Effect of different compression–decompression cycles on haemodynamics during ACD–CPR in pigs
Introduction
Active compression–decompression cardiopulmonary resuscitation (ACD–CPR) has been reported to increase both coronary, carotid and cerebral blood flow 1, 2, 3, 4, coronary perfusion pressure 3, 5, 6, velocity time integral (an analog of cardiac output) 5, 7end-tidal CO2 2, 3, 8and arterial blood pressure 3, 4, 5, 6, 7compared with standard CPR (S-CPR). In all these experimental studies 1, 2, 3, 4, 5, 6, 7, 8compression–decompression duty cycles of 50/50 have been used. This is the presently recommended duty cycle [9], but we are unaware of studies comparing the effects of various duty cycles during ACD–CPR.
In two recent studies from two different EMS systems paramedics trained in manual ACD–CPR with the Cardiopump® (Ambu International, Glostrup, Denmark) were unable to adhere to this recommendation. In both studies the compression time was only 31% 10, 11. If this is a common trend also in other EMS systems, and such variations in duty cycle affect the results of ACD–CPR, this might explain why the results of clinical ACD–CPR studies so far 12, 13, 14, 15, 16are less convincing than would be expected from the laboratory studies 1, 2, 3, 4, 5, 6, 7, 8.
Therefore, we have examined the effects of three different duty cycles (30/70, 50/50 and 70/30) on cerebral, myocardial and other organ blood flow and various blood pressures including the coronary perfusion pressure in anaesthetized pigs. To be able to control and rapidly change the compression and decompression periods in each animal we used an automatic hydraulic compression–decompression device (Heartsaver 2000®, Medreco, Bodø, Norway).
Section snippets
Animal preparation
The study was approved by the Norwegian Council for Animal Research. Ten domestic healthy pigs of either sex (17–23 kg) were anaesthetized with Ketalar 30 mg kg−1 and Atropine 1 mg i.m. A catheter was placed in an ear vein for infusion of 30 ml kg−1h−1. Ringer acetate and a target mean aortic pressure was set at 75 mmHg<MAP<120 mmHg. The pigs were placed supine with the chest in a U-shaped trough and the limbs secured to prevent lateral displacement of the chest during the ACD–CPR. A specially
Results
Ventricular fibrillation (VF) was obtained in nine pigs by the first trans-thoracic electric shock, while one pig needed three electric shocks because of electrode displacement. Three pigs were excluded. One had severe hypertension with MABP>120 mmHg despite adequate anaesthesia (no movement in unparalyzed animal), one had thrombotic emboli and a large cardiac infarction and one had air-embolus, probably occurring during instrumentation in connection with an intrapleural bleeding from a lung.
Discussion
In the present study in anaesthetized pigs with ventricular fibrillation (VF), the brain circulation was much lower during ACD–CPR with a 30 vs. 50 or 70% compression phase, while the relative duration of the compression phase did not affect myocardial blood flow, the coronary perfusion pressure or the flow to other organs.
Previous reports of positive hemodynamic effects of ACD–CPR compared to standard CPR (S-CPR) in pigs 1, 2, 3, dogs 4, 5and human 6, 7, 8all report the use of a 50%
Acknowledgements
This study was supported by a grant from the Norwegian Air Ambulance, Drobak, Norway, Laerdal Foundation of Acute Medicine, Stavanger, Norway, Anders Jahre's Foundation, the Norwegian Heart and Vessel Council and Glaxo Wellcome. Special thanks to Torunn Flatebø, Bjørn Kristiansen, Gerd Torgersen, Turid Verpe, Morten Eriksen, Sonja Flagestad and Severin Leraand for their technical assistance.
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