What is the difference between positive and negative pressure isolation in a clinical setting?

Difference Between Positive and Negative Pressure Isolation

Negative pressure isolation rooms contain airborne pathogens inside the room by creating lower air pressure than surrounding areas, protecting healthcare workers and other patients from infectious diseases like tuberculosis and COVID-19, while positive pressure rooms protect immunocompromised patients by preventing external contaminants from entering the room. 1, 2

Negative Pressure Isolation (Airborne Infection Isolation Rooms)

Primary Purpose and Mechanism

• Negative pressure rooms prevent the spread of contagious airborne pathogens from room to room by creating lower air pressure inside the patient's room compared to adjacent areas 1
• Air flows INTO the room from surrounding areas and is exhausted directly outside or filtered through HEPA filters before recirculation, preventing pathogen escape 1
• The ventilation system allows extra air to enter the isolated room by differential pressure, maintaining containment of infectious droplet nuclei 1

Clinical Indications

• Required for patients with airborne infectious diseases including tuberculosis, measles, and COVID-19 1
• Mandatory for aerosol-generating procedures (tracheal intubation, bronchoscopies, non-invasive positive pressure ventilation) on patients with COVID-19 or other airborne pathogens 1
• Essential during SARS and similar epidemic situations to prevent cross-contamination 1

Technical Specifications

• Minimum pressure differential of 2.5 Pa (0.01 inches of water) in US standards, though some countries require up to 15 Pa for enhanced containment 1, 3
• Minimum of 6-12 air changes per hour required, with WHO recommending at least 12 air changes per hour for COVID-19 1
• Pressure should be monitored at the bottom of the door where airflow enters the room 1
• HEPA filtration with 99.97% removal efficiency for particles ≥0.3 μm diameter must be used if air is recirculated 1

Monitoring Requirements

• Daily pressure checks required while rooms are actively used for isolation 1
• Monthly verification needed for rooms not currently in use but available for isolation 1
• Pressure-sensing devices should incorporate time-delayed audible warnings to account for door opening without false alarms 1
• Visual smoke tube testing can verify negative pressure when door is closed 1

Positive Pressure Isolation (Protective Environment Rooms)

Primary Purpose and Mechanism

• Positive pressure rooms protect immunocompromised patients by preventing external contaminants from entering the patient's environment 2
• Air pressure inside the room is higher than surrounding areas, causing air to flow OUT of the room when doors open 2
• Prevents environmental or airborne pathogens from reaching vulnerable patients 2

Clinical Indications

• Patients requiring protection from infections due to immunocompromised status 2
• Bone marrow transplant recipients and severely neutropenic patients 2

Critical Operational Differences

Airflow Direction

• Negative pressure: Air flows INTO the room from corridors (higher to lower pressure) 1
• Positive pressure: Air flows OUT of the room into corridors (higher to lower pressure) 2

Protection Target

• Negative pressure protects everyone OUTSIDE the room from the infectious patient inside 1, 2
• Positive pressure protects the vulnerable patient INSIDE the room from external pathogens 2

Impact of Healthcare Provider Movement

• Provider traffic through negative pressure rooms significantly reduces containment effectiveness, with particle escape increasing during door opening and movement 3
• Containment improves with increasingly negative pressure differential (2.5 Pa vs 11 Pa vs 20 Pa tested) 3
• Anteroom use is critical for limiting particle escape, especially during provider movement 3

Alternative Pressure Rooms

Concept and Limitations

• Some facilities have explored "alternative pressure rooms" with ventilation systems capable of switching between positive and negative pressure based on patient needs 2
• Current evidence shows unenthusiastic adoption despite no scientific evidence against their use, likely due to complexity and potential for operational errors 2

Common Pitfalls to Avoid

For Negative Pressure Rooms

• Never assume the room maintains negative pressure without verification - pressure can vary at different door locations (negative at middle, positive at bottom) 1
• Do not use pressure-sensing devices that cannot measure pressures as low as 0.001 inch of water, as this necessitates impractically high negative pressures 1
• Avoid excessive provider traffic through isolation rooms as this dramatically reduces containment effectiveness even with proper pressure differentials 3
• Do not recirculate air from TB isolation rooms without HEPA filtration achieving 99.97% efficiency 1

For Both Systems

• Never rely solely on pressure differential without adequate air changes per hour - both parameters are essential for effective isolation 1
• Do not assume isolation rooms are functioning properly without regular monitoring and verification 1