Evaluation of 2 Weight-Based Protocols: METHODS

19 Dec
2010

A retrospective, open-label observational study was conducted over a period of 5 months (September 2006 to January 2007). Approval to conduct this study was obtained from the University of British Columbia Clinical Research Ethics Board and the Vancouver Coastal Health Research Institute. The 2 current protocols were implemented in August 2006. The decision as to which protocol would be appropriate for an individual patient was left to the discretion of the physician, on the basis of the clinical indication. Patients to be included in the study were identified from a drug report generated daily by the pharmacy computer system. The goal was to enrol a convenience sample of 50 patients for whom the standard protocol (Appendix 1) was used and 50 patients for whom the lower-target protocol (Appendix 2) was used, inde­pendent of indication. Patients were excluded if they had received heparin for less than 24 h or if there had been any deliberate, documented changes in the heparin protocols, other than omitting the bolus dose (e.g., changes in target PTT range specified in writing by the physician).

PTT was monitored for the first 48 h of continuous IV infusion of heparin (or longer if the therapeutic target was not achieved within 48 h). The time to the first PTT measurement and the corresponding PTT value, the time to reach PTT above the lower limit of the therapeutic range, and the time to achieve PTT within the therapeutic range were collected from each patient’s chart. The percentage of patients who had reached the therapeutic range at any point within the first 24 h was also determined. If the initial PTT value was above 200 s (the limit of detection for PTT measurement), the number of adjustments to the rate of heparin infusion required to lower the PTT to within the therapeutic range within the first 48 h was documented. In order for the first PTT value to be included in the efficacy analysis, it had to be measured at least 4 h and less than 8 h after initiation of heparin therapy. The indication for heparin therapy, the duration of therapy, and the appropriateness of choice of protocol were also collected.
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For all patients included in the study, PTT was determined using the STA-PTT Automate 5 activated PTT reagent, with interpretation by the STA-R Evolution coagulation analyzer (Diagnostica Stago, Asnieres, France). The PTT range was determined by the hematopathology department at the authors’ hospital site, on the basis of anti-Xa levels obtained from a series of patient samples. These values were graphed on the x axis against the patients’ PTT levels to generate a regression line, which allowed ascertainment of PTT values at various anti-Xa levels (C. Carter, MD, FRCPC, hematopathologist, Vancouver General Hospital, personal communication by email, October 15, 2008).

Adverse events were assessed for the entire course of heparin therapy. Major bleeding was defined as overt bleeding with one or more of the following: a decrease in hemoglobin of 20 g/L, transfusion of 2 or more units of blood, and hemorrhage in the retroperitoneum, the cranium, or a prosthetic joint. The PTT at the time of bleeding was also recorded. Recurrence of deep vein thrombosis or pulmonary embolism was determined on the basis of radiographic confirmation or high clinical suspicion. The cause of death was documented for patients who died while receiving heparin therapy. Apcalis Oral Jelly

Compliance with the heparin protocol was evaluated for the first 48 h of therapy. Information in the patients’ charts was assessed for the following protocol violations: errors in the bolus dose, incorrect adjustments to the rate of maintenance infusion, incorrect infusion hold time for patients with high PTT values, incorrect sampling time for initial PTT (defined as first PTT sample drawn more than 2 h before or after the scheduled time), omission of PTT documentation, omission of a coagulation test, or failure of nursing staff to contact the physician after 3 consecutive subtherapeutic or supratherapeutic PTT values.

The primary efficacy outcomes were the time to achieve PTT above the lower limit of the therapeutic range and within the therapeutic range. The primary safety outcomes were the incidence of major bleeding and recurrence of deep vein thrombosis or pulmonary embolism. The secondary outcome measures were the total number and types of protocol violations and their associated effects on the primary efficacy outcomes.
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A convenience sample size of 50 patients for each heparin protocol was chosen to match the sample size of the 1996 study. Summary descriptive and inferential statistics were obtained using SPSS 15.0, with means and standard deviations reported for normally distributed data and medians and ranges for nonparametric data. The efficacy outcomes of the two 2006 heparin protocols were analyzed and compared using the Mann-Whitney U test for nonparametric data. The level of significance was set atp < 0.05. Because the original data for the 1996 study were irretrievable, summary means and standard deviations were used to qualitatively compare the 2006 and 1996 protocols.

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