The old school of thought regarding performing chest compressions was that compressing the heart would mechanically pump blood out thus simulating natural heartbeats. The new school says that compressing causes a negative pressure in the thoracic cavity which upon releasing the compression sucks blood into the heart (via the vena cava). The effect of sucking blood in causes some blood to be pushed out or overflow. The blood ejected during CPR represents 25-33% of the 100cc found in the heart during diastole. The blood ejected during a normal systole is approximately 70%. Though this is a fairly large margin, it is still enough to circulate the bare essentials to the cells.

Push Hard, Push Fast. The rate of compressions should be around 100 per minute. Though this is higher than the normal heart rate of 70 beats per minute, it is important to note that we are not looking to mimic the heart but moreover compensate for the decreased cardiac output. Going slower may not circulate enough blood and going faster is also dangerous because you may not allow the heart sufficient time to fill well. Pushing hard is necessary to obtain adequate compression of the heart and thoracic cavity in order to create the pressures needed to circulate blood throughout the body. Recall that when you release the compression, that is the time when the heart is filling i.e. simulated diastole. In 2005, the American Heart Association modified it's guidelines regarding the ratio of compressions to breaths. It was felt that early, on, compressions were more important than ventilations to maintain adequate cardiac output and blood flow to the heart and brain. Consequently, the ratio of compressions to breaths was changed to 30:2.

Alternatives to compressions and breaths CPR exist. Compression only CPR was discussed earlier as an option when there is suspect blood around the victim or the rescuer is uncomfortable performing mouth to mouth. This approach has been discussed a lot lately since The Cerebral Resuscitation Group of Belgium showed no difference in outcome of CPR between victims who received compressions with ventilations and those who received compressions only. How does this make sense?

1. The negative pressure generated during compressions sucks in air as well as blood.
2. Oxygen saturation in the blood stays at a sufficient level for 12 minutes if the person is not breathing.

Other options include:

• IAC-CPR: CPR with manual compression of the abdomen (between the xiphoid process and belly button) during the relaxation phase of chest compressions. This is thought to potentate the negative pressure / suction of blood into the heart effect.
• ACD-CPR: a suction cup like device attached to the victim actively lifts the anterior chest during decompression thereby also increasing the suction of blood into the heart
• Vest CPR: a vest that inflates and deflates is strapped to the victim and mimics compressions
• Mechanical piston CPR: a mechanical device that depresses the sternum
• Simultaneous ventilation-compression CPR: uses the entire thorax as a pump
• Phased thoracic-abdominal compression decompression CPR: a hand-held device that performs the alternating chest and abdominal compressions (see IAC-CPR)

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