Physiologic measurements
Subjects, at the beginning of their ED shift, were instructed to avoid
any mask use for at least 15 minutes, whilst isolated away from the
clinical area, to ensure baseline measurements were obtained under
normal breathing. Participants were then asked to wear the N95
respirator continuously and begin their ED shift. All subjects were
provided N95 respirators (Kimberly-Clark, Irving, Texas, US) for this
study. Physiological measurements, including oxygen saturation and heart
rate (HR), were captured at baseline and each hour up to 4 hours using
an O2 saturation oximeter (Welech allyn- Vital Signs
Monitor 6000, Skaneateles Falls, NY, USA). A 2CC of venous blood sample
was drawn at baseline and at 4-hours (before the N95 mask was removed),
using a syringe washed with heparin. The sample was immediately analyzed
using a gas analyzer machine (Siemens RAPIDPoint 500, Siemens Healthcare
Limited, UK). pH level, partial pressure of venous oxygen
(PvO2), partial pressure of venous carbon dioxide
(PvCO2), and bicarbonate (HCO3) level
were recorded. End‐tidal carbon dioxide (EtCO2) level
was measured through non-invasive nasal prongs (Microstream CapmoLine,
Philips, UK) representing the EtCO2 levels at 4-hours.
After ensuring the first EtCO2 level and a typical
capnography waveform, participants were asked to remove the respirator
while the EtCO2 levels were continuously monitored. The
lowest EtCO2 level at room air and the time required to
reach it were recorded.