On 2015 Feb 03, David Mage commented:

From the perspective of a chemical engineer, a most critical parameter for calculating the extent of rebreathing of exhalations with high CO2 and low O2 from the presence of a facial obstruction is the exact millimeters of clearance, if any, between the infant's nostrils and the obstruction. Because the usual natural practice of the shocked discoverer of an apparently moribund infant is to immediately pick the infant up to revive it, that critical measurement is lost forever.

On 2015 Feb 03, David Mage commented:

From the perspective of a chemical engineer, a most critical parameter for calculating the extent of rebreathing of exhalations with high CO2 and low O2 from the presence of a facial obstruction is the exact millimeters of clearance, if any, between the infant's nostrils and the obstruction. Because the usual natural practice of the shocked discoverer of an apparently moribund infant is to immediately pick the infant up to revive it, that critical measurement is lost forever.