Once compressions are resumed, perform the same 30 compressions to 2 breaths as recommended in 2005. Chest compressions are one of the few class I interventions that we know help patients. When performing CPR, be sure to "push hard and push fast," as there has been a change in the rate and depth of compressions. On adult patients, the rate has changed from about 100 per minute to at least 100 per minute, and compression depth is now at least 2 inches. Both of these changes are class IIa recommendations.3 While initially these seem like subtle changes, they actually are quite significant. Increasing compression depth and rate helps improve cardiac output and generates a greater circulatory pressure.
The compressions rate for adult patients of at least 100 per minute (class IIa) is not the actual number performed, but rather the speed. Since there are breaks, or periods of time when no compressions are performed, the actual number of compressions is quite a bit lower. One study correlated the best ROSC when there are at least 80 compressions per minute. There has been some research on "high-frequency" chest compressions with rates exceeding 120 per minute. These studies are very limited and have small sample sizes, but do show that high-frequency compressions improve the patient's hemodynamics, although they have not impacted survival. Thus, while these 2010 recommendations do not recommend the routine use of high-frequency compressions, when properly used, they are an acceptable alternative (class IIb).4
Research has shown that the quality of compressions deteriorates rapidly over time as rescuers fatigue, leading to inadequate oxygenation of the brain and heart. EMS crews need to ensure proper and quality depth compressions are performed throughout cardiac arrest to provide the patient with the best opportunity for survival, which is accomplished by changing compressors every two minutes and ensuring complete chest recoil. Rescuer fatigue deteriorates the quality of chest compressions after about 1 minute; however, rescuers often do not note it for up to 5 minutes.4 This timing is designed to eliminate extra stops in compressions and prevent excessive fatigue.
Allowing chest recoil improves the negative pressure inside the chest, which is essential for the circulatory system to have good preload--the pressure that helps the heart fill with blood. Negative pressure occurs normally when we breathe (chest expansion) and during a cardiac arrest, when the chest returns to its normal shape following compressions. This negative pressure not only causes air to be drawn into the chest, it also pulls blood through the inferior and superior venae cavae toward the heart. If there is as little as 10 pounds of pressure on the chest, the equivalent of leaning with both arms on the chest just before a compression, the pressure change inside of the chest causes a decrease in the amount of blood that can flow through the venae cavae. With less blood flowing, less blood returns to the heart and pressure within the system decreases. Incomplete recoil has clear links to decreased coronary and cerebral perfusion. To prevent this, allow hands to release pressure on the chest in between each compression. Also consider using a cardiac monitor with built-in, real-time feedback devices that can tell you if compressions are not deep enough or if chest recoil is not adequate.
Chest compressions now begin before ventilations (Class IIb). The goal of this change is to shorten the delay to compressions and thus return of some circulation. This means that as soon as a patient is known to be pulseless, or a rescuer is not positive he feels a pulse, begin compressions. The compression-to-ventilation ratio remains the same at 30:2 (class IIb), based on expert consensus. The ideal ratio has not been determined and is under further research. Once an advanced airway is in place, class IIa recommends continuous compressions with an interspaced breath every 6-8 seconds.
While lay rescuers will be taught and coached to provide compressions-only CPR, all EMS providers are expected to also provide ventilations at an appropriate rate once they arrive on scene.
There has been no change in the recommendation to limit pulse and rhythm checks to two-minute intervals (five cycles of 30:2 CPR); however, pulse checks are deemphasized. Detecting a carotid or femoral pulse in the back of a moving ambulance is difficult even when patients have an adequate blood pressure. If a pulse is not definitely felt, or there are no signs the patient is breathing normally within 10 seconds of beginning a pulse check, immediately resume chest compressions (class IIa).3