Does hypoglycemia (low blood sugar) cause syncope (fainting)?

From the Guidelines

Yes, hypoglycemia can cause syncope (fainting). When blood glucose levels drop too low, typically below 70 mg/dL, the brain becomes deprived of its primary energy source, leading to impaired brain function that can progress to loss of consciousness 1. This occurs because the brain requires a constant supply of glucose to function properly. Hypoglycemic syncope is particularly common in diabetic patients taking insulin or sulfonylureas, which can cause blood sugar to drop too low. The progression typically involves warning symptoms such as sweating, trembling, hunger, confusion, and heart palpitations before syncope occurs.

According to the American Diabetes Association standards of medical care in diabetes, severe hypoglycemia can progress to loss of consciousness, seizure, coma, or death 1. The International Hypoglycaemia Study Group classification scheme outlines the severity of hypoglycemia, with severe hypoglycemia requiring the assistance of another person and being a medical emergency 1.

Treatment of hypoglycemia requires immediate glucose administration, either through oral glucose (15-20g) for conscious patients or intravenous dextrose (D50W) for unconscious patients. Glucagon injection (1mg) is an alternative for unconscious patients when IV access isn't available 1. To prevent recurrence, patients should be educated about recognizing early warning signs, carrying fast-acting carbohydrates, regular blood glucose monitoring, and potentially adjusting diabetes medications under medical supervision.

Key points to consider in managing hypoglycemia include:

• Recognizing early warning signs of hypoglycemia, such as shakiness, irritability, confusion, tachycardia, and hunger 1
• Carrying fast-acting carbohydrates, such as glucose tablets, to quickly reverse hypoglycemia 1
• Regular blood glucose monitoring to detect hypoglycemia early and prevent severe episodes 1
• Potentially adjusting diabetes medications under medical supervision to minimize the risk of hypoglycemia 1

In terms of first aid for hypoglycemia, the American Heart Association and American Red Cross guidelines recommend calling for EMS immediately if the person is unconscious, exhibits seizures, or is unable to follow simple commands or swallow safely 1. If the person is able to follow simple commands and swallow, oral glucose should be given to attempt to resolve the hypoglycemia, with glucose tablets being the preferred option if available 1.

From the FDA Drug Label

Hypoglycemia is the most common adverse effect of insulins... Such situations may result in severe hypoglycemia (and, possibly, loss of consciousness) prior to patients’ awareness of hypoglycemia. If you take too much Levemir, your blood sugar may fall low (hypoglycemia). You can treat mild low blood sugar (hypoglycemia) by drinking or eating something sugary right away... It is important to treat low blood sugar (hypoglycemia) right away because it could get worse and you could pass out (become unconscious) Severe low blood sugar can cause unconsciousness (passing out), seizures, and death.

Hypoglycemia can cause loss of consciousness or passing out, which is also known as syncope. Therefore, hypoglycemia can cause syncope 2 2.

• Key points:
  • Hypoglycemia is a common adverse effect of insulins
  • Severe hypoglycemia can cause loss of consciousness
  • Loss of consciousness is a form of syncope
• Clinical decision: Hypoglycemia can cause syncope, and it is essential to treat hypoglycemia promptly to prevent severe consequences.

From the Research

Hypoglycemia and Syncope

• Hypoglycemia can cause syncope, as stated in the study 3, which lists syncope as a possible symptom of hypoglycemia, along with confusion, headache, and disturbances of vision.
• Another study 4 reports a case of a patient with diabetes mellitus who presented with episodes of syncope due to recurrent hypoglycemia caused by an insulinoma.
• The study 5 discusses the consequences of hypoglycemia, including the stimulation of a stress response that can lead to a fall in plasma glucose concentrations, potentially causing syncope.
• While the studies 6 and 7 do not directly address the relationship between hypoglycemia and syncope, they provide information on the management and prevention of hypoglycemia, which can help reduce the risk of syncope.

Symptoms and Consequences

• The symptoms of hypoglycemia can progress from mild to severe, with syncope being a possible consequence of untreated hypoglycemia 3.
• The study 4 highlights the importance of considering other causes of hypoglycemia in patients with diabetes mellitus who experience repeated episodes of hypoglycemia despite withdrawal of hypoglycemic agents.
• The consequences of hypoglycemia can be acute or cumulative, and may include syncope, as well as other symptoms such as confusion, headache, and disturbances of vision 5.