Can the minimum loop volume practice limit effective CO2 scrubbing?

dteubner

Great question.

In fact the loop volume is not the important thing (unless, as has been pointed out too low a loop volume makes you breathe too shallowly).

The determinants of reaction time are the volume of air in the scrubber and the inspiratory flow rate.

The volume of air in a scubber is not all that obvious but I guess we can work it out.

5 litres of dragersorb weighs 4.15kg, so each kg of it occupies 1.2 litres. Given the density of CaOH is 2.24 this means that each kg of dragersorb is composed of 450 ml of solid and 750ml of air. If you fill a Sport KISS scrubber with a 2.5kg capacity you have about 1.9 litres of air in it.

Now it gets a bit complicated because there is not a steady state flow through the scrubber. For a dwell time of shorter than 0.5 seconds the peak flow rate would have to be more than 3.8 litres per second in my example above and this is pretty close to the theoretical maximum you can achieve.

As the sorb is used, however, there is less and less volume of air which can participate in the reaction and the peak inspiratory flow required to cause breakthrough will decrease, so that at parts of inspiration there may be CO2 in the inspired gas.

Dave T

PS I chose dragersorb and the SportKISS because I have a box of the one on my desk at work and have the scrubber capacity of the other in my head.