CPR Update Series Part 2 – Depth of Compression

In Medical Concepts by Stuart NethertonLeave a Comment

Editor’s note: This post marks the second in a series of posts outlining the evidence surrounding various aspects of CPR by Dr. Stu Netherton. Follow along as he covers Rate of Compression, Depth of Compression, Chest Wall Recoil, Minimizing Interruptions, and Avoiding Excessive Ventilation.

To guide the depth of our compressions during CPR, the 2015 AHA guidelines state:

“During manual CPR, rescuers should perform chest compressions at a depth of at least 2 inches or 5 cm for an average adult, while avoiding excessive chest compression depths (greater than 2.4 inches [6 cm])”

This was a change from the 2010 guidelines in which there was no upper limit to guide compression depth: The 2010 AHA Guidelines for CPR recommend a single minimum depth for compressions of ≥2 inches (50 mm) in adults.

Before worrying about how deep to go, can we go too shallow? The answer is yes. Compression depth of < 38mm has been shown to be associated with decreased ROSC and decreased survival.1,2 The other question to ask is, can we go too deep? And again, the answer is yes. The upper limit was added in the 2015 guidelines as a compression depth of greater than 6 centimeters (or 2.4 inches) was found to be associated with an increased risk of non-life-threatening harm (mainly rib and sternal fractures).3

So we know we shouldn’t go too shallow, and we shouldn’t go too deep, so what is our optimal depth of compression? The answer is somewhere between those two extremes. While the research in this area is rather heterogeneous, it does suggest that achieving a target depth close to 5cm leads to more favourable outcomes compared to shallower depths of compression. 1,2,4–6 The largest study to date showed improved outcomes with compression depth between 40.3 to 55.3 mm, with a peak of positive outcomes at depth of 45.6 mm. 2

It is relatively easy to count your compression rate, someone can watch you to ensure you’re not leaning on the chest during your compressions, but how do we accurately assess our depth? Someone can’t be at the bedside with a ruler. How often do you assess whether or not you’re compressing 1/3 of the anterior-posterior AP chest diameter? How do we know we’re achieving a depth of 45.6mm and not 37mm? Can a CPR provider really know the difference between a few millimetres of compression depth? It has been shown that trained providers of CPR tend to be too shallow, i.e. less than 40mm, and rarely reach a depth over 55mm2, but the use of CPR feedback and debriefing can help. The use of a standalone CPR feedback device, or one integrated into the defibrilator – which provides real-time rate and depth of compressions – during a resuscitation has been shown to help guide the providers efforts, improving the quality of CPR. 7,8Including data from feedback devices when debriefing the resuscitation teams has also shown to improve ROSC on subsequent resuscitation attempts.9 Embracing emerging technologies and constructive team debriefings are easy ways to build high functioning resuscitation teams.

As with all things CPR, each component is closely related to one another. Depth of compressions is no exception. Studies have shown that at compression rates greater than 120 per minute, there is a dose-dependent decrease in depth of compressions 10, and that shallower compression depths have been associated with defibrillation failure.4

Adequate depth can be a difficult part of CPR delivery to achieve, but with feedback devices, feedback simulation sessions, knowing our target depth and practice, we can continue to improve.

Uploaded by Amy Chung.


Stiell I, Brown S, Christenson J, et al. What is the Role of Chest Compression Depth during Out-of-Hospital Cardiac Arrest Resuscitation? Crit Care Med. 2012;40(4):1192-1198. [PMC]
Stiell I, Brown S, Nichol G, et al. What is the optimal chest compression depth during out-of-hospital cardiac arrest resuscitation of adult patients? Circulation. 2014;130(22):1962-1970. [PubMed]
Hellevuo H, Sainio M, Nevalainen R, et al. Deeper chest compression – more complications for cardiac arrest patients? Resuscitation. 2013;84(6):760-765. [PubMed]
Edelson D, Abella B, Kramer-Johansen J, et al. Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest. Resuscitation. 2006;71(2):137-145. [PubMed]
Hostler D, Everson-Stewart S, Rea T, et al. Effect of real-time feedback during cardiopulmonary resuscitation outside hospital: prospective, cluster-randomised trial. BMJ. 2011;342:d512. [PubMed]
Vadeboncoeur T, Stolz U, Panchal A, et al. Chest compression depth and survival in out-of-hospital cardiac arrest. Resuscitation. 2014;85(2):182-188. [PubMed]
Kramer-Johansen J, Myklebust H, Wik L, et al. Quality of out-of-hospital cardiopulmonary resuscitation with real time automated feedback: a prospective interventional study. Resuscitation. 2006;71(3):283-292. [PubMed]
Bohn A, Weber T, Wecker S, et al. The addition of voice prompts to audiovisual feedback and debriefing does not modify CPR quality or outcomes in out of hospital cardiac arrest–a prospective, randomized trial. Resuscitation. 2011;82(3):257-262. [PubMed]
Edelson D, Litzinger B, Arora V, et al. Improving in-hospital cardiac arrest process and outcomes with performance debriefing. Arch Intern Med. 2008;168(10):1063-1069. [PubMed]
Idris A, Guffey D, Pepe P, et al. Chest compression rates and survival following out-of-hospital cardiac arrest. Crit Care Med. 2015;43(4):840-848. [PubMed]

Reviewing with the staff

Adequate depth is critical to create any significant blood flow during CPR. During cardiac arrest the only way to ensure adequate depth is through CPR feedback in real-time. This is absolutely critical. Many device manufacturers do not provide CPR feedback on depth nor the ability to assess depth post-resuscitation but to increase survival, depth is critical and CPR feedback is a must. The AHA is now recommending that as of 2018 all CPR training programs must incorporate real-time CPR feedback to ensure adequate performance of high quality CPR.

Sheldon Cheskes, MD CCFP(EM) FCFP
Dr. Sheldon Cheskes is the Medical Director at the Regions of Halton and Peel, Sunnybrook Centre for Prehospital Medicine. He is an Associate Professor with the Department of Family and Community Medicine, Division of Emergency Medicine at the University of Toronto. Dr. Cheskes is recognized as an authority in the area of CPR quality. He has published extensively in the area of prehospital management and cardiac arrest resuscitation.

Stuart Netherton

Dr. Stuart Netherton is a resident in the FRCPC Emergency Medicine training program at the University of Saskatchewan, in Saskatoon. He has an interest in Emergency Medicine research including out-of-hospital cardiac arrest and resuscitation science