Air Movement in Laminar Flow with Different Patient Warming Systems

This demonstration was set up in an orthopaedic operating theatre under a laminar flow operating canopy. A mannequin was used in place of a patient, covered with a forced air warming blanket under sterile surgical drapes. Lights were positioned for the best view of the surgical site.

Airflow was visualised using neutral density helium soap bubbles. These remain suspended still in air unless ambient airflow moves them - allowing them to be used to see air currents as they move.

There is sound with this video. As the clips are high definition it may take a few minutes for them to load on a slow connection. Pausing them until the progress bar at the bottom of the player is full will reduce stuttering during playback.

The video clip shows a half size anaesthetic screen and the soap bubbles originating in dirty air at the patients head. The appearance of the bubbles at the surgical field when the forced air warming blanket is on is a cause for concern.



Critical to this is the position of the lights - air appears to circulate in a turbulent fashion under the "shadow" of lights or other obstructions such as light booms. If lights are placed above a wound then the wound is not in laminar flow.





We ran a series of experiments looking at the amount of dirty air that travelled from the "patient's" head to the surgical site. We used a forced air warming blanket, or conductive warming blankets, with differing heights of anaesthetic screen.

The results are available in the previous post - see below. In summary forced air warming with a half-height anaesthetic screen (the video clip above) showed the most contamination. Having no screen or a 2 metre screen was better. Using conductive warming there was no such contamination in any set up.



We now recommend using conductive warming when we can - we don't yet have enough for all orthopaedic procedures. Taping a large anaesthetic screen directly to the canopy appears to avoid contamination and this seems to work even when using forced air warming. Logically however it means that you should place a very high screen for all cases if you use forced air warming - most hospitals currently tend to only do this for joint replacement. Light positioning appears to be critical. Ideally you should avoid it being over the wound but, this is difficult and we are still working on an ideal position. At the start of the case, when setting up and draping, it seems important to put the lights safely out of the way - not over kit or patients.


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