The security of the scrub nurse: the need to stop cement vapours in the surgical room
Dr. Pere Mir
The acrylic cement (acrylic resins) is used in different types of medical procedures, mainly in Orthodontics and Orthopaedic Surgery and Traumatology (vertebroplasty, prostheses …). The surgical procedures in which they are more used are hip and knee prosthesis. The cement mix is composed of a liquid and a powder that are mixed and get hard in 8 to 15 minutes. At the time of the mix and in following minutes are produced toxic vapours. Mainly they are two components (both in the liquid): the methyl methacrylate (98%) and the dimethyl-p-toluidine (1.5%). The first, methyl methacrylate, is the most important and most volatile. There are two more potential toxic substances in very low concentrations: hydroquinone (in the liquid) and benzoyl peroxide (in powder form).
The risks of acrylic cements are:
- Irritation of the respiratory system (cough, bronchitis ,…).
- Irritations of mucous membranes (sinusitis, stomatitis, ..).
- Conjunctival irritation (conjunctivitis).
- Contact Dermatitis (eczema).
- Dizziness and headache.
- Gastrointestinal disorders and alterations in the liver enzymes.
- Effects not described are carcinogenic, teratogenic, mutagenic or reproductive toxicity.
The toxicity of methyl-methacrylate affects respiratory airways, skin and mucous membranes, as well as the skin hypersensibility (has the note “sen”). It is considered a level with R 11-37 / 38-43 by Real Spanish Decreto 363/1995. The limits of exposure in Spain in the year 2008 are Environmental Maximum Values (VLA) of 50 ppm (208 mg / m3) and a VLA-EC 100 ppm (416 mg /m3).
Methyl methacrylate is one of the nine main chemical hospital risks: 1. Inhalational anaesthetics, 2: Cytostatics, 3: Disinfectants and sterilizers, 4: Formaldehyde 5: Surgical smoke, 6: Latex, 7: Mercury, 8: Methyl methacrylate, and 9: Xylenes.
Prospective trials in different surgical areas done by the Analytical Methods NIOSH 2537 (Ohio, 2003) observed that the person who realizes the cement mixing is the most exposed. In some papers it arrives to the limit of 50 ppm in the atmosphere which is the maximum allowed by law.
Nowadays exists systems totally closed or tight where the vapour in any moment is in contact with the air of operating theatre until his exhibition through the introduction cannula (already in the minute 2 or 3). This reduces until 90% the vapour that are produced in operating theatre. Palacos ProR is the newest system that allow to realise the process of mixing and air suction in a totally closed compartment. The nurse does not realise the mixture on contact to the air. In these systems the maximum values achieved are 5 ppm of methyl-methacrylate (moment in which the cement is injected by the tip of the syringe), and in some of the procedures are systematically 0 ppm.
We need to improve the prevention of labour risks, especially important in the prevention of chemical pollutants, raising for 10 proposals:
- Closed systems of mixing the cement. The vapours produced the first minutes are directly suctioned with a negative pressure. For example, the use of Palacos ProR requires a constant vacuum of approximately 100 mbar, which must be generated by a vacuum pump of adequate power.
- Have of respiratory mask with suitable filter for matter particulates and organic dissolvent. No mask protects completely of chemical vapours. The mask need accreditation for humid manipulation of liquid and gases: IN 14683:2005, that defines the minimum requirements that has to have. The masks FF3 have an efficiency of leak of 98% (until environmental concentrations with VLA 50 ppm). In the open cement system, we need to use protective glasses to avoid dots.
- In the open systems: mix the liquid on the dust, and no wrong side out. That is to say, place first the dust and next the liquid.
- Gloves impermeable to methacrylate (polyethylene or nitrile gloves are the most appropriate) and change the surface gloves after handling the cement if double latex gloves are used. PVP gloves (three-layer polyethylene, ethylene-vinyl alcohol copolymer, polyethylene) and VitonR / butyl gloves have demonstrated their protective efficacy over an extended period. It is recommended to use in each two overlapping gloves, for example, a polyethylene surgical glove over another surgical latex glove. Latex or polystyrene-butadiene gloves alone are not enough.
- Suitable system of ventilation of operating theatre. Carry out a periodic control of the ventilation of operating theatre and have of systems of positive pressure to facilitate this ventilation (+15 milibars to the interior of operating theatre). The filters of the air have to be absolute type HEPA (EU=4). They have to effect between 15 and 20 renewals of air for hour with 100% new air from outside. The recommended temperature is between 18or and 22oC.
- Suitable management of the waste of cement (excess cement) placing them in exchanges closed to avoid the evaporation of the methacrylate residual.
- The scrub nurse cannot wear soft contact lenses. Manufacturers of soft contact lenses recommend that they be removed in the presence of irritating vapours. Since soft contact lenses are permeable to liquids and gases, they should not be used in the operating room if methyl methacrylate is used in open systems. Personnel wearing contact lenses should not be near or involved in the preparation of the cement.
- Wide operating theatres (upper to 40 m2). The operating theatres where realise prosthesis usually are the largest available for the number of instrumental boxes needed and the 3 or 4 necessary tables, but another top reason is that the maximum levels of methyl-methacrylate are determined by the ppm or mg/m3. Its recommends do these procedures in operating theatres of more than 40 m2 and upper than 2.5 metres to reduce the concentration of vapours.
- Determine twice a year the air levels of methyl-methacrylate vapours in standard surgeries of prostheses of knee (exists more exposition for the nurse in the knee than in the hip, although this comes conditioned by the surgeon’s preferred technique of cement application to the prosthesis).
- Unit of Labour Health: conscientiousness, active, and periodic meetings with the staff (not only with heads of the departments) on this and other topics. The medical reviews of the personnel of the surgical area have to be annual.
There is no doubt that there is a long way to improve about preventive topics, so in the future we will cancel these professional chemical expositions.
Dr. Pere MirLeave a reply →