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Arterial Blood Gas Analysis & interpretation

Mohammed A. El-haj MPH07/12/2011

What is an ABG?The ComponentspH / PaCO2 / PaO2 / HCO3 / O2sat / BEDesired RangespH - 7.35 - 7.45PaCO2 - 35-45 mmHgPaO2 - 80-100 mmHgHCO3 - 21-27O2sat - 95-100%Base Excess - +/-2 mEq/L

Why Order an ABG?Aids in establishing a diagnosis Helps guide treatment planAids in ventilator managementImprovement in acid/base management allows for optimal function of medicationsAcid/base status may alter electrolyte levels critical to patient status/care

LogisticsWhen to order an arterial line --Need for continuous BP monitoringNeed for multiple ABGsWhere to place -- the optionsRadialFemoral BrachialDorsalis PedisAxillary

Acid Base BalanceThe body produces acids daily15,000 mmol CO250-100 mEq Nonvolatile acids

The lungs and kidneys attempt to maintain balance

Acid Base BalanceAssessment of status via bicarbonate-carbon dioxide buffer system

CO2 + H2O H2CO3 HCO3- + H+

pH = 6.10 + log ([HCO3] / [0.03 x PCO2])

Normal values

Compensation 7.4

7.35 7.45Partial compensated Partial

Respiratory AcidosispH, CO2, VentilationCausesCNS depressionPleural diseaseCOPD/ARDSMusculoskeletal disordersCompensation for metabolic alkalosis

Respiratory AcidosisAcute vs ChronicAcute - little kidney involvement. Buffering via titration via Hb for examplepH by 0.08 for 10mmHg in CO2Chronic - Renal compensation via synthesis and retention of HCO3 (Cl to balance charges hypochloremia)pH by 0.03 for 10mmHg in CO2

Respiratory AlkalosispH, CO2, Ventilation CO2 HCO3 (Cl to balance charges hyperchloremia)CausesIntracerebral hemorrhageSalicylate and Progesterone drug usageAnxiety lung complianceCirrhosis of the liverSepsis

Respiratory AlkalosisAcute vs. ChronicAcute - HCO3 by 2 mEq/L for every 10mmHg in PCO2Chronic - Ratio increases to 4 mEq/L of HCO3 for every 10mmHg in PCO2

Decreased bicarb reabsorption and decreased ammonium excretion to normalize pH

Metabolic AcidosispH, HCO312-24 hours for complete activation of respiratory compensation PCO2 by 1.2mmHg for every 1 mEq/L HCO3 The degree of compensation is assessed via the Winters Formula PCO2 = 1.5(HCO3) +8 2

The CausesMetabolic Gap Acidosis

M - MethanolU - UremiaD - DKAP - ParaldehydeI - INHL - Lactic AcidosisE - Ehylene GlycolS - Salicylate

Non Gap Metabolic Acidosis

HyperalimentationAcetazolamideRTA (Calculate urine anion gap)DiarrheaPancreatic Fistula

Metabolic AlkalosispH, HCO3 PCO2 by 0.7 for every 1mEq/L in HCO3CausesVomitingChronic diarrheaHypokalemiaRenal Failure

Mixed Acid-Base DisordersPatients may have two or more acid-base disorders at one time

Delta GapDelta HCO3 = HCO3 + Change in anion gap >24 = metabolic alkalosis

The six steps to ABGs analysisLook at the pH if it is normal/acidotic/alkaloticLook at the PaCO2 if it is normal/acidotic/alkaloticLook at the HCO3 if it is normal/acidotic/alkaloticIf the pH match with the PCO2 or with the HCO3 If the value goes opposite direction of the pH (determine the compensation).Look at the Po2 and oxygen saturation

Sample problempH 7.49PCO2 40HCO3 28Uncompensated metabolic alkalosisVomiting/dearrheaIn this example the Bicarb is matching the pHNo compensation (Partial)

Sample problempH 7.10PCO2 25HCO3 7Uncompensated metabolic acidosisDKA/Dearrhea/shock/bleeding/sepsisIn this example the Bicarb is matching the pHNo compensation (Partial)Severe metabolic acidosis

Sample problempH 7.42PCO2 18HCO3 11PO2 150O2 sat 99%compensated respiratory alkalosisThis pt is hyperventilated for too long (blowing off CO2)

Sample problempH 7.35PCO2 60HCO3 32PO2 92O2 sat 96%

No need for correction or treatment because pH is normalCompensation is bringing the pH to the side of 7.4 but doesn't to the opposite side (stop in 7.4)

Sample problempH 7.37PCO2 33HCO3 18

Metabolic acidosisFully compensated

Sample problempH 7.36PCO2 62HCO3 34PO2 70O2 sat. 90%

Respiratory acidosisFully compensatedE.g. COPD

Respiratory AlkalosisMost common causes of respiratory alkalosis are:Hypoxemia ( PaO2< 60mmHg and O2 sat.

hypoxemiaConditions causing V/Q (Ventilation perfusion) miss matchShunt: loss of alveolar surface areaDead spaceDiffusion defect

Danger a headHypoxemia

Respiratory alkalosisIncreased W.O.BMusclefatigueRespiratoryAcidosis

Danger a head( Hypoxemia causing fatigue and respiratory acidosis)

In the path from respiratory alkalosis to respiratory acidosis, the acid/base will temporarily appear normal, however the Ve (minute ventilation) will be increased (and probably the W.O.B)

RespiratoryAlkalosisNormal ABGRespiratoryAcidosis

Case 1A 26 year old man with unknown past medical history is brought in to the ER by ambulance, after friends found him unresponsive in his apartment. He had last been seen at a party four hours prior.ABG: pH 7.25Chem : Na+ 137 PCO2 60K+ 4.5 HCO3- 26Cl- 100 PO2 55 HCO3- 25

Case 2A 67 year old man with diabetes and early diabetic nephropathy (without overt renal failure) presents for a routine clinic visit. He is currently asymptomatic. Because of some abnormalities on his routine blood chemistries, you elect to send him for an ABG.

ABG: pH 7.35Chem : Na+ 135 PCO2 34K+ 5.1 HCO3- 18Cl- 110 PO292 HCO3- 16 Cr 1.4

Urine pH:5.0

Case 3A 68 year old woman with metastatic colon cancer presents to the ER with 1 hour of chest pain and shortness of breath. She has no known previous cardiac or pulmonary problems.

ABG: pH 7.49Chem : Na+ 133 PCO2 28K+ 3.9 HCO3- 21Cl- 102 PO2 52HCO3- 22

DefinitionsAcidemia: Blood pH < 7.35Alkalemia: Blood pH > 7.45Acidosis:is a process that will result in acidemia if left unopposed. Alkalosis:is a process that will result in alkalemia if left unopposed Metabolic refers to a disorder that results from a primary alteration in [H+] or [HCO3-].Respiratory refers to a disorder that results from a primary alteration in PCO2 due to altered CO2 elimination. Normal HCO3- 24 meq/L; Normal PCO2 40 mm Hg ; Normal pH 7.35-7.45

Definitions (Continued)

PH: - is a negative logarithm of Hydrogen ion concentration; and it is the initials of these two wards (puiessence Hydrogen) that mean the power of hydrogen

Definitions (Continued)An acid: - is a hydrogen ion or proton donor, and a substance which causes a rise in H+ concentration on being added to water. A base: - is a hydrogen ion or proton acceptor, and a substance which causes a rise in OH- concentration when added to water. Strength of acids or bases refers to their ability to donate and accept H+ ions respectively.

Importance of acid-base balanceThe hydrogen ion (H+)concentration must be precisely maintained within a narrow physiological range

Small changes from normal can produce marked changes in enzyme activity & chemical reactions within the body

Acidosis - CNS depression, coma (pH ~ 6.9) Alkalosis - CNS excitability, tetany, siezures Hydrogen ion concentration is most commonly expressed as pH (= negative logarithm of the H+ concentration)

ACID-BASE CALCULATIONSThe Henderson equation is easier to use, but only applies when pH is between 7.2 and 7.6. For this equation, one must calculate [H+] from pH. [H+] = 40 nEq/L when pH is 7.4. The [H+] increases 10 nEq/L for a 0.1 unit drop in pH.Henderson Eq. [H+] = 24 PCO2 / [HCO3-]

phH+ (nmol/l) 71007.1807.2637.3507.36447.4407.44367.5327.6257.720

Normal pH:

Arterial blood: 7.35 - 7.45 Venous blood, interstitial fluid: 7.35 Intracellular: 6.0-7.4 (average 7.0)

Regulation of pH*Buffer systems - very rapid (seconds), incomplete *Respiratory responses - rapid (minutes), incomplete *Renal responses - slow (hours to days), complete

Background H+ + H+CO3- H2CO3 H2O + CO2

-Metabolic Disorders: Affect HCO3-: (Normal 22-26 meq/L) -Metabolic Acidosis Acid neutralizes HCO3- H+CO3-, pH -Metabolic Alkalosis H+CO3- Production Drives Rxn to Right H+ pH

Primary Abnormality in Acid Base DisordersH+ + H+CO3- H2CO3 H2O + CO2

AcidosisAlkalosisRespiratory pCO2Metabolic


AcidosisAlkalosisRespiratory pCO2 pCO2Metabolic


AcidosisAlkalosisRespiratory pCO2 pCO2Metabolic H+CO3-


AcidosisAlkalosisRespiratory pCO2 pCO2Metabolic H+CO3- H+CO3-

Simple Acid-Base Disorders:

Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

(

(

(

Metabolic Alkalosis

Acute Respiratory Acidosis

Chronic Respiratory Acidosis

Acute Respiratory Alkalosis

Chronic Respiratory Alkalosis


Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

Metabolic Alkalosis

(

(






Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

Metabolic Alkalosis

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Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

Metabolic Alkalosis


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(


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Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

Metabolic Alkalosis


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(

(


(

(

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Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

Metabolic Alkalosis




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(


(

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Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

Metabolic Alkalosis




(

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Type of Disorder

pH

PaCO2

[HCO3]

Metabolic Acidosis

(

(

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Metabolic Alkalosis

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CompensationFor each acid-base disorder , there is a compensatory response mediated by the kidneys or the lungs that tends to bring the pH back towards normal. Compensation is never complete (i.e. pH never returns to 7.4). Therefore if the pH < 7.4, the primary process is an acidosis. If the pH > 7.4 the primary process is an alkalosis

Compensated Abnormality in Acid Base Disorders H+CO3- H+CO3- pCO2 pCO2H+ + H+CO3- H2CO3 H2O + CO2

AcidosisAlkalosis1 Respiratory

Compensation pCO2 pCO2 1 Metabolic

Compensation H+CO3- H+CO3-

Compensation (Continued)Formulas predict normal compensation in both acute and chronic conditions.Inadequate compensation tells you that something else is wrong!Metabolic compensation takes time and is more complete in chronic conditions than acutely

Buffer SystemsA substance that can prevent major changes in the pH of body fluids by removed or releasing hydrogen ions ,they can act quickly to prevent excessive changes in hydrogen ion concentration Bicarbonate, phosphate and protein buffering systems are the three major buffering systems

Bicarbonate buffer system

*Primary extracellular buffer system (>50% of extracellular buffering) *Accurate assessment - readily calculated from PCO2 and pH using available blood gas machines *Consists of carbonic acid (weak acid) and bicarbonate

*CO2 regulated by the lungs - rapidly*HCO3- is regulated by the kidneys slowly *Not powerful *pKa = 6.1)the pK of a buffer system identifies the pH at which the concentration of acid and base in that system is equal)

Protein buffer system*Most powerful *75 % of all intracellular buffering *Hemoglobin -important extracellular buffer due to large concentration of hemoglobin in blood -buffering capacity varies with oxygenation -reduced hemoglobin is a weaker acid than oxyhemoglobin -dissociation of oxyhemoglobin results in more base available to combine w/ H+

Plasma protein

*acid buffer *important intracellular buffer system

Phosphate buffer system

*H2PO4- and HPO42- *important renal buffering system*extracellular concentration, 1/12 that of bicarbonate *pKa = 6.8 *phosphate is concentrated in the renal tubules

Respiratory Responsesoccurs within minutes of alteration in pH due to stimulation/depression of respiratory centers in the CNS H+ acts directly on respiratory center in Medulla Oblongata alveolar ventilation increases/decreases in response to changes in CO2 alveolar ventilation is inversely proportional to PaCO2 *2 x ventilation pH 7.4 to 7.63 * ventilation pH 7.4 to 7.0 incomplete response because as the change in alveolar ventilation brings pH back towards normal, the stimulus responsible for the change in ventilation decreases .

Renal Responsesthe kidneys regulate pH by either acidification or alkalinization of the urine complex response that occurs primarily in the proximal renal tubules with acidosis, rate of H+ secretion exceeds HCO3- filtration with alkalosis, rate of HCO3- filtration exceeds H+ secretion occurs over hours/days, and is capable of nearly complete restoration of acid/base balance

Renal & Respiratory Compensation

Primary DisorderPrimary changePredicted Compensatory ResponseMetabolic acidosis HCO31.2 PaCO2 per 1 meg HCO3Metabolic Alkalosis HCO3.7 PaCO2 per 1meq HCO3Respiratory acidosis: AcutePaCO21 meq HCO3 per 10 mm PaCO2Respiratory acidosis: ChronicPaCO23.5 meq HCO3 per 10 mm PaCO2Respiratory alkalosis: AcutePaCO22 meq HCO3 per 10mm PaCO2Respiratory alkalosis: ChronicPaCO24 meq HCO3 per 10mm PaCO2

SUMMARY OF SIMPLE ACID-BASE DISORDERS AND COMPENSATION

Primary Acid-Base Disorder Primary Defect Effect onpH Compensatory Response Expected Range of Compensation Limits of Compensation Respiratory Acidosis Hypoventilation (PCO2) HCO3- Generation [HCO3-] =1-4 mEq/L for each 10 mm Hg PCO2 [HCO3-] =45 mEq/L Respiratory AlkalosisHyperventilation (PCO2) HCO3- Consumption [HCO3-] =2-5 mEq/L for each 10 mm Hg PCO2 [HCO3-] =12-15 mEq/L Metabolic Acidosis Loss of HCO3- or gain of H+( HCO3-) Increase in Ventilation(PCO2) PCO2 =1.5[HCO3-] + 8 PCO2 =12-14 mm Hg Metabolic Alkalosis Gain of HCO3- or loss of H+( HCO3-) Decrease in Ventilation (PCO2 ( PCO2 =0.6 mm Hg for each 1 mEq/L [HCO3-] PCO2 =55 mm Hg

GENERAL ASPECTS OF ACID-BASE DISORDERS A primary alteration in [H+], [HCO3-] or PCO2 results in abnormal pH. The body has several mechanisms to correct pH towards the normal range. -In the acute phase (minutes to hours), the extra- and intra-cellular buffer systems (most importantly the bicarbonate system) minimize the pH changes. - In the chronic phase (hours to days), renal or respiratory compensation partially or completely restore pH towards normal. There are limits to both types of compensation. Compensation does not result in over correction of pH.

DATA REQUIRED TO DIAGNOSE ACID-BASE DISORDERSAn arterial blood gas shows the blood pH, PCO2 and [HCO3-]. A chemistry panel shows the [total CO2], [Cl-], [K+] and [Na+], [glucose], [BUN] and [creatinine]. The [total CO2] is the sum of the measured [CO2] + [HCO3-]. Thus the [HCO3-] from the blood gas and the [total CO2] from the electrolyte panel usually are within 2 mEq/L. Otherwise the measurements are in error or were taken at different times.

NORMAL LABORATORY VALUES Arterial Blood Gas: pH7.35-7.45[H+]35-45 nmol/L or neq/LPCO235-45 mm Hg[HCO3-]22-26 mmol/L or mEq/LPlasma Electrolytes [Na+] 135-145 mEq/L [K+ ]3.5-5.0 mEq/L [Cl-]96-109 mEq/L [total CO2]24-30 mEq/L

SIMPLE ACID-BASE DISORDERSSimple acid-base disorders have one primary abnormality. The four primary disorders are respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis.Mixed acid-base disorders have more than one abnormality. Two to three primary disorders can be combined together to result in a mixed disorder.

Metabolic AcidosisSecondary to Acid production or H+CO3- lossCharacterized by low serum H+CO3-( by hyperventilation PCO2 HCO3- )Divided into two categories:Anion gap metabolic acidosis (High anion gap)NonAnion gap metabolic acidosis (Normal anion gap)

Anion GapThe anion gap (AG) represents the difference between the major plasma cations and anions ,and reflects usually unmeasured anions such as sulfate. Anion Gap = [Na+] - ( [H+CO3-] + [Cl-] )Normal 14 +/- 2

Why does this help us in patients with metabolic acidosis?Secondary to Acid production or H+CO3- lossIn disorders associated with acid production there anions accumulate anion gap whereasIn disorders associated with H+CO3- loss, there is no accumulation of unmeasured anions and the anion gap is normal

Unmeasured anions which accumulate Anion Gap AcidosisLactateKetonesSulfates and phosphatesOther organic acids

NameTitle

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Name

Company Name

Company NameDepartment Name

Metabolic Acidosis

Anion Gap Acidosis

NonAnion Gap Acidosis

Ketoacidosis

Uremic Acidosis

Lactic Acidosis

Organic Acidosis

Lactic AcidosisFundamentally what causes a lactic acidosis?Answer: Anaerobic metabolism

The differential diagnosis of Lactic AcidosisLactic acidosis occurs whenever the cells are unable to utilize aerobic respiration: i.e. whenever the cells are unable to obtain or utilize oxygenConsider Murphys law: Whatever can go wrong will go wrong! (i.e. take each step in oxygen absorption and distributionany one of them can go away and cause lactic acidosis.)

The differential diagnosis of Lactic Acidosis (2)Low environmental O2Inability to absorb O2O2 unable to bind HgUnable to pump O2Tissues unable to utilize O2High altitudeLung DiseaseCO poisoningShock (cardiogenic)Septic shockFocal vascular obstructionCyanide poisoning

NameTitle

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Name

Company Name

Company NameDepartment Name

Metabolic Acidosis

Anion Gap Acidosis


Ketoacidosis

Uremic Acidosis

Lactic Acidosis

Organic Acidosis

Lung DiseaseCO poiseningCardiogenic shockSeptic shockHypovolemic shockFocal vascular obstructionCyanide poisening

KetoAcidosisOccurs whenever the cells are unable to utilize glucose

KetoAcidosisThree etiologiesDiabetic KetoacidosisPrimarily in type 1 diabetes mellitusSevere, life threateningOften associated with precipitating illnessStarvation ketoacidosisMild acidosisAlcoholic ketoacidosisMild acidosis

NameTitle

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Metabolic Acidosis

Anion Gap Acidosis


Ketoacidosis

Uremic Acidosis

Lactic Acidosis

Organic Acidosis

Lung DiseaseCO poiseningShock (cardiogenic)Septic shockFocal vascular obstructionCyanide poisening

DKA (Type 1)StarvationAlcoholic

Other anion gap acidosisUremiaFailure to excrete daily metabolic acid loadAccumulation of phosphates and sulfatesOrganic acidosisMethanolEthylene GlycolSalicylates

NameTitle

NameTitle

Metabolic Acidosis

Anion Gap Acidosis


Ketoacidosis

Uremic Acidosis

Lactic Acidosis

Organic Acidosis



MethanolEthylene GlycolSalicylate intoxication

Non-anion gap metabolic acidosis Bicarbonate lossDiarrheaSevere BurnsUrinary loss (renal tubular acidosis)

NameTitle

NameTitle

Metabolic Acidosis

Anion Gap Acidosis


Ketoacidosis

Uremic Acidosis

Lactic Acidosis

Organic Acidosis




DiarrheaBurns (severe)RTA

Clinical ManifestationHeadacheConfusionDrowsiness RR and depthNausea and vomitingPeripheral vasodilation and decreased Cardiac output (pH 7 )BPHyperkalemias

Metabolic Acidosis: TreatmentTreat underlying causeAlkali replacementAcute metabolic acidosisindicated when is pH less than ~7.15goal is to raise serum [HCO3] to ~15mmol/Lbicarbonate dose = 0.5 x BW (kg) x{[HCO3]desired - [HCO3]actual}Chronic metabolic acidosisgoal of treatment is to prevent long term sequelaeserum [HCO3] should be normalized

Metabolic AlkalosisGeneration

Maintenance

Metabolic Alkalosis: GenerationAcid lossrenal acid lossesdiuretic therapymineralocorticoid excessCushings syndromesevere potassium depletionBartters syndromeLiddles syndrome

gastrointestinal lossesgastric acid losschloride diarrhea

Metabolic Alkalosis: GenerationAlkali gainbicarbonate administrationmilk alkali syndromeinfusion of organic anionscitrateacetatelactaterapid correction of chronic hypercapnia

Metabolic Alkalosis: MaintenanceDecreased GFRrenal failureIncreased proximal HCO3- reabsorptionchloride depletionIncreased distal tubular H+ secretion hypokalemia

Metabolic Alkalosis: TreatmentSaline responsiveintravascular volume expansion with normal salinepotassium repletionSaline resistantpotassium repletionmineralocorticoid antagonistsacetazolamide

Respiratory AcidosisThink Murphys Law againFrom Brain to alveolus, many problems can cause hypoventilation PaCO2 pH (Respiratory acidosis)

Respiratory AcidosisBrain

Spinal Cord

Peripheral NerveNeuroMuscular JunctionLung and Pleural diseaseStrokeDrug IntoxicationC spine injury,

Guillan BarreMyasthenia GravisAsthma, COPD, ARDS, etc

Clinical Manifestation HypercapniaPulse RRBPMental cloudinessFeeling of fullness in the headICP HeadacheHyperkalemia

Respiratory AlkalosisHyperventilation PaCO2 pHEtiologiesFeverPainAnxietyPulmonary diseaseSepsisSalicylate intoxicationNeurologic disorders

MIXED ACID-BASE DISORDERSMixed acid-base disorders include all combinations of 2-3 simple acid base disorders. One must be able to recognize mixed acid-base disorders. This can be accomplished by examining the degree of compensation and calculating an anion gap. If the pH, PCO2 and [HCO3-] do not fit the rules of compensation for a simple disorder, one must hypothesize that there is a mixed acid-base disorder (or hypothesize that there is an error in the data).

If there is extreme acidemia or alkalemia, one could hypothesize multiple acid-base disorders that that are additive. If there is a mild acidemia or alkalemia, or pH is normal, particularly with an anion gap one could hypothesize multiple acid-base disorders that cancel each other out.

Summary of the Approach to ABGsCheck the pHCheck the pCO2Select the appropriate compensation formulaDetermine if compensation is appropriateCheck the anion gapIf the anion gap is elevated, check the delta-deltaIf a metabolic acidosis is present, check urine pHGenerate a differential diagnosis

Putting it Together

What is the clinical picture?Generate hypothesis!

What is the pH?

Acidemia

Alkalemia

Check HCO3- & PaCO2Is it respiratory or metabolic?

Check: Is compensation appropriate?

Check Anion Gap

Reach Final Diagnosis

Case 1A 26 year old man with unknown past medical history is brought in to the ER by ambulance, after friends found him unresponsive in his apartment. He had last been seen at a party four hours prior.ABG: pH 7.25Chem 7:Na+ 137 PCO2 60K+ 4.5 HCO3- 26Cl- 100 PO255 HCO3- 25

Case 2A 67 year old man with diabetes and early diabetic nephropathy (without overt renal failure) presents for a routine clinic visit. He is currently asymptomatic. Because of some abnormalities on his routine blood chemistries, you elect to send him for an ABG.

ABG: pH 7.35Chem 7:Na+ 135 PCO2 34K+ 5.1 HCO3- 18Cl- 110 PO292 HCO3- 16 Cr 1.4Urine pH:5.0

Case 3A 68 year old woman with metastatic colon cancer presents to the ER with 1 hour of chest pain and shortness of breath. She has no known previous cardiac or pulmonary problems.

ABG: pH 7.49Chem 7:Na+ 133 PCO228K+ 3.9 HCO3- 21Cl- 102 PO252HCO3- 22

pH7.34, PaCO2 60 , HCO3- 31

Primary DisorderPrimary changePredicted Compensatory ResponseMetabolic acidosis HCO31.2 PaCO2 per 1 meg HCO3Metabolic Alkalosis HCO3.7 PaCO2 per 1meq HCO3Respiratory acidosis: AcutePaCO21 meq HCO3 per 10 mm PaCO2Respiratory acidosis: ChronicPaCO23.5 meq HCO3 per 10 mm PaCO2Respiratory alkalosis: AcutePaCO22 meq HCO3 per 10mm PaCO2Respiratory alkalosis: ChronicPaCO24 meq HCO3 per 10mm PaCO2

Case 1A 52 y.o. man with COPD is admitted to the hospital with a lower extremity cellulitis.HypothesisLabs: Na+ 139, K+ 4.9, Cl- 98, HCO3- 31ABG: pH 7.34, PaCO2 60, PaO2 69Is he acidemic or alkalemic?Is this metabolic (from sepsis) or respiratory (from COPD)?Is this acute or chronic? Why does that matter?

Case 1: AnswerA 52 y.o. man with COPD is admitted to the hospital with a lower extremity cellulitis.Labs: Na+ 139, K+ 4.9, Cl- 98, HCO3- 31ABG: pH 7.34, PaCO2 60, PaO2 69Why is he acidemic?Is this metabolic (from sepsis) or respiratory (from COPD)?Is this acute or chronic? Why does that matter?Dx: Chronic Respiratory AcidosisNot from sepsisNo need for intubation or ICU careNote AG 10

Case 2A 45 y.o. man reports 6 days of persistent nausea and vomiting. PE supine BP 100/60 pulse 105; Standing BP 85/55 pulse 125. Neck veins are flatHypotheses?Labs: Na+ 140, K+ 2.2, Cl- 86, HCO3 42 BUN 80, Cr 1.9ABG: pH 7.53, PaCO2 53, PaO2 82Urine Na+ 2 meg/LAcidemic or Alkalemic?Metabolic or Respiratory?What is his acid base disorder?Why is he alkalemic? How would you fix it? Whats with the urine sodium?Answer: Metabolic alkalosis. Correct with NaCL

Case 379 y.o. woman with CC of abdominal painPatient c/o abdominal pain for 2 days. Pain is moderately severe & diffuse, associated with vomiting. She reports passing no bowel movements or flatus for 2 days.PE: Elderly appearing woman in moderate distress; Vital signs T 38.5, RR 20, BP 115/60, HR 95. Abdominal exam: absent bowel sounds, diffusely distended, mild tenderness, without rebound or guarding. Rectal FOBT negative

Case 3 (continued)Labs:WBC 18K, 82% neutrophils, 10% bandsHCT 37Na 138, K 4.2 HCO3- 6 CL 106 BUN 45 Cr. 1.0 Glucose 110ABG: pH 7.10, PaCO2 20mm Hg, PaO2 90What is her acid base disorder? What does it tell you?

NameTitle

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Metabolic Acidosis

Anion Gap Acidosis


Ketoacidosis

Uremic Acidosis

Lactic Acidosis

Organic Acidosis




DiarrheaBurns (severe)RTA

Who gets your last ICU bed? 75 y.o. WF with COPD with CC cough & SOB R.A. ABG 7.35, PaC02 60, Pa02 48.

70 y.o. WM with COPD with CC purulent sputum, SOB. ABG on 4L 7.2, PaC02 60, Pa02 of 70

What is the clinical picture?Generate hypothesis!

What is the pH?

Acidemia

Alkalemia

Check HCO3- & PaCO2Is it respiratory or metabolic?

Check: Is compensation appropriate?

Check Anion Gap

Reach Final Diagnosis

Arterial puncture

Problems of taking arterial blood samples Bleeding Vessel obstruction Infection

Allen's test. The radial and ulnar arteries are occluded by firm pressure while the fist is clenched. The hand is opened and the arteries released one at a time to check their ability to return blood flow to the hand

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