What does HHS (Hyperosmolar hyperglycemic state) refer to in medical terminology?

What is HHS in Medical Terms?

HHS stands for Hyperosmolar Hyperglycemic State (also called Hyperosmolar Hyperglycemic Syndrome), a life-threatening acute metabolic complication of diabetes characterized by severe hyperglycemia, marked hyperosmolarity, profound dehydration, and altered mental status without significant ketoacidosis. 1

Key Defining Features

HHS is diagnosed by the following criteria 1, 2:

• Marked hyperglycemia: Blood glucose ≥30 mmol/L (≥540 mg/dL), typically >600 mg/dL
• Severe hyperosmolarity: Effective serum osmolality ≥320 mOsm/kg (calculated as [2×Na+ + glucose + urea])
• Absence of significant ketoacidosis: Ketones ≤3.0 mmol/L
• Minimal acidosis: pH >7.3 and bicarbonate ≥15 mmol/L
• Profound dehydration: Fluid losses of 100-220 ml/kg body weight

Important caveat: Recent evidence shows that 65.5% of HHS cases actually have concurrent diabetic ketoacidosis (DKA), suggesting the traditional exclusion of significant ketonemia may need reconsideration 3. When ketoacidosis is present alongside HHS criteria, this is termed "combined HHS-DKA" 4.

Clinical Presentation

The evolution differs markedly from DKA 1:

• HHS develops over days to weeks (versus 24 hours for DKA)
• Neurologic symptoms are prominent: altered mental status ranging from lethargy to coma (more frequent than in DKA)
• Physical findings include profound dehydration, poor skin turgor, tachycardia, hypotension, and potential shock
• Classical symptoms: polyuria, polydipsia, weight loss, weakness

Epidemiology and Prognosis

HHS carries significantly higher mortality than DKA 1, 5:

• Mortality rate: 10-20% (compared to <5% for DKA in experienced centers)
• Incidence: <1% of hospital admissions in patients with diabetes
• Primarily affects patients with type 2 diabetes, though increasingly seen in younger adults and children 2
• In one-third of cases, HHS is the first presentation of previously undiagnosed diabetes 4

Pathophysiology

The underlying mechanism involves 1:

• Reduction in effective circulating insulin action
• Elevation of counterregulatory hormones (glucagon, catecholamines, cortisol, growth hormone)
• Increased hepatic and renal glucose production with impaired peripheral glucose utilization
• Critical difference from DKA: Residual insulin levels are adequate to prevent lipolysis and ketogenesis, but insufficient for glucose control
• Severe osmotic diuresis leading to massive fluid and electrolyte losses

Common Precipitating Factors

The most common triggers are 6, 7:

• Underlying infections (especially genitourinary and respiratory)
• Acute cardiovascular disease or stroke
• Medication non-adherence or inappropriate therapy
• Conditions preventing adequate water intake during osmotic diuresis
• Undiagnosed diabetes mellitus
• Coexisting serious medical conditions

Important Clinical Distinctions

Emerging subtype recognition 8, 3:

• Euglycemic hyperosmolar hypernatremic state: Glucose 180-600 mg/dL (not meeting traditional >600 mg/dL threshold) but with effective osmolality >320 mOsm/kg and hypernatremia. This variant has higher mortality (35.3% vs 0% for traditional HHS) and requires similar aggressive treatment 8.

• Hypernatremia prevalence: While only 8% have measured sodium >145 mmol/L, 95.4% have hypernatremia when sodium is corrected for hyperglycemia, making HHS with hypernatremia the predominant subtype 3.

Management Principles

HHS is a medical emergency requiring ICU admission 2, 6:

Primary treatment goals 2:

• Restore circulating volume and correct dehydration by 24 hours
• Gradual decline in osmolality (3.0-8.0 mOsm/kg/h) to minimize neurological complications
• Target blood glucose 10-15 mmol/L (180-270 mg/dL) in first 24 hours
• Prevent hypoglycemia, hypokalaemia, and complications (VTE, osmotic demyelination, fluid overload)

Key treatment components 9, 2, 6:

1. Aggressive fluid resuscitation: 0.9% sodium chloride (average 9L over 48 hours in adults; replace ~50% of estimated fluid loss within first 12 hours)
2. Insulin therapy: Fixed-rate IV insulin infusion should be commenced only after osmolality stops falling with fluid replacement alone, unless ketonaemia is present 2
3. Electrolyte monitoring: Hypokalaemia occurs in ~50% during treatment and severe hypokalaemia (<2.5 mEq/L) is associated with increased mortality 9
4. Identify and treat precipitating causes

Critical pitfall: Avoid rapid correction of osmolality, sodium, and glucose to prevent cerebral edema and osmotic demyelination syndrome 10, 6.