Blood Gases Analysis

8/9/2019 Blood Gases Analysis

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Marc D. Berg, MD DeVos Childrens Hospital

Rita R. Ongjoco, DO Sinai Hospital of Baltimore

12/30/02 ABG Interpretation 1


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ABG InterpretationABG Interpretation

First, does the patient have an acidosis or anFirst, does the patient have an acidosis or analkalosisalkalosis

Second, what is the primary problemSecond, what is the primary problem

metabolic or respiratorymetabolic or respiratory Third, is there any compensation by theThird, is there any compensation by the

patientpatient respiratory compensation isrespiratory compensation isimmediate while renal compensation takesimmediate while renal compensation takestimetime



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ABG InterpretationABG Interpretation

It would be extremely unusual for either theIt would be extremely unusual for either the

respiratory or renal system torespiratory or renal system to

overcompensateovercompensate

The pH determines the primary problemThe pH determines the primary problem

After determining the primary andAfter determining the primary and

compensatory acid/base balance, evaluatecompensatory acid/base balance, evaluate

the effectiveness of oxygenationthe effectiveness of oxygenation



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Normal ValuesNormal Values

pH 7.35 to 7.45pH 7.35 to 7.45

paCOpaCO22 36 to 44 mm Hg36 to 44 mm Hg

HCOHCO33 22 to 26 meq/L22 to 26 meq/L



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Abnormal ValuesAbnormal Values

pH < 7.35pH < 7.35

yy Acidosis (metabolic and/orAcidosis (metabolic and/or

respiratory)respiratory)

pH > 7.45pH > 7.45yy Alkalosis (metabolic and/orAlkalosis (metabolic and/or

respiratory)respiratory)

paCOpaCO22 > 44> 44 mmHgmmHg

yy Respiratory acidosisRespiratory acidosis

(alveolar hypoventilation)(alveolar hypoventilation)

paCOpaCO22 < 36< 36 mmHgmmHg

yy Respiratory alkalosisRespiratory alkalosis

(alveolar hyperventilation)(alveolar hyperventilation)

HCOHCO33 < 22 meq/L< 22 meq/Lyy Metabolic acidosisMetabolic acidosis

HCOHCO33 > 26 meq/L> 26 meq/L

yy Metabolic alkalosisMetabolic alkalosis



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Putting It TogetherPutting It Together -- RespiratoryRespiratory

SoSo

paCOpaCO22 > 44 with a pH < 7.35 represents a> 44 with a pH < 7.35 represents arespiratory acidosisrespiratory acidosis

paCOpaCO22 < 36 with a pH > 7.45 represents a< 36 with a pH > 7.45 represents arespiratory alkalosisrespiratory alkalosis

For a primary respiratory problem, pH andFor a primary respiratory problem, pH andpaCOpaCO22 move in the opposite directionmove in the opposite direction

yy For each deviation in paCOFor each deviation in paCO22 of 10 mm Hg in eitherof 10 mm Hg in eitherdirection, 0. 08 pH units change in the oppositedirection, 0. 08 pH units change in the oppositedirectiondirection



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Putting It TogetherPutting It Together -- MetabolicMetabolic

AndAnd

HCOHCO33 < 22 with a pH < 7.35 represents a< 22 with a pH < 7.35 represents ametabolic acidosismetabolic acidosis

HCOHCO33 > 26 with a pH > 7.45 represents a> 26 with a pH > 7.45 represents ametabolic alkalosismetabolic alkalosis

For a primary metabolic problem, pH andFor a primary metabolic problem, pH and

HCOHCO33 are in the same direction, and paCOare in the same direction, and paCO22is also in the same directionis also in the same direction



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CompensationCompensation

The bodys attempt to return the acid/baseThe bodys attempt to return the acid/base

status to normal (i.e. pH closer to 7.4)status to normal (i.e. pH closer to 7.4)

Primary ProblemPrimary Problem CompensationCompensation

respiratory acidosisrespiratory acidosis metabolic alkalosismetabolic alkalosis

respiratory alkalosisrespiratory alkalosis metabolic acidosismetabolic acidosis

metabolic acidosismetabolic acidosis respiratory alkalosisrespiratory alkalosis

metabolic alkalosismetabolic alkalosis respiratory acidosisrespiratory acidosis



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Expected CompensationExpected Compensation

Respiratory acidosisRespiratory acidosis

AcuteAcute

yy

thethe pH decreases 0.08 units for every 10 mm HgpH decreases 0.08 units for every 10 mm Hgincrease in paCOincrease in paCO22;;

yy HCOHCO33 oo0.10.1--1 mEq/liter per1 mEq/liter peroo10 mm Hg paCO10 mm Hg paCO22

ChronicChronic

yy thethe pH decreases 0.03 units for every 10 mm HgpH decreases 0.03 units for every 10 mm Hgincrease in paCOincrease in paCO22;;

yy HCOHCO33 oo1.11.1--3.5 mEq/liter per3.5 mEq/liter peroo10 mm Hg paCO10 mm Hg paCO22



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Respiratory alkalosisRespiratory alkalosis

AcuteAcute

yy

thethe pH increases 0.08 units for every 10 mm HgpH increases 0.08 units for every 10 mm Hgdecrease in paCOdecrease in paCO22;;

yy HCOHCO33 qq00--2 mEq/liter per2 mEq/liter perqq10 mm Hg paCO10 mm Hg paCO22

ChronicChronic

yy thethe pH increases 0.17 units for every 10 mm HgpH increases 0.17 units for every 10 mm Hgdecrease in paCOdecrease in paCO22;;

yy HCOHCO33 qq2.12.1--5 mEq/liter per5 mEq/liter perqq10 mm Hg paCO10 mm Hg paCO22



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Metabolic acidosisMetabolic acidosis

paCOpaCO22 = 1.5(HCO= 1.5(HCO33) + 8 () + 8 (ss2)2)

paCOpaCO22 qq11--1.5 per1.5 perqq1 mEq/liter HCO1 mEq/liter HCO33Metabolic alkalosisMetabolic alkalosis

paCOpaCO22 = 0.7(HCO= 0.7(HCO33) + 20) + 20 ((ss1.5)1.5)

paCOpaCO22oo

0.50.5--1.0 per1.0 peroo

1 mEq/liter HCO1 mEq/liter HCO33



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Classification of primary acidClassification of primary acid--basebase

disturbances and compensationdisturbances and compensation

Acceptable ventilatory and metabolic acidAcceptable ventilatory and metabolic acid--basebasestatusstatus

Respiratory acidosis (alveolar hypoventilation)Respiratory acidosis (alveolar hypoventilation) --

acute, chronicacute, chronic Respiratory alkalosis (alveolar hyperventilation)Respiratory alkalosis (alveolar hyperventilation)

-- acute, chronicacute, chronic

Metabolic acidosisMetabolic acidosis uncompensated,uncompensated,

compensatedcompensated Metabolic alkalosisMetabolic alkalosis uncompensated, partiallyuncompensated, partially

compensatedcompensated



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Acute Respiratory AcidosisAcute Respiratory Acidosis

paCOpaCO22 is elevated and pH is acidoticis elevated and pH is acidotic

The decrease in pH is accounted for entirelyThe decrease in pH is accounted for entirely

by the increase in paCOby the increase in paCO22

Bicarbonate and base excess will be in theBicarbonate and base excess will be in the

normal range because the kidneys have notnormal range because the kidneys have not

had adequate time to establish effectivehad adequate time to establish effective

compensatory mechanismscompensatory mechanisms



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Acute Respiratory AcidosisAcute Respiratory Acidosis

CausesCauses

yy Respiratory pathophysiologyRespiratory pathophysiology -- airway obstruction,airway obstruction,

severe pneumonia, chest trauma/pneumothoraxsevere pneumonia, chest trauma/pneumothorax

yyAcute drug intoxication (narcotics, sedatives)Acute drug intoxication (narcotics, sedatives)

yy Residual neuromuscular blockadeResidual neuromuscular blockade

yy CNS disease (head trauma)CNS disease (head trauma)



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Chronic Respiratory AcidosisChronic Respiratory Acidosis

paCOpaCO22 is elevated with a pH in theis elevated with a pH in the

acceptable rangeacceptable range

Renal mechanisms increase the excretion ofRenal mechanisms increase the excretion of

HH++ within 24 hours and may correct thewithin 24 hours and may correct the

resulting acidosis caused by chronicresulting acidosis caused by chronic

retention of COretention of CO22 to a certain extentto a certain extent



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Chronic Respiratory AcidosisChronic Respiratory Acidosis

CausesCauses

yy Chronic lung disease (BPD, COPD)Chronic lung disease (BPD, COPD)

yy Neuromuscular diseaseNeuromuscular disease

yy Extreme obesityExtreme obesity

yy Chest wall deformityChest wall deformity



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Acute Respiratory AlkalosisAcute Respiratory Alkalosis

paCOpaCO22 is low and the pH is alkaloticis low and the pH is alkalotic

The increase in pH is accounted for entirelyThe increase in pH is accounted for entirely

by the decrease in paCOby the decrease in paCO22

Bicarbonate and base excess will be in theBicarbonate and base excess will be in the

normal range because the kidneys have notnormal range because the kidneys have not

had sufficient time to establish effectivehad sufficient time to establish effective

compensatory mechanismscompensatory mechanisms



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Respiratory AlkalosisRespiratory Alkalosis

CausesCauses

yy PainPain

yy AnxietyAnxiety

yy HypoxemiaHypoxemiayy Restrictive lungRestrictive lung

diseasedisease

yy Severe congestiveSevere congestive

heart failureheart failure

yy Pulmonary emboliPulmonary emboli

yy DrugsDrugs

yy SepsisSepsis

yy FeverFever

yyThyrotoxicosisThyrotoxicosis

yy PregnancyPregnancy

yy OveraggressiveOveraggressive

mechanicalmechanical

ventilationventilation

yy Hepatic failureHepatic failure



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Uncompensated Metabolic AcidosisUncompensated Metabolic Acidosis

Normal paCONormal paCO22, low HCO, low HCO33, and a pH less, and a pH lessthan 7.30than 7.30

Occurs as a result of increased production ofOccurs as a result of increased production of

acids and/or failure to eliminate these acidsacids and/or failure to eliminate these acids Respiratory system is not compensating byRespiratory system is not compensating by

increasing alveolar ventilationincreasing alveolar ventilation(hyperventilation)(hyperventilation)



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Compensated Metabolic AcidosisCompensated Metabolic Acidosis

paCOpaCO22 less than 30, low HCOless than 30, low HCO33, with a pH of, with a pH of

7.37.3--7.47.4

Patients with chronic metabolic acidosis arePatients with chronic metabolic acidosis are

unable to hyperventilate sufficiently to lowerunable to hyperventilate sufficiently to lower

paCOpaCO22 for complete compensation to 7.4for complete compensation to 7.4



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Metabolic AcidosisMetabolic Acidosis

Elevated Anion GapElevated Anion Gap

CausesCauses

yy KetoacidosisKetoacidosis -- diabetic, alcoholic, starvationdiabetic, alcoholic, starvation

yy Lactic acidosisLactic acidosis -- hypoxia, shock, sepsis, seizureshypoxia, shock, sepsis, seizures

yy Toxic ingestionToxic ingestion salicylates, methanol, ethylenesalicylates, methanol, ethylene

glycol, ethanol, isopropyl alcohol, paraldehyde,glycol, ethanol, isopropyl alcohol, paraldehyde,

toluenetoluene

yy Renal failureRenal failure -- uremiauremia



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Metabolic AcidosisMetabolic Acidosis

Normal Anion GapNormal Anion Gap

CausesCausesyy Renal tubularRenal tubular

acidosisacidosis

yy Post respiratoryPost respiratoryalkalosisalkalosis

yy HypoaldosteronismHypoaldosteronism

yy Potassium sparingPotassium sparing

diureticsdiuretics

yy Pancreatic loss ofPancreatic loss of

bicarbonatebicarbonate

yy DiarrheaDiarrhea

yy Carbonic anhydraseCarbonic anhydrase

inhibitorsinhibitors

yy Acid administrationAcid administration

(HCl, NH(HCl, NH44Cl, arginineCl, arginine

HCl)HCl)

yy SulfamylonSulfamylon

yy CholestyramineCholestyramine

yy Ureteral diversionsUreteral diversions



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Effectiveness of OxygenationEffectiveness of Oxygenation

Further evaluation of the arterial blood gasFurther evaluation of the arterial blood gas

requires assessment of the effectiveness ofrequires assessment of the effectiveness of

oxygenation of the bloodoxygenation of the blood

HypoxemiaHypoxemia decreased oxygen content ofdecreased oxygen content ofbloodblood -- paOpaO22 less than 60 mm Hg and theless than 60 mm Hg and the

saturation is less than 90%saturation is less than 90%

HypoxiaHypoxia inadequate amount of oxygeninadequate amount of oxygen

available to or used by tissues for metabolicavailable to or used by tissues for metabolic

needsneeds



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Mechanisms of HypoxemiaMechanisms of Hypoxemia

Inadequate inspiratory partial pressure ofInadequate inspiratory partial pressure of

oxygenoxygen

HypoventilationHypoventilation

Right to left shuntRight to left shunt

VentilationVentilation--perfusion mismatchperfusion mismatch

Incomplete diffusion equilibriumIncomplete diffusion equilibrium



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Assessment of Gas ExchangeAssessment of Gas Exchange

AlveolarAlveolar--arterial Oarterial O22 tension differencetension differenceyy AA--a gradienta gradient

yy PAOPAO22--PaOPaO22

yy PAOPAO22 = FIO= FIO22(PB(PB -- PHPH22O)O) -- PaCOPaCO22/RQ*/RQ* arterialarterial--Alveolar OAlveolar O22 tension ratiotension ratio

yy PaOPaO22/PAO/PAO22

arterialarterial--inspired Oinspired O22 ratioratio

yy PaOPaO22/FIO/FIO22yy P/F ratioP/F ratio

*RQ=respiratory quotient= 0.8*RQ=respiratory quotient= 0.8



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Assessment of Gas ExchangeAssessment of Gas Exchange

ABGABG AA--a grada grad

PaOPaO22 PaCOPaCO22 RARA 100%100%

Low FIOLow FIO22 qq qq N*N* NN

Alveolar hypoventilationAlveolar hypoventilation qq oo NN NN

Altered gas exchangeAltered gas exchange

Regional V/Q mismatchRegional V/Q mismatch qq oo/N//N/qq oo N/N/oo

Intrapulmonary R to L shuntIntrapulmonary R to L shunt qq N/N/qq oo oo

Impaired diffusionImpaired diffusion qq N/N/qq oo NN

Anatomical R to L shuntAnatomical R to L shunt(intrapulmonary or intracardiac)(intrapulmonary or intracardiac) qq N/N/qq oo oo

* N=normal* N=normal



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SummarySummary

First, does the patient have an acidosis or anFirst, does the patient have an acidosis or an

alkalosisalkalosis

yy Look at the pHLook at the pH

Second, what is the primary problemSecond, what is the primary problem metabolic or respiratorymetabolic or respiratory

yy Look at the pCOLook at the pCO22

yy If the pCOIf the pCO22 change is in the opposite direction of thechange is in the opposite direction of the

pH change, the primary problem is respiratorypH change, the primary problem is respiratory



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SummarySummary

Third, is there any compensation by theThird, is there any compensation by thepatientpatient -- do the calculationsdo the calculationsyy For a primary respiratory problem, is the pHFor a primary respiratory problem, is the pH

change completely accounted for by the changechange completely accounted for by the changein pCOin pCO22 if yes, then there is no metabolic compensationif yes, then there is no metabolic compensation

if not, then there is either partial compensation orif not, then there is either partial compensation orconcomitant metabolic problemconcomitant metabolic problem



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SummarySummary

yy For a metabolic problem, calculate the expectedFor a metabolic problem, calculate the expectedpCOpCO22 if equal to calculated, then there is appropriateif equal to calculated, then there is appropriate

respiratory compensationrespiratory compensation

if higher than calculated, there is concomitantif higher than calculated, there is concomitantrespiratory acidosisrespiratory acidosis

if lower than calculated, there is concomitantif lower than calculated, there is concomitantrespiratory alkalosisrespiratory alkalosis



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SummarySummary

Next, dont forget to look at the effectivenessNext, dont forget to look at the effectiveness

of oxygenation, (and look at the patient)of oxygenation, (and look at the patient)

yy your patient may have a significantly increasedyour patient may have a significantly increased

work of breathing in order to maintain a normalwork of breathing in order to maintain a normalblood gasblood gas

yy metabolic acidosis with a concomitant respiratorymetabolic acidosis with a concomitant respiratory

acidosis is concerningacidosis is concerning



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Case 1Case 1

Little Billy got into some of dads barbiturates.Little Billy got into some of dads barbiturates.

He suffers a significant depression of mentalHe suffers a significant depression of mental

status and respiration. You see him in thestatus and respiration. You see him in the

ER 3 hours after ingestion with a respiratoryER 3 hours after ingestion with a respiratoryrate of 4. A blood gas is obtained (afterrate of 4. A blood gas is obtained (after

doing the ABCs, of course). It shows pH =doing the ABCs, of course). It shows pH =

7.16, pCO7.16, pCO22 = 70, HCO= 70, HCO33 = 22= 22



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Case 1Case 1

What is the acid/base abnormality?What is the acid/base abnormality?

1.1. Uncompensated metabolic acidosisUncompensated metabolic acidosis

2.2. Compensated respiratory acidosisCompensated respiratory acidosis3.3. Uncompensated respiratory acidosisUncompensated respiratory acidosis

4.4. Compensated metabolic alkalosisCompensated metabolic alkalosis



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Case 1Case 1

Uncompensated respiratory acidosisUncompensated respiratory acidosis

There has not been time for metabolicThere has not been time for metabolic

compensation to occur. As the barbituratecompensation to occur. As the barbiturate

toxicity took hold, this child slowed histoxicity took hold, this child slowed his

respirations significantly, pCOrespirations significantly, pCO22 built up in thebuilt up in the

blood, and an acidosis ensued.blood, and an acidosis ensued.



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Case 2Case 2

Little Suzie has had vomiting and diarrhea for 3Little Suzie has had vomiting and diarrhea for 3

days. In her moms words, She cant keepdays. In her moms words, She cant keep

anything down and shes runnin out. Sheanything down and shes runnin out. She

has had 1 wet diaper in the last 24 hours.has had 1 wet diaper in the last 24 hours.She appears lethargic and cool to touch withShe appears lethargic and cool to touch with

a prolonged capillary refill time. Aftera prolonged capillary refill time. After

addressing her ABCs, her blood gas reveals:addressing her ABCs, her blood gas reveals:pH=7.34, pCOpH=7.34, pCO22=26, HCO=26, HCO33=12=12



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Case 2Case 2

What is the acid/base abnormality?What is the acid/base abnormality?

1.1. Uncompensated metabolic acidosisUncompensated metabolic acidosis

2.2. Compensated respiratory alkalosisCompensated respiratory alkalosis3.3. Uncompensated respiratory acidosisUncompensated respiratory acidosis

4.4. Compensated metabolic acidosisCompensated metabolic acidosis



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Case 2Case 2

Compensated metabolic acidosisCompensated metabolic acidosis

The prolong history of fluid loss throughThe prolong history of fluid loss through

diarrhea has caused a metabolic acidosis. Thediarrhea has caused a metabolic acidosis. The

mechanisms probably are twofold. First there ismechanisms probably are twofold. First there islactic acid production from the hypovolemia andlactic acid production from the hypovolemia and

tissue hypoperfusion. Second, there may betissue hypoperfusion. Second, there may be

significant bicarbonate losses in the stool. Thesignificant bicarbonate losses in the stool. The

body has compensated by blowing off the CObody has compensated by blowing off the CO22with increased respirations.with increased respirations.



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Case 3Case 3

You are evaluating a 15 year old female in theYou are evaluating a 15 year old female in theER who was brought in by EMS from schoolER who was brought in by EMS from schoolbecause of abdominal pain and vomiting.because of abdominal pain and vomiting.

Review of system is negative except for a 10Review of system is negative except for a 10lb. weight loss over the past 2 months andlb. weight loss over the past 2 months andpolyuria for the past 2 weeks. She has nopolyuria for the past 2 weeks. She has noother medical problems and denies anyother medical problems and denies any

sexual activity or drug use. On exam, she issexual activity or drug use. On exam, she isalert and oriented, afebrile, HR 115, RR 26alert and oriented, afebrile, HR 115, RR 26and regular, BP 114/75, pulse ox 95% on RA.and regular, BP 114/75, pulse ox 95% on RA.



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Case 3Case 3

Exam is unremarkable except for mild abdominalExam is unremarkable except for mild abdominal

tenderness on palpation in the midepigastrictenderness on palpation in the midepigastric

region and capillary refill time of 3 seconds.region and capillary refill time of 3 seconds.

The nurse has already seen the patient and hasThe nurse has already seen the patient and hassent off routine blood work. She hands yousent off routine blood work. She hands you

the result of the blood gas. pH = 7.21 pCOthe result of the blood gas. pH = 7.21 pCO22==

24 pO24 pO22 = 45 HCO= 45 HCO33 = 10 BE == 10 BE = --10 saturation =10 saturation =

72%72%



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Case 3Case 3

What is the blood gas interpretation?What is the blood gas interpretation?

Uncompensated respiratory acidosis withUncompensated respiratory acidosis with

severe hypoxiasevere hypoxia

Uncompensated metabolic alkalosisUncompensated metabolic alkalosis

Combined metabolic acidosis and respiratoryCombined metabolic acidosis and respiratory

acidosis with severe hypoxiaacidosis with severe hypoxia

Metabolic acidosis with respiratoryMetabolic acidosis with respiratorycompensationcompensation



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Case 3Case 3

Metabolic acidosis with respiratory compensationMetabolic acidosis with respiratory compensation

This is a patient with new onset diabetesThis is a patient with new onset diabetes

mellitus in ketoacidosis. Her pulse oximetrymellitus in ketoacidosis. Her pulse oximetry

saturation and clinical examination do not revealsaturation and clinical examination do not revealany respiratory problems except for tachypneaany respiratory problems except for tachypnea

which is her compensatory mechanism for thewhich is her compensatory mechanism for the

metabolic acidosis. The nurse obtained themetabolic acidosis. The nurse obtained the

blood gas sample from the venous stick whenblood gas sample from the venous stick whenshe sent off the other labs.she sent off the other labs.



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ReferencesReferences

The ICU BookThe ICU Book Paul L. Marino, 1991,Paul L. Marino, 1991,Algorithms for acidAlgorithms for acid--base interpretations, p415base interpretations, p415--426426

Textbook of Pediatric Intensive Care 3Textbook of Pediatric Intensive Care 3rdrd EditionEdition edited by Mark C. Rogers, 1996, Respiratoryedited by Mark C. Rogers, 1996, RespiratoryMonitoring: Interpretation of clinical blood gasMonitoring: Interpretation of clinical blood gasvalues, p355values, p355--361361

Pediatric Critical CarePediatric Critical Care Bradley Fuhrman andBradley Fuhrman and

Jerry Zimmerman, 1992, AcidJerry Zimmerman, 1992, Acid--Base BalanceBase Balanceand Disorders, p689and Disorders, p689--696696

Critical Care PhysiologyCritical Care Physiology Robert Bartlett, 1996,Robert Bartlett, 1996,AcidAcid--Base physiology p165Base physiology p165--173.173.


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Blood Gases Analysis

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