Forced-air warming and ultra-clean ventilation do not mix: an investigation of theatre ventilation, patient warming and joint replacement infection in orthopaedics.
McGovern PD, Albrecht M, Belani KG, Nachtsheim C, Partington PF, Carluke I, Reed MR.
J Bone Joint Surg Br. 2011 Nov;93(11):1537-44.
http://web.jbjs.org.uk/content/93-B/11/1537.abstract
Sunday 29 January 2012
Saturday 19 June 2010
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.
Non-exclusive permission is granted to use the videos on this blog for non-profit, academic or educational use only, on condition that notice is given of any such use to us at orthopodresearch@gmail.com
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.
Non-exclusive permission is granted to use the videos on this blog for non-profit, academic or educational use only, on condition that notice is given of any such use to us at orthopodresearch@gmail.com
Air movement in Laminar Flow With Different Patient Warming Systems
Forced Air Warming (FAW) Versus Conductive Fabric Blankets (CFB): A Randomized Trial of Laminar Flow Disruption in Orthopedics
Laminar ventilation protects the surgical site from airborne pathogens. However, ventilation performance is fragile and can be compromised by flow obstructions and thermals. Patient warming systems represent a potential source of ventilation disruption via the waste heat they generate. For equivalent patient warming, forced air warming (FAW) generates ≈800 watts of waste heat compared to ≈100 watts with conductive fabric blankets (CFB). We compared the effects of these alternative systems on ventilation performance during a mock hip replacement surgery.
Methods: In an orthopedic operating theatre (0.5m/s airflow and 19.0ºC), a mannequin was draped in the lateral position and operated on by a surgeon and anesthesiologist at a table of comfortable height (95cm) with lights in their normal position. A replicated factorial experiment was used to randomly assign the warming system (FAW or CFB) and anesthesia screen position to no screen (drapes lying-over-patients head), half screen (1.5-meters-tented), or Full screen (2.0-meters-tented). Neutrally buoyant soap bubbles were created using a mix of helium and air and these were introduced under the drape near the mannequin’s mouth. Laminar ventilation performance was assessed by counting the number of bubbles reaching the surgical site via photography.
Results: Using bubbles present in the operative field as the assessment of contamination there was no contamination when using CFB. When using FAW there was a mean of 13.6 bubbles with a half screen, 0.6 with no screen and 0.2 with a full screen. A significant increase in laminar ventilation disruption was detected using Poisson regression for FAW versus CFB with no screen (6 versus 0 bubbles; p<0.01) and half screen set ups (146 versus 0; p<0.01); ventilation disruption was non-significant when the full anesthetic screen was used(2 versus 0; p=0.16).
Conclusion: FAW, with high waste heat, disrupts laminar ventilation performance and mobilized potentially contaminated under-drape air against the downward laminar flow and into the surgical site; CFB, with low waste heat load had no mobilizing effect. The common combination of FAW with a half anesthesia screen was associated with the highest contamination. The authors can clearly demonstrate the effect using video footage.
Laminar ventilation protects the surgical site from airborne pathogens. However, ventilation performance is fragile and can be compromised by flow obstructions and thermals. Patient warming systems represent a potential source of ventilation disruption via the waste heat they generate. For equivalent patient warming, forced air warming (FAW) generates ≈800 watts of waste heat compared to ≈100 watts with conductive fabric blankets (CFB). We compared the effects of these alternative systems on ventilation performance during a mock hip replacement surgery.
Methods: In an orthopedic operating theatre (0.5m/s airflow and 19.0ºC), a mannequin was draped in the lateral position and operated on by a surgeon and anesthesiologist at a table of comfortable height (95cm) with lights in their normal position. A replicated factorial experiment was used to randomly assign the warming system (FAW or CFB) and anesthesia screen position to no screen (drapes lying-over-patients head), half screen (1.5-meters-tented), or Full screen (2.0-meters-tented). Neutrally buoyant soap bubbles were created using a mix of helium and air and these were introduced under the drape near the mannequin’s mouth. Laminar ventilation performance was assessed by counting the number of bubbles reaching the surgical site via photography.
Results: Using bubbles present in the operative field as the assessment of contamination there was no contamination when using CFB. When using FAW there was a mean of 13.6 bubbles with a half screen, 0.6 with no screen and 0.2 with a full screen. A significant increase in laminar ventilation disruption was detected using Poisson regression for FAW versus CFB with no screen (6 versus 0 bubbles; p<0.01) and half screen set ups (146 versus 0; p<0.01); ventilation disruption was non-significant when the full anesthetic screen was used(2 versus 0; p=0.16).
Conclusion: FAW, with high waste heat, disrupts laminar ventilation performance and mobilized potentially contaminated under-drape air against the downward laminar flow and into the surgical site; CFB, with low waste heat load had no mobilizing effect. The common combination of FAW with a half anesthesia screen was associated with the highest contamination. The authors can clearly demonstrate the effect using video footage.
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