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Robert C Hollander, M.D. PGY-30 Gainesville VA The Approach That Never Fails

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1. Acidemia v. Alkalemia 2. Metabolic v. Respiratory 3. ?Anion Gap 4. Does the Δ AG = Δ HCO 3 ? 5. Is there appropriate compensation?

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1. Acidemia v. Alkalemia 2. Metabolic v. Respiratory 3. ?Anion Gap 4. Does the Δ AG = Δ HCO 3 ? 5. Is there appropriate compensation? Pre-supposes you have an ABG Accurate conclusions cannot be drawn from HCO 3 alone Normal range: If there is an abnormal pCO 2, HCO 3 or AG, then 7.4 is the dividing line

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1. Acidemia v. Alkalemia 2. Metabolic v. Respiratory 3. ?Anion Gap 4. Does the Δ AG = Δ HCO 3 ? 5. Is there appropriate compensation? Ask yourself out loud (softly if others are around) What explains the acidemia? Or What explains the alkalemia? If HCO 3 Metabolic If pCO 2 Respiratory If both, pick one and the Foolproof Approach will catch the other later.

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1. Acidemia v. Alkalemia 2. Metabolic v. Respiratory 3. ?Anion Gap 4. Does the Δ AG = Δ HCO 3 ? 5. Is there appropriate compensation? AG = Na – (Cl + HCO 3 ) AG = Unmeasured Anions – Unmeasured Cations AG= an artifact of laboratory measurement AG allows inferences about unmeasured anions Albumin excepted, the Unmeasured Anions are salts of organic acids Therefore, AG elevations Metabolic Acidosis Exceptions exists

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M M ethanol U U remia D D KA P P ropylene glycol (not paraldehyde) I I NH (impaired hepatic clearance of lactate) L L actic acidosis E E thanol/Ethylene Glycol S S alicylates

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BaselineAbnormal Sodium136 Chloride Bicarbonate2414 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? Diarrhea, RTA, carbonic anhydrase inhibitors, ureteral diversions Dilutional acidosis, post hypocapnic Non-Anion Gap Metabolic Acidosis

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1. Acidemia v. Alkalemia 2. Metabolic v. Respiratory 3. ?Anion Gap 4. Does the Δ AG = Δ HCO 3 ? 5. Is there appropriate compensation? towards Compensation will return the pH towards normal Compensation is either: Appropriate, or If not, indicative of another acid-base disturbance If Metabolic Acidosis prevails then the Winter Formula applies, predicting the ventilatory response (know this formula!) pCO 2 = 1.5(HCO 3 ) + 8 ± 2

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BaselineAbnormal Sodium136 Chloride102 Bicarbonate2414 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation?

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1. Acidemia v. Alkalemia 2. Metabolic v. Respiratory 3. ?Anion Gap 4. Does the Δ AG = Δ HCO 3 ? 5. Is there appropriate compensation? METABOLIC If Δ AG = Δ HCO 3 one METABOLIC disturbance METABOLIC If Δ AG ≠ Δ HCO 3 >1 METABOLIC disturbance Rationale: X meq acid will titrate X meq HCO 3 HCO 3 will fall by x, AG will rise by x If Δ AG ≠ Δ HCO 3, then another metabolic disturbance accounts for the difference

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BaselineAbnormal Sodium136 Chloride Bicarbonate24 14 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? DKA + vomiting, AKA + vomiting, Sepsis + vomiting, Sepsis + NG suction AG Metabolic Acidosis + Metabolic Alkalosis

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BaselineAbnormal Sodium136 Chloride102 Bicarbonate2414 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? DKA with respiratory failure (from any cause), Sepsis with respiratory failure (pneumonia + sepsis)

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BaselineAbnormal Sodium136 Chloride102 Bicarbonate24 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? Hypoxia (from any cause), pain, sepsis/endotoxemia, ASA toxicity, anxiety (diagnosis of exclusion)

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BaselineAbnormal Sodium136 Chloride10292 Bicarbonate2431 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? Severe COPD, OSA, Advanced neuromuscular disease

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BaselineAbnormal Abnormal Baseline Sodium136 Chloride10292 Bicarbonate2431 Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? Loop diuretics or vomiting with any primary Respiratory Alkalosis The Chronic CO2 retainer who stops retaining from either pain, hypoxia, sepsis, acute PE or any other acute Respiratory Alkalosis. Learn to recognize the patient who starts from an abnormal baseline.

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BaselineAdmission #1A month later Sodium Chloride Bicarbonate Anion Gap10 Δ Anion Gap- Δ Bicarbonate- pH pCO ] Acidemia v. Alkalemia 2] Metabolic v. Respiratory 3] Anion Gap? 4] ∆ Anion Gap 5] Compensation? Two interpretations, one unifying diagnosis

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