A Portable Negative Pressure Unit Reduces Bone Cement Vapors in a Simulated Operating Room
bone cement1,2,3 is a two-component synthetic formulation that hardens at room temperature upon mixing to form a rigid material that secures implants. Although formulations currently supplied may vary, bone cement generally consists primarily of poly(methyl methacrylate) (PMMA), methyl methacrylate monomer and a polymerization initiator (benzoyl peroxide) (see Fig. 1) . For improved cure and stability, the formulation will also contain an accelerator (typically a tertiary aromatic amine) and an inhibitor (eg hydroquinone). Additionally, antibiotics (eg gentamicin), a radiopacifier (usually barium sulfate or zirconium dioxide) and a coloring agent (eg chlorophyll VIII) for better visualization are usually present. The polymer-containing component of the premixed system is a powder and the monomer-containing component is a liquid. Upon mixing the two components, the methyl methacrylate will gradually undergo exothermic free radical polymerization, resulting in a high viscosity paste and ultimately a fully hardened and rigid material.
Methyl methacrylate, the main volatile substance in bone cement, is a low molecular weight organic molecule with a strong smell. It has a boiling point of about 101°C and a vapor pressure of about 4 kPa at 20°C, making it a relatively volatile organic compound. Upon mixing, some of the methyl methacrylate (and potentially other small molecules present as impurities, additives or by-products and low molecular weight oligomers generated during free radical polymerization) evaporates in the air. Heat is generated both as a by-product of the exothermic polymerization reaction and due to friction caused by mixing. As the viscosity increases, the localized heat induced by mixing increases. When the temperature increases, methyl methacrylate escapes more easily into the air. Throughout the mixing process, the smell increases in intensity as the fumes pollute the immediate environment. Note that mixing is done within the perimeter of the operating room (OR) where downward airflow is not present, leaving healthcare workers vulnerable to potentially high concentrations of VOCs.
Inhalation of methyl methacrylate may cause respiratory tract irritation, headache, nausea, vomiting, dizziness and fatigue4. Asthma associated with methyl methacrylate has been reported5,6,7. Methyl methacrylate may contain trace amounts of methacrylic acid impurities, which can cause respiratory tract burns and pulmonary edema when high concentrations are inhaled. Methyl methacrylate is rapidly metabolized to methacrylic acid in humans. In medical applications, while time-weighted averages are typically below 100 ppm, maximum exposure levels of up to 374 ppm have been recorded.8. Methyl methacrylate is considered unclassifiable with respect to carcinogenicity9. In general, it is recommended to minimize exposure to chemicals, regardless of known risks. The health risks of a given chemical may be updated as more data becomes available. The deployment of effective measures to mitigate exposure improves the working environment in terms of health, safety and productive work.
Various methods of protecting healthcare workers from bone cement fumes have been described. The use of masks impregnated with activated carbon to limit exposure to methyl methacrylate vapors has been reportedten. Placing small suction tubes near the mixing bowl has been described as qualitatively improving inhaled air near the mixing station11. Vacuum bone cement mixing has been shown to reduce bone cement fumes in the breathing zone with performance varying depending on the mixing system used12,13,14. Another improvement is pre-packaged bone cement mixing systems; however, methyl methacrylate vapors can still be detected when using these systems15.
Developing engineering controls to address exposure to bone cement fumes will improve the working environment in operating theatres. Additionally, such technology would potentially have applications in industrial environments where hardening processes16 generate VOCs. In general, there is great interest in reducing volatile and semi-volatile organic compounds in indoor environments due to health and comfort concerns. In hospitals, air cleaning technologies are used to minimize exposure to harmful materials. Portable filtration units17,18,19 that control localized airflow have been deployed in several healthcare scenarios to improve air quality. For example, portable air handlers have already proven effective in removing synthetic aerosols the size of Mycobacterium tuberculosis20. Additionally, air decontamination devices that generate negative pressure at point sources have been shown to be effective in removing electrocoagulation smoke generated during electrosurgical procedures.21. Portable devices that allow localized negative pressure offer a potentially flexible and effective approach to removing bone cement fumes in operating theaters and other environments.
In this report, we show that bone cement fumes can be detected with a VOC sensor during manual mixing of a two-component bone cement system and that a portable negative pressure (PNP) unit reduces the concentration of VOCs. fumes in the localized mixing zone. The advantages of the method include the portability of the device and the relative ease of incorporating negative pressure into the mixing process in a non-disruptive manner. Additionally, the device can be used for other purposes in the operating room, including the removal of bioaerosols emitted during aerosol-generating procedures.22 and the elimination of surgical smoke generated during electrosurgical procedures. Although we focus on bone cement in this report, in principle the PNP unit could be used in any environment in which volatile, semi-volatile and particulate matter is generated.