A sterile field is a designated area, typically within an operating room or other procedural setting, that is prepared to be free of all living microorganisms and spores. This zone includes the draped patient, the instrument tables, and the appropriately gowned and gloved surgical team. Creating this environment prevents the introduction of microbes into a patient’s open wound or internal body cavity during an invasive procedure. Preventing contamination reduces the risk of a Surgical Site Infection (SSI), a significant complication for patients undergoing surgery. The duration a field can remain open is a central concern for infection control policies.
The Core Principle of Timeliness
The most fundamental guideline in maintaining an aseptic environment is that a sterile field must be prepared and opened as close as possible to the time of use. This principle minimizes the duration during which the field is exposed to the ambient environment, thereby reducing the potential for contamination. The rationale behind this is simple: the longer a sterile surface is exposed, the greater the opportunity for airborne particles to settle and compromise its integrity.
In most institutions, the ideal practice is to set up the field immediately before the patient enters the room or just as the surgical team is preparing to scrub. While professional organizations, such as the Association of periOperative Registered Nurses (AORN), have no universally mandated time limit, institutional practice for an uncovered field is often limited to a few minutes. The lack of a specific time limit reflects the dependence on highly variable factors like the operating room’s air quality and traffic control.
If a delay occurs, some facilities may allow a field to remain open under strict controls for a limited period, often citing a maximum of one to two hours. This extended time is only acceptable if the field is continuously monitored and properly covered, and it is considered a secondary strategy, not a routine practice. The concept that “time is contamination” is upheld because every passing minute allows microscopic bioburden from the air to accumulate on exposed instrument surfaces, increasing the probability of infection.
Environmental Factors That Compromise Sterility
The integrity of an open sterile field is constantly under threat from the surrounding environment, primarily through three mechanisms: air movement, moisture, and proximity of non-sterile objects. Air movement and the flow of personnel are significant sources of contamination in the operating room. Every person in the room sheds skin cells, which are carriers of bacteria, and movement causes these particles to be suspended in the air.
The heating, ventilation, and air conditioning (HVAC) system in the operating room is designed to maintain a positive pressure gradient and a minimum number of air exchanges per hour to push potential contaminants out. However, frequent opening and closing of doors or excessive staff traffic disrupts this directional airflow, allowing unfiltered air and increased particle counts to enter the sterile zone. Limiting the number of non-essential staff and keeping doors closed during setup and procedures are practices intended to support the room’s environmental controls.
Moisture is another major pathway for contamination, often referred to as “strike-through.” Sterile drapes and wrappers are designed to be fluid-resistant, but they are not impenetrable when wet. If a sterile drape becomes damp from a spilled solution or condensation, microorganisms can be drawn through the material via capillary action from a non-sterile surface to the sterile instruments. Any sterile item that becomes visibly wet is immediately considered contaminated and must be discarded or replaced.
The principles of distance and line of sight define the sterile perimeter and its vulnerability. A sterile field is only considered sterile from the top of the surface downward; anything that hangs below the table level is non-sterile. A margin of safety, typically a one-inch border around the edge of a sterile drape, is also considered unsterile. Any non-sterile person or object that comes too close or reaches over the field can introduce contamination, and an extended duration increases the chances of an accidental breach.
Protocols for Monitoring and Remediation
To combat the inherent risks posed by an open field, healthcare teams employ strict protocols for continuous monitoring and immediate remediation. The scrub person is primarily responsible for the continuous visual surveillance of the sterile field, looking for any sign of a break in technique. This monitoring includes checking for tears or punctures in the drapes, any evidence of moisture or spill contamination, and ensuring that all personnel maintain the appropriate distance from the sterile barrier.
If a procedure is delayed after the field has been opened, the team may temporarily cover the sterile instruments and supplies using a specific technique, such as the two-cuffed drape method. This covering is only permitted for a delay and not as a routine measure to allow early setup. When covering a field, the setup time and the covering time must be documented, as institutional policies dictate the maximum covered duration, which is often significantly shorter than 24 hours.
If the allowed time limit for the covered field is exceeded, or if any event compromises the integrity of the field, the policy is absolute: the field must be considered contaminated. This requires the immediate breakdown of the entire setup. All instruments and supplies must be removed, taken to a reprocessing area, and a completely new sterile field must be established with fresh supplies. This approach ensures that patient safety is not jeopardized by using supplies with questionable sterility.