Metabolic Acidosis Evaluation & Management

Algorithm Steps

1. ▶

   Start

   Low Serum Bicarbonate

   HCO3 <22 mEq/L or pH <7.35 with metabolic component

   1. ●

      Action

      Confirm Metabolic Acidosis

      Review ABG and basic metabolic panel

      • Check arterial or venous blood gas
      • pH <7.35 confirms acidemia
      • Low HCO3 with appropriate pCO2 response
      • Expected pCO2 = 1.5 × [HCO3] + 8 (±2) - Winter's formula
      • If pCO2 different: Mixed disorder
      1. ●

         Action

         Calculate Anion Gap

         AG = Na - (Cl + HCO3)

         • Normal AG: 8-12 mEq/L
         • MUST correct for albumin:
         • Corrected AG = AG + 2.5 × (4 - albumin g/dL)
         • Each 1 g/dL decrease in albumin lowers AG by ~2.5
         1. ◆

            Decision

            Anion Gap Elevated?

            Corrected AG >12 mEq/L

            1. ●

               Action

               High Anion Gap Metabolic Acidosis (HAGMA)

               MUDPILES or GOLDMARK mnemonic

               • M - Methanol
               • U - Uremia (renal failure)
               • D - DKA/Diabetic ketoacidosis
               • P - Propylene glycol, Paraldehyde
               • I - INH, Iron
               • L - Lactic acidosis
               • E - Ethylene glycol
               • S - Salicylates
               • Order: Lactate, ketones, BUN/Cr, osmolar gap, toxicology
               1. ●

                  Action

                  Calculate Delta-Delta Ratio

                  Check for concurrent metabolic disorders

                  • Delta AG = (AG - 12)
                  • Delta HCO3 = (24 - HCO3)
                  • Ratio = Delta AG / Delta HCO3
                  • <1: Concurrent NAGMA
                  • 1-2: Pure HAGMA
                  • >2: Concurrent metabolic alkalosis
                  1. ◆

                     Decision

                     Elevated Lactate?

                     Lactate >2 mmol/L

                     1. ⚠

                        Warning

                        Lactic Acidosis

                        Most common cause of HAGMA

                        • Type A (hypoxic): Shock, hypoxia, sepsis, seizures
                        • Type B (non-hypoxic): Metformin, malignancy, liver failure
                        • Treatment: Address underlying cause
                        • Bicarb controversial, consider if pH <7.0-7.1
                        1. ●

                           Action

                           Treatment Approach

                           Treat underlying cause first

                           • Primary: Address underlying etiology
                           • Bicarbonate therapy:
                           • - Generally reserved for pH <7.1-7.2 or HCO3 <8
                           • - Calculate deficit: 0.5 × wt × (24 - HCO3)
                           • - Give 50% of deficit, reassess
                           • - Caution: Volume overload, overshoot alkalosis
                           • RTA: Oral bicarbonate or citrate supplementation
                           1. ✓

                              Outcome

                              Acidosis Corrected

                              pH normalizing, address underlying cause

                           2. ✓

                              Outcome

                              Ongoing Management

                              Chronic RTA, CKD, or recurrent episodes

                     2. ●

                        Action

                        Ketoacidosis

                        DKA, AKA, or starvation

                        • DKA: Hyperglycemia, check beta-hydroxybutyrate
                        • AKA: Recent alcohol binge, often normal glucose
                        • Starvation ketosis: Usually mild
                        • Treatment: Insulin (DKA), fluids, correct electrolytes
                     3. ⚠

                        Warning

                        Toxic Alcohol Ingestion?

                        Check osmolar gap if suspected

                        • Osmolar gap = Measured osm - Calculated osm
                        • Calculated = 2×Na + Glu/18 + BUN/2.8
                        • Gap >10: Consider methanol, ethylene glycol
                        • Treatment: Fomepizole, HD if severe
                        • Poison control consultation
            2. ●

               Action

               Normal Anion Gap Metabolic Acidosis (NAGMA)

               Also called hyperchloremic acidosis

               • GI losses: Diarrhea, fistulas, ureteral diversion
               • Renal: RTA types 1, 2, 4
               • Dilutional: Large volume NS resuscitation
               • Early renal failure
               • Carbonic anhydrase inhibitors (acetazolamide)
               • Check: Urine anion gap, urine pH
               1. ●

                  Action

                  Calculate Urine Anion Gap

                  UAG = (Urine Na + Urine K) - Urine Cl

                  • Negative UAG: GI losses (appropriate NH4 excretion)
                  • Positive UAG: Renal cause (impaired NH4 excretion)
                  • - RTA Type 1 (distal): UAG positive, urine pH >5.5
                  • - RTA Type 2 (proximal): UAG variable, bicarbonaturia
                  • - RTA Type 4: UAG positive, hyperkalemia
                  1. ●

                     Action

                     RTA Classification

                     Based on urine studies and serum K+

                     • Type 1 (Distal): Cannot acidify urine, urine pH >5.5, hypokalemia
                     • - Causes: Autoimmune, drugs, obstruction
                     • Type 2 (Proximal): Bicarbonate wasting, urine pH <5.5 eventually
                     • - Causes: Fanconi, drugs, myeloma
                     • Type 4: Aldosterone deficiency/resistance, hyperkalemia
                     • - Causes: Diabetes, ACEi/ARB, adrenal insufficiency