The most common adverse reaction to blood donation, seen with increased frequency in young donors, first-time donors, and female donors (especially so if all three are true!). Vasovagal reactions result from (prepare for boring physiology details) stimulation of the parasympathetic nervous system in response to blood donation, anticipation of blood donation, or general freaking out about blood donation! As a result, two main things happen: The donor’s blood pressure declines, and the donor’s pulse declines in concert with the blood pressure (hypotension with bradycardia). This is a really bad combination, and results in the classic “lightheadedness” that some donors feel before, during, or after donation. The symptoms may be very mild, with sweating and “clammy skin” accompanying the lightheadedness, or the patient may actually lose consciousness (syncope). Other symptoms may include nausea, vomiting, and for the very unfortunate, incontinence of urine and/or stool.
The best way to manage vasovagal reactions is to prevent them in the first place! All blood centers should have a protocol addressing preventive measures for at-risk donors, which may include things like encouraging water intake, distraction techniques, muscle contraction, etc. The interventions that blood bank staff perform in response to these reactions (reclining the donor, loosening clothing, putting cold cloths on the donor’s neck) probably don’t make much difference. These reactions pretty much resolve when they are ready to resolve, most commonly within an hour, but sometimes as long as a day or two (uncommon).