One assumption many people make is that if they learn CPR, they will be able to perform it when the opportunity presents itself.
But that's not always the case.
According to Bob Trenkamp, President of slicc.org: "the amount of force required to compress a human chest to a two-inch depth depends upon the stiffness of the victim's chest."
A rescuer's ability to compress that chest depends upon the rescuer's weight and weight distribution, and the method of compression used (hand or heel). Those who were taught to crunch their abdominal muscles during the down-stroke can generate some additional force, but I've never seen anybody be able to do that for more than two minutes."
The average adult chest stiffness requires 130 pounds to get a two-inch compression. The average rescuer has to weigh somewhere about 25% more than the victim's chest stiffness, if performing compression manually - a bit less if performing compression with the heel of the foot - to get a two-inch depth.
About 70% of all cardiac arrests occur in a private residence. Two-thirds of arrest victims are male. A study by Trenkamp and Perez presented at the AHA Q-COR conference in Alexandria, VA in the spring of 2017 suggested that the percentage of all homes with two adults where each adult could perform a single two-inch compression on the other was zero percent. The cohort was assembled from zip code 31411. Households responding with data for only one person were excluded. The age distribution was significantly biased toward people in their 70's, probably due to (a) where the sample was recruited, and (b) people who took the time to fill out the response and return it.
By this point in the discussion, someone has usually said "But ANY CPR is better than no CPR!" Let me offer two other considerations: (1) with sufficiently shallower than guideline compression depth, there is an enhanced chance that the after the heart is re-started, the victim will not be able to handle the activities of daily living without assistance. (2) Dr. Vadebancoeur et al in Resuscitation 84 (2014) 182-188 reported on chest compression depth and survival in 593 out-of-hospital cardiac arrests. The survivors received 2.11 inch depth compression, on the average. The non-survivors received 1.92 inch depth compressions.
