Invasive v. non-invasive measurement of arterial pressure. Comparison of two automatic methods and simultaneously measured direct intra-arterial pressure.

Two indirect arterial pressure monitors, the Finapres and the Accutorr, were investigated and compared with the direct measurement of intra-arterial pressure. Pressures in patients in a variety of circulatory states were measured and analysed in relation to two types of random error: first, the "intra-individual standard error" (within one session of measurement) and second, the "inter-individual standard error" (between sessions). (This distinction is important, since in routine monitoring of arterial pressure one is usually dealing with the first type of error only.) This study showed that sudden changes in pressure were closely followed by the Finapres. A pressure reading of the Accutorr takes about 15-20 s, meaning that, within this period, variations will not be observed. The accuracy or reproducibility of each method, as expressed in intra-individual variance, diminished in the order Intra-Arterial-Line, Finapres, Accutorr. The inter-individual variation decreased in the order Intra-Arterial-Line, Accutorr, Finapres. Most of the inter-individual variance of the Finapres is probably real because of the more peripheral position of its cuff. A correlation between malfunctioning of the Finapres and vasoconstriction or hypothermia of the finger could not be demonstrated.