Blood gas and acid-base balance during cardiopulmonary resuscitation by intrathoracic and abdominal pressure variations.

The blood gases and acid-base balance in a modified cardiopulmonary resuscitation (CPR) technique, based on intrathoracic and abdominal pressure variations by means of circumferential chest and abdominal balloon inflation, were examined in seven mongrel dogs. CPR proceeded for periods lasting 30 min or more and was monitored by measurements of aortic and right ventricular pressures and carotid blood flow during the compression (artificial systole) and the relaxation phase (artificial diastole). The carotid blood flow was 21.7 +/- 7.8 (mean +/- SD) ml/min, which was 0.18 +/- 0.6 (mean +/- SD) of the baseline mean carotid flow. Arterial blood was well oxygenated throughout the experiments, and low PCO2 levels (5-9 mm Hg) caused an initial severe alkalosis (pH = 7.94). However, a gradual decline in the pH was observed, reaching a value of 7.34 +/- 0.11 in the arterial blood after 30 min of CPR. The venous blood had a very low oxygen content (less than 25.5%) with a low PO2 and a normal PCO2 (43.7 +/- 7.3 mm Hg) throughout the experiment. A gradually developing metabolic acidosis was reflected in the pH values, and an increase in base deficit from 2.25 +/- 5.6 meq/1 prior to CPR to 16.7 +/- 3.2 meq/1 after 30 min of CPR was observed. High arteriovenous differences in oxygen content (greater than 66.4%) and CO2 tension (30.1-41.5 mm Hg) with a slowly developing metabolic acidosis were noted. Thus, CPR by thoracic and abdominal pressure variations is associated with a slowly developing metabolic acidosis which is the result of the combination of hyperventilation and a low perfusion state.