Fainting from needles may be alleviated by reducing pain – study

Feeling faint after your booster shot? A team of SFU researchers found that needle pain may increase the conditions that lead some people to faint. In a recent paper published in the journal Clinical Autonomic Research, the researchers suggest those with a fear of needles or history of fainting could benefit from topical anesthetics to help reduce the pain.

“We know that 16 per cent of adults avoid getting a flu shot because of a fear of blood or needles,” says Victoria Claydon, study lead and professor, SFU Biomedical Physiology and Kinesiology. Her team set out to study how psychological and physiological factors influence whether people might faint after receiving needles in their arms.

“By reducing needle pain, we can help alleviate these fears and improve blood pressure control, helping people have a better experience that avoids causing distress and fainting.”

Study participants completed questionnaires to evaluate their general anxiety and fears related to blood donation and medical situations. Over three visits, each was asked to look away as a doctor or nurse inserted an IV into their arm, or pretended to do so, taping the IV in place without piercing the skin. The IV was either inserted after applying EMLA cream, which acts as an anesthetic to numb the skin, or inserted without anesthetic.

The participants then underwent an orthostatic stress test to determine their likelihood of fainting following the procedure. The table the participant was lying down on was tilted up while a device monitored changes in blood pressure. The test was continued until just before a faint would have occurred. Each day, the person was asked to rate the pain associated with the IV procedure on a scale of one (no pain) to five (most painful).

When the IV procedure was painful, blood pressure control was impaired, and blood vessel responses less robust, making fainting more likely. With anaesthetic use blood pressure was stabilised and fainting less likely.

Claydon adds that this is the first placebo-controlled study to investigate the impact of intravascular instrumentation on orthostatic tolerance, or the measure of a person's susceptibility to fainting, looking at the impact of psychological stress, pain and physical trauma to the blood vessels on orthostatic tolerance and orthostatic cardiovascular responses. Moving forward, this study shows that mitigating pain with the use of topical anaesthetics before procedures involving needles is likely to reduce the risk of fainting.