Monitoring of unfractionated heparin in critically ill patients

In critically ill patients, dosing of unfractionated heparin (UFH) is difficult due to unpredictable pharmacokinetics, which has an impact on the time to reach therapeutic anticoagulation. We evaluated the quality of UFH therapy in critically ill patients in terms of activated partial thromboplastin time (APTT) test values and time to therapeutic range.

Patients admitted to the Intensive Care Unit (ICU) and Medium Care Unit (MCU) were screened for intravenous UFH administration. Time to therapeutic range was categorised into 0-12, 13-24 and >24 hours. APTT results were classified into categories of subtherapeutic, supratherapeutic and therapeutic tests. We identified to what extent the sub- and upratherapeutic values were aberrant of the limit of the therapeutic range (15%).

In 101 patients admitted to the ICU and MCU, time to therapeutic range was 24 hours in 56% of the population, whereas in 10% of the patients no therapeutic APTT was achieved during UFH treatment. Among the APTT levels, 29% of all test results measured in 24 hours were within the therapeutic range. Subtherapeutic values were found in 53% of the test results, of which 160/203 were more than 15% under the lower limit, whereas 18% of the test results were supratherapeutic, of which 40/69 more than 15% above the upper limit.

In this cohort of critically ill patients, therapeutic APTT values were reached within 24 hours in 56% of the patients. We conclude that intravenous UFH therapy can be improved in critically ill patients.