Metabolic Acidosis

1. Mendoza, Donn Paulo; Mendoza, Gracielle; Mendoza, Trisha; Mindanao, Malvin Ace, Miranda, Maria Carmela; Molina, Ramon Miguel; Monzon, Jerry West; Morales, Arriane; Musni, MerwenMitchel; Nallas, Anna Pauline; Naval Ayne Rangel C7 Metabolic Acidosis

2. Salient Features:

3. HISTORY • 45 y/o, female • Diabetic • 4 days of acute illness • Fever (39.5 C) • Chills, myalgia • Diarrhea • Denied taking any medications, drugs nor alcohol

4. Physical Examination • Vital Signs • BP – 84/52 (supine) • PR – 118 bpm • RR – 42 bpm • Mucous membranes- dry • Neck veins- flat • No edema • Abdomen- distended, firm, mildly tender • Hyperactive bowel sounds • Blood Indices • Hgb – 15.5 g/dL • Hct – 48% • WBC count – 22,800 • Segmented neutrophils – 66% • Bands – 23%

5. LABORATORY RESULTS • Serum Na – 138.0 meq/L • Serum K – 4.2 meq/L • Serum Cl – 108.0 meq/L • HCO3 – 10.0 meq/L • BUN – 28.0 mg/dL • Serum Creatinine – 2.4 mg/dL • Glucose – 342.0 mg/dL • Ketones – none • Lactate – 3.0 meq/L • pH – 7.39 • pCO2 – 17.0 mmHg

7. Acid-base disturbance • Metabolic Acidosis • Compensated • pH – 7.39 (normal) • HCO3 – 10.0 meq/L • pCO2 – 17.0 mmHg • Lactate – 3.0 meq/L

8. Algorithm for the Diagnosis of the acid base disorder

9. Steps in acid base diagnosis • Obtain arterial blood gas (ABG) and electrolytes simultaneously • Compare [HCO3-] on ABG and electrolytes to verify accuracy • Calculate anion gap (AG) • Know four causes of high-AG acidosis • ketoacidosis • lactic acid acidosis • renal failure • toxins

10. Steps in acid base diagnosis • Know two causes of hyperchloremic or nongap acidosis • bicarbonate loss from GI tract • renal tubular acidosis • Estimate compensatory response • Compare AG and HCO3- • Compare change in [Cl-] with change in [Na+]

11. Prediction of compensatory responses

12. Rule of Thumb: Metabolic acidosis • PaCO2= (1.5x HCO3-) + 8 or • PaCO2 will 1.25 mmHg per mmol/L in HCO3- or • PaCO2= HCO3- + 15

13. Rule of Thumb Metabolic alkalosis • PaCO2 will 0.75 mmHg per mmol/L in HCO3- or • PaCO2 will 6 mmHg per 10 mmol/L in HCO3- or • PaCO2= HCO3- + 15

14. Rule of Thumb Respiratory alkalosis • Acute: • HCO3- will 2 mmol/L per 10 mmHg in PaCO2 • Chronic: • HCO3- will 4 mmol/L per 10 mmHg in PaCO2

15. Rule of Thumb Respiratory Acidosis • Acute: • HCO3- will 1 mmol/L per 10 mmHg in PaCO2 • Chronic: • HCO3- will 4 mmol/L per 10 mmHg in PaCO2

16. Pattern of Compensatory Changes

17. Anion Gap

18. Anion Gap • represents the concentration of all the unmeasured anions in the plasma • concentrations are expressed in units of milliequivalents/liter (mEq/L) • NV: 8-16 mEq/L

19. Major Clinical Uses of the Anion Gap • To signal the presence of a metabolic acidosis and confirm other findings • Help differentiate between causes of a metabolic acidosis: high anion gap versus normal anion gap metabolic acidosis. • To assist in assessing the biochemical severity of the acidosis and follow the response to treatment

20. Anion Gap With potassium = ( [Na+]+[K+] ) − ( [Cl−]+[HCO3−] ) = (138 + 4.2) – (108+10) = 24.2 mEq/L - HIGH Without potassium = ( [Na+] ) − ( [Cl−]+[HCO3−] ) = (138) – (108+10) = 20.0 mEq/L - HIGH

21. Causes of high anion gap acidosis and normal anion gap acidosis

22. Anion GapSodium - (chloride + bicarbonate) • Normal Anion Gap • Hyperchloremic acidosis • GI or renal Loss of bicarbonate • Impaired renal acid secretion • Reabsorption of Chloride • Examples: • Diarrhea • Renal Tubular Acidosis • Carbonic Anhydrase Inhibition • High Anion Gap • Acid retention • Examples: • Lactic Acidosis: most common • Ketoacidosis • Advanced Renal Failure • Drug and Toxin Induced

23. HIGH ANION GAP • Lactic Acidosis • Increase in plasma lactate • Secondary to poor tissue perfusion (Type A) • Aerobic disorders (Type B) • Ketoacidosis • Increase fatty acid metabolism • Accumulation of ketoacids (Acetoacetate & -hydroxybutyrate) • Diabetic ketoacidosis, alcoholic ketoacidosis

24. HIGH ANION GAP • Drug and toxin induced • Salicylates: ketones, lactate, salicylate • ethylene glycol: glycolate, oxalate • Methanol or formaldehyde: Formate • Advanced Renal failure: Sulfate, phosphate, urate

25. HIGH ANION GAP • Advanced RF ↓ # of functioning nephrons Dec. NH4+ prod. and excretion Failure to balance w/ net acid production Inc. anion gap

26. DIARRHEA ↑ loss of HCO3 along w/ vol. depletion Metabolic acidosis and hypokalemia ↑renal synthesis and excretion of NH4 NORMAL ANION GAP

27. RENAL TUBULAR ACIDOSIS (GFR bet. 20 and 50 mL/min) ↓ # of functioning nephrons Proximal RTA: ↓ HCO3 tubular reabsorption OR Distal RTA: ↓ acid excretion ↑renal synthesis and excretion of NH4

28. OTHER CAUSES OF NORMAL ANION GAP Carbonic anhydrase inhibition Drug-induced hyperkalemia (With renal insufficiency)

29. Management

30. Treatment • Depends primarily on the cause • Need to control diabetes with insulin 

31. High Anion Gap Acidosis Treatment • Diabetic Ketoacidosis • Fluid resuscitation with isotonic saline • IV regular insulin

32. High Anion Gap Acidosis Treatment • Lactic Acidosis • Alkali therapy  acute acidemia to improve cardiac function and lactate utilization • Infuse sufficient NaHCO3 to raise arterial pH to no more than 7.2 over 30-40 minutes

33. Treatment • Metabolic acidosis may also be treated directly • If the acidosis is mild - administration of intravenous fluids may be all that is needed • If the acidosis is very severe- bicarbonate may be given intravenously • However, bicarbonate provides only temporary relief and may cause harm

34. Treatment • Potential Complications of Bicarbonate Therapy • Volume overload • Hypokalemia • CNS acidosis • Hypercapnia • Tissue hypoxia • Continuous monitoring of pH and electrolytes

36. Thank you.