According to the most recent guidelines, compressions should be at a depth of 1.5- 2 inch for children and adults respectively and 1.5 inch or a 1/3 of an infant’s chest deep. (Rates of compression is discussed in another section). With full recoil, that should be enough to allow the heart to fill with blood and pump enough of it to the rest of the body with every compression. In theory, this should work well but it is not as effective as actual heart beats. However, the point of cardiopulmonary resuscitation, or CPR, is to try to mimic normal cardiopulmonary function as best as possible in order to maintain the functions of the other bodily systems.
Anatomy of the Heart
In reality, the heart does not compress inward between the sternum (the flat bony part of the chest where the ribs meet in the center) and the spine. Normally, the heart actually squeezes as a muscle within itself. Furthermore, the heart, as a unit actually pumps twice. If you remember your anatomy, the heart has four chambers- two on the ‘top’ and two on the ‘bottom’. The top chambers are called the atriums and the bottom chambers are called the ventricles. As a unit, the atriums pump first to push blood and fill the ventricles. The ventricles would then pump to push blood to the lungs and the body. The force of each pump pushes the blood to circulate around the rest of the body to return to the heart via the atrium. The cycle would then repeat itself.
Why Stress and Compress?
Abnormal heart rhythms associated with CPR such as ventricular tachycardia, ventricular fibrillation and asystole or ‘no rhythm’ disrupts this circulatory process of the blood through the heart. It is because of this that compressions are important. Is the recommended depth enough or too much? The truth is that the depth of compression varies from victim to victim. The number proposed for adults, 2 inches for example, is an average estimate.
Consider The Victim
First of all, not everyone’s chest depth is the same. Consider your own heart. Sometime in the past, some of us were told that the size of our heart is about the size of our own closed fist. Add this to the size of our ribs, the fat and the muscle surrounding the heart and depth of our chests adds up. Now look at thin and obese folks around you and imagine whether conducting chest compressions on them would be the same or as effective compared to your own chest depth. As for me, chest compression depth may not require the full 2 inches, however, it may require more for others. Second, of all, how can one really measure 2 inches, 1.5 inches or a third of a victim’s chest? In an emergency, I have yet to see anyone with a ruler. I obviously am kidding but my point should be clear. There is no real way to determine if a rescuer is fulfilling the recommended depth of chest compressions.
So How Do We Really Know?
You can’t. This is why the recommendations included words such as ‘quality chest compressions’ in their guidelines. These ‘quality chest compressions’ include:
- Pushing hard
- Pushing fast
- Allow complete recoil of the chest
- Avoid excessive interruptions during CPR
- Begin CPR with chest compressions
By following these recommendations, a rescuer can have a certain level of assurance that despite not fully functioning as an organ, the heart is still being utilized in such a way provide a level of blood flow around the body. Second, the heart is not a closed organ. It has valves and ‘tunnels’ that lead to wherever the blood needs to go. With each compression, you are providing enough pressure that pushes blood forward and past the valves.
This opens another question. Will the blood also push blood backward? The answer is yes if there is damage on the valves. Blood return backwards in the heart is called regurgitation and during CPR, there is a small level of regurgitation occurring but for the most part, the valves opened at different pressures during a normal heartbeat or compression does not allow regurgitation or backflow. The way the heart functions is unique in this matter. When blood fills a chamber in the heart, a valve opens to let blood flow in, when the heart compresses, the pressure closes that valve but opens another valve to allow blood to flow out again. The concept is similar during CPR.
Does the Inches Matter Then During Compression?
In a sense, it does because it is a guideline. Guidelines help provide order and a direction of a process. If you follow the other guidelines regarding compressions and keep the depth in inches in mind, you will provide that ‘high quality CPR’ that is sought in each and every rescuer. Add breaths and the use of an AED and you increase the chance of that victim’s survival.
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