A 75-year-old patient weighing 78kg was admitted with an acute pulmonary embolism. A heparin infusion was commenced with a dose of 1550 U/hr. Forty-eight hours later the following results were obtained:
|
Parameter |
Patient Value |
Adult Normal Range |
|
Prothrombin time |
16 sec |
12.0-16.5 |
|
INR (International Normalized Ratio) |
1.1 |
0.9-1.3 |
|
APTT (activated partial thromboplastin time) |
40 sec* |
27.0-38.5 |
|
Platelet count |
339 x 109/L |
150-350 |
|
Fibrinogen |
4.0 g/L |
2.0-4.0 |
3.3.1 Explain the above results and list the most likely cause. (1 mark)
3.3.2 List two potential treatment strategies. (1 mark)
Syllabus topic/section:
2.1.21 Applied Pharmacology in Intensive Care.
Aim:
To identify, assess and manage common coagulation abnormalities of critically ill patients.
Discussion:
Candidates should be commended for the depth of knowledge displayed here. Causes of thrombocytopenia were correctly noted and prioritised, Investigations including BMAT, SRA, PF4 ELISA test and were correctly identified.
Coagulation tests, Heparin resistance and the corresponding treatment strategies were explained well.
Heparin resistance again? This has come up in Question 13.2 from the first paper of 2012, Question 8.1 from the first paper of 2011 and Question 6.2 from the second paper of 2008. In short, the patient's APTT has failed to inrease with heparin for some reason. Possible explanations include:
There are several reasons one might be resistant to heparin:
Potential treatment strategies include:
Anderson, J. A. M., and E. L. Saenko. "Editorial I Heparin resistance." British journal of anaesthesia 88.4 (2002): 467-469.
Young, E., et al. "Heparin binding to plasma proteins, an important mechanism for heparin resistance." Thrombosis and haemostasis 67.6 (1992): 639-643.
Hirsh, J., et al. "Heparin kinetics in venous thrombosis and pulmonary embolism." Circulation 53.4 (1976): 691-695.
Beresford, C. H. "Antithrombin III deficiency." Blood reviews 2.4 (1988): 239-250.
The PROTECT Investigators for the Canadian Critical Care Trials Group and the Australian and New Zealand Intensive Care Society Clinical Trials Group Dalteparin versus Unfractionated Heparin in Critically Ill Patients N Engl J Med 2011; 364:1305-1314April 7, 2011
Koster, Andreas, et al. "Management of heparin resistance during cardiopulmonary bypass: the effect of five different anticoagulation strategies on hemostatic activation." Journal of cardiothoracic and vascular anesthesia 17.2 (2003): 171-175.
Isil, Canan Tulay, et al. "Management of heparin resistance in an emergency cardiac surgical patient." Indian journal of anaesthesia 56.4 (2012): 430.