From the Guidelines
Some people faint at the sight of blood due to a condition called vasovagal syncope, which is triggered by specific stimuli like seeing blood, experiencing pain, or emotional distress. When exposed to blood, these individuals experience a two-phase response: first, their blood pressure and heart rate increase (fight-or-flight response), followed by a sudden drop in blood pressure and heart rate as the vagus nerve overreacts, reducing blood flow to the brain and causing fainting 1. This response is involuntary and affects approximately 3-4% of people.
Key Characteristics of Vasovagal Syncope
- It is the most common form of reflex syncope mediated by the vasovagal reflex
- Typically characterized by diaphoresis, warmth, nausea, and pallor
- Associated with vasodepressor hypotension and/or inappropriate bradycardia
- Often preceded by identifiable triggers and/or by a characteristic prodrome Those prone to this reaction can prevent fainting by:
- Lying down with legs elevated when feeling lightheaded
- Applying counter-pressure techniques like crossing and tensing their legs
- Gradually exposing themselves to blood-related stimuli under professional guidance to reduce sensitivity The condition is generally harmless but can cause injury from falling, so recognizing early warning signs like nausea, sweating, or lightheadedness is important for prevention, as defined by the 2017 ACC/AHA/HRS guideline for the evaluation and management of patients with syncope 1.
From the Research
Vasovagal Syncope and Fainting at the Sight of Blood
- Vasovagal syncope is a common disorder of autonomic cardiovascular regulation that can cause fainting in response to certain triggers, including the sight of blood 2.
- The condition is characterized by a complex neurologic reflex that can lead to a sudden loss of consciousness due to reduced perfusion to the brain 3.
- In some cases, people may faint at the sight of blood due to a vasovagal response, which can be triggered by the emotional or psychological impact of seeing blood 4.
Treatment and Management
- Conservative measures, such as increased fluid and salt intake, physical counterpressure maneuvers, and avoidance of triggers, are often recommended as the first line of treatment for vasovagal syncope 5, 2, 3.
- For patients who continue to experience fainting episodes despite conservative measures, pharmacological interventions such as midodrine and fludrocortisone may be effective in reducing syncope recurrences 3, 6, 4.
- Other treatments, such as orthostatic training and yoga, may also be helpful, although their efficacy and mechanisms are not fully understood 4.
Research and Studies
- Several studies have investigated the efficacy of different treatments for vasovagal syncope, including midodrine, fludrocortisone, and beta-blockers 5, 2, 3, 6, 4.
- The COMFORTS trial, a multi-center randomized controlled trial, aims to compare the outcomes of midodrine and fludrocortisone in treating vasovagal syncope 6.
- Recent guidelines from the European and North American cardiac societies recommend a stepped approach to the treatment of vasovagal syncope, starting with conservative measures and progressing to pharmacological interventions as needed 4.