Fainting and Tremors During Blood Draws: A Neurology Perspective

Loss of consciousness during blood draw, accompanied by whole-body tremors and wide-open eyes?

Whenever I have a slightly larger blood draw (or if I haven't eaten before the blood draw), I experience a series of symptoms: my vision goes dark, I lose consciousness, my eyes widen, my body trembles (with a sensation similar to convulsions), and I feel like I can't breathe (during this phase, I am unconscious).
Afterward, I feel completely weak and am then moved to a hospital bed.
Not long after, I wake up and feel fine.
During the trembling phase, the nursing staff kept calling my name, and I briefly regained consciousness; at that moment, I felt a continuous shivering sensation throughout my body, but then I lost consciousness again.
I would like to know which medical specialty I should consult and why this happens.
Thank you.

Xiao Bai, 20~29 year old female. Ask Date: 2020/10/20

Dr. Cai Zongzhang reply Neurology

This symptom is likely neurogenic syncope; it is recommended to undergo a detailed examination by a neurologist.

Reply Date: 2020/10/20

More Info

Fainting, or syncope, during blood draws can be a concerning experience, and understanding the underlying mechanisms can help in addressing the issue effectively. Based on your description, it seems that you experience a series of symptoms that include visual disturbances, loss of consciousness, tremors, and a feeling of weakness. These symptoms can be attributed to several physiological responses, particularly related to the autonomic nervous system and blood pressure regulation.

When blood is drawn, especially in larger quantities or when the individual has not eaten, it can lead to a sudden drop in blood volume and blood pressure. This phenomenon is known as vasovagal syncope, which is a common cause of fainting. The body reacts to the stress of the blood draw by triggering a reflex that causes blood vessels to dilate, leading to a decrease in blood flow to the brain. This can result in the visual disturbances you experience, such as "seeing black," followed by loss of consciousness.

The tremors and shaking you describe during the episode could be a result of muscle contractions as your body reacts to the sudden drop in blood pressure and the lack of oxygen to the brain. This can sometimes mimic seizure-like activity, but it is important to note that this is not the same as a true seizure. The feeling of coldness and weakness afterward is also common as the body recovers from the episode.

Given these symptoms, it would be advisable to consult with a neurologist, as they specialize in conditions related to the nervous system and can help determine if there are any underlying neurological issues contributing to your episodes. They may conduct a thorough evaluation, including a physical examination, a review of your medical history, and possibly tests such as an electrocardiogram (ECG) or an echocardiogram to assess your heart's function, as cardiac issues can also lead to syncope.

Additionally, it may be beneficial to discuss your experiences with a primary care physician who can provide a comprehensive approach to your health. They can help rule out other potential causes of your symptoms, such as dehydration, anemia, or other metabolic conditions that could exacerbate your response to blood draws.

In the meantime, there are some strategies you can employ to potentially mitigate these episodes. Ensuring you are well-hydrated and have eaten before a blood draw can help maintain your blood pressure and blood volume. Informing the healthcare staff about your history of fainting can also allow them to take precautions, such as having you lie down during the procedure or drawing blood in a more controlled environment.

In summary, your symptoms during blood draws are likely related to a vasovagal response, but it is essential to consult with a neurologist to rule out any other underlying conditions. By taking proactive steps and seeking appropriate medical advice, you can better manage your experiences during blood draws and improve your overall health.

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