Fluid Management in HHS When Glucose Drops Below 200 mg/dL
Yes, you should change to D5 (5% dextrose) with 0.45% NaCl when blood glucose falls below 200 mg/dL in HHS, and continue IV fluids at a rate sufficient to replace the estimated fluid deficit while maintaining adequate hydration. 1, 2
Fluid Transition Protocol
When glucose reaches 200 mg/dL during HHS treatment:
- Switch from 0.9% NaCl to 5% dextrose with 0.45-0.75% NaCl 3, 1
- Continue insulin infusion at the same time—do NOT stop insulin just because glucose is falling 1, 4
- Add 20-40 mEq/L potassium to each liter of the dextrose-containing fluid (2/3 KCl and 1/3 KPO4) 3, 1
The rationale is critical: In HHS, the hyperosmolality takes longer to resolve than hyperglycemia alone. 5, 2 You must continue insulin therapy to fully correct the metabolic derangement, but adding dextrose prevents hypoglycemia while this occurs. 1, 4
Fluid Rate Adjustments
Initial fluid resuscitation (first 1-4 hours):
- Use 0.9% NaCl at 10-20 mL/kg/h (up to 50 mL/kg over first 4 hours maximum) 3
- This aggressive initial rate restores circulating volume and addresses severe dehydration 3, 2
After glucose falls below 200 mg/dL:
- Reduce to maintenance rates of 75-125 mL/hour for average adults 1
- Aim to replace 50% of the estimated fluid deficit in the first 8-12 hours 1
- Total fluid losses in HHS are typically 100-220 mL/kg, requiring careful replacement over 24-48 hours 2, 6
Target osmolality reduction: 3-8 mOsm/kg/h 5, 2 This gradual decline minimizes the risk of cerebral edema and osmotic demyelination syndrome, which are life-threatening complications of too-rapid correction. 5, 2
Critical Monitoring Parameters
Check every 2-4 hours until stable: 3, 1
- Blood glucose
- Serum osmolality (calculated as 2×Na + glucose/18 + BUN/2.8) 3, 2
- Electrolytes, especially potassium (maintain 4-5 mEq/L) 3, 1
- Renal function and urine output (target ≥0.5 mL/kg/h) 2
Common Pitfalls to Avoid
Never stop insulin infusion when glucose falls below 200 mg/dL—this is the most common error and causes persistent hyperosmolality. 1, 4 Instead, add dextrose to the fluids and continue insulin until osmolality normalizes (<300 mOsm/kg). 1, 2
Do not use hypotonic fluids (0.45% NaCl) initially—start with 0.9% NaCl for volume resuscitation, then transition to 0.45% NaCl with dextrose once glucose drops. 3, 5, 7 An initial rise in sodium is expected and does not require immediate hypotonic fluids. 5
Avoid starting insulin too early—in pure HHS (without significant ketosis), fluid replacement alone will lower glucose initially. 5, 2 Start insulin only when glucose stops falling with fluids alone, or if ketonemia is present. 5, 2
Monitor for fluid overload, especially in elderly patients and those with cardiac or renal disease—frequent assessment of cardiac, renal, and mental status is mandatory. 3
Resolution Criteria for HHS
Continue dextrose-containing fluids until ALL of the following are met: 2
- Osmolality <300 mOsm/kg
- Hypovolemia corrected (urine output ≥0.5 mL/kg/h)
- Cognitive status returned to baseline
- Blood glucose <15 mmol/L (270 mg/dL)
Once these criteria are met and the patient tolerates oral intake, you can discontinue IV fluids and transition to subcutaneous insulin. 1 Remember to overlap IV insulin with subcutaneous basal insulin by 1-2 hours to prevent rebound hyperglycemia. 1, 4