Assess Circulation and Initiate Compressions

The carotid artery is generally the most reliable and accessible location to palpate a pulse. The artery can be located by placing two fingers on the trachea and then sliding them down to the groove between the trachea and the sternocleidomastoid muscle. Simultaneous palpation of both carotid arteries should not be performed because this could obstruct cerebral blood flow. In low-pressure states, forceful palpation may interfere with the ability to detect a pulse. The femoral artery may be used as an alternative site to palpate a pulse. This can be found just below the inguinal ligament approximately halfway between the anterosuperior iliac spine and the pubic tubercle. If no pulse is felt after 5 to 10 s, chest compressions should begin.

PHYSIOLOGY OF CLOSED-CHEST COMPRESSIONS Since the technique of closed-chest compressions was put forth initially by Kouwenhoven and colleagues in the 1960s, there has been an active debate as to the mechanism of blood flow.34 In a closed system, liquid flows when pressure gradients develop. There are two basic theories for how pressure gradients and flow are produced during closed-chest cardiac massage. 5 The conventional theory of blood flow during compressions is called the cardiac pump theory. This postulates that direct compression of the heart between the spine and the sternum leads to increased pressure in the ventricles. This causes closure of the mitral and tricuspid valves, leading to blood flow into the aorta and the pulmonary arteries. The thoracic pump theory postulates that compressions lead to an increase in pressure throughout the thoracic cavity, leading to a pressure gradient from intrathoracic to extrathoracic arteries. It is possible that both mechanisms produce blood flow to varying degrees during closed-chest cardiac massage in humans. However, regardless of mechanism, conventional chest compressions generate one-fourth to one-third of physiologic cardiac output. Lower ratios can be expected with delays in initiating compressions.

TECHNIQUE OF CLOSED-CHEST COMPRESSIONS Upon confirmation that an individual is without a pulse, serial rhythmic closed-chest compressions should be initiated. The victim is placed supine on a firm surface with the rescuer at the side. The care provider places the heel of one hand midline on the lower half of the sternum, approximately 2 in cephalad of the xiphoid process (Fig 8.-9). The heel of the hand should be parallel with the long axis of the patient's body. The second hand is then placed on top of the first hand so that the hands are parallel with each other. The fingers of the two hands may be interlaced if desired. The arms should be straight and the elbows preferably locked. The vector of the compression force should start from the rescuer's shoulders and be directed downward; lateral forces

will decrease efficiency of the compressions and increase the likelihood of complications. The sternum should be depressed 1 2 to 2 in (3.8 to 5.1 cm) in an adult at a minimum rate of 80 to 100 compressions per minute. Rates less than this are inadequate. The compression-release phases should be roughly equal. With a single rescuer, 2 ventilations should be given after every 15 compressions; with two rescuers, a ventilation should be given after every fifth compression.

There are currently several experimental techniques for closed-chest cardiac massage. In one method, circumferential chest compressions are performed by a pneumatic vest CPR to more effectively increase intrathoracic pressure during chest compressions. 6 In interposed abdominal compression CPR, abdominal compression occurs during the relaxation phase of chest compression, causing increased aortic diastolic pressure and leading to improved blood flow to organs above the diaphragm.7 In active compression-decompression CPR, a hand-held suction device is used to decrease intrathoracic pressure during the relaxation phase of chest compression and to improve ventricular filling.8 Additionally, self-initiated cardiopulmonary resuscitation can be performed by forceful coughing. This increases intrathoracic pressure, leading to blood flow to the brain for as long as the patient remains conscious and able to cough. 9

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