Surgical Helmets Linked to Elevated CO₂ During Arthroplasty

Key Highlights

• Mean intra-helmet carbon dioxide was 3,401 ppm across 132 hip and knee arthroplasties performed by 9 surgeons.
• Mean concentrations exceeded 2,500 ppm in 71.2% of cases; peak concentrations reached at least 5,000 ppm in 53.8% of cases.
• Low fan speed, absence of a mask, and reusable green gowns were independently associated with higher mean concentrations.

Surgical helmet systems permitted substantial carbon dioxide (CO₂) accumulation during hip and knee arthroplasty, according to an abstract for the American Association of Hip and Knee Surgeons (AAHKS) Annual Meeting 2026. After multivariable analysis, mean concentrations did not differ significantly among helmet systems, while several use factors were independently associated with higher concentrations.

The researchers noted that contemporary positive-pressure helmets circulate filtered air without a dedicated pathway for actively removing exhaled gases. This differs from Charnley’s original body exhaust suit, which used negative-pressure suction to remove contaminated air. The investigators hypothesized that intra-helmet CO₂ would frequently exceed 2,500 ppm, a threshold the abstract described as linked to cognitive performance changes.

The single-center, prospective observational study measured real-time intra-helmet CO₂ during 132 procedures performed by 9 surgeons, each of whom trialed multiple helmet systems. Outcomes included case-level mean, median, and peak concentrations and the percentage of hood time at or above 2,500 and 5,000 ppm. Analyses included ANOVA, Kruskal-Wallis and Fisher exact testing, and multivariable linear regression adjusting for helmet system, fan speed, mask status, gown type, procedure type, hood time, surgeon body mass index, and exercise level.

Study Findings

Mean intra-helmet CO₂ was 3,401 ± 1,318 ppm, and the maximum recorded concentration was 15,202 ppm. Concentrations were at least 2,500 ppm for 68.3% ± 35.3% of the hood time. Mean concentrations exceeded 2,500 ppm in 71.2% of cases, while peak concentrations reached at least 5,000 ppm in 53.8%.

Compared with high fan speed, low fan speed was independently associated with a 2,567-ppm higher mean concentration (P < .001). No mask was associated with a 930-ppm higher mean concentration (P < .001), and reusable green gowns were associated with a 634-ppm higher mean concentration than disposable blue gowns (P = .004).

Clinical Implications

According to the study authors, helmet model drove intra-helmet CO₂ exposure less than modifiable use factors, particularly fan speed. They described the accumulation as an underrecognized physiologic consideration and supported further evaluation of ventilation strategies that preserve protective function while reducing CO₂ accumulation.

Expert Commentary

“These findings highlight an underrecognized physiologic consideration and support further evaluation of ventilation strategies that preserve protective function while minimizing intra-helmet CO₂ accumulation,” the researchers concluded.

Reference

Premkumar A, Chowdary A, Muffly B, et al. The hidden cost of protection: surgical helmets expose arthroplasty surgeons to high CO2 levels. Paper #11. Abstract for: American Association of Hip and Knee Surgeons Annual Meeting; 2026.