Acid Base Disturbances

Acid and Base DisturbancesAcid and Base DisturbancesD. W. Daugherty, DOD. W. Daugherty, DO

SURGICAL CRITICAL CARESURGICAL CRITICAL CARE

Simple vs. MixedSimple vs. Mixed

• SimpleSimple When compensation is appropriateWhen compensation is appropriate

• MixedMixed When compensation is inappropriateWhen compensation is inappropriate

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 CushingCushing’’s – metabolic alkalosiss – 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

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.




Calculate anion gapCalculate anion gap Anion gap = {Na - (Cl + COAnion gap = {Na - (Cl + CO22 content)} content)}






Calculate anion gapCalculate anion gap Anion gap = {Na - (Cl + COAnion gap = {Na - (Cl + CO22 content)} (normal = 8-12) content)} (normal = 8-12)



Compensations for Metabolic DisturbancesCompensations for Metabolic Disturbances

• 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 increase increases by 7 for every 10 mEq increase

in HCOin 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 H(and H22POPO44

-- ) )

Urine pH Urine pH < 5.5< 5.5

Urine anion gap NegativeUrine anion gap Negative

Compensations for Respiratory AcidosisCompensations for Respiratory Acidosis

• Acute respiratory acidosisAcute respiratory acidosis HCOHCO33 increases by 1 for every 10 increase in increases by 1 for every 10 increase in

pCOpCO22

• Chronic respiratory acidosisChronic respiratory acidosis HCOHCO33 increases by 3 for every 10 increase in increases by 3 for every 10 increase in

pCOpCO22

Compensations for Respiratory AlkalosisCompensations for Respiratory Alkalosis

• Acute respiratory alkalosisAcute respiratory alkalosis HCOHCO33 decreases by 2 for every 10 decrease in decreases by 2 for every 10 decrease in

pCOpCO22

• Chronic respiratory alkalosisChronic respiratory alkalosis HCOHCO33 decreases by 4 for every 10 decrease in decreases by 4 for every 10 decrease in

pCOpCO22

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.

Na 140K 1.8Cl 125CO2 6Gap 9

pH 6.84 (H+ 144)pCO2 30HCO3 5

Interpretation of Case 1Interpretation of Case 1

Patient has normal gap Patient has normal gap metabolic acidosismetabolic acidosis


• Next determine the appropriateness of respiratory Next determine the appropriateness of respiratory compensationcompensation 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 patientThe patient’s pCO’s pCO22 is 30 is 30

• The respiratory compensation is inappropriateThe respiratory compensation is inappropriate


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 HCOconsistent with HCO33 loss from the GI tract loss from the GI tract

or kidneyor kidney

How do you differentiate a How do you differentiate a normal gap acidosis resulting normal gap acidosis resulting from GI HCOfrom GI HCO33 loss (diarrhea) loss (diarrhea)

vs RTA?vs RTA?

Diarrhea vs RTADiarrhea vs RTA

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

anion gapanion gap

• RTARTA 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.

Na 133K 3.1Cl 90CO2 32Gap 11

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

UNa 52 / UK 50 / UCl 0 / UpH 8


• Determine the appropriateness of respiratory Determine the appropriateness of respiratory compensationcompensation 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 patientThe patient’’s pCOs 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 amount Urine pH = 8 suggests presence of large amount

of HCOof HCO33. The increased UNa and UK are to . The increased UNa and UK are to

accompany HCOaccompany HCO3 3 excretion. The kidney excretion. The kidney

conserves Cl conserves Cl The findings are consistent with loss of HCl The findings are consistent with loss of HCl

from the GI tractfrom 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, low UClHigh UNa, UK, low 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 High UNa, UK and ClHigh UNa, UK and Cl 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 chest A 40 year old man developed pleuritic chest pain and hemoptysis. His BP 80/50. pain and hemoptysis. His BP 80/50.

pH 7.4pH 7.4

pCOpCO22 25 25

HCOHCO33 15 15

pOpO22 50 50


A normal pH suggests mixed disturbancesA normal pH suggests mixed disturbances

Interpretation of Case 3Interpretation of Case 3 His pCOHis pCO22 is 25, his HCO is 25, his HCO33 15 15

If this is acute respiratory alkalosis his HCOIf this is acute respiratory alkalosis his HCO33

should have been 25-{(40-25) x 2/10}= 22should have been 25-{(40-25) x 2/10}= 22

If this is chronic respiratory alkalosis, his HCOIf this is chronic respiratory alkalosis, his HCO33

should have been 25 – {(40-25) x 4/10} = 19should have been 25 – {(40-25) x 4/10} = 19

If this is metabolic acidosis, his pCOIf this is metabolic acidosis, his pCO22 should have should have

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

Interpretation of Case 3Interpretation of Case 3 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 treatmenttreatmentpH 7.35pH 7.35

pCOpCO22 60 60

HCOHCO33 32 32

During treatment with diuretics he vomited a few During treatment with diuretics he vomited a few times. His pH after treatment was times. His pH after treatment was pH7.42 / pCOpH7.42 / pCO22 80 / HCO 80 / HCO33 48 48


PtPt’’s data pH 7.35, pCOs data pH 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 by increases by

1, his HCO3 should have been 25 + (60-40) x 1/10 = 1, his HCO3 should have been 25 + (60-40) x 1/10 = 2727

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

Interpretation of Case 4Interpretation of Case 4 PtPt’’s data pH 7.35, pCOs data pH 7.35, pCO22 60 and HCO 60 and HCO33 32 32

For chronic respiratory acidosisFor chronic respiratory acidosis For every 10mm elevation of pCOFor every 10mm elevation of pCO22, HCO, HCO33 increases by 3 increases by 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

Interpretation of Case 4Interpretation of Case 4 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 confusedA cirrhotic patient was found to be confused. .

Na 133Na 133

K 3.3K 3.3

Cl 115Cl 115

COCO22 14 14

Gap 4Gap 4

pH 7.44 (HpH 7.44 (H+ + 36) 36)

pCOpCO22 20 20

HCOHCO33 13 13

Interpretation of Case 5Interpretation of Case 5 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 PatientPatient’’s HCO3 is 13, suggesting a metabolic acidotic s HCO3 is 13, 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

Acid Base Disturbances

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