Importance of Prolonged Compression during Cardiopulmonary Resuscitation in Man

Taylor GJ, Tucker WM, Greene HL, Rudikoff MT, Weisfeldt ML New England Journal of Medicine 1977 Vol 296 Pages 1515-1517

The authors examine the effects of varying compression rate and duration on velocity of carotid artery flow and arterial pressure during CPR in 8 cardiac arrest subjects. Within 30 minutes of the start of CPR, manual external cardiac compressions were replaced by a pneumatic piston, computer-driven, chest compression device whose rate and duration of compression could be altered without interruption of cardiac compression. The force of the piston was set to depress the sternum 4-6 cm, with a compression rate of 60/min and duration of 40% of cycle length. Arterial blood flow (carotid in 7 patients and femoral in 1) was measured using a directional doppler flow meter. Rate or duration of compression was then randomly changed with compression durations of 30, 40,50 and 60%, and rates of 40, 60 and 80/min studied. Flow values were integrated for time and expressed as a percentage of the control values obtained at 60/min and 40%. Longer duration of compression increased the arterial flow index. At a compression rate of 60, lowering duration from 40 to 30%, reduced the index to 63% +/- 4.5 of the control, while raising duration to 50 and 60% increased the index to 134 +/-6.6 (P<0.001) and 185 +/- 29% (P<0.001) respectively. Similar changes in flow index were obtained at 80 compressions/min: At a 30% compression duration, flow index was 40 +/- 5%, while at 50-60%, flow index was 156 +/- 34% of control. Changing the compression rate at 60% did not change the flow index. At the optimal duration of 60%, rates of 40, 60 and 80/min, produced indexes of 181.5, 185 and 156 % of control (not significant). Mean arterial pressure at the control settings was 60 +/- 14 mmHg. Directionally similar changes in MAP and flow index occurred with changes in compression duration. At 30%, MAP was 53.2 +/- 6.2 mmHg (P<0.05), while at 60%, it was 64.2 +/- 4.7 mmHg (P<0.005). Effectiveness of external cardiac compression is dependent on duration of compression. Prolongation of compression appears to increase blood flow in large arteries as well as to increase arterial pressure. Improved flow should lead to a more favourable outcome of resuscitation. Although the data suggests that compression rates of 40/min would be as effective as 60/min, a longer pause at peak compression is required to achieve a compression duration of 60% at the slower rate. Since the authors have observed that this pause is technically difficult and tiring during manual massage, they recommend continuing instruction at a rate of approximately 60 compressions/min.