Wednesday, October 07, 2009

How Far Do Germs Travel?

BrooklynDodger(s) comment: Seems like 3 feet is the standard travel distance, for sneezes and for patient ventilation.

Chest 2009;136 998-1005

Exhaled Air Dispersion Distances During Noninvasive Ventilation via Different Respironics Face Masks

  1. David S. Hui, MD, FCCP,
  2. Benny K. Chow, MPH,
  3. Susanna S. Ng, MBChB,
  4. Leo C. Y. Chu, MBChB,
  5. Stephen D. Hall, PhD,
  6. Tony Gin, MD,
  7. Joseph J. Y. Sung, MD and
  8. Matthew T. V. Chan, MD

+ Author Affiliations

  1. From the Department of Medicine and Therapeutics (Drs. Hui, Ng, and Sung, and Mr. Chow), the Center for Housing Innovations (Mr. Chow), Institute of Space and Earth Information Science, and the Department of Anesthesia and Intensive Care (Drs. Chu, Gin, and Chan), The Chinese University of Hong Kong, Hong Kong, People's Republic of China; and the School of Mechanical Engineering (Dr. Hall), The University of New South Wales, Sydney, NSW, Australia.
  1. David S. Hui, MD, FCCP, Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Prince of Wales Hospital, 30-32 Ngan Shing St, Shatin, NT, Hong Kong, People's Republic of China; e-mail:


Background: As part of our influenza pandemic preparedness, we studied the exhaled air dispersion distances and directions through two different face masks (Respironics; Murrysville, PA) attached to a human-patient simulator (HPS) during noninvasive positive-pressure ventilation (NPPV) in an isolation room with pressure of −5 Pa.

Methods: The HPS was positioned at 45° on the bed and programmed to mimic mild lung injury (oxygen consumption, 300 mL/min; lung compliance, 35 mL/cm H2O). Airflow was marked with intrapulmonary smoke for visualization. Inspiratory positive airway pressure (IPAP) started at 10 cm H2O and gradually increased to 18 cm H2O, whereas expiratory pressure was maintained at 4 cm H2O. A leakage jet plume was revealed by a laser light sheet, and images were captured by high definition video. Normalized exhaled air concentration in the plume was estimated from the light scattered by the smoke particles.

Findings: As IPAP increased from 10 to 18 cm H2O, the exhaled air of a low normalized concentration through the ComfortFull 2 mask (Respironics) increased from 0.65 to 0.85 m at a direction perpendicular to the head of the HPS along the median sagittal plane. When the IPAP of 10 cm H2O was applied via the Image 3 mask (Respironics) connected to the whisper swivel, the exhaled air dispersed to 0.95 m toward the end of the bed along the median sagittal plane, whereas higher IPAP resulted in wider spread of a higher concentration of smoke.

Conclusions: Substantial exposure to exhaled air occurs within a 1-m region, from patients receiving NPPV via the ComfortFull 2 mask and the Image 3 mask, with more diffuse leakage from the latter, especially at higher IPAP.

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