During cardiopulmonary resuscitation, the sternum should drop at least

The heart is one of the important organs of the human body, and every part of the body is controlled by it. If there is a disease in the heart, it is easy to cause sternum depression during CPR. Problems may also occur in the heart and lungs. Heart palpitations and heart calmness are common symptoms. The distance of the sternum depression is determined by the health of the heart. This situation must be resolved in time, otherwise diseases such as myocardial infarction will occur.

1. Ventricular fibrillation: The ventricular muscle vibrates rapidly, irregularly, and uncoordinatedly. The electrocardiogram shows the disappearance of the QRS complex and its replacement by irregular continuous ventricular fibrillation waves with a frequency of 200-500 beats/minute. This type of cardiac arrest is the most common type, accounting for about 80%. If ventricular fibrillation can be defibrillated immediately, the success rate of resuscitation is higher.

2. Ventricular asthenia: The ventricular muscle completely loses its contractile activity and is in a static state. The electrocardiogram shows a straight line or only atrial waves, which usually appears after a period of cardiac arrest (such as 3 to 5 minutes).

3. Electrocardiographic-mechanical dissociation: This condition is a slow and ineffective ventricular autonomous rhythm. The ventricular muscle may intermittently exhibit slow, extremely weak, and incomplete contractions. The electrocardiogram shows intermittent and gradually widening QRS complexes, with a frequency of less than 20-30 times/minute. Because the heart has no effective pumping function, there are no heart sounds when auscultating, and no pulsation can be felt in the peripheral arteries. This type of heart attack is often the result of severe myocardial damage, which eventually ends in ventricular asystole and makes resuscitation difficult.

Although the above three types of ECG and heart activity of cardiac arrest have their own characteristics, the common result is that the heart loses its effective pumping function, leading to circulatory arrest. When systemic tissues are suffering from acute ischemia and hypoxia, the activity of the body's sympathetic adrenal system is enhanced, releasing large amounts of catecholamines and related hormones, causing peripheral vasoconstriction to ensure blood supply to important organs such as the brain and heart; hypoxia leads to anaerobic metabolism and increased lactic acid, causing metabolic acidosis. Acute hypoxia causes the most serious damage to organs, especially the brain. With the rapid drop in cerebral blood flow, the adenosine triphosphate (ATP) content of brain neurons decreases rapidly, and the cells cannot maintain the ion gradient inside and outside the membrane. In addition, lactate accumulates, cells edema and acidosis occur, and then cell metabolism stops, cells degenerate and lysosomal enzymes are released, leading to irreversible damage to brain and other tissue cells. The impact of hypoxia on the heart can be due to increased catecholamines and acidosis, which increase the automaticity of the His bundle and Purkinje system and reduce the ventricular fibrillation threshold; severe hypoxia causes damage to the myocardial ultrastructure and causes irreversible damage. Prolonged ischemia and hypoxia can cause complications such as acute tubular necrosis, central lobular necrosis of the liver, and other organ damage and dysfunction or failure.