Hypoglycaemia
Summary
Hypoglycaemia is defined as a blood glucose < 4.0 mmol/L. It is the most common endocrine emergency, primarily affecting patients with diabetes treated with Insulin or Sulfonylureas. The brain is obligatorily dependent on glucose. Prolonged neuroglycopenia causes permanent brain injury or death ("Dead in Bed" syndrome). Evaluation of non-diabetic hypoglycaemia requires Whipple's Triad: (1) Low Glucose, (2) Compatible Symptoms, (3) Resolution with Carbohydrate. [1,2]
Clinical Pearls
"4 is the Floor": Treat any glucose < 4.0 mmol/L, even if asymptomatic. The threshold for cognitive impairment begins around 3.0, but the safety buffer is crucial.
Unawareness: Patients with long-standing T1DM lose their Glucagon response first, then their Adrenaline response. This leads to Hypoglycaemia Unawareness, where the patient goes straight from "Fine" to "Unconscious" without the sweating/shaking warning.
Glucagon & Alcohol: IM Glucagon works by mobilizing liver glycogen. In alcoholics (or starved patients), liver glycogen is depleted. Glucagon WILL NOT WORK. Give IV Dextrose immediately.
Sulfonylureas: These drugs (Gliclazide) stimulate insulin release for 12-24 hours. A patient treated for a "Gliclazide Hypo" may recover, then crash again 6 hours later. Admit these patients for observation.
Risk Factors
- Drugs: Insulin (most common), Sulfonylureas, Meglitinides.
- Lifestyle: Missed meals, Alcohol, Exercise (increases insulin sensitivity).
- Medical: Renal failure (Insulin accumulates), Liver failure, Sepsis, Addison's disease.
- Rare: Insulinoma, IGF-2 secreting tumour.
Counter-Regulation
The body defends against falling glucose stepwise:
- Reduce Insulin: (First defence).
- Increase Glucagon: (Key defence).
- Increase Adrenaline: (Causes the "Autonomic" symptoms - warning).
- Increase Cortisol/GH: (Late defence, hours later).
The Brain
- The brain consumes ~120g of glucose daily. It cannot store glycogen. Glucose enters via GLUT1/GLUT3 (non-insulin dependent).
- When serum glucose drops, brain flux drops -> Neuroglycopenia.
| Condition | Glucose | Features |
|---|---|---|
| Hypoglycaemia | < 4.0 | Sweaty, Pale, Rapid response to sugar |
| Stroke/TIA | Normal | Focal neurology |
| Postprandial Hypotension | Normal | Post-meal dizziness |
| Vasovagal Syncope | Normal | Postural trigger |
| Alcohol Intoxication | Often Low | Smell of alcohol, History |
Autonomic Symptoms (Early Warning - >3.0 mmol/L)
Neuroglycopenic Symptoms (Danger - less than 3.0 mmol/L)
Bedside
- Capillary Blood Glucose (CBG): The fingerprick. Immediate.
- Venous Glucose: Gold standard confirmatory.
Insulinoma Screen (If non-diabetic & recurrent)
- Take during a spontaneous hypo:
- Insulin: High (Inappropriate).
- C-Peptide: High (Endogenous production).
- Proinsulin: High.
- Beta-Hydroxybutyrate: Low (Insulin suppresses ketones).
- Sulfonylurea Screen: Negative (Rule out factitious).
Management Algorithm (The "15-15" Rule)
Check Glucose after 15 mins. If still low, Repeat.
HYPOGLYCAEMIA (< 4.0)
↓
PATIENT CONSCIOUS?
┌───────────┴───────────┐
YES (Mild) NO (Severe)
↓ ↓
ORAL FAST ACTING IM GLUCAGON (1mg)
15-20g Carbohydrate (Family/Paramedic)
- 4-5 Jelly Babies OR
- 150ml Coke (Full sugar) IV DEXTROSE
- 200ml Orange Juice (Hospital Setting)
- GlucoJuice - 100ml of 10%
- 50ml of 20%
↓ ↓
WAIT 15 MINS RECOVERY?
RECHECK CBG (Usually rapid)
↓ ↓
STILL < 4.0? LONG ACTING CARB
Repeat Above (Once able to swallow)
↓ (e.g., Toast/Sandwich)
GLUCOSE > 4.0?
↓
LONG ACTING CARB
(Prevent recurrence)
- 2 Biscuits
- Slice of Toast
- Next Meal
1. IV Glucose Choices
- 10% Dextrose: Safe, less phlebitic. Give 100-200ml.
- 20% Dextrose: More irritant. Give 50-100ml.
- 50% Dextrose: Avoid. High risk of extravasation necrosis and rebound hyperglycaemia. Exception: tiny volumes in emergencies if nothing else.
2. Driving (DVLA UK Rules)
- "5 to Drive": You must not drive if glucose is < 4.0.
- If hypo occurs: Stop, Treat, Wait 45 mins after glucose returns to normal (brain recovery time).
- Implication: Recurrent severe hypos = License Revoked.
- Acute: Seizures, Aspiration pneumonia, Traffic accidents.
- Chronic: Fear of hypos (driving sugars high), Weight gain (overtreating), Cognitive decline.
- "Dead in Bed": Nocturnal severe hypo causing arrhythmia (Prolonged QTc).
- Most recover fully with rapid treatment.
- Prolonged coma (>4-6 hours) can cause permanent cortical laminar necrosis.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Hypoglycaemia | JBDS-IP (2022) | Standard hospital protocol (15-20g carb). Avoid 50% Dextrose. |
| Driving | DVLA | Group 1 vs Group 2 license rules. |
Landmark Evidence
1. DCCT Trial
- Showed that tight glycaemic control reduces microvascular complications but significantly increases the risk of severe hypoglycaemia (x3). The trade-off.
What is a Hypo?
It means your blood sugar has dropped too low (below 4). This acts like running out of fuel for your car—the engine (your brain) starts to stutter.
What does it feel like?
Usually, your body warns you with "fight or flight" feelings: shaking, sweating, heart pounding, or feeling very hungry. If you ignore this, you can become confused, act drunk, or eventually faint.
How do I treat it?
You need fast sugar immediately.
- Eat/Drink 15g of fast sugar (5 Jelly babies, small can of full-sugar coke, or 4 glucose tablets).
- Wait 15 minutes.
- Check limits.
- If back to normal, eat a slow snack (toast/biscuit) to keep it up.
Can I drive?
Check your sugar before you drive. It must be above 5 ("5 to Drive"). If you have a hypo while driving, stop safely, take the keys out, treat the hypo, and wait 45 minutes before driving again.
Primary Sources
- Joint British Diabetes Societies (JBDS). The Hospital Management of Hypoglycaemia in Adults with Diabetes Mellitus. 2022.
- Cryer PE. Hypoglycemia, functional brain failure, and brain death. J Clin Invest. 2007.
Common Exam Questions
- Management: "Unconscious diabetic?"
- Answer: IV 10% Dextrose (Hospital) or IM Glucagon (Community).
- Safety: "Alcoholic with hypo?"
- Answer: Give IV Dextrose + Thiamine (Pabrinex). Glucagon won't work.
- Diagnosis: "Triad for Insulinoma?"
- Answer: Whipple's Triad.
- Pharmacology: "Which drug hides hypo symptoms?"
- Answer: Beta-blockers (Blunt the tachycardia/tremor).
Viva Points
- C-Peptide: Why measure it? C-Peptide is released 1:1 with endogenous insulin. Exogenous insulin (injected) has no C-Peptide. High Insulin + Low C-Peptide = Factitious (Surreptitious injection). High Insulin + High C-Peptide = Insulinoma or Sulfonylurea.
- Factitious Hypoglycaemia: Common in healthcare workers.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.