Monitoring of Unfractionated Heparin Therapy in the Intensive Care Unit Using a Point-of-Care aPTT: A Comparative, Longitudinal Observational Study with Laboratory-Based aPTT and Anti-Xa Activity Measurement

Clinical guidance for unfractionated heparin dosing and monitoring in critically ill patients

INTRODUCTION

Unfractionated heparin is a widely used anticoagulant in critically ill patients. It has a well-established safety profile and remains an attractive option for clinicians due to its short half-life and reversibility. Heparin has a unique pharmacokinetic profile, which contributes to significant inter-patient and intra-patient variability in effect. The variability in anticoagulant effect combined with heparin's short half-life mean close monitoring is required for clinical efficacy and preventing adverse effects. To optimize heparin use in critically ill patients, effective monitoring assays and dose adjustment strategies are needed.

AREAS COVERED

This paper explores the use of heparin as an anticoagulant and optimal approaches to monitoring in critically ill patients.

EXPERT OPINION

Conventional monitoring assays for heparin dosing have significant limitations. Emerging data appear to favor using anti-Xa assay monitoring for heparin anticoagulation, which many centers have successfully adopted as the standard. The anti-Xa assay appears have important benefits relative to the aPTT for heparin monitoring in critically ill patients, and should be considered for broader use.

Acute pulmonary embolism in cancer patients admitted to intensive care unit: Impact of anticoagulant treatment on 90-day mortality and risk factors, results of a multicentre retrospective study

BACKGROUND

Acute pulmonary embolism (PE) is a life-threatening situation in cancer patients. In this situation, anticoagulant therapy is complex to administer due to the risk of bleeding. Only few studies have been conducted when these patients are admitted to the intensive care unit (ICU). The aim of this study was to assess the association between anticoagulation strategies as well as other factors with 90-day mortality in patients with cancer and PE admitted to ICU. Major bleeding was also evaluated according to the type of anticoagulation.

METHODS

Retrospective study carried out in 4 ICUs in France over a 12-year period (2009-2021). All patients with cancer and PE were included. An overlap propensity score weighting analysis was performed in the subgroup of patients treated with either unfractionated heparins (UFH) alone or low-molecular-weight heparins (LMWH) alone on 90-day mortality and major bleeding.

RESULTS

A total of 218 consecutive cancer patients admitted to ICU and presenting PE were included. The 90-day mortality rate was 42 % for the global cohort. After propensity score analysis in the subgroup of patients treated with either "UFH alone" (n = 80) or "LMWH alone" (n = 71), the 90-day mortality was similar in patients treated with UFH alone (42.6 %) vs LMWH alone (39.9 %): OR = 1.124, CI 95 % [0.571-2.214], p = 0.750. There was a significant increased toward major bleeding rates in the "UFH alone" group (25.5 %) as compared to "LMWH alone" group (11.5 %), p = 0.04.

CONCLUSION

In 218 patients admitted to ICU and presenting PE, the 90-day mortality rate was 42 %. Treatment with UFH alone was associated with a mortality comparable to treatment with LMWH alone but it appeared to be more prone to major bleeding.

Laboratory Monitoring of Heparin Anticoagulation in Hemodialysis: Rationale and Strategies

Unfractionated heparin (UFH) and low-molecular-weight heparins (LMWHs) are commonly used to prevent clotting of the hemodialysis extracorporeal circuit and optimize hemodialysis adequacy. There is no consensus on the optimal dosing for UFH and LMWHs during hemodialysis. In clinical practice, semiquantitative clotting scoring of the dialyzer and venous chamber may help to guide UFH and LMWH dose adjustment. Laboratory monitoring has not been shown to improve clinical outcomes and is therefore not routinely indicated in most hemodialysis patients. It might, however, be considered in select patients, such as those with extremes of body weight or history of repeated clotting or bleeding. Methods for laboratory monitoring include the activated partial thromboplastin time, activated clotting time, and antifactor Xa assays for UFH and antifactor Xa assay for LMWHs. Target ranges for anticoagulation in hemodialysis have been suggested but not clearly defined. When utilizing these tests, issues such as availability, standardization, interfering factors, and interpretation must be considered. In this narrative review, we discuss the rationale and methods of monitoring anticoagulation in hemodialysis.

Application of anti-Xa assay in monitoring unfractionated heparin therapy in contemporary antithrombotic management

INTRODUCTION

Unfractionated heparin remains the most widely used agent in the prevention and acute treatment of thrombosis. Pharmacological complexities of this intriguing agent mandate frequent monitoring of its anticoagulant properties to maintain safe and effective hematological outcomes. Although activated partial thromboplastin time has been the standard test to monitor unfractionated heparin therapy for many decades, the anti-Xa assay has emerged as a substitute or adjunct in many institutions.

AREAS COVERED

This brief report outlines the key features of anti-Xa assay in monitoring unfractionated heparin in acute management of thrombosis in various contemporary settings, with emphasis on evidence for clinical outcomes. PubMed.gov database was utilized to obtain the pertinent literature.

EXPERT OPINION

The anti-Xa activity is primarily a reflection of UFH concentration and does not account for other hematological variables frequently present in contemporary anticoagulation management. The advantage of the anti-Xa assay in monitoring UFH therapy is predicated upon its limitations to account for global physiological hemostasis. There are significant disease and drug interactions that may potentially result in false in-vitro analysis of anti-Xa activity. Routine application of the anti-Xa assay is not evidence-based at this time.

Whole-blood Point-of-Care Activated Partial Thromboplastin Time Ratio (APR) is not Accurate Enough to Monitor Heparin Therapy in Patients with Severe Respiratory Failure Secondary to SARS-Cov-2 Infection Supported with Veno-Venous Extracorporeal Membrane Oxygenation (VV-ECMO)

Support with VV-ECMO requires anticoagulation with unfractionated heparin to prevent thrombotic complications. This must be monitored due to bleeding risk. A point-of-care (POC) method of testing aPTT and APR was evaluated for agreement with laboratory methods. In a prospective observational study, patients supported on VV-ECMO as a result of severe respiratory failure secondary to Covid-19 infection were given heparin as part of standard therapy. The aPTT was measured (i) at the bedside using the Hemochron Signature Elite device and (ii) at the hospital laboratory. Duplicate results were compared. Agreement between the POC and laboratory tests was poor, as assessed using the Bland-Altman method. The maximum difference between POC and laboratory methods was 133% and the minimum was 0%. Overall bias was 7.3% and limits of agreement were between -43.8% and 58.5%. Correlation increased when results were normalised to platelet count and creatinine. This POC test is insufficiently accurate for use as the primary method of heparin monitoring in patients requiring VV-ECMO for Covid-19. Platelets and renal function may influence the result of this whole blood POC test.

An Agreement Study Between Point-of-Care and Laboratory Activated Partial Thromboplastin Time for Anticoagulation Monitoring During Extracorporeal Membrane Oxygenation

Background

Laboratory activated partial thromboplastin time (LAB-aPTT) is a widely used laboratory assay for monitoring unfractionated heparin (UFH) therapy during extracorporeal membrane oxygenation (ECMO). But LAB-aPTT is confined to a central laboratory, and the procedure is time-consuming. In comparison, point-of-care aPTT (POC-aPTT) is a convenient and quick assay, which might be a promising method for anticoagulation monitoring in ECMO. This study was aimed to evaluate the agreement between POC-aPTT (hemochron Jr. Signature instruments) and LAB-aPTT for anticoagulation monitoring in adult ECMO patients.

Methods

Data of ECMO-supported adult patients anticoagulated with UFH in our institute from January 2017 to December 2020 was retrospectively reviewed. POC-aPTT and LAB-aPTT results measured simultaneously were paired and included in the analysis. The correlation between POC-aPTT and LAB-aPTT was assessed using Spearman’s correlation coefficient. Bias between POC-aPTT and LAB-aPTT were described with the Bland-Altman method. Influence factors for bias were identified using multinomial logistic regression analysis.

Results

A total 286 pairs of aPTT results from 63 patients were included in the analysis. POC-aPTT and LAB-aPTT correlated weakly (r = 0.385, P < 0.001). The overall bias between POC-aPTT and LAB-aPTT was 7.78 [95%CI (−32.49, 48.05)] s. The overall bias between POC-aPTT and LAB-aPTT ratio (to normal value) was 0.54 [95%CI (−0.68, 1.76)]. A higher plasma fibrinogen level [OR 1.353 (1.057, 1.733), P = 0.017] was associated with a higher chance of POC-aPTT underestimating LAB-aPTT. While a lower plasma fibrinogen level [OR 0.809 (0.679, 0.963), P = 0.017] and lower UFH rate [OR 0.928 (0.868, 0.992), P = 0.029] were associated with a higher chance of POC-aPTT overestimating LAB-aPTT.

Conclusion

The present study showed poor agreement between POC-aPTT and LAB-aPTT. POC-aPTT was not suitable for anticoagulation monitoring in adult ECMO patients.