To the uninitiated the literature on shock is confusing and difficult to understand. As used in the clinical literature of the last thirty years, the term shock has described a clinical picture characterized either by a sharp fall in arterial pressure or by the peripheral signs and symptoms of a decrease in cardiac output. When a physician said that a patient was in shock he was describing the general appearance of the patient. The term had no specific physiologic connotation. It did not indicate why the circulation had failed; it simply implied that it had failed.
From time to time various authors, including ourselves,1 have attempted to restrict the use of the term shock to the circulatory insufficiency produced by a failure of venous return to the heart. Further work in the clinic has convinced us that a physician many times cannot determine at once the physiologic basis of