Hyperosmolar Hyperglycemic State — Adult

Key Points

• HHS is defined by hyperosmolality and severe dehydration with minimal ketosis, not by a glucose threshold alone.
• Measure beta-hydroxybutyrate and venous pH because mixed DKA-HHS requires more intensive insulin treatment.
• Fluid resuscitation is the first major intervention and can lower glucose substantially before insulin is started.
• Potassium must be assessed repeatedly; significant hypokalemia should be corrected before insulin is intensified.
• Pure HHS generally uses a lower insulin infusion rate than DKA.
• Do not chase an early sodium rise caused by falling glucose; follow effective osmolality, volume status, and the full electrolyte trend.
• Neurologic deterioration during treatment requires immediate reassessment for overly rapid osmotic change, stroke, infection, or another complication.
• Resolution means restored perfusion and mental status with acceptable osmolality, not glucose normalization alone.

Algorithm

1. Confirm severe hyperglycemia and calculate osmolality while measuring beta-hydroxybutyrate, venous pH, electrolytes, and renal function.
2. Assess airway, circulation, mental status, dehydration, and the likely precipitating illness.
3. Begin isotonic or balanced crystalloid with individualized rate and frequent reassessment.
4. Check potassium before insulin; replace and delay insulin if potassium is dangerously low.
5. Start lower-dose IV insulin for pure HHS or a DKA regimen for mixed DKA-HHS.
6. Add dextrose as glucose falls so insulin can continue while osmolality and any ketosis resolve.
7. Trend glucose, sodium, potassium, renal function, osmolality, urine output, and neurologic status at protocol-defined intervals.
8. Transition to subcutaneous diabetes therapy only after HHS has resolved and a safe nutrition and follow-up plan is established.

Clinical Synopsis & Reasoning

HHS should be considered in a patient with severe hyperglycemia plus dehydration, neurologic change, or an obvious precipitating illness. The 2024 international hyperglycemic-crisis consensus defines HHS using hyperglycemia, hyperosmolality, lack of significant ketonemia, and absence of substantial acidosis rather than glucose alone. Neurologic manifestations range from lethargy and confusion to focal deficits, seizures, and coma, and correlate more closely with effective osmolality than with glucose concentration. Infection, myocardial infarction, stroke, medications, missed diabetes therapy, and newly diagnosed diabetes are common precipitants. Physical examination should assess volume depletion, perfusion, mental status, airway protection, and signs of infection or vascular events. Measure glucose, electrolytes, creatinine, venous pH, beta-hydroxybutyrate, and calculated effective and total serum osmolality. Corrected sodium helps interpret the water deficit, but treatment should follow the measured sodium and osmolality trajectory rather than a single corrected value. Mixed DKA-HHS is common; significant ketonemia or acidosis changes insulin intensity and monitoring. Pseudohyponatremia is not the central issue in modern direct ion-selective measurement, and serum sodium often rises initially as glucose falls because water shifts back intracellularly.

Treatment Strategy & Disposition

Begin with isotonic or balanced crystalloid, adjusting the rate for age, heart failure, kidney disease, blood pressure, urine output, and the degree of dehydration. Volume replacement alone can substantially lower glucose. Replace potassium before or during insulin according to the serum concentration; if potassium is markedly low, defer insulin until replacement has begun because insulin can precipitate dangerous hypokalemia. In pure HHS without significant ketosis, insulin is generally started at a lower continuous infusion rate than for DKA after initial fluid therapy and potassium assessment. When mixed DKA-HHS is present, use a DKA-level insulin regimen. Add dextrose-containing fluid once glucose approaches the treatment threshold so insulin can continue while hyperosmolality resolves. Avoid overly rapid osmotic change. The consensus approach limits the fall in glucose and osmolality to controlled rates, with sodium correction interpreted in context. Treat the precipitating disorder, use venous thromboembolism prophylaxis unless contraindicated, and monitor closely for fluid overload, hypoglycemia, hypokalemia, acute kidney injury, thrombosis, and neurologic deterioration. Resolution requires improvement in osmolality and clinical status, not merely a normal glucose.

Epidemiology / Risk Factors

• HHS occurs most often in older adults with type 2 diabetes but can occur at other ages and in previously undiagnosed diabetes.
• Infection is a frequent precipitant, especially pneumonia and urinary infection.
• Stroke, myocardial infarction, pancreatitis, glucocorticoids, antipsychotics, and inability to access water or medications are other important triggers.
• Mortality is higher than in uncomplicated DKA because affected patients are often older and have more severe comorbidity and precipitating illness.
• Mixed DKA-HHS presentations are common enough that ketone and acid-base testing should be routine.

Investigations

DKA vs HHS (Typical)

Pharmacology

Prognosis / Complications

• Outcome depends heavily on age, baseline organ function, severity of dehydration and hyperosmolality, and the precipitating illness.
• Thrombosis, acute kidney injury, electrolyte disturbances, aspiration, and neurologic complications contribute to morbidity.
• Most patients improve with careful protocol-based fluid, electrolyte, and insulin treatment.
• Recurrent crisis is often preventable when access, medication understanding, sick-day planning, and diabetes follow-up are addressed.
• Persistent altered mental status after osmolality improves should prompt evaluation for stroke, infection, toxic-metabolic disease, or another neurologic diagnosis.

Patient Education / Counseling

• Explain that HHS develops from both very high glucose and profound dehydration, so prevention requires hydration and early action during illness.
• Review home glucose monitoring, medication adherence, and a written sick-day plan, including when to call a clinician or seek urgent care.
• Teach warning signs such as persistent glucose elevation, inability to drink, vomiting, confusion, weakness, fever, or reduced urine output.
• Ensure the patient and caregivers understand any changes to insulin or noninsulin diabetes therapy before discharge.
• Address practical barriers including medication cost, access to testing supplies, cognitive impairment, and caregiver support.

Notes

HHS treatment should be judged by physiology rather than the bedside glucose meter alone. The patient has lost a large amount of water and electrolytes over days, and rapid normalization of glucose can occur before the hyperosmolar state is safely corrected. Careful fluids, potassium surveillance, appropriately dosed insulin, and frequent osmolality and neurologic reassessment are therefore more important than reaching a normal glucose quickly. Every episode also requires a search for the precipitating infection, vascular event, medication problem, or access barrier that allowed the crisis to develop.

References

1. Hyperglycemic Crises in Adults With Diabetes: A Consensus Report, 2024 — Link