ACID BASE DISORDER DR UZMA MALIK ASSISTANT PROFESSOR

ACID BASE DISORDER DR UZMA MALIK ASSISTANT PROFESSOR MEDICINE(EAST MEDICAL WARD) FCPS(Medicine)FCPS (Endocrinology)

Example EXAMPLE p. O 2= p. H= p. CO 2= HCO 3= 28. 3 76 7. 2 84

SOLUTION EXAMPLE Po 2= 76 p. H= 7. 2 p. CO 2= 84 HCO 3= 28. 3 1. Type 2 resp. failure 2. Acidosis 3. Respiratory acidosis 4. Metabolic compensation 5. Calculation forexpected compensation ∆HCO 3=0. 1 X ( 84 -40) ∆HCO 3=0. 1 X 44 ∆HCO 3=4. 4 Expected HCO 3=24+4. 4=28. 4 Type 2 respiratory failure Partially compensated acute respiratory acidosis

Interpretation of ABGs

Interpretation of ABGs Respiratory failure • Type 1 • Type 2 Acid base disorder • Acidosis • Alkalosis

NORMAL VALUES p. H = 7. 35 - 7. 45 ( 7. 4 ) p. CO 2 = 33 - 45 ( 40 ) m. Eq/L HCO 3 = 22 - 28 ( 24 ) m. Eq/L p. O 2 = 80 - 100 mm. Hg

Interpretation of ABGs Respiratory failure • Type 1; p. O 2 low • Type 2; p. O 2 low, p. CO 2 high

Respiratory Acidosis Respiratory Alkalosis Acid Base disorder Metabolic Acidosis Metabolic Alkalosis

BASIC CONCEPTS p. H~ CO 2 ↔ H 2 CO 3 ↔ H+ HCO 3

Respiratory Acidosis p. H~ PATHOGENESIS Retention of CO 2

Respiratory Acidosis Causes Anatomical Site Disorder CNS depression of resp. centre trauma, barbiturate Upper airway obstruction; Acute epiglotitis croup Resp. muscles paralysis ALS, phrenic nerve injury, GBS, poliomyelitis, hypokalemia, hypophsphatemia( ATP) Lungs obstructive diseases; chronic bronchitis, cystic fibros other; pulmonary edema, ARDS, severe bronchial asthma

Respiratory Acidosis COMPENSATION Metabolic alkalosis HCO 3 < 30 m. Eq/L in acute respiratory acidosis HCO 3 > 30 m. Eq/L in chronic respiratory acidosis CALCULATION OF EXPECTED COMPENSATION Acute resp. acidosis ∆HCO 3=0. 1 X ∆p. CO 2 Chronic resp. acidosis ∆HCO 3=0. 4 X ∆p. CO 2

Respiratory Acidosis EXAMPLE p. H= p. CO 2= HCO 3= 27 7. 2 74 ∆HCO 3=0. 1 X ( 74 -40) ∆HCO 3=0. 1 X 34 ∆HCO 3=3. 4 Expected HCO 3=24+3. 4=27. 4

Respiratory Acidosis EXAMPLE p. H= p. CO 2= HCO 3= 32 7. 34 60 ∆HCO 3=0. 4 X ( 60 -40) ∆HCO 3=0. 4 X 20 ∆HCO 3=8 Expected HCO 3=24+8=32

Respiratory Alkalosis p. H~ PATHOGENESIS Elimination of CO 2

Respiratory Alkalosis Causes Anatomical Site Disorder CNS over stimulation of resp. centre anxiety, high altitude, pregnancy, salicylate poisonin endotoxic shock, cirrhosis Resp. muscles rib fracture; hyper ventilate from pain Lungs restrictive diseases; sarcoidosis, asbestosis, others; pulmonary embolus, mild bronchial asthma

Respiratory Alkalosis COMPENSATION Metabolic acidosis HCO 3 > 18 m. Eq/L in acute respiratory alkalosis HCO 3 < 18 but >12 m. Eq/L in chronic respiratory alkalosis CALCULATION OF EXPECTED COMPENSATION Acute resp. alkalosis ∆HCO 3=0. 2 X ∆p. CO 2 Chronic resp. alkalosis ∆HCO 3=0. 5 X ∆p. CO 2

Respiratory Alkalosis EXAMPLE p. H= p. CO 2= HCO 3= 21 7. 56 24 ∆HCO 3=0. 2 X ( 40 -24) ∆HCO 3=0. 2 X 16 ∆HCO 3=3. 2 Expected HCO 3=24 -3. 2=20. 8

Respiratory Alkalosis EXAMPLE p. H= p. CO 2= HCO 3= 13 7. 47 18 ∆HCO 3=0. 5 X ( 40 -18) ∆HCO 3=0. 5 X 22 ∆HCO 3=11 Expected HCO 3=24 -11=13

Metabolic Acidosis p. H~ PATHOGENESIS 1. Addition of an acid ( increased anion gap ) 2. Loss of HCO 3 or inability to synthesize HCO 3( normal anion gap )

Metabolic Acidosis COMPENSATION Resp. alkalosis CALCULATION OF EXPECTED COMPENSATION ∆p. CO 2 =1. 2 X ∆HCO 3 +/- 2

Metabolic Acidosis EXAMPLE p. H= p. CO 2= HCO 3= 12 7. 27 27 ∆p. CO 2 =1. 2 X ∆ HCO 3 +/- 2 ∆p. CO 2 =1. 2 X ( 24 -12) +/- 2 ∆p. CO 2 =1. 2 X 12 +/- 2 ∆p. CO 2 =14. 4 +/- 2 Expected p. CO 2= 40 – 14. 4= 25. 6 +/- 2= 23. 6 to 27. 6

Metabolic Acidosis INCREASED ANION GAP TYPE Formula AG= serum Na – (serum Cl + serum HCO 3 )= 12 +/- 2 Example Na = 130 ( 135 - 147) Cl = 88 ( 95 – 105 ) HCO 3 = 10 ( 22 – 28 ) AG= 130 – ( 88+10) = 130 – 98= 32

Metabolic Acidosis INCREASED ANION GAP TYPE Causes Lactic acidosis Ketoacidosis Renal failure ( retention of organic acids) Salicylate poisoning Ethylene glycol poisoning Methyl alcohalpoisoning

Metabolic Acidosis NORMAL ANION GAP TYPE Formula AG= serum Na – (serum Cl + serum HCO 3 )= 12 +/- 2 Example Na = 136 ( 135 - 147) Cl = 110 ( 95 – 105 ) HCO 3 = 14 ( 22 – 28 ) AG= 136 – ( 110+14) = 136 – 124= 12

Metabolic Acidosis NORMAL ANION GAP TYPE CAUSES Diarrhoea Cholestyramine Drainage of bile or pancreatic secretions Type 1 distal renal tubular acidosis Type 11 proximal renal tubular acidosis Type IV renal tubular acidosis

Metabolic Alkalosis p. H~ PATHOGENESIS Loss of hydrogen ion Gain of HCO 3

Metabolic Alkalosis COMPENSATION Resp. acidosis CALCULATION OF EXPECTED COMPENSATION ∆p. CO 2 =0. 7 X ∆ HCO 3 +/- 2

Metabolic Alkalosis EXAMPLE p. H= p. CO 2= HCO 3= 39 7. 58 49 ∆p. CO 2 =0. 7 X ∆ HCO 3 +/- 2 ∆p. CO 2 =0. 7 X ( 39 -24) +/- 2 ∆p. CO 2 =0. 7 X 15 +/- 2 ∆p. CO 2 =10. 5 +/- 2 Expected p. CO 2= 40 + 10. 5= 50. 5 +/- 2= 48. 5 to 52. 5

Metabolic Alkalosis CAUSES Vomiting Mineralocorticoid excess Thiazide and loop diuretics

5 easy steps Look at p. O 2 Look at p. H Look at p. CO 2 Look at HCO 3 Calculate expected compensation

5 easy steps 1. Look for p. O 2 Respiratory failure • Type 1; p. O 2 low • Type 2; p. O 2 low, p. CO 2 high

5 easy steps 2. Look for p. H acidosis p. H alkalosis

5 easy steps 3. Look for p. CO 2 acidosis p. CO 2 alkalosis

5 easy steps 4. Look for HCO 3 acidosis HCO 3 alkalosis

5 easy steps 5. Calculate for expected compensation If compensation within expected range one primary disorder If compensation outside normal range more than one primary disorder

5 easy steps 5. Compensation uncompensated disorder expected compensation in normal range partially compensated disorder Expected compensation moves outside the normal range, But does not bring p. H in normal range full compensation Expected compensation moves outside the normal range, and brings p. H in normal range

Primary disorder Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis p. H p. CO 2 HCO 3

Example EXAMPLE p. O 2= p. H= p. CO 2= HCO 3= 28. 3 76 7. 2 84

SOLUTION EXAMPLE Po 2= 76 p. H= 7. 2 p. CO 2= 84 HCO 3= 28. 3 1. Type 2 resp. failure 2. Acidosis 3. Respiratory acidosis 4. Metabolic compensation 5. Calculation forexpected compensation ∆HCO 3=0. 1 X ( 84 -40) ∆HCO 3=0. 1 X 44 ∆HCO 3=4. 4 Expected HCO 3=24+4. 4=28. 4 Type 2 respiratory failure Partially compensated acute respiratory acidosis

p 02 K N A H T U O Y p. H~