Real time monitoring of carbon dioxide levels in surgical helmet systems worn during hip and knee arthroplasty.

Background: Orthopaedic surgical helmet systems (SHS) rely on an intrinsic fan to force clean external air over the wearer. Carbon dioxide (CO) is produced through aerobic metabolism and can potentially accumulate inside the SHS. Levels above 2500 ppm have previously been shown to affect cognitive and practical function. Maximum Health and Safety Executive (HSE) 8-h exposure limit is 5000 ppm. There is a paucity of data on real-world CO levels experienced during arthroplasty surgery whilst wearing a SHS.

Objectives: To determine intra-operative levels of CO experienced within SHS.

Methods: CO levels were continuously recorded during 30 elective arthroplasties, both primary and revision. Data was recorded at 0.5Hz throughout the procedure utilising a Bluetooth CO detector, worn inside a surgical helmet worn with a toga gown. Five surgeons contributed real time data to the study.

Results: The average CO level across all procedures was 3006 ppm, with 23 of the cases measured within the surgeons' helmets having a mean above 2500 ppm, but none having a mean above 5000 ppm. For each procedure, the time spent above 2500 and 5000 ppm was calculated, with the means being 72.6 % and 5.4 % respectively. Minimum fan speed was associated with only a marginally higher mean CO value than maximum fan speed.

Discussion: The use of surgical helmet systems for elective orthopaedic surgery, can result in CO levels regularly rising to a point which may affect cognitive function.

Conclusion: Further research is needed to corroborate these findings however, we recommend that future designs of SHS include active management of exhaust gases, possibly returning to Charnley's original design principles of the body exhaust system.