The 'heparin lock': cause for iatrogenic coagulopathy

The reasons for coagulopathy may be multiple and the identification of the underlying cause is often difficult. Recently, we identified two patients showing characteristics of heparin overdose during surgery. We hypothesised that filling a Shaldon dialysis catheter with heparin prior to closure, so-called heparin lock, might have triggered this coagulation disorder. Therefore, the aim of this in vitro study was to show whether this procedure can lead to an iatrogenic administration of heparin.

A Shaldon catheter (GamCath; Joka Kathetertechnik, Hechingen, Germany) was hung up in a container filled with NaCl solution 0.9% 5 mL and a heparin lock was simulated. Instead of using heparin solution we injected 1 mL of a KCl solution (1 mol L(-1)) into the Shaldon catheter, because the measurement of the potassium concentration is faster and more reliable than that of heparin. Ten measurements were taken after fast (0.5 s) and slow (3 s) injection speeds.

Although the catheter volume is specified as 1.07 mL, an amount up to 0.51 mL KCl solution on average was detectable in the solution after locking the catheter with 1 mL KCl solution.

Following a heparin lock a considerable amount of the injected solution is accidentally administered to the patient. Only 49.1% of the injected volume may remain in the Shaldon catheter. This could lead to an increased risk of coagulopathy.