Adjusting heparin infusion rates from the initial response to activated coagulation time

Anticoagulation in intermittent hemodialysis: pathways, protocols, and pitfalls

Several methods to prevent extracorporeal circuit clotting during hemodialysis have been used in human medicine. Unfractionated (UF) heparin remains the mainstay of anticoagulant therapy in both human and veterinary intermittent hemodialysis. Different UF heparin regimes may be used depending on the bleeding risk of the patient. In patients with active bleeding or with a recent history of surgery or hemorrhagic episodes, hemodialysis may be performed without any anticoagulation or with regional anticoagulation.

Achieving Target Antifactor Xa Activity with a Heparin Protocol Based on Sex, Age, Height, and Weight

STUDY OBJECTIVES

To develop and validate an improved unfractionated heparin (UFH) dosage protocol, using antifactor Xa levels as the outcome variable.

DESIGN

Prospective case series.

SETTING

A 625-bed, adults-only private, tertiary care teaching hospital.

PATIENTS

Three hundred seventy-two patients receiving UFH for eight different indications were in the protocol derivation group. One hundred ninety-seven patients were in the final validation group. Intervention. Variables that predicted successful UFH treatment were determined by analysis of variance and regression.

MEASUREMENTS AND MAIN RESULTS

Sex, age, height, weight, UFH dosage, and antifactor Xa levels were variables. A regression model using sex, age, height, and weight was superior to a weight-only model in predicting UFH dosage. Target-range antifactor Xa levels were achieved with the new protocol in 122 (87%) of 140 patients within 24 hours of start of therapy.

CONCLUSION

A UFH dosage protocol based on patient sex, age, height, and weight produced improved initial target antifactor Xa levels compared with a weight-based protocol. The protocol is computerized and easy to apply.

Watering down the clots, or are we?

Fluid resuscitation is an essential part of managing patients with major trauma, as well as in the perioperative setting. Common misconceptions exist regarding the role of fluid therapy in maintaining, enhancing or inhibiting normal coagulation and haemostasis. This review provides an overview of the basic coagulation processes, as well as the influence of intravenous crystalloid and colloid preparations on haemostasis and coagulation. The use of point-of-care devices is encouraged as a feasible way of monitoring these effects in the acute setting.

Heparin resistance as detected with an antifactor Xa assay is not more common in venous thromboembolism than in other thromboembolic conditions

STUDY OBJECTIVE

To identify whether heparin resistance when measured with an antifactor Xa assay is more frequent in patients with venous thromboembolic disease than in patients with other thromboembolic conditions.

DESIGN

Prospective observational cohort study.

SETTING

A 625-bed, adults-only, private teaching hospital.

PATIENTS

Three hundred seventy-two patients receiving intravenous unfractionated heparin for a variety of indications classified as either venous thromboembolism or arterial thromboembolism.

INTERVENTION

All patients received an initial unfractionated heparin dosage according to a protocol based on age and estimated blood volume. Targeted antifactor Xa was 0.35-0.65 U/ml.

MEASUREMENTS AND MAIN RESULTS

A modest increase in heparin dosage requirement was noted in patients with venous thromboembolism that was entirely related to lower hemoglobin concentration in that group compared with the arterial thromboembolism group. Low hemoglobin concentration was significantly associated with increased heparin resistance regardless of treatment indication.

CONCLUSIONS

True heparin resistance seen with an antifactor Xa assay is not more common in venous thromboembolism than in other conditions. Low hemoglobin concentration, rather than treatment indication, appears to be associated with increased heparin resistance.

New method to predict patients' intravenous heparin dose requirements

OBJECTIVE

To predict intravenous heparin dose requirements of patients treated for thromboembolic disorders.

DESIGN

A retrospective cohort study in which we used simple linear regression to predict patients' effective maintenance dose (EMD) of heparin (units/kg/hour needed to achieve and maintain APTT therapeutic range) from patients' "heparin responsiveness" (the APTT increase after the initial 6 hours of heparin treatment per units/kg/hour received).

SETTING/PATIENTS

The model was derived from 46 patients treated at one hospital (Hospital A) and then tested in 42 patients treated at another hospital (Hospital B).

MEASUREMENTS AND MAIN RESULTS

Among Hospital A patients, there was a strong linear correlation (r = -.880; p < .001) between EMD (mean 16.02 units/kg/hour; 95% CI 14.9, 17.15) and "heparin responsiveness" (HR): EMD = 25.651 - [95.118 x HR]. This model accurately predicted Hospital B patients' EMD: 97% (37/38) fell within the model's 95% prediction interval; the mean absolute difference between predicted and actual EMD was 1.73 units/kg/hour (95% CI 1.39, 2.08); and only 16% of patients had EMD's more than 3 units/kg/hour different from that predicted by the regression model. The model's accuracy was comparable to that of our gold standard, the weight-based heparin dosing nomogram.

CONCLUSION

The infusion dose of intravenous heparin effective for an individual patient can be predicted accurately from the patient's body weight and APTT response to the initial 6 hours of treatment. Especially in hospitals where validated heparin dosing nomograms are not used, clinicians may find this simple technique useful in achieving timely therapeutic anticoagulation.