Sodium bicarbonate in CPR

Article Abstract:

During cardiac arrest, acidosis (increased acidity) decreases the ability of the heart muscle to contract (myocardial contractility) and keeps the heart from responding to catecholamines (chemicals in the body that regulate the heart). For this reason, doctors began to administer sodium bicarbonate to counteract acidosis. In 1974 it was reported that sodium bicarbonate increased in-hospital deaths after initially successful resuscitation. Acidosis within the heart muscle cells reduces the heart's ability to pump. Extracellular ''metabolic'' acidosis does not affect it. Sodium bicarbonate corrects extracellular acidosis, but at the same time makes intracellular acidosis worse. The chemical mechanism of this process is described. Past experiments showed that administration of tromethamine (TRIS or THAM) during cardiac arrest reduced aortic diastolic pressure (pressure between contractions) and coronary perfusion pressure (CPP, pressure of the blood flow through the heart) during chest compression of cardiopulmonary resuscitation (CPR). TRIS increased the number of deaths. Fulvio Kette and his colleagues, in the October 16, 1991 issue of the Journal of the American Medical Association, gave an explanation for the failure of sodium bicarbonate during experimental cardiac arrest in pigs. The solutions failed to affect acidity within the heart muscle itself. In addition, survival during this experiment was related to coronary perfusion pressure, which the buffer solutions reduced by half, not acid levels. Administration of sodium bicarbonate for cardiac arrest is therefore not a practice supported by the evidence. Treatment during CPR should consist of hyperventilation (greatly increased oxygen administration), vigorous chest compression, and epinephrine to increase perfusion pressure. (Consumer Summary produced by Reliance Medical Information, Inc.)

Sodium metabolism

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Buffer solutions may compromise cardiac resuscitation by reducing coronary perfusion pressure

Article Abstract:

Coronary perfusion (blood circulation through the heart) is an important indicator of whether a patient can be resuscitated. The goal of cardiopulmonary resuscitation (CPR) is to increase circulation by increasing coronary perfusion pressure (CPP), thereby reversing the reduction in blood supply to the heart (myocardial ischemia). Hypertonic or buffer solutions of either sodium bicarbonate or sodium chloride are routinely used to counteract acidosis (increased acidity) during cardiac arrest because it was thought that this would improve the ability of the heart muscle (myocardium) to pump. However, recent research on the effects of buffer solutions shows that they do not alleviate acidosis within the heart cells, but they do decrease CPP. The reduction in CPP is likely to reduce blood flow during CPR when blood flow is maintained artificially by compression on the chest. The effects of buffer solutions on cardiac arrest were tested in 44 four-month-old anesthetized pigs. The pigs received either sodium bicarbonate, a mixture of sodium bicarbonate and sodium carbonate, sodium chloride, or a neutral solution. Confirming earlier mammalian studies, the buffer solutions increased plasma osmolality (a function of salt concentration affecting the ability of the solution to cross semipermeable membranes) but decreased arterial pressure. An earlier study found that use of another buffer, tromethamine (TRIS) reduced the success of cardiac resuscitation because of reduced CPP. This study shows that these buffer solutions also reduced the success of resuscitation because they decreased CPP. (Consumer Summary produced by Reliance Medical Information, Inc.)

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New approaches to CPR: four hands, a plunger, or a vest

Article Abstract:

There are three new techniques to improve the effectiveness of cardiopulmonary resuscitation (CPR) in patients in cardiac arrest. One, called interposed abdominal counterpulsation (IAC-CPR), involves a second person performing abdominal compressions while the first person compresses the chest. The second involves using a mechanical device to actively decompress the chest in between compressions. The third involves a vest worn by the patient that alternately inflates and deflates. All of these techniques have one common goal: to create a pressure difference between the right atrium, the upper chamber of the heart, and the aorta, the major blood vessel leaving the heart. Studies have shown that a pressure difference of more than 16 to 20 millimeters of mercury is necessary to restore heart function. So far, only IAC-CPR has been shown to improve survival in humans.

Innovations, CPR (First aid), Cardiopulmonary resuscitation

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