AcidBase Determination

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Acid-Base Determination

• Spring Semester, 2006
• Nursing 2904
• Carol Isaac MacKusick, MSN, RN, CNN

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Arterial Blood Gases

• Technique for ABG Sampling
• Allens Test
• Once arterial site is selected, must test for
  collateral circulation
• Allen test used for radial and ulnar arteries
• Simultaneously compress the radial and ulnar
  arteries, ask client to make fist until hand
  blanches, ask client to open fist, release
  pressure from ulnar artery, check for return of
  pinkness to hand

3
ABG Technique

• Indwelling arterial catheter or arterial puncture
• If arterial puncture
• Painful to client
• Same procedure as catheter except for flushing
  line
• HOLD pressure
• Complications Arterial vessel tears, air
  embolism, hemorrhage, arterial obstruction, loss
  of an extremity, and infection

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ABG Technique

• Arterial line (a-line)
• Used to obtain direct and continuous BP
  measurements in critically ill clients and to
  obtain frequent ABG measurements
• Nursing responsibilities for a-line
• Setting up the equipment
• Calibrating equipment to ensure accurate readings
• Assist physician with procedure of inserting
  a-line

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ABG Technique

• A-line Nursing Responsibilities
• Secure pressure tubing to prevent dislodgement
  and possible exsanguination
• Put a pressure bag around the flush solution bag
  and inflate to about 300 mmHg to prevent blood
  from backing up into pressure tubing
• Flush solution may or may not have heparin added

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ABG Technique

• A-line Nursing Responsibilities
• Monitor circulation distal to insertion site
• Notify physician of any alteration in circulation
• Observe for signs of infection
• ABGs and blood samples can be drawn without pain
  or discomfort to client
• Manual baseline blood pressures should be taken
  at least once per shift to correlate with
  arterial readings

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A-Line

• Works with stopcocks
• Discard 3-5 ccs to clear catheter of any flush
  system fluid
• Obtain 1 cc sample in a heparinized syringe
• Remove air and place on airtight cap
• Put on ice to ensure accuracy
• Flush the line

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ABG Interpretation

• Look at PaO2
• Reflects 3 of total oxygen in blood
• Normal range 80-100 mmHg at sea level lower at
  higher elevations
• Normal level for infants breathing room air is
  40-70
• Older adults, 80 mmHg 1 mmHg for every year
  over the age of 60

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ABG Interpretation

• PaO2
• If PaO2 more than lowest level for age, it is
  normal
• Abnormally low PaO2 hypoxemia
• At any age, PaO2 lower than 40 mmHg represents a
  life-threatening situation

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ABG Interpretation

• Look at pH
• Normal 7.35-7.45
• Below 7.35 Acidosis
• Higher than 7.45 Alkalosis

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ABG Interpretation

• Look at PaCO2
• Indicates whether the client can ventilate well
  enough to rid the body of waste products from
  metabolism
• Normal 35-45 mmHg
• Less than 35, alkalosis
• Greater than 45, acidosis

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Respiratory Alkalosis

• Clinical Presentation
• Cardiovascular
• Increased myocardial irritability, palpitations
• Increased HR
• Increased sensitivity to digitalis
• Respiratory
• Rapid, shallow breathing
• Chest tightness and palpitations

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Respiratory Alkalosis

• Clinical presentation
• CNS
• Dizziness, lightheadedness, anxiety, panic,
  tetany, convulsions, difficulty concentrating,
  blurred vision, numbness and tingling in
  extremities, hyperactive reflexes
• Diagnostic findings
• High pH, low PaCO2
• Hypokalemia, hypocalcemia

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Respiratory Alkalosis

• Compensation
• Kidneys conserve H and excrete HCO3
• Low HCO3 indicates bodys attempt to compensate
• With partial compensation, pH is elevated
• With full compensation, pH returns to normal

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Respiratory Alkalosis

• Priority nursing diagnoses
• Sensory perceptual alterations R/T neurological
  deficits
• Altered thought processes R/T altered cerebral
  functioning
• Ineffective breathing pattern R/T
  hyperventilation
• Risk for injury R/T weakness, seizures

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Respiratory Alkalosis

• Management
• Treat underlying cause
• Rebreathe CO2 using a rebreather mask or paper
  bag
• Give oxygen if hypoxic
• Medicate as needed with antianxiety drugs

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Respiratory Alkalosis

• Planning and Implementation
• Provide support and reassurance
• Monitor VS and ABGs
• Assist client to breathe slowly
• Provide paper bag or rebreather mask
• Protect from injury
• Administer antianxiety medications and monitor
  response

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ABG Interpretation

• Look at PaCO2
• gt 45 is acidosis
• Acute ventilatory failure results when PaCO2
  exceeds 50 mmHg pH lt 7.30
• Chronic ventilatory failure when PaCO2 gt50 and pH
  gt 7.30

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Respiratory Acidosis

• Clinical presentation
• Cardiovascular
• Hypotension
• Delayed cardiac conduction that can lead to heart
  block, peaked T waves, prolonged PR intervals,
  and widened QRS complexes
• Peripheral vasodilation with thready, weak pulse
• Tachycardia
• Warm, flushed skin

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Respiratory Acidosis

• Clinical Presentation
• Respiratory
• Dyspnea, may have hypoventilation with hypoxia
• CNS
• Headache, seizures, altered mental status,
  papilledema, muscle twitching, decreased LOC,
  drowsiness -gt coma
• Diagnostics
• Decreased pH, elevated PaCO2
• Hyperkalemia

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Respiratory Acidosis

• Compensation
• Increased rate and depth of respirations to blow
  off CO2
• Kidneys eliminate H ions and retain HCO3
• HCO3 levels rise when body attempts to compensate
• With partial compensation, pH remains decreased
• With full compensation, pH returns to normal

22
Respiratory Acidosis

• Priority Nursing Diagnoses
• Ineffective breathing pattern R/T hypoventilation
• Impaired gas exchange R/T alveolar
  hypoventilation
• Sensory-perceptual alterations R/T acid-base
  alterations
• Anxiety R/T breathlessness
• Risk for injury R/T decreased LOC
• Risk for decreased CO R/T dysrhythmias

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Respiratory Acidosis

• Management
• Treatment directed at underlying cause and
  improving ventilation
• Implement pulmonary hygiene measures
• Provide adequate fluid intake
• Administer supplemental oxygen cautiously in
  client with chronic respiratory acidosis
• Mechanical ventilation if necessary

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Respiratory Acidosis

• Planning and Implementation
• Assess respiratory rate and depth
• Monitor for complications and response to tx
• Assess for tachycardia and irregularities
• Assess LOC
• Monitor ECG for dysrhythmias
• Monitor serum electrolytes and ABGs
• Administer oxygen as indicated and ordered

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Respiratory Acidosis

• Planning and Implementation
• Administer medications as ordered and indicated
• Bronchodilators to decrease bronchospasm
• Antibiotics to treat infections
• Respiratory agents to decrease viscosity of
  secretions
• Anticoagulants and thrombolytics to prevent or
  treat PE
• Provide good oral hygiene frequently
• Maintain safe positioning

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Respiratory Acidosis

• Planning and Implementation
• Keep a calm, quiet environment
• Assess for cyanosis
• Orient confused client frequently
• Position to facilitate maximum lung expansion
• Provide adequate fluid intake

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ABG Interpretation

• Look at HCO3 level
• Reflects kidney function
• Normal 22-26 mEq/L
• lt 22, Metabolic Acidosis
• gt 26, Metabolic Alkalosis
• Causes Ketoacidosis, lactic acidosis, CKD,
  diarrhea, severe infection, fever, trauma,
  starvation, laxative abuse

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Metabolic Acidosis

• Clinical presentation
• Cardiovascular
• Hypotension, dysrhythmias, peripheral
  vasodilation, cold, clammy skin
• Respiratory
• Deep, rapid, Kussmauls respirations
• CNS
• Drowsiness, coma, HA, confusion, lethargy,
  weakness

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Metabolic Acidosis

• Clinical presentation
• GI
• N, V, diarrhea, abdominal pain
• Diagnostics
• pH low, HCO3 low, hyperkalemia
• ECG changes related to high potassium levels
• Tall, tented T waves
• Increased anion gap calculations
• Base excess decreases

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Metabolic Acidosis

• Compensation
• Lungs eliminate CO2
• Kidneys conserve HCO3
• Urine pH less than 6
• PaCO2 decreases with compensation
• pH returns to normal with full compensation

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Metabolic Acidosis

• Priority Nursing Diagnoses
• Decreased CO R/T dysrhythmias or FVD
• Risk for sensory/perceptual alterations
• Risk for injury
• Risk for FVD

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Metabolic Acidosis

• Management
• Treat underlying problem
• Provide hydration to restore water, nutrients,
  electrolytes
• Administer IV alkalotic solution (NaHCO3 or
  sodium lactate) may be indicated
• Mechanical ventilation if necessary

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Metabolic Acidosis

• Planning and Implementation
• Monitor ABGs
• Monitor IO
• Measure daily weights
• Assess VS, especially respirations
• Assess LOC
• Assess GI function

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Metabolic Acidosis

• Planning and Implementation
• Monitor ECG for conduction problems
• Monitor serum electrolytes
• Protect from injury
• Administer medications and fluids as needed

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ABG Interpretation

• Look at HCO3 level
• If gt 26, metabolic alkalosis
• Causes Fluid loss from UGI tract, diuretic
  therapy, severe hypokalemia, alkali
  administration or steroid therapy, excessive
  ingestion of bicarbonate-based antacids, binge
  purge syndrome

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Metabolic Alkalosis

• Clinical Presentation
• Cardiovascular
• Tachycardia, dysrhythmias, hypertension, atrial
  tachycardia, PVCs
• Respiratory
• Hypoventilation, respiratory failure
• CNS
• Dizziness, irritability, nervousness, confusion,
  tremors, muscle cramps, hyperreflexia, tetany,
  paresthesias, seizures

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Metabolic Alkalosis

• Clinical presentation
• GI
• Anorexia, N, V, paralytic ileus
• Diagnostics
• High pH and HCO3, hypokalemia, hypocalcemia,
  hyponatremia, hypochloremia
• Base excess increases

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Metabolic Alkalosis

• Compensation
• Lungs retain CO2 and kidneys conserve H and
  excrete HCO3
• PaCO2 increases with compensation
• Urine pH greater than 6
• pH returns to normal with full compensation

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Metabolic Alkalosis

• Priority Nursing Diagnoses
• FVD R/T excessive GI losses
• Decreased Cardiac Output R/T FVD and conduction
  problems secondary to hypokalemia and alkalosis
• Knowledge deficit R/T appropriate use of
  K-wasting diuretics and antacids
• Risk for impaired gas exchange
• Risk for injury R/T hypotension

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Metabolic Alkalosis

• Management
• Treat underlying cause
• Provide sufficient chloride to enhance renal
  absorption of Na and excretion of HCO3
• Restore fluid balance

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Metabolic Alkalosis

• Planning and Implementation
• Assess LOC
• Assess VS, especially respirations
• Administer medication and IV fluids as indicated
• NS based IV fluid replacement
• Potassium supplementation if hypokalemic
• Histamine-2 receptor antagonists (Tagamet,
  Zantac) to reduce production of H ions and loss
  of H ions from GI drainage
• Correct other electrolyte imbalances

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Metabolic Alkalosis

• Planning and Implementation
• Monitor IO
• Monitor response to therapy
• Protect from injury
• Monitor ECG for conduction abnormalities
• Monitor ABGs
• Monitor serum electrolytes

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ABG Interpretation

• Look back at pH
• If abnormal, the PaCO2 or HCO3 level will be
  abnormal Uncompensated
• Abnormal pH, PaCO2, and HCO3 Partially
  compensated
• Normal pH, abnormal PaCO2 and HCO3 Compensated
• Primary disorder is the abnormality that caused
  the pH to shift initially. Look to see on which
  side of 7.4 is pH

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ABG Interpretation

• O2 saturation
• Measurement of amount of oxygen bound to
  available hemoglobin
• Assessed through ABGs (SaO2) or noninvasively
  through pulse oximetry (SpO2)
• Normal 93-97
• Must evaluate the hemoglobin level

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ABG Interpretation

• O2 Content
• Measures total amount of oxygen carried in the
  blood, including the amount dissolved in plasma
  and the amount bound to hemoglobin
• Normal is 20 ml per 100 ml blood

46
ABG Interpretation

• Base Excess or Base Deficit
• Non-respiratory contribution to acid-base balance
• Normal -2 to 2 mEq/L
• Below -2, base deficit, metabolic acidosis
• Above 2, base excess, metabolic alkalosis

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Expected PaO2

• Multiply FIO2 X 5
• Represents oxygen level achievable with healthy
  lungs
• Pulmonary disease will radically decrease
  expected levels
• Cannot apply rule when client on delivery system
  using L/min
• must be oxygen received

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Mixed Acid-Base Disturbances

• Occurs when two or more independent acid-base
  disorders occur at the same time
• Example Client with metabolic acidosis from
  acute renal failure may also have a very slow
  respiratory rate and retain CO2 -gt respiratory
  acidosis

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Mixed

• Mixed acidosis
• pH 7.25, PaCO2 56, PaO2 80, HCO3 15
• Acute pulmonary edema, cardiac arrest
• Mixed alkalosis
• pH 7.55, PaCO2 26, PaO2 80, HCO3 28
• Postoperative clients with severe hemorrhage,
  massive transfusions, excessive NG drainage

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Problems

• Please remove the ABG worksheet to review
  assigned problems for review