Anticoagulants: Heparin

37,787views

00:00 / 00:00

Flashcards

Anticoagulants: Heparin

of complete

Questions

USMLE® Step 1 style questions USMLE

of complete

USMLE® Step 2 style questions USMLE

of complete

A 65-year-old woman comes to the emergency department complaining of chest pain and shortness of breath. Her symptoms began three hours ago. Past medical history is notable for hypertension and alcoholic liver disease. Upon arrival, her temperature is 37.8°C (100.0°F), pulse is 102/min, blood pressure is 142/75 mmHg, and respiratory rate is 21/min. Swelling and erythema is observed in the right lower extremity. The liver is palpated 2 centimeters below the right costal margin. There is no evidence of jaundice, scleral icterus, or abdominal ascites. Pulmonary CT angiography is ordered and reveals a pulmonary embolism in the left lung. The patient is started on the appropriate anticoagulant therapy. Two days later, the patient develops nausea, abdominal pain, and hematochezia. Laboratory testing is shown below. Which of the following is the best next step in the management of this patient?  

Laboratory Value
Results
Hemoglobin
11.0 g/dL
Hematocrit
33%
Leukocyte Count  
8,700/mm3
Platelet Count  
170,000/mm3  
Partial thromboplastin time  (activated)  
105 seconds
Prothrombin time  
14 seconds

External References

First Aid

2024

2023

2022

2021

Acute coronary syndrome

heparin for p. 440

Bleeding

heparin p. 440

Deep venous thrombosis (DVT) p. 691

heparin for p. 440

Factor Xa

heparin effect on p. 441

Heparin p. 440

acute coronary syndromes p. 314

for anticoagulation p. 419

in basophils p. 414

in coagulation cascade p. 418

deep venous thrombosis p. 690

mast cells and p. 409

osteoporosis p. 249

thrombocytopenia p. 249

toxicity treatment p. 247

warfarin vs p. 441

Intrinsic pathway p. 204

heparin and p. 441

Myocardial infarction (MI) p. 308

heparin for p. 440

Osteoporosis p. 467

heparin p. 440

Pregnancy p. 651

heparin in p. 440

Pulmonary embolism p. 691

heparin for p. 440

Thrombocytes (platelets) p. 413

heparin adverse effects p. 440

Thrombocytopenia p. 413

heparin adverse effects p. 440

Venous thrombosis p. 415

heparin for p. 440

Warfarin p. 441

heparin vs p. 441

Transcript

Watch video only

Anticoagulant medications are used to prevent blood clots from forming. These medications work by interfering with the normal function of plasma proteins called coagulation factors, which take part in secondary hemostasis-- where hemo refers to blood, and stasis meaning to halt or stop. In this video we’re going to focus on heparin, which works by indirectly inhibiting two clotting factors called thrombin and factor Xa by binding to and enhancing the activity of an anticoagulant protein called antithrombin III.

Now, before we discuss heparin in detail, we need to talk about the coagulation cascade, which is where heparin exerts its effect. The coagulation cascade begins via two pathways --the extrinsic and intrinsic pathways. The intrinsic pathway starts when circulating factor XII comes into contact with the surface of activated platelets or collagen. Activated factor XII, then activates factor XI, which activates factor IX which activates factor X. Factor Xa starts the common pathway where it activates factor II, or thrombin, which activates factor I that builds the fibrin mesh. When factor II gets activated it also activates 4 other factors: V, VIII, IX, and XIII. Factor V gets activated and acts as a cofactor for X, factor VIII acts as a cofactor for factor IX, and factor XIII helps factor I, or fibrin, form crosslinks. In the extrinsic pathway, exposed tissue factor activates factor VII, which activates factor X and starts the common pathway.

Now, the most important point of clot regulation is when a coagulation factor called thrombin is produced. Thrombin, or activated factor II, is a very important clotting factor, because it has multiple pro-coagulative functions. Think of thrombin as the accelerator on a car--the pedal that takes secondary hemostasis from 20 miles per hour to 100 miles per hour! First, thrombin binds to receptors on platelets causing them to activate. Activated platelets change their shape to form tentacle-like arms that allow them to stick to other platelets. Second, thrombin activates two cofactors; factor V used in the common pathway, and factor VIII used in the intrinsic pathway. Third, thrombin proteolytically cleaves fibrinogen or factor I, into fibrin or factor Ia which binds with other fibrin proteins to form a fibrin mesh. And finally, thrombin proteolytically cleaves stabilizing factor or factor XIII into factor XIIIa. Factor XIIIa combines with a calcium ion cofactor to form cross links between the fibrin chains, further reinforcing the fibrin mesh.

Sources

  1. "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
  2. "Rang and Dale's Pharmacology" Elsevier (2019)
  3. "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
  4. "Overview of hemostasis" J.C. Aster, H. Bunn (Eds.), Pathophysiology of Blood Disorders, 2e. McGraw-Hill (2016)
  5. "Critical Issues and Recent Advances in Anticoagulant Therapy: A Review" Neurology India (2019)
  6. "Heparinoid Complex-Based Heparin-Binding Cytokines and Cell Delivery Carriers" Molecules (2019)
Elsevier

Copyright © 2024 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.

RELX