Acid base balance

Acid–Base Balance andAcid–Base Balance and
Arterial Blood GasesArterial Blood Gases

PurposePurpose
 To maintain a balance between acidsTo maintain a balance between acids
and bases to achieve homeostasisand bases to achieve homeostasis
 Arterial blood shows the make-up ofArterial blood shows the make-up of
blood before it is distributed to theblood before it is distributed to the
tissuestissues

pHpH
 Indirect measure of H+ ionIndirect measure of H+ ion
concentrationconcentration
 Ratio of base (HCORatio of base (HCO33) to acid (CO) to acid (CO22))
 Acids give up (donate) H+ ions, whileAcids give up (donate) H+ ions, while
bases pick up H+ ionsbases pick up H+ ions

pHpH
 Body maintains a slightly alkaline pHBody maintains a slightly alkaline pH
of 7.35 - 7.45of 7.35 - 7.45
 Metabolic and respiratory processesMetabolic and respiratory processes
work together to keep hydrogen (H+)work together to keep hydrogen (H+)
levels in a normal rangelevels in a normal range

Regulators of Acid/BaseRegulators of Acid/Base
1.1. BuffersBuffers
2.2. Respiratory systemRespiratory system
3.3. Renal systemRenal system

1.1. Buffers (e.g., bicarbonate,Buffers (e.g., bicarbonate,
proteins, hemoglobinproteins, hemoglobin))
– Primary regulatorsPrimary regulators
– Act immediatelyAct immediately
– Present in blood and tissuesPresent in blood and tissues
– Take up extra H+ ions orTake up extra H+ ions or
release H+release H+

2. Respiratory system2. Respiratory system
– Eliminates COEliminates CO22
– Respiratory centre in medullaRespiratory centre in medulla
controls breathingcontrols breathing
– Increased respirations leads toIncreased respirations leads to ↑↑
COCO22 elimination from body andelimination from body and ↓↓
COCO22 in bloodin blood

 Respiratory systemRespiratory system
– Decreased respirations leads toDecreased respirations leads to ↓↓
COCO22 elimination from body and ↑elimination from body and ↑
COCO22 in bloodin blood
– Responds within minutes to hours toResponds within minutes to hours to
changes in acid/basechanges in acid/base

3. Renal system3. Renal system
– Secretes hydrogen (H+) ions andSecretes hydrogen (H+) ions and
reabsorbs bicarbonate (HCOreabsorbs bicarbonate (HCO33) ions) ions
– Reabsorption and secretion ofReabsorption and secretion of
electrolytes (e.g., Na, Cl)electrolytes (e.g., Na, Cl)
– Responds within hours to daysResponds within hours to days

Acid – Base BalanceAcid – Base Balance
COCO22 + H+ H220 H0 H22COCO33 HH++
+ HCO+ HCO33
--
LungsLungs
RespiratoryRespiratory
FastFast
KidneysKidneys
MetabolicMetabolic
SlowSlow

ABG Normal ValuesABG Normal Values
 pH 7.35 - 7.45 overall statepH 7.35 - 7.45 overall state
 PaCOPaCO22 35 - 45 mm Hg (respiratory35 - 45 mm Hg (respiratory
component)component)
 HCOHCO33 22 - 26 mEq/L (metabolic22 - 26 mEq/L (metabolic
component)component)

ABG Normal ValuesABG Normal Values
 PaOPaO22 80-100 mmHg partial pressure80-100 mmHg partial pressure
of oxygen in arterial bloodof oxygen in arterial blood
 SaOSaO22 96-100% arterial O96-100% arterial O22 saturationsaturation

Normal ValuesNormal Values
Sea LevelSea Level MixedMixed
VenousVenous
pHpH 7.35 - 7.457.35 - 7.45 7.34 -7.377.34 -7.37
PaCOPaCO22 35 - 4535 - 45 44 - 4644 - 46
HCOHCO33 22 - 2622 - 26 24 - 3024 - 30
PaOPaO22 80 - 10080 - 100 38 - 4238 - 42
SaOSaO22 > 95%> 95% 60 - 80%60 - 80%

How to Obtain Arterial BloodHow to Obtain Arterial Blood
 Heparinized syringeHeparinized syringe
 Blood from an arteryBlood from an artery
 On iceOn ice
 Prompt delivery to labPrompt delivery to lab
 IncludeInclude
– Time drawnTime drawn
– FIOFIO22
– Client temperatureClient temperature

Interpretation of ABGsInterpretation of ABGs
 Evaluate pH: this determines acidosisEvaluate pH: this determines acidosis
or alkalosisor alkalosis
 7.40 is in the middle of the normal7.40 is in the middle of the normal
range of 7.35 - 7.45range of 7.35 - 7.45
 Value below 7.40 is moving towardsValue below 7.40 is moving towards
acidosisacidosis
 Value above 7.40 is moving towardsValue above 7.40 is moving towards
alkalosisalkalosis

 Evaluate respiratory componentEvaluate respiratory component
(PaCO(PaCO22))
– If PaCOIf PaCO22 < 35, the value is alkalotic< 35, the value is alkalotic
– If PaCOIf PaCO22 > 45, the value is acidotic> 45, the value is acidotic

 Evaluate the metabolic componentEvaluate the metabolic component
(HCO(HCO33))
– If HCOIf HCO33 > 26 mEq/L, the value is> 26 mEq/L, the value is
alkaloticalkalotic
– If HCOIf HCO33 < 22 mEq/L, the value is< 22 mEq/L, the value is
acidoticacidotic

 Determine which component (PaCODetermine which component (PaCO22
or HCOor HCO33) matches the pH) matches the pH
 If pH is decreased or increased, is theIf pH is decreased or increased, is the
underlying disorder respiratory orunderlying disorder respiratory or
metabolic?metabolic?

 RespiratoryRespiratory
– ↑↑ pH, ↓ PaCOpH, ↓ PaCO22
– ↓↓ pH, ↑ PaCOpH, ↑ PaCO22
 MetabolicMetabolic
– ↑↑ pH, ↑ HCOpH, ↑ HCO33
– ↓↓ pH, ↓ HCOpH, ↓ HCO33

 If both respiratory and metabolicIf both respiratory and metabolic
components match the pH, maybe itcomponents match the pH, maybe it
is a mixed disorderis a mixed disorder

 Determine the degree ofDetermine the degree of
compensationcompensation
Absent:Absent:
• pH is not within normal rangepH is not within normal range
• The component that does notThe component that does not
match the pH imbalance is stillmatch the pH imbalance is still
within its normal rangewithin its normal range

 Determine the degree ofDetermine the degree of
Partial:Partial:
• pH is not within normal rangepH is not within normal range
• The component that does notThe component that does not
match the pH disorder is abovematch the pH disorder is above
or below the normal rangeor below the normal range

 Determine the degree ofDetermine the degree of
Complete:Complete:
• pH is within the normal rangepH is within the normal range
and both components are eitherand both components are either
above or below normal rangeabove or below normal range

 If appropriate, treat underlying causeIf appropriate, treat underlying cause
and then treat acid/base imbalanceand then treat acid/base imbalance

 pH 7.36pH 7.36
 PaCOPaCO22 6767
 PaOPaO22 4747
 HCOHCO33 3737
 What is this?What is this?
– Respiratory acidosisRespiratory acidosis

 pH 7.18pH 7.18
 PaCOPaCO22 3838
 PaOPaO22 7070
 HCOHCO33 1515
– Metabolic acidosisMetabolic acidosis

 pH 7.60pH 7.60
 PaCOPaCO22 3030
 PaOPaO22 6060
 HCOHCO33 2222
– Respiratory alkalosisRespiratory alkalosis

 pH 7.58pH 7.58
 PaCOPaCO22 3535
 PaOPaO22 7575
 HCOHCO33 5050
– Metabolic alkalosisMetabolic alkalosis

 pH 7.28pH 7.28
 PaCOPaCO22 2828
 PaOPaO22 7070
 HCOHCO33 1818
– Metabolic acidosis partialMetabolic acidosis partial

Steps to Acid – Base AnalysisSteps to Acid – Base Analysis
 pHpH
– Acidotic, alkalotic, or normal?Acidotic, alkalotic, or normal?
 PaCOPaCO22
– High or low?High or low?
– Causing or compensating?Causing or compensating?

Steps to Acid – Base AnalysisSteps to Acid – Base Analysis
 HCOHCO33
– High, low, or normal?High, low, or normal?
– Causing or compensating?Causing or compensating?
• Short- or long-term problem?Short- or long-term problem?

Respiratory AcidosisRespiratory Acidosis
pHpH PaCOPaCO22 HCOHCO33
AcidosisAcidosis nlnl

Respiratory AcidosisRespiratory Acidosis
 CausesCauses
– HypoventilationHypoventilation
– Respiratory failureRespiratory failure

Compensated Respiratory AcidosisCompensated Respiratory Acidosis
AcidosisAcidosis
CompensatedCompensated
AcidosisAcidosis
nlnl
nlnl

Compensated Respiratory AcidosisCompensated Respiratory Acidosis
 CausesCauses
– Long-standing respiratoryLong-standing respiratory
insufficiency, COPDinsufficiency, COPD

AcidosisAcidosis
AcidosisAcidosis
AlkalosisAlkalosis
nlnl
nlnl
Respiratory AlkalosisRespiratory Alkalosis
nlnl

Respiratory AlkalosisRespiratory Alkalosis
 CausesCauses
– HyperventilationHyperventilation

AcidosisAcidosis
AcidosisAcidosis
AlkalosisAlkalosis
MetabolicMetabolic
AcidosisAcidosis
nlnl
nlnl
Metabolic AcidosisMetabolic Acidosis
nlnl
nlnl

Metabolic AcidosisMetabolic Acidosis
 CausesCauses
– Anaerobic metabolismAnaerobic metabolism
– Lactic acidosisLactic acidosis
– AnoxiaAnoxia
– PoisoningPoisoning
– OverdoseOverdose

AcidosisAcidosis
AcidosisAcidosis
AlkalosisAlkalosis
MetabolicMetabolic
AcidosisAcidosis
MetabolicMetabolic
AlkalosisAlkalosis
nlnl
nlnl
Metabolic AlkalosisMetabolic Alkalosis
nlnl
nlnl
nlnl

Metabolic AlkalosisMetabolic Alkalosis
 CausesCauses
– VomitingVomiting
– PoisoningPoisoning
– OverdoseOverdose

Acid/Base Mnemonic- ROMEAcid/Base Mnemonic- ROME
 RR (respiratory)(respiratory)
 OO (opposite)(opposite)
– pHpH PaCOPaCO22 alkalosisalkalosis
– pHpH PaCOPaCO22 acidosisacidosis
 MM (metabolic)(metabolic)
 EE (equivalent)(equivalent)
– pHpH HCOHCO33 acidosisacidosis
– pHpH HCOHCO33 alkalosisalkalosis

More Fun with AcidMore Fun with Acid––BaseBase
 Mixed diagnosesMixed diagnoses
– More than one problemMore than one problem
• Acute and compensatedAcute and compensated
respiratory acidosisrespiratory acidosis
• Respiratory and metabolicRespiratory and metabolic
acidosisacidosis

More Fun with AcidMore Fun with Acid––BaseBase
 HyperkalemiaHyperkalemia
– H+ drives K+ out of cells intoH+ drives K+ out of cells into
serumserum
– Treat acidosis, hyperkalemiaTreat acidosis, hyperkalemia
resolvesresolves

Case Study 1Case Study 1
 A woman has taken an overdose ofA woman has taken an overdose of
sleeping tabletssleeping tablets
 Friends are unable to awaken herFriends are unable to awaken her
 Assessment reveals level of consciousnessAssessment reveals level of consciousness
difficult to arousedifficult to arouse
 Respiratory rate 8Respiratory rate 8
 Shallow breathing patternShallow breathing pattern
 Diminished breath soundsDiminished breath sounds

1.1. What ABGs do you expect?What ABGs do you expect?
2.2. What is your treatment?What is your treatment?

 A woman has presented to the ER afterA woman has presented to the ER after
receiving bad news of the death of herreceiving bad news of the death of her
husbandhusband
 Physical exam reveals hystericalPhysical exam reveals hysterical
emotional distressemotional distress
 Lungs clearLungs clear
 OO22 sat 96%sat 96%

1.1. What ABGs do you expect?What ABGs do you expect?
2.2. What is your treatment?What is your treatment?

 History of fever, aches, and chillsHistory of fever, aches, and chills
 Generally feeling illGenerally feeling ill
 Cough productive of yellow, thick sputumCough productive of yellow, thick sputum
for the past 4 daysfor the past 4 days

 Exam reveals temp 38.4Exam reveals temp 38.4°C°C
 Lungs with crackles in left lower lobesLungs with crackles in left lower lobes

1. What ABGs do you expect?1. What ABGs do you expect?
2. What is your treatment?2. What is your treatment?

 15 years old boy15 years old boy
 History ofHistory of
– feeling badfeeling bad
– fatiguefatigue
– constant thirstconstant thirst
– frequent urinationfrequent urination

 Blood sugar is 26.9 mmol/L (484 mg/dL)Blood sugar is 26.9 mmol/L (484 mg/dL)
 Respirations are 28 and deepRespirations are 28 and deep
 Breath has a fruity odourBreath has a fruity odour
 His lungs are clearHis lungs are clear

1. What ABGs do you expect?1. What ABGs do you expect?
2. What is your treatment?2. What is your treatment?

 ABG results are: pH 7.20, PaCOABG results are: pH 7.20, PaCO22 58,58,
PaOPaO22 59, HCO59, HCO33 2424
1.1. Describe a client that would haveDescribe a client that would have
these ABGs, including history andthese ABGs, including history and
assessment.assessment.
2.2. What is the treatmentWhat is the treatment??

1. Describe a client that would have1. Describe a client that would have
2.2. What is the treatment?What is the treatment?

1.1. Describe a client that would haveDescribe a client that would have

Acid base balance

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