Anti-factor Xa Assay is a Superior Correlate of Heparin Dose Than Activated Partial Thromboplastin Time or Activated Clotting Time in Pediatric Extracorporeal Membrane Oxygenation*

Objective: To assess the utility of activated clotting time, activated partial thromboplastin time, and anti-Factor Xa assay for the monitoring and dosing of heparin in pediatric patients requiring support with extracorporeal membrane oxygenation.

Design: Retrospective chart review.

Setting: PICU in a single, tertiary care, academic children's hospital.

Patients: Seventeen patients (age 1 d to 13.9 yr, median 0.83 yr) managed on pulmonary and cardiac extracorporeal membrane oxygenation between March 2010 and August 2012 by a single surgeon.

Interventions: None.

Measurements And Main Results: Twice daily measurements of anti-Factor Xa assay, activated clotting time, and activated partial thromboplastin time were determined from the same blood specimen. Data were analyzed using SAS system v9.2. Fourteen patients (82.4%) were successfully weaned from extracorporeal membrane oxygenation and 12 (70.6%) were discharged from the hospital. Pearson correlations were used to compare heparin dose and activated clotting time, activated partial thromboplastin time, and anti-Factor Xa assay. Analysis showed negative Pearson correlations in 11 of 17 patients between the activated clotting time and heparin, as compared with seven of 17 for activated partial thromboplastin time and only one for heparin and anti-Factor Xa assay. Only four patients had moderate to strong positive correlations between activated clotting time and heparin as compared with a moderate to strong positive correlation in 10 patients for anti-Factor Xa assay and heparin.

Conclusions: The anti-Factor Xa assay correlated better with heparin dosing than activated clotting time or activated partial thromboplastin time. Activated clotting time has a poor correlation to heparin doses commonly associated with extracorporeal membrane oxygenation. In pediatric extracorporeal membrane oxygenation, anti-Factor Xa assay may be a more valuable monitor of heparin administration.