The surgical mask is a universally recognized piece of operating room attire, serving as a mandated barrier worn by healthcare professionals during invasive procedures. Its purpose is a dual-function protocol, creating a physical shield to protect both the sterile environment and the wearer. The mask forms a foundational component of aseptic technique, which is the practice of keeping the patient, the operating environment, and the equipment free from infection-causing microorganisms.
Preventing Contamination of the Sterile Field
The primary historical and ongoing reason for wearing a surgical mask is to protect the patient from the surgical team’s respiratory emissions. When a person breathes, speaks, coughs, or sneezes, they expel respiratory droplets that contain microorganisms, including bacteria and viruses, from the mouth and nose. The mask acts as source control, capturing these large droplets before they can travel from the wearer’s face into the environment.
The operating room is centered around the “sterile field,” which is the area immediately surrounding the patient’s open surgical site and the sterile instruments. Even minimal contamination from the surgical team poses a high risk to the patient, as a direct pathway exists for microorganisms to enter the body through the surgical incision. Surgical masks are highly effective at containing droplets larger than four micrometers, with filtration efficiencies approaching 100% for these larger particles expelled during respiratory activities like speaking.
The mask material, typically non-woven polypropylene, works as a mechanical barrier to prevent the transfer of bacteria and saliva from the wearer’s mouth and nose toward the vulnerable open wound. By containing these bio-aerosols, the mask significantly reduces the bioburden, or the number of microorganisms, shed by the surgical team. This preventative measure is a core part of reducing the incidence of surgical site infections (SSIs), which are a serious post-operative complication.
Shielding the Surgical Team from Patient Fluids
The reciprocal function of the surgical mask is to protect the wearer, particularly the mucous membranes of the nose and mouth, from exposure to patient fluids. Surgical procedures often involve the generation of splatter, which includes blood, saline, irrigation fluids, and other biological materials. High-pressure activities, such as drilling in orthopedic surgery or the use of electrosurgical devices, can aerosolize or spray these fluids.
The mask serves as a physical fluid barrier, preventing infectious materials from contacting the surgeon’s face. This protection is especially important for preventing the transmission of bloodborne pathogens. To ensure adequate fluid resistance, surgical masks are tested against a synthetic blood challenge at varying pressures.
For instance, a high-level mask, such as an ASTM Level 3, is certified to resist penetration by synthetic blood at a pressure of 160 mmHg. This high fluid resistance is necessary to guard against the forceful splashes that can occur during trauma or procedures that use high-pressure irrigation.
Understanding Mask Design and Filtration Limits
Surgical masks are loose-fitting, disposable devices designed primarily as a fluid barrier and large-droplet containment system. Their performance is standardized by bodies like ASTM International, which specifies requirements for bacterial filtration efficiency (BFE), breathability, and fluid resistance. For example, Level 2 and Level 3 masks must achieve a bacterial filtration efficiency of 98% or greater against three-micrometer particles.
It is important to distinguish the surgical mask from a tight-fitting respirator, such as an N95. Unlike a respirator, the surgical mask does not form a perfect seal around the face, meaning air can leak around the edges. This lack of a tight seal is why surgical masks are not intended to provide reliable respiratory protection to the wearer from inhaling microscopic airborne particles, or aerosols. While the mask material itself may efficiently filter a high percentage of small particles, the loose fit allows significant perimeter leakage.