Operating rooms are kept cold, typically between 68°F and 77°F (20–25°C), for a combination of reasons that protect patients from infection, keep surgical staff comfortable under heavy gowns and hot lights, and help sensitive equipment run reliably. That temperature range, set by the Association of periOperative Registered Nurses (AORN) and reinforced by federal quality measures, is a deliberate tradeoff: the room stays cool enough to benefit the surgical team and reduce bacterial growth, while warming devices keep the patient’s core temperature safe.
Cooler Air Slows Bacterial Growth
Bacteria thrive in warm, humid environments. Their enzymes work fastest at an optimal temperature, driving rapid metabolism and reproduction. When air temperature drops below that sweet spot, enzyme activity slows, metabolism decreases, and bacteria reproduce more sluggishly. In an operating room where a patient’s body cavity may be open for hours, even a modest reduction in airborne microbial activity matters. Keeping the room cool is one layer of infection control alongside filtered airflow, sterile drapes, and antiseptic technique.
Surgical Staff Work Under Intense Heat
Surgeons and nurses spend hours in sterile gowns, gloves, masks, and sometimes lead aprons for radiation protection. Overhead surgical lights radiate significant heat directly onto the team. Robotic surgical systems and other powered equipment add to the thermal load in the room. All of this means the people doing the most physically and mentally demanding work are essentially wearing insulated layers under heat lamps.
A study comparing surgical staff performance at around 75°F versus 87°F during burn surgeries (which require higher room temperatures to protect exposed patients) found telling results. At the higher temperature, staff experienced increased heart rate, higher core body temperature, and greater fluid loss. They also reported significantly more mental demand, physical demand, frustration, discomfort, and fatigue. Interestingly, their manual dexterity and cognitive accuracy did not measurably decline at the hotter temperature, suggesting the human body compensates in the short term. But the increased strain and subjective workload are real concerns for longer procedures, where accumulated fatigue could eventually affect performance.
Keeping the room in the low 70s helps the surgical team stay focused and physically comfortable across operations that can last many hours.
The Patient Pays the Price
The obvious downside of a cold OR is that patients get cold. Under general anesthesia, your body loses its normal ability to regulate temperature. Anesthetic drugs dilate blood vessels, pushing warm blood from your core to your skin, where heat escapes quickly. Add in an open surgical site, cold IV fluids, and exposed skin, and core temperature can drop fast.
This isn’t just uncomfortable. Perioperative hypothermia, defined as a core temperature below about 95°F (35°C), carries serious risks. A systematic review published in the European Medical Journal found that in patients who didn’t receive active warming, the risk of surgical site infection increased by 221% for every degree Celsius their temperature fell below that 35°C threshold. Hypothermia also impairs blood clotting, increases blood loss, slows drug metabolism, and prolongs recovery time.
That’s why surgical teams actively warm patients rather than warming the room. Forced-air warming blankets are the most widely used solution. These devices blow heated air through a disposable blanket draped over parts of the body not involved in the surgery. IV fluids and irrigation solutions are also warmed to about 100°F (38°C) before entering the body. Sterile drapes cover as much exposed skin as possible. Together, these measures maintain the patient’s core temperature while allowing the room itself to stay cool.
Equipment Runs Better When Cool
Modern operating rooms contain millions of dollars in heat-sensitive technology. Robotic surgical systems, high-definition cameras, powered instruments, and monitors all generate heat during operation and perform best within controlled temperature ranges. Thermal management for robotic surgical systems is considered crucial for both surgical efficiency and system reliability. Cooling pathways built into these machines work more effectively when ambient air temperature is already low, reducing the risk of overheating during long procedures.
Humidity matters too. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) requires operating room humidity to stay between 20% and 60%. Keeping the room cool makes it easier to control humidity within that window, which in turn reduces the risk of electrostatic discharge near oxygen-rich environments and flammable surgical gases.
Some Surgeries Need Warmer Rooms
Not every OR runs at the same temperature. Certain patients and procedures call for intentionally warmer environments. Burn surgery is a common example: patients with large areas of damaged or missing skin lose heat extremely fast, so rooms may be heated to 87°F or higher. Pediatric and neonatal surgeries also tend to use warmer settings because small bodies lose heat much more quickly relative to their size.
Cardiac surgery on children presents a more complex picture. Some pediatric heart procedures historically used deep cooling to protect the brain and organs during periods when blood flow is temporarily stopped. But clinicians have increasingly moved toward warmer approaches to reduce complications from extreme cold, keeping body temperatures closer to 86–90°F (30–32°C) during critical phases of the operation rather than cooling patients down as aggressively as in the past.
Why It Feels So Cold to You
If you’ve ever been wheeled into an OR and felt a shock of cold air, there’s a reason it hits harder than a similarly cool room would in everyday life. You’re typically wearing only a thin hospital gown. You may already be anxious, which can heighten your perception of cold. Pre-operative fasting means your metabolism is running lower than usual. And if you’ve already received sedation or an IV, your blood vessels may be dilating before you even reach the table.
Once anesthesia begins, your body essentially stops shivering and loses its ability to constrict blood vessels to conserve heat. The combination of a cool room, minimal clothing, open body cavities, and a pharmacologically disabled thermostat is why surgical teams treat temperature management as an active, ongoing task throughout the procedure, not something they leave to chance.