Elsevier

Journal of Critical Care

Volume 30, Issue 6, December 2015, Pages 1190-1194
Journal of Critical Care

Cardiovascular
Clinically suspected heparin-induced thrombocytopenia during extracorporeal membrane oxygenation

https://doi.org/10.1016/j.jcrc.2015.07.030Get rights and content

Abstract

Purpose

Patients receiving extracorporeal membrane oxygenation (ECMO) are at risk for thrombocytopenia including heparin-induced thrombocytopenia (HIT). The purpose of this study was to determine the frequency of suspected HIT in patients receiving ECMO and unfractionated heparin (UFH).

Materials and methods

We conducted a retrospective review in adult patients on ECMO. Patients were included if they received ECMO for at least 5 days and concomitant UFH.

Results

There were 119 patients who met inclusion criteria. Twenty-three patients (19%) had a heparin–platelet factor 4 immunoassay performed. Patients with suspected HIT had a significantly lower platelet count within the first 3 days of ECMO, 69 × 109/L (22-126 × 109/L) vs 87.5 × 109/L (63-149 × 109/L); P = .04. The lowest platelet count on the day of HIT testing was 43 × 109/L (26-73), representing a 71% reduction from baseline. Twenty patients (87%) had an optical density score less than 0.4, and all patients had a score less than 1.0. A functional assay was performed in 7 patients (30%), with only 1 patient having laboratory-confirmed HIT.

Conclusions

The evaluation of HIT occurred in a small percentage of patients, with HIT rarely being detected. Patients who had heparin–platelet factor 4 immunoassay testing exhibited lower platelet counts with a similar duration of ECMO and UFH exposure.

Introduction

Extracorporeal membrane oxygenation (ECMO) is a form of mechanical circulatory support used in critically ill patients with respiratory or cardiac failure. Systemic anticoagulation is used to mitigate the thrombotic complications that may occur when blood is exposed to artificial surfaces within the ECMO circuit [1]. Unfractionated heparin (UFH) is the most common anticoagulant used to prevent the formation of thrombus within the ECMO circuit [1]. A rare but potential serious adverse effect of UFH is immune-mediated heparin-induced thrombocytopenia (HIT), with an incidence as high as 5%, depending on the patient population [2], [3]. However, the incidence of HIT in patients receiving ECMO is not well characterized [4], [5], [6].

The diagnosis of HIT is based on both clinical suspicion and pathologic confirmation. Clinical suspicion of HIT typically occurs with declining platelet counts in the setting of active heparin use. However, thrombocytopenia in critically ill patients is often multifactorial and may be due to various inciting events. The use of mechanical circulatory support can simultaneously result in thrombocytopenia and thrombosis through platelet activation and consumption, mimicking the presentation of HIT [1], [7]. In addition, mechanical circulatory support may influence the development of HIT as a result of continued platelet activation and ongoing release of platelet factor 4 (PF4) [8], [9]. This retrospective review will evaluate the frequency of suspected HIT in patients receiving ECMO in a single, academic medical center.

Section snippets

Patients

This was a retrospective chart review of all patients who received ECMO between January 2011 and June 2013. Patients were included if they were at least 18 years of age, had no prior history of HIT, were anticoagulated with UFH within 24 hours of ECMO initiation, and received ECMO for at least 5 continuous days. The study was approved by the institutional review board. Individual patient consent was waived because of the retrospective nature of the study.

Anticoagulation in ECMO

Our institutional guideline for the

Patient characteristics

Our cohort consisted of 119 patients, 19% of whom had a clinical suspicion of HIT. Baseline demographic data are listed in Table 1. Groups were similar with respect to age, weight, comorbidities, ECMO configuration, and baseline platelet count. Thirty percent of cardiac patients had HIT testing sent compared to 7.5% of medical patients (P = .08). Although patients with clinical suspicion of HIT had a higher median APACHE II score as compared to those who did not (25 vs 22; P = .06), it was not

Discussion

In this cohort of 119 adults receiving ECMO and UFH, we found that 19% of patients had clinical suspicion of HIT, with only 1 patient having laboratory-confirmed HIT. Patients suspected of HIT had significantly lower platelet counts with a similar duration of ECMO, baseline platelet count, and total UFH exposure. We found no significant differences in ICU and hospital lengths of stay, but significantly higher inhospital mortality in patients suspected of HIT.

Thrombocytopenia, typically defined

Conclusions

In conclusion, although the suspicion of HIT occurs frequently in patients supported with ECMO, there appears to be a very low incidence of laboratory-confirmed HIT. This clinical problem still remains elusive, as the low incidence in this cohort should not preclude further evaluation. Nonetheless, incorrectly labeling a patient as having HIT has significant implications and should only be investigated after careful clinical evaluation.

Conflicts of interest

Daryl Glick: None

Amy L. Dzierba: None

Darryl Abrams: None

Justin Muir: None

Andrew Eisenberger: None

David Diuguid: None

Erik Abel: None

Cara Agerstrand: None

Matthew Bacchetta: None

Daniel Brodie: Research support and research consulting for Maquet Cardiovascular, Medical Advisory Board for ALung Technologies. All compensation paid to Columbia University.

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    Institution where work was completed: NewYork-Presbyterian Hospital, Columbia University Medical Center, 177 Fort Washington Avenue, New York, NY 10032. At the time of data collection, Daryl Glick was a PGY-2 Critical Care Pharmacy Resident at NewYork-Presbyterian Hospital. She now works at Mount Sinai Beth Israel.

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