Understanding VOC Crises in Sickle Cell Patients: Causes, Risk Factors, Pathophysiology, Molecular Biology, and Management.

Mohamad-Ali Salloum, PharmD • July 17, 2024

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Introduction:


Sickle cell disease is a genetic blood disorder characterized by the presence of abnormal hemoglobin, leading to the production of sickle-shaped red blood cells. One of the most common complications associated with sickle cell disease is vaso-occlusive crises (VOC), which can cause severe pain and organ damage. This essay aims to explain VOC crises in simple terms, exploring their causes, risk factors, pathophysiology, molecular biology, and both non-pharmacologic and pharmacologic management strategies.


Causes and Risk Factors:

 

VOC crises occur when sickle-shaped red blood cells clump together, blocking the normal flow of blood through the blood vessels. This blockage can result from various triggers, including infection, dehydration, stress, cold temperatures, or altitude changes. Certain risk factors, such as a history of previous VOC episodes, smoking, and pregnancy, can increase the likelihood of experiencing VOC crises. 


Pathophysiology:  


In individuals with sickle cell disease, the abnormal hemoglobin causes red blood cells to become rigid and sticky, making it difficult for them to flow smoothly through blood vessels. When triggered, sickle cells can become even more deformed, leading to the formation of clumps that block blood flow. This process can occur in any organ or tissue, causing pain and potentially damaging the affected area. 


Molecular Biology:  


The primary defect in sickle cell disease lies in the hemoglobin molecule. Unlike normal hemoglobin, which remains flexible and allows red blood cells to pass smoothly through blood vessels, the abnormal hemoglobin in sickle cell disease can polymerize under certain conditions. This polymerization causes red blood cells to change shape, forming the characteristic sickle shape. These sickle cells are less efficient in carrying oxygen and are more prone to clumping, leading to VOC crises. 


Non-pharmacologic Management:  


Non-pharmacologic management strategies aim to prevent VOC crises by addressing triggers and promoting overall health. Patients are advised to stay well-hydrated, avoid extreme temperatures, manage stress levels, and receive regular vaccinations to prevent infections. Additionally, adopting a healthy lifestyle, including a balanced diet and regular exercise, can help reduce the frequency and severity of VOC episodes. 


Pharmacologic Management:  


  1. Pain Management: Pain is the most immediate and distressing symptom of a VOC. Non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen can be used for mild to moderate pain. For severe pain, opioids such as morphine may be prescribed. It’s important to note that these medications should be used under the supervision of a healthcare provider due to their potential side effects and risk of dependency. 
  2. Hydroxyurea: Hydroxyurea is an oral medication that reduces the frequency of VOCs by increasing the production of fetal hemoglobin. Fetal hemoglobin is a type of hemoglobin that does not sickle, so its presence in the blood can prevent the formation of sickle cells. The typical starting dose for adults is 15mg/kg per day, which can be increased gradually to a maximum of 35mg/kg per day based on the patient’s response and tolerance. Regular blood tests are required to monitor the effects of hydroxyurea and adjust the dose if necessary. 
  3. Blood Transfusions: Regular blood transfusions can reduce the number of sickle cells in the body, thereby decreasing the frequency of VOCs. However, repeated blood transfusions can lead to complications such as iron overload, so they are typically reserved for severe cases. 
  4. L-glutamine oral powder: It is a medication that helps to reduce the acute complications of sickle cell disease. It works by reducing oxidative stress in sickle cells, which can help to prevent cell sickling and the subsequent blockage of blood vessels. The typical dose is 5 grams (1 packet) taken orally twice daily. 
  5. Voxelotor: It is a medication that increases hemoglobin’s affinity for oxygen, preventing the cells from sickling. The typical dose is 1500 mg taken orally once daily. This medication can cause side effects such as headache, diarrhea, abdominal pain, nausea, fatigue, rash, and fever. 
  6. Crizanlizumab: It is a monoclonal antibody that blocks P-selectin, a substance on the surface of cells that contributes to the blockage of blood vessels in sickle cell disease. By blocking P-selectin, crizanlizumab can help to prevent VOCs. The typical dose is 5 mg/kg given by intravenous infusion on days 1, 8, 15 and then every 4 weeks. 


Please remember that this is a simplified explanation, and the actual management of sickle cell disease can be quite complex and should always be overseen by a healthcare provider. Always consult with a healthcare provider for medical advice. 



Resources:

1)Platt OS, Brambilla DJ, Rosse WF, et al. Mortality in sickle cell disease. Life expectancy and risk factors for early death. N Engl J Med. 1994;330(23):1639-1644. 

 

2)Brousseau DC, Panepinto JA, Nimmer M, et al. The number of people with sickle-cell disease in the United States: national and state estimates. Am J Hematol. 2010;85(1):77-78. Gladwin MT, Vichinsky E. Pulmonary complications of sickle cell disease. N Engl J Med. 2008;359(21):2254-2265. 

 

3)Steinberg MH. Management of sickle cell disease. N Engl J Med. 1999;340(13):1021-1030. Charache S, Terrin ML, Moore RD, et al. Effect of hydroxyurea on the frequency of painful crises in sickle cell anemia. N Engl J Med. 1995;332(20):1317-1322. 

 

4)Ballas SK. Sickle cell pain: a critical reappraisal. Blood. 2015;125(23):3685-3691. 

 

5)Platt OS. Sickle cell anemia as an inflammatory disease. J Clin Invest. 2000;106(3):337-338. Kato GJ, Steinberg MH, Gladwin MT. Intravascular hemolysis and the pathophysiology of sickle cell disease. J Clin Invest. 2017;127(3):750-760. 

 

6)Telen MJ. Beyond hydroxyurea: new and old drugs in the pipeline for sickle cell disease. Blood. 2016;127(7):810 819. 

 

7)National Heart, Lung, and Blood Institute. Evidence-based management of sickle cell disease: expert panel report, 2014. Accessed September 15, 2021. https://www.nhlbi.nih.gov/health-topics/evidence-based-management-sickle-cell-disease 

 


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    ABOUT THE AUTHOR

    Mohamad-Ali Salloum, PharmD

    Mohamad Ali Salloum LinkedIn Profile

    Mohamad-Ali Salloum is a Pharmacist and science writer. He loves simplifying science to the general public and healthcare students through words and illustrations. When he's not working, you can usually find him in the gym, reading a book, or learning a new skill.

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