NEW YORK (Reuters Health) -The masks used for non-invasive positive-pressure ventilation (NPPV) allow dispersion of exhaled air within a 1-meter region from the patient, which could cause contamination of the hospital room, according to a report in the October Chest.

"Healthcare workers should take adequate precautions when providing noninvasive ventilatory support to patients with pneumonia of unknown etiology complicated by respiratory failure," Dr. David S. Hui from Prince of Wales Hospital, Hong Kong, People’s Republic of China told Reuters Health.

As part of their influenza pandemic preparedness, Dr. Hui and colleagues examined the directions and dispersion distances of exhaled air during application of NPPV via the ComfortFull 2 and Image 3 masks attached to a human-patient simulator.

The maximum dispersion distance of smoke particles from the ComfortFull 2 mask reached 0.65 meter, with a high concentration reaching 0.36 meter, the authors report.

The maximum dispersion distance of exhaled air increased as the inspiratory positive airway pressure (IPAP) increased, with low-concentration air reaching 0.85 meter and high-concentration air reaching 0.51 meter when IPAP reached 18 cm water.

Exhaled air leakage was much more diffuse with the Image 3 mask connected to the Whisper Swivel (to prevent carbon dioxide rebreathing), with low-concentration exhaled air reaching 0.95 meter toward the end of the bed at an IPAP of 10 cm water.

At an IPAP of 18 cm water, low-concentration exhaled air from the Image 3 mask dispersed diffusely throughout most of the isolation room, medium-concentration air reached 0.8 meter, and high-concentration air extended 0.34 meter from the center of the mask along the median sagittal plane of the simulator.

"Avoid high pressures if noninvasive ventilation is needed for patients with respiratory failure due to unknown cause of pneumonia," Dr. Hui advised. "Avoid use of masks which require connection to exhalation device which may disperse exhaled air diffusely."

"NPPV should be provided in an adequately-ventilated single room and addition of an expiratory port with a bacterial/viral filter can reduce aerosol emission," Dr. Hui added.

Chest 2009;136:998-1005.