Exhaled air dispersion distances during noninvasive ventilation via different Respironics face masks

Abstract

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 degrees on the bed and programmed to mimic mild lung injury (oxygen consumption, 300 mL/min; lung compliance, 35 mL/cm H(2)O). Airflow was marked with intrapulmonary smoke for visualization. Inspiratory positive airway pressure (IPAP) started at 10 cm H(2)O and gradually increased to 18 cm H(2)O, whereas expiratory pressure was maintained at 4 cm H(2)O. 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 H(2)O, 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 H(2)O 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.

Figure 1

The room dimension and equipment layout inside the negative-pressure isolation room. The camera (arrow a) and the laser device (arrow b) were positioned along the coronal plane on the left side of the patient and along the sagittal plane of the patient at the end of the bed, respectively. Two fresh air diffusers, serving as air inlets, were mounted on the ceiling (arrow c). The negative pressure of the isolation room was provided by the air exhausts positioned at the bottom of the bed (arrow d).

Figure 2

A: a ComfortFull 2 full face mask with three pairs of exhalation diffusers (arrow a) for quiet exhalation and an entrainment valve (arrow b) that provides quick access to room air if the pressure falls below 3 cm H₂O. B: an Image 3 full face mask, with an entrainment valve (arrow a) that provides quick access to room air if the pressure falls below 3 cm H₂O connected to a Whisper Swivel exhalation port (arrow b).

Figure 3

A: the ComfortFull 2 mask was attached to a high-fidelity HPS. The photograph was taken with the room light switched off and revealed exhaled smoke dispersion through the exhalation diffuser of the mask attached to the HPS. B: B to D refer to data related to the ComfortFull 2 mask. The x-axis represents the distance from the center of the mask along the median sagittal plane, whereas the y-axis represents the vertical distance from the center of the mask. Normalized concentration in the plume was estimated by computer analysis from the light scattered by smoke particles. Shown at IPAP of 10 cm H₂O and EPAP of 4 cm H₂O. The white color code and the red color code represented regions consisting of 100% and 70%, respectively, of exhaled air, whereas the background of the isolation room (deep blue code) was essentially free of exhaled air. C: at IPAP of 14 cm H₂O. D: at IPAP of increased to 18 cm H₂O.

Figure 4

Data related to the Image 3 full face mask. A: at IPAP of 10 cm H₂O. B: at IPAP of 10 to 14 cm H₂O. C: at IPAP of 18 cm H₂O.

Figure 5

Maximum exhaled air dispersion distances during the application of NPPV to the HPS via different face masks. In the study of the ResMed Ultra Mirage mask, tidal volume was set at 500 mL, and a respiratory rate of 14 breaths/min was used to represent a patient with very mild lung injury. For the study of Respironics masks, tidal volume was set as 300 mL, and a respiratory rate of 25 breaths/min was used to represent a patient with mild lung injury., EPAP was maintained at 4 cm H₂O throughout the studies.