The Minimalist approach to The Minimalist approach to acid/base disturbancesacid/base disturbances

ABG’s so easy….a GEICO rep can do itABG’s so easy….a GEICO rep can do it

OBJECTIVESOBJECTIVES

Acid/Base terminology and definitionsAcid/Base terminology and definitions

Normal physiologic acid/base regulation Normal physiologic acid/base regulation

Acid/base disturbances Acid/base disturbances

ABG interpretationABG interpretation

Case studiesCase studies

Acid/Base terminology and Acid/Base terminology and definitionsdefinitions

Acid/Base regulation / Control Acid/Base regulation / Control of( H+)concentrationof( H+)concentration– Acid—proton (H+) donor increases (H+)Acid—proton (H+) donor increases (H+)– Base—proton (H+) acceptor decreases (H+) Base—proton (H+) acceptor decreases (H+)

Ph is the logarithmic/exponential Ph is the logarithmic/exponential representation of (H+) concentration in representation of (H+) concentration in eq/litereq/liter

What is log????What is log????

10 =10(1) log 10= 110 =10(1) log 10= 1

100=10(2) log 100=2100=10(2) log 100=2

1000=10 (3) log1000=31000=10 (3) log1000=3

0.1= 10 (-1) log 0.1 = -10.1= 10 (-1) log 0.1 = -1

0.01 = 10 (-2) log 0.01= -20.01 = 10 (-2) log 0.01= -2

ph = - Log (H+)ph = - Log (H+)

ph = 6 (H+) = 10 (-6) eq/liter 0.000001 ph = 6 (H+) = 10 (-6) eq/liter 0.000001 eq/litereq/liter

ph = 7 (H+) = 10 (-7) eq/liter ph = 7 (H+) = 10 (-7) eq/liter 0.0000001eq/liter0.0000001eq/liter

ph = (H+) = 10(-8) eq/liter ph = (H+) = 10(-8) eq/liter 0.00000001 eq/liter0.00000001 eq/liter

H20 <<<<< (H+) + ( OH-)H20 <<<<< (H+) + ( OH-)

(H+) = 10(-7) eq/liter(H+) = 10(-7) eq/liter

Pure Water has a ph 7(chemical neutral)Pure Water has a ph 7(chemical neutral)

Physiologic regulation of Physiologic regulation of extracellular phextracellular ph

Normal physiologic ph = 7.4Normal physiologic ph = 7.4

Essential for normal enzymatic reactionsEssential for normal enzymatic reactions

Control Mechanisms/ Normal Control Mechanisms/ Normal physiologyphysiology

Buffer systems (immediate)Buffer systems (immediate)

Respiratory (seconds)Respiratory (seconds)

Renal (hours-days)Renal (hours-days)

Buffer solutionsBuffer solutions

Solution of two or more compoundsSolution of two or more compounds

Prevent marked changes in ph when acid Prevent marked changes in ph when acid or base is addedor base is added

Bicarbonate BufferBicarbonate Buffer

H20 + CO2 <<< H2CO3 <<( H+)+ HCO3-H20 + CO2 <<< H2CO3 <<( H+)+ HCO3-

Henderson/Haselbalch EquationHenderson/Haselbalch Equation

ph = 6.1 + log HCO3-/ CO2ph = 6.1 + log HCO3-/ CO2

HCO3-/CO2= 20HCO3-/CO2= 20

Ph= 7.4Ph= 7.4

Ph is dependent on HCO3- Ph is dependent on HCO3- (direct) and CO2(inverse)(direct) and CO2(inverse)

HCO3 increases--- ph increasesHCO3 increases--- ph increases

HCO3 decreases ---- ph decreasesHCO3 decreases ---- ph decreases

CO2 increases---- ph decreasesCO2 increases---- ph decreases

CO2 decreases--- ph increaseCO2 decreases--- ph increase

Physiologic Response to Physiologic Response to chronic acid loadchronic acid load

Bicarbonate Buffer system (immediate)Bicarbonate Buffer system (immediate)– HCL + NaHCO3 >>>H2CO3 (CO2) +NaCLHCL + NaHCO3 >>>H2CO3 (CO2) +NaCL

Pulmonary Control (seconds to minutes)Pulmonary Control (seconds to minutes)– Ventilation of newly created CO2 in buffer Ventilation of newly created CO2 in buffer

systemsystem

Renal control (hours to days)Renal control (hours to days)– Secretes H+ to reabsorb and regenerate Secretes H+ to reabsorb and regenerate

HCO3 consumed by bufferHCO3 consumed by buffer

Pathophysiology/ Acid/Base Pathophysiology/ Acid/Base disturbancesdisturbances

Acidosis---any process that lowers phAcidosis---any process that lowers ph– Lowers HCO3- or raises PCO2Lowers HCO3- or raises PCO2

Alkalosis--- any process that raises phAlkalosis--- any process that raises ph– Raises HCO3- or lowers PCO2Raises HCO3- or lowers PCO2

DefinitionsDefinitions

NeutralNeutral– Ph 7.35-7.45Ph 7.35-7.45

AcidemiaAcidemia– Ph < 7.35Ph < 7.35

AlkalemiaAlkalemia– Ph > 7.45Ph > 7.45

More DefinitonsMore Definitons

Isoelectric principleIsoelectric principle– + ions (cations) = -ions (anions) + ions (cations) = -ions (anions)

Anion Gap—(Na + K) – (CL + HCO3) nl Anion Gap—(Na + K) – (CL + HCO3) nl =15=15– Measures minor/unmeasured anionsMeasures minor/unmeasured anions– Endogenous/exogenous anionsEndogenous/exogenous anions

Acid/Base disturbancesAcid/Base disturbances

PrimaryPrimary

Secondary- a response to a primary Secondary- a response to a primary disturbancedisturbance– Opposite direction from primaryOpposite direction from primary– Compensation is partial and incompleteCompensation is partial and incomplete

Acid/Base disturbacesAcid/Base disturbaces

Respiratory--- alteration in pCO2Respiratory--- alteration in pCO2

Metabolic --- alteration in HCO3Metabolic --- alteration in HCO3

Acute Respiratory Acidosis-Acute Respiratory Acidosis-Elevation in PCO2Elevation in PCO2

CNS vs. pulmonaryCNS vs. pulmonary– CNS – coma, strokeCNS – coma, stroke– Pulmonary-asthma, COPD, pneumonia (very late)Pulmonary-asthma, COPD, pneumonia (very late)

.08 ph drop for every 10mm increase in PCO2.08 ph drop for every 10mm increase in PCO2– Typical abg’s 7.32/50/62 7.24/60/47Typical abg’s 7.32/50/62 7.24/60/47

No metabolic compensation/ HCO3 unchangedNo metabolic compensation/ HCO3 unchanged

Treatment- Fix the problemTreatment- Fix the problem– Bronchodilators/cpap/bipap/intubationBronchodilators/cpap/bipap/intubation

Chronic Respiratory AcidosisChronic Respiratory Acidosis

Chronic/slow PCO2 elevationChronic/slow PCO2 elevation– COPD/sleep apnea/obesityCOPD/sleep apnea/obesity

Compensatory metabolic alkalosis a major Compensatory metabolic alkalosis a major componentcomponent– Kidneys increase H+ secretion –increase HCO3Kidneys increase H+ secretion –increase HCO3

.02 ph drop / 10 mm increase in PCO2.02 ph drop / 10 mm increase in PCO2– Typical abg’s 7.38/50 /50 7.36/60/55Typical abg’s 7.38/50 /50 7.36/60/55

Treat underlying conditionTreat underlying condition– Beware excess O2Beware excess O2

Acute Respiratory Alkalosis/ Acute Respiratory Alkalosis/ decreased PCO2decreased PCO2

CNS vs pulmonaryCNS vs pulmonary– CNS stress, drugs, anxiety, sepsis, toxins CNS stress, drugs, anxiety, sepsis, toxins – Pulmonary pneumonia/asthma/pulmonary embolism Pulmonary pneumonia/asthma/pulmonary embolism

.08 ph increase 10 mm decrease in PCO2.08 ph increase 10 mm decrease in PCO2– Typical abg’s 7.48/30/62Typical abg’s 7.48/30/62

No metabolic compensationNo metabolic compensation

Treat underlying conditionTreat underlying condition– Supplement O2Supplement O2– Beware of paper bagBeware of paper bag

Chronic Respiratory AlkalosisChronic Respiratory Alkalosis

Extremely rare…some other time…. Extremely rare…some other time….

Acute Metabolic AcidosisAcute Metabolic Acidosis

Decreased HCO3 Decreased HCO3 – Direct HCO3 loss via GI/kidneysDirect HCO3 loss via GI/kidneys– Decreased HCO3 from H+ bufferingDecreased HCO3 from H+ buffering

Metabolic Acidosis - defined by Metabolic Acidosis - defined by the associated anion the associated anion

Anion gap acidosis- increased minor Anion gap acidosis- increased minor anionsanions– Endogenous/ExogenousEndogenous/Exogenous

Non anion gap acidosis-hyperchloremicNon anion gap acidosis-hyperchloremic– HCO3 loss from GI/kidneysHCO3 loss from GI/kidneys– Increased reabsorption of CL-Increased reabsorption of CL-

Acute metabolic acidosisAcute metabolic acidosis

Compensatory respiratory alkalosisCompensatory respiratory alkalosis

Compensation is rapid but incompleteCompensation is rapid but incomplete

PCO2 drop= HCO3 dropPCO2 drop= HCO3 drop– Typical abg 7.34/35/98 serum HCO3 =20Typical abg 7.34/35/98 serum HCO3 =20

Treatment of Metabolic AcidosisTreatment of Metabolic Acidosis

Define and treat the underlying conditionDefine and treat the underlying condition

Watch for elevations in K+Watch for elevations in K+

Beware HCO3-Beware HCO3-

Pitfalls of HCO3- treatmentPitfalls of HCO3- treatment

Paradoxical CNS and intracellular acidosisParadoxical CNS and intracellular acidosis

Over correction alkalosisOver correction alkalosis

Aggressive Na loadAggressive Na load

Indications for HCO3- therapyIndications for HCO3- therapy

HCO3 < 5HCO3 < 5

Ph <7.10Ph <7.10

Cardiovascular instablity or irritabilityCardiovascular instablity or irritability

More likely to use on ventilated patients as More likely to use on ventilated patients as CO2 is “blown off”CO2 is “blown off”

Anion Gap Acidosis MUDPILESAnion Gap Acidosis MUDPILES

MethanolMethanol

UremiaUremia

Diabetic (ketones)Diabetic (ketones)

ParaldehydeParaldehyde

IronIron

LactateLactate

Ethylene glycolEthylene glycol

SalicylateSalicylate

Alternative Classification of Alternative Classification of anion gap acidosisanion gap acidosis

KetoacidosisKetoacidosis

Lactic acidosisLactic acidosis

Exogenous poisoningsExogenous poisonings

UremiaUremia

KetoacidosisKetoacidosis

DiabeticDiabetic

alcoholicalcoholic

Diabetic ketoacidosisDiabetic ketoacidosis

Insulin lackInsulin lack– HyperglycemiaHyperglycemia– Fatty acid breakdown Ketone accumulationFatty acid breakdown Ketone accumulation

TreatmentTreatment– Correct underlying disorderCorrect underlying disorder– fluidsfluids– insulininsulin– maintenance of electrolytes especially K+maintenance of electrolytes especially K+

Alcoholic KetoacidosisAlcoholic Ketoacidosis

EtOH use followed by vomiting/starvationEtOH use followed by vomiting/starvation– Excessive ketone accumulationExcessive ketone accumulation– DehydrationDehydration– Hypo or normoglycemiaHypo or normoglycemia

TreatmentTreatment– FluidsFluids– Maintenance of electrolytresMaintenance of electrolytres– GlucoseGlucose

Lactic AcidosisLactic Acidosis

Type A tissue hypoxia/underperfusionType A tissue hypoxia/underperfusion

Type B abnormal lactate utilizationType B abnormal lactate utilization

TreatmentTreatment

Correct underlying causeCorrect underlying cause– AntibioticsAntibiotics– Blood transfusionBlood transfusion– Goal directed sepsis therapyGoal directed sepsis therapy– Fluids/pressorsFluids/pressors

Exogenous toxinsExogenous toxins

AlcoholsAlcohols– Methanol/ethylene glycolMethanol/ethylene glycol

SalicylateSalicylate

Alcohol poisoningAlcohol poisoning

Ethanol not usually a major cause of Ethanol not usually a major cause of acidosisacidosis

MethanolEthylene GlycolMethanolEthylene Glycol– Formate/Oxylate accumulationFormate/Oxylate accumulation– Increased osmolar gapIncreased osmolar gap– Renal failure/oxylate crystalsRenal failure/oxylate crystals

Treatment for methanol/ethylene glycolTreatment for methanol/ethylene glycol– Ethanol dripEthanol drip– DialysisDialysis

Clues to diagnosis for ethylene Clues to diagnosis for ethylene glycol/methanol intoxglycol/methanol intox

HistoryHistory– ““sterno” or anti freeze ingestionsterno” or anti freeze ingestion

Altered mental statusAltered mental status

Unexplained visual disturbances/comaUnexplained visual disturbances/coma

Unexplained anion gap acidosisUnexplained anion gap acidosis

Renal failureRenal failure

Diagnostic AidesDiagnostic Aides

ABG/ HCO3ABG/ HCO3

Serum osmSerum osm

ETOH levelETOH level

Osmolar gapOsmolar gap

Oxylate crystalsOxylate crystals

Salicylate ToxicitySalicylate Toxicity

Altered mental statusAltered mental status

Anion gap acidosisAnion gap acidosis

Primary respiratory alkalosis as wellPrimary respiratory alkalosis as well– Typical abg 7.35/20/110 serum HCO3 15Typical abg 7.35/20/110 serum HCO3 15

TreatmentTreatment– Alkalinazation of the urineAlkalinazation of the urine– K+ replacementK+ replacement– DialysisDialysis

Lab Evaluation of anion gap Lab Evaluation of anion gap Metabolic AcidosisMetabolic Acidosis

KetonesKetones

SalicylateSalicylate

LactateLactate

Etoh/serum osmEtoh/serum osm

Osmolar gap = measured-calc serum osmOsmolar gap = measured-calc serum osm

Non Anion Gap-Hyperchloremic Non Anion Gap-Hyperchloremic acidosisacidosis

GI or renal HCO3- lossGI or renal HCO3- loss

Compensatory CL- resorptionCompensatory CL- resorption

Usually associated with Usually associated with hypo/hyperkalemiahypo/hyperkalemia

Metabolic AlkalosisMetabolic Alkalosis

Primary elevation in extracellular HCO3-Primary elevation in extracellular HCO3-– H + losses from GI (vomiting)H + losses from GI (vomiting)– Excessive renal H+ excretion/ elevated HCO3 Excessive renal H+ excretion/ elevated HCO3

resorpbtionresorpbtion– Exogenous ingestionExogenous ingestion

Respiratory compensationRespiratory compensation– If HCO3 goes up by 10 pco2 goes up by 7If HCO3 goes up by 10 pco2 goes up by 7– Typical abg 7.47/47/100 HCO3 =34Typical abg 7.47/47/100 HCO3 =34

Metabolic AlkalosisMetabolic Alkalosis

Physical effectsPhysical effects– TetanyTetany– Neuromuscular hyperactivityNeuromuscular hyperactivity– SeizuresSeizures– Decreased K+/ionized Ca 2+Decreased K+/ionized Ca 2+

TreatmentTreatment– Correct underlying causeCorrect underlying cause– Acetazolamide---causes renal HCO3 lossAcetazolamide---causes renal HCO3 loss– Correct electrolytesCorrect electrolytes

ABG interpretationABG interpretation

Step 1 obtain ABG/ HCO3- (electrolytes Step 1 obtain ABG/ HCO3- (electrolytes SMA7/Istat)SMA7/Istat)

Step 2 ph determination to determineStep 2 ph determination to determine– ph 7.35-7.45 = nuetralph 7.35-7.45 = nuetral– ph < 7.35 = academiaph < 7.35 = academia– ph > 7.45 + alkalemiaph > 7.45 + alkalemia

Acidemia Flow chart to Acidemia Flow chart to determine underlying processdetermine underlying processHCO3 low- primary process is metabolic HCO3 low- primary process is metabolic acidosisacidosis

pCO2 elevated- primary process is pCO2 elevated- primary process is respiratory acidosisrespiratory acidosis

Metabolic AcidosisMetabolic Acidosis

What is the anion gap????What is the anion gap????

Is the respiratory compensation Is the respiratory compensation appropriateappropriate– Appropriate PCO2/HCO3 =1 HCO3 =15/ Appropriate PCO2/HCO3 =1 HCO3 =15/

PCO2 =30PCO2 =30– PCO2/HCO3 > 1 resp alkalosis HCO3=15 PCO2/HCO3 > 1 resp alkalosis HCO3=15

PCO2= 20PCO2= 20

PCO2/HCO3 < 1 resp acidosis HCO3= PCO2/HCO3 < 1 resp acidosis HCO3= 15 PCO2 =4315 PCO2 =43

Respiratory AcidosisRespiratory Acidosis

Is the acidosis acute/chronic?Is the acidosis acute/chronic?– Acute –ph down .08/10 mmPCO2 elevationAcute –ph down .08/10 mmPCO2 elevation– Chronic ph down .03/10mm PCO2 elevationChronic ph down .03/10mm PCO2 elevation– Acute on chronic 7.35/50/50Acute on chronic 7.35/50/50– Outside limits—second primary processOutside limits—second primary process

Alkalemia flow chartAlkalemia flow chart

HCO3 elevated- primary metabolic HCO3 elevated- primary metabolic alkalosisalkalosis

pCO2 decreased- primary respiratory pCO2 decreased- primary respiratory alkalosisalkalosis

Metabolic AlkalosisMetabolic Alkalosis

Is the respiratory response appropriate?Is the respiratory response appropriate?– PCO2/HCO3 = .7 7.48/47/75 HCO3 =35PCO2/HCO3 = .7 7.48/47/75 HCO3 =35

Respiratory AlkalosisRespiratory Alkalosis

Acute—is the ph response appropriateAcute—is the ph response appropriate– Ph .08 up for every 10 mm decrease in PCO2Ph .08 up for every 10 mm decrease in PCO2

Nuetral phNuetral ph

Look for mixed primary disturbancesLook for mixed primary disturbances– PCO2PCO2– Anion gapAnion gap– HCO3HCO3

Case studiesCase studies

Having FUN yet???/Having FUN yet???/

Follow the flow charts!!!!!Follow the flow charts!!!!!

Case #1Case #1

57 y.o acutely SOB57 y.o acutely SOB

7.32/60/55 7.32/60/55

HCO3=32 HCO3=32

SMA 7 and anion gap otherwise normalSMA 7 and anion gap otherwise normal

Case #2Case #2

31 y.o homeless male unresponsive in 31 y.o homeless male unresponsive in parkpark

7.24/29/107 7.24/29/107

Na 140 K 5.4 Cl 97 HCO3 14 glucose Na 140 K 5.4 Cl 97 HCO3 14 glucose 110 110

Renal function normalRenal function normal

Case #3Case #3

61 y.o with severe arthritis confused and 61 y.o with severe arthritis confused and agitatedagitated

7.34/18/1107.34/18/110

Na 142 K 2.9 CL 99 HCO3 12Na 142 K 2.9 CL 99 HCO3 12

Glucose/renal function wnlGlucose/renal function wnl

Case #4Case #4

19 y.o. diabetic with vomiting19 y.o. diabetic with vomiting

7.38/38/1107.38/38/110

Na 140 K 2.8 CL 95 HCO3 24Na 140 K 2.8 CL 95 HCO3 24

Glucose 440 renal function wnlGlucose 440 renal function wnl