[Sample taking through central venous catheter for the control of partial thromboplastin time in patients with heparin sodium perfusion]

The need to systematically monitor activated partial thromboplastin time (APTT) in patients undergoing continuous perfusion of heparin sodium (non-fractionated) in order to maintain therapeutic levels of anticoagulation leads to two questions: 1. can blood be withdrawn from the catheter through which the heparin solution is being perfused without altering APTT values? and 2. how much blood should be discarded so that APTT values remain unchanged? To obtain APTT values in these patients, two samples were extracted simultaneously: one through the central venous catheter through which the heparin was being perfused, after previously discarding 10 or 20 ml of blood according to the group to which the patient was assigned and the other through direct venous puncture or through the peripheral catheter inserted in the arm not being used for heparin perfusion. The values obtained by both methods were analyzed for statistical significance. Comparison of the results of APPT in the samples, having previously extracted 10 or 20 ml of blood, with those obtained through venous puncture or through peripheral venous catheter revealed statistically significant differences. These differences were lower when 20 ml were discarded than when 10 ml were discarded. In conclusion, APPT monitoring should be performed whether the sample is obtained through direct venous puncture or through a peripheral catheter inserted in the arm not being used for heparin perfusion.