# 🔍 Metabolic Acidosis & Acid-Base Analysis ## 🚨 Emergency Management Priority ### Critical pH Thresholds - **pH \< 7.1:** Life-threatening - immediate intervention - **pH \< 7.2:** Severe - aggressive treatment - **pH 7.2-7.35:** Moderate - treat underlying cause **Immediate Actions:** 1. Ensure adequate ventilation (respiratory compensation) 2. IV access and volume status assessment 3. Calculate anion gap and assess for mixed disorders 4. Treat underlying cause (DKA, lactic acidosis, toxins) 5. Consider bicarbonate ONLY if pH \<7.15 with shock ## 🔬 The ABC Method: Systematic Acid-Base Analysis ### Step A: Assess pH - **Acidemia:** pH \< 7.40 - **Alkalemia:** pH \> 7.40 - **Remember:** Acidosis ≠ Acidemia - **Note:** Can have acidosis with normal/high pH due to compensation ### Step B: Primary Disorder - **Metabolic:** Primary HCO₃⁻ change - **Respiratory:** Primary pCO₂ change - **Mixed:** Both systems affected - **Key:** Which change explains the pH? ### Step C: Check Compensation - **Never complete:** pH always abnormal - **Never overcompensates:** pH doesn't cross 7.40 - **Winter's Formula:** Expected pCO₂ = 1.5 × \[HCO₃⁻\] + 8 ± 2 - **If overcompensation:** Mixed disorder present ## 🧮 Anion Gap: The Diagnostic Key ### Anion Gap Calculation AG = Na⁺ - (Cl⁻ + HCO₃⁻) **Normal AG:** 8-12 mEq/L (modern analyzers) **Traditional AG:** 12±4 mEq/L (older labs) ⚠️ Know your lab's normal range! ### High Anion Gap Acidosis (MUDPILES) - **M:** Methanol - **U:** Uremia (BUN \>100) - **D:** DKA, alcoholic ketoacidosis - **P:** Propylene glycol (IV Ativan!) - **I:** Isoniazid, Iron - **L:** Lactic acidosis (most common) - **E:** Ethylene glycol - **S:** Salicylates **Clinical Pearl:** Lactic acidosis is the most common cause of high AG metabolic acidosis in hospitalized patients. ### Normal AG Acidosis (USED CARP) #### Normal Kidney Function (UAG \< 0): - **U:** Ureterosigmoidostomy - **S:** Small bowel fistulae - **E:** Extra Cl⁻ (normal saline) - **D:** Diarrhea (most common) #### Impaired Kidney Function (UAG \> 0): - **C:** Chronic kidney disease - **A:** Acetazolamide, Addison's - **R:** Renal tubular acidosis - **P:** Protein overfeeding ### Urinary Anion Gap (UAG) for Normal AG Acidosis UAG = (Urinary Na⁺ + K⁺) - Cl⁻ #### UAG \< 0 (Negative) **Meaning:** Appropriate NH₄⁺ production **Cause:** Extra-renal HCO₃⁻ loss **Examples:** Diarrhea, fistulae, saline administration #### UAG \> 0 (Positive) **Meaning:** Impaired NH₄⁺ production **Cause:** Renal acid excretion defect **Examples:** RTA, CKD, hypoaldosteronism ## 🔄 Delta-Delta Ratio: Detecting Mixed Disorders ### The Delta-Delta Calculation Δ AG = Measured AG - Normal AG (10) Δ HCO₃⁻ = Normal HCO₃⁻ (24) - Measured HCO₃⁻ Delta/Delta Ratio = Δ AG / Δ HCO₃⁻ ### Ratio \< 1.0 **Interpretation:** Mixed disorder - High AG metabolic acidosis - PLUS normal AG metabolic acidosis **Example:** DKA + diarrhea ### Ratio 1.0-2.0 **Interpretation:** Pure disorder - High AG metabolic acidosis only - Expected compensation pattern **Example:** Isolated DKA or lactic acidosis ### Ratio \> 2.0 **Interpretation:** Mixed disorder - High AG metabolic acidosis - PLUS metabolic alkalosis **Example:** DKA + vomiting/diuretics ### Alternative: Potential Bicarbonate Method Potential HCO₃⁻ = Measured HCO₃⁻ + Δ AG **\< 22 mEq/L**\ Concurrent NAG acidosis **22-26 mEq/L**\ Pure AG acidosis **\> 26 mEq/L**\ Concurrent alkalosis ## 🧮 Interactive Acid-Base Calculator pH: pCO₂ (mmHg): HCO₃⁻ (mEq/L): Na⁺ (mEq/L): Cl⁻ (mEq/L): Albumin (g/dL): ## 📋 Clinical Case Applications ### Case 1: ICU Patient with Sepsis **Clinical:** 55M, severe sepsis, received 15L normal saline, on lorazepam drip **Labs:** pH 7.10, pCO₂ 19, HCO₃⁻ 6, Na 135, Cl 110, UAG -55 #### Analysis: 1. Severe acidemia (pH 7.10) 2. Primary metabolic acidosis (HCO₃⁻ 6) 3. Appropriate respiratory compensation (expected pCO₂ 17±2) 4. AG = 135-110-6 = 19 (elevated) 5. Delta/Delta = 9/18 = 0.5 (\<1 = mixed) **Diagnosis:** AG acidosis (propylene glycol from lorazepam) + NAG acidosis (NS-induced) ### Case 2: DKA with Fungal Sepsis **Clinical:** 60M, DM, fungal sepsis **Labs:** pH 7.01, pCO₂ 39, HCO₃⁻ 10, glucose 480, β-hydroxybutyrate 3, lactate 8 #### Analysis: 1. Severe acidemia with inadequate respiratory compensation 2. Expected pCO₂ = 1.5×10 + 8 = 23 ± 2 (actual 39 = respiratory acidosis too) 3. Multiple causes: DKA + lactic acidosis + respiratory failure 4. Triple acid-base disorder **Management:** Insulin, fluids, ventilatory support, treat sepsis ### Case 3: C. diff Colitis vs RTA **Clinical:** 67F, C. diff colitis **Labs:** pH 6.91, pCO₂ 40, HCO₃⁻ 8, Na 135, Cl 110, UAG -40 #### Analysis: 1. Severe acidemia with minimal respiratory compensation (concerning) 2. AG = 17 (elevated, likely from uremia/dehydration) 3. UAG = -40 (negative = appropriate NH₄⁺ production) 4. Negative UAG confirms diarrheal losses **Diagnosis:** Mixed uremic acidosis + diarrhea-induced NAG acidosis ## 💊 Treatment Principles ### Primary Rule: Treat the Underlying Cause Correcting pH without addressing the underlying pathophysiology is ineffective and potentially harmful. ### High AG Metabolic Acidosis - **DKA:** Insulin, fluids, electrolyte replacement - **Lactic acidosis:** Improve tissue perfusion - **Uremia:** Dialysis for severe cases - **Toxic ingestions:** Specific antidotes, dialysis - **Ketoacidosis:** Thiamine, glucose, insulin **Pearl:** Bicarbonate therapy rarely indicated; may worsen intracellular acidosis. ### Normal AG Metabolic Acidosis - **Diarrhea:** Volume and electrolyte replacement - **RTA:** Alkali therapy (K-citrate preferred) - **Saline-induced:** Switch to balanced crystalloids - **Hypoaldosteronism:** Mineralocorticoid replacement **Pearl:** Always correct hypokalemia and hypomagnesemia first. ### ⚠️ Bicarbonate Therapy: Use Sparingly #### Consider Only When: - pH \< 7.15 with hemodynamic instability - Severe hyperkalemia with ECG changes - Certain toxic ingestions (salicylates, methanol, TCA) - Severe RTA with failure to thrive #### Risks of Bicarbonate Therapy: - Paradoxical CSF acidosis - Hypokalemia and hypocalcemia - Volume overload - Rebound alkalosis - Shift of O₂-hemoglobin curve **Dosing (if absolutely necessary):**\ HCO₃⁻ deficit = 0.5 × weight (kg) × (desired HCO₃⁻ - current HCO₃⁻)\ Give 1/2 to 1/3 of calculated deficit over 3-4 hours ## 🎯 Key Learning Points ### Systematic Approach - Always use the ABC method for acid-base analysis - Compensation is never complete or overcompensating - Check for mixed disorders in all complex cases - Use Winter's formula to assess appropriate compensation ### Anion Gap Mastery - Know your lab's normal AG range (8-12 vs 12±4) - Always correct for albumin in critically ill patients - Use UAG to differentiate renal vs GI causes of NAG acidosis - Delta-delta ratio reveals mixed metabolic disorders ### Treatment Priority - Always treat the underlying cause, not just the pH - Bicarbonate therapy is rarely indicated and often harmful - Support ventilation for respiratory compensation - Address volume status and electrolyte abnormalities 📚 For Educational Purposes Only © 2025 University of Dubuque PA Program - All Rights Reserved --- [Website version](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/acid-base/metabolic-acidosis.html) · Markdown synchronized October 3, 2026. ## Day 1 mechanism infographics — October 21, 2026 ### Ketoacidosis can hide behind a modest glucose SGLT2 therapy, poor intake, and illness can uncouple glucose from ketones [Full infographic, text companion and sources](https://urinenephrology.org/visual-reference/day1-edka-potassium.html) SGLT2 inhibition reduces proximal tubular glucose reabsorption. Glycosuria moderates the blood glucose reading while illness, reduced intake and relative insulin deficiency can promote lipolysis and hepatic ketone production. In Case 3, glucose is 206 mg/dL and beta-hydroxybutyrate is 5.8 mmol/L. This is SGLT2-associated ketoacidosis with modest glucose; 206 is just above the 2024 consensus definition of euglycemic DKA at glucose below 200.