Hyperosmolar hyperglycaemic state (HHS) is a critical metabolic emergency most commonly arising in individuals with type 2 diabetes mellitus 1,5. It is precipitated by conditions that increase insulin resistance and counter-regulatory hormone release, compounded by progressive, unrecognized fluid loss over days or weeks 1,5. The condition is clinically defined by severe dehydration, marked hyperosmolality (typically $320\text{ mOsm/kg}$ or greater), extreme hyperglycaemia (often $30\text{ mmol/L}$ or greater), and the absence of significant ketoacidosis 1. Because symptoms evolve insidiously compared to diabetic ketoacidosis (DKA), patients frequently present with profound neurological impairment ranging from confusion to coma 5,6. Management requires meticulous, stepwise fluid resuscitation, careful electrolyte repletion, and gradual blood glucose lowering to prevent neurological complications 1,5.
1. Etiology & Risk Factors
- Infectious Triggers: Pneumonia, urinary tract infections, sepsis, and intra-abdominal infections represent the most frequent inciting events, accounting for nearly half of all cases 3.
- Non-Infective Illnesses: Myocardial infarction, cerebrovascular accidents, acute pancreatitis, pulmonary embolism, and severe trauma 3.
- Medication Non-Adherence & Iatrogenic Agents: Omission of oral hypoglycaemic agents or insulin, alongside medications that impair glucose tolerance or promote fluid loss, such as glucocorticoids, thiazide diuretics, atypical antipsychotics, and sympathomimetics.
- Substance Use & Comorbidities: Heavy alcohol intake, chronic kidney disease, advanced age, cognitive impairment limiting fluid access, and institutionalized living environments.
- Emerging Demographics: While traditionally associated with older adults with type 2 diabetes, HHS is increasingly diagnosed in younger adults, adolescents, and occasionally children, sometimes presenting as mixed DKA/HHS states 1.
2. Pathophysiology
The development of HHS hinges on a dual insult: an absolute or relative reduction in effective circulating insulin coupled with a concurrent elevation in counter-regulatory hormones (glucagon, catecholamines, cortisol, and growth hormone) 1,4. This hormonal imbalance accelerates hepatic glucose production via glycogenolysis and gluconeogenesis while severely impairing peripheral glucose uptake by skeletal muscle and adipose tissue 4.
As blood glucose concentrations climb past the renal threshold for reabsorption, massive glucosuria ensues. Glucose acts as an osmotic agent within the renal tubules, obligating profound water excretion and electrolyte wasting—a process termed osmotic diuresis 1. Unlike DKA, the residual basal insulin present in HHS is generally sufficient to inhibit hormone-sensitive lipase and hepatic ketogenesis, preventing the massive accumulation of circulating ketone bodies and preserving physiological blood pH 1.
Without adequate fluid intake to match urinary losses, extracellular fluid volume plummets, concentrating plasma solutes and driving serum osmolality well above $320\text{ mOsm/kg}$ 1. The resulting hyperosmolality exerts osmotic pressure across cellular membranes, drawing free water out of intracellular compartments—most notably neurons—into the vascular and interstitial spaces. This cellular dehydration accounts for the hallmark neuropsychiatric manifestations of the disorder 5,6. Furthermore, hemoconcentration and systemic inflammation create a profound prothrombotic and hyperviscous state, elevating the risk of microvascular and macrovascular occlusive events 6,7.
3. Clinical Presentation & Classic Clinical Signs
- History & Cardinal Symptoms: Patients typically report an insidious prodrome of polyuria, polydipsia, weight loss, and generalized weakness developing over several days to weeks 1,5. As dehydration worsens, symptoms progress to lethargy, confusion, focal neurological deficits, hallucinations, or generalized seizures 5,6.
- Physical Examination & Named Clinical Signs: Examination reveals profound clinical signs of dehydration, including dry mucous membranes, decreased skin turgor, sunken eyeballs, tachycardia, and severe orthostatic or frank hypotension. Neurological examination may demonstrate varying degrees of depressed Glasgow Coma Scale (GCS) scores, hemiparesis mimicking acute ischemic stroke, or hyperreflexia 5,6. Kussmaul breathing is characteristically absent unless a concurrent metabolic acidosis (such as lactic acidosis or mixed DKA) is present 1.
4. Diagnostic Workup & Interpretation (Laboratory, Imaging & ECG/Pathology)
| Diagnostic Modality / Test | Expected Clinical & Radiological / Laboratory Finding |
|---|---|
| Gold-Standard Investigation | Calculated effective serum osmolality equation: $2 \times \text{Measured } \text{Na}^+ (\text{mmol/L}) + \text{Glucose} (\text{mmol/L})$, yielding a result of $320\text{ mOsm/kg}$ or greater 1. |
| Laboratory Panel | Venous or arterial blood glucose $30\text{ mmol/L}$ or greater; serum sodium often normal or elevated (pseudohyponatremia or hypernatraemic dehydration); serum bicarbonate $15\text{ mmol/L}$ or greater; arterial blood gas pH greater than $7.3$; blood urea nitrogen and serum creatinine markedly elevated due to prerenal azotaemia; blood ketonaemia $3.0\text{ mmol/L}$ or less 1. |
| Imaging / Radiology (X-ray, US, CT, MRI) | Chest radiography to evaluate for occult pneumonia; computed tomography (CT) or magnetic resonance imaging (MRI) of the brain to exclude intracranial hemorrhage, cerebral oedema, or stroke mimics when focal neurological deficits persist despite metabolic correction 5,6. |
| ECG / Histopathology / Procedural | Electrocardiogram (ECG) to screen for silent myocardial infarction, electrolyte-induced dysrhythmias (such as peaked T-waves of hyperkalaemia or U-waves of hypokalaemia), and baseline cardiovascular status 5. |
5. Staging, Classification & Clinical Scoring Systems
| Criterion / Stage / Score Component | Clinical Threshold, Points & Management Implication |
|---|---|
| Blood Glucose Threshold | Greater than or equal to $30.0\text{ mmol/L}$ ($540\text{ mg/dL}$), mandating urgent volume expansion and glycemic control 1,2. |
| Serum Osmolality Threshold | Effective osmolality greater than or equal to $320\text{ mOsm/kg}$, defining the severity of cellular dehydration and dictating the target rate of fluid and solute correction 1,2. |
| Acid-Base Status | Arterial pH greater than $7.3$ and serum bicarbonate greater than or equal to $15\text{ mmol/L}$, distinguishing pure HHS from mixed DKA/HHS presentations 1. |
| Ketone Status | Serum ketones $3.0\text{ mmol/L}$ or less, or mild ketonuria, reflecting preserved basal portal insulin secretion sufficient to inhibit runaway lipolysis 1. |
6. Differential Diagnosis
| Differential Condition | Distinguishing Clinical, Biochemical & Imaging Features |
|---|---|
| Diabetic Ketoacidosis (DKA) | Presents with a more rapid onset (within hours), prominent metabolic acidosis (pH less than $7.3$, bicarbonate less than $15\text{ mmol/L}$), significant ketonaemia (greater than $3.0\text{ mmol/L}$), and Kussmaul respirations 1,5. |
| Mixed DKA / HHS | Exhibits features of both conditions concurrently, featuring severe hyperglycaemia and hyperosmolality alongside significant metabolic acidosis and ketosis, requiring combined therapeutic pathways 1. |
| Hyperosmolar Hyperglycaemic Non-Ketotic Lactic Acidosis | Marked by severe metabolic acidosis with a high anion gap driven by profound tissue hypoperfusion and elevated serum lactate levels, distinct from uncomplicated HHS 1. |
| Acute Ischemic Stroke or Intracranial Hemorrhage | Presents with acute focal neurological deficits; can either mimic HHS neurological presentation or occur concurrently as a vascular complication of hyperviscosity 6. |
7. Management & Treatment Protocol
- Initial Stabilization & Resuscitation: Secure airway, breathing, and circulation. Immediate establishment of large-bore intravenous access and continuous cardiac monitoring. Identify and treat underlying precipitating factors (e.g., broad-spectrum antibiotics for suspected infection) 1.
- First-Line Medical / Pharmacological Therapy (with exact adult dosing):
- Fluid Resuscitation: Infuse $0.9\%$ sodium chloride intravenously to restore intravascular volume and correct hemodynamic instability. Initial infusion rates typically range from $1000\text{ mL}$ to $1500\text{ mL}$ in the first hour, adjusted thereafter according to central venous pressure and clinical response 1,2. Once blood glucose drops below $14\text{ mmol/L}$, switch to $0.45\%$ sodium chloride with added potassium chloride to prevent rapid osmolar shifts and hyponatremia.
- Insulin Therapy: Do not rush insulin administration prior to adequate fluid resuscitation, as sudden intravascular volume contraction combined with insulin can precipitate vascular collapse. Initiate a fixed-rate regular human insulin infusion at $0.05\text{ units/kg/h}$ (or a maximum of $0.1\text{ units/kg/h}$ without an initial bolus). The therapeutic goal is a controlled, gradual decline in serum osmolality by $3\text{ to } 8\text{ mOsm/kg/h}$ and a blood glucose reduction of $4\text{ to } 5\text{ mmol/L per hour}$ 1,5.
- Electrolyte Management: Monitor and replace potassium aggressively. Maintain serum potassium between $4.0\text{ and } 5.0\text{ mmol/L}$ by adding $20\text{ to } 40\text{ mmol}$ of potassium chloride to each liter of IV fluid once urine output is established.
- Surgical / Interventional Indications: Urgent thrombectomy for large vessel occlusive arterial thrombosis, surgical debridement for severe foot ulceration or infected foci, and prompt intervention for acute intra-abdominal surgical emergencies 1,7.
8. Complications & Prognosis
- Acute Complications: Cerebral oedema resulting from overly rapid correction of serum osmolality or aggressive drop in blood glucose; central pontine myelinolysis (osmotic demyelination syndrome); acute kidney injury due to severe volume depletion; arterial and venous thromboembolism, including myocardial infarction, stroke, and large vessel occlusive thrombosis driven by hyperviscosity 1,5,6,7.
- Prognosis & Mortality: HHS carries a substantially higher mortality rate than DKA, historically ranging between $5\%$ and $20\%$, largely driven by advanced patient age, severe comorbidities, delayed presentation, and concurrent multiorgan failure 1,3,5.