonetheless, it is common practice for pregnant members of the operative team, including nursing staff, anesthesia providers, and surgeons or surgical trainees to leave the operative room during cementing procedures to avoid inhaling MMA.

Although other industries routinely utilize face masks for the reduction of organic vapor inhalation, this method has not been introduced in orthopedic surgery. The purpose of this study was to identify a disposable face mask to reduce MMA organic vapor inhalation in the operative suite in order to reduce occupational exposure to a potentially hazardous substance. With this intervention, we anticipate effecting an improved working environment for surgical personnel and minimizing interruptions in patient care.

Methods

Determination of MMA Vapor Breakthrough:

The testing system included a cement curing chamber and an exposure chamber. MMA bone cement (Depuy Synthes Companies, Raynham, MA) was mixed as directed in a mixing bowl and placed into the curing chamber. Carrier air flowed through the cement mixing chamber into the exposure chamber at 0.1 liter per minute (LPM) to maintain steady state conditions of approximately 150 MMA ppm in the exposure chamber. A ToxiRae Pro (Rae Systems, San Jose,CA) was utilized to measure MMA levels in the exposure chamber, which is sensitive to within 5% of the indicated measurement (8ppm). A representative section of the activate carbon impregnated filtering face mask (Model 8514, 3M Inc., Maplewood, MN) was placed in a pass-through column; the mask section was sealed between two cylinders with an inner diameter of 2.7 cm. This allowed for sampling of air after it passed through the mask and thus was filtered. This system was designed to mimic the air velocity entering an entire face mask while breathing with a mean inspiratory airflow rate of 30 LPM. This air flow rate was based on breathing rates for occupations with high metabolic rate and moderate intensity.⁶ Trials were conducted until a detectable amount of MMA was achieved in the filtered air. A PPB Rae 3000 (Rae Systems, San Jose, Calif) was used to measure MMA levels of filtered air to within 1 part per billion (ppb). Four trials were performed (Figure 1).

Figure 1.

Determination of breakthrough of detectable levels of methyl methacrylate (MMA) vapor. The face mask showed undetectable levels of MMA vapor for >40 minutes when exposed to 150 ppm MMA vapor.

Field Test in the Operating Room During Primary Total Knee Arthroplasty:

The effectiveness of the face mask was evaluated in the operative suite during cement mixing. The face mask was worn as directed by manufacturer instructions on the face under a standard personal protection hood and Flyte surgical helmet system (Stryker, Kalamazoo, MI) by a surgical trainee who aided in both mixing with a mixing bowl and application of the bone cement. The TSI Fit Tester probe kit (Gerson, Olathe, KS) was utilized to allow for sampling of filtered air “behind the mask” by securing a push nut through the mask and securing the tubing to a PPB Rae 3000 detection device. Experiments were performed in laminar airflow operating rooms. As a control, the MMA ppm under the hood was measured with a ToxiRae Pro affixed to the test subject’s scrub neckline near the jaw line to measure MMA ppm in air that would be otherwise inhaled. Three trials were performed (Figure 2).

Figure 2.

Determination of breakthrough of detectable levels of methyl methacrylate (MMA) vapor in the operative suite during total knee arthroplasty. The face mask showed undetectable levels of MMA vapor during mixing and curing of cement in the operative suite.

Results

Determination of MMA Vapor Breakthrough: The testing system included a cement curing chamber and an exposure chamber. MMA bone cement (Depuy Synthes Companies, Raynham, MA) was mixed as directed in a mixing bowl and placed into the curing chamber. Carrier air flowed through the cement mixing chamber into the exposure chamber at 0.1 liter per minute (LPM) to maintain steady state conditions of approximately 150 MMA ppm in the exposure chamber. A ToxiRae Pro (Rae Systems, San Jose,CA) was utilized to measure MMA levels in the exposure chamber, which is sensitive to within 5% of the indicated measurement (8ppm). A representative section of the activate carbon impregnated filtering face mask (Model 8514, 3M Inc., Maplewood, MN) was placed in a pass-through column; the mask section was sealed between two cylinders with an inner diameter of 2.7 cm. This allowed for sampling of air after it passed through the mask and thus was filtered. This system was designed to mimic the air velocity entering an entire face mask while breathing with a mean inspiratory airflow rate of 30 LPM. This air flow rate was based on breathing rates for occupations with high metabolic rate and moderate intensity.⁶ Trials were conducted until a detectable amount of MMA was achieved in the filtered air. A PPB Rae 3000 (Rae Systems, San Jose, Calif) was used to measure MMA levels of filtered air to within 1 part per billion (ppb). Four trials were performed (Figure 1).

Field Test in the Operating Room During Primary Total Knee Arthroplasty: The effectiveness of the face mask was evaluated in the operative suite during cement mixing. The face mask was worn as directed by manufacturer instructions on the face under a standard personal protection hood and Flyte surgical helmet system (Stryker, Kalamazoo, MI) by a surgical trainee who aided in both mixing with a mixing bowl and application of the bone cement. The TSI Fit Tester probe kit (Gerson, Olathe, KS) was utilized to allow for sampling of filtered air “behind the mask” by securing a push nut through the mask and securing the tubing to a PPB Rae 3000 detection device. Experiments were performed in laminar airflow operating rooms. As a control, the MMA ppm under the hood was measured with a ToxiRae Pro affixed to the test subject’s scrub neckline near the jaw line to measure MMA ppm in air that would be otherwise inhaled. Three trials were performed (Figure 2).

Discussion

MMA presents an occupational hazard to the orthopedic surgeon; due to its toxic properties OSHA limits its exposure. Although the effects of MMA fumes on the developing human fetus are unknown, pregnant personnel are commonly encouraged to leave the operating room during the mixing and application of poly-MMA bone cement. Currently, there are no comparable studies in the scientific literature that identify and evaluate personal protective equipment for MMA vapor exposure in the operative setting.

The tested activated carbon impregnated face mask effectively reduced inhalation of MMA vapors from 150 ppm to <1.0 ppm for greater than 40 minutes in the laboratory. In the operating room, filtered air behind the face mask did not show detectable MMA vapor levels throughout the mixing and curing of cement. Thus, the 3M Model 3514 face mask offers a solution for the orthopedic surgeon and supporting personnel who wish to limit their exposure to MMA vapors due to health concerns.