Abstract 123: Chest Stiffness: Getting to a 6 cm Compression Depth Expectation
Introduction: AHA guidelines suggest that it’s reasonable for healthcare providers to perform CPR with compression depths of at least 5 cm. However, forces needed to reach these depths can be large. We studied the force-depth relation obtained in clinical studies and determined the patient populations chest stiffness distribution. The data shows the forces needed to obtain guideline compressions and the ability of the average rescuer to exert these forces.
Methods: 225 cardiac arrest patients (EMS and hospital) received manual CPR with the Philips Heartstart MRx, that recorded continuous depth and force. Mattress effect (if applicable) was corrected by dividing depth with a factor 1.34. A parallel spring damper model was used to describe the force-depth relation. Damping was modeled as being linear with depth. The elastic term was modeled by a single parameter exponential function (the chest stiffness b1) as many biological tissues follow an exponential stress-strain relation:
Force(x) [N] = b1 · (eb2·x+b1 - eb1), with x compression depth [cm] and b2 = 0.42 · e-0.46 · b1 + 1.57 - 0.05
Data from individual compressions were fitted to the model. A distribution of chest stiffnesses was made. Compression forces needed to obtain guideline depths were estimated. Secondly, stiffness versus compression depth was studied.
Results: A total of 244994 compressions were studied. Chest stiffness was logistically distributed. A decrease in average compression depth was seen at increasing stiffness. Forces required for 5 and 6 cm depth at a given percentile are shown. If 60% of the professional rescuers can exert forces up to 56 kg, our data shows that only 75% of patients then receive compressions of at least 5 cm.
Conclusion: Large forces are needed to reach guideline compressions. Especially at target depths of 6 cm, 50% of patients require more than 80 kg force. The 2010 guideline target depth increase resulted in unrealistic demands for many rescuers and shows the need for automated CPR.
- © 2013 by American Heart Association, Inc.