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63 Cards in this Set
- Front
- Back
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What is PaO2?
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Partial pressure of oxygen dissolved in arterial blood
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What is SaO2
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Arterial oxygen saturation of hemoglobin
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What is the normal value of PaO2?
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80 - 100 mmHg
60 - 80 in people aged 60 or older |
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What is the normal value of SaO2?
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93% - 99%
This is important because most oxygen supplied to the tissues is transported via hemoglobin. |
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What is the relationship between PaO2 and SaO2?
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Large changes in the PaO2 result in only small changes in the SaO2.
EX: PaO2 97 = SaO2 97% PaO2 80 = SaO2 95% PaO2 60 = SaO2 90% |
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With a drop of PaO2 from 97 to 60, is the patient compromised?
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Not immediately because the hemoglobin is still well saturated.
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When does it become critical?
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It occurs when the PaO2 decreases to less than 60 mm Hg. At this point, the curve slopes sharply, and small changes in PaO2 are reflected in large changes in the oxygen saturation. THESE CHANGES IN SaO2 MAY CAUSE A SIGNIFICANT DECREASE IN OXYGEN DELIVERED TO THE TISSUES.
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What blood gases reflect ventilation and acid-base or metabolic status?
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pH, partial pressure of carbon dioxide (PaCO2), and bicarbonate (HCO3).
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What is pH?
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The concentration of hydrogen ions in the blood.
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What is the normal range of pH?
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7.35 - 7.45
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What happens if the H+ increases?
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The pH falls, resulting in acidemia
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What happens if the H+ decreases?
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The pH increases, resulting in alkalemia
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What is the "panic" value of pH?
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<7.2 or > 7.6
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What is PaCO2?
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The partial pressure of carbon dioxide dissolved in arterial plasma.
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What is the normal PaCO2?
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35 - 45 mm Hg
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How is the PaCO2 regulated?
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In the lungs.
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What does a PaCO2 greater than 45 indicate?
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respiratory acidosis
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What does a PaCO2 less than 35 indicate?
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respiratory alkalosis
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What happens to the level of PaCO2 if a patient hyperventilates?
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PaCO2 will decrease causing respiratory alkalosis
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What happens to the level of PaCO2 if a patient hypoventilates?
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PaCO2 will increase causing respiratory acidosis.
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What is HCO3-?
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The concentration of sodium bicarbonate in the blood.
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What is the normal level of HCO3-?
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22 - 26 mEq/L
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How is HCO3- regulated?
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By the kidneys.
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What does a HCO3- level greater than 26 indicate?
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Metabolic alkalosis.
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What does a HCO3- level less than 22 indicate?
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Metabolic acidosis
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What is the "buffer system"?
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The way the body regulates acid-base balance.
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How many buffer systems are there?
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Three. The buffer system in the blood, the respiratory system and the kidneys
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How is the blood buffer system activated?
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It is activated as the H+ concentration changes.
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What happens when the H+ level increases?
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The pH falls, resulting in acidosis. HCO3- then combines with H+ to form carbonic acid (H2CO3). Carbonic acid then breaks down into carbon dioxide (which is excreted through the lungs) and water (H2O).
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What is the equation for the buffer system regulated by the blood?
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H+ + HCO3- -> H2CO3 -> H2O + CO2
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How does the respiratory buffer system work?
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by excreting excess carbon dioxide from the lungs.
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What activates the respiratory buffer system?
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IMMEDIATELY after an acid-base alteration is noted.
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What activates the renal buffer system?
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SLOWLY after an acid-base alteration is noted (may take up to 2 days to regulate).
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How does the renal buffer system work?
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By excreting excess H+ and retaining bicarbonate.
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What are the four steps when interpreting blood gases?
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(1) evaluate oxygenation status
(2) Determine acid-base imbalance (3) Determine the primary cause of the acid-base imbalance (4) Assess for a compensatory response (either respiratory or renal attempting to bring pH back into balance). |
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When evaluating oxygenation, when is hypoxemia considered to be a significant problem?
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When PaO2 falls to less than 60 OR
when SaO2 falls to less than 90% |
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When SaO2 stays at the same level, but PaO2 decreases or increases (usually by 10) what is happening?
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This is a shift to the left which means that hemoglobin clings to oxygen.
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What conditions cause a shift to the left (SaO2 same and PaO2 decreases or increases)?
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Alkalemia, lowered metabolism, high altitude, carbon monoxide poisoning and decreased 2,3-DPG level (administration of stored bank blood, septic shock and hypophosphatemia).
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When PaO2 stays at the same level, but SaO2 decreases or increases (usually by 10) what is happening?
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This is a shift to the right which means that oxygen is more readily released to the tissues (decreased affinity).
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What conditions cause a shift to the right (PaO2 same and SaO2 decreases or increases)?
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acidemia, increased metabolism (ex: fever), increased levels of 2,3-DGP (which is a glucose metabolite). 2,3-DGP increase in anemia, chronic hypoxemia, and low cardiac output states.
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When is hypoxemia classified as mile
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When PaO2 is 60 - 79 mm Hg
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When is hypoxemia classified as moderate?
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When PaO2 is 40 - 59 mm Hg
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When is hypoxemia classified as severe?
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When PaO2 is less than 40 mm Hg
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When supplemental oxygen is used to correct hypoxemia, how do you know it is working?
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When PaO2 is 60 - 100 mm Hg
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When evaluating acid-base status, a pH of less than 7.35 indicates what?
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Acidemia
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When evaluating acid-base status, a pH of more than 7.35 indicates what?
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Alkalemia.
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When evaluating acid-base status, a PaCO2 of less than 35 mm Hg indicates what?
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The presence of respiratory alkalosis
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When evaluating acid-base status, what does a PaCO2 greater than 45 mm Hg indicate?
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Respiratory acidosis.
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When evaluating acid-base status, what does a HCO3- of less than 22 mm Hg indicate?
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Metabolic acidosis.
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When evaluating acid-base status, what does a HCO3- of greater than 26 mm Hg indicate?
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Metabolic alkalosis.
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How is the primary cause of the acid-base imbalance determined?
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By the evaluation of the pH.
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If the pH is less than 7.4, what is the primary disorder?
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Acidosis
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If the pH is greater than 7.4, what is the primary disorder?
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Alkalosis.
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Give an example of how two primary disorders may occur simultaneously (mixed acid-base imbalance).
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During cardiac arrest, both respiratory acidosis and metabolic acidosis commonly occur because of hypoventilation and lactic acidosis.
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When determining if a compensatory response has taken place: If a patient has respiratory acidosis, such as occurs in COPD (low pH, high PaCO2), how would this be compensated?
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The kidney respond by retaining more HCO3- and and excreting H+ (metabolic alkalosis).
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When determining if a compensatory response has taken place: If a patient is in metabolic acidosis, such as occurs in diabetic ketoacidosis (low pH, low HCO3-), how would the body compensate for this?
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The lungs respond by hyperventilation and excretion of carbon dioxide (respiratory alkalosis).
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If the patient is experiencing respiratory acidosis (high PCO2, low pH), what is the usual compensatory method?
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Metabolic alkalosis
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If the patient is experiencing respiratory alkalosis (low PCO2, high pH) what is the usual compensatory method?
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Metabolic acidosis
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If the patient is experiencing metabolic acidosis (low HCO3-, low pH) what is the usual compensatory method?
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Respiratory alkalosis
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If the patient is experiencing metabolic alkalosis (high HCO3-, high pH), what is the usual compensatory method?
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Respiratory acidosis.
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Interpret these blood gasses:
PaO2 80 mm Hg pH 7.30 mm Hg PaCO2 50 mm Hg HCO3 22 mm Hg |
Respiratory acidosis; no compensation
PaO2 80 mm Hg (normal) pH 7.30 mm Hg (low;acidosis) PaCO2 50 mm Hg (high; resp. acidosis) HCO3- 22 mEq/L (normal) |
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Interpret these blood gases:
PaO2 80 mm Hg pH 7.35 mm Hg PaCO2 50 mm Hg HCO3- 28 mEq/L |
Partly compensated respiratory acidosis. The arterial blood gases are only partly compensated because the pH is not yet within normal limits
PaO2 80 mm Hg (normal) pH 7.35 mm Hg (low;acidosis) PaCO2 50 mm Hg (high;resp acid) HCO3- 28 mEq/L (high;met.alka) |
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Interpret these blood gases:
PaO2 80 mm Hg pH 7.36 mm Hg PaCO2 50 mm Hg HCO3- 29 mEq/L |
Completely compensated respiratory acidosis. the pH is now within normal limits; therefore, complete compensation has occurred.
PaO2 80 mm Hg (normal) pH 7.36 mm Hg (normal) PaCO2 50 mm Hg (high;resp.acid) HCO3- 29 mEq/L (high;met.alk) |
