Effect of Parallel Halothane - Containlng Controls Blood on p 02 Values

To the Editor: In a recent Case Report (1) the abnormal electrocardiographic findings were not confirmed by the enzyme changes as is usually the case in documented myocardial infarction. We would like to point out that some work has been done indicating that serum zinc concentrations decline rapidly after a myocardial infarct (2, 3). After four days the concentration gradually increased to within normal limits (2). This was generally the case in 11 patients who fulfilled all other criteria for myocardial infarction. In contrast, there was no comparable change in the serum zinc concentrations of seven patients who had chest pains caused by myocardial ischemia without the electrocardiographic or enzyme changes characteristic of infarction. Therefore measurement of plasma or serum zinc may be helpful in diagnosing myocardial infarction. Although determination of zinc in body fluids is somewhat complex and requires special instrumentation, it is becoming increasingly available. Zinc in plasma can be measured with precision and accuracy by atomic absorption spectroscopy (4). Special precautions must be taken to prevent contamination in view of the fact that zinc is ubiquitous in the environment. The usual evacuated tubes used for drawing blood contaminate the sample and invalidate the results. However, if the sample has been properly obtained without contamination (4), plasma zinc determination may be useful in documenting a true infarct, especially in caseswhere there is conflict between the variables usually measured.