Plasma donation, known as plasmapheresis, separates plasma from whole blood before returning the remaining red blood cells to the body. Since plasma is mostly water and proteins, removing this fluid volume temporarily affects the circulatory system. While the process is generally safe, fainting (syncope) is a possibility, though infrequent. The risk is managed through careful screening, preparation, and immediate intervention by trained staff if symptoms of lightheadedness or dizziness occur.
The Physiological Reasons for Fainting
The most common cause of fainting during or immediately following donation is the vasovagal reaction, also known as neurocardiogenic syncope. This response is an exaggerated reflex of the autonomic nervous system, often triggered by anxiety, the sight of the needle, or the stress of the procedure. The reaction leads to a sudden, simultaneous drop in both heart rate (bradycardia) and blood pressure (hypotension).
This dual drop causes a momentary reduction in blood flow to the brain, resulting in transient global cerebral hypoperfusion. This manifests as lightheadedness or a loss of consciousness. The body’s normal mechanism for maintaining blood pressure is overwhelmed, leading to the temporary failure of blood flow regulation. While the reaction is typically benign and self-limiting, it serves as a warning sign that the circulatory system is struggling to compensate.
A secondary factor specific to plasmapheresis is the reaction to the anticoagulant citrate, which is mixed with the blood to prevent clotting. Citrate temporarily binds to calcium in the bloodstream, causing a mild reduction in circulating calcium levels (hypocalcemia). This can cause symptoms like a metallic taste, tingling in the lips or fingertips, and a general feeling of unease that may contribute to pre-syncopal symptoms.
The physical loss of plasma volume also plays a role, as it removes fluid from the circulatory system. This temporary reduction in total blood volume makes the cardiovascular system less able to compensate for posture changes or emotional triggers. Younger donors, first-time donors, and those with a lower body weight are statistically more likely to experience a vasovagal event.
Essential Preparation to Minimize Syncope Risk
The most impactful preventative measure involves increasing intravascular volume through proper hydration. Because plasma is approximately 92% water, drinking at least 16 to 24 ounces of water in the hour before the appointment is recommended to maintain adequate blood volume. Acute water loading may also help by stretching the stomach wall, triggering a reflex that mildly increases sympathetic nervous system activity and helps stabilize blood pressure.
Consuming a full, balanced meal within two to three hours of the donation is another fundamental step, as it prevents blood sugar from dropping. A meal rich in protein and iron, but moderate in fat, helps ensure the body has sufficient energy reserves to handle the physiological stress of the process. Getting a full night of sleep beforehand also reduces baseline stress and anxiety, which are known precursors for the vasovagal response.
During the donation, a technique called Applied Muscle Tension (AMT) can be effective in minimizing risk. This method involves repeatedly tensing the muscles in the lower body, such as crossing the legs and squeezing the knees and gluteal muscles for five seconds, followed by a five-second release. The physical contraction of these large muscle groups mechanically increases venous return and raises blood pressure immediately. This helps to counteract the hypotensive effects of the vasovagal reflex.
What Happens If You Feel Faint During Donation
If a donor begins to feel symptoms of pre-syncope, such as lightheadedness, nausea, clammy skin, or visual changes, they must alert the staff immediately. The donation procedure will be stopped instantly, and the safety team will take over monitoring and care. Recognizing these early warning signs allows for intervention before a full loss of consciousness occurs.
The primary intervention is a change in physical position to restore blood flow to the brain. Staff will immediately recline the donor chair and often elevate the donor’s legs above the heart (a modified Trendelenburg position). This maneuver uses gravity to quickly shift blood from the lower extremities back toward the core and the brain, helping to normalize cerebral perfusion pressure.
The donor will be monitored closely until all symptoms have resolved, which typically happens within a few minutes once blood pressure stabilizes. They will be offered fluids and a snack to aid recovery and replenish volume. Donors are only cleared to leave the recovery area after a period of observation and when staff are satisfied they are no longer experiencing dizziness or lightheadedness.