Acid Base BalanceAcid Base Balance

NURS 108NURS 108

ECCECCMajuvy L. Sulse MSN, RN, CCRNMajuvy L. Sulse MSN, RN, CCRN

TERMSTERMS

AcidAcid• Substance that dissociates or lose ionsSubstance that dissociates or lose ions

AcidosisAcidosis• Process that adds acids or eliminates base from body fluidsProcess that adds acids or eliminates base from body fluids• Hydrogen ions increasedHydrogen ions increased• pH is decreased<7.35pH is decreased<7.35

BaseBase• Substance that accepts ionsSubstance that accepts ions

AlkalosisAlkalosis• Process that adds base or eliminates acid from body fluidsProcess that adds base or eliminates acid from body fluids

TERMSTERMS

pHpH• Negative logarithm of hydrogen ion concentration in the Negative logarithm of hydrogen ion concentration in the

bloodblood• Normal range-7.35-7.45 (N=7.40)Normal range-7.35-7.45 (N=7.40)• Inversely proportional to hydrogen concentrationInversely proportional to hydrogen concentration

Increase in H ions=low pH (acidosis)Increase in H ions=low pH (acidosis) Decrease in H ions=high pH (alkalosis)Decrease in H ions=high pH (alkalosis)

Anion gapAnion gap• Normal=5-15Normal=5-15• Helpful in differential diagnosis of acidosisHelpful in differential diagnosis of acidosis• Calculated by subtracting anions from cationsCalculated by subtracting anions from cations

(Anion gap=Na+K –Cl+HCO3)(Anion gap=Na+K –Cl+HCO3)

TERMSTERMS

PaO2PaO2• Partial pressure of O2 dissolved in arterial bloodPartial pressure of O2 dissolved in arterial blood• Normal value= 80-100mmHgNormal value= 80-100mmHg

SaO2SaO2• Amount of O2 bound to hemoglobinAmount of O2 bound to hemoglobin

3% of O2 dissolved in plasma3% of O2 dissolved in plasma 97% bound to hemoglobin97% bound to hemoglobin

• Normal range-93-100%Normal range-93-100%

TERMSTERMS

PaCO2PaCO2• Partial pressure of carbon dioxide dissolved in arterial bloodPartial pressure of carbon dioxide dissolved in arterial blood• Normal range =35-45mmHgNormal range =35-45mmHg• Regulated in the lungsRegulated in the lungs

Hypoventilation- respiratory acidosis-CO2 retentionHypoventilation- respiratory acidosis-CO2 retention Hyperventilation- respiratory alkalosis- CO2 excretionHyperventilation- respiratory alkalosis- CO2 excretion

HCO3HCO3• Concentration of sodium bicarbonate in the bloodConcentration of sodium bicarbonate in the blood• Normal range= 22-26mEqNormal range= 22-26mEq• Regulated in the kidneysRegulated in the kidneys

Metabolic alkalosis >26mEqMetabolic alkalosis >26mEq Metabolic acidosis < 22mEqMetabolic acidosis < 22mEq

Oxyhemoglobin Dissociation CurveOxyhemoglobin Dissociation Curve

Oxyhemoglobin Dissociation CurveOxyhemoglobin Dissociation Curve

Low paO2 at tissue level (hypoxia)=Shift Low paO2 at tissue level (hypoxia)=Shift to right-O2 readily released from the to right-O2 readily released from the hemoglobinhemoglobin

• Acidemia, Hyperthermia, hypercarbiaAcidemia, Hyperthermia, hypercarbia

High PaCO2 at pulmonary capillary High PaCO2 at pulmonary capillary level=Shift to left-O2 more bound to level=Shift to left-O2 more bound to hemoglobinhemoglobin

• Alkalosis, hypothermia, hypocarbia, high altitude, Alkalosis, hypothermia, hypocarbia, high altitude, carcon monoxide poisoiningcarcon monoxide poisoining

Acid-Base RegulationAcid-Base Regulation

Buffer systemBuffer system Substance that reacts with an acid or base to prevent Substance that reacts with an acid or base to prevent

a large change in pHa large change in pH Fast acting and a primary regulator of acid base Fast acting and a primary regulator of acid base

balancebalance Can react in two waysCan react in two ways

• As an acid-releasing H ionsAs an acid-releasing H ions• As a base-binding a H ionAs a base-binding a H ion

Carbonic acid/bicarbonate systemCarbonic acid/bicarbonate system

H+HCO3=H2CO3=H20+ CO2H+HCO3=H2CO3=H20+ CO2

Respiratory MechanismRespiratory Mechanism

22ndnd line of defense against changes in fluid pH line of defense against changes in fluid pH Under control of the nervous systemUnder control of the nervous system Regulates the excretion and retention of Regulates the excretion and retention of

carbonic acidcarbonic acid If pH is down-rate & depth of ventilation If pH is down-rate & depth of ventilation

increased increased If pH is up- rate and depth of ventilation is If pH is up- rate and depth of ventilation is

decreaseddecreased Rapid action following alteration in acid base Rapid action following alteration in acid base

balance balance

Neural regulation of respiration and Neural regulation of respiration and Hydrogen Ion concentrationHydrogen Ion concentration

Decreased rate and depth of respiration

Inhibition of central chemoreceptors

Decreased PaCO2 Decreased H+

IncreasedPaCO2

Increased H+

Stimulation of Chemoreceptors

Increased rate and depth of respiration

Renal MechanismRenal Mechanism

33rdrd line of defense line of defense Strongest of all mechanisms but takes Strongest of all mechanisms but takes

long to completely respond (24-48 hrs)long to completely respond (24-48 hrs) Operates on 3 mechanismsOperates on 3 mechanisms

Movement of bicarbonateMovement of bicarbonate Formation of acidsFormation of acids Formation of ammoniumFormation of ammonium

Renal MechanismRenal Mechanism

Movement of bicarbonateMovement of bicarbonate• When H ions are high-bicarbonates are reabsorbed from the When H ions are high-bicarbonates are reabsorbed from the

kidneys and back to circulationkidneys and back to circulation• When H ions are low-bicarbonates remain in the kidneys and When H ions are low-bicarbonates remain in the kidneys and

excreted in the urineexcreted in the urine Formation of acidsFormation of acids

• Phosphate (HPO4) draws and combines with H ions into the Phosphate (HPO4) draws and combines with H ions into the urine forming an acid (H2PO4) and excreted in the urineurine forming an acid (H2PO4) and excreted in the urine

Formation of ammoniumFormation of ammonium• Ammonia (NH3) is secreted in the urine-combines with H Ammonia (NH3) is secreted in the urine-combines with H

ions to form Ammonium (NH4)-excreted in urineions to form Ammonium (NH4)-excreted in urine

CompensationCompensation

Body attempts to correct for the changes in Body attempts to correct for the changes in body/blood pHbody/blood pH

Respiratory system- more sensitive to aci-base Respiratory system- more sensitive to aci-base changes thus can begin compensation within changes thus can begin compensation within seconds to minutesseconds to minutes

Renal compensation-more powerful but does not Renal compensation-more powerful but does not get stimulated until imbalance is sustained for get stimulated until imbalance is sustained for several hours to daysseveral hours to days

CompensationCompensation Respiratory- RapidRespiratory- Rapid

• Metabolic acidosis- increase in depth and rate of Metabolic acidosis- increase in depth and rate of respiration to blow off CO2-pH returns to normalrespiration to blow off CO2-pH returns to normal

• Metabolic alkalosis-lungs decrease the rate & Metabolic alkalosis-lungs decrease the rate & depth of respiration-paCO2 returns to normaldepth of respiration-paCO2 returns to normal

RenalRenal• Respiratory acidosis-kidneys increase excretion of Respiratory acidosis-kidneys increase excretion of

H ions or increase reabsorption of bicarbonates-pH H ions or increase reabsorption of bicarbonates-pH returns to normal returns to normal

• Respiratory alkalosis-kidneys reabsorb more H Respiratory alkalosis-kidneys reabsorb more H ions or excreteions or excrete

more bicarbonatesmore bicarbonates

CompensationCompensation

pH –within normal 7.35-7.45pH –within normal 7.35-7.45 HCO3-must be abnormalHCO3-must be abnormal pCO2- & HCO3 going in the same pCO2- & HCO3 going in the same

directiondirection ExampleExample

• pH -7.37 pCO2-60 HCO3- 38pH -7.37 pCO2-60 HCO3- 38

Acid Base ImbalancesAcid Base Imbalances Metabolic Acidosis-low pH, low HCO3,K elevated,Metabolic Acidosis-low pH, low HCO3,K elevated,

• Overproduction of H ionsOverproduction of H ions Excessive breakdown of fatty acids-ketoacidosis Excessive breakdown of fatty acids-ketoacidosis

(DKA & Starvation) releases H ions(DKA & Starvation) releases H ions Hypermetabolism-lactic acidosis- excessive exercise, Hypermetabolism-lactic acidosis- excessive exercise,

seizure, fever, hypoxiaseizure, fever, hypoxia Excessive intake of acid substances-ASA, alcoholic Excessive intake of acid substances-ASA, alcoholic

beveragesbeverages• Under elimination of H ions –kidney failureUnder elimination of H ions –kidney failure• Underproduction of bicarbonates-renal/liver failure, Underproduction of bicarbonates-renal/liver failure,

dehydrationdehydration• Overproduction of bicarbonates-but presence of diarrheaOverproduction of bicarbonates-but presence of diarrhea

Metabolic Acidosis-Clinical Metabolic Acidosis-Clinical ManifestationsManifestations

Neurologic-Neurologic-• Headache, drowsiness, confusion, comaHeadache, drowsiness, confusion, coma

NeuromascularNeuromascular• Decrease in muscle tone and deep tendon reflexesDecrease in muscle tone and deep tendon reflexes

RespiratoryRespiratory• Deep rapid respirations-Kaussmaul breathingDeep rapid respirations-Kaussmaul breathing

CardiovascularCardiovascular• Low BP arrhythmiasLow BP arrhythmias• Warm flushed skin due to vasodilationWarm flushed skin due to vasodilation

GIGI• Nausea, vomiting, diarrhea, abdominal painNausea, vomiting, diarrhea, abdominal pain

Metabolic Acidosis-InterventionsMetabolic Acidosis-Interventions

HydrationHydration Treat or control the causative causeTreat or control the causative cause

• DKA- hydration & insulin DKA- hydration & insulin • Diarrhea-rehydration & antidiarrhealsDiarrhea-rehydration & antidiarrheals

Bicarbonate is administered only if serum Bicarbonate is administered only if serum bicarbonate levels are lowbicarbonate levels are low

Acid Base ImbalancesAcid Base Imbalances

Respiratory Acidosis-low pH, high pCO2, KRespiratory Acidosis-low pH, high pCO2, K Retention of CO2Retention of CO2 Respiratory depressionRespiratory depression

• Anesthesia, drugs, trauma, neurologic disease,Anesthesia, drugs, trauma, neurologic disease, Inadequate chest expansionInadequate chest expansion

• Skeletal deformities, muscle weakness, obesity, tumorSkeletal deformities, muscle weakness, obesity, tumor Airway obstructionAirway obstruction

• asthma, COPD, bronchiolitisasthma, COPD, bronchiolitis Reduced alveolar-capillary diffusionReduced alveolar-capillary diffusion

• Thrombus, pneumonia, TB, Cystic fibrosis, atelectasis, Thrombus, pneumonia, TB, Cystic fibrosis, atelectasis, ARDS, ARDS,

NeurologicNeurologic• Disorientation, drowsiness, dizziness, headache, Disorientation, drowsiness, dizziness, headache,

comacoma

RespiratoryRespiratory• hypoventilationhypoventilation

CardiovascularCardiovascular• Low BP, arrhythmiasLow BP, arrhythmias

NeuromascularNeuromascular• seizuresseizures

Respiratory Acidosis- ManifestationsRespiratory Acidosis- Manifestations

Respiratory Acidosis-InterventionsRespiratory Acidosis-Interventions

Maintain patent airway, enhance gas exchange, Maintain patent airway, enhance gas exchange, adequate oxygenationadequate oxygenation

Pulmonary hygiene-positioning breathing Pulmonary hygiene-positioning breathing techniquestechniques

Ventilatory supportVentilatory support Prevention of complicationsPrevention of complications Drug therapy aimed atDrug therapy aimed at

Increasing diameter of airwaysIncreasing diameter of airways• Induce relaxationInduce relaxation• Increase bronchodilationIncrease bronchodilation

Thin secretionsThin secretions

Combined Respiratory & Metabolic Combined Respiratory & Metabolic AcidosisAcidosis

Can occur simultaneouslyCan occur simultaneously Leads to anaerobic metabolism and lactic Leads to anaerobic metabolism and lactic

acidosisacidosis Acidosis more profound than that caused Acidosis more profound than that caused

by respiratory or metabolic acidosisby respiratory or metabolic acidosis May lead to cardiac arrestMay lead to cardiac arrest

Acid Base ImbalancesAcid Base Imbalances

Metabolic Alkalosis-high pH hallmarked by Metabolic Alkalosis-high pH hallmarked by an increased in bicarbonate and rising an increased in bicarbonate and rising paCO2, low K & CapaCO2, low K & Ca Base excessBase excess

• Ingestion of bicarbonates, acetates, citrates, and Ingestion of bicarbonates, acetates, citrates, and lactateslactates

Acid deficitAcid deficit• Prolonged vomiting, Cushing’s syndrome, Thiazide Prolonged vomiting, Cushing’s syndrome, Thiazide

diuretics, prolonged NGT suctioningdiuretics, prolonged NGT suctioning

Metabolic Alkalosis-Metabolic Alkalosis-ManifestationsManifestations

NeurologicNeurologic• Dizziness, irritability, nervousness, confusionDizziness, irritability, nervousness, confusion

RespiratoryRespiratory• Hypoventilation-a compensatory actionHypoventilation-a compensatory action

CardiovascularCardiovascular• Tachycardia, arrhythmia related to low KTachycardia, arrhythmia related to low K

NeuromascularNeuromascular• Tetany, tremors, tingling of fingers & toes, hypertonic Tetany, tremors, tingling of fingers & toes, hypertonic

muscles, cramps & seizuresmuscles, cramps & seizures GIGI

• Anorexia, nausea & vomitingAnorexia, nausea & vomiting

Metabolic Alkalosis-Metabolic Alkalosis-InterventionsInterventions

Restore normal fluid & electrolyte balanceRestore normal fluid & electrolyte balance Drug therapy to restore electrolyte balanceDrug therapy to restore electrolyte balance

• K sparing diureticsK sparing diuretics• AntiemeticsAntiemetics

Avoid administration of alkaline Avoid administration of alkaline substances-Na Bicarbonate or antacidssubstances-Na Bicarbonate or antacids

Acid Base ImbalancesAcid Base Imbalances

Respiratory Alkalosis-high pH, low Respiratory Alkalosis-high pH, low bicarbonate, low PaCo2,low K & Cabicarbonate, low PaCo2,low K & Ca

Co2 level is so low because of Co2 level is so low because of hyperventilationhyperventilation Direct stimulation of respiratory center due to Direct stimulation of respiratory center due to

fever, compensation for metabolic acidosis, fever, compensation for metabolic acidosis, CNS lesions, drugs, painCNS lesions, drugs, pain

ventilation settings too high or fastventilation settings too high or fast Anxiety, fearAnxiety, fear

Respiratory alkalosis-Respiratory alkalosis-ManifestationsManifestations

NeurologicNeurologic• Light headedness, lethargy, confusionLight headedness, lethargy, confusion

RespiratoryRespiratory• Hyperventilation- lungs cannot compensate for the Hyperventilation- lungs cannot compensate for the

respiratory problemrespiratory problem CardiovascularCardiovascular

• Tachycardia, arrhythmias Tachycardia, arrhythmias NeuromascularNeuromascular

• Numbness, tetany, tingling of extremity,Numbness, tetany, tingling of extremity,• Hyperflexia, seizuresHyperflexia, seizures

GIGI• Nausea, vomiting, epigastric painNausea, vomiting, epigastric pain

Respiratory alkalosis-InterventionsRespiratory alkalosis-Interventions

Monitor for indications of respiratory failureMonitor for indications of respiratory failure Use rebreather mask Use rebreather mask Provide mechanical ventilatory supportProvide mechanical ventilatory support Reduce O2 consumption to minimize Reduce O2 consumption to minimize

hyperventilation-reduce fever, pain, hyperventilation-reduce fever, pain, anxiety and promote comfortanxiety and promote comfort

Monitor labs-ABGs, lytesMonitor labs-ABGs, lytes

Arterial Blood GasesArterial Blood Gases

Provides acid-base statusProvides acid-base status Provides information on the origin of the Provides information on the origin of the

imbalanceimbalance Provides an idea of body’s ability to regulate pHProvides an idea of body’s ability to regulate pH Provides reflection of overall oxygenation statusProvides reflection of overall oxygenation status Finding interpreted in conjunction with patient Finding interpreted in conjunction with patient

clinical history, physical assessment, and clinical history, physical assessment, and previous ABGprevious ABG

Steps in determining ABGsSteps in determining ABGs 1)Determine if pH is acidotic or alkalotic1)Determine if pH is acidotic or alkalotic 2)Analyze the pCO2 to determine respiratory acidosis or 2)Analyze the pCO2 to determine respiratory acidosis or

metabolic. CO2 is controlled by the lungs, metabolic. CO2 is controlled by the lungs, • high CO2=acidosis, low CO2 =alkalosishigh CO2=acidosis, low CO2 =alkalosis

3)Analyze HCO3 to determine metabolic acidosis or 3)Analyze HCO3 to determine metabolic acidosis or alkalosis. HCO3 is the metabolic component controlled alkalosis. HCO3 is the metabolic component controlled by the kidneyby the kidney

• high HCO3=alkalosis, low HCO3=acidosishigh HCO3=alkalosis, low HCO3=acidosis 4)Determine if CO2 or HCO3 matches the acid or base 4)Determine if CO2 or HCO3 matches the acid or base

alteration of pH.alteration of pH.• If pH is acidotic and CO2 is high=respiratory acidosisIf pH is acidotic and CO2 is high=respiratory acidosis• .If pH and HCO3 high= metabolic acidosis.If pH and HCO3 high= metabolic acidosis

5)Decide if the body is attempting to compensate for the 5)Decide if the body is attempting to compensate for the pH changepH change

Normal Blood Gas ValuesNormal Blood Gas Values

ParameterParameter ArterialArterial VenousVenous

pHpH 7.35-7.457.35-7.45 7.35-7.457.35-7.45

pCO2pCO2 35-45mmHg35-45mmHg 40-45mmHg40-45mmHg

pO2pO2 80-100mmHg80-100mmHg 40-50mmHg40-50mmHg

HCO3HCO3 22-26mEq/L22-26mEq/L 22-26mEq/L22-26mEq/L

O2 SaturationO2 Saturation 96-100%96-100% 60-85%60-85%

Base excessBase excess +/-2.omEq/L+/-2.omEq/L +/-2.omEq/L+/-2.omEq/L

What acid-base disorders are What acid-base disorders are represented by the following arterial represented by the following arterial

blood testsblood tests

pHpH pCo2pCo2 HCO3HCO3 7.187.18 6868 2828 7.567.56 5050 3232 7.217.21 5151 1919 7.327.32 4949 2222 7.507.50 2222 2929 7.497.49 3232 3131 7. 377. 37 5757 1717