THE VALUE OF MONITORS IN CARDIAC SURGERY

Abstract

Abstract Instruments used as monitors during cardiac surgery are believed by most workers in this field to be of considerable value. Among these instruments are the electrocardiogram, electroencephalogram, pH meter, pressure transducers for arterial and venous pressure and continuously registering thermometer. The electrocardiogram provides useful information concerning the cardiac rate and rhythm especially in presenting evidence of an irritable myocardium in the appearance of ectopic ventricular beats. It must not, however, be regarded as a monitor of efficient cardiac action, as a tracing of normal appearance may be present during episodes of low cardiac output and severe hypotension. When the technic of induced cardiac arrest is used, the electrocardiogram is useful in showing when a normal heart rhythm has reappeared. The electroencephalogram indicates roughly whether or not the internal respiration of the brain is adequate. Gross changes in the pattern indicate that something is wrong in this mechanism: low blood pressure, poorly oxygenated blood, excess carbon dioxide in the blood, hypothermia or overdosage of anesthetic agent. Changes in the pattern alert the anesthesiologist to the fact that some defect is present which demands immediate diagnosis and correction. The pH meter calls attention to the presence of acidosis of respiratory or metabolic origin, so that measures for correction may be begun early (increased ventilation or intravenous administration of sodium bicarbonate). Pressure transducers are helpful in demonstrating hypotension or hypertension before, during and after the use of the artificial heartlung device. Body temperature is important in the safe administration of anesthesia. Especially in children, it is often beneficial to carry the patient with a moderately reduced temperature, or at least to prevent the occurrence of hyperthermia. It should be clearly understood that all these devices are to be considered only as adjuncts in the administration of safe anesthesia. The information they provide must be interpreted by a skilled and careful anesthesiologist to be of full value. A competent anesthesiologist who does not use any or all of these monitors may administer a safer anesthesia than one who depends heavily upon instruments.