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Acid-Base Acid-Base DisordersDisorders
Adapted from Haber, R.J.: “A practical Approach to Acid-Base Adapted from Haber, R.J.: “A practical Approach to Acid-Base Disorders.” Disorders.” West J. Med West J. Med 1991 Aug; 155:156-1511991 Aug; 155:156-151
Allison B. Ludwig, M.D.Allison B. Ludwig, M.D.
Site Director, Jacobi Medicine Site Director, Jacobi Medicine ClerkshipClerkship
Goals:Goals:
Learn to work through acid-base Learn to work through acid-base disorders without nomograms or disorders without nomograms or complicated mathematical formulascomplicated mathematical formulas
Be able to recognize and work through Be able to recognize and work through multiple offsetting disorders that are multiple offsetting disorders that are coincident in the same patientcoincident in the same patient
Outline:Outline:
Data Base, Terms and DefinitionsData Base, Terms and Definitions Simple-Acid Base DisordersSimple-Acid Base Disorders Mixed Acid-Base DisordersMixed Acid-Base Disorders
Data BaseData Base
Arterial pHArterial pH Arterial pCO2Arterial pCO2 Serum HCO3 (best from blood chemistry)Serum HCO3 (best from blood chemistry)
Terms and DefinitionsTerms and Definitions
VariableVariable Primary Primary DisorderDisorder
Normal Range, Normal Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35 - 7.457.35 - 7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
Respiratory compensation for metabolic disorders is rapidRespiratory compensation for metabolic disorders is rapid Full metabolic compensation for respiratory disturbances Full metabolic compensation for respiratory disturbances
requires renal adjustment and takes 3-5 days requires renal adjustment and takes 3-5 days
Outline:Outline:
Data Base, Terms and DefinitionsData Base, Terms and Definitions
Simple-Acid Base DisordersSimple-Acid Base Disorders Mixed Acid-Base DisordersMixed Acid-Base Disorders
Simple Acid-Base Simple Acid-Base DisordersDisorders
Look at the pH in order to determine the Look at the pH in order to determine the primary abnormalityprimary abnormality
Pathophysiologic principle: body does not Pathophysiologic principle: body does not fully compensate even for chronic acid-base fully compensate even for chronic acid-base disordersdisorders
Example #1Example #1
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
pHpH 7.507.50
pCO2pCO2 2929
HCO3HCO3 2222
Acute Respiratory Alkalosis
Causes of Acute Causes of Acute Respiratory AlkalosisRespiratory Alkalosis
AnxietyAnxiety HypoxiaHypoxia Lung disease with or without hypoxiaLung disease with or without hypoxia CNS diseaseCNS disease Drug use—salicylates, catecholamines, Drug use—salicylates, catecholamines,
progesteroneprogesterone PregnancyPregnancy SepsisSepsis Hepatic EncephalopathyHepatic Encephalopathy Mechanical VentilationMechanical Ventilation
Example #2Example #2
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
pHpH 7.257.25
pCO2pCO2 6060
HCO3HCO3 2626
Acute Respiratory Acidosis
Causes of Acute Causes of Acute Respiratory AcidosisRespiratory Acidosis
CNS depression—drugs, CNS eventCNS depression—drugs, CNS event Neuromuscular disorders—myopathies, Neuromuscular disorders—myopathies,
neuropathiesneuropathies Acute airway obstruction—upper airway, Acute airway obstruction—upper airway,
laryngospasm, bronchospasmlaryngospasm, bronchospasm Severe pneumonia or pulmonary edemaSevere pneumonia or pulmonary edema Impaired lung motion—hemothorax, Impaired lung motion—hemothorax,
pneumothoraxpneumothorax Thoracic cage injury—flail chestThoracic cage injury—flail chest Ventilator dysfunctionVentilator dysfunction
Example #3Example #3
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
pHpH 7.347.34
pCO2pCO2 6060
HCO3HCO3 3131
Chronic Respiratory Acidosis with Metabolic Compensation
Causes of Chronic Causes of Chronic Respiratory AcidosisRespiratory Acidosis
Chronic lung disease—obstructive or Chronic lung disease—obstructive or restrictiverestrictive
Chronic neuromuscular disordersChronic neuromuscular disorders Chronic respiratory center depression—Chronic respiratory center depression—
central hypoventilationcentral hypoventilation
Example #4Example #4
VariablVariablee
Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
pHpH 7.507.50
pCO2pCO2 4848
HCO3HCO3 3636
Metabolic Alkalosis
Causes of Metabolic Causes of Metabolic AlkalosisAlkalosis
VomitingVomiting DiureticsDiuretics Excess mineralocorticoid activity—Cushing’s Excess mineralocorticoid activity—Cushing’s
syndrome, Conn’s syndrome, exogenous syndrome, Conn’s syndrome, exogenous steroids, licorice ingestion, increased renin steroids, licorice ingestion, increased renin states, Bartter’s syndromestates, Bartter’s syndrome
Excess alkali administrationExcess alkali administration Refeeding alkalosisRefeeding alkalosis
Example #5Example #5
VariablVariablee
Primary Primary DisorderDisorder
Normal Range, Normal Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
pHpH 7.207.20
pCO2pCO2 2121
HCO3HCO3 88
Metabolic Acidosis with Respiratory Compensation
Causes of Metabolic Causes of Metabolic AcidosisAcidosis
Non-GapNon-Gap GI HCO3 loss: diarrhea, ureteral diversionsGI HCO3 loss: diarrhea, ureteral diversions Renal HCO3 loss: RTA, aldosterone inhibitors, Renal HCO3 loss: RTA, aldosterone inhibitors,
carbonic anhydrase inhibitorscarbonic anhydrase inhibitors Iatrogenic: normal saline Iatrogenic: normal saline
Anion GapAnion Gap Ketoacidosis: diabetic, alcoholicKetoacidosis: diabetic, alcoholic Renal failureRenal failure Lactic AcidosisLactic Acidosis RhabdomyolysisRhabdomyolysis Toxins: methanol, ethylene glycol, paraldehyde, Toxins: methanol, ethylene glycol, paraldehyde,
salicylatessalicylates
Outline:Outline:
Data Base, Terms and DefinitionsData Base, Terms and Definitions Simple-Acid Base DisordersSimple-Acid Base Disorders
Mixed Acid-Base DisordersMixed Acid-Base Disorders
The RulesThe Rules Look at the pH: whichever side of 7.40 the pH is on, the 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 process that caused it to shift to that side is the primary abnormalityabnormality Principle: the body doesn’t fully compensate for primary acid-base Principle: the body doesn’t fully compensate for primary acid-base
disordersdisorders Calculate the anion gap: Na – (Cl + HCO3): if the anion Calculate the anion gap: Na – (Cl + HCO3): if the anion
gap is >20, there is a primary metabolic acidosis regardless gap is >20, there is a primary metabolic acidosis regardless of pH or HCO3of pH or HCO3 Principle: the body doesn’t generate a large anion gap to Principle: the body doesn’t generate a large anion gap to
compensate for a primary disordercompensate for a primary disorder Calculate the excess anion gap (total anion gap minus the Calculate the excess anion gap (total anion gap minus the
normal anion gap) and add this to the measured HCO3 normal anion gap) and add this to the measured HCO3 concentration, if >30, there is underlying metabolic concentration, if >30, there is underlying metabolic alkalosis; if <24, there is underlying non-gap metabolic alkalosis; if <24, there is underlying non-gap metabolic acidosisacidosis Principle: 1 mmol of unmeasured acid titrates 1 mmol of Principle: 1 mmol of unmeasured acid titrates 1 mmol of
bicarbonatebicarbonate
Understanding the anion Understanding the anion gapgap
Each millimolar decrease in HCO3 is accompanied by Each millimolar decrease in HCO3 is accompanied by a millimolar increase in the anion gap, the sum of the a millimolar increase in the anion gap, the sum of the new (excess) anion gap and the remaining (measured) new (excess) anion gap and the remaining (measured) HCO3 value should be equal to a normal bicarbonate HCO3 value should be equal to a normal bicarbonate concentrationconcentration
Example #6Example #6
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
Respiratory Alkalosis and Anion Gap Metabolic Acidosis
1.1. Look at the pH to determine the Look at the pH to determine the primary process. primary process.
2.2. Calculate the anion gap: Na – (Cl + Calculate the anion gap: Na – (Cl + HCO3) HCO3)
3.3. Calculate the excess anion gap (total Calculate the excess anion gap (total anion gap minus the normal anion anion gap minus the normal anion gap) and add this to the measured gap) and add this to the measured HCO3 concentration, if >30, there is HCO3 concentration, if >30, there is underlying metabolic alkalosis; if underlying metabolic alkalosis; if <24, there is underlying non-gap <24, there is underlying non-gap metabolic acidosismetabolic acidosis
pHpH 7.507.50
pCO2pCO2 2020
HCO3HCO3 1515
NaNa 140140
ClCl 103103
What’s the Diagnosis?What’s the Diagnosis?
Salicylate OverdoseSalicylate Overdose
Example #7Example #7
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.35-7.457.45
AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
Anion Gap Metabolic Acidosis and Metabolic Alkalosis
pHpH 7.407.40
pCO2pCO2 4040
HCO3HCO3 2424
NaNa 145145
ClCl 1001001.1. Look at the pH to determine the Look at the pH to determine the
primary process. primary process. 2.2. Calculate the anion gap: Na – (Cl + Calculate the anion gap: Na – (Cl +
HCO3) HCO3) 3.3. Calculate the excess anion gap (total Calculate the excess anion gap (total
anion gap minus the normal anion anion gap minus the normal anion gap) and add this to the measured gap) and add this to the measured HCO3 concentration, if >30, there is HCO3 concentration, if >30, there is underlying metabolic alkalosis; if underlying metabolic alkalosis; if <24, there is underlying non-gap <24, there is underlying non-gap metabolic acidosismetabolic acidosis
What’s the Diagnosis?What’s the Diagnosis?
Chronic renal failure in a Chronic renal failure in a patient with vomiting as patient with vomiting as
his uremia worsened.his uremia worsened.
Example #8Example #8
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
Respiratory alkalosis, Anion Gap Metabolic Acidosis and Metabolic Alkalosis
pHpH 7.507.50
pCO2pCO2 2020
HCO3HCO3 1515
NaNa 145145
ClCl 1001001.1. Look at the pH to determine the Look at the pH to determine the
primary process. primary process. 2.2. Calculate the anion gap: Na – (Cl + Calculate the anion gap: Na – (Cl +
HCO3) HCO3) 3.3. Calculate the excess anion gap (total Calculate the excess anion gap (total
anion gap minus the normal anion anion gap minus the normal anion gap) and add this to the measured gap) and add this to the measured HCO3 concentration, if >30, there is HCO3 concentration, if >30, there is underlying metabolic alkalosis; if underlying metabolic alkalosis; if <24, there is underlying non-gap <24, there is underlying non-gap metabolic acidosismetabolic acidosis
What’s the Diagnosis?What’s the Diagnosis?
History of vomiting History of vomiting (metabolic alkalosis), (metabolic alkalosis), alcoholic ketoacidosis alcoholic ketoacidosis
(metabolic acidosis), and (metabolic acidosis), and bacterial pneumonia bacterial pneumonia
(respiratory alkalosis)(respiratory alkalosis)
Example #9Example #9
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
Respiratory Acidosis, Anion gap Metabolic Acidosis, Metabolic Alkalosis
1.1. Look at the pH to determine the Look at the pH to determine the primary process. primary process.
2.2. Calculate the anion gap: Na – (Cl + Calculate the anion gap: Na – (Cl + HCO3) HCO3)
3.3. Calculate the excess anion gap (total Calculate the excess anion gap (total anion gap minus the normal anion anion gap minus the normal anion gap) and add this to the measured gap) and add this to the measured HCO3 concentration, if >30, there is HCO3 concentration, if >30, there is underlying metabolic alkalosis; if underlying metabolic alkalosis; if <24, there is underlying non-gap <24, there is underlying non-gap metabolic acidosismetabolic acidosis
pHpH 7.107.10
pCO2pCO2 5050
HCO3HCO3 1515
NaNa 145145
ClCl 100100
What’s the Diagnosis?What’s the Diagnosis?
Patient presented in an obtunded state Patient presented in an obtunded state (respiratory acidosis), history of vomiting (respiratory acidosis), history of vomiting
(metabolic alkalosis), DKA (anion gap (metabolic alkalosis), DKA (anion gap metabolic acidosis)metabolic acidosis)
OrOr
Chronic respiratory acidosis and metabolic Chronic respiratory acidosis and metabolic compensation in whom an acute anion gap compensation in whom an acute anion gap
metabolic acidosis developedmetabolic acidosis developed
Example #10Example #10
VariableVariable Primary Primary DisorderDisorder
Normal Normal Range, Range, arterial Gasarterial Gas
Primary Primary DisorderDisorder
pHpH AcidemiaAcidemia 7.35-7.457.35-7.45 AlkalemiaAlkalemia
pCO2pCO2 Respiratory Respiratory alkalosisalkalosis
35 - 4535 - 45 Respiratory Respiratory acidosisacidosis
HCO3HCO3 Metabolic Metabolic acidosisacidosis
22 – 2622 – 26 Metabolic Metabolic AlkalosisAlkalosis
Anion Gap and Non-Anion Gap Metabolic Acidoses
1.1. Look at the pH to determine the Look at the pH to determine the primary process. primary process.
2.2. Calculate the anion gap: Na – (Cl + Calculate the anion gap: Na – (Cl + HCO3) HCO3)
3.3. Calculate the excess anion gap (total Calculate the excess anion gap (total anion gap minus the normal anion anion gap minus the normal anion gap) and add this to the measured gap) and add this to the measured HCO3 concentration, if >30, there is HCO3 concentration, if >30, there is underlying metabolic alkalosis; if underlying metabolic alkalosis; if <24, there is underlying non-gap <24, there is underlying non-gap metabolic acidosismetabolic acidosis
pHpH 7.157.15
pCO2pCO2 1515
HCO3HCO3 55
NaNa 140140
ClCl 110110
What’s the Diagnosis?What’s the Diagnosis?
DKA with non-gap DKA with non-gap acidosis during recovery acidosis during recovery
phase of DKA due to phase of DKA due to failure to regenerate failure to regenerate
HCO3 from keto-acids HCO3 from keto-acids lost in the urinelost in the urine
ConclusionsConclusions
Acid-base disturbances are easy to analyze if Acid-base disturbances are easy to analyze if approached systematicallyapproached systematically
Determine primary abnormalities based on pHDetermine primary abnormalities based on pH Calculate the anion gapCalculate the anion gap Calculate the delta gap and add to the Calculate the delta gap and add to the
measured HCO3 measured HCO3 Calculate an anion gap on EVERY chemistry Calculate an anion gap on EVERY chemistry
you seeyou see If there is an elevated anion gap, remember to If there is an elevated anion gap, remember to
get an ABG!!get an ABG!!