Can Hyperosmolar Hyperglycemic State (HHS) present with alkalosis, specifically a Venous Blood Gas (VBG) pH of 7.55?

Hyperosmolar Hyperglycemic State (HHS) and Alkalosis

HHS typically presents with mild acidosis or normal pH, but alkalosis (pH 7.55) can occur in HHS due to compensatory mechanisms or concurrent conditions, though this is not a typical presentation. 1, 2

Typical Acid-Base Status in HHS

HHS is classically characterized by:

• Marked hyperglycemia (≥30 mmol/L or ≥540 mg/dL)
• Hyperosmolality (≥320 mOsm/kg)
• Absence of significant ketosis (≤3.0 mmol/L)
• Absence of significant acidosis (pH >7.3 and bicarbonate ≥15 mmol/L) 1

Unlike diabetic ketoacidosis (DKA), which presents with metabolic acidosis, HHS typically has minimal or no acidosis. The Joint British Diabetes Societies guidelines specifically note that HHS presents with pH >7.3 and bicarbonate ≥15 mmol/L 1.

Mechanisms for Alkalosis in HHS

While not typical, alkalosis (pH 7.55) in HHS could occur due to:

1. Compensatory respiratory alkalosis: Severe dehydration can lead to hyperventilation as a compensatory mechanism, resulting in respiratory alkalosis.

2. Contraction alkalosis: The profound dehydration in HHS (fluid losses of 100-220 ml/kg) 1 can cause contraction alkalosis due to concentration of bicarbonate in the extracellular fluid.

3. Vomiting: A common precipitating factor in HHS that can cause loss of gastric acid and metabolic alkalosis.

4. Diuretic use: Many HHS patients are elderly with comorbidities requiring diuretics, which can cause metabolic alkalosis through various mechanisms 3.

5. Mixed acid-base disorders: HHS patients often have multiple comorbidities that can result in complex acid-base disturbances.

Clinical Implications

When encountering HHS with alkalosis (pH 7.55):

• Consider mixed disorders: Look for additional conditions causing alkalosis (vomiting, diuretic use, respiratory disorders).
• Assess volume status carefully: Profound dehydration in HHS (100-220 ml/kg fluid loss) 1 requires aggressive fluid resuscitation, typically with 0.9% sodium chloride.
• Monitor electrolytes closely: Particularly potassium, as alkalosis can worsen hypokalemia.

Management Considerations

For HHS with alkalosis:

• Fluid resuscitation remains the priority: Use 0.9% sodium chloride as the principal fluid to restore circulating volume 2.
• Delay insulin therapy: Withhold insulin until blood glucose is no longer falling with IV fluids alone (unless ketonemia is present) 2, 1.
• Monitor osmolality: Aim to reduce osmolality by 3-8 mOsm/kg/h to prevent neurological complications 1.
• Address the cause of alkalosis: Treat underlying conditions (e.g., stop offending medications, correct volume status).

Pitfalls to Avoid

• Don't rush insulin therapy: Early insulin use before adequate fluid resuscitation may be detrimental in HHS 2.
• Avoid rapid osmolality correction: This can lead to cerebral edema or central pontine myelinolysis 2.
• Don't ignore potassium: Alkalosis can mask hypokalemia, which may worsen with treatment.
• Don't miss mixed disorders: HHS rarely presents with alkalosis, so investigate for concurrent conditions.

In summary, while HHS typically presents with normal pH or mild acidosis, alkalosis can occur due to compensatory mechanisms or concurrent conditions. The management principles remain focused on careful fluid resuscitation, gradual correction of osmolality, and appropriate timing of insulin therapy.