Adaptive control of anticoagulation during hemodialysis

Induction of hemodialysis with an arteriovenous fistula in a patient with hemophilia A

An 88-year-old man with congenital hemophilia A developed end-stage renal disease due to microscopic polyangiitis. He was at risk for catheter-related infection because he was taking immunosuppressive agents for the treatment of polyangiitis. He was also unable to manipulate the peritoneal dialysis device. Therefore, hemodialysis using an arteriovenous fistula was induced for renal replacement therapy. Recombinant coagulation factor VIII (1000 IU) was administered via the venous chamber of the hemodialysis circuit 10 min before the end of each hemodialysis session, and nafamostat mesylate (25 mg/h) was employed as an anticoagulant during hemodialysis. His clotting factor VIII activity level increased to > 50% and activated partial thromboplastin time decreased to 50 s at the end of each hemodialysis session. This method allowed him to achieve hemostasis at the puncture site of the arteriovenous fistula and undergo stable hemodialysis with no complications, including bleeding. This case suggests that hemodialysis using an arteriovenous fistula with coagulation factor replacement and nafamostat mesylate in each hemodialysis session is a therapeutic option for end-stage renal disease in patients of advanced age with hemophilia at high risk of bleeding.

Use and safety of unfractionated heparin for anticoagulation during maintenance hemodialysis

Anticoagulation is essential to hemodialysis, and unfractionated heparin (UFH) is the most commonly used anticoagulant in the United States. However, there is no universally accepted standard for its administration in long-term hemodialysis. Dosage schedules vary and include weight-based protocols and low-dose protocols for those at high risk of bleeding, as well as regional anticoagulation with heparin and heparin-coated dialyzers. Adjustments are based largely on clinical signs of under- and overanticoagulation. Risks of UFH use include bleeding, heparin-induced thrombocytopenia, hypertriglyceridemia, anaphylaxis, and possibly bone mineral disease, hyperkalemia, and catheter-associated sepsis. Alternative anticoagulants include low-molecular-weight heparin, direct thrombin inhibitors, heparinoids, and citrate. Anticoagulant-free hemodialysis and peritoneal dialysis also are potential substitutes. However, some of these alternative treatments are not as available as or are more costly than UFH, are dependent on country and health care system, and present dosing challenges. When properly monitored, UFH is a relatively safe and economical choice for anticoagulation in long-term hemodialysis for most patients.

Improved dialyzer reuse after use of a population pharmacodynamic model to determine heparin doses

Anticoagulation with heparin is performed to prevent clotting during dialysis. However, heparin doses are usually determined empirically, and dialyzer clotting is a common reason for discarding reused dialyzers. We hypothesized that using a population pharmacodynamic model to determine individual heparin doses would improve dialyzer reuse rates. A previously published model was used to determine the loading dose and infusion rate of heparin needed to increase the intradialytic whole-blood clotting time to 150% of the predialysis value. The effectiveness of the model was assessed by comparing dialyzer reuse rates and delivered Kt/V(urea) before and after implementation of the model in 22 chronic hemodialysis patients. As an additional control, a similar group of 22 patients were followed up during the same period without adjustment of their heparin doses. Implementation of the model resulted in no change in the average loading dose (2,382 +/- 628 versus 2,425 +/- 908 IU; P = not significant) or average infusion rate (1,398 +/- 367 versus 1,393 +/- 532 IU/h; P = not significant) of heparin. However, individual patients required changes in loading dose or infusion rate. Dialyzer reuse rates increased significantly over time in the treatment group but remained unchanged in the control group (P < 0.003). Kt/V(urea) remained unchanged throughout the study period in both patient groups. From these data, we conclude that the use of a heparin model can improve dialyzer reuse rates without compromising the delivered dose of dialysis.

Automated heparin-delivery system to control activated partial thromboplastin time: evaluation in normal volunteers

BACKGROUND

Unfractionated heparin is used widely; however, control of the level of anticoagulation remains its greatest problem, with fewer than 35% of patients having activated partial thromboplastin times (aPTTs) within a range of 55 to 85 seconds in recent trials.

METHODS AND RESULTS

We developed and tested a prototype of an automated heparin control system (AutoHep) in which a computer-based titration algorithm adjusted the heparin infusion to reach a target aPTT. In 1 study, 12 healthy male subjects received an intravenous infusion of heparin with the rate determined by AutoHep and were randomized to receive an initial bolus or no bolus of heparin preceding the infusion. A second study evaluated the automated blood sampling system in 12 subjects. Of the 344 end-point aPTT measurements, 78% were within +/-10 seconds of the target (prespecified primary end point), and 89% were within a +/-15-second range. The time to achieve a target aPTT was 93 minutes without and 150 minutes with an initial heparin bolus. The total percentage of time within the target range +/-15 seconds was 46 of 48 hours (96%). The automatic blood sampling system successfully obtained 96% of all scheduled samples.

CONCLUSIONS

These results suggest that the AutoHep system has the potential to significantly improve aPTT control of intravenous heparin compared with current clinical practice.

Prediction of anticoagulation during hemodialysis by population kinetics and an artificial neural network

All systems currently used for routine hemodialysis require heparin administration to prevent blood clotting in the extracorporeal circuit. We tested the hypothesis that population-based statistical techniques can be used to predict heparin concentrations during routine hemodialysis. Two predictive models were developed, one based on nonlinear mixed effects modeling (NONMEM) and the other on a multilayer perceptron neural network. Serial clotting time data were obtained from forty-nine patients and used to develop the models. The models were used to predict the clotting times of 70 patients in a prospective test. We determined that the neural network provided greater precision, had fewer outliers in its predictions, and did not have the model misspecification in bolus administration that the NONMEM predictions demonstrated. A final NONMEM model was developed using all data from 119 patients to identify important covariates for predicting the heparin pharmacodynamic parameters, volume of distribution, and clearance. Both the volume of distribution and clearance increased following the initiation of dialysis and as the patient's baseline clotting time increased. The volume of distribution also increased as the patient's weight increased but was decreased by smoking and diabetes. Population-based statistical techniques may provide a useful alternative to existing methods for prescribing heparin.

The approach to anticoagulation in patients treated with extracorporeal therapy in the intensive care unit

No wholly satisfactory drug or system has yet been devised for preventing thrombosis in extracorporeal blood circuits needed for renal replacement treatments. Heparin is still regarded by some as a standard approach, but advances in many areas of intensive care unit (ICU) medicine have created the potential for saving the lives of many patients in whom heparin anticoagulation is no longer appropriate. Several nonheparin methods are now readily performed, and the great risk of bleeding that is imposed by the use of heparin demands that citrate or other nonheparin methods be made available in the ICUs of all major medical centers that deal with trauma or major surgical procedures. Details of the practicalities, difficulties, and advantages are compared for low-dose heparin, regional heparin, low-molecular-weight heparin, no-anticoagulant systems, citrate, and other anticoagulants for both intermittent and continuous modalities. The clinical features and complications in individual patients that impact on the selection of the best method of management are reviewed.

Closed-loop drug infusion for control of heart-rate trajectory in pharmacological stress tests

The diagnosis of coronary artery disease (CAD) is an important task in the management of cardiology patients. Recently, the use of pharmacological stress testing has become available as an alternative to exercise stress testing (ETT). A new system (device-drug combination) was developed specifically for the diagnosis of coronary artery disease. The system uses a novel catecholamine, arbutamine, which is infused intravenously to increase heart rate (HR) and cardiac contractility in order to evoke signs of ischemia. The development of a closed-loop control algorithm for the delivery of this drug and a pharmacodynamic (PD) model representing the HR response to arbutamine infusions are presented. Model parameters are estimated from clinical data on normal volunteers and patients. Based on this mathematical model, a rule-based control algorithm is designed. The structure of the control algorithm is discussed and testing of the algorithm based on simulations and animal and human trials are summarized. Results from clinical trials shows that the algorithm controls the HR increase according to a selected trajectory. The automated delivery of the drug can provide the cardiologist with an efficient, effective, and safe method for administering a pharmacological stress test.

Heparinization for routine hemodialysis

Routine hemodialysis requires anticoagulation with heparin to prevent clotting in the extracorporeal circuit. Activated whole blood clotting times are used to measure the level of anticoagulation during dialysis. The magnitude of the clotting time obtained for a given level of heparin depends on the test used, and each dialysis unit must establish its own target range. The preferred dosage regimen for heparin is an initial loading dose, followed by a constant infusion. Dosage regimens based on intermittent boluses of heparin are associated with periods of under- and over-anticoagulation and require more staff attention during dialysis. Because patient responses to heparin differ markedly, the doses required to achieve suitable anticoagulation must be determined on an individual basis. The doses of heparin for an individual patient are best determined using a simple pharmacodynamic model, although they can be found empirically through trial and error. In spite of careful anticoagulation, an unsatisfactory outcome may still result. Patient-specific factors may be responsible for some of these adverse outcomes; however, in most cases they result from poor technique, including failure to deliver the prescribed dose of heparin, turbulence and foam formation in the extracorporeal circuit, and excessive access recirculation.