Compression force-depth relationship during out-of-hospital cardiopulmonary resuscitation

Background: Recent clinical studies reporting the high frequency of inadequate chest compression depth (< 38 mm) during CPR, have prompted the question if adult human chest characteristics render it difficult to attain the recommended compression depth in certain patients. Material and methods: Using a specially designed monitor/defibrillator equipped with a sternal pad fitted with an accelerometer and a pressure sensor, compression force and depth was measured during CPR in 91 adult out-of-hospital cardiac arrest patients. Results: There was a strong non-linear relationship between the force of compression and depth achieved. Mean applied force for all patients was 30.3 +/- 8.2 kg and mean absolute compression depth 42 8 mm. For 87 of 91 patients 38 mm compression depth was obtained with less than 50 kg. Stiffer chests were compressed more forcefully than softer chests (p < 0.001), but softer chests were compressed more deeply than stiffer chests (p=0.001). The force needed to reach 38mm compression depth (F38) and mean compression force were higher for mates than for females: 29.8 +/- 14.5 kg versus 22.5 +/- 10.2 kg (p < 0.02), and 32.0 +/- 8.3 kg versus 27.0 +/- 7.0 kg (p < 0.01), respectively. There was no significant variation in F38 or compression depth with age, but a significant 1.5 kg mean decrease in applied force for each 10 years increase in age (p < 0.05). Chest stiffness decreased significantly (p < 0.0001) with an increasing number of compressions performed. Average residual force during decompression was 1.7 +/- 1.0 kg, corresponding to an average residual depth of 3 +/- 2 mm. Conclusion: In most out-of-hospitaL cardiac arrest victims adequate chest compression depth can be achieved by a force < 50kg, indicating that an average sized and fit rescuer should be able to perform effective CPR in most adult patients. (c) 2006 Elsevier Ireland Ltd. All rights reserved.