Figure 32-13 Effect of patient position on the relationship between direct arterial blood pressure (ART) and indirect noninvasive blood pressure (NIBP) measurements. A, In a supine patient, pressures measured from the right (R) or left (L) arms by either technique will be the same. B, In the right lateral decubitus position, ART recorded directly from the right and left radial arteries will remain unchanged as long as the respective pressure transducers remain at heart level. However, NIBP will be higher in the dependent right arm and lower in the nondependent left arm. Differences in NIBP are determined by the positions of the arms above and below the level of the heart and are equal to the hydrostatic pressure differences between the level of the heart and the respective arm. A 20-cm difference in height produces a 15-mm Hg difference in pressure. (Redrawn from Mark JB: Atlas of Cardiovascular Monitoring. New York, Churchill Livingstone, 1998, Fig. 9-22.)