Carbon Dioxide Levels Under the Hood

Study examines breathing air quality during arthroplasty

An orthopaedic surgeon wearing a surgical gown, gloves, and a hood during joint replacement surgery is a familiar image. However, the safety of some of this personal protective wear has yet to be proven, according to the authors of Scientific Poster P014. Their study examined the air quality under the hood, in particular the carbon dioxide (CO2) levels.

Because CO2 displaces oxygen, breathing air rich in CO2 can result in headache, malaise, dizziness, and discomfort. According to the Occupational Safety and Health Administration (OSHA), the permissible exposure limit is 5,000 parts per million (ppm) over an 8-hour workday, which is equivalent to 0.5 percent CO2 by volume of air. Although miners, brewers, carbonated beverage workers, and grain elevator workers are most at risk for breathing CO2, orthopaedic surgeons wearing surgical hooded protection shields may rebreathe their own exhalations, resulting in elevated CO2 levels.

For this study, six healthy individuals (four male, two female) donned standard surgical gowns, gloves, and hooded protection shields. The hood fans were set at the highest setting. Levels of oxygen and CO2 were continuously measured using mass spectrometry. A cycle ergometer configured for upper body exercise at fixed workloads of 12 watts (W) and 25W was used to simulate the physical activity during a total joint arthroplasty procedure.

Inspired gas levels were measured at rest, at 12W, and at 25W activity levels. In addition, the battery was unplugged and measurements taken of how long it took for CO2 to reach 0.5 percent and 1.0 percent air volume.

As could be expected, physical activity had a significant effect on the concentration of CO2. Similarly, turning the fan off resulted in a significant increase in the inspired CO2 concentration, regardless of whether the individual was at rest or active. After the fan was turned off, inspired CO2 rapidly reached the 0.5 percent and 1.0 percent air concentrations, but the time was highly variable. For example, it took approximately 12 seconds (± 9 seconds) for CO2 to reach the 0.5 percent concentration, and approximately 26 seconds (± 15 seconds) for levels to reach the 1.0 percent concentration. Restoring air to safe concentrations after the fan was off took 20 seconds (± 37 seconds).

According to the authors, in the best case scenario (fan at the highest setting and physiologically healthy, young individuals), CO2 levels remained with OSHA standards at all physical levels. If the fan malfunctioned, however, CO2 levels would rapidly exceed OSHA standards, posing health risks to providers. They call for more investigations on intraoperative use, prolonged use, lower fan settings, and older individuals.

Coauthors for P014 “Monitoring Carbon Dioxide Levels in Modern Total Joint Hoods: Are They Safe?” are Michael J. Lim, MD; Suhani Patel, MSc; Steven Copp, MD; Adam Rosen, DO; Gordon K. Prisk, PhD; and John West, MD, PhD.

Details of the authors’ disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at