Evaluation of 2 Weight-Based Protocols: DISCUSSION

22 Dec
2010

The results of this study suggest that the 2006 standard and lower-target weight-based heparin protocols used at the authors’ institution were equally efficacious in achieving therapeutic PTT levels early in therapy, with comparable low incidences of adverse events. These protocols compared favourably to the original 1996 weight-based heparin protocol, which was evaluated previously.1 Achieving anticoagulation early (within the first 24 h) after a thromboembolic event is critical to the optimization of patient outcomes. Although the current protocols could not be compared by statistical testing with the 1996 protocol, there appeared to be greater percentages of patients with PTT values above the lower limit of the target range within 24 h in both the standard and lower-target protocol groups than in the 1996 analysis. As well, the time to achieve therapeutic anticoagulation for both of the 2006 protocols appeared shorter than for the 1996 protocol. With respect to safety, there was only 1 episode of major bleeding, which was induced by a fall. The rate of major bleeding in the current study (1%) was much lower than in the original study (10%) and was comparable to rates observed in recent clinical trials of patients treated with IV heparin for venous thrombo­embolism (less than 3%).”

Protocol compliance remained an issue, as it was in the 1996 study, and violations of the protocol had a significant impact on the primary outcomes. The times to achieve PTT above the lower limit in the lower-target protocol group and within the therapeutic range in the standard protocol group were prolonged for patients with at least one protocol violation. Of note, the reported rates of compliance were likely under­estimated, as compliance was assessed only during the first 48 h of therapy. Incorrect adjustments of the infusion rate and incorrect sampling times for PTT measurement were the major compliance errors observed. The importance of protocol adherence in achieving adequate anticoagulation and thus improving patient outcomes needs to be emphasized. To prevent these problems in the future, the findings of this study were reported in the local pharmacy newsletter, which was distributed to various institutional sites in the region, targeting medical and nursing staff, as well as allied health care professionals.
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Patients in the standard protocol group with initially supratherapeutic PTT values (above 200 s) required at least 2 or 3 adjustments to the infusion rate to reach the therapeutic range. For those in the lower-target group with initially supratherapeutic PTT, only 1 or 2 rate adjustments were necessary. The multiple adjustments required probably contributed to the lower percentage of patients who achieved

PTT values within the therapeutic range within 24 h relative to the percentage who achieved levels above the lower limit of therapeutic range (80% versus 94%-96%). Because of the risks of prolonged overanticoagulation, the standard protocol has been further modified since completion of the study reported here, with more aggressive dose reductions for patients with PTT values above the upper limit of detection (200 s): instead of reducing the infusion rate by 150 units/h (as shown in Appendices 1 and 2), the rate is reduced by 200 units/h in the new protocol. Even though potential overanticoagulation was not a concern for the lower-target protocol group, both of the 2006 protocols were changed in April 2007 for overall consistency.

IV heparin boluses are intended for immediate anticoagu­lation when infusion is initiated. The findings of this study suggest that a heparin bolus may not affect the primary efficacy outcomes, nor does it contribute to initially suprather- apeutic PTT values. While these observations are interesting, they are no more than hypothesis-generating, as this subgroup analysis was underpowered. As such, clinicians should contin­ue with current dosing guidelines with respect to bolus doses.
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The study reported here had several limitations. It might have been subject to the known biases of a retrospective analysis with nonprobability sampling, observational design, and comparison with historical controls. Although strict inclusion and exclusion criteria, standard study definitions, clear procedures for data collection, and objective study end points were used, reporting in the patients’ health records may have been incomplete or inaccurate. This observational study was conducted over a relatively short period of time using a small convenience sample of 50 consecutive patients for each protocol, to correspond with the sample size in the 1996 study. As well, the effects of heparin therapy were analyzed for only the first 48 h, and the initial efficacy of attaining therapeutic PTT must be balanced with the effectiveness, safety, and efficiency of the protocol for maintaining therapeutic PTT for the duration of therapy. This study was undertaken to replicate and allow comparison with the 1996 study; however, the indi­vidual patient data from the original study were irretrievable, and statistical comparisons could not be performed. Finally, the applicability of these findings to current practice may be limited. Almost 1 in 3 patients in this study had a protocol violation, and in January 2007, the laboratory changed its method of determining PTT (using less sensitive reagents), which has altered the therapeutic PTT ranges for both protocols. The heparin protocols were also modified shortly after completion of the study, as previously described, with more aggressive dose reductions for PTT values above the upper limit of detection. viagra 50 mg

In conclusion, the standard and lower-target heparin protocols implemented in August 2006 appeared equally efficacious and safe in achieving rapid therapeutic anticoagulation. Protocol violations significantly delayed the time to achieve therapeutic anticoagulation; reinforcement of protocol compliance is therefore critical to achieve rapid and safe anticoagulation.

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