Acid-Base Disorders Adapted from Haber, R.J.:

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Acid-Base DisordersAdapted from Haber, R.J. A
practical Approach to Acid-Base Disorders. West
J. Med 1991 Aug 155156-151

• Allison B. Ludwig, M.D.
• Site Director, Jacobi Medicine Clerkship

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Goals

• Learn to work through acid-base disorders without
  nomograms or complicated mathematical formulas
• Be able to recognize and work through multiple
  offsetting disorders that are coincident in the
  same patient

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Outline

• Data Base, Terms and Definitions
• Simple-Acid Base Disorders
• Mixed Acid-Base Disorders

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Data Base

• Arterial pH
• Arterial pCO2
• Serum HCO3 (best from blood chemistry)

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Terms and Definitions
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35 - 7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis

• Respiratory compensation for metabolic disorders
  is rapid
• Full metabolic compensation for respiratory
  disturbances requires renal adjustment and takes
  3-5 days

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Outline

• Data Base, Terms and Definitions
• Simple-Acid Base Disorders
• Mixed Acid-Base Disorders

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Simple Acid-Base Disorders

• Look at the pH in order to determine the primary
  abnormality
• Pathophysiologic principle body does not fully
  compensate even for chronic acid-base disorders

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Example 1
Acute Respiratory Alkalosis
pH 7.50
pCO2 29
HCO3 22
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis
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Causes of Acute Respiratory Alkalosis

• Anxiety
• Hypoxia
• Lung disease with or without hypoxia
• CNS disease
• Drug usesalicylates, catecholamines,
  progesterone
• Pregnancy
• Sepsis
• Hepatic Encephalopathy
• Mechanical Ventilation

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Example 2
Acute Respiratory Acidosis
pH 7.25
pCO2 60
HCO3 26
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis
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Causes of Acute Respiratory Acidosis

• CNS depressiondrugs, CNS event
• Neuromuscular disordersmyopathies, neuropathies
• Acute airway obstructionupper airway,
  laryngospasm, bronchospasm
• Severe pneumonia or pulmonary edema
• Impaired lung motionhemothorax, pneumothorax
• Thoracic cage injuryflail chest
• Ventilator dysfunction

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Example 3
Chronic Respiratory Acidosis with Metabolic
Compensation
pH 7.34
pCO2 60
HCO3 31
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis
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Causes of Chronic Respiratory Acidosis

• Chronic lung diseaseobstructive or restrictive
• Chronic neuromuscular disorders
• Chronic respiratory center depressioncentral
  hypoventilation

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Example 4
Metabolic Alkalosis
pH 7.50
pCO2 48
HCO3 36
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis
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Causes of Metabolic Alkalosis

• Vomiting
• Diuretics
• Excess mineralocorticoid activityCushings
  syndrome, Conns syndrome, exogenous steroids,
  licorice ingestion, increased renin states,
  Bartters syndrome
• Excess alkali administration
• Refeeding alkalosis

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Example 5
Metabolic Acidosis with Respiratory Compensation
pH 7.20
pCO2 21
HCO3 8
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis
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Causes of Metabolic Acidosis

• Non-Gap
• GI HCO3 loss diarrhea, ureteral diversions
• Renal HCO3 loss RTA, aldosterone inhibitors,
  carbonic anhydrase inhibitors
• Iatrogenic normal saline
• Anion Gap
• Ketoacidosis diabetic, alcoholic
• Renal failure
• Lactic Acidosis
• Rhabdomyolysis
• Toxins methanol, ethylene glycol, paraldehyde,
  salicylates

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Outline

• Data Base, Terms and Definitions
• Simple-Acid Base Disorders
• Mixed Acid-Base Disorders

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The Rules

• Look at the pH whichever side of 7.40 the pH is
  on, the process that caused it to shift to that
  side is the primary abnormality
• Principle the body doesnt fully compensate for
  primary acid-base disorders
• Calculate the anion gap Na (Cl HCO3) if
  the anion gap is gt20, there is a primary
  metabolic acidosis regardless of pH or HCO3
• Principle the body doesnt generate a large
  anion gap to compensate for a primary disorder
• Calculate the excess anion gap (total anion gap
  minus the normal anion gap) and add this to the
  measured HCO3 concentration, if gt30, there is
  underlying metabolic alkalosis if lt24, there is
  underlying non-gap metabolic acidosis
• Principle 1 mmol of unmeasured acid titrates 1
  mmol of bicarbonate

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Understanding the anion gap

• Each millimolar decrease in HCO3 is accompanied
  by a millimolar increase in the anion gap, the
  sum of the new (excess) anion gap and the
  remaining (measured) HCO3 value should be equal
  to a normal bicarbonate concentration

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Example 6
pH 7.50
pCO2 20
HCO3 15
Na 140
Cl 103
Respiratory Alkalosis and Anion Gap Metabolic
Acidosis
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis

1. Look at the pH to determine the primary process.
2. Calculate the anion gap Na (Cl HCO3)
3. Calculate the excess anion gap (total anion gap
   minus the normal anion gap) and add this to the
   measured HCO3 concentration, if gt30, there is
   underlying metabolic alkalosis if lt24, there is
   underlying non-gap metabolic acidosis

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Whats the Diagnosis?

• Salicylate Overdose

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Example 7
pH 7.40
pCO2 40
HCO3 24
Na 145
Cl 100
Anion Gap Metabolic Acidosis and Metabolic
Alkalosis
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis

1. Look at the pH to determine the primary process.
2. Calculate the anion gap Na (Cl HCO3)
3. Calculate the excess anion gap (total anion gap
   minus the normal anion gap) and add this to the
   measured HCO3 concentration, if gt30, there is
   underlying metabolic alkalosis if lt24, there is
   underlying non-gap metabolic acidosis

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Whats the Diagnosis?

• Chronic renal failure in a patient with vomiting
  as his uremia worsened.

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Example 8
pH 7.50
pCO2 20
HCO3 15
Na 145
Cl 100
Respiratory alkalosis, Anion Gap Metabolic
Acidosis and Metabolic Alkalosis
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis

1. Look at the pH to determine the primary process.
2. Calculate the anion gap Na (Cl HCO3)
3. Calculate the excess anion gap (total anion gap
   minus the normal anion gap) and add this to the
   measured HCO3 concentration, if gt30, there is
   underlying metabolic alkalosis if lt24, there is
   underlying non-gap metabolic acidosis

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Whats the Diagnosis?

• History of vomiting (metabolic alkalosis),
  alcoholic ketoacidosis (metabolic acidosis), and
  bacterial pneumonia (respiratory alkalosis)

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Example 9
pH 7.10
pCO2 50
HCO3 15
Na 145
Cl 100
Respiratory Acidosis, Anion gap Metabolic
Acidosis, Metabolic Alkalosis
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis

1. Look at the pH to determine the primary process.
2. Calculate the anion gap Na (Cl HCO3)
3. Calculate the excess anion gap (total anion gap
   minus the normal anion gap) and add this to the
   measured HCO3 concentration, if gt30, there is
   underlying metabolic alkalosis if lt24, there is
   underlying non-gap metabolic acidosis

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Whats the Diagnosis?

• Patient presented in an obtunded state
  (respiratory acidosis), history of vomiting
  (metabolic alkalosis), DKA (anion gap metabolic
  acidosis)
• Or
• Chronic respiratory acidosis and metabolic
  compensation in whom an acute anion gap metabolic
  acidosis developed

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Example 10
pH 7.15
pCO2 15
HCO3 5
Na 140
Cl 110
Anion Gap and Non-Anion Gap Metabolic Acidoses
Variable Primary Disorder Normal Range, arterial Gas Primary Disorder
pH Acidemia ?7.35-7.45? Alkalemia
pCO2 Respiratory alkalosis ?35 - 45? Respiratory acidosis
HCO3 Metabolic acidosis ?22 26? Metabolic Alkalosis

1. Look at the pH to determine the primary process.
2. Calculate the anion gap Na (Cl HCO3)
3. Calculate the excess anion gap (total anion gap
   minus the normal anion gap) and add this to the
   measured HCO3 concentration, if gt30, there is
   underlying metabolic alkalosis if lt24, there is
   underlying non-gap metabolic acidosis

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Whats the Diagnosis?

• DKA with non-gap acidosis during recovery phase
  of DKA due to failure to regenerate HCO3 from
  keto-acids lost in the urine

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Conclusions

• Acid-base disturbances are easy to analyze if
  approached systematically
• Determine primary abnormalities based on pH
• Calculate the anion gap
• Calculate the delta gap and add to the measured
  HCO3
• Calculate an anion gap on EVERY chemistry you see
• If there is an elevated anion gap, remember to
  get an ABG!!