IS THE IV OBSTRUCTED OR INFILTRATED - A SIMPLE CLINICAL-TEST

Objective. The objective of our study was to determine if clinical obs ervation of pressure-flow relationships (PFR) can differentiate betwee n partial external obstruction (obstruction) and infiltration as a cau se of poor performance of gravity-fed infusions. Methods. A total of 2 4 patients with functional intravenous cannulae in situ had obstructio n simulated by the application of a tourniquet proximal to the cannula . The change in flow (Delta F) for a discrete change in pressure (Delt a P) was determined in each case by counting drop rates at two differe nt elevations of the fluid reservoir level, 10 cm apart. The same proc ess was repeated in 15 patients in whom the cannula was in an extra va scular location (infiltration). Three sizes of cannula-16-gauge, 18-ga uge, and 20-gauge-were examined, with equal distribution of sizes in e ach group. The effect on flow rates of inflating a blood pressure (BP) cuff proximally on the cannulated limb was assessed. The ratio Delta P/Delta F is the total resistance of the infusion system, and by subtr acting known values for resistance of infusion tubing and cannula, the venous or tissue resistance was calculated. Results. There was a stat istically significant difference between the change in flow for obstru cted compared with infiltrated cannulae for the same change in pressur e for each cannula size. The mean venous resistance was 23 mm Hg/L/hr, while that of tissue was 280 mm Hg/L/hr, with no overlap between grou ps. There was no effect on flow rate with blood pressure cuff inflatio n in the infiltrated group whereas flow progressively fell in the obst ructed group. Conclusions. Clinical observation of PFRs in poorly func tioning gravity-fed IV infusions can assist in detecting infiltration as a cause. Inflation of a blood pressure cuff will further impair flo w where the cannula is intravascular, but will have no effect in an ex travascular location.