The Minimalist approach The Minimalist approach to acid/base to acid/base disturbances disturbances ABG’s so easy….a GEICO rep can do it ABG’s so easy….a GEICO rep can do it
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