Acid-Base DisordersAcid-Base Disorders

Robert Fields, DORobert Fields, DO

St Joseph’s Mercy Hospital St Joseph’s Mercy Hospital Emergency Dept.Emergency Dept.

5 Steps is all you need5 Steps is all you need

Check the pH Check the pH Find the primary disorder (Look at Find the primary disorder (Look at

pCO2 and HCO3)pCO2 and HCO3) Calculate the anion gap (AG=Na – Calculate the anion gap (AG=Na –

(HCO3 + Cl-)(HCO3 + Cl-) Calculate the excess anion gap (AGp - Calculate the excess anion gap (AGp -

AGn + HCO3p = X) AGn + HCO3p = X) Winters formula pCO2 = 1.5(HCO3-) + Winters formula pCO2 = 1.5(HCO3-) +

88

What do you really need to do What do you really need to do this?this?

ABG, with pCO2 and pHABG, with pCO2 and pH Chem 7 with Na+, Cl-, HCO3-Chem 7 with Na+, Cl-, HCO3-

STEP 1, Check the pHSTEP 1, Check the pH

Acidemia, pH < 7.35Acidemia, pH < 7.35 Alkalemia, pH >7.45Alkalemia, pH >7.45 Made Simpler! Made Simpler!

Acidemia<7.40>AlkalemiaAcidemia<7.40>Alkalemia Acidosis/Alkalosis vs. Acidemia/AlkalemiaAcidosis/Alkalosis vs. Acidemia/Alkalemia Know the “normals” of the rest. (This is Know the “normals” of the rest. (This is

not to hard as it is printed in the not to hard as it is printed in the computer) computer)

STEP 2, Find the Basic STEP 2, Find the Basic ProblemProblem

Look at the pCO2 and the HCO3-Look at the pCO2 and the HCO3- Respiratory problems relate to pCO2 Respiratory problems relate to pCO2 Metabolic problems relate to HCO3-Metabolic problems relate to HCO3-

Respiratory AcidosisRespiratory Acidosis

CausesCauses CNS depressionCNS depression NMS disordersNMS disorders Pulmonary edemaPulmonary edema Ventilatory dysfunctionVentilatory dysfunction

Respiratory AlkalosisRespiratory Alkalosis

CausesCauses AnxietyAnxiety HypoxiaHypoxia CNS stimulantsCNS stimulants PregnancyPregnancy Sepsis Sepsis Excessive mechanical ventilationExcessive mechanical ventilation

Metabolic AlkalosisMetabolic Alkalosis

Chloride Chloride responsiveresponsive

VomitingVomiting DiureticsDiuretics DehydrationDehydration

Chloride Chloride unresponsiveunresponsive

Excess mineral Excess mineral corticoid activitycorticoid activity

Cushing's, Conn’sCushing's, Conn’s The infamous The infamous

licorice ingestionlicorice ingestion

STEP 3, Check the Anion STEP 3, Check the Anion GapGap

What What is is the Anion Gap?the Anion Gap?

Cations = AnionsCations = Anions Na+ + K+ etc. = HC03- + Cl- + Alb + Na+ + K+ etc. = HC03- + Cl- + Alb +

etcetc SimplifiedSimplified Na+ = HC03- + Cl- + othersNa+ = HC03- + Cl- + others We will call the others, AG (anion gap) We will call the others, AG (anion gap)

and solve for AG.and solve for AG. Therefore AG = Na+ - (HCO3- + Cl-)Therefore AG = Na+ - (HCO3- + Cl-)

Increased Anion GapIncreased Anion Gap Metabolic Acidosis Metabolic Acidosis

Methanol Methanol UremiaUremia DKA (starvation ketosis, alcohol ketosis)DKA (starvation ketosis, alcohol ketosis) ParaldehydeParaldehyde INH, IronINH, Iron Lactic Acidemia (type A, B, D)Lactic Acidemia (type A, B, D) Ethanol, Ethylene GlycolEthanol, Ethylene Glycol SalicylatesSalicylates

Columbia Encyclopedia: paraldehyde (pârăl'dəhīd') , nervous system depressant similar to alcohol in its effects and

used as a sedative. A colorless flammable liquid with a disagreeable odor, paraldehyde produces sleep for up to 12 hr. with little or no muscle, heart, or

respiratory depression. It is often given to alcoholics having delirium tremens, to induce sleep, and is also used to calm psychiatric patients. Like

alcohol and other depressants it is addictive (see drug addiction and drug abuse). Paraldehyde is also used in the manufacture of synthetic resins, as a preservative, and in preparing leather. It is produced

by treating acetaldehyde with a small amount of sulfuric acid.

Normal Anion GapNormal Anion GapMetabolic AcidosisMetabolic Acidosis

Gastrointestinal Gastrointestinal

DiarrheaDiarrhea

Ureteral diversionUreteral diversion

Renal LossRenal Loss

RTARTA

Early renal failureEarly renal failure

AcetozolamideAcetozolamide

Aldosterone Aldosterone inhibitorsinhibitors

140

104

24

12

Na+ Normal AG

mm

ol/

L

Na+/Cl- HCO3 AG

+ H+

Lactic Acid ProductionLactic Acid Production

++ H+ H+ ++ HCO3-HCO3-

H2CO3H2CO3 CO2 + H2O CO2 + H2O ++

Buffering SpeciesBuffering Species

CO2 + H2O <----> H2CO3 CO2 + H2O <----> H2CO3

carbonic anyhdrasecarbonic anyhdrase

H2CO3 <----> HCO3- + H+H2CO3 <----> HCO3- + H+

140

104

24

12

Na+ Normal AG

mm

ol/

L

Na+/Cl- HCO3 AG

140

104 104

24 12

12 24

Na+ Normal AG Acidosis

mm

ol/

L

Na+/Cl- HCO3 AG

STEP 4, Check the Anion Gap STEP 4, Check the Anion Gap ExcessExcess

This is going to help you determine if This is going to help you determine if there is an alkalosis or acidosis that there is an alkalosis or acidosis that is NOT related to the anion gap.is NOT related to the anion gap.

This done by doing this equationThis done by doing this equation AGp – AGn + HCO3-p = XAGp – AGn + HCO3-p = X X should equal 24 if there is no X should equal 24 if there is no

additional acidosis or alkalosis.additional acidosis or alkalosis.

The results of Step 4The results of Step 4

If you calculated < 20 mmol/LIf you calculated < 20 mmol/L

There is a an acidosis present that is There is a an acidosis present that is unrelated to the AG.unrelated to the AG.

If you calculated >30 mmol/L there is If you calculated >30 mmol/L there is an alkalosis present.an alkalosis present.

What we are doing so far ?What we are doing so far ?

1. Determine the pH1. Determine the pH 2. Finding primary disorder2. Finding primary disorder 3. Finding AG Metabolic Acidosis if not 3. Finding AG Metabolic Acidosis if not

already recognizedalready recognized 4. Finding Metabolic Acidosis 4. Finding Metabolic Acidosis

(unrelated to the AG) and/or (unrelated to the AG) and/or metabolic Alkalosis if not yet metabolic Alkalosis if not yet recognized.recognized.

So What’s Left?So What’s Left?

Respiratory Alkalosis or Acidosis that Respiratory Alkalosis or Acidosis that may have gone unrecognized.may have gone unrecognized.

Winter’s formulaWinter’s formula pCO2 = 1.5 (HCO3) + 8 +-2pCO2 = 1.5 (HCO3) + 8 +-2

ExamplesExamples

Example 1Example 1

pH, 7.50pH, 7.50 pCO2, 20mm HgpCO2, 20mm Hg Na+, 140 mmol/LNa+, 140 mmol/L Cl-, 103 mmol/LCl-, 103 mmol/L HCO3-, 15HCO3-, 15

ResultsResults

AlkalemiaAlkalemia Primary disorder, respiratoryPrimary disorder, respiratory AG is 22, Therefore metabolic acidosis AG is 22, Therefore metabolic acidosis

with AG. A-ha! Two disorders are present.with AG. A-ha! Two disorders are present. Excess AG, 22- 12 + 15 = 25 , no alkalosis Excess AG, 22- 12 + 15 = 25 , no alkalosis

or acidosis otherwise present.or acidosis otherwise present. Don’t need to do Winter’s as you can only Don’t need to do Winter’s as you can only

have one respiratory problem.have one respiratory problem. Clinical correlation?Clinical correlation?

Salicylate ToxicitySalicylate Toxicity

Example 2Example 2

pH, 7.40pH, 7.40 pCO2, 40mm HgpCO2, 40mm Hg Na+, 145 mmol/LNa+, 145 mmol/L Cl-, 100 mmol/LCl-, 100 mmol/L HCO3-, 24HCO3-, 24

ResultsResults

pH? NormalpH? Normal Primary, What Primary?Primary, What Primary? Anion Gap = 21Anion Gap = 21 Excess anion gap = 21-12 + 24 =33, Excess anion gap = 21-12 + 24 =33,

A significant metabolic alkalosis is A significant metabolic alkalosis is present too!present too!

Winter’s ? Nothing too bad here. Winter’s ? Nothing too bad here. Clinical Correlation?Clinical Correlation?

CRI (AG acidosis) with vomiting CRI (AG acidosis) with vomiting as uremia worsenedas uremia worsened

Example 3Example 3

pH, 7.50pH, 7.50 pCO2, 20mm HgpCO2, 20mm Hg Na+, 145 mmol/LNa+, 145 mmol/L Cl-, 100 mmol/LCl-, 100 mmol/L HCO3-, 15HCO3-, 15

Example 3Example 3

AlkalemiaAlkalemia Respiratory primarilyRespiratory primarily Anion Gap is 30, AG MA (MUDPILES)Anion Gap is 30, AG MA (MUDPILES) Excess anion gap plus HC03 = 30-12 Excess anion gap plus HC03 = 30-12

+ 15 = 33, There it is the triple threat.+ 15 = 33, There it is the triple threat. Don’t need Winter’s, respiratory Don’t need Winter’s, respiratory

determined as primary.determined as primary.

Clinical CorrelationClinical Correlation

Vomiting (metabolic alkalosis)Vomiting (metabolic alkalosis) Alcoholic ketoacidosis (AG metabolic Alcoholic ketoacidosis (AG metabolic

acidosis)acidosis) Pneumonia, (Respiratory alkalosis)Pneumonia, (Respiratory alkalosis)

Example 4Example 4

pH, 7.10pH, 7.10 pCO2, 50mm HgpCO2, 50mm Hg Na+, 145 mmol/LNa+, 145 mmol/L Cl-, 100 mmol/LCl-, 100 mmol/L HCO3-, 15HCO3-, 15

Example 4Example 4

AcidemiaAcidemia Respiratory and MetabolicRespiratory and Metabolic Anion Gap is 30, you know the drillAnion Gap is 30, you know the drill Excess AG + HCO3 = 30-12+15=33, Excess AG + HCO3 = 30-12+15=33,

Metabolic Alkalosis.Metabolic Alkalosis. Clinical Correlation?Clinical Correlation?

Clinical CorrelationClinical Correlation

DKA with vomiting, followed by DKA with vomiting, followed by aspiration and unresponsive.aspiration and unresponsive.

Example 5Example 5

pH 7.25pH 7.25 pCO2, 45pCO2, 45 Na+, 137Na+, 137 Cl-, 79Cl-, 79 HCO3-, 20HCO3-, 20

Example 5Example 5

AcidemiaAcidemia MetabolicMetabolic AG=38AG=38 38-12 + 20 = 4638-12 + 20 = 46 Winter’s ! 1.5(20) + 8 = 38Winter’s ! 1.5(20) + 8 = 38

Clinical CorrelationClinical Correlation

Borhaave’s Esophageal RuptureBorhaave’s Esophageal Rupture Anion Gap Acidosis from lactic acid Anion Gap Acidosis from lactic acid

and ketoacidosisand ketoacidosis Metabolic alkalosis from profound Metabolic alkalosis from profound

dehydration and loss of gastric HCL dehydration and loss of gastric HCL into chest wallinto chest wall

Respiratory acidosis from large Respiratory acidosis from large pleural effusion.pleural effusion.

ReferencesReferences

1991 West J. Medicine, A Practical 1991 West J. Medicine, A Practical Approach to Acid-Base Disorders.Approach to Acid-Base Disorders.