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. Acid Base Disturbance:

4. Algorithm for the Diagnosis of the acid base disorder

5. 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)

6. 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+]

7. Prediction of compensatory responses

8. 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

9. 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

10. 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

11. 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

12. Pattern of Compensatory Changes

13. Anion Gap

14. 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

15. 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

16. 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

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

18. 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

19. Management

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

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

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

23. 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

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