Detection of intravenous fluid extravasation using resistance measurements

Resistance to fluid infusion can be derived from measurements of pressure at two or more flow rates. We measured resistance in 31 patients using a pressure-monitoring infusion pump (Model 560, IVAC) by recording pressure at five flow rates (0, 50, 100, 200, and 300 mL/hr), and computing resistance as the slope of the pressure versus flow curve. Resistance was measured subcutaneously (Rtissue) and intravenously (Rvein) immediately after unsuccessful or successful IV catheter placement. In all patients, Rtissue was always greater than Rvein. The difference ranged from 23 resistance units (RU) to 4166 RU, with a mean difference of 1147 RU (p < 0.0001, Student's t-test). Unpaired analysis of the data was performed to assess the ability of resistance to indicate extravasation in the absence of prior Rvein measurement. The median value for Rvein was 62 RU (range -13.6 to 420 RU), and for Rtissue, 544 RU (range 65.7 to 4170 RU). Receiver operating characteristic (ROC) analysis revealed that a 200-RU threshold detected infiltration with 0.90 sensitivity and 0.91 specificity. We conclude that elevated resistance during fluid infusion is an important early and easily measurable finding in fluid extravasation.