A Bair Hugger is a medical warming device used during surgery to keep your body temperature from dropping too low. It works by blowing warm air through a lightweight, disposable blanket draped over parts of your body not involved in the operation. If you’re having surgery soon and your care team mentioned a Bair Hugger, this is what to expect.
How the Device Works
The system has two main parts: a warming unit (about the size of a small suitcase) and a single-use inflatable blanket. The warming unit heats air and pushes it through a rubber hose into the blanket, which has tiny perforations that let the warm air flow evenly across your skin. This process, called convective warming, transfers heat from the moving air to your body’s surface, keeping your core temperature stable while you’re under anesthesia.
Modern units like the Model 775 offer several temperature settings. The lowest blows air at roughly 90°F (32°C), a middle setting runs at about 100°F (38°C), and the highest reaches around 109°F (43°C). There’s also an ambient mode that circulates air just slightly warmer than room temperature. Your anesthesia team selects the setting based on how your body is responding during the procedure. Built-in safety systems automatically shut the heater and blower off if the air temperature climbs too high, triggering both a visual warning light and an audible alarm.
Why Surgeons Use It
Your body loses heat surprisingly fast during surgery. Anesthesia impairs your body’s natural temperature regulation, the operating room is kept cool for the surgical team, and large areas of skin or internal tissue may be exposed to open air. When core temperature drops below 96.8°F (36°C), a condition called intraoperative hypothermia, the consequences can be serious.
Hypothermia during surgery impairs your blood’s ability to clot, increases bleeding, and raises the risk of surgical site infection by two to three times. It also slows the breakdown of anesthetic drugs, which can delay your wake-up and extend your time in the recovery room. In more severe cases, it can trigger cardiovascular complications. All of this adds up to longer hospital stays, higher costs, and worse outcomes. Forced-air warming is the most widely used method to prevent these problems, and the Bair Hugger is the dominant brand in this category.
What It Feels Like as a Patient
If you’ve ever used a heated blanket at home, the sensation is similar but gentler. The blanket inflates slightly as warm air fills it, creating a cushion of steady warmth over your legs, torso, or upper body, depending on the type of surgery. You’ll typically feel the blanket placed on you shortly before or after anesthesia is administered. Because you’re sedated for the procedure itself, you won’t notice it during surgery. Many patients do feel its warmth in the pre-op area and again in recovery, where it’s often used to help you rewarm comfortably.
The Infection Controversy
The Bair Hugger has been at the center of a long-running debate in orthopedic surgery. The concern centers on what happens to the warm air after it passes through the blanket. That exhaust heat rises from beneath the surgical drapes and can disrupt the carefully controlled airflow patterns in the operating room, potentially carrying bacteria from the floor or surrounding environment into the sterile surgical field.
This matters most during joint replacement surgery. Unlike soft tissue infections, which typically require a massive number of bacteria to take hold, a prosthetic joint infection can start from a single airborne bacterium landing on an implant. A multicenter study published in Orthopedic Reviews found that when three hospitals stopped using forced-air warming during joint replacements and switched to an air-free warming alternative, prosthetic joint infection rates dropped by 78%. A separate large retrospective study reported a 74% reduction in joint infections after making the same switch. At least seven peer-reviewed studies have confirmed that waste heat from forced-air warming systems contaminates the sterile surgical field.
This does not mean the device is dangerous in all surgeries. The infection risk appears most significant in procedures involving implanted materials, where even minimal contamination can lead to a devastating infection. For general surgeries, soft tissue procedures, and operations that don’t involve permanent implants, the warming benefits are widely considered to outweigh the airflow concerns. Some hospitals have responded by restricting forced-air warming use specifically during joint replacements while continuing to use it for other operations.
Alternatives to Forced-Air Warming
Several other warming methods exist, and your surgical team may choose one based on the type of procedure. Conductive warming pads sit beneath you on the operating table and transfer heat directly through contact with your skin, with no air circulation involved. Resistive heating blankets use electric elements similar to a home heating pad. Warmed intravenous fluids can also help maintain core temperature from the inside. Each approach has trade-offs in effectiveness, cost, and practicality, but the key advantage of air-free alternatives is that they don’t disturb operating room airflow patterns.
For most patients, the warming method used during surgery isn’t something you need to choose yourself. But if you’re scheduled for a joint replacement or another procedure involving an implant, it’s reasonable to ask your surgical team which warming method they plan to use and whether they’ve considered the airflow concerns associated with forced-air systems.