Exhaled air dispersion during noninvasive ventilation via helmets and a total facemask

Abstract

Background: Noninvasive ventilation (NIV) via helmet or total facemask is an option for managing patients with respiratory infections in respiratory failure. However, the risk of nosocomial infection is unknown.

Methods: We examined exhaled air dispersion during NIV using a human patient simulator reclined at 45° in a negative pressure room with 12 air changes/h by two different helmets via a ventilator and a total facemask via a bilevel positive airway pressure device. Exhaled air was marked by intrapulmonary smoke particles, illuminated by laser light sheet, and captured by a video camera for data analysis. Significant exposure was defined as where there was ≥ 20% of normalized smoke concentration.

Results: During NIV via a helmet with the simulator programmed in mild lung injury, exhaled air leaked through the neck-helmet interface with a radial distance of 150 to 230 mm when inspiratory positive airway pressure was increased from 12 to 20 cm H2O, respectively, while keeping the expiratory pressure at 10 cm H2O. During NIV via a helmet with air cushion around the neck, there was negligible air leakage. During NIV via a total facemask for mild lung injury, air leaked through the exhalation port to 618 and 812 mm when inspiratory pressure was increased from 10 to 18 cm H2O, respectively, with the expiratory pressure at 5 cm H2O.

Conclusions: A helmet with a good seal around the neck is needed to prevent nosocomial infection during NIV for patients with respiratory infections.

Figure 1 –

A-C, Application of noninvasive ventilation via the Sea-Long helmet (A), StarMed CaStar R helmet (B), and the Respironics total face mask (C) on the human patient simulator (HPS). The HPS represented a 70-kg adult man sitting on a 45°-inclined hospital bed and was programmed to mimic normal breathing, mild lung injury, and severe lung injury. Exhaled air, marked by the smoke particles, is illuminated by the laser light-sheet, with dispersion through the neck interface of the Sea-Long helmet (A) and through the exhalation port of the total face mask attached to the HPS (C). No significant leakage was noted with the StarMed CaStar R helmet.

Figure 2 –

The room measured 6.1 (width) × 7.4 (depth) × 3.0 (height) m. The digital camera and the laser device 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. Fresh air diffusers, as air inlet, were mounted on the ceiling. The negative pressure of the isolation room was produced by the air exhausts located near the floor.

Figure 3 –

A-C, Exhaled air dispersions through the neck interface during application of noninvasive ventilation via a servoventilator with double limb circuit and filters to the HPS using the Sea-Long head tent. EPAP was maintained at 10 cm H₂O, and IPAP was increased from 12 to 14, 18, and 20 cm H₂O gradually in four experiment settings. With normal lung condition, the mean (± SD) exhaled air dispersion distances with 20% normalized smoke concentration were 170 ± 39 mm, 200 ± 23 mm, 219 ± 32 mm, and 270 ± 20 mm, respectively. With mild lung injury, the exhaled air dispersion distances were 150 ± 12 mm, 200 ± 17 mm, 210 ± 28 mm, and 230 ± 37 mm, respectively. With severe lung injury, the corresponding values were 150 ± 7 mm, 160 ± 17 mm, 170 ± 21 mm, and 180 ± 22 mm, respectively. EPAP = expiratory positive airway pressure; IPAP = inspiratory positive airway pressure. See Figure 1 legend for expansion of other abbreviation.

Figure 4 –

A-C, Exhaled air dispersions during application of noninvasive ventilation using a bilevel positive airway pressure device with a single circuit to the HPS via the Respironics total facemask. IPAP was increased in three experiment settings from 10 to 14 and 18 cm H₂O, respectively, while maintaining EPAP at 5 cm H₂O. With normal lung condition, the mean (± SD) exhaled air dispersion distances with 20% normalized smoke concentration were 693 ± 83 mm, 704 ± 57 mm, and 916 ± 35 mm, respectively. With mild lung injury, the exhaled air dispersion distances were 618 ± 67 mm, 698 ± 48 mm, and 812 ± 65 mm, respectively. With severe lung injury, the corresponding values were 580 ± 72 mm, 638 ± 53 mm, and 710 ± 103 mm, respectively. Se Figure 1 and 3 legends for expansion of abbreviations.