Medical procedures designed to treat or diagnose patients can sometimes create an unintended consequence: the release of tiny airborne particles that may carry infectious agents. These specific actions, performed primarily in clinical settings, are known as Aerosol Generating Procedures (AGPs). Understanding AGPs is crucial for infection control, especially during respiratory disease outbreaks, as they temporarily change the risk profile for healthcare workers and other patients. The designation of a procedure as an AGP determines the specialized infection prevention precautions that must be implemented.
Defining Aerosol Generating Procedures
An Aerosol Generating Procedure is any medical treatment or diagnostic test that stimulates the respiratory tract, resulting in the production of fine, suspended airborne particles from respiratory secretions. The defining characteristic of an aerosol is its small size, typically less than 5 to 10 micrometers (µm) in diameter. These minute particles are light enough to remain suspended in the air for extended periods and can travel greater distances away from the source patient.
This distinguishes them from larger respiratory droplets (greater than 10 µm), which fall quickly to the ground or nearby surfaces due to gravity. AGPs utilize mechanisms like high shear stresses or high-velocity gas flows that mechanically disrupt the surface tension of fluids in the respiratory tract. This process forces the generation of these small, respirable particles in concentrations not typically produced by ordinary actions like talking or simple breathing.
Common Examples in Healthcare Settings
Many procedures are recognized for their potential to generate aerosols, often because they involve manipulating a patient’s airway or using pressurized air.
Tracheal intubation and extubation, which involve the placement and removal of a breathing tube, are common examples that can provoke coughing or gagging, creating a forceful expulsion of aerosols. Cardiopulmonary resuscitation (CPR), particularly when involving airway manipulation and manual ventilation, is also classified as an AGP due to the high-force air movement involved.
Non-invasive ventilation (NIV), including treatments like Bi-level Positive Airway Pressure (BiPAP) and Continuous Positive Airway Pressure (CPAP), forces air into the lungs. This can lead to leaks around the mask, which aerosolize respiratory secretions.
Other procedures that generate aerosols include:
- Nebulizer treatments, which turn liquid medication into a fine mist for inhalation.
- Bronchoscopy, which involves inserting a flexible tube into the airways.
- Open respiratory tract suctioning, especially if performed deep into the airway.
Significance of AGPs for Disease Transmission
The concern surrounding AGPs stems from the physical properties of the generated aerosols and the potential for a high concentration of infectious material. Because aerosols are small, they can bypass the body’s natural upper airway defenses and penetrate deep into the lower respiratory tract of an exposed person. This deep penetration increases the potential for infection, especially with pathogens like SARS-CoV-2 or influenza.
Aerosols can remain viable and suspended in the air for hours, allowing them to travel on air currents throughout a room or beyond the immediate patient area. This airborne dispersal increases the exposure risk to healthcare personnel and other patients. The proximity and duration of exposure required for the procedure mean that the healthcare worker is exposed to a higher concentration of potentially infectious particles than during routine care. This elevated risk necessitates a specialized set of infection control precautions that go beyond standard droplet precautions.
Mitigating Risk Through Environmental Controls
When an AGP must be performed, the primary strategy for risk reduction involves environmental and engineering controls to manage the air. Ideally, these procedures are performed in an Airborne Infection Isolation Room (AIIR), commonly known as a negative pressure room. This specialized room maintains a lower air pressure than the surrounding corridor, ensuring that any contaminated air is drawn into the room and cannot escape when the door opens.
The air within the negative pressure room is then exhausted safely to the outside or filtered through a High-Efficiency Particulate Air (HEPA) filter before being recirculated. Portable HEPA filtration units can also be brought into standard rooms to supplement existing ventilation and rapidly clean the air.
Procedural controls are also implemented, such as limiting the number of personnel present to only those necessary. Another control is ensuring a specific air clearance time, or “fallow time,” after the procedure is complete before the room is safely entered again without specialized protection. Specialized personal protective equipment, such as a fit-tested N95 respirator, is required for personnel to protect themselves against inhaling these fine particles.