Resucitation in 2005: New Ways to Optimize Manual CPR

A better understanding of the fundamental mechanisms that govern perfusion during CPR will help EMS providers optimize their CPR performance. This primer highlights some new insights to optimizing blood flow to the vital organs during CPR and emphasizes new ways to enhance blood flow to the heart and brain during CPR in adults in order to maximize the chances for a return of spontaneous circulation and successful resuscitation.

Compression and Release

The goal of CPR is to provide blood flow to the vital organs. Compressing the sternum increases pressure within the chest, forcing blood out of the heart to vital organs and air out of the lungs. New data support the importance of providing, as much as possible, uninterrupted chest compressions, since every interruption causes a dramatic decrease in perfusion pressure.¹ Compressions should be at a rate of 100 a minute and the chest should be compressed 1½–2 inches, with half the time spent compressing the chest and half spent allowing the chest to fully recoil.

Full release (full chest-wall recoil) is also essential. New data have shown that a small vacuum (negative pressure) develops within the thorax each time the chest is allowed to fully recoil; this vacuum draws blood back into the heart (preload) and some air into the lungs.² It is during the chest-recoil phase that blood flows through the coronary arteries, providing the heart muscle with blood. One way to promote complete chest-wall recoil is to compress the chest with the palm of one hand, with the second hand on top of the first and the fingers interlocked. Allow the fingers of the lower hand to stay in light contact with the chest to maintain proper hand position (see Figure 1). During the recoil or release phase, lift the palm slightly but completely off the chest to enable full recoil. Performing CPR in this manner, with continuous compressions and full chest-wall recoil, will optimize blood flow to the heart and brain.³ Finally, CPR is tiring; make sure you rotate compression duties every several minutes to avoid fatigue.

Ventilation

New studies demonstrate that ventilations are often performed too fast, and that this hyperventilation can be deadly. In one study, overzealous rescuers ventilated an average of 30 times a minute instead of the recommended 12.⁴ Each time a breath is delivered to the patient, pressure inside the chest increases. While ventilation provides oxygenation, the increase in pressure impedes blood from returning to the heart. This decreases the amount of blood that fills the heart (preload) during the decompression (chest-wall recoil) phase of CPR, which in turn results in less blood being delivered to the heart and brain in subsequent compressions. In light of this critical interaction between the lungs and heart, it is important to provide enough oxygen, but not too much.

Ventilations should be performed with a compression-to-ventilation ratio of 15:2 with an unsecured airway and at a rate of 12 breaths per minute with a secured airway, as currently recommended by the American Heart Association (AHA).⁵ When the airway is secure, make sure each breath is given over one second, to avoid prolonged increases in intrathoracic pressure with each breath.⁵ New research suggests that in the future, even less frequent ventilations may further enhance circulation during CPR.^6–8

As has been recommended by the AHA for years, the facemask should be held securely by one rescuer while maintaining an open airway. A second rescuer, if available, should focus only on compressing the bag-valve resuscitator with supplemental oxygen, delivering breaths over 1–2 seconds at recommended tidal volumes. To perform this two-person ventilation technique, tilt the head back and pull the jaw toward you to open the airway, as shown in Figure 2. Too high a volume or delivery of the breath over too long a period of time will decrease blood flow to the heart and brain for the same reason that rapid ventilation rates are dangerous.⁴ A good continuous facemask seal during both ventilations and chest compressions is critical when using an impedance threshold device (ITD, described below) to enhance circulation.