Acid Base Balance

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Acid Base Balance

• NURS 108
• ECC
• Majuvy L. Sulse MSN, RN, CCRN

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TERMS

• Acid
• Substance that dissociates or lose ions
• Acidosis
• Process that adds acids or eliminates base from
  body fluids
• Hydrogen ions increased
• pH is decreasedlt7.35
• Base
• Substance that accepts ions
• Alkalosis
• Process that adds base or eliminates acid from
  body fluids

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TERMS

• pH
• Negative logarithm of hydrogen ion concentration
  in the blood
• Normal range-7.35-7.45 (N7.40)
• Inversely proportional to hydrogen concentration
• Increase in H ionslow pH (acidosis)
• Decrease in H ionshigh pH (alkalosis)
• Anion gap
• Normal5-15
• Helpful in differential diagnosis of acidosis
• Calculated by subtracting anions from cations
• (Anion gapNaK ClHCO3)

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TERMS

• PaO2
• Partial pressure of O2 dissolved in arterial
  blood
• Normal value 80-100mmHg
• SaO2
• Amount of O2 bound to hemoglobin
• 3 of O2 dissolved in plasma
• 97 bound to hemoglobin
• Normal range-93-100

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TERMS

• PaCO2
• Partial pressure of carbon dioxide dissolved in
  arterial blood
• Normal range 35-45mmHg
• Regulated in the lungs
• Hypoventilation- respiratory acidosis-CO2
  retention
• Hyperventilation- respiratory alkalosis- CO2
  excretion
• HCO3
• Concentration of sodium bicarbonate in the blood
• Normal range 22-26mEq
• Regulated in the kidneys
• Metabolic alkalosis gt26mEq
• Metabolic acidosis lt 22mEq

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Oxyhemoglobin Dissociation Curve
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Oxyhemoglobin Dissociation Curve

• Low paO2 at tissue level (hypoxia)Shift to
  right-O2 readily released from the hemoglobin
• Acidemia, Hyperthermia, hypercarbia
• High PaCO2 at pulmonary capillary levelShift to
  left-O2 more bound to hemoglobin
• Alkalosis, hypothermia, hypocarbia, high
  altitude, carcon monoxide poisoining

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Acid-Base Regulation

• Buffer system
• Substance that reacts with an acid or base to
  prevent a large change in pH
• Fast acting and a primary regulator of acid base
  balance
• Can react in two ways
• As an acid-releasing H ions
• As a base-binding a H ion
• Carbonic acid/bicarbonate system
• HHCO3H2CO3H20 CO2

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Respiratory Mechanism

• 2nd line of defense against changes in fluid pH
• Under control of the nervous system
• Regulates the excretion and retention of carbonic
  acid
• If pH is down-rate depth of ventilation
  increased
• If pH is up- rate and depth of ventilation is
  decreased
• Rapid action following alteration in acid base
  balance

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Neural regulation of respiration and Hydrogen Ion
concentration
IncreasedPaCO2 Increased H
Decreased rate and depth of respiration
Inhibition of central chemoreceptors
Stimulation of Chemoreceptors
Decreased PaCO2 Decreased H
Increased rate and depth of respiration
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Renal Mechanism

• 3rd line of defense
• Strongest of all mechanisms but takes long to
  completely respond (24-48 hrs)
• Operates on 3 mechanisms
• Movement of bicarbonate
• Formation of acids
• Formation of ammonium

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Renal Mechanism

• Movement of bicarbonate
• When H ions are high-bicarbonates are reabsorbed
  from the kidneys and back to circulation
• When H ions are low-bicarbonates remain in the
  kidneys and excreted in the urine
• Formation of acids
• Phosphate (HPO4) draws and combines with H ions
  into the urine forming an acid (H2PO4) and
  excreted in the urine
• Formation of ammonium
• Ammonia (NH3) is secreted in the urine-combines
  with H ions to form Ammonium (NH4)-excreted in
  urine

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Compensation

• Body attempts to correct for the changes in
  body/blood pH
• Respiratory system- more sensitive to aci-base
  changes thus can begin compensation within
  seconds to minutes
• Renal compensation-more powerful but does not get
  stimulated until imbalance is sustained for
  several hours to days

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Compensation

• Respiratory- Rapid
• Metabolic acidosis- increase in depth and rate of
  respiration to blow off CO2-pH returns to normal
• Metabolic alkalosis-lungs decrease the rate
  depth of respiration-paCO2 returns to normal
• Renal
• Respiratory acidosis-kidneys increase excretion
  of H ions or increase reabsorption of
  bicarbonates-pH returns to normal
• Respiratory alkalosis-kidneys reabsorb more H
  ions or excrete
• more bicarbonates

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Compensation

• pH within normal 7.35-7.45
• HCO3-must be abnormal
• pCO2- HCO3 going in the same direction
• Example
• pH -7.37 pCO2-60 HCO3- 38

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Acid Base Imbalances

• Metabolic Acidosis-low pH, low HCO3,K elevated,
• Overproduction of H ions
• Excessive breakdown of fatty acids-ketoacidosis
  (DKA Starvation) releases H ions
• Hypermetabolism-lactic acidosis- excessive
  exercise, seizure, fever, hypoxia
• Excessive intake of acid substances-ASA,
  alcoholic beverages
• Under elimination of H ions kidney failure
• Underproduction of bicarbonates-renal/liver
  failure, dehydration
• Overproduction of bicarbonates-but presence of
  diarrhea

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Metabolic Acidosis-Clinical Manifestations

• Neurologic-
• Headache, drowsiness, confusion, coma
• Neuromascular
• Decrease in muscle tone and deep tendon reflexes
• Respiratory
• Deep rapid respirations-Kaussmaul breathing
• Cardiovascular
• Low BP arrhythmias
• Warm flushed skin due to vasodilation
• GI
• Nausea, vomiting, diarrhea, abdominal pain

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Metabolic Acidosis-Interventions

• Hydration
• Treat or control the causative cause
• DKA- hydration insulin
• Diarrhea-rehydration antidiarrheals
• Bicarbonate is administered only if serum
  bicarbonate levels are low

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Acid Base Imbalances

• Respiratory Acidosis-low pH, high pCO2, K
• Retention of CO2
• Respiratory depression
• Anesthesia, drugs, trauma, neurologic disease,
• Inadequate chest expansion
• Skeletal deformities, muscle weakness, obesity,
  tumor
• Airway obstruction
• asthma, COPD, bronchiolitis
• Reduced alveolar-capillary diffusion
• Thrombus, pneumonia, TB, Cystic fibrosis,
  atelectasis, ARDS,

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Respiratory Acidosis- Manifestations

• Neurologic
• Disorientation, drowsiness, dizziness, headache,
  coma
• Respiratory
• hypoventilation
• Cardiovascular
• Low BP, arrhythmias
• Neuromascular
• seizures

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Respiratory Acidosis-Interventions

• Maintain patent airway, enhance gas exchange,
  adequate oxygenation
• Pulmonary hygiene-positioning breathing
  techniques
• Ventilatory support
• Prevention of complications
• Drug therapy aimed at
• Increasing diameter of airways
• Induce relaxation
• Increase bronchodilation
• Thin secretions

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Combined Respiratory Metabolic Acidosis

• Can occur simultaneously
• Leads to anaerobic metabolism and lactic acidosis
• Acidosis more profound than that caused by
  respiratory or metabolic acidosis
• May lead to cardiac arrest

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Acid Base Imbalances

• Metabolic Alkalosis-high pH hallmarked by an
  increased in bicarbonate and rising paCO2, low K
  Ca
• Base excess
• Ingestion of bicarbonates, acetates, citrates,
  and lactates
• Acid deficit
• Prolonged vomiting, Cushings syndrome, Thiazide
  diuretics, prolonged NGT suctioning

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Metabolic Alkalosis-Manifestations

• Neurologic
• Dizziness, irritability, nervousness, confusion
• Respiratory
• Hypoventilation-a compensatory action
• Cardiovascular
• Tachycardia, arrhythmia related to low K
• Neuromascular
• Tetany, tremors, tingling of fingers toes,
  hypertonic muscles, cramps seizures
• GI
• Anorexia, nausea vomiting

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Metabolic Alkalosis-Interventions

• Restore normal fluid electrolyte balance
• Drug therapy to restore electrolyte balance
• K sparing diuretics
• Antiemetics
• Avoid administration of alkaline substances-Na
  Bicarbonate or antacids

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Acid Base Imbalances

• Respiratory Alkalosis-high pH, low bicarbonate,
  low PaCo2,low K Ca
• Co2 level is so low because of hyperventilation
• Direct stimulation of respiratory center due to
  fever, compensation for metabolic acidosis, CNS
  lesions, drugs, pain
• ventilation settings too high or fast
• Anxiety, fear

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Respiratory alkalosis-Manifestations

• Neurologic
• Light headedness, lethargy, confusion
• Respiratory
• Hyperventilation- lungs cannot compensate for the
  respiratory problem
• Cardiovascular
• Tachycardia, arrhythmias
• Neuromascular
• Numbness, tetany, tingling of extremity,
• Hyperflexia, seizures
• GI
• Nausea, vomiting, epigastric pain

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Respiratory alkalosis-Interventions

• Monitor for indications of respiratory failure
• Use rebreather mask
• Provide mechanical ventilatory support
• Reduce O2 consumption to minimize
  hyperventilation-reduce fever, pain, anxiety and
  promote comfort
• Monitor labs-ABGs, lytes

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Arterial Blood Gases

• Provides acid-base status
• Provides information on the origin of the
  imbalance
• Provides an idea of bodys ability to regulate pH
• Provides reflection of overall oxygenation status
• Finding interpreted in conjunction with patient
  clinical history, physical assessment, and
  previous ABG

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Steps in determining ABGs

• 1)Determine if pH is acidotic or alkalotic
• 2)Analyze the pCO2 to determine respiratory
  acidosis or metabolic. CO2 is controlled by the
  lungs,
• high CO2acidosis, low CO2 alkalosis
• 3)Analyze HCO3 to determine metabolic acidosis or
  alkalosis. HCO3 is the metabolic component
  controlled by the kidney
• high HCO3alkalosis, low HCO3acidosis
• 4)Determine if CO2 or HCO3 matches the acid or
  base alteration of pH.
• If pH is acidotic and CO2 is highrespiratory
  acidosis
• .If pH and HCO3 high metabolic acidosis
• 5)Decide if the body is attempting to compensate
  for the pH change

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Normal Blood Gas Values
Parameter Arterial Venous
pH 7.35-7.45 7.35-7.45
pCO2 35-45mmHg 40-45mmHg
pO2 80-100mmHg 40-50mmHg
HCO3 22-26mEq/L 22-26mEq/L
O2 Saturation 96-100 60-85
Base excess /-2.omEq/L /-2.omEq/L
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What acid-base disorders are represented by the
following arterial blood tests

• pH pCo2 HCO3
• 7.18 68 28
• 7.56 50 32
• 7.21 51 19
• 7.32 49 22
• 7.50 22 29
• 7.49 32 31
• 7. 37 57 17