Passing out, fainting or vasovagal syncope is a sudden, temporary loss of consciousness.1 Passing out is common when getting blood drawn. You might need a blood draw for a test or to donate blood. In this article, you will find out why people pass out, how to avoid passing out and what to do if you feel like passing out when getting blood drawn.
Causes for passing out
Passing out is the result of a sudden drop in blood pressure and heart rate, and a slow return of blood to the heart. Consequently, the oxygen supply to the brain reduces. Your brain gets enough blood and oxygen even when there are minor fluctuations. But when your blood pressure suddenly drops, you might experience a fainting spell or pass out.2
Fainting is common and no cause for alarm. 4 in 10 people faint at least once in their life, and 2 in 10 people faint more than once. Fainting affects people of all ages and sexes.3
There are different reasons why people faint. Some researchers have studied the role genes play in fainting. This is because fainting runs in families. Others suspect that people faint as a special response to trauma—getting blood drawn in this case. This response lowers blood pressure and heart rate to prevent excessive bleeding.4
However, there are different fainting triggers. The triggers could be physical:
- Standing too long
- Sitting upright for too long
- Physical pain
- Getting up too quickly after getting blood drawn
- Prolonged waiting time (of more than 15 mins) before a blood draw.
Or triggers could be emotional:
- Seeing or thinking about blood
- Watching medical procedures
- Fear of a needle
- Fixating on the amount of blood to be drawn, especially if more than 5 blood collection tubes are used. 5, 6
Tips to avoid passing out
These hacks will help you avoid passing out when getting blood drawn.
Applied tension technique
This technique returns blood to your heart by squeezing your veins. It stops blood from pooling at your extremities (your arms or legs).6 Performing applied tension could also help you feel more in control and less afraid during your blood draw. To perform this technique, you need to alternately tense and relax your muscles.
- Tense the muscles of your arms, torso, and legs for 10-15 seconds or until your face feels warm.
- Release tension but don’t relax completely.
- Repeat again after 20-30 seconds have passed.
- Repeat this exercise 5 times.
You should be able to talk while tensing your body to avoid initiating the Valsalva manoeuvre. You initiate this manoeuvre when you tense your muscles and hold your breath. This manoeuvre could accelerate fainting because it reduces heart rate and slows the return of blood to the heart.6 It helps if you practice the applied tension technique (3 times a day) before you go for a blood draw.
There are other ways you can compress your veins:
- Cross your legs. You can do this if you are seated during your blood draw.
- Clench your buttocks. You can do this while standing, sitting, or lying. But remember to unclench at intervals.
- Contract your arms. Arm contractions are inconspicuous and easy to perform if you are getting blood drawn in public. Be careful not to contract the arm with the needle as doing this could make your blood draw painful. Practice contracting just one arm before your procedure.
- Alternate leg lifting. You can do this if you get your blood drawn while on a bed. Lift one leg approximately 12 inches above the bed and then the next.
- Squatting. You can squat before getting blood drawn to increase blood flow to your brain.1, 6
You should let your healthcare providers know what technique you are performing so they can assist and advise you.
It's important that you don't skip a meal before getting blood drawn. You need enough nutrients so you don't become hypoglycemic. You also need salt from food to increase the volume of your blood. But be cautious about taking salt if you have heart failure, kidney failure, or hypertension.6 There are no specific foods you should avoid if you are prone to passing out, but you should minimise caffeine and alcohol intake. There are some foods to eat if you pass out frequently. These include whole grains, fruits, bread, rice, and pasta.
You should also drink a lot of water before getting your blood drawn. Water increases your blood volume which reduces the chance of your brain not getting enough blood.6 You should take approximately 500 ml of water 30 mins before getting blood drawn to observe this effect.7
Breathing techniques and meditation
It's important you take deep, long, steady breaths while getting blood drawn. Breathing this way ensures that your brain gets enough oxygen so you don't pass out. You can also perform guided yoga prior to getting your blood drawn to avoid passing out.
What to do if you feel like you are going to pass out
Before you pass out, you might:
- Feel nauseous
- Get dizzy
- Sweat/feel hot
- Become pale
- Experience blurred or tunnel vision
- Get confused
- Feel weak
- Experience palpitations (an abnormal heart rhythm)
- Become flushed.2,5,8
If you notice any warning signs when getting blood drawn or observe them in someone else, here’s what you can do:
- Lie down immediately with your head up. This not only reduces your chance of passing out but it prevents injury if you fall.6 Lying down returns blood from the extremities to the heart. Also, it helps that the heart won’t have to pump blood to the brain against gravity.
- Place your head between your knees. This sends blood to the brain quickly.1
It’s no cause for alarm if you pass out while getting blood drawn. But you can prevent it. Speak with your doctor if you are prone to passing out.