Incomplete global myocardial ischemia during cardiac arrest and resuscitation

During cardiac arrest (no flow) and CPR (low flow), the onset of myocardial ischemia is followed by myocardial respiratory acidosis. Myocardial contractility is more decreased by respiratory than by metabolic acidosis. We demonstrated in a porcine model of cardiac arrest and in human patients increases in mixed venous PCO2 during CPR, whereas PaCO2 was decreased. Consequently, there was a striking increase in the venoarterial gradients for both [H+] and CO2. Both cardiac output (pulmonary blood flow) and the concentration of expired CO2 were simultaneously decreased. In great cardiac vein blood, even more profound respiratory acidosis with only minor decreases in bicarbonate and only moderate increases in lactate were observed. Intramyocardial pH was profoundly decreased. The severity of respiratory acidosis as a determinant of resuscitability and survival should be further investigated.