11.1 Diabetic Ketoacidosis (DKA) & Hyperosmolar Hyperglycemic State (HHS)

11.1 Diabetic Ketoacidosis (DKA) & Hyperosmolar Hyperglycemic State (HHS)

Pathophysiological Divergence & Diagnostic Criteria

Diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) represent life-threatening extremes of decompensated diabetes mellitus. While both conditions share the root etiology of inadequate effective circulating insulin coupled with elevated counter-regulatory hormones (glucagon, catecholamines, cortisol, and growth hormone), their metabolic pathways diverge fundamentally in the magnitude of insulin deficiency and hepatic ketogenesis.

                    PATHOPHYSIOLOGIC DIVERGENCE: DKA VS HHS
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │ Diabetic Ketoacidosis (DKA):                                                │
  │   • Absolute (or severe relative) insulin deficiency                        │
  │   • Unrestrained lipolysis ──> Free fatty acid surge to liver               │
  │   • Hepatic mitochondrial beta-oxidation ──> Acetoacetate & Beta-OHB        │
  │   • Severe high anion gap metabolic acidosis; fluid deficit ~3–6 L (100 mL/kg)│
  ├─────────────────────────────────────────────────────────────────────────────┤
  │ Hyperosmolar Hyperglycemic State (HHS):                                     │
  │   • Relative insulin deficiency (sufficient to suppress lipolysis/ketogenesis)│
  │   • Massive gluconeogenesis + impaired peripheral glucose uptake            │
  │   • Severe hyperglycemia (>600 to >1,200 mg/dL) ──> Severe osmotic diuresis  │
  │   • Hyperosmolality (>320 mOsm/kg); profound fluid deficit 8–12 L (100–200 mL/kg)│
  └─────────────────────────────────────────────────────────────────────────────┘

The Ketogenic Cascade in DKA

In DKA, an absolute or profound relative insulin deficiency removes the normal inhibitory brake on hormone-sensitive lipase in adipose tissue. Adipocytes release massive fluxes of free fatty acids (FFAs) into the portal circulation. In hepatocytes, the loss of insulin and surge of glucagon activates carnitine palmitoyltransferase-1 (CPT-1), which shunts FFAs into mitochondrial beta-oxidation. Excess acetyl-CoA condenses into acetoacetate, which is enzymatically reduced to $\beta$-hydroxybutyrate ($\beta$-OHB) by beta-hydroxybutyrate dehydrogenase. In severe unresuscitated DKA, the circulating ratio of $\beta$-OHB to acetoacetate shifts from a normal 1:1 to greater than 3:1 or 5:1. Because conventional nitroprusside urine and serum ketone dipsticks react only with acetoacetate and acetone (not $\beta$-OHB), direct quantitative serum $\beta$-hydroxybutyrate measurement is the standard of care for diagnosis and tracking resolution.

Hyperosmolality and Fluid Shifts in HHS

In HHS, patients typically have type 2 diabetes with sufficient endogenous basal insulin secretion to inhibit adipose lipolysis and prevent ketogenesis, but insufficient insulin to stimulate skeletal muscle glucose uptake or suppress hepatic gluconeogenesis. Over days to weeks, progressive hyperglycemia triggers severe osmotic diuresis, leading to massive kaliuresis, natriuresis, and water loss. As intravascular volume contracts, renal plasma flow drops, impairing the kidney's ability to excrete glucose. Serum glucose accelerates past 600 to 1,200 mg/dL, causing effective serum osmolality to exceed 320 mOsm/kg and resulting in intracellular dehydration, central nervous system depression, and stupor or coma.

Diagnostic Criteria (2024 Consensus)

The 2024 ADA/EASD/JBDS/AACE/DTS consensus report on hyperglycemic crises (Umpierrez et al., Diabetes Care 2024) replaced the 2009 ADA criteria. DKA now requires three components, D, K and A:

HHS requires all four of the following:

Mixed DKA-HHS presentations are common. Measure β-hydroxybutyrate directly: nitroprusside ketone tests detect only acetoacetate, so they underestimate ketosis at presentation and overestimate it during recovery. The anion gap is no longer a first-line diagnostic or resolution criterion.

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Resuscitation Algorithm: Fluids, Sodium & Potassium Prior to Insulin

The management of DKA and HHS follows an ordered physiological sequence: volume expansion first, electrolyte stabilization second, and insulin administration third. Initiating insulin before adequate fluid resuscitation or potassium assessment is a critical medication safety error.

                    DKA / HHS TREATMENT PATHWAY (2024 CONSENSUS)
  STEP 1  FLUIDS: severe hypovolemia -> 0.9% NaCl or balanced crystalloid ~1 L/h;
          then replace ~50% of the deficit over 8-12 h (balanced fluids resolve DKA faster)
  STEP 2  POTASSIUM (check before insulin):
          K+ < 3.5 mmol/L  -> HOLD insulin; give K+ 10-20 mmol/h until > 3.5
          K+ 3.5-5.0       -> add 10-20 mmol K+ per liter; keep K+ 4-5 mmol/L
          K+ > 5.0         -> start insulin without K+; recheck every 2 h
  STEP 3  INSULIN: moderate/severe DKA 0.1 units/kg/h IV (bolus only if pump delayed);
          mild DKA may use SC rapid-acting analog 0.1 units/kg q1h or 0.2 units/kg q2h;
          HHS 0.05 units/kg/h
  STEP 4  GLUCOSE < 250 mg/dL -> add D5-D10 and cut insulin to 0.05 units/kg/h;
          keep glucose 150-200 (DKA) or 200-250 mg/dL (HHS) until resolution

Step 1: Fluid Replacement & Corrected Sodium Calculation

Intravascular volume expansion restores renal perfusion, reduces circulating counter-regulatory stress hormones, enhances peripheral insulin sensitivity, and lowers plasma glucose by 35 to 70 mg/dL/h through urinary glycosuria alone before insulin takes effect.

• Initial Resuscitation: With severe hypovolemia, give about 1 L/h of 0.9% saline or another isotonic crystalloid, then aim to replace roughly half of the estimated deficit over the first 8 to 12 hours. The 2024 consensus cites trials and meta-analyses showing that balanced crystalloids (lactated Ringer's, Plasma-Lyte) resolve DKA faster than saline, with less hyperchloremic acidosis. Use smaller volumes with hemodynamic monitoring in heart or kidney failure.
• Corrected Sodium Calculation: Severe hyperglycemia exerts an osmotic draw that shifts free water from the intracellular space into the intravascular space, diluting measured serum sodium (pseudohyponatremia). Corrected sodium reflects true tonicity: $\text{Corrected Sodium (mEq/L)} = \text{Measured }[\text{Na}^+] + 0.016 \times (\text{Plasma Glucose} - 100)$ (Alternatively: add 1.6 mEq/L to measured sodium for every 100 mg/dL elevation of glucose above 100 mg/dL; for glucose $>400\text{ mg/dL}$, many clinicians use a correction factor of 2.0 to 2.4 mEq/L).
• Maintenance Fluid Selection:
  • If corrected sodium is normal or elevated ($\ge 135\text{ mEq/L}$): Infuse 0.45% NaCl at 250 to 500 mL/h to provide hypotonic free water for ongoing intracellular rehydration.
  • If corrected sodium is low ($< 135\text{ mEq/L}$): Continue 0.9% NaCl or balanced crystalloid at 250 to 500 mL/h.
• Adding Dextrose: When plasma glucose falls below 250 mg/dL, add 5% or 10% dextrose to the crystalloid and reduce insulin to about 0.05 units/kg/h. Keep glucose at 150–200 mg/dL in DKA and 200–250 mg/dL in HHS until resolution. This allows uninterrupted insulin infusion to suppress lipolysis, clear circulating ketoacids, and close the anion gap while preventing hypoglycemia and abrupt drops in plasma osmolality that trigger cerebral edema.

Step 2: Potassium Stratification Prior to Insulin

Total-body potassium is depleted in all DKA and HHS patients by 300 to 600 mEq due to urinary kaliuresis from osmotic diuresis and secondary hyperaldosteronism. However, measured baseline serum potassium is often normal or elevated because acidemia (excess extracellular $H^+$ exchanged for intracellular $K^+$), hypertonicity (solvent drag), and insulin deficiency trap potassium in the extracellular fluid.

Administering insulin drives potassium into skeletal muscle and hepatic cells via stimulation of the sodium-potassium ATPase ($Na^+/K^+$ ATPase) pump. Initiating insulin in a patient with uncorrected hypokalemia can cause catastrophic cardiac dysrhythmias (prolonged QT interval, Torsades de Pointes, ventricular fibrillation) and respiratory arrest from diaphragmatic paralysis.

The 2024 consensus raised the hold threshold from the 2009 value of 3.3 to 3.5 mmol/L, and it starts replacement below 5.0 mmol/L rather than 5.2. Potassium typically falls 1 to 2 mmol/L in the first 48 hours of treatment.

Step 3: Regular Insulin Infusion Strategy

• Dosing Regimen: For moderate or severe DKA, a fixed-rate infusion of regular insulin at 0.1 units/kg/h. A 0.1 units/kg IV (or IM) bolus is only needed if setting up the infusion will be delayed. For mild DKA, subcutaneous rapid-acting analog (0.1 units/kg every hour or 0.2 units/kg every 2 hours) is an effective alternative outside the ICU. For HHS, start at 0.05 units/kg/h, and some experts wait until fluids alone stop lowering the glucose.
• Target Glycemic Rate of Fall: 50 to 75 mg/dL per hour.
  • If blood glucose does not fall by at least 50 mg/dL in the first hour: Verify fluid resuscitation status. If adequate, double the insulin infusion rate every hour until a steady glucose decline of 50 to 75 mg/dL/h is achieved.
  • If blood glucose falls faster than 75 to 100 mg/dL/h: Add 5% or 10% dextrose and adjust insulin to avoid rapid osmolar shifts, which raise the risk of cerebral edema in children and young adults. In HHS, aim for a slow fall in osmolality (roughly 3–8 mOsm/kg/h).

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Euglycemic DKA (euDKA) & SGLT2 Inhibitor Toxicity

Euglycemic diabetic ketoacidosis (euDKA) is a life-threatening emergency defined by severe high anion gap metabolic ketoacidosis occurring with normal or only mildly elevated blood glucose concentrations ($<200\text{ to }250\text{ mg/dL}$). The widespread adoption of Sodium-Glucose Cotransporter-2 (SGLT2) inhibitors—including empagliflozin, dapagliflozin, canagliflozin, and ertugliflozin—has dramatically increased the incidence of euDKA in emergency departments.

Molecular Mechanism of euDKA Under SGLT2 Inhibition

1. Renal Glycosuria: SGLT2 inhibitors block glucose reabsorption in the proximal convoluted tubule, forcing urinary excretion of 70 to 100 grams of glucose daily. This sustained glycosuria maintains plasma glucose below the renal threshold even during severe metabolic decompensation.
2. Suppression of Endogenous Insulin: Lower circulating plasma glucose diminishes pancreatic beta-cell stimulation, reducing endogenous insulin secretion.
3. Glucagon Surge: SGLT2 inhibition directly stimulates pancreatic alpha-cells, producing an elevated glucagon-to-insulin ratio.
4. Unchecked Ketogenesis: The high glucagon-to-insulin ratio accelerates lipolysis and activates hepatic CPT-1, driving massive beta-oxidation of FFAs into acetoacetate and $\beta$-hydroxybutyrate.

                  SGLT2 INHIBITOR EUGLYCEMIC DKA CASCADE
  ┌─────────────────────────────────────────────────────────────────────────────┐
  │ SGLT2 Inhibitor (Dapagliflozin / Empagliflozin)                             │
  │   │                                                                         │
  │   ├─> Proximal tubule glucose reabsorption blocked ──> Glycosuria (70–100g/d)│
  │   │     └─> Plasma glucose appears normal or near-normal (<250 mg/dL)       │
  │   │                                                                         │
  │   └─> Decreased insulin secretion + Increased pancreatic glucagon surge     │
  │         │                                                                   │
  │         └─> High Glucagon-to-Insulin Ratio ──> Uncontrolled Lipolysis       │
  │               │                                                             │
  │               └─> Hepatic CPT-1 Activation ──> Massive Ketone Production    │
  │                     │                                                       │
  │                     └─> Severe High Anion Gap Metabolic Acidosis (euDKA)    │
  └─────────────────────────────────────────────────────────────────────────────┘

Clinical Triggers & Emergency Pharmacotherapy of euDKA

• Precipitating Triggers: Acute surgical stress, severe sepsis, reduced oral intake or fasting, ketogenic (low-carbohydrate) diets, dehydration, excessive alcohol intake, or insulin dose reduction.
• Diagnostic Trap: Clinicians who screen solely with fingerstick blood glucose will miss euDKA. In any sick patient taking an SGLT2 inhibitor who presents with tachypnea (Kussmaul breathing), nausea, vomiting, or abdominal pain, order a basic metabolic panel, serum $\beta$-hydroxybutyrate, and blood gas analysis.
• Treatment Protocol:
  1. Discontinue SGLT2 Inhibitor Immediately.
  2. Initiate Dextrose-Containing Crystalloids Early: Because blood glucose is already $<250\text{ mg/dL}$, infuse D5W with 0.45% NaCl or D10W from the onset of therapy.
  3. Initiate Regular Insulin Infusion: Administer continuous regular insulin at 0.05 to 0.1 units/kg/h. Insulin is required not to lower blood glucose, but to suppress lipolysis, halt hepatic ketogenesis, and close the anion gap. The co-administered dextrose allows adequate insulin administration without inducing hypoglycemia.

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Bicarbonate & Phosphate Management in DKA

Bicarbonate Administration: Narrow Indications

Routine sodium bicarbonate therapy in DKA is not recommended by ADA guidelines. Randomized prospective trials have demonstrated that bicarbonate does not accelerate clinical recovery or arterial pH correction, but introduces significant hazards:

• Paradoxical Central Nervous System Acidosis: Exogenous sodium bicarbonate combines with hydrogen ions to generate carbonic acid, which dissociates into $H_2O$ and $CO_2$. While charged bicarbonate cannot cross the blood-brain barrier, uncharged lipid-soluble $CO_2$ rapidly diffuses into the cerebrospinal fluid, lowering CSF pH and worsening cerebral acidosis.
• Hypocalcemia & Hypokalemia: Alkalinization drives extracellular potassium and ionized calcium into intracellular compartments.
• Impaired Oxygen Delivery: Alkalemia shifts the oxyhemoglobin dissociation curve to the left (Bohr effect), impairing oxygen unloading in ischemic peripheral tissues.
• Delayed Ketone Clearance: Hepatic ketone clearance is prolonged following bicarbonate administration.

Phosphate Replacement Indications

Phosphate is shifted extracellularly and lost in urine during osmotic diuresis. While routine phosphate replacement does not alter DKA outcomes, severe hypophosphatemia ($< 1.0\text{ mg/dL}$) causes skeletal muscle weakness, respiratory depression, acute hemolytic anemia, and cardiac dysfunction.

• The 2024 consensus reserves phosphate for severe hypophosphatemia with muscle weakness, respiratory compromise or cardiac dysfunction. In that case, replace with 20 to 30 mmol Potassium Phosphate (or sodium phosphate if potassium is elevated) added to IV replacement fluids over 4 to 6 hours.

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DKA Resolution Criteria & Safe Subcutaneous Transition Protocol

Premature discontinuation of intravenous insulin or transitioning without adequate subcutaneous basal coverage is the single leading cause of recurrent ketoacidosis in the emergency department and intensive care unit.

The 2009 criteria (glucose below 200 mg/dL plus two of bicarbonate 15 or more, pH above 7.3 and a normal anion gap) appear in older references. Use clinical judgment: the consensus says not to delay a change in level of care solely to meet every number.

The Mandatory Subcutaneous Overlap Rule

The elimination half-life of intravenous regular insulin is 4 to 9 minutes. If an intravenous insulin infusion is abruptly stopped without established subcutaneous basal insulin, circulating insulin concentrations collapse to zero within 20 to 30 minutes. Unrestrained lipolysis resumes immediately, and ketoacidosis recurs rapidly.

1. Overlap Basal Insulin: Give subcutaneous long-acting basal insulin (glargine or degludec, or NPH) at least 1 to 2 hours before stopping the IV regular insulin infusion; the 2024 consensus describes continuing the infusion for 1 to 2 hours after the subcutaneous dose. Giving a low dose of basal insulin (0.15–0.3 units/kg) early, while the infusion is still running, shortens time to resolution and reduces rebound hyperglycemia.
2. Dosing in Insulin-Naive Patients: Calculate total daily dose (TDD) as 0.5 to 0.6 units/kg/day (about 0.3 units/kg/day with kidney failure, frailty or other hypoglycemia risks).
   • Allocate 50% of TDD as basal insulin (given once daily).
   • Allocate 50% of TDD as rapid-acting prandial insulin (lispro, aspart, or glulisine) divided equally across three meals.
3. Dosing in Established Patients: In patients with pre-existing insulin regimens, re-institute their home basal insulin dose, provided their baseline control was acceptable and renal function has recovered.