Cardiopulmonary resuscitation physiology

Basic CPR physiology indicates that several mechanisms of blood flow generation may be in operation and that, in an individual patient, the mechanism may change over time going from a cardiac or vascular compression mechanism to a thoracic-pump mechanism. Most importantly, CPP, defined as the aortic diastolic pressure minus right atrial diastolic pressure minus right atrial diastolic pressure, is the driving force for myocardial blood flow production during the resuscitation effort. The higher the CPP achieved, the greater the myocardial blood flow and the more likely a successful outcome will result. The effect of coronary artery lesions on myocardial blood flow during resuscitation is just now being explored, but does appear important and may limit distal myocardial perfusion where such lesions exist. Finally, a noninvasive alternative to measuring CPP gradients during CPR is to measure expired end-tidal CO₂. Useful prognostic information during the actual performance of CPR can be inferred from the expired end-trial CO₂ levels.