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214 Clinical Assessment in Respiratory Care > Blood gas interpretation Module 6 > Flashcards

Blood gas interpretation Module 6 Flashcards

1
Q

Why is arterial blood used to assess respiratory function?

A

its oxygen and CO2 levels are determined primarily by the lungs.

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2
Q

Why is the radial artery the preferred site for ABG sampling?

A

It’s easy to access, has good collateral circulation, and is easy to stabilize post puncture.

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3
Q

how is collateral circulation assessed before puncturing to do the arterial blood sample?

A

using the ALLEN TEST. if the collateral circulation is adequate, the hand should return to pink within 10 - 15 seconds after release of the ulnar artery.

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4
Q

How long should you hold the puncture site after taking blood sample if clotting problems exist.

A

3-5 minutes longer

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5
Q

what does the PaO2 reflect?

A

The ability of the lungs to allow the transfer of oxygen from the environment to the circulating blood

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6
Q

What does a PaO2 below the predicted range for a patient breathing room air regardless of the actual FiO2 mean?

A

hypoxemia

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7
Q

Hypoxia

A

a condition in which tissue oxygenation is inadequates

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8
Q

What amount of PaO2 would be considered hypoxemia at any age?

What amount would be considered severe hypoxemia?

A
  1. <65mm Hg is hypoxemia at any age
  2. <40mm Hg is considered severe hypoxemia
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9
Q

List 5 things that would cause hypoxemia to occur, ie’ it is secondary to these things.

A
  1. ventilation/perfusion (V/Q) mismatch
  2. shunt
  3. diffusion defect
  4. hypoventilation
  5. reduced partial pressure of oxygen in the inhaled gas (PiO2)
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10
Q

What is the most common cause of hypoxemia?

A

V/Q mismatch

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11
Q

What is V/Q mismatch?

A
  1. a defect in which ventilation (the exchange of air between the lungs and the environment) and perfusion (the passage of blood through the lungs) are not evenly matched.
  2. typical in COPD
  3. it is the most common cause of hypoxemia
  4. and a component of most causes of respiratory failure
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12
Q

ventilation

A

The air that reaches the alveoli

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13
Q

What defines ventilation? (blood gas results?)

What determines Ventilation

A
  1. PaCo2 and pH
  2. Alveolar minute ventilation
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14
Q

Perfusion (Q)

A

is the blood which reaches the alveoli

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15
Q

V/Q ratio

A
  1. the ratio of the amount of air reaching the alveoli to the amount of blood reaching the alveoli
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16
Q

Oxygenation 3points

A
  1. is separate from ventilation
  2. defined by PaO2 and SaO2
  3. a is arterial
  4. determined by
  • spontaneously breathing: FiO2
  • PPV: FiO2 and mean airway pressure
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17
Q

PPV

A

positive pressure ventilation

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18
Q

List the Normal ranges and goal ranges for

  1. pH
  2. PaCO2 mmHg
  3. PaO2 mmHg
  4. HCO3 mmol/L
  5. Base Excess
  6. SaO2
A

Normal: Goal:

  1. 7.35-7.45 pH 7.35-7.45
  2. 35-45 PaCO2 35-45mmHg
  3. 80-100 PaO2 60-100mmHg
  4. 22-26 HCO3
  5. +-2 Base Excess
  6. 95-100% SaO2 >=90%
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19
Q

How do sudden changes in PaCO2 impact pH?

A
  1. Sudden changes in PaO2 = changes in pH
  2. when PaO2 increases, pH decreases
  3. for every 10mmHg increase in PaO2, there is a corresponding decrease in pH by 0.06
  4. when PaO2 decreases pH increases
  5. For every 10 mmHg decrease in PaO2, there is a corresponding increase in pH by 0.10
20
Q

What disorders in a patient would shift the oxyhemoglobin curve to the left , resulting in HIGHER SaO2 values at the SAME PaO2

A
  1. Alkalosis
  2. hypocapnia
  3. hypothermia
  4. fetal Hb
  5. HbCO
21
Q

Which disorders in a patient would shift the oxyhemoglobin curve to the right and result in LOWER SaO2 values for the same PaO2?

A
  1. Acidosis
  2. hypercapnia
  3. fever
22
Q

How does an oxyhemoglobin shift to the left impact Oxygenation of the tissues?

A

shifts to the left cause O2 to be more tightly bound to Hb, and make unloading of oxygen at tissues more difficult.

23
Q

How does an oxyhemoglobin shift to the right impact oxygenation of the tissues?

A

results in decreased O2 affinity for Hb, and allows easier unloading of O2 at the tissues

24
Q

what is the pH a reflection of?

A

the acid-base status of arterial blood

25
Q

What is the most reliable measure for evaluating the effectiveness of ventilation?

and what should be taken into account when interpreting it?

A
  1. PaCO2
  2. should be interpreted in light of the patients minute volume VE
26
Q

what is the HCO-3 level a reflection of?

how is HCO-3 level regulated

A
  1. Primarily a reflection of the metabolic component of acid-base balance
  2. it is regulated by the renal system
27
Q

What is the Henderson-Hasselbalch equation?, what does it demonstrate?

A
  1. Demonstrates that arterial blood pH is determined by the ratio of HCO-3 to PaCO2
  2. the ratio is normally 20:1
28
Q

When would we consider a pt to have respiratory acidosis?

A

When the PaCO2 is elevated above normal OR when it is higher than the expected level of compensation

29
Q

When would we consider a patient to have METABOLIC ACIDOSIS?

A

when plasma HCO-3 or BE falls below normal

30
Q

When would we consider a patient to have respiratory Alkalosis?

A

PaCO2 below the expected level

this indicates that ventilation is exceeding the normal level

31
Q

When would we consider a patient to have Metabolic alkalosis?

A

when there is an above normal elevation of the plasma HCO-3

32
Q

Describe what is happening with the blood gases in a MIXED ACID-BASE DISORDER?

A

When metabolic acidosis is accompanied by a PaCO2 that is lower than the predicted level for the degree of acidosis, a respiratory alkalosis is occuring simultaneously.

33
Q

What would a pH of 7.40 occuring simultaneously with significant abnormalities in PaCO2 and plasma HCO-3 indicate? and why?

A
  1. indicates a mixed disorder
  2. normal compensation of a single disorder NEVER returns the pH to 7.40
  3. The body will NOT overcompensate
34
Q

What impact does a change in PaCO2 have on the level of HCO-3 in the blood?

A
  1. As PaCO2 levels change so will the bicarb
  2. for every 10 mmHg increase in PaCO2 the HCO-3 increases 1mmol/L
  3. foe every 10 mmHg decrease in PaCO2 the HCO-3 decreases by 2mmol/L

Based on the Hydrolysis equation

do not confuse this normal relationship with compensation

35
Q
A
36
Q

What would the systematic approach to blood gas interpretation be?

A
  1. Acid-base assessment
  • acidemia, alkalemia or normal?
  • respiratory of metabolic in origin?
  • is it compensation occurring?
  • simple vs. mixed disorder?
  1. Assess Oxygenation
    * adequacy of oxygenation?

for all ABG interpretation you need to consider the patient history and current clinical status.

37
Q

What are the normal values for pH?

what would be considered Acidemia?

What would be considered Alkalemia?

A
  1. 7.35-7.45
  2. <7.35
  3. >7.45
38
Q

What other than normal could a pH in the normal range of 7.35-7.45 indicate?

A

it could indicate a norma, fully compensated disorder, or a mixed disorder.

39
Q

what values would indicate that the respiratory system is the primary cause of an Acid-Base disorder?

A
  1. if PaCO2 is abnormal and in the OPPOSITE direction of the pH then the respiratory system is the primary cause.
40
Q

what ABG values would indicate that an Acid-base disorder is metabolic

A
  1. If HCO3- is abnormal and in the SAME direction of the pH, then the disorder is metabolic (primarily)
41
Q
A
42
Q

How do we know compensation is occuring when the original problem is respiratory?

A
  1. the metabolic system compensatesby either increasing or decreasing the HCO3- levels to “correct” the pH back to normal
43
Q

How do you determine if the original problem is metabolic when compensation is occuring in an acid-base disorder?

A
  1. the respiratory system responds by either increasing or decreasing minute volume resulting in decrease or increase of PaCO2 respectively
  2. this new PaCO2 counteracts the metabolic problem and “corrects” the pH
  3. this results in both PaCO2 and HCO3- being abnormal but the end result is a pH that is normal or closer to normal.

Important to note: the body does NOT overcompensate.

44
Q

How would we determine if an acid base disorder is simple or mixed?

A
  • for every 10mmHg increase in PaCO2, there is a decrease in pH by 0.06
  • for every 10mmHg decrease in PaCO2, there is a corresponding increase in pH by 0.10

Calculate the predicted pH:

if PaCO2 = 40: predicted pH=measured pH

PaCO2>40: predicted pH=7.40-[(PaCO2-40)* .006]

PaCO2<40: Predicted pH=7.40+[(40-PaCO2)*.01]

Compare the predicted pH to the actual: if the actual pH does not = the predicted pH, then a mixed disorder is occuring.

45
Q
A

214 Clinical Assessment in Respiratory Care (2 decks)

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