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Interesting piece. I’d like to add a little something to your understanding of respiratory and cardiovascular physiology though. The respiratory system is mostly controlling the pH of our blood. Increasing CO2 leads to acidosis and acidosis leads to ineffective function of many of our hormones like epinephrine and norepinephrine so it actually makes sense to have pH as the trigger. One can actually survive with very low levels of blood oxygen as long as blood pH is maintained which is via circulation and ventilation. Ventilation meaning CO2 removal and circulation meaning keeping blood flowing

It has been demonstrated that one can do completely effective CPR with chest compressions only and no mouth to mouth breathing. Many CPR classes now teach that providers simply pump on the chest 100-110 times per minute. Many people don’t do effective breathing any way and are rightfully concerned about doing mouth to mouth on a stranger. Keeping blood flowing with compressions eliminates CO2 ( because there is still some ventilation from the chest compressions alone) There have been witnessed cardiac arrests where ONLY chest compressions were done for over an hour and patient survived. A key point here is “witnessed” arrest. As long as compressions are started promptly survival is possible. Each minute matters. CO2 rises 4-6 mmHg per minute for first couple minutes and about 2-4 each subsequent minute so five minutes of apnea /loss of circulation leads to increase of CO2 of almost 20mmHg. Quite significant

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