Guide — Endocrine
Hyperosmolar Hyperglycemic State (HHS)
HHS is a life-threatening hyperglycemic emergency occurring primarily in Type 2 diabetes — extreme hyperglycemia, profound dehydration, hyperosmolality, and altered mental status without significant ketoacidosis.
10 min read · Endocrine
Educational use only. HHS treatment — fluid resuscitation, insulin therapy, and electrolyte replacement — is provider-directed and protocol-driven. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
HHS carries higher mortality than DKA (10–20% vs 1–5%). The extreme dehydration, altered mental status, and thrombotic risk make it a medical emergency requiring aggressive, careful management.
Pathophysiology
HHS occurs when there is enough residual insulin to prevent ketogenesis but not enough to prevent extreme hyperglycemia. This is the key physiological distinction from DKA.
- Relative insulin deficiency → glucose rises dramatically but lipolysis is suppressed (residual insulin prevents significant ketone formation)
- Extreme hyperglycemia (often >600 mg/dL) → massive osmotic diuresis → profound fluid and electrolyte depletion
- Patients cannot adequately replace fluids (elderly, disabled, cognitively impaired) → progressive dehydration over days to weeks
- Serum osmolality rises dramatically (>320 mOsm/kg) → cerebral dehydration → altered mental status, seizures, coma
- Hypercoagulable state → DVT, PE, arterial thrombosis risk significantly elevated
Precipitating Causes
| Cause | Clinical Note |
|---|---|
| Infection (most common) | Pneumonia, UTI, sepsis — raises counter-regulatory hormones; impairs oral fluid intake |
| Undiagnosed Type 2 DM | May be the presenting event; patient had no known diabetes history |
| Inadequate fluid intake | Elderly or disabled patients with limited access to water; cognitive impairment; nursing home residents |
| Medications | Thiazide diuretics, steroids, atypical antipsychotics, phenytoin, immunosuppressants |
| Acute illness | MI, stroke, GI bleed, pancreatitis — stress hyperglycemia + fluid shifts |
| Dialysis | Peritoneal or hemodialysis with high-glucose dialysate |
Clinical Manifestations
HHS develops insidiously over days to weeks (versus the rapid onset of DKA over hours). By the time patients present, they are profoundly dehydrated and often altered.
Neurological (prominent in HHS)
- ✦Altered mental status — confusion to coma
- ✦Focal neurological deficits (focal weakness)
- ✦Seizures (focal or generalized)
- ✦Visual disturbances, hallucinations
Dehydration
- ✦Profound dehydration (5–10+ L fluid deficit)
- ✦Dry mucous membranes, poor turgor
- ✦Tachycardia, hypotension
- ✦Oliguria → anuria
Absent/Minimal in HHS
- ✦No Kussmaul respirations
- ✦No fruity breath
- ✦No significant nausea/vomiting from ketosis
- ✦Ketones absent or trace
Thrombotic Risk
- ✦DVT, pulmonary embolism
- ✦Arterial thrombosis (stroke, limb ischemia)
- ✦Hyperviscosity from extreme dehydration
- ✦Prophylactic anticoagulation often indicated
Laboratory Findings
| Lab | HHS Finding | Clinical Note |
|---|---|---|
| Glucose | >600 mg/dL (often 800–1,200+) | Extremely high — far exceeds typical DKA levels |
| Serum osmolality | >320 mOsm/kg (effective) | Calculated: 2(Na) + glucose/18. This is the defining lab. |
| pH | >7.3 (normal or near-normal) | NO significant acidosis — residual insulin prevents ketogenesis |
| Bicarbonate | >15 mEq/L (normal or near-normal) | Distinguishes HHS from DKA |
| Ketones | Negative or trace | Minimal ketone production — hallmark difference from DKA |
| Anion gap | Normal or mildly elevated | Lactic acidosis may co-exist from poor perfusion |
| Sodium | Variable — correct for glucose | Corrected Na: add 1.6 mEq/L per 100 mg/dL glucose above 100 |
| BUN/Creatinine | Markedly elevated | Profound prerenal azotemia; BUN:Cr ratio often >20:1 |
| Osmolality (effective) | >320 mOsm/kg is diagnostic threshold | Formula: 2(Na⁺) + glucose(mg/dL)/18 |
Key Differences: HHS vs DKA
| Feature | HHS | DKA |
|---|---|---|
| Typical patient | Type 2 DM — elderly, nursing home resident | Type 1 DM — younger; or Type 2 under severe stress |
| Glucose | >600 mg/dL (often >1,000) | >250 mg/dL (250–600 typical) |
| Ketones | Absent or trace | Strongly positive |
| Acidosis | None significant (pH >7.3) | Significant (pH <7.3, bicarb <18) |
| Osmolality | >320 mOsm/kg | Mildly elevated |
| Onset | Days to weeks (insidious) | Hours (acute) |
| Kussmaul breathing | Absent | Present |
| Fluid deficit | 5–10+ L (profound) | 3–6 L (significant) |
| Neurological changes | Prominent — confusion, coma, focal deficits | Variable — may be alert or confused |
| Mortality | 10–20% (higher) | 1–5% with treatment |
Treatment Overview
Aggressive fluid resuscitation (critical priority)
NS 0.9% at 1 L/hr initially. Larger volumes than DKA often required (5–10 L deficit). Switch to 0.45% NaCl after initial resuscitation if Na⁺ rising. Add D5 when glucose reaches 250–300 mg/dL. Correct slowly — fluid shifts can cause cerebral edema.
Insulin therapy (after fluids started, K⁺ adequate)
Low-dose regular insulin IV drip — typically 0.1 units/kg/hr. Glucose will fall with fluids alone — avoid overcorrecting too quickly. Goal: lower glucose 50–75 mg/dL/hour. Avoid hypoglycemia.
Electrolyte replacement
Potassium: replace aggressively. Total body K⁺ deficit large due to osmotic diuresis. Phosphate: replace if <1 mg/dL. Magnesium: monitor and replace.
Thrombosis prevention
Extreme hypercoagulability — prophylactic anticoagulation (subcutaneous heparin or LMWH) per order. Compression stockings. Mobility as soon as safe.
Identify and treat precipitant
Infection is most common — broad-spectrum antibiotics if suspected. ECG to rule out MI. Neuroimaging if focal neurological signs persist after initial treatment.
NCLEX Pearls
- ✦HHS = Type 2 DM primarily. DKA = Type 1 DM primarily. Elderly patient with extreme glucose and no ketones = HHS.
- ✦HHS hallmarks: glucose >600, osmolality >320, NO significant ketones, NO significant acidosis.
- ✦Mortality is HIGHER in HHS (10–20%) than DKA (1–5%) — extreme dehydration and age of typical patient.
- ✦Neurological symptoms are more prominent in HHS due to extreme hyperosmolality causing cerebral dehydration.
- ✦HHS develops over DAYS TO WEEKS — patient often cannot verbalize thirst (elderly, dementia).
- ✦Thrombosis risk is elevated — prophylactic anticoagulation is often ordered.
- ✦Never skip checking effective osmolality (2 × Na + glucose/18) — this is the diagnostic key.
- ✦Replace fluids before insulin — fluids alone drop glucose significantly in HHS.
- ✦Correct slowly — rapid fluid/glucose correction risks cerebral edema.
Related Resources
Standards & sources
Fact-checked Jun 20, 2026This page is written to align with American Diabetes Association (ADA) Standards of Care · American Association of Clinical Endocrinology (AACE). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →