Share this article on:

Patient Warming Excess Heat: The Effects on Orthopedic Operating Room Ventilation Performance

Belani, Kumar G. MBBS, MS*; Albrecht, Mark MStat, MBA, BSME; McGovern, Paul D. BSc, MBBS, MRCS, PGCME, FHEA; Reed, Mike MBBS, MD, FRCS (T&O)§; Nachtsheim, Christopher PhD

doi: 10.1213/ANE.0b013e31825f81e2
Patient Safety: Research Report

BACKGROUND: Patient warming has become a standard of care for the prevention of unintentional hypothermia based on benefits established in general surgery. However, these benefits may not fully translate to contamination-sensitive surgery (i.e., implants), because patient warming devices release excess heat that may disrupt the intended ceiling-to-floor ventilation airflows and expose the surgical site to added contamination. Therefore, we studied the effects of 2 popular patient warming technologies, forced air and conductive fabric, versus control conditions on ventilation performance in an orthopedic operating room with a mannequin draped for total knee replacement.

METHODS: Ventilation performance was assessed by releasing neutrally buoyant detergent bubbles (“bubbles”) into the nonsterile region under the head-side of the anesthesia drape. We then tracked whether the excess heat from upper body patient warming mobilized the “bubbles” into the surgical site. Formally, a randomized replicated design assessed the effect of device (forced air, conductive fabric, control) and anesthesia drape height (low-drape, high-drape) on the number of bubbles photographed over the surgical site.

RESULTS: The direct mass-flow exhaust from forced air warming generated hot air convection currents that mobilized bubbles over the anesthesia drape and into the surgical site, resulting in a significant increase in bubble counts for the factor of patient warming device (P < 0.001). Forced air had an average count of 132.5 versus 0.48 for conductive fabric (P = 0.003) and 0.01 for control conditions (P = 0.008) across both drape heights. Differences in average bubble counts across both drape heights were insignificant between conductive fabric and control conditions (P = 0.87). The factor of drape height had no significant effect (P = 0.94) on bubble counts.

CONCLUSIONS: Excess heat from forced air warming resulted in the disruption of ventilation airflows over the surgical site, whereas conductive patient warming devices had no noticeable effect on ventilation airflows. These findings warrant future research into the effects of forced air warming excess heat on clinical outcomes during contamination-sensitive surgery.

Published ahead of print July 19, 2012.

From the *Department of Anesthesiology and Carlson School of Management, University of Minnesota, Minneapolis, Minnesota; Bioinformatics, National Marrow Donor Program, Minneapolis, Minnesota; Medway Maritime Hospital, Kent, United Kingdom; and §Northumbria Healthcare NHS Foundation Trust, Ashington, Northumberland, United Kingdom.

Accepted for publication April 16, 2012.

Published ahead of print July 19, 2012.

Supported by Augustine Temperature Management, Eden Prairie, MN.

See Disclosures at end of article for Author Conflicts of Interest.

Reprints will not be available from the authors.

Address correspondence to Mark Albrecht, MBA, MStat, BSME, National Marrow Donor Program, 3001 Broadway St. NE, Suite 500, Minneapolis, MN 55413. Address e-mail to

© 2013 International Anesthesia Research Society