- ABG INTERPRETATION - Flashcards

1
Q

What do ABGs measure?

A
• Partial pressure of O2
• pH
• Partial pressure of CO2
(PaCO2)
• Bicarbonate (HCO3) concentration
• Base excess
• Anion gap
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2
Q

Discuss the role of PaO2 in oxygenation

A
  • partial pressure of oxygen in arterial blood
  • guide to efficiency of gas exchange from the lungs into the blood
  • normal 80-100mmHg on 21% of FiO2
  • should be assessed in conjunction with FiO2
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3
Q

What is the estimated PaO2, relative to FiO2

A

FiO2 40% - PaO2 200mmHg
FiO2 60% - PaO2 300mmHg
FiO2 80% - PaO2 400mmHg

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4
Q

Discuss the role of SaO2 in oxygenation

A
  • the percentage of Hb molecules saturated with O2
  • measure of their ability to carry O2
  • important for oxygen content and delivery to the tissues
  • normal 95-100% on 21% of FiO2
  • should be assessed in conjunction with FiO2
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5
Q

Discuss full, partial and uncompensated metabolic and respiratory abnormalities

A

• Full compensation – pH within normal limits with values of respiratory and
metabolic components outside normal range and in opposite directions
• Partial compensation – compensation goes in the same direction as the
cause but unable to normalise pH
• Uncompensated – one system has made no correction

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6
Q

List the causes of respiratory acidosis

A
  • hypoventilation
  • CNS/respiratory centre depression
  • airway obstruction
  • lung disease
  • neuromuscular interference
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7
Q

List the causes of metabolic acidosis

A

increased production H+
(ketoacidosis
• altered cellular metabolism (lactic acidosis)
• ingestion toxins increase lactate production
• renal failure (decreased excretion H+)
• excessive loss HCO3
(diarrhoea, renal tubular acidosis)

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8
Q

List the causes of respiratory alkalosis

A
  • hyperventilation/CNS irritation
  • hypoxia/hypoxaemia
  • anxiety
  • mechanical ventilation
  • fever/sepsis
  • hyperthyroidism
  • lung disorders
  • liver failure
  • drugs - salicylates
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9
Q

List the causes of metabolic alkalosis

A
  • excess loss H+ (vomiting, NG suctioning, Cl- wasting diarrhoea)
  • excess HCO3 - (diuretic therapy, overuse antacids, citrate in blood transfusion)
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10
Q

Discuss the role of the Anion Gap

A

The anion gap is the difference between the plasma concentration of the major measured cation (Na+ & K+ ) and the sum of the measured anions (Cl- & HCO3 - )
It is useful in identifying the cause of metabolic acidosis

Normal anion gap < 18 mEq/L

AG = (Na+ + K+ ) – (HCO3 - + Cl)

A high AG means there is an accumulation of acid in body fluids that is not being buffered (loss of HCO3 - without a subsequent increase in Cl)

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11
Q

Discuss the normal ranges on an ABG

A
pH 7.35 – 7.45
PaO2 80 – 100 mmHg
SaO2 95 - 100%
PaCO2 35 – 45 mmHg
HCO3
- 22 – 26 mEq/L
Base Excess -2 - +2
Anion Gap <18
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12
Q

Discuss a clinical approach to ABG analysis

A
  1. Look at oxygenation (PaO2)
    Hypoxia?
  2. Look at pH
    Is the pH normal?
    Is your patient acidotic (pH < 7.35)
    Is your patient alkolitic (pH > 7.45)
  3. Look at PaCO2
    to determine if respiratory or metabolic
    Is pCO2 normal?
    Is pCO2 increased? (acidosis or compensation)
    Is pCO2 decreased? (alkolosis or compensation)
  4. Look at HCO3
    - Is the HCO3 normal?
    Is the HCO3 increased (alkolosis or compensated)
    Is the HCO3 decreased? (acidosis or compensated)
  5. Look at anion gap
    Na+ + K+ – Cl- + HCO3 <18 accumulation of acid in body fluid (lactic, ketones, uric, phosphoric etc.)
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