Key Facts

HHS has much higher mortality than DKA. The cornerstone of treatment is careful rehydration. Insulin is secondary and given at lower doses than DKA. Rapid correction of osmolality must be avoided.

Epidemiology

Incidence increasing with T2DM prevalence. Primarily affects elderly (>60 years). Mortality 15-20% (vs ~1% for DKA). Often occurs in residential care settings with poor fluid access.

Aetiology

Precipitants: infection (30-60% — UTI, pneumonia), MI, stroke, surgery, drugs (steroids, thiazides), poor fluid intake (dementia, reduced mobility), new diagnosis of T2DM.

Pathophysiology

Relative (not absolute) insulin deficiency → sufficient insulin to prevent lipolysis/ketogenesis (hence minimal ketones) but insufficient to control hepatic glucose output → progressive hyperglycaemia → osmotic diuresis → severe dehydration (often 100-220 mL/kg deficit). Hyperosmolality → intracellular dehydration → confusion → coma. Prothrombotic state (hyperviscosity) → high VTE/arterial thrombosis risk.

Symptoms

• Insidious onset over days-weeks (slower than DKA)
• Polyuria, polydipsia → reduced oral intake → profound dehydration
• Confusion, drowsiness → stupor → coma (correlates with osmolality)
• Weakness, leg cramps

Signs

• Severe dehydration: dry mucous membranes, reduced skin turgor, tachycardia, hypotension
• Altered consciousness (often GCS <12)
• Focal neurological signs may occur (seizures, hemiparesis — can mimic stroke)
• No Kussmaul breathing (not acidotic)
• No ketotic breath

Red Flags

• GCS <12 → severe HHS; ITU
• Focal neurological deficit → exclude stroke (CT head)
• Serum Na⁺ >160 mmol/L → very high osmolality; extreme caution with fluid correction
• K⁺ abnormalities → cardiac monitoring

Immediate

• Blood glucose: often >30 mmol/L (may be >100)
• Serum osmolality: >320 mOsm/kg (calculated: 2(Na⁺ + K⁺) + glucose + urea)
• Blood ketones: <3.0 mmol/L (minimal)
• VBG: pH >7.3, bicarb >15 (no significant acidosis)
• U&Es: Na⁺ (often raised; calculate corrected Na⁺), K⁺, renal function
• FBC, CRP: infection screen
• Blood cultures, urine MC&S, CXR: identify precipitant
• ECG: MI, arrhythmia, electrolyte changes
• CT head: if focal neurological deficit (exclude stroke)

Monitoring (JBDS-IP)

• Hourly glucose, 2-hourly Na⁺ and osmolality
• Target: osmolality fall 3-8 mOsm/kg/hr
• Fluid balance: strict I/O; catheterise if oliguric

IV Fluids (Cornerstone — JBDS-IP)

• 0.9% NaCl: 1L over 1 hour → 1L over 2 hours → subsequent fluids guided by clinical response and osmolality trend
• Aim to replace ~50% of fluid deficit in first 12 hours, remainder over next 12-24 hours
• Slower than DKA (avoid rapid osmolality shifts)
• If osmolality not falling despite 0.9% NaCl → consider 0.45% NaCl (half-normal saline); ONLY under specialist guidance
• When glucose <14 mmol/L: add 5% or 10% glucose

Insulin

• NOT first-line in HHS (unlike DKA) — fluids alone often reduce glucose significantly
• Start 0.05 units/kg/hr FRII ONLY if: ketones >1.0 mmol/L, or glucose not falling at ≥5 mmol/L/hr with fluids alone
• Target glucose fall: 4-6 mmol/L/hr (NOT faster — risk of cerebral oedema)

Potassium

• Replace as per DKA protocol (guided by serum K⁺)
• K⁺ <3.5: replace BEFORE insulin

VTE Prophylaxis (Essential)

• LMWH (enoxaparin 40 mg SC OD) for ALL patients — HHS is extremely prothrombotic
• Continue throughout admission

Other

• Treat precipitant (antibiotics, MI pathway)
• Foot care (neuropathy + dehydration → high ulceration risk)
• Monitor for complications: VTE, rhabdomyolysis, acute kidney injury

Referral Criteria

• Medical/endocrine emergency admission
• ITU/HDU: GCS <12, severe comorbidity
• Diabetes team: before discharge

Mortality ~15-20% (primarily due to age, comorbidities, and thromboembolic complications rather than hyperglycaemia per se). VTE is a major contributor to mortality. Full recovery is common with prompt appropriate treatment. Cerebral oedema from over-rapid correction is avoidable. Many patients diagnosed with HHS were previously undiagnosed T2DM. Post-discharge: optimise diabetes management, educate on sick-day rules.

HHS vs DKA