Intravenous pressure may be estimated clinically by either direct or indirect methods. The former is accomplished by the use of a hollow needle or trocar inserted into a vein and connected with a suitable manometer, while the indirect methods are based on the principle of measuring the external pressure necessary to obliterate the vein so that it is no longer visible above the surface of the skin.
Determination of intravenous pressure by direct methods has been described by Moritz and von Tabora,1 Schott,2 Bedford and Wright3 and others. Such direct methods, while more accurate, have certain disadvantages which preclude their general use in clinical medicine. The more important objections are the impossibility of frequent determinations in the same patient, the necessary prerequisite of strict asepsis, the possibility of formation of clot in the needle, which interferes with accurate readings and the difficulty sometimes encountered in puncturing a