In this study the authors analyzed all courses of heparin therapy given to all patients admitted to the coronary care unit of the Hopital du Sacre-Creur de Montreal over a 5-month period. The patients’ medical records were reviewed to obtain data on the heparin treatments.
At the authors’ centre, heparin is administered intravenously to patients with cardiac disease who are admitted to the coronary care unit according to a protocol approved by the Pharmacology and Therapeutics Committee. The protocol used at the time of this study is presented in Appendix 1. In brief, the treating physician orders the initial loading dose and specifies the infusion rate according to the protocol. Both the loading dose and the initial infusion rate can be adjusted for the patient’s body weight if the physician so desires. Nurses are subsequently responsible for ordering tests of aPTT (6 h after the loading dose, 6 h after each dosage change, and daily thereafter), monitoring the results, and making the appropriate dosage adjustments on the basis of the protocol. The protocol does not account for weight in subsequent adjustments but rather dictates a percent increase or decrease in the infusion rate based on the extent of the discrepancy between actual and desired aPTT values. The goal is to achieve a target aPTT of 45-75 s or 1.5-2.5 times control. Nonetheless, physicians are allowed to make dosage changes that do not conform to the protocol if they deem it necessary.
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For the purposes of this study, the times at which changes in heparin dosage were ordered and the actual dose administered were recorded, as were the times at which aPTT tests were ordered and the actual values obtained; these data were compared with the protocol to evaluate the compliance of any adjustments with the protocol. In addition, the time necessary to attain a therapeutic value of aPTT and the time spent in the therapeutic range were estimated by calculating the slope of the line between each set of 2 consecutive data points that rested on each side of 1 of the 2 therapeutic aPTT boundaries (less than 45 s or greater than 75 s) and estimating the time at which the boundary would be crossed; from this estimation, time spent in the therapeutic range was calculated for that interval. All time intervals inside or outside the therapeutic range were then summed, as needed. Finally, the impact of noncompliance with the protocol on time spent in the therapeutic range and time necessary to attain a therapeutic aPTT was evaluated and compared with that of compliant interventions.
The results are expressed as mean values ± standard deviation or number (and percentage) of patients. Differences between groups were evaluated by analysis of variance (for continuous data) or by chi-square analysis (for categorical variables). A p value of less than 0.05 was considered significant.
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