In this study, half of the patients underwent at least one heparin dosing adjustment that was noncompliant with the titration protocol; such noncompliant adjustments were performed by both physicians and nurses. The most common types of noncompliant adjustment appeared to involve calculation of new infusion rates. These “out of protocol” interventions were associated with a delay in reaching therapeutic aPTT and a decrease in the time spent in the therapeutic aPTT range.
Delays in achieving therapeutic aPTT levels may be detrimental to patients. In a cohort of patients with acute myocardial infarction who were receiving recombinant tissue-type plasminogen activator, Hsia and others6 found that early anticoagulation (therapeutic aPTT at 8 and 12 h after the start of fibrinolysis) resulted in a greater proportion of patients with patency of the infarct-related artery. Conversely, elevated aPTT levels have resulted in an increased risk of bleeding, reinfarction, stroke, and death.
Several researchers have tried to find ways to improve heparin anticoagulation, in particular through rapid achievement of a desired range of anticoagulation. Nomograms for weight-adjusted dosing are in most cases superior to standard-dose heparin or non-weight-based heparin nomograms in achieving rapid therapeutic anticoagulation. Hochman and others compared the efficacy of 2 weight-adjusted heparin regimens (70 U/kg bolus, maximum of 5000 U, followed by 15 U/kg per hour, maximum of 1000 U/h [n = 19 patients]; or 60 U/kg bolus, maximum of 4000 U, followed by 12 U/kg per hour, maximum of 900 U/h [n = 38 patients]) with that of standard heparin dosing (5000 U bolus, followed by infusion of 1000 U/h [n = 23 patients]) in patients with acute coronary syndromes. Of the patients receiving standard heparin dosing, 52% were within the therapeutic range at 24 h, whereas 79% of those with the high-dose weight-adjusted regimen and 74% of those with the low-dose weight-adjusted regimen reached thetherapeutic range within 24 h. In the present study, 32% of the patients were initiated on a weight-adjusted heparin regimen, and only 53% of these patients achieved a therapeutic aPTT level within 24 h after initiation of heparin therapy.
Although use of a weight-based heparin dosing protocol improves the clinical efficacy of heparin treatment by reducing the time needed to achieve therapeutic anticoagulation or increasing the time spent in the therapeutic window, the existence of such protocols does not guarantee compliance or absence of dosing errors. In fact, a weight-based nomogram might be associated with an even greater potential for error. Sherman and others assessed protocol compliance in the treatment of 20 patients with heart failure who required heparin therapy. Of 334 interventions, 12% were noncompliant, and 61% of the noncompliant adjustments were accounted for by dosing errors. The remaining noncompliant interventions were related to aPTT testing, which was either performed at an incorrect time or was not performed at all. In another study of 100 patients with deep vein thrombosis or pulmonary embolism, the noncompliance rate was 64%, and 47% of the noncompliant adjustments were dosing errors.
In this study of 190 heparin treatments, the noncompliance rate among the 397 interventions performed by nursing personnel was 17%, similar to that observed by Sherman and others, whose study focused on nurses. Noncompliance was associated with a significantly shorter time spent in the therapeutic range and fewer patients reaching therapeutic anticoagulation within 24 h. Most of the noncompliant interventions were related to dosing, and only 6% were associated with testing of aPTT.
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A variety of approaches could be used to improve the compliance rate. The protocol used in the authors’ institution is based on percentage increases or decreases in infusion rate rather than absolute increases or decreases. Given that a significant proportion of the noncompliant interventions were related to miscalculations, it appears that compliance could be improved if the protocol was modified to dictate absolute changes in the infusion rate instead of percentage changes. In addition, a computer- based heparin dosing protocol might improve compliance and reduce dosing errors. Kershaw and others demonstrated that pharmacy-based, computer- assisted heparin dosing resulted in faster treatment (median time to reach therapeutic aPTT 15 h vs 7 h in historical control and computer-assisted dosing groups, respectively; p < 0.001) and more accurate dosing (time with aPTT in the therapeutic range 43% vs 75%, p < 0.001).
The current study had several limitations, including study design (a chart review). As such, interventions that were deemed noncompliant might not have been considered noncompliant in a prospective study. Another drawback was the relatively small number of patients and the fact that they were from a single centre, which limited the external validity. Several authors have already confirmed the superiority of a weight-adjusted heparin regimen over standard dosing. Therapeutic aPTT values would probably have been achieved more quickly had a weight-adjusted heparin protocol been used. However, although such a practice has been recommended by the American College of Cardiology and the American Heart Association, it was not standard practice at the authors’ institution at the time this study was conducted. Finally, the recommendations for heparin dosing in patients with acute coronary syndromes have changed since this study was performed, and the results regarding the efficiency of the protocol cannot be extrapolated to current practice.
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In conclusion, use of a heparin protocol for cardiac patients was associated with achievement of target aPTT in 70% of cases, but aPTT was in the therapeutic range only 63% of the time, on average. Physicians and nursing personnel made noncompliant adjustments in applying the protocol, which were associated with suboptimal anticoagulation. Development of a weight-based heparin nomogram that specifies changes in infusion rates in absolute terms, rather than percentages, may decrease the time necessary to reach the therapeutic range and reduce the number of non- compliant interventions.