Focus on Acid-Base Balance and Arterial Blood Gases (Relates to Chapter 17, “Fluid, Electrolyte,...

Focus onFocus onAcid-Base Balance and Acid-Base Balance and Arterial Blood GasesArterial Blood Gases

(Relates to Chapter 17, (Relates to Chapter 17, “Fluid, Electrolyte, and Acid-Base “Fluid, Electrolyte, and Acid-Base

Imbalances,” Imbalances,” in the textbook)in the textbook)

Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

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PurposePurpose

•Maintain a steady balance Maintain a steady balance between acids and bases to between acids and bases to achieve homeostasisachieve homeostasis

•Health problems lead to Health problems lead to imbalanceimbalance•Diabetes mellitusDiabetes mellitus•Vomiting and diarrhea Vomiting and diarrhea •Respiratory conditionsRespiratory conditions


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pHpH

•Measure of HMeasure of H++ ion ion concentrationconcentration

•Blood is slightly alkaline at Blood is slightly alkaline at pH 7.35 to 7.45.pH 7.35 to 7.45.•<7.35 is acidosis.<7.35 is acidosis.•>7.45 is alkalosis.>7.45 is alkalosis.


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Range of pHRange of pH


Fig. 17-16. The normal range of plasma pH is 7.35 to 7.45. A normal pH is maintained by a ratio of 1 partcarbonic acid to 20 parts bicarbonate.

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Regulators of Acid/BaseRegulators of Acid/Base

•Metabolic processes Metabolic processes produce acids that must be produce acids that must be neutralized and excreted. neutralized and excreted.

•Regulatory mechanismsRegulatory mechanisms•BuffersBuffers•Respiratory systemRespiratory system•Renal systemRenal system


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•Buffers: Act chemically to Buffers: Act chemically to neutralize acids or change neutralize acids or change strong acids to weak acidsstrong acids to weak acids•Primary regulatorsPrimary regulators•React immediatelyReact immediately•Cannot maintain pH without Cannot maintain pH without

adequate respiratory and adequate respiratory and renal functionrenal function


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•Respiratory system:Respiratory system: Eliminates Eliminates COCO22

•Respiratory center in medullaRespiratory center in medullacontrols breathing.controls breathing.

•Responds within minutes/hours to Responds within minutes/hours to changes in acid/base.changes in acid/base.

• Increased respirations lead to Increased respirations lead to increasedincreased CO CO22 elimination and elimination and decreased COdecreased CO22 in blood. in blood.


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•Renal system:Renal system: Eliminates H Eliminates H++ and reabsorbs HCOand reabsorbs HCO33

•Reabsorption and secretion Reabsorption and secretion

of electrolytes (e.g., Naof electrolytes (e.g., Na++, Cl, Cl))•Responds within hours to Responds within hours to

daysdays


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Alterations in Acid-Base Alterations in Acid-Base BalanceBalance

• Imbalances occur when Imbalances occur when compensatory mechanisms compensatory mechanisms fail.fail.

•Classification of imbalancesClassification of imbalances•Respiratory:Respiratory: Affect carbonic Affect carbonic

acid concentrationacid concentration•Metabolic:Metabolic: Affect bicarbonate Affect bicarbonate


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Respiratory AcidosisRespiratory Acidosis

•Carbonic acid excess Carbonic acid excess caused bycaused by•HypoventilationHypoventilation•Respiratory failureRespiratory failure

•CompensationCompensation•Kidneys conserve HCOKidneys conserve HCO33

and and secrete Hsecrete H+ + into urine.into urine.


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Types of Acid-Base Types of Acid-Base ImbalancesImbalances


Fig. 17-17. Kinds of acid-base imbalances. A, Respiratory imbalances caused by carbonic acid (CA) excess andcarbonic acid deficit. B, Metabolic imbalances caused by base bicarbonate (BB) deficit and base bicarbonateexcess.

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Respiratory AlkalosisRespiratory Alkalosis

•Carbonic acid deficit caused Carbonic acid deficit caused byby•HyperventilationHyperventilation•Hypoxemia from acute Hypoxemia from acute

pulmonary disorderspulmonary disorders•CompensationCompensation•Rarely occurs because of Rarely occurs because of

aggressive treatment of causes aggressive treatment of causes of hypoxemiaof hypoxemia


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Metabolic AcidosisMetabolic Acidosis

•Base bicarbonate deficit Base bicarbonate deficit caused bycaused by•KetoacidosisKetoacidosis•Lactic acid accumulation Lactic acid accumulation

(shock)(shock)•Severe diarrheaSevere diarrhea•Kidney diseaseKidney disease


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Metabolic AcidosisMetabolic Acidosis

•Compensatory mechanismsCompensatory mechanisms• Increased COIncreased CO22 excretion by excretion by

lungslungs Kussmaul respirations (deep Kussmaul respirations (deep and rapid)and rapid)

•Kidneys excrete acidKidneys excrete acid


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Metabolic AlkalosisMetabolic Alkalosis

•Base bicarbonate excess Base bicarbonate excess caused bycaused by•Prolonged vomiting or Prolonged vomiting or

gastric suctiongastric suction•Gain of HCOGain of HCO33


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Metabolic AlkalosisMetabolic Alkalosis

•Compensatory mechanismsCompensatory mechanisms•Decreased respiratory rate to Decreased respiratory rate to

increase plasma COincrease plasma CO22

•Renal excretion of HCORenal excretion of HCO33


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Blood Gas ValuesBlood Gas Values

•Arterial blood gas (ABG) Arterial blood gas (ABG) values provide information values provide information about about •Acid-base statusAcid-base status•Underlying cause of Underlying cause of

imbalance imbalance •Body’s ability to regulate pHBody’s ability to regulate pH•Overall oxygen statusOverall oxygen status


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Interpretation of ABGsInterpretation of ABGs

•Diagnosis in six steps:Diagnosis in six steps:•Evaluate pH. Evaluate pH. •Analyze PaCOAnalyze PaCO22..•Analyze HCOAnalyze HCO33

•Determine if CODetermine if CO22 or HCO or HCO33

matches the alteration.matches the alteration.

•Decide if the body is Decide if the body is attempting to compensate.attempting to compensate.


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Normal Blood Gas ValuesNormal Blood Gas Values


Table 17-15. Normal Arterial Blood Gas Values *.

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Sample ABG Sample ABG InterpretationInterpretation


Table 17-16. Arterial Blood Gas (ABG) Analysis.

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Acid-Base Mnemonic—Acid-Base Mnemonic—ROMEROME

•RRespiratoryespiratory•OOppositepposite•AlkalosisAlkalosis ↑ ↑ pHpH ↓ ↓ PaCOPaCO22

•AcidosisAcidosis ↓ ↓ pHpH ↑ ↑ PaCOPaCO22

•MMetabolicetabolic• EEqualqual•AcidosisAcidosis ↓ ↓ pHpH ↓ HCO3↓ HCO3•AlkalosisAlkalosis ↑ ↑ pHpH ↑ ↑ HCO3 HCO3


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•pH 7.36pH 7.36•PaCOPaCO22 67 mm Hg 67 mm Hg•PaOPaO22 47 mm Hg 47 mm Hg•HCOHCO33 37 mEq/L 37 mEq/L•What is this?What is this?•Respiratory acidosisRespiratory acidosis


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•pH 7.18pH 7.18•PaCOPaCO22 38 mm Hg 38 mm Hg•PaOPaO22 70 mm Hg 70 mm Hg•HCOHCO33

15 mEq/L 15 mEq/L•What is this?What is this?•Metabolic acidosisMetabolic acidosis


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22 mEq/L 22 mEq/L•What is this?What is this?•Respiratory alkalosisRespiratory alkalosis


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50 mEq/L 50 mEq/L•What is this?What is this?•Metabolic alkalosisMetabolic alkalosis


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18 mEq/L 18 mEq/L•What is this ?What is this ?•Metabolic acidosis partialMetabolic acidosis partial


A patient with an acid-base imbalance has an A patient with an acid-base imbalance has an altered altered

potassium level. The nurse recognizes that the potassium level. The nurse recognizes that the potassium potassium

level is altered because:level is altered because:

1. Potassium is returned to extracellular fluid 1. Potassium is returned to extracellular fluid when metabolic acidosis is corrected.when metabolic acidosis is corrected.

2. Hyperkalemia causes an alkalosis that results in 2. Hyperkalemia causes an alkalosis that results in potassium being shifted into the cells.potassium being shifted into the cells.

3. Acidosis causes hydrogen ions in the blood to 3. Acidosis causes hydrogen ions in the blood to be exchanged for potassium from the cells.be exchanged for potassium from the cells.

4. In alkalosis, potassium is shifted into 4. In alkalosis, potassium is shifted into extracellular fluid to bind excessive bicarbonate.extracellular fluid to bind excessive bicarbonate.

Audience Response Question

Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc. 27

A patient has the following arterial blood A patient has the following arterial blood gas (ABG) results: pH 7.48, PaOgas (ABG) results: pH 7.48, PaO22 86 mm 86 mm Hg, PaCOHg, PaCO22 44 mm Hg, HCO 44 mm Hg, HCO33 29 mEq/L. 29 mEq/L. When assessing the patient, the nurse When assessing the patient, the nurse would expect the patient to experience:would expect the patient to experience:

1. Warm, flushed skin.1. Warm, flushed skin. 2. Respiratory rate of 36.2. Respiratory rate of 36.3. Blood pressure of 94/52.3. Blood pressure of 94/52.4. Hypertonic muscles with cramping.4. Hypertonic muscles with cramping.

Audience Response Question


Case StudiesCase Studies


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Case Study 1: JeriCase Study 1: Jeri

• Jeri’s been on a 3-day party Jeri’s been on a 3-day party binge.binge.

• Friends are unable to awaken Friends are unable to awaken her.her.

•Assessment reveals level of Assessment reveals level of consciousness difficult to arouse.consciousness difficult to arouse.


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•Respiratory rate 8Respiratory rate 8

•Shallow breathing patternShallow breathing pattern

•Diminished breath soundsDiminished breath sounds


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1.1. What ABGs do you What ABGs do you expect?expect?

2.2. What is your treatment?What is your treatment?


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Case Study 2: MaynaCase Study 2: Mayna

•Presented to the ED after a Presented to the ED after a sexual assaultsexual assault

• Examination reveals Examination reveals hysteria and emotional hysteria and emotional distress.distress.


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• Lungs clearLungs clear

•OO22 sat 96% sat 96%


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Case Study 3: GlenCase Study 3: Glen

•History of fever, aches, and History of fever, aches, and chillschills

•Generally feeling illGenerally feeling ill

•Cough productive of yellow, Cough productive of yellow, thick sputum for the past 4 thick sputum for the past 4 daysdays


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• Examination reveals temp Examination reveals temp 38.438.4° C° C


• Lungs with crackles in left Lungs with crackles in left lower lobeslower lobes


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Case Study 4: AlanCase Study 4: Alan

• 17 years old17 years old

•History ofHistory of •Feeling badFeeling bad•FatigueFatigue•Constant thirstConstant thirst•Frequent urinationFrequent urination


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•Blood sugar is 484 mg/dL.Blood sugar is 484 mg/dL.

•Respirations are 28 and Respirations are 28 and deep.deep.

•Breath has a fruity odor.Breath has a fruity odor.

• Lungs are clear.Lungs are clear.Copyright © 2011, 2007 by Mosby, Inc., an affiliate of Elsevier Inc.

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Case Study 5: AnthonyCase Study 5: Anthony

•History of nausea and History of nausea and vomiting for the past weekvomiting for the past week

•Has been self-medicating Has been self-medicating himself with baking soda to himself with baking soda to control his abdominal control his abdominal discomfortdiscomfort


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Case Study 5: AnthonyCase Study 5: Anthony




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Case Study 6: Susan Case Study 6: Susan

• ABG results are as ABG results are as follows: follows:

• pH 7.20pH 7.20• PaCOPaCO2 2 58 mm Hg58 mm Hg• PaOPaO2 2 59 mm Hg 59 mm Hg • HCOHCO33

24 24 mEq/LmEq/L


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Case Study 6: Susan Case Study 6: Susan

1.1. Describe a patient who Describe a patient who would have these ABGs, would have these ABGs, including history and including history and assessment.assessment.

2.2. What is the treatment?What is the treatment?


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Case Study 7: FernandoCase Study 7: Fernando


• pH 7.39pH 7.39• PaCOPaCO22 38 mm Hg 38 mm Hg • PaOPaO22 44 mm Hg 44 mm Hg • HCOHCO33

24 24 mEq/LmEq/L


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Case Study 7: FernandoCase Study 7: Fernando




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Case Study 8: BriannaCase Study 8: Brianna


• pH 7.36pH 7.36• PaCOPaCO22 58 mm Hg 58 mm Hg• PaOPaO22 50 mm Hg 50 mm Hg• HCOHCO33

33 33 mEq/LmEq/L


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Case Study 8: BriannaCase Study 8: Brianna




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Case Study 9: MonicaCase Study 9: Monica


• pH 7.50pH 7.50• PaCOPaCO22 28 mm Hg 28 mm Hg• PaOPaO22 85 mm Hg 85 mm Hg• HCOHCO33

24 24 mEq/LmEq/L


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Case Study 9: MonicaCase Study 9: Monica




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Case Study 10: MikeCase Study 10: Mike


• pH 7.20pH 7.20• PaCOPaCO22 28 mm Hg 28 mm Hg • PaOPaO22 81 mm Hg 81 mm Hg• HCOHCO33

18 18 mEq/LmEq/L


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Case Study 10: MikeCase Study 10: Mike




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Case Study 11: JeremyCase Study 11: Jeremy


• pH 7.57pH 7.57• PaCOPaCO2 2 46 mm Hg46 mm Hg• PaOPaO2 2 87 mm Hg87 mm Hg• HCOHCO33

38 38 mEq/LmEq/L


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Case Study 11: JeremyCase Study 11: Jeremy




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Focus on Acid-Base Balance and Arterial Blood Gases (Relates to Chapter 17, “Fluid, Electrolyte,...

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