A condition closely allied to circulatory shock is cir-culatory arrest, in which all blood flow stops. This occurs frequently on the surgical operating table as a result of cardiac arrest or ventricular fibrillation.
Ventricular fibrillation can usually be stopped by strong electroshock of the heart.
Cardiac arrest often results from too little oxygen in the anesthetic gaseous mixture or from a depressant effect of the anesthesia itself. A normal cardiac rhythm can usually be restored by removing the anesthetic and immediately applying cardiopulmonary resuscitation procedures, while at the same time supplying the patient’s lungs with adequate quantities of ventilatory oxygen.
A special problem in circulatory arrest is to prevent detrimental effects in the brain as a result of the arrest. In general, more than 5 to 8 minutes of total circula-tory arrest can cause at least some degree of perma-nent brain damage in more than half of patients. Circulatory arrest for as long as 10 to 15 minutes almost always permanently destroys significant amounts of mental power.
For many years, it was taught that this detrimental effect on the brain was caused by the acute cerebral hypoxia that occurs during circulatory arrest. However, experiments have shown that if blood clots are prevented from occurring in the blood vessels of the brain, this will also prevent most of the early dete-rioration of the brain during circulatory arrest. For instance, in animal experiments performed by Crowell, all the blood was removed from the animal’s blood vessels at the beginning of circulatory arrest and then replaced at the end of circulatory arrest so that no intravascular blood clotting could occur. In this experiment, the brain was usually able to withstand up to 30 minutes of circulatory arrest without permanent brain damage.Also, administration of heparin or strep-tokinase (to prevent blood coagulation) before cardiac arrest was shown to increase the survivability of the brain up to two to four times longer than usual.
It is likely that the severe brain damage that occurs from circulatory arrest is caused mainly by permanent blockage of many small blood vessels by blood clots, thus leading to prolonged ischemia and eventual death of the neurons.
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