Diabetic Ketoacidosis ll: Pathophysiology

In type 1 diabetes, insulin deficiency is typically absolute due to pancreatic beta cell destruction. In type 2 diabetes, severe relative insulin deficiency develops during physiological stressors like infection. Both scenarios impair glucose uptake and trigger counterregulatory hormones, worsening hyperglycemia and initiating the cascade toward metabolic emergency.

Without insulin, lipolysis proceeds unchecked, releasing free fatty acids from adipose tissue. The liver undergoes increased fatty acid beta-oxidation, generating acetyl-CoA that converts into ketone bodies—acetoacetate, beta-hydroxybutyrate, and acetone. Excess ketone accumulation causes high anion gap metabolic acidosis, a hallmark of DKA.

Hyperglycemia exceeds the renal threshold, causing glucose excretion in urine. This osmotic diuresis depletes water, sodium, potassium, and phosphate, leading to polyuria and volume depletion. Continued fluid loss reduces renal perfusion, further impairing clearance of glucose and ketones, worsening the metabolic emergency.

Acidosis and insulin deficiency drive potassium shifts from intracellular to extracellular compartments, masking severe total-body depletion. Serum levels may appear normal or elevated despite significant losses. When insulin therapy and acidosis correction begin, potassium rapidly re-enters cells, creating dangerous hypokalemia unless potassium is replaced.

Insulin deficiency allows unopposed actions of glucagon, cortisol, catecholamines, and growth hormone. These counterregulatory hormones drive gluconeogenesis and glycogenolysis in the liver while blocking glucose uptake in insulin-dependent tissues. The result is marked hyperglycemia that exceeds the renal threshold for reabsorption.

Rising plasma osmolality, often exceeding 330 mOsm/kg, causes cerebral dehydration leading to confusion, stupor, or coma. Hyperosmolality, rather than acidosis alone, is the primary cause of altered consciousness. Kussmaul respirations develop as the respiratory center responds to acidosis, lowering CO2 to compensate.

Diabetic ketoacidosis is characterized by three interconnected metabolic derangements: hyperglycemia from impaired glucose uptake and increased hepatic production, metabolic acidosis from ketone body accumulation, and fluid and electrolyte loss from osmotic diuresis. Together, these disturbances define the pathophysiologic basis of this life-threatening emergency.