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Exhaled Air Dispersion During Oxygen Delivery Via a Simple Oxygen Mask^*

^* From the Stanley Ho Centre for Emerging Infectious Diseases (Drs. Hui and Sung), and the Departments of Medicine and Therapeutics (Dr. Ng), Anesthesia and Intensive Care (Drs. Chan and Gin), and Architecture (Mr. Chow), The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People’s Republic of China; and the School of Mechanical Engineering (Dr. Hall), The University of New South Wales, Sydney, NSW, Australia.

Correspondence to: 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, New Territories, Hong Kong, People’s Republic of China; e-mail: dschui{at}cuhk.edu.hk

Abstract

Background: Pneumonia viruses such as influenza may potentially spread by airborne transmission. We studied the dispersion of exhaled air through a simple oxygen mask applied to a human patient simulator (HPS) during the delivery of different oxygen flow in a room free of air currents.

Methods: The HPS represented a 70-kg adult male individual in a semi-sitting position on a hospital bed inclined at 45°. A simple oxygen mask was fitted to the HPS in the normal fashion. The head, neck, and internal airways of the HPS were configured to allow realistic airflow modeling in the airways and around the face. The HPS was programmed to breathe at a respiratory rate of 14 breaths/min with a tidal volume of 0.5 L. Airflow was marked with intrapulmonary smoke for visualization. A leakage jet plume was revealed by a laser light-sheet, and images were captured by high-resolution video. Smoke concentration in the exhaled plume was estimated from the total light intensity scattered by smoke particles.

Findings: A jet plume of air leaked through the side vents of the simple oxygen mask to lateral distances of 0.2, 0.22, 0.3, and 0.4 m from the sagittal plane during the delivery of oxygen at 4, 6, 8, and 10 L/min, respectively. Coughing could extend the dispersion distance beyond 0.4 m.

Conclusion: Substantial exposure to exhaled air occurs generally within 0.4 m from patients receiving supplemental oxygen via a simple mask. Health-care workers should take precautions when managing patients with community-acquired pneumonia of unknown etiology that is complicated by respiratory failure.

Key Words: dispersion • exhaled air • influenza • oxygen therapy • severe acute respiratory syndrome