why do people faint after giving blood

During a full blood donation, a person gives 450 ml of blood. That is about 10 percent of an adults blood volume. Giving this amount is safe and doesnt typically cause any ill effects. Infrequently (e. g. 1 percent of donations at our Blood Centre) the donor may experience side reactions during or after the donation: weakness, dizziness, cold sweat, fainting and other symptoms). Risks of adverse reactions can be increased by: emotional stress (anxiety about the procedure, seeing blood or other donors giving blood)
Fainting or a feeling of faintness or dizziness can be caused by a drop in blood pressure. Always make sure you are healthy, rested and have eaten before you give blood. Remember: to drink plenty of fluids before and after giving blood, including on the day after making a donation; to prefer lean and iron-rich food (red meat, liver, dark greens and colourful vegetables etc); if your blood pressure tends to be low, eat saltier food increase your salt intake before and after the donation, as this will help raise your blood pressure; to consume plenty of fluids after giving blood as well; the Blood Centre offers complimentary tea, coffee and juice.


And nibble on snacks sweet cookies and salty biscuits; to rest after giving blood, before you go on with your everyday activities, and let your body get used to the lower blood volume; its advisable to avoid strenuous physical exertion on the day of the donation and the following day (working out, saunas, swimming) on the day you give blood and the day after. Fainting while giving blood is usually caused by psychological factors, however. To prevent this: the Blood Centre worker is by your side throughout the procedure and ready to help you if needed. Tensing your muscles also keeps blood pressure from dropping: squeeze a rubber ball, periodically contract your gluteal and leg muscles. After giving blood, you may feel faint if you stand up abruptly or if you have been standing for a long time. If you feel that you are getting weak, then to avoid fainting: do exercises using your muscles: cross your legs, tense your muscles all over your body or your gluteal muscles this will keep blood pressure from dropping; if possible. lie down and elevate your legs; consume salt (salty biscuits at the Blood Centre, salty meal after leaving the centre); consume fluids.


We hope that your donation is a pleasant experience and free of adverse effects. Contact: Christopher France, 614/ 593-1079 ATHENS, Ohio -- Researchers at Ohio University have found a way to predict which people may feel faint or nauseated while giving blood, allowing workers in blood collection agencies to prevent these problems before they happen. Their study shows that a 10-question form, completed by people before they donate blood, identifies donors who are more sensitive to sights and smells associated with medical procedures, such as human blood or needles. These people are more likely to experience dizziness, nausea or fainting when they donate blood, said Christopher France, associate professor of psychology and co-author of the study. While research shows only about 3 percent of blood donors faint, significantly more experience minor reactions such as dizziness that discourage them from donating again. The American Red Cross, which collaborated with Ohio University on the study, estimates that if the number of repeat donors was increased, agencies could collect five times the amount of blood needed to meet demands in most areas. "The best way to solve the problem of a low blood supply is to increase the number of repeat donors, and the best way to do that is to improve their donation experience," France said.


The study, published in a recent issue of the Journal of Psychosomatic Research, involved volunteer blood donors at blood drives in southeast Ohio. Before donating blood, participants in the study completed a questionnaire to measure anxiety levels and pain sensitivity. Donors were given a list of items -- such as open wounds, injections, human or animal blood, and medical odors -- and asked to rate how uneasy each made them feel on a scale of 0 to 5, with 5 being extremely sensitive. They found that donors who became dizzy or nauseated when they gave blood also reported a high level of sensitivity to items on the list. The researchers then shortened the questionnaire to five items and had new donors complete the form before donating blood. The list included statements related to sensitivity to medical procedures,needles and the sight of blood. "This short form worked as well as or better than longer questionnaires and allowed us topredict who would most likely become dizzy, weak or nauseated from donating blood," France said.


Donors with high scores on the anxiety questionnaire -- which takes about five minutes to complete and score -- could be targeted for stress-reducing techniques that can prevent fainting spells or other problems. "One bad experience can be enough to convince someone not to donate blood again," France said. "If collection workers can know ahead of time who will have a negative reaction, theagencies can take steps to prevent those problems. " Prevention techniques could include reclining a donor's chair during the donation or talking with donors to distract them from needles or the sight of blood. Collection workers could also show donors how to temporarily increase blood pressure using applied tension -- flexing muscles in the legs and arms to increase blood flow, which increases blood pressure. Other authors of the study were Michelle Meade, a graduate student in psychology; and Lisa Peterson, a former student in psychology, both from Ohio University.

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