Acid-Base Disturbances Clinical Approach 2006 Pravit Cadnapaphornchai

Acid-Base Acid-Base DisturbancesDisturbances

Clinical ApproachClinical Approach

20062006

Pravit CadnapaphornchaiPravit Cadnapaphornchai

Simple vs MixedSimple vs Mixed

SimpleSimple When compensation is appropriateWhen compensation is appropriate

MixedMixed When compensation is When compensation is ininappropriateappropriate

Simple Acid-Base DisturbancesSimple Acid-Base Disturbances

When compensation is appropriateWhen compensation is appropriate

Metabolic acidosis (Metabolic acidosis (↓ HCO↓ HCO33, ↓ pCO, ↓ pCO22))

Metabolic alkalosis (Metabolic alkalosis (↑ HCO↑ HCO33, ↑ pCO, ↑ pCO22))

Respiratory acidosis (Respiratory acidosis (↑ pCO↑ pCO22, ↑ HCO, ↑ HCO33))

Respiratory alkalosis (Respiratory alkalosis (↓ pCO↓ pCO22, ↓ HCO, ↓ HCO33))

Stepwise ApproachesStepwise Approaches

History & physical examinationHistory & physical examination Arterial blood gas for pH, pCOArterial blood gas for pH, pCO22, (HCO, (HCO33))

Use the HCOUse the HCO33 from ABG to determine compensation from ABG to determine compensation Serum Na, K, Cl, COSerum Na, K, Cl, CO22 content content

Use COUse CO22 content to calculate anion gap content to calculate anion gap Calculate anion gapCalculate anion gap

Anion gap = {Na - (Cl + COAnion gap = {Na - (Cl + CO22 content)} content)} Determine appropriate compensationDetermine appropriate compensation Determine the primary causeDetermine the primary cause

Organ dysfunctionOrgan dysfunction

CNSCNS – – respiratory acidosis (suppression) and alkalosis respiratory acidosis (suppression) and alkalosis (stimulation)(stimulation)

PulmonaryPulmonary – – respiratory acidosis (COPD) and alkalosis respiratory acidosis (COPD) and alkalosis (hypoxia, pulmonary embolism)(hypoxia, pulmonary embolism)

CardiacCardiac – – respiratory alkalosis, respiratory acidosis, respiratory alkalosis, respiratory acidosis, metabolic acidosis (pulmonary edema)metabolic acidosis (pulmonary edema)

GIGI – – metabolic alkalosis (vomiting) and acidosis metabolic alkalosis (vomiting) and acidosis (diarrhea)(diarrhea)

LiverLiver – respiratory alkalosis, metabolic acidosis (liver – respiratory alkalosis, metabolic acidosis (liver failure)failure)

KidneyKidney – metabolic acidosis (RTA) and alkalosis (1 – metabolic acidosis (RTA) and alkalosis (1stst aldosteone)aldosteone)

Organ DysfunctionOrgan Dysfunction

EndocrineEndocrine Diabetes mellitus – Diabetes mellitus – metabolic acidosismetabolic acidosis Adrenal insufficiency – metabolic acidosisAdrenal insufficiency – metabolic acidosis Cushing’s – metabolic alkalosisCushing’s – metabolic alkalosis Primary aldosteronism – metabolic alkalosisPrimary aldosteronism – metabolic alkalosis

Drugs/toxinsDrugs/toxins Toxic alcohols – metabolic acidosis Toxic alcohols – metabolic acidosis ASA – metabolic acidosis and respiratory alkalosisASA – metabolic acidosis and respiratory alkalosis Theophylline overdose – respiratory alkalosisTheophylline overdose – respiratory alkalosis






pH

< 7.35 7.4 >7.45

Acidosis

MetabolicRespiratory

Mixed Alkalosis

MetabolicRespiratory



Use the HCOUse the HCO33 from ABG to determine compensation from ABG to determine compensation Serum Na, K, Cl, Serum Na, K, Cl, COCO22 content content



CO2 content

Low Normal High

Metabolic acidosis Normal Metabolic alkalosis Resp alkalosis Mixed Resp acidosis

A normal CO2 content + high anion gap = metabolic acidosis +Metabolic alkalosis or metabolic ac + compensatory respiratory ac.






Calculation of Anion Gap in Calculation of Anion Gap in Metabolic AcidosisMetabolic Acidosis

Anion gap = Na – (Cl + HCO3)

Normal 8 ± 2

Correction for low serum albumin

Add (4-serum albumin g/dL) X 2.5 to the anion gap






Compensations for Metabolic Compensations for Metabolic DisturbancesDisturbances

Metabolic acidosisMetabolic acidosis pCOpCO22 = 1.5 x HCO = 1.5 x HCO33 + 8 ( + 8 ( ±± 2) 2)

Metabolic alkalosisMetabolic alkalosis pCOpCO22 increases by 7 for every 10 mEq increases by 7 for every 10 mEq

increases in HCOincreases in HCO33

How does the kidney How does the kidney compensate for metabolic compensate for metabolic

acidosis?acidosis?

How does the kidney compensate for How does the kidney compensate for metabolic acidosis?metabolic acidosis?

By reabsorbing all filtered HCOBy reabsorbing all filtered HCO33

By excreting HBy excreting H+ + as NHas NH44+ + (and (and

HH22POPO44-- ) )

InterpretationsInterpretations

Urine pH Urine pH < 5.5< 5.5

Urine anion gap Urine anion gap NegativeNegative

Compensations for Respiratory Compensations for Respiratory AcidosisAcidosis

Acute respiratory acidosisAcute respiratory acidosis HCOHCO33 increases by 1 for every 10 mm increases by 1 for every 10 mm

increases in pCOincreases in pCO22

Chronic respiratory acidosisChronic respiratory acidosis HCOHCO33 increases by 3 for every 10 mm increases by 3 for every 10 mm

increases in pCOincreases in pCO22

If you don’t have kidneys, can you have If you don’t have kidneys, can you have chronic respiratory acidosis?chronic respiratory acidosis?

Compensations for Respiratory Compensations for Respiratory AlkalosisAlkalosis

Acute respiratory alkalosisAcute respiratory alkalosis HCOHCO33 decreases by 2 for every 10 mm decreases by 2 for every 10 mm

decrease in pCOdecrease in pCO22

Chronic respiratory alkalosisChronic respiratory alkalosis HCOHCO33 decreases by 4 for every 10 mm decreases by 4 for every 10 mm

decrease in pCOdecrease in pCO22

If you don’t have kidneys can you have chronic If you don’t have kidneys can you have chronic respiratory alkalosis?respiratory alkalosis?

Mixed Acid-Base DisordersMixed Acid-Base Disorders

Mixed respiratory alkalosis & metabolic Mixed respiratory alkalosis & metabolic acidosisacidosis ASA overdoseASA overdose SepsisSepsis Liver failureLiver failure

Mixed respiratory acidosis & metabolic Mixed respiratory acidosis & metabolic alkalosisalkalosis COPD with excessive use of diureticsCOPD with excessive use of diuretics

Mixed Acid-Base DisordersMixed Acid-Base Disorders

Mixed respiratory acidosis & metabolic Mixed respiratory acidosis & metabolic acidosisacidosis Cardiopulmonary arrestCardiopulmonary arrest Severe pulmonary edemaSevere pulmonary edema

Mixed high gap metabolic acidosis & Mixed high gap metabolic acidosis & metabolic alkalosismetabolic alkalosis Renal failure with vomitingRenal failure with vomiting DKA with severe vomitingDKA with severe vomiting






Generation of Metabolic AcidosisGeneration of Metabolic Acidosis

H+

HCO3

-

Exogenous acids ASA Toxic alcohol

Endogenous acids ketoacids DKA starvation alcoholic Lactic acid L-lactic D-lactate

Administration of HCl, NH4

+Cl, CaCl2, lysine HCl

Loss of HCO3

diarrhea

Compensations

Buffers

Lungs

Kidneys

High gap Normal gap If kidney function is normal, urine anion gap Neg

H

HCO3

Loss of H+ from GIVomiting, NG suctionCongenital Cl diarrhea

Loss of H+ from kidney1st & 2nd aldosteroneACTHDiureticsBartter’s, Gitelman’s, Liddle’sInhibition of β – OH steroid deh

Gain of HCO3 Administered HCO3, Acetate, citrate, lactatePlasma protein products

Compensations

Buffer

Respiratory

Forget the kidney

CASE 1 CASE 1

A 24 year old diabetic was admitted for weakness.

Serum Na 140, K 1.8, Cl 125, CO2 6, anion gap 9.

pH 6.84 (H+ 144) pCO2 30, HCO3 5

Interpretation of Case 1Interpretation of Case 1

Patient has normal gap metabolic Patient has normal gap metabolic acidosisacidosis


Next determine the appropriateness of Next determine the appropriateness of respiratory compensationrespiratory compensation pCOpCO22 = 1.5 x HCO = 1.5 x HCO33 + 8 ( + 8 ( ±± 2) 2)

pCOpCO22 = 1.5 x 5 + 8 + 2 = 17.5 = 1.5 x 5 + 8 + 2 = 17.5 The patient’s pCOThe patient’s pCO22 is 30 is 30

The respiratory compensation is The respiratory compensation is inappropriateinappropriate


This patient has normal anion gap metabolic This patient has normal anion gap metabolic acidosis with inappropriate respiratory acidosis with inappropriate respiratory compensationcompensation

The finding does not fit DKA but is The finding does not fit DKA but is consistent with consistent with HCOHCO33 loss from the GI tract loss from the GI tract

or kidneyor kidney

How to differentiate normal How to differentiate normal gap acidosis resulting from GI gap acidosis resulting from GI

HCOHCO33 loss (diarrhea) vs dRTA? loss (diarrhea) vs dRTA?

Diarrhea vs RTADiarrhea vs RTA

DiarrheaDiarrhea HistoryHistory Urine pH < 5.5Urine pH < 5.5 Negative urine Negative urine

anion gapanion gap

dRTAdRTA HistoryHistory Urine pH > 5.5Urine pH > 5.5 Positive urine Positive urine

anion gapanion gap

Case 2Case 2A 26 year old woman, complains of weakness. She denies vomiting or taking medications.

P.E. A thin woman with contracted ECF.

Serum Na 133, K 3.1, Cl 90, CO2 content 32, anion gap11.

pH 7.48 (H+ 32), pCO2 43, HCO3 32.

UNa 52, UK 50, UCl 0, UpH 8


Determine the appropriateness of Determine the appropriateness of respiratory compensationrespiratory compensation For every increase of HCOFor every increase of HCO33 by 1, pCO by 1, pCO22 should should

increase by 0.7increase by 0.7 pCOpCO22 = 40 + (32-25) x 0.7 = 44.9 = 40 + (32-25) x 0.7 = 44.9

The patient’s pCOThe patient’s pCO22 = 43 = 43


This patient has metabolic alkalosis with This patient has metabolic alkalosis with appropriate respiratory compensationappropriate respiratory compensation


Urine NaUrine Na++ 52, UK 52, UK++ 50, Cl 50, Cl-- 0, pH 8 0, pH 8 Urine pH = 8 suggests presence of large Urine pH = 8 suggests presence of large

amount of HCOamount of HCO33. The increased UNa and UK . The increased UNa and UK

are to accompany HCOare to accompany HCO3 3 excretion. The excretion. The

kidney conserves Clkidney conserves Cl The findings are consistent with loss of The findings are consistent with loss of

HCl from the GI tractHCl from the GI tract Final diagnosis = Self-induced vomitingFinal diagnosis = Self-induced vomiting

Vomiting vs DiureticVomiting vs Diuretic

Active vomitingActive vomiting ECF depletionECF depletion Metabolic alkalosisMetabolic alkalosis High UNa, UK, High UNa, UK, low UCllow UCl Urine pH > 6.5Urine pH > 6.5

Remote vomitingRemote vomiting ECF depletionECF depletion Metabolic alkalosisMetabolic alkalosis Low UNa, high UK, low Low UNa, high UK, low

ClCl Urine pH 6Urine pH 6

Active diureticActive diuretic ECF depletionECF depletion Metabolic alkalosisMetabolic alkalosis HighHigh UNa, UK and UNa, UK and ClCl Urine pH 5-5.5Urine pH 5-5.5

Remote diureticRemote diuretic ECF depletionECF depletion Metabolic alkalosisMetabolic alkalosis Low UNa, high UK, low Low UNa, high UK, low

ClCl Urine pH 5-6Urine pH 5-6

Case 3Case 3

A 40 year old man developed pleuritic A 40 year old man developed pleuritic chest pain and hemoptysis. His BP 80/50. chest pain and hemoptysis. His BP 80/50. pH 7.4pH 7.4, , pCOpCO22 25 25, , HCOHCO33 15 15 and pO and pO22 50 50


A normal pH suggests mixed A normal pH suggests mixed disturbancesdisturbances


His pCOHis pCO22 is is 2525, his HCO, his HCO33 1515 If this is acute respiratory alkalosis his HCOIf this is acute respiratory alkalosis his HCO33

should have been 25-{(40-25) x 2/10}= should have been 25-{(40-25) x 2/10}= 2222 If this is chronic respiratory alkalosis, his HCOIf this is chronic respiratory alkalosis, his HCO33

should have been 25 – {(40-25) x 4/10} = should have been 25 – {(40-25) x 4/10} = 1919 If this is metabolic acidosis, his pCOIf this is metabolic acidosis, his pCO22 should have should have

been 1.5 x 15 + 8 = been 1.5 x 15 + 8 = 30-3130-31


He has combined respiratory alkalosis and He has combined respiratory alkalosis and metabolic acidosismetabolic acidosis

The likely diagnosis is pulmonary embolism with The likely diagnosis is pulmonary embolism with hypotension and lactic acidosis or pneumonia hypotension and lactic acidosis or pneumonia with sepsis and lactic acidosiswith sepsis and lactic acidosis

Other conditions are ASA overdose, sepsis, liver Other conditions are ASA overdose, sepsis, liver failurefailure

Case 4Case 4

A patient with COPD developed CHF. Prior to A patient with COPD developed CHF. Prior to treatment his treatment his pH 7.35, pCOpH 7.35, pCO22 was 60 and HCO was 60 and HCO33

3232. During treatment with diuretics he vomited a . During treatment with diuretics he vomited a few times. His pH after treatment was few times. His pH after treatment was 7.42, pCO7.42, pCO22

80, HCO80, HCO33 48. 48.


Pt’s data Pt’s data pH 7.35, pCOpH 7.35, pCO22 60 and HCO 60 and HCO33 32 32 For acute respiratory acidosis For acute respiratory acidosis

For every 10 mm elevation of pCOFor every 10 mm elevation of pCO22, HCO, HCO33 increases increases

by 1, his HCO3 should have been 25 + (60-40) x by 1, his HCO3 should have been 25 + (60-40) x 1/10 = 271/10 = 27

He did not have acute respiratory acidosisHe did not have acute respiratory acidosis


Pt’s data Pt’s data pH 7.35, pCOpH 7.35, pCO22 60 and HCO 60 and HCO33 32 32.. For chronic respiratory acidosisFor chronic respiratory acidosis

For every 10 mm elevation of pCOFor every 10 mm elevation of pCO22, HCO, HCO33 increases increases

by 3by 3 His HCOHis HCO33 should have been 25 + (60-40) x 3/10 = 31 should have been 25 + (60-40) x 3/10 = 31

His HCOHis HCO33 is 32 is 32

He had well compensated chronic respiratory He had well compensated chronic respiratory acidosisacidosis


His pH is now 7.42, pCOHis pH is now 7.42, pCO22 80, HCO 80, HCO33 48 48

If pCOIf pCO22 of 80 is due to chronic respiratory of 80 is due to chronic respiratory

acidosis, HCOacidosis, HCO33 should only be 32 +(80-60) x should only be 32 +(80-60) x

3/10=38 and not 483/10=38 and not 48 He had combined metabolic alkalosis and He had combined metabolic alkalosis and

respiratory acidosis after treatment of CHFrespiratory acidosis after treatment of CHF

Case 5Case 5

A cirrhotic patient was found to be A cirrhotic patient was found to be confusedconfused. Serum Na 133, K 3.3, Cl 115, . Serum Na 133, K 3.3, Cl 115, COCO22

content 14, anion gap 4content 14, anion gap 4 pH 7.44pH 7.44 (H (H+ + 36), 36), pCOpCO22 20, HCO 20, HCO33 13 13


Determine the respiratory compensationDetermine the respiratory compensation For chronic respiratory alkalosis, every 10 reduction in pCOFor chronic respiratory alkalosis, every 10 reduction in pCO22, ,

HCOHCO33 should decrease by 4 should decrease by 4 HCOHCO33 should be 25 - (40-20) x 4/10=17 should be 25 - (40-20) x 4/10=17 For acute respiratory alkalosis, HCOFor acute respiratory alkalosis, HCO33 = 21 = 21 Patient’s HCO3 is 13Patient’s HCO3 is 13, suggesting a metabolic acidotic , suggesting a metabolic acidotic

component is presentcomponent is present Anion gap is 4, even corrected for low albumin, is still low Anion gap is 4, even corrected for low albumin, is still low

suggesting a normal gap metabolic acidosissuggesting a normal gap metabolic acidosis Patient had combined metabolic acidosis and respiratory alkalosisPatient had combined metabolic acidosis and respiratory alkalosis

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Acid-Base Disturbances Clinical Approach 2006 Pravit Cadnapaphornchai