What are the key differences in managing Hyperosmolar Hyperglycemic State (HHS) versus Diabetic Ketoacidosis (DKA) in an older adult patient with type 2 diabetes?

Key Differences in Managing HHS versus DKA

HHS requires more aggressive and prolonged fluid resuscitation as the cornerstone of therapy, while DKA prioritizes earlier insulin administration, with HHS patients needing insulin withheld until glucose stops falling with fluids alone unless ketonemic. 1

Fundamental Pathophysiologic Distinctions

Time Course and Presentation

• HHS evolves over several days to weeks, allowing for more severe dehydration and higher glucose levels, whereas DKA develops much more rapidly (hours to days) 2
• HHS mortality remains significantly higher at 15% compared to DKA mortality of <5% in experienced centers 2, 3
• HHS occurs predominantly in older adults with type 2 diabetes, while DKA is more common in younger patients with type 1 diabetes 4

Metabolic Differences

• HHS patients retain enough residual insulin (evidenced by C-peptide) to prevent lipolysis and ketogenesis but insufficient to control hyperglycemia 2
• DKA features prominent ketoacidosis (pH <7.3, bicarbonate <15 mEq/L) with moderate hyperglycemia (>250 mg/dL), while HHS presents with extreme hyperglycemia (>600 mg/dL) without significant ketosis (pH >7.3, bicarbonate >15 mEq/L) 1

Critical Management Differences

Fluid Resuscitation Strategy

For HHS:

• Fluid replacement is the absolute cornerstone of therapy and takes priority over insulin 5
• Begin with isotonic saline (0.9% NaCl) at 15-20 mL/kg/hour during the first hour 1
• Total fluid deficits in HHS are typically 8-10 liters (versus 5-7 liters in DKA), requiring more aggressive and prolonged rehydration 5
• Switch to 0.45% NaCl if corrected sodium is normal or elevated 1

For DKA:

• Fluid resuscitation is critical but insulin therapy can begin earlier once adequate hydration is established 6
• Same initial rate of 15-20 mL/kg/hour isotonic saline 1
• When glucose reaches 250 mg/dL, switch to 5% dextrose with 0.45-0.75% saline to prevent hypoglycemia while continuing insulin 6

Insulin Administration Timing

For HHS:

• Withhold insulin until blood glucose stops falling with IV fluids alone, unless the patient is ketonemic 1
• This critical distinction prevents precipitous drops in osmolality that increase risk of cerebral edema and vascular complications 5
• Once insulin is started, use continuous IV regular insulin at 0.1 units/kg/hour 1

For DKA:

• Start continuous IV regular insulin at 0.1 units/kg/hour without initial bolus once potassium >3.3 mEq/L 1
• Insulin is the cornerstone of DKA therapy and should not be delayed once fluid resuscitation begins 5
• Target glucose decline of 50-75 mg/dL per hour 6

Rate of Correction

For HHS:

• Slower correction is essential to prevent devastating complications 5
• In older adults with HHS, rapid correction increases risk of vascular occlusion, seizures, and central pontine myelinolysis 1
• Aim for gradual osmolality reduction over 24-48 hours 5

For DKA:

• More rapid correction is generally safe in adults (cerebral edema risk is primarily in children) 5
• Resolution typically occurs within 12-24 hours 2

Monitoring Differences

HHS-Specific Monitoring

• Check serum osmolality every 2-4 hours to ensure gradual correction 1
• Monitor for altered mental status more closely, as HHS patients often present with severe dehydration and altered consciousness 1
• Watch for vascular complications (thrombosis, stroke, MI) which are more common in HHS 1

DKA-Specific Monitoring

• Monitor venous pH and anion gap every 2-4 hours to track ketoacidosis resolution 1
• Check blood glucose every 1-2 hours 1
• β-hydroxybutyrate measurement is preferred for monitoring ketone resolution 6

Potassium Management (Similar but Critical in Both)

• Delay insulin if K+ <3.3 mEq/L in both conditions to prevent life-threatening arrhythmias 1
• Add 20-40 mEq/L potassium (2/3 KCl, 1/3 KPO4) once K+ <5.5 mEq/L and urine output confirmed 1
• Total body potassium depletion is universal in both conditions despite variable presenting levels 6
• Target serum potassium 4-5 mEq/L throughout treatment 1

Resolution Criteria

DKA Resolution requires ALL of:

• Glucose <200 mg/dL
• Serum bicarbonate ≥18 mEq/L
• Venous pH >7.3
• Anion gap ≤12 mEq/L 1, 6

HHS Resolution is less clearly defined but includes:

• Improved mental status
• Serum osmolality <315 mOsm/kg
• Adequate hydration status 1

Transition to Subcutaneous Insulin

For both conditions:

• Administer basal insulin (intermediate or long-acting) 2-4 hours BEFORE stopping IV insulin to prevent rebound hyperglycemia and ketoacidosis 1, 6
• This overlap period is absolutely essential 2

Key difference:

• HHS patients may not require long-term insulin if they have type 2 diabetes with adequate residual beta-cell function 5
• DKA patients, especially with type 1 diabetes, require lifelong insulin therapy 5

Common Pitfalls Specific to Each Condition

HHS Pitfalls:

• Starting insulin too early before adequate fluid resuscitation causes dangerous osmolality shifts 5
• Overly rapid correction leading to cerebral edema, seizures, or central pontine myelinolysis 1
• Underestimating fluid deficits in elderly patients who may not tolerate aggressive resuscitation 7

DKA Pitfalls:

• Stopping insulin when glucose normalizes before ketoacidosis resolves—continue insulin and add dextrose 6
• Inadequate potassium monitoring and replacement leading to fatal arrhythmias 6
• Premature discontinuation of IV insulin without prior basal insulin administration 2

Special Considerations in Older Adults

• HHS patients are typically older and may have significant comorbidities (heart failure, renal disease) requiring careful fluid management 7
• Monitor for fluid overload with clinical examination and consider central venous pressure monitoring in high-risk patients 7
• Inadequate supervision in nursing homes is a common precipitant of HHS—address this in discharge planning 1