Temperature and Humidity Variations in the Perioperative Environment

Temperature or relative humidity variations that fall outside the recommended parameters for the perioperative environment can have serious implications for patient safety and satisfaction as well as business continuity. Some pathogenic microbes can thrive in prolonged elevated humidity. Supplies and equipment in perioperative environments exposed to variations in temperature and humidity may become sources of infection or undergo alterations in function, putting patients at increased risk of harm. Other negative effects include increased costs, legal liability, and decreased patient satisfaction stemming from delays or rescheduled procedures.

Maintaining the appropriate operating room temperature during surgery is crucial for patient comfort and safety. Here are some key points related to temperature management in the operating room.

Initial Room Temperature

• The operating room is often initially set to a warmer temperature (around 70°F or 21°C) to ensure patient comfort and prevent hypothermia. This initial warmth helps patients maintain appropriate hemostasis during major surgical procedures.

The “Golden Hour”

• The first hour in the operating room is often referred to as the “golden hour.” During this time, the patient’s body temperature tends to drop by 1 to 3 degrees. After the first hour, body temperature usually stabilizes.

Adjusting Ambient Temperature

• After the golden hour, the surgical team can lower the ambient temperature for their own comfort. This adjustment helps balance the need for patient warmth with the comfort of the surgical staff.
• Remember that temperature monitoring and thermal management are critical responsibilities for anesthesia professionals. Maintaining normothermia (core temperature around 35.5°C) is essential to prevent complications during surgery.

Surgeons’ preferences for operating room temperatures can vary, but there are some general guidelines. Let’s explore the factors that influence temperature settings in operating rooms.

Comfort of OR Personnel

• The primary reason operating rooms are kept cool is for the comfort of the surgical team, especially the surgeon. Wearing a sterile gown under warm OR lights can make the surgeon quite hot, so maintaining a cooler room temperature helps keep everyone comfortable.

Standard Guidelines

• ANSI/ASHRAE/ASHE Standard 170-2013 defines recommended space temperatures for operating rooms. According to this standard, operating rooms should be designed to maintain space temperatures between 68°F to 75°F (20°C to 24°C) with space relative humidity between 20% and 60%.

Surgeon Preferences

• Surgeons may have individual preferences beyond the standard guidelines. Some surgeons expect a lower room temperature than what is stated in the guidelines. Factors like personal comfort and familiarity with specific conditions may influence their preferences.

Humidity is Important Too

Relative humidity (RH) is the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature. RH depends on the temperature and pressure of the system of interest. To acutely decrease the RH level of an operating room, either remove water vapor or increase temperature (it is unlikely that one would increase the atmospheric pressure). Cold operating rooms have a higher RH than warm operating rooms with the same absolute humidity.

The relative humidity (RH) in the operating room should be maintained at between 50% and 60% to both inhibit microorganism growth (such as fungi and bacteria) and decrease risks associated with static electricity. The RH requirements in other perioperative areas, such as the sterile stock room, is between 35% and 70% and perioperative environment is between 40% and 60%.

The rationale for the current 30% lower limit is that Low RH

• Decreases the shelf-life of certain supplies, such as biological indicators and chemical indicators, used for sterilization monitoring and electrocardiogramelectrodes.
• Increases the chance of electrostatic discharge that could harm or interfere with electromedical equipment, and potentially spark a fire (this is less of a recent issue because the risk of electrostatic discharge is less with non-flammable anesthetics and antistatic surgical gowns).

The rationale for the current 60% upper limit is that High RH

• Increases the chance of surface mold and mildew growth.
• May increase the risk of wound infections.
• Is less comfortable for operating room personnel.

It should be noted that there is sparse experimental evidence documenting the exact levels where these risks increase.

Here is a grid to assist you in keeping your perioperative areas in compliance.

Humidity and Temperature Thresholds

Area	Relative Humidity (%)	Temperature oC	Time	Corrective Action
Operating Room	Upper limit >60 Lower limit <35	Upper limit >22 Lower limit <18	2 hours	Inform facility engineers
Sterile stock area	Upper limit >70 Lower limit <35	Upper limit >25 Lower limit <18	8 hours	Conduct a risk assessment
Perioperative environment (ie: PACU, other supporting areas)	Upper limit >60 Lower limit <40	Upper limit >25 Lower limit <18	24 hours	Notify hospital management, engineers

A risk assessment may be used as evidence that the operational breach had no negative safety consequence and may also be used as a basis for future performance evaluations. The following considerations should be given when conducting a risk assessment:

• Identification or likely cause of the variation.
• The duration of the expected outage and any likely reoccurrence risk (for example, predicted weather patterns and power access).
• The duration and magnitude of the variation in temperature and humidity, if any.
• Evidence of condensation, dampness, water splashes or water damage.
• Concern for compromise of equipment function or supply sterility.
• The risk profile of the potentially affected supplies.
• The manufacturers' instruction for use (IFU) regarding supply or medication storage.
• The level of gross contamination (for example, for water intrusion, if any).
• The presence or possibility of visible environmental fungi or microorganisms.
• The effect on functionality of fixed and mobile equipment.

Summary

Maintaining optimal humidity and temperature in the operating room is essential for both patient safety and the well-being of the surgical team.  Ensure that any variations in these parameters are documented and reported.  Any surgeon requests for changes in temperature and humidity in their surgical suite must also be documented for tracking and trending purposes in the event of an adverse event (infection, fire, etc.).

References

• Management and Mitigation of Temperature and Humidity Events in the Perioperative Setting,
  Melanie S. Curless MSPH, RN, CIC, Lindsay Bow MS, CIC, Tom Lentz MS, MBA, Polly Trexler MS, CIC, Lisa L. Maragakis MD, MPH, AORN, 30 November 2021.

• ANSI/ASHRAE/ASHE Standard 170-2013
• Risk assessment and escalation of temperature or humidity variation in perioperative and sterile stock environments, NSW Government, Clinical Excellence Commission, Apil 2024.

For questions or to learn more contact the C&A team at 704-573-4535 or email us at info@courtemanche-assocs.com.