Risk for excessive anticoagulation during hemodialysis is associated with type of vascular access and bedside coagulation testing: Results of a cross-sectional study

Abstract

Background: Recommendations and practice patterns for heparin dosing during hemodialysis show substantial heterogeneity and are scantly supported by evidence. This study assessed the variability in unfractionated heparin (UFH) dosing during hemodialysis and its clinical and biological anticoagulatory effects, and identified explanatory factors of heparin dosing.

Methods: Cross-sectional study assessing UFH dosing, coagulation tests - activated partial thromboplastin time (aPTT) and activated clotting time (ACT) before dialysis start, 1 h after start and at treatment end (4 h) - and measurement of residual blood compartment volume of used dialyzers.

Results: 101 patients, 58% male, with a median dialysis vintage of 33 (6-71) months received hemodialysis using a total UFH dose of 9,306 ± 4,079 (range 3,000-23,050) IU/session. Use of a dialysis catheter (n = 56, 55%) was associated with a 1.4 times higher UFH dose (p < 0.001) irrespective of prior access function. aPTT increased significantly more than ACT both 1 h and 4 h after dialysis start, independent of the dialysis access used. 53% of patients with catheter access and ACT ratio < 1.5, 1 h after dialysis start had simultaneous aPTT ratios > 2.5. Similar findings were present at 1 h for patients with AVF/AVG and at dialysis end for catheter use. No clinically significant clotting of the extracorporeal circuit was noted during the studied sessions. Dialyzer's blood compartment volume was reduced with a median of 9% (6-20%) without significant effect of UFH dose, aPTT or ACT measurements and vascular access type.

Conclusion: UFH dose adaptations based on ACT measurements frequently result in excessive anticoagulation according to aPTT results. Higher doses of UFH are used in patients with hemodialysis catheters without evidence that this reduces dialyzer clotting.

Keywords: activated clotting time; activated partial thromboplastin time; anticoagulation; bleeding risk; dialyzer; extracorporeal circuit clotting; hemodialysis; heparin.

FIGURE 1

Semiquantitative scoring system for dialyzer membrane and venous chamber. During the quality improvement project, the hemodialysis nurses scored both the dialyzer and the venous chamber after each hemodialysis session according to the above scoring scheme. Scores were noted on the electronic data sheet of the hemodialysis session.

FIGURE 2

Hemodialysis session selection for study inclusion. This study included 101 patients with hemodialysis session data on 92 sessions with simultaneous activated partial thromboplastin time (aPTT) and activated clotting time (ACT) monitoring and 87 sessions with simultaneous aPTT and blood compartment volume measurements.

FIGURE 3

UFH loading, maintenance and total dose within study subjects, according to vascular access. UFH, unfractionated heparin; IU, international units; kg, kilogram; h, hour; AVF/AVG, arteriovenous fistula/arteriovenous graft. The orange “+”-signs represent the median, the green dashed lines represent the 75th percentile and the red dashed lines represent the 25th percentile.

FIGURE 4

Relation between aPTT and ACT ratios both 1 h (left panel) and 4 h (right panel) after dialysis start. The red horizontal and vertical reference lines represent the ACT and aPTT ratios of × 1.5 and × 2.5, defining the therapeutic range of anticoagulation. The blue dots represent patients with an arteriovenous fistula or graft, the red circles represent patients with a catheter access. The shorter infusion time of unfractionated heparin in case of AVF/AVG use explains the shift toward lower left for AVF/AVG patients in the right graph. aPTT, activated partial thromboplastin time; ACT, activated clotting time; AVF/AVG, arteriovenous fistula/arteriovenous graft.

FIGURE 5

Bland and Altman analysis comparing aPTT and ACT ratios according to vascular access. These Bland and Altman graphs show the difference between aPTT and ACT ratios over the average of aPTT and ACT ratios. Bland and Altman plots are shown for aPTT and ACT values 1 h after dialysis start over baseline (upper panel) and for aPTT and ACT values 4 h after dialysis start over baseline (lower panel) according to access type.

FIGURE 6

Relation of blood compartment volumes of used dialyzers with UFH dose and dialyzer clotting score. The blood compartment volume of used dialyzers, expressed as the proportion (%) of the measured volume after use over the theoretical volume, is shown according to the total dose of unfractionated heparin administered during the hemodialysis session (upper panel) and the clotting score of the dialyzer (lower panel). The blue dots represent patients with an arteriovenous fistula or graft, the red circles represent patients with a catheter access.