Okay, if I may. You really can’t bring a patient on a vent with Assist control mode for a more matter of fact any mode on a vent into a scuba diving question. Two totally different worlds. Not only are you forcing the breath into the patient (positive pressure ventilation) but also have additional dead space from the vent circuit as well as the ET tube. The ventilation of patients is Mainly based on only two things: height and gender. You might ask why not weight. Because we have to go with IBW (ideal body weight) because once you reach adulthood your lungs do not grow larger with every pound you put on (talking about obesity). Every patient is breathing at one ata, unless they are in the hyperbaric chamber. We seldom even think about gas density unless we are using helium (and that getting to deep for this discussion). Now what the article does not tell you is that when changing vent settings of the rate or tidal volume we have to look at not only the ABG (arterial blood gas) but also the patient’s PIP (peak inspiratory pressure). If the patient’s PIP is about 36cmH2O or higher then increasing their TV could result in blowing their lungs and now we are putting in chest tubes.
Now a snorkel has a lot more dead space than a reg. A reg is in your mouth and the exhaust is a couple of inches away (a little longer for us Poseidon reg. users). So if we are talking about regs. We have to factor in the critical opening pressure or just how hard you have to suck in in order to get the valve to open and give you a breath. If too hard then you will have an increased WOB (work of breathing). This can cause a lot of problems and stress as well as possible Co2 retention. This is where you hear terms like over breathing the reg, air starve, etc. Like I said before, the rebreather is so temperamental in it’s breathing depending on your position in the water column and loop volume.
Other areas we have not even touch on is the physical condition of the dive, kit awareness, number of dives, dive conditions, water temp, comfort level, age, etc. In other words, and I don’t mean this in a judging manner, if you are out of shape, use your kit or rent a couple of times a year, have a cheap reg. then your SAC rate will be high. Some of the ones that posted on here have well over 500 + dives, have a vast amount of additional training, own our kits and dive them almost once a week, have quality gear, try to stay fit, very comfortably in the aquatic environment, etc.
So once, again too many variables.
OBTW, don’t knock yourself if you are under a 100 dives, your SAC rate will improve over time.