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British Hip Society (BHS) meeting, held online, 9–11 June 2021.


Orthopaedic surgical hoods rely on an intrinsic fan to force clean external air over the wearer and allow potentially contaminated and expired air to flow down and away from the surgical field. Carbon dioxide (CO2) is produced through aerobic metabolism and can potentially accumulate inside the hood. Levels above 2500ppm have been shown to affect cognitive and practical function in flight simulator studies. Maximum Health and Safety Executive (HSE) 8-hour exposure limit is 5000ppm There is a paucity of data on real-world CO2 levels experienced during arthroplasty surgery whilst wearing a hood.

CO2 levels were continuously recorded during 31 elective arthroplasties, both primary and revision. Data was collected for surgeon and assistant. Data was recorded at 0.5Hz throughout the procedure utilising a Bluetooth CO2 detector, worn inside a Stryker Flyte surgical helmet worn with a toga gown. Four surgeons contributed real time data to the study. This data was augmented with experimental data, investigating varying fan speeds and activity levels.

Median operative duration was 82 minutes (range 36–207).

The average CO2 level across all procedures was 2952ppm, with 22 of the cases having a mean above 2500ppm, but none having a mean above 5000ppm.

For each procedure, the time spent above 2500 and 5000 ppm was calculated, with the average being 68.4 % and 5.6% respectively.

The experimental data demonstrated higher CO2 levels with lower fan speed, and at higher activity levels, and levels exceeding 15000 ppm during gentle exercise. During operative cases, low fan speed cases did have a marginally higher mean CO2 value than high fan speed (3033.02 and 2903.56 respectively) but the small numbers of cases (n=10) where this data was captured limit the relevance of this difference.

The use of surgical helmets for elective orthopaedic surgery, can results in CO2 levels regularly rising to a point which may affect cognitive function. This study recommends the use of a higher fan speed where possible to minimise the risk of such CO2 levels, and recommends further research in this area.