Acid-Base Disorders

1
Acid-Base Disorders

• Sharon Anderson, M.D.
• Division of Nephrology and Hypertension
• May 2003

2
General Acid-Base Relationships

• Henderson-Hasselbach equation
• pH pK log HCO3 _ /pCO2
• H 24 x pCO2/HCO3_
• ???0.1?pH unit ? 10 nm/L H

3
Approach to Acid-Base Disorders

• 1. Consider the clinical setting!
• 2. Is the patient acidemic or alkalemic?
• 3. Is the primary process metabolic or
  respiratory?
• 4. If metabolic acidosis, gap or non-gap?
• 5. Is compensation appropriate?
• 6. Is more than one disorder present?

4
Simple Acid-Base Disorders

• Primary Compensatory
• Disorder pH H Disorder
  Response
• Metabolic acidosis ? ??? ??HCO3_ ? pCO2
• Metabolic alkalosis ? ???????HCO3_ ?
  pCO2
• Respiratory acidosis ? ???????pCO2 ? HCO3_
• Respiratory alkalosis ? ???????pCO2 ? HCO3_

5
Metabolic Acidosis

• Etiology Inability of the kidney to excrete the
  dietary H load, or increase in the generation of
  H (due to addition of H or loss of HCO3-)

6
Metabolic Acidosis Elevated Anion Gap

• AG Na - (Cl- HCO3-) 12 2
• Note Diagnostic utility is best when AG gt 25
• Causes Ketoacidosis
• Lactic acidosis
• Intoxications
• Renal failure
• Rhabdomyolysis

7
Anion Gap in Hypoalbuminemia

• The true anion gap is underestimated in
  hypoalbuminemia ( fall in unmeasured anions) AG
  must be adjusted
• Formulas for adjusted AG
• For every 1.0 fall in albumin, increase AG by 2.5
• Consider the patients normal AG to be (2 x
  alb) (0.5 x phosphate)
• Adjusted AG Observed AG (2.5 x normal alb -
  adjusted alb

8
Ketosis

• Diabetes
• Starvation
• Alcoholic
• Isopropyl alcohol
• Ketosis with normal AG and HCO3_

9
Ketosis Points to Remember

• -- Normal AG and HCO3_ isopropyl alcohol
• -- Beta-hydroxbutyrate not seen by ketotest
• -- Acetoacetate spuriously ? Cr
• -- False positive ketotest
• paraldehyde, disulfiram, captopril

10
Lactic Acidosis

• Type A Hypoxic
• Lactatepyruvate gt 101
• Type B Glycolytic
• Lactatepyruvate 101

11
Intoxications Causing High AG Acidosis

• Aspirin - high salicylate level also primary
  respiratory alkalosis
• Methanol - optic papillitis
• Ethylene Glycol - calcium oxalate crystals
• Paraldehyde

12
Use of venous vs. arterial pH

• As compared with arterial blood gasses
• pH ? 0.03-0.04
• pCO2 ? 7-8 mmHg
• HCO3 ? 2 mEq/L

13
The Delta/Delta ? AG/ ? HC03

• Rationale
• For each unit INCREASE in AG (above normal), HC03
  should DECREASE one unit (below normal)
• Normal values AG 12, HC03 24

14
Use of the Delta/Delta Examples

• AG HCO3 Diagnosis
• 18 (? 6) 18 (? 6) Appropriate pure AG acidosis
• 18 (? 6) 22 (? 2) HCO3 has ? less than
• 
  predicted, so HCO3 is too high
• 
  mixed AG acidosis AND met alk
• 18 (? 6) 12 (? 12) HCO3 has ? more
  than
• 
  predicted, so HCO3 is too low
• 
  mixed AG AND non-AG acidosis

15
Causes of Low Anion Gap

• Etiology Fall in unmeasured anions
• or rise in unmeasured cations
• Hyperkalemia Lithium intoxication
• Hypercalcemia Multiple myeloma
• Hypermagnesemia
• Artefactual hypernatremia, bromide,
  hyperlipidemia

16
Osmolar Gap

• Measured serum osmolality gt
• calculated serum osmolality by gt 10 mOsm
• Calc Sosm (2 x Na) BUN/2.8 Glu/18

17
Causes of High Osmolar Gap

• Isotonic hyponatremia
• Hyperlipidemia
• Hyperproteinemia
• Mannitol
• Glycine infusion
• Chronic renal failure
• Ingestions
• Ethanol, isopropyl alcohol, ethylene glycol,
  mannitol
• Contrast Media

18
Relationship between AG and Osmolar Gap

• AG Osm gap Comments
• Ethylene glycol
  Double gap
• Methanol
  Double gap
• Renal failure
  Double gap
• Isopropyl alcohol -
  
• Ethanol -
• Lipids, proteins -

19
Causes of Normal AG (Hyperchloremic) Metabolic
Acidosis

• High K Low K
• Adrenal insufficiency Diarrhea
• Interstitial nephritis RTA
• NH4Cl, Arg HCl Ureteral diversion

20
Use of the Urine Anion Gap (UAG) in Normal AG
AcidosisBatlle et al. NEJM 318594, 1988

• Urine AG (Na K) - Cl
• Negative UAG Normal, or GI loss of HCO3
• Positive UAG altered distal renal acidification
• Caveats Less accurate in patients with volume
  depletion (low urinary Na) and in patients with
  increased excretion of unmeasured anions (e.g.
  ketoacidosis), where there is increased excretion
  of Na and K to maintain electroneutrality)

21
Use of the Urinary AG in Normal Gap
AcidosisBatlle et al. NEJM 318594, 1988

• Plasma K UAG U pH Diagnosis
• Normal - lt 5.5 Normal
• Normal-low - gt 5.5 GI HCO3 loss
• High lt 5.5 Aldo deficiency
• High gt 5.5 Distal RTA
• Normal-low gt 5.5 Proximal RTA

22
Use of the Urine Osmolal Gap

• When UAG is positive, and it is unclear if
  increased cation excretion is responsible, urine
  NH4 concentration can be estimated from urine
  osmolal gap
• Calc Uosm (2 x NaK) urea nitrogen/2.8
  glu/18
• The gap between the calculated and measured Uosm
  mostly ammonium
• In patients with metabolic acidosis, urine
  ammonium should be gt 20 mEq/L. Lower value
  impaired acidification

23
Renal Tubular Acidosis

• Type 1 (distal) Type 2 (proximal) Type 4
• Defect ??distal acid. ??prox HCO3 reab
  ??aldo
• HCO3 May be lt 10 12-20 gt 17
• Urine pH gt 5.3 Variable lt 5.3
• Plasma K Usually low Usually low High
• Response Good Poor Fair
• to HCO3 Rx

24
Calculation of Bicarbonate Deficit

• Bicarb deficit HCO3- space x HCO3-
  deficit/liter
• HCO3- space 0.4 x lean body wt (kg)
• HCO3- deficit/liter desired HCO3- - measured
  HCO3-

25
Approach to Metabolic Acidosis
Anion Gap
Normal
High
Osmolar Gap
GI Fluid Loss?
No
Yes
Normal
Increased
Diarrhea Ileostomy Enteric fistula
Urine pH
Uremia Lactate Ketoacids Salicylate
Ethylene glycol Methanol
lt 5.5
gt 5.5
Serum K
Distal RTA (Type 1)
High
Low
Type 4 RTA
Proximal RTA (Type 2)
26
Metabolic Alkalosis

• Etiology Requires both generation of metabolic
  alkalosis (loss of H through GI tract or
  kidneys) and maintenance of alkalosis (impairment
  in renal HCO3 excretion)
• Causes of metabolic alkalosis
• Loss of hydrogen
• Retention of bicarbonate
• Contraction alkalosis
• Maintenance factors Decrease in GFR, increase
  in HCO3 reabsorption

27
Use of Spot Urine Cl and K
Very Low (lt 10 mEq/L)
Vomiting, NG suction Postdiuretic,
posthypercapneic Villous adenoma,
congenital chloridorrhea, post- alkali
Urine Chloride
gt 20 mEq/L
Low (lt 20 mEq/L)
Urine Potassium
Laxative abuse Other profound K depletion
gt 30 mEq/L
Diuretic phase of diuretic Rx, Bartters,
Gitelmans, primary aldo, Cushings, Liddles,
secondary aldosteronism
28
Treatment of Metabolic Alkalosis

• 1. Remove offending culprits.
• 2. Chloride (saline) responsive alkalosis
  Replete volume with NaCl.
• 3. Chloride non-responsive (saline resistant)
  alkalosis
• Acetazolamide (CA inhibitor)
• Hydrochloric acid infusion
• Correct hypokalemia if present

29
Calculation of Bicarbonate Excess

• Bicarb excess HCO3- space x HCO3- excess/liter
• HCO3- space 0.5 x lean body wt (kg)
• HCO3- excess/liter measured HCO3- - desired
  HCO3-

30
Respiratory Acidosis

• Causes of Respiratory Acidosis
• Inhibition of medullary respiratory center
• Disorders of respiratory muscles and chest wall
• Upper airway obstruction
• Disorders affecting gas exchange across
  pulmonary capillaries
• Mechanical ventilation

31
Respiratory Alkalosis

• Causes of Respiratory Alkalosis
• Hypoxemia
• Pulmonary disease
• Stimulation of medullary respiratory center
• Mechanical ventilation

32
Mixed Acid-Base Disorders Clues

• -- Degree of compensation for primary
• disorder is inappropriate
• -- Delta AG/delta HCO3_ too high or too low
• -- Clinical history

33
Problem 1

• A 30-yo man with DM presents with a week of
  polyuria, polydipsia, fever to 102, nausea, and
  abdominal pain. He is orthostatic on admission.
• 130 I 94 I 75 I 906 pH 7.14
• 6.1 I 6 I 2.3 pCO2 18
• pO2 102

34
Problem 1, cont.
130 I 94 I 75 I 906 7.14/18/102 6.1 I 6 I
2.3

• 1. Anticipate the disorder
• DKA (with anion gap acidosis)
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH acidemic must be metabolic (low HCO3, low
  pCO2)
• 4. If metabolic acidosis gap or non-gap?
• AG 30 anion gap metabolic acidosis
• 5. Is compensation appropriate?
• pCO2 should last 2 digits of pH 18 or (1.5 x
  HCO3) 8 17
• 6. Mixed disorder?
• AG 30 ( 18) HCO3 6 ( 18) thus simple AG
  met acidosis

35
Problem 2

• A 30-yo man with DM presents with a week of
  polyuria, polydipsia, fever to 102, and vomiting
  for four days.
• 135 I 89 I 50 I 1181 pH 7.26
• 6.1 I 10 I 2.3 pCO2 23
• pO2 88

36
Problem 2, cont.
135 I 89 I 50 I 1181 7.26/23/88 6.1 I 10 I 2.3

• 1. Anticipate the disorder
• DKA (AG acidosis) met alk from vomiting
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH acidemic must be metabolic (low HCO3, low
  pCO2)
• 4. If metabolic acidosis gap or non-gap?
• AG 36 anion gap metabolic acidosis
• 5. Is compensation appropriate?
• pCO2 should last 2 digits of pH 26 or (1.5 x
  HCO3) 8 23
• 6. Mixed disorder?
• AG 36 ( 24) HCO3 10 ( 14) HCO3 is too
  high mixed AG metabolic acidosis and metabolic
  alkalosis

37
Problem 3

• A 30-yo man with DM presents with a week of
  polyuria, polydipsia, fever to 102, and diarrhea.
• 138 I 111I 49 I 650 pH 7.26
• 5.5 I 8I 1.4 pCO2 23
• pO2 88

38
Problem 3, cont.
138 I 111 I 49 I 650 7.26/23/88 5.51 I 8 I
1.4

• 1. Anticipate the disorder
• DKA (AG acidosis) nongap met acidosis from
  diarrhea
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH acidemic must be metabolic (low HCO3, low
  pCO2)
• 4. If metabolic acidosis gap or non-gap?
• AG 19 anion gap metabolic acidosis
• 5. Is compensation appropriate?
• pCO2 should last 2 digits of pH 26 or (1.5 x
  HCO3) 8 23
• 6. Mixed disorder?
• AG 19 ( 7) HCO3 8 ( 16) HCO3 is too low
  mixed AG metabolic acidosis and metabolic
  acidosis (nongap)

39
Problem 4

• A 30-yo man with DM presents with a week of
  polyuria, polydipsia, fever, cough, and prurulent
  sputum.
• 140 I 104 I 75 I 1008 pH 6.95
• 7.0 I 7 I 2.6 pCO2 33
• pO2 60

40
Problem 4, cont.
140 I 104 I 75 I 1008 6.95/33/60 7.0 I
7 I 2.6

• 1. Anticipate the disorder
• DKA (AG acidosis) resp alk or resp acidosis
  from hypoxemia/pneumonia
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH acidemic must be metabolic (low HCO3, low
  pCO2)
• 4. If metabolic acidosis gap or non-gap?
• AG 29 anion gap metabolic acidosis

41
Problem 4, cont.
140 I 104 I 75 I 1008 6.95/33/60 7.0 I
7 I 2.6

• 5. Is compensation appropriate?
• pCO2 should last 2 digits of pH 95!! or (1.5
  x HCO3) 8 18 pCO2 is too high so he has a
  superimposed respiratory acidosis
• 6. Mixed disorder?
• AG 29 ( 17) HCO3 7 ( 17) so metabolic
  acidosis is pure AG acidosis. Thus, mixed AG
  metabolic acidosis and respiratory acidosis

42
Problem 5

• A 31-yo woman who is 33 weeks pregnant presents
  with a 2-day history of vomiting.
• 140 I 104 I 8 I 85 pH 7.64
• 3.0 I 26 I 0.6 pCO2 25
• pO2 93

43
Problem 5, cont.
140 I 104 I 8 I 85 7.64/25/93 3.0
I 26 I 0.6

• 1. Anticipate the disorder
• Pregnancy resp alk Vomiting met alk
• 2. Acidemic or alkalemic?
• pH alkalemic
• 3. Metabolic or respiratory?
• If resp, HCO3 should be low if metabolic, then
  pCO2 should be high must have both
• 4. If metabolic acidosis gap or non-gap?
• N/A no acidosis no AG

44
Problem 5, cont.
140 I 104 I 8 I 85 7.64/25/93 3.0
I 26 I 0.6

• 5. Is compensation appropriate?
• NO (by eyeball, for reasons listed above)
• 6. Mixed disorder?
• Yes, mixed metabolic and respiratory alkalosis.
  No acidosis component.

45
Problem 6

• A 60-yo man has crushing chest pain, SOB and
  diaphoresis. He has HTN, for which he takes
  HCTZ. Exam shows BP 88/60, bilateral crackles,
  S3. EKG shows ischemia CXR pulmonary edema.
• 140 I 94 I 45 I 300 pH 7.14
• 5.9 I 20 I 1.9 pCO2 60
• pO2 52

46
Problem 6, cont.
140 I 94 I 45 I 300 7.14/60/52 5.9
I 20 I 1.9

• 1. Anticipate the disorder
• Pulm edema -gt resp alk or resp acidosis shock
  -gt metabolic acidosis HCTZ -gt metabolic
  alkalosis
• 2. Acidemic or alkalemic?
• pH acidemic
• 3. Metabolic or respiratory?
• If resp, HCO3 should be gt 24 in compensation if
  metabolic, then pCO2 should lt 40 must have both
  respiratory and metabolic acidoses
• 4. If metabolic acidosis gap or non-gap?
• AG 26 anion gap metabolic acidosis

47
Problem 6, cont.
140 I 94 I 45 I 300 7.14/60/52 5.9
I 20 I 1.9

• 5. Is compensation appropriate?
• NO (by eyeball, for reasons listed above)
• 6. Mixed disorder? Anything else?
• AG 26 ( 14) HCO3 20 ( 4) so HCO3 is too
  high must have a superimposed metabolic
  alkalosis.
• Thus, triple disorder respiratory acidosis,
  anion gap metabolic acidosis, and metabolic
  alkalosis

48
Problem 7

• A 55-yo woman with a history of a CVA presents to
  clinic complaining of shortness of breath.
• 140 I 100 I 30 I 115 pH 7.36
• 3.9 I 30 I 1.5 pCO2 38
• pO2 91

49
Problem 7, cont.
140 I 100 I 30 I 115 7.36/38/91
3.9 I 30 I 1.5

• 1. Anticipate the disorder
• Resp alk due to CNS disorder or acute pulmonary
  process
• 2. Acidemic or alkalemic?
• pH acidemic
• 3. Metabolic or respiratory? 4. If metabolic
  acidosis AG?
• HCO3 is high (not metabolic acidosis) pCO2 is lt
  40 (not respiratory acidosis) AG is normal (10),
  so whats going on??

50
Problem 7, cont.
140 I 100 I 30 I 115 7.36/38/91
3.9 I 30 I 1.5

• LAB ERROR!
• By Henderson-Hasselbach
• H 24 x pCO2/HCO3 24 x (38/30) 30
• pH should be 7.50

51
Problem 8

• You are in the ER, and are aware that the lab has
  been having intermittent problems with the
  chemistry autoanalyzer. A 30-yo diabetic man,
  well known to you from previous visits, comes in
  with severe nausea and vomiting. His blood
  alcohol level is very high. The ER attending
  advises you to check his labs and send him home
  if they are OK.
• 140 I 84I 28 I 160 pH 7.40
• 3.0 I 24I 1.3 pCO2 40
• pO2 88

52
Problem 8, cont.
140 I 84 I 28 I 160 7.40/40/88
3.0 I 24 I 1.3

• 1. Anticipate the disorder
• Vomiting -gt met alk if unconscious, resp
  acidosis
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH, pCO2 and HC03 are all normal --gt no apparent
  disorder
• 4. Lab error? Check H-H equations.
• H 24 x (pCO2/HCO3) 24 x (40/24) 40, so pH
  7.40
• 5. Do you send him home?

53
Problem 8, cont.
140 I 84 I 28 I 160 7.40/40/88
3.0 I 24 I 1.3

• 5. Do you send him home?
• AG 32 anion gap acidosis
• AG 32 ( 20) HCO3 24 ( 0) so HCO3 is too
  high must have a superimposed metabolic
  alkalosis.
• Thus, mixed AG acidosis and metabolic alkalosis
  

54
Problem 9

• A 58-yo man with cirrhosis and Type 2 DM presents
  with fever, abdominal pain, SOB, and vomiting.
• 159 I 112 I 55 I 160 pH 7.31
• 3.3 I 12 I 2.8 pCO2 19
• pO2 77

55
Problem 9, cont.
159 I 112 I 55 I 160 7.31/19/77
3.3 I 12 I 2.8

• 1. Anticipate the disorder
• Renal dis --gt acidosis dead gut --gt lactic
  acidosis vomiting --gt met alk pain --gt resp
  alk liver disease --gt resp alk
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH acidemic must be metabolic (low HCO3, low
  pCO2)
• 4. If metabolic acidosis gap or non-gap?
• AG 35 anion gap metabolic acidosis

56
Problem 9, cont.
159 I 112 I 55 I 160 7.31/19/77
3.3 I 12 I 2.8

• 5. Is compensation appropriate?
• pCO2 should last 2 digits of pH 31 not or
  (1.5 x HCO3) 8 26 pCO2 is too low so he has
  a superimposed respiratory alkalosis
• 6. Mixed disorder?
• AG 35 ( 23) HCO3 12 ( 12) so HCO3 is too
  high, so there must be a metabolic alkalosis.
• Thus, triple disorder AG metabolic acidosis,
  respiratory alkalosis, and metabolic alkalosis

57
Problem 10

• A 70-yo man presents with vomiting and abdominal
  pain, for which he has been taking Rolaids. He
  is hypotensive and has a tender abdomen.
• 140 I 69 I 40 I 118 pH 7.74
• 3.4 I 40 I 1.5 pCO2 30
• pO2 105

58
Problem 10, cont.
140 I 69 I 40 I 118 7.74/30/105
3.4 I 40 I 1.5

• 1. Anticipate the disorder
• Dead gut --gt lactic acidosis vomiting or
  Rolaids --gt met alk pain --gt resp alk
• 2. Acidemic or alkalemic? 3. Metabolic or
  respiratory?
• pH alkalemic must be both metabolic (high
  HCO3) and respiratory (low pCO2)
• 4. If metabolic acidosis gap or non-gap?
• AG 31 anion gap metabolic acidosis

59
Problem 10, cont.
140 I 69 I 40 I 118 7.74/30/105
3.4 I 40 I 1.5

• 5. Is compensation appropriate?
• Cannot compute, too many disorders
• 6. Mixed disorder?
• AG 31 ( 19) HCO3 40, not down so HCO3 is
  too high, so there must be a metabolic alkalosis.
• Thus, triple disorder AG metabolic acidosis,
  respiratory alkalosis, and metabolic alkalosis