Endocrine Emergency Deep Pathophysiology
DKA vs HHS: The Complete Pathophysiology
A comprehensive exploration of diabetic ketoacidosis and hyperosmolar hyperglycemic state—understanding why insulin deficiency manifests so differently and how this knowledge transforms management.
Foundations: Two Syndromes, One Hormone
DKA and HHS both result from insulin deficiency, yet their presentations are dramatically different. Understanding why requires understanding insulin's role in metabolism and what happens when it fails.
Why Do DKA and HHS Look So Different?
Both conditions share the same fundamental problem—inadequate insulin action—yet one produces severe acidosis with modest hyperglycemia, while the other produces extreme hyperglycemia without significant ketosis. The difference lies in the DEGREE of insulin deficiency and the patient population affected.
Insulin: Absolute deficiency (near zero)
Glucose: 250-600 mg/dL (moderate)
Ketones: Markedly elevated
pH: <7.30 (acidotic)
Osmolality: Variable (usually <320)
Patient: Typically Type 1 DM
Onset: Hours to 1-2 days
Mortality: ~1-5%
Insulin: Relative deficiency (some present)
Glucose: >600 mg/dL (often >1000)
Ketones: Minimal or absent
pH: >7.30 (usually normal)
Osmolality: >320 mOsm/kg (severely elevated)
Patient: Typically Type 2 DM, elderly
Onset: Days to weeks
Mortality: ~10-20%
The Key Question: Why Ketones in DKA but Not HHS?
Why does DKA produce ketones while HHS does not?
Ketogenesis requires near-complete insulin deficiency. In DKA, insulin is virtually absent, allowing unrestricted lipolysis and hepatic ketone production. In HHS, residual insulin (even small amounts) is sufficient to suppress lipolysis and prevent ketosis, even though it cannot control glucose.
Why does a small amount of insulin prevent ketosis?
Insulin's effect on fat metabolism is exquisitely sensitive—much more so than its effect on glucose. The IC50 (concentration for 50% inhibition) for lipolysis is ~10× lower than for glucose uptake. Even 10-20% of normal insulin levels can suppress lipolysis while being completely inadequate for glucose control. This is why Type 2 diabetics (with residual insulin) rarely develop DKA.
Why is glucose higher in HHS than DKA?
Two reasons: (1) HHS develops more slowly (days to weeks), allowing progressive glucose accumulation; (2) The severe dehydration of HHS concentrates glucose further. DKA presents earlier because acidosis causes symptoms (nausea, vomiting, Kussmaul breathing) that bring patients to medical attention before glucose reaches extreme levels.
Why is HHS mortality higher than DKA?
HHS patients are typically older with more comorbidities. The profound hyperosmolality causes severe neurologic dysfunction. The precipitating illness (MI, infection, stroke) contributes to mortality. And the insidious onset means patients present later in their course with more severe derangements.
Can patients have features of both DKA and HHS?
Yes—up to 30% of patients have "overlap" with both ketoacidosis AND hyperosmolality. This typically occurs in Type 2 diabetics under severe stress (when insulin resistance overwhelms residual secretion) or Type 1 diabetics with prolonged illness. These patients require aggressive management of both components.
Who Gets What?
DKA Demographics
Classic Patient: Young Type 1 diabetic with new diagnosis, insulin omission, or precipitating illness.
Increasing in Type 2: Ketosis-prone Type 2 DM (often African American, Hispanic) can present with DKA. SGLT2 inhibitors can cause euglycemic DKA (normal glucose but ketotic).
Precipitants: Infection (30-40%), insulin omission/noncompliance (20-30%), new diagnosis (20-25%), other (MI, pancreatitis, drugs, cocaine).
HHS Demographics
Classic Patient: Elderly Type 2 diabetic, often with limited access to water (nursing home, dementia, post-stroke).
Key Risk Factor: Impaired thirst mechanism or inability to access fluids. A younger patient who can drink freely will rarely develop HHS—they'll drink enough to prevent extreme hyperglycemia.
Precipitants: Infection (40-60%), cardiovascular event (MI, stroke), medications (steroids, thiazides), new diagnosis, inadequate fluid intake.
Evidence Base
Kitabchi AE, et al. Hyperglycemic Crises in Adult Patients With Diabetes. Diabetes Care 2009 • Umpierrez GE, et al. Diabetic emergencies—ketoacidosis, hyperglycaemic hyperosmolar state and hypoglycaemia. Nat Rev Endocrinol 2016 • Pasquel FJ, Umpierrez GE. Hyperosmolar Hyperglycemic State. Nat Rev Dis Primers 2014
Insulin Physiology: The Master Metabolic Regulator
To understand DKA and HHS, we must first understand what insulin does—and therefore what goes wrong when it's absent. Insulin is not just a "glucose hormone"; it is the master switch between fed and fasted metabolic states.
What Insulin Does: The Fed State
Insulin is released from pancreatic β-cells in response to glucose (primary stimulus), amino acids, and incretins (GLP-1, GIP). Its actions promote energy storage and anabolism.
Glucose Uptake (Muscle, Adipose)
Insulin binds its receptor → tyrosine kinase activation → PI3K/Akt pathway → GLUT4 translocation to cell membrane. Glucose enters cells. Without insulin, glucose cannot enter insulin-sensitive tissues and accumulates in blood.
Suppression of Hepatic Glucose Production
Insulin inhibits gluconeogenesis (making new glucose from amino acids, lactate, glycerol) and glycogenolysis (breaking down glycogen). The liver normally produces 150-200 g glucose/day in fasting; insulin keeps this in check. Without insulin, the liver produces glucose unchecked.
Suppression of Lipolysis
Insulin inhibits hormone-sensitive lipase (HSL) in adipocytes. This prevents triglyceride breakdown into free fatty acids (FFAs) and glycerol. This is insulin's most sensitive action—requires only tiny amounts of insulin. Without insulin, FFAs flood the circulation and become substrate for ketogenesis.
Suppression of Ketogenesis
Insulin inhibits CPT-1 (carnitine palmitoyltransferase-1), the rate-limiting enzyme for fatty acid entry into mitochondria for β-oxidation and ketogenesis. Even with abundant FFAs, ketogenesis is limited if insulin is present. Without insulin, FFAs freely enter mitochondria and become ketones.
Protein Anabolism
Insulin promotes amino acid uptake and protein synthesis while inhibiting protein breakdown. Without insulin, muscle proteolysis releases amino acids that fuel hepatic gluconeogenesis, worsening hyperglycemia.
The Opposition: Glucagon, Cortisol, Catecholamines, Growth Hormone
Insulin doesn't act alone—it exists in dynamic tension with counter-regulatory hormones that promote the opposite (fasted/stress) state. In DKA and HHS, these hormones are markedly elevated, amplifying the effects of insulin deficiency.
Glucagon
Released from pancreatic α-cells when glucose/insulin fall. Stimulates hepatic glycogenolysis and gluconeogenesis. Activates CPT-1, promoting ketogenesis. The glucagon:insulin ratio is the key determinant of hepatic metabolism—in DKA, this ratio is massively elevated.
Cortisol
Released from adrenal cortex in response to stress. Promotes gluconeogenesis, protein catabolism, and insulin resistance. Also stimulates lipolysis. Elevated in any acute illness, amplifying hyperglycemia.
Catecholamines (Epinephrine, Norepinephrine)
Released from adrenal medulla in stress. Stimulate glycogenolysis (rapid glucose release), gluconeogenesis, and lipolysis. Also inhibit insulin secretion (α-adrenergic effect) and cause insulin resistance. Major driver of stress hyperglycemia.
Growth Hormone
Released from pituitary. Promotes lipolysis and insulin resistance. Contributes to FFA availability for ketogenesis. Less acute role than glucagon/catecholamines but contributes to sustained metabolic derangement.
The Hormonal Storm
DKA and HHS are not simply "insulin deficiency"—they are insulin deficiency PLUS marked elevation of all counter-regulatory hormones. The precipitating illness (infection, MI, etc.) drives cortisol and catecholamine release, which worsens insulin resistance and directly stimulates gluconeogenesis and lipolysis. This is why treating the precipitant is as important as treating the glucose.
Why Small Amounts of Insulin Prevent Ketosis
What is the hierarchy of insulin sensitivity?
Insulin's metabolic effects have different dose-response curves. Suppression of lipolysis requires the LEAST insulin. Suppression of hepatic glucose output requires MORE. Stimulation of peripheral glucose uptake requires the MOST. This is why Type 2 diabetics (with residual insulin) can have severe hyperglycemia without ketosis.
What does this mean clinically?
A patient with 10-20% residual insulin function: lipolysis is suppressed (no ketones), but hepatic glucose production is elevated (hyperglycemia), and peripheral uptake is minimal (worsening hyperglycemia). This is the HHS phenotype. A patient with <5% insulin function loses ALL regulatory effects—DKA ensues.
How does this explain "euglycemic DKA" from SGLT2 inhibitors?
SGLT2 inhibitors cause glucosuria (glucose wasting in urine), lowering blood glucose. The lower glucose reduces insulin secretion. If insulin falls below the threshold for lipolysis suppression, ketogenesis begins—but glucose may be normal or only mildly elevated because of ongoing urinary losses. This creates the dangerous scenario of DKA without the typical glucose warning sign.
The Molecular Mechanism
Insulin inhibits lipolysis by activating phosphodiesterase 3B (PDE3B), which degrades cAMP. Without cAMP, hormone-sensitive lipase (HSL) remains inactive. This pathway is highly sensitive to insulin—even low insulin levels maintain PDE3B activity. In contrast, GLUT4 translocation requires higher insulin receptor activation and full engagement of the PI3K-Akt pathway.
Evidence Base
Petersen MC, Shulman GI. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev 2018 • McGarry JD. Banting Lecture: Dysregulation of Fatty Acid Metabolism in the Etiology of Type 2 Diabetes. Diabetes 2002 • Kitabchi AE, Nyenwe EA. Hyperglycemic Crises in Diabetes Mellitus. Nat Clin Pract Endocrinol Metab 2006
DKA Pathophysiology: The Ketoacidotic Cascade
DKA results from near-absolute insulin deficiency combined with counter-regulatory hormone excess. The result is uncontrolled gluconeogenesis, lipolysis, and ketogenesis—a metabolic emergency that can kill within hours.
Step-by-Step: From Insulin Deficiency to Acidosis
Why Glucose Rises (But Not As High As HHS)
What causes hyperglycemia in DKA?
Three simultaneous processes: (1) Increased hepatic glucose production (gluconeogenesis from amino acids, lactate, glycerol; glycogenolysis from stored glycogen); (2) Decreased peripheral glucose uptake (no GLUT4 translocation without insulin); (3) Continued intestinal absorption if eating. The liver can produce >500 g glucose/day in uncontrolled DKA.
Why is DKA glucose (250-600) lower than HHS (>600)?
DKA patients present EARLIER because acidosis causes symptoms. Nausea, vomiting, abdominal pain, and Kussmaul respirations bring patients to attention before glucose reaches extreme levels. Also, younger DKA patients have intact thirst/drinking, which dilutes glucose. HHS develops insidiously over days-weeks in patients who can't access water.
Why does glucosuria limit hyperglycemia?
When glucose exceeds the renal threshold (~180 mg/dL), glucose spills into urine. This acts as a "safety valve," limiting how high glucose can rise—but at the cost of massive water and electrolyte losses. In severe dehydration (HHS), reduced GFR limits glucosuria, allowing glucose to climb higher.
Why Acidosis Develops in DKA
The Chemistry of Ketoacidosis
Ketone Bodies: β-hydroxybutyrate (βHB), acetoacetate (AcAc), and acetone. βHB and AcAc are organic acids with pKa ~4—they are fully dissociated at physiologic pH and release H⁺ ions.
Buffering: Bicarbonate buffers the acid load: H⁺ + HCO₃⁻ → H₂CO₃ → CO₂ + H₂O. The CO₂ is exhaled. As ketoacids accumulate, bicarbonate is consumed and pH falls.
Anion Gap: Ketone bodies are unmeasured anions. AG = Na - (Cl + HCO₃). Normal ~8-12. In DKA, AG rises as ketoacids accumulate and bicarbonate falls. AG >20 is typical; AG >30 indicates severe DKA.
Respiratory Compensation: Low pH stimulates chemoreceptors → hyperventilation → ↓pCO₂. This is Kussmaul breathing—deep, rapid respirations that partially compensate for metabolic acidosis. Expected pCO₂ = 1.5 × HCO₃ + 8 (±2). If measured pCO₂ differs, suspect a mixed disorder.
The Osmotic Diuresis Cascade
Why do DKA patients have severe volume depletion?
Osmotic diuresis: glucose in the tubular fluid obligates water excretion. Each gram of glucose in urine drags ~15-20 mL water. With massive glucosuria, patients can lose 5-10 liters of fluid. Add to this vomiting (from ketosis/gastric stasis) and inability to drink.
Why are electrolytes depleted?
The osmotic diuresis carries electrolytes with it. Sodium, potassium, chloride, phosphate, and magnesium are all lost in the urine. Vomiting adds gastric losses. Despite TOTAL body depletion, SERUM levels may be normal or even elevated initially due to concentration effects and shifts.
Why is serum potassium often normal or high initially?
Despite massive total body K⁺ depletion (typically 3-5 mEq/kg), serum K⁺ is often normal or elevated because: (1) Insulin normally drives K⁺ into cells—without insulin, K⁺ stays extracellular; (2) Acidosis causes H⁺/K⁺ exchange—H⁺ enters cells, K⁺ exits; (3) Hyperosmolality causes water to leave cells, carrying K⁺ with it. Once insulin is given, K⁺ will plummet—this is why K⁺ repletion must begin early.
Why does sodium appear low?
Pseudohyponatremia: glucose is osmotically active—it draws water from intracellular space into plasma, diluting sodium. For every 100 mg/dL glucose above normal, measured Na⁺ falls ~1.6-2.4 mEq/L. The "corrected sodium" reveals true sodium status: Corrected Na = Measured Na + 0.024 × (glucose - 100).
The Potassium Danger
Total body potassium is ALWAYS depleted in DKA—patients have lost 3-5 mEq/kg (200-500 mEq total). But serum K⁺ may be high, normal, or low depending on the balance of forces.
If serum K⁺ is LOW at presentation: This indicates SEVERE total body depletion. The patient needs aggressive K⁺ repletion BEFORE insulin (insulin will drive K⁺ into cells, potentially causing fatal hypokalemia).
If serum K⁺ is HIGH at presentation: Do NOT be reassured. Once insulin is given and acidosis corrects, K⁺ will fall rapidly. Begin K⁺ replacement as soon as K⁺ <5.2 and urine output is adequate.
Evidence Base
Kitabchi AE, et al. Management of Hyperglycemic Crises in Patients With Diabetes. Diabetes Care 2001 • Nyenwe EA, Kitabchi AE. The evolution of diabetic ketoacidosis. Metabolism 2016 • Dhatariya KK, Vellanki P. Treatment of DKA/HHS: Novel Advances in the Management of Hyperglycemic Crises. Curr Diab Rep 2017
HHS Pathophysiology: The Hyperosmolar Crisis
HHS develops when residual insulin prevents ketosis but cannot control glucose. The result is extreme hyperglycemia, profound dehydration, and hyperosmolality—a slower but equally deadly emergency.
Step-by-Step: From Insulin Resistance to Hyperosmolar Coma
Why Hyperosmolality Is the Defining Feature
How does hyperosmolality develop?
Effective osmolality = 2×Na + Glucose/18. In HHS, glucose can exceed 1000 mg/dL, adding >55 mOsm/kg from glucose alone. Dehydration concentrates sodium further. The result: effective osmolality >320 (often >350, sometimes >400 mOsm/kg).
Why does hyperosmolality cause neurologic dysfunction?
Brain cells cannot rapidly adjust their intracellular osmolality. Acute hyperosmolality draws water out of brain cells, causing cellular shrinkage, tearing of bridging veins, and neuronal dysfunction. The degree of obtundation correlates with osmolality: >320 = altered; >340 = stupor; >360 = coma.
Why is dehydration so severe in HHS?
HHS develops slowly (days to weeks), allowing progressive fluid losses. Typical fluid deficit is 8-12 liters (vs 5-7 L in DKA). The patient population (elderly, impaired thirst, dependent on others) cannot compensate by drinking. By the time HHS is recognized, dehydration is profound.
Why does dehydration worsen hyperglycemia?
A vicious cycle: (1) Dehydration reduces GFR, limiting glucosuria (the body's escape valve); (2) Reduced renal glucose excretion allows plasma glucose to climb higher; (3) Higher glucose worsens osmotic diuresis and dehydration. This is why HHS glucose levels far exceed DKA—the system that should limit hyperglycemia (glucosuria) is impaired.
The Residual Insulin Effect
The Critical Difference
HHS patients have Type 2 DM with residual β-cell function. Their insulin levels are LOW relative to needs but not ZERO. This residual insulin:
CAN suppress lipolysis: Hormone-sensitive lipase remains inhibited. FFAs do not flood the circulation. Without FFA substrate, the liver cannot produce ketones at pathologic rates.
CANNOT suppress hepatic glucose production: The higher insulin levels required for this effect are not achieved, especially with counter-regulatory hormone excess from illness.
CANNOT stimulate peripheral glucose uptake: GLUT4 translocation requires even higher insulin levels. Skeletal muscle and adipose tissue cannot take up glucose efficiently.
The result: extreme hyperglycemia (from glucose overproduction and underutilization) without ketoacidosis (because lipolysis is suppressed).
The Portal-Peripheral Gradient
Insulin secreted by the pancreas enters the portal circulation first. The liver sees ~3× higher insulin concentration than peripheral tissues. This "portal-peripheral gradient" means even modest insulin secretion can suppress hepatic ketogenesis more effectively than it stimulates peripheral glucose uptake. This is another reason why ketosis is prevented while hyperglycemia worsens.
The Dehydration Emergency
Water deficit: 5-7 liters
Sodium deficit: 7-10 mEq/kg
Potassium deficit: 3-5 mEq/kg
Phosphate deficit: 1.0-1.5 mmol/kg
Onset: Hours to 1-2 days
Water deficit: 8-12 liters
Sodium deficit: 5-13 mEq/kg
Potassium deficit: 4-6 mEq/kg
Phosphate deficit: 1.0-1.5 mmol/kg
Onset: Days to weeks
The Sodium Paradox in HHS
Despite losing sodium in urine, measured serum Na⁺ in HHS may be low, normal, or HIGH:
Pseudohyponatremia: Hyperglycemia draws water into plasma, diluting sodium. Correct using: Corrected Na = Measured Na + 0.024 × (glucose - 100).
If corrected Na is HIGH: Indicates free water loss exceeds sodium loss—severe hyperosmolality. These patients need relatively more free water (hypotonic fluids) than sodium.
If corrected Na is LOW: Indicates sodium loss exceeds water loss—use isotonic saline initially.
From Confusion to Coma
Hyperosmolality causes neuronal dehydration. Brain cells lose water to the hyperosmolar extracellular fluid, leading to cellular shrinkage and dysfunction.
Additionally, severe hyperglycemia directly impairs neuronal function through: oxidative stress, disruption of neurotransmitter balance, and cerebral blood flow alterations.
The relationship between osmolality and mental status is roughly linear: Osm 320-340 → confusion/lethargy; Osm 340-360 → stupor; Osm >360 → coma.
HHS can cause focal neurologic deficits including hemiparesis, hemisensory loss, and seizures—mimicking stroke. These are thought to result from focal cerebral hypoperfusion and metabolic dysfunction rather than infarction.
Critical point: Focal deficits in HHS are often REVERSIBLE with treatment. Don't assume stroke without imaging confirmation. However, also consider that stroke may have precipitated the HHS.
Seizures occur in up to 25% of HHS patients—much more common than in DKA. Mechanisms include: hyperosmolar neuronal dysfunction, focal areas of cerebral ischemia, and electrolyte abnormalities (hyponatremia from treatment, hypocalcemia, hypomagnesemia).
Treat with standard anticonvulsants if seizures occur, but the primary treatment is correcting the metabolic derangement.
Evidence Base
Pasquel FJ, Umpierrez GE. Hyperosmolar Hyperglycemic State: A Historic Review of the Clinical Presentation, Diagnosis, and Treatment. Diabetes Care 2014 • Stoner GD. Hyperosmolar Hyperglycemic State. Am Fam Physician 2017 • Magee MF, Bhatt BA. Management of Decompensated Diabetes: DKA and HHS. Crit Care Clin 2001
Ketone Biology: The Biochemistry of Ketogenesis
Understanding ketone metabolism explains why DKA causes acidosis, why β-hydroxybutyrate is the dominant ketone, why the urine ketone test can be misleading, and why ketones can actually be beneficial fuel.
The Three Ketone Bodies
The dominant ketone (78% in DKA)
Formed by reduction of acetoacetate
Measured by point-of-care blood tests
The best marker of DKA severity
NOT detected by urine ketone tests
The intermediate ketone (20%)
First ketone produced in liver
In equilibrium with βHB (redox state)
DETECTED by urine ketone tests
Converts to βHB in hypoxia/shock
Acetone: The Volatile Ketone
Acetone (~2%) is formed by spontaneous decarboxylation of acetoacetate. It cannot be metabolized back to useful fuel. It is exhaled via the lungs—this is the "fruity breath" of DKA. Acetone is also detected by urine ketone tests but contributes little to acidosis (it's not an acid).
How the Liver Makes Ketones
Lipolysis in Adipose Tissue
Without insulin's inhibition, hormone-sensitive lipase (HSL) is activated by glucagon and catecholamines. Triglycerides are hydrolyzed to free fatty acids (FFAs) and glycerol. FFAs flood into the circulation, bound to albumin.
FFA Uptake by Liver
The liver takes up FFAs in proportion to plasma concentration. With massive lipolysis, the liver is overwhelmed with FFA substrate. In the fed state, FFAs would be re-esterified to triglycerides. In insulin deficiency, they're directed toward oxidation.
The CPT-1 Gateway
FFAs must enter mitochondria for β-oxidation. This requires carnitine palmitoyltransferase-1 (CPT-1) on the outer mitochondrial membrane. CPT-1 is inhibited by malonyl-CoA (produced in fed state) and activated by glucagon. In DKA, CPT-1 is maximally active—FFAs pour into mitochondria.
β-Oxidation
Inside mitochondria, FFAs undergo β-oxidation, generating acetyl-CoA. Normally, acetyl-CoA enters the TCA cycle. But in DKA, the liver's TCA cycle is overwhelmed with acetyl-CoA (and oxaloacetate is depleted by gluconeogenesis). Excess acetyl-CoA is diverted to ketogenesis.
Ketone Synthesis
Two acetyl-CoA → acetoacetyl-CoA → HMG-CoA → acetoacetate + acetyl-CoA. Acetoacetate is then reduced to β-hydroxybutyrate by β-hydroxybutyrate dehydrogenase. The ratio βHB:AcAc depends on mitochondrial redox state (NADH:NAD⁺).
The Malonyl-CoA Switch
Malonyl-CoA is the key regulator of ketogenesis. It's produced by acetyl-CoA carboxylase (ACC) in the fed state and inhibits CPT-1, preventing fatty acid entry into mitochondria. Insulin activates ACC; glucagon inhibits it. In DKA, glucagon dominance → low malonyl-CoA → CPT-1 active → ketogenesis proceeds unchecked.
Why Urine Ketones Can Be Misleading
What do urine and blood ketone tests actually measure?
Urine ketone tests (nitroprusside reaction) detect acetoacetate and acetone but NOT β-hydroxybutyrate. Blood ketone tests (POC meters) measure β-hydroxybutyrate specifically. Since βHB is 78% of total ketones in DKA, urine tests significantly underestimate ketosis.
Why might urine ketones paradoxically increase during treatment?
As DKA resolves, the redox state shifts. With improved oxygenation and circulation, βHB is converted back to acetoacetate. Urine ketone tests may become MORE positive even as the patient improves (because they now detect the acetoacetate). Following blood βHB avoids this confusion.
Why is βHB the preferred measurement?
Blood βHB directly reflects the ketone causing acidosis. It correlates with severity of DKA. It decreases predictably with treatment. Point-of-care βHB testing is now widely available. Target for resolution: βHB <0.6 mmol/L (or <1.0 with closed anion gap).
Interpreting Blood βHB Levels
<0.6 mmol/L: Normal (no significant ketosis)
0.6-1.5 mmol/L: Mild ketosis (possible starvation, early DKA)
1.5-3.0 mmol/L: Moderate ketosis (DKA likely)
>3.0 mmol/L: Severe ketosis (significant DKA)
The Paradox: Ketones Are Actually Useful
Ketones: Danger and Salvation
Ketones are not inherently bad—they're an alternative fuel for brain, heart, and muscle during fasting or carbohydrate restriction. The brain normally uses only glucose, but during prolonged fasting, ketones can provide up to 70% of cerebral energy needs.
The problem in DKA: Ketone production is massively excessive (10-20× normal). Production exceeds utilization. The accumulating ketoacids overwhelm buffering capacity and cause acidosis. It's the RATE and AMOUNT of production, not the ketones themselves, that creates danger.
During DKA treatment: Some ketones are actually being utilized as fuel—this is part of recovery. The goal is not to eliminate all ketones instantly but to stop overproduction and allow utilization to catch up.
Evidence Base
Puchalska P, Crawford PA. Multi-dimensional Roles of Ketone Bodies. Cell Metab 2017 • Newman JC, Verdin E. Ketone bodies as signaling metabolites. Trends Endocrinol Metab 2014 • Sheikh-Ali M, et al. Can serum β-hydroxybutyrate be used to diagnose DKA? Diabetes Care 2008
Complications: What Can Go Wrong
DKA and HHS carry significant mortality from complications—some from the disease, others from treatment.
Cerebral Edema
Occurs in 0.5-1% of pediatric DKA with 20-25% mortality. Develops 4-12 hours into treatment. Mechanism: brain cells accumulate idiogenic osmoles during DKA; rapid osmolality correction draws water into brain. Prevention: glucose decline 50-75 mg/dL/hr; add dextrose when glucose 200-250. Treatment: mannitol 0.5-1 g/kg or hypertonic saline 3% 2.5-5 mL/kg.
Potassium: The Most Dangerous
Total body K⁺ ALWAYS depleted (3-5 mEq/kg). Serum K⁺ may be high initially (acidosis shifts K⁺ out of cells). Once insulin given, K⁺ plummets. If K⁺ <3.3: HOLD insulin until repleted. Replace K⁺ when <5.2 and urine output present. Most DKA deaths from electrolytes are from hypokalemia.
Cardiovascular and Respiratory
Arrhythmias from K⁺ abnormalities (hypo- and hyperkalemia). Thrombosis from dehydration/hyperviscosity. ARDS from aggressive fluid resuscitation. Aspiration from gastroparesis and altered mental status. Always search for and treat the precipitant (infection in 40-60%).
Evidence Base
Glaser N, et al. Risk factors for cerebral edema in children with DKA. NEJM 2001 • Edge JA, et al. Cerebral oedema during DKA. Arch Dis Child 2001
Clinical Integration: Mechanism-Based Management
Understanding pathophysiology transforms DKA and HHS management from protocol-following to physiologically-reasoned care.
Treatment Principles
Fluid Resuscitation
Restores volume, improves perfusion, lowers glucose via dilution and increased GFR. Start NS 1-1.5 L/hr first hour, then 250-500 mL/hr. Switch to 0.45% NaCl when corrected Na normal/high. Add dextrose when glucose 200-250.
Insulin Therapy
Stops ketogenesis and gluconeogenesis. Regular insulin 0.1 U/kg/hr. Target glucose decline 50-75 mg/dL/hr. Continue until anion gap closes (DKA) or mental status normalizes (HHS)—NOT until glucose normalizes.
Potassium Replacement
K⁺ <3.3: HOLD insulin, replace K⁺ first. K⁺ 3.3-5.2: Add 20-40 mEq/L to fluids, start insulin. K⁺ >5.2: Start insulin, hold K⁺, recheck q2h. Goal: maintain K⁺ 4.0-5.0.
Treat the Precipitant
DKA/HHS will recur without addressing cause. Infection most common (40-60%). Also: MI, stroke, medication non-compliance, new diagnosis.
When Is It Over?
Glucose <200 mg/dL
PLUS two of:
• Anion gap ≤12
• Bicarbonate ≥15
• pH >7.30
Osmolality <315
Mental status at baseline
Glucose <300 mg/dL
Patient able to eat/drink
Critical Transition
Give subcutaneous long-acting insulin 2-4 HOURS before stopping IV insulin. IV insulin half-life is ~5 minutes—stopping without SC coverage causes rebound hyperglycemia/ketosis.
— The Principle of Diabetic Emergencies
Key References
Kitabchi AE, et al. Hyperglycemic Crises in Adult Patients With Diabetes. Diabetes Care 2009 • ADA Standards of Care 2024 • Joint British Diabetes Societies Guidelines 2023