Effect of different compression--decompression cycles on haemodynamics during ACD-CPR in pigs

The haemodynamic effects of variations in the relative duration of the compression and active decompression (4 cm/2 cm) during active compression-decompression cardiopulmonary resuscitation (ACD-CPR), 30/70, 50/50 and 70/30, were tested in a randomized cross-over design during ventricular fibrillation in seven anaesthetized pigs (17-23 kg) using an automatic hydraulic chest compression-decompression device. Duty cycles of 50/50 and 70/30 gave significantly higher values than 30/70 for mean carotid blood flow (32 and 36 vs. 21 ml min-1, transit time flow probe, cerebral blood flow (30 and 34 vs. 19, radionuclide microspheres), mean aortic pressure (35 and 41 vs. 29 mmHg) and mean right atrial pressure (24 and 33 vs. 16 mmHg). A higher mean aortic, mean right atrial and mean left ventricular pressure for 70/30 were the only significant differences between 50/50 and 70/30. There were no differences in myocardial blood flow (radionuclide microspheres) or coronary perfusion pressure (CPP, aortic-right atrial pressure) between the three different duty cycles. CPP was positive in both the early and late compression period and during the whole decompression period. The expired CO2 was significantly higher with 70/30 than 30/70 during the compression phase of ACD-CPR. Beyond that no significant differences in the expired CO2 levels were observed. In conclusion a reduction of the compression period to 30% during ACD-CPR reduced the cerebral circulation, the mean aortic and right atrial pressures with no effect on the myocardial blood flow of varying the compression-decompression cycle.