Clinical meaning
The nurse practitioner must rapidly differentiate DKA from HHS and initiate appropriate management, as the two conditions share hyperglycemia but differ in pathogenesis, presentation, severity, and nuanced treatment approach.
DKA diagnostic criteria (ADA): blood glucose >250 mg/dL, arterial pH <7.30, serum bicarbonate <18 mEq/L, elevated anion gap (>12), positive serum/urine ketones (beta-hydroxybutyrate >3 mmol/L). Severity classification: Mild (pH 7.25-7.30, bicarb 15-18, alert), Moderate (pH 7.00-7.24, bicarb 10-14, drowsy), Severe (pH <7.00, bicarb <10, stuporous/coma).
HHS diagnostic criteria: blood glucose >600 mg/dL, effective serum osmolality >320 mOsm/kg, pH >7.30, serum bicarbonate >18 mEq/L, absent or trace ketones, altered mental status (typically correlating with osmolality >320).
Critical pathophysiological distinction: In DKA, ABSOLUTE insulin deficiency allows unopposed lipolysis → free fatty acid release → hepatic beta-oxidation → ketone body production (acetoacetate, beta-hydroxybutyrate, acetone) → metabolic acidosis. In HHS, RELATIVE insulin deficiency (enough insulin to suppress lipolysis but not enough to promote peripheral glucose uptake or suppress hepatic glucose output) → progressive hyperglycemia over days to weeks → osmotic diuresis → profound dehydration (8-12 L deficit) → hyperosmolality → CNS dysfunction.
Overlap syndrome: approximately 30% of hyperglycemic emergencies have features of BOTH DKA and HHS (e.g., glucose >600 with pH <7.3 and ketones). These 'DKA-HHS overlap' presentations carry higher mortality than either condition alone and should be managed aggressively with both fluid resuscitation (HHS protocol volumes) and insulin (DKA protocol dosing).