The document discusses acid-base balance and provides information on: 1. Normal acid-base balance is tightly controlled through chemical buffering, carbon dioxide levels, and bicarbonate concentration. 2. There are two types of acids - carbonic acids from carbon dioxide and non-carbonic acids from protein metabolism. 3. Diagnosis of acid-base imbalances involves obtaining a history, physical exam, and measuring pH, bicarbonate, carbon dioxide, and checking the adequacy of compensation.

1. Acid – Base Balance
Institute of Nephrology and
Hypertension
Carmel Medical Center

2. Acid – Base Balance
Institute of Nephrology and
Hypertension
Carmel Medical Center

3. Acid – base balance

4. Acid – Base Balance
 Normal concentration of H + in
extracellular fluid is 40 nmol/L.

5. Acid – Base Balance
 Roughly one millionth the concentration of
Na , K, Cl and Bicarb.

6. Acid – Base Balance
 In normal conditions this concentration is
very well controlled

7. Acid – Base Balance
 Three basic steps
1 – Chemical Buffering
2 - Control of PP of CO 2 ( alveolar
ventilation)
3 – Control of Bicarb concentration
( H excretion ).

8. Acid – Base Balance
Two kinds of acids
1- Carbonic
2- Non Carbonic

9. Acid – Base Balance
 Metabolism results in the generation of
approximately 15000 mmol CO2
 CO 2 + H2O = H2CO3

10. Acid – Base Balance
 An acid is a substance that can donate H +
 A base is a substance that can accept H +
 H2CO3 , HCl, NH4, H2PO4 can act as
acids

11. Acid – Base Balance
Non Carbonic acids are derived from protein
metabolism .
50 to 100 meq/day of H + are produced daily
and excreted in the urine

12. Acid – Base Balance
If HCl is added
HCl + Na2HPO4 -----NaCl + NaH2PO4

13. Acid – Base Balance
H CO3 + H+ ------ H2O + CO2

14. Acid – Base Balance
HCO3 (Salt)=20
 pH= pK + log
H2CO3=pCO2 (Acid)=1

15. Acid – Base Balance
 Stop
 Think
 Get anamnesis
 Physical examination
 pH
 Bicarbonate
 pCO2
 Adequacy of compensation

16. Diagnosis
 The evaluation always starts with the anamnesis
 Then determine the pH
 See if compensation adequate
 Remember, compensation is never complete
 Metabolic acidosis, determine anion gap
 Metabolic alkalosis, determine volume status

17. Metabolic Acidosis
 Characterized by a fall in the plasma
bicarbonate and a low pH
 Either by bicarbonate loss
 Or addition of acid
 This results in compensatory decrease of
pCO2

18. Metabolic Acidosis
 Normal anion gap
 Gastro- intestinal loss of bicarbonate
 Renal loss:
a. Proximal RTA
b. Distal RTA
c. Type IV RTA (Hypoaldosteronism)
d. Ammonium chloride
e. Hyperalimentation

20. Acid – base balance
 If metabolic acidosis, determine anion gap
 If metabolic alkalosis, determine volume status

21. Metabolic acidosis
High anion gap
 Lactic acidosis
 Ketoacidosis
 Renal failure - Organic acids
 Intoxications
a. Salicilate
b. Methanol
c. Ethylene glycol
d. Sulfur
 Rhabdomyolysis

22. Metabolic Alkalosis
 How do patients become alkalotic?
 How do patients remain alkalotic?

23. Metabolic Alkalosis
 Results from elevation of plasma
bicarbonate associated with high pH
 May be due to bicarbonate administration
 May be due to H+ loss
 Respiratory compensation consists of
hypoventilation and pCO2 elevation

24. Causes of Metabolic Alkalosis
 Loss of H+: Gastrointestinal loss
Renal loss: Diuretics
Mineralocorticoid excess
Penicillins
Hypercalcemia
 Hydrogen movement into the cells - Hypokalemia
 Retention of bicarbonate: Blood transfusion
Bicarb administration
 Contraction alkalosis: Diuretics

26. Metabolic Alkalosis
Impaired HCO3 excretion with perpetuation of
metabolic alkalosis
 Decreased GFR
Volume depletion
 Increased tubular reabsorption
Volume depletion
Chloride depletion
Hypokalemia
Hyperaldosteronism

27. Diagnosis
Metabolic alkalosis, determine chloride in
urine to differentiate volume dependency
or not

28. Urine Cl- in Metabolic Alkalosis
Less than 25 mEq/l More than 40 mEq/l
 Vomiting  Mineralocorticoid
 Diuretics excess
 Cystic Fibrosis  Diuretics (early)
 Alkali load
 Severe Hypokalemia

30. Example
Na 140
K 3.4
Cl 77
Bicarbonate 9
Anion gap 54
pH 7.23
pCO2 23
Ketonuria: traces
Creatinine 2.3
 Why do they remain alkalotics

31. Compensations
Metabolic Alkalosis
pCO2 = 40+ 0.6 delta BIC
Metabolic Acidosis
pCO2 = 2 last numbers of pH
pCO2 = 1.5 x ( HCO3) + 8

32. Compensations?
Respiratory Acidosis Respiratory Alkalosis
Acute Acute
HCO3 = + 1 mEq/10 mm HCO3 = - 1-2 mEq/10
Hg pCO2 mm Hg pCO2
Chronic Chronic
HCO3 = + 3.5 mEq/10 HCO3 = - 5 mEq/10 mm
mm Hg pCO2 Hg pCO2

33. Example
BUN 100
Na 142
Cl 120
pH 7.4
pCO2 20
Bicarbonate 13

34. Example
BUN 15
Na 140
Cl 105
pH 7.02
pCO2 40
Bicarbonate 10

35. Example
BUN 12
Na 146
Cl 100
pH 7.60
pCO2 37
Bicarbonate 35
K 3.5

36. Example
BUN 14
Na 140
Cl 108
pH 7.37
pCO2 20
Bicarbonate 11
K 3.8

37. Example
20 y old vomiting, lethargy, tachypnea,
tachycardia BP 150/100. IDDM , no insulin
lately. Almost no food last few days, Na
142, K 3.6, Cl 106, Bic 16, Gluc 230, Urea
190 , Creatinine pending, pH 7.28, PCO2
34. Urine Ketones moderately positive-a
couple of hours ago. No urine since.

38. continuation
 Diabetic ketoacidosis
 Treated with insulin,2.5 Lt saline and Potassium
chloride
 After 3 hours patient lethargic, Met Ac not
improved, Gluc 70, jugular ++ reflux++
 Rales +++
 Anuria
 At last, Creatinine results………12…..

39. continuation
 LESSONS
 Consider all possibilities
 Urine Ketones positive in starvation and
vomiting
 Check urine output before giving IV
 Control your patient often !!!

40. EXERCISE
 pH 7.49
 Bic 35
 PCO2 48
 Anion Gap16

41. CONTINUATION
 Compensation – PCO2 40+ 0.6 x Delta bic
 ( 35 – 24 ) = 8 48mm-
 The anion gap is normal
 Simple Metabolic Alkalosis

42. EXERCISE
 pH 7.68
 Bic 40
 pCO2 35
 Anion Gap 14

43. Continuation
 pCO2 should be 40+ 0.6 ( 40-24) = 49.6
 Anion Gap is |normal
 Combined Metabolic and Respiratory
Alkalosis

44. EXERCISE
 pH 7.26
 pCO2 60
 Bic 26

45. CONTINUATION
 Compensation is +1 mEq/10 mm CO2
 Bic is 26 – pCO2 is up 20mm Hg-
compensation is adequate for

46. CONTINUATION
 Acute respiratory Acidosis

47. EXERCISE
 Complains of difficulty in breathing for the
last 4 days
 pH 7.42
 pCO2 30
 Bic 19
 Anion Gap 16

48. continuation
Chronic Respiratory Alkalosis

49. Continuation
 Adequate compensation is ( - ) 5 mEq
 Bicarbonate / 10 mm Hg
 If acute, Bic should be 23
 Since it is Chronic Respiratory Alkalosis ( more
than 48 hours) Bic should be ( 24- 5)= 19
 Anion Gap is normal- there is no hidden Met Ac
 Simple Chronic Respiratory Acidosis

50. EXERCISE
 pH 7.45
 Bic 44
 pCO2 65
 Anion Gap 14

51. CONTINUATION
 For Met Alk pCO2 should be 40
= 0.6( 44-24)= 52
 pCO2 is to high ( 65 ), so
 Metabolic Alkalosis + Respiratory Acidosis
 Why not respiratory acidosis +
compensation?

52. EXERCISE
 21 y old IDDM presents with vomiting
 pH 7.75
 pCO2 24
 BIC 32
 Anion Gap 30

53. CONTINUATION
 Adequate Compensation : pCO2 should be
 40+ 0.6 ( 32-24 )= 44.8, so
 Respiratory Alkalosis.
 Anion Gap is 30 , so
 Hidden Metabolic Acidosis.
 Delta Anion Gap 16, Bic should have fallen to
+ - 6-8, but is 32

54. CONTINUATION
 Severe Respiratory Alkalosis + Severe High
Anion Gap Metabolic Acidosis+ Severe
Metabolic Alkalosis.

55. The End
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