The R2D ReBreather uses a circular gas flow through twin can- isters of soda lime as the scrubber. The soda lime is comprised of granules of calcium hydroxide with a small percentage of sodium hydroxide, and an added dye which changes colour to indicate any granule deterioration. Soda lime is a very effective absorber of CO2
and is widely use in anaesthetic respirators. Although it is
more bulky than lithium hydroxide, it is cheaper, and the associ- ated dye provides a simple safety check on its efficacy. .
The biggest problem with any DeBreather is the need to main- tain a closed gas system. No external air can be allowed into the closed system. This means there must be a reliable seal between the facemask and the face, even when facial muscle tone changes as consciousness is lost. As discussed in the COVID-19 Chapter, Exit suspects that further modifications to the DeBreather, by way of CPAP or BiPAP masks (which are positive pressure systems), may be a further welcome development.
This problem with ensuring a good seal can also aggravated by the presence of significant facial hair/ beard etc. In one of Ogden’s reported deaths, the oxygen level in the system was found to pla- teau, fluctuating around 15%. This was due to air leakage caused by a poor facemask seal. At 13 minutes, the assistant had to ap- plied pressure on to the mask to ensure a seal; the oxygen then dropped steadily till death occurred (see graph below).
Oxygen level with time in an assisted death using the Smith Hofsess Debreather