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PHTY3250 > ILP 3: CAL 1 ABGs > Flashcards

ILP 3: CAL 1 ABGs Flashcards

1
Q

What are normal values for:

  • pH
  • PaCO2
  • HCO3
  • PaO2
A
  • pH 7.35 – 7.45
  • PaCO2 35 – 45mmHg
  • HCO3 22 – 28meq/l
  • PaO2 80 – 100mmHg

It is important to know the normal values of arterial blood gases (ABGs) to detect abnormalities.

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2
Q

What are the 3 components of ABGs?

A
  1. PaCO2
  2. pH
  3. HCO3

They are measures of this chemical equation that occurs in the body. It is important to consider the effects of these three components when analysing ABGs.

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3
Q

What is pH as a component of ABGs?

A

a measure of acid/alkali balance in the body and is influenced by the amount of hydrogen ion (H+) in the blood.

  • An increase in H+ acts to decrease the pH (ACIDOTIC).
  • A decrease in H+ acts to increase the pH (ALKALOTIC).
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4
Q

What is PaCO2 as a component of ABGs?

A

PaCO2 is influenced by respiration.

  • Increased minute ventilation (MV) decreases CO2 (ALKALOTIC).
  • Decreased in MV increases the CO2 (ACIDOTIC).
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5
Q

What is HCO3 as a component of ABGs?

A

The resultant bicarbonate ion (HCO3) reflects the metabolic component of the equation.

An increase in HCO3 results in ALKALOSIS, and a decrease results in ACIDOSIS.

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6
Q

What are the 6 steps to analyse ABGs?

A
  1. Look at pH
    • Is it acidotic/alkalotic?
  2. Look at PaCO2
    • Is it high or low?
  3. Look at HCO3
    • Is it high or low?
  4. Which of PaCO2 or HCO3 agrees with the pH?
  5. Is there any compensation?
  6. Is there any hypoxaemia?
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7
Q

What is pH is acidosis VS alkalosis?

A
  • pH < 7.35 => Acidosis
  • pH > 7.45 => Alkalosis
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8
Q

pH 7.23, PaCO2 50mmHg, HCO3 24, PaO2 60mmHg

Is the pH in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

pH < 7.35 => Acidosis

The pH is acidotic, as it is less than 7.35.

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9
Q

What PaCO2 is respiratory acidosis VS alkalosis?

A
  • PaCO2 > 45 => Respiratory acidosis
  • PaCO2 < 35 => Respiratory alkalosis
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10
Q

pH 7.23, PaCO2 50mmHg, HCO3 24, PaO2 60mmHg

Is the PaCO2 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

PaCO2 > 45 => Respiratory acidosis

  • PaCO2 is acidotic, as it is greater than 45mmHg.
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11
Q

What HCO3 is metabolic acidosis VS alkalosis?

A
  • HCO3 < 22 => Metabolic acidosis
  • HCO3 > 28 => Metabolic alkalosis
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12
Q

pH 7.23, PaCO2 50mmHg, HCO3 24, PaO2 60mmHg

Is the HCO3 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

HCO3 22-28 => Normal range

HCO3 is within normal range, as it is between 22 and 28.

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13
Q

pH 7.23 = Acidotic

PaCO2 50mmHg = Acidotic

HCO3 24 = Normal range

PaO2 60mmHg

Which of PaCO2 or HCO3 agrees with pH?

A

The PaCO2 and pH are both acidotic

PaCO2 that is acidotic and therefore agrees with pH (primary system).

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14
Q

pH 7.23, PaCO2 50mmHg, HCO3 24, PaO2 60mmHg

What is important to look at (for compensation)?

A
  1. Is the other system (metabolic in this case) trying to compensate for the disruption to pH?
  2. Look at the pH
    1. is it within normal range?
    2. is it outside normal range?
  3. Look at the other system – HCO3 in this case
    1. is it within normal range?
    2. Is it outside normal range?
  4. It is important to look at the pH and the HCO3 to see if there is any compensation occurring.
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15
Q

What are 3 types of compensation in the ABG analysis?

A
  1. Complete compensation:
    1. Other system outside normal range
    2. pH within normal range
    3. Therefore, one system is able to offset a change and pH returns to normal limits.
  2. Incomplete/Partial:
    1. Other system outside normal range
    2. pH outside normal range
    3. Therefore, one system begun to offset the change but not enough to return pH to normal range.
  3. No compensation:
    1. Other system within normal range
    2. pH outside normal range
    3. Therefore, no attempt at offsetting pH.
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16
Q

What are 3 characteristics of complete compensation in ABG analysis?

A
  1. Other system outside normal range
  2. pH within normal range
  3. Therefore, one system is able to offset a change and pH returns to normal limits.
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17
Q

What are 3 characteristics of incomplete compensation in ABG analysis?

A
  1. Other system outside normal range
  2. pH outside normal range
  3. Therefore, one system begun to offset the change but not enough to return pH to normal range.
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18
Q

What are 3 characteristics of no compensation in ABG analysis?

A
  1. Other system within normal range
  2. pH outside normal range
  3. Therefore, no attempt at offsetting pH.
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19
Q

pH 7.23, PaCO2 50mmHg, HCO3 24, PaO2 60mmHg

pH 7.23 = Acidotic (outside normal range)

PaCO2 50mmHg = Acidotic

HCO3 24 (within normal range)

PaO2 60mmHg

Is there any compensation occurring?

A

No compensation

pH is within normal range, no attempt by metabolic system to compensate (HCO3 24).

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20
Q

What is PaO2 is normal levels VS hypoxaemia VS severe hypoxaemia?

A
  • PaO2 80 - 100 mmHg = Normal levels
  • PaO2 < 80mmHg = Hypoxaemia
  • PaO2 < 60mmHg = Severe hypoxaemia
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21
Q

pH 7.23, PaCO2 50mmHg, HCO3 24, PaO2 60mmHg

Is there any hypoxaemia?

  1. Hypoxaemia
  2. Severe hypoxaemia
  3. No hypoxaemia
A

PaO2 < 60mmHg = Severe hypoxaemia

PaO2 is 60mmHg, therefore the patient is in severe hypoxaemia.

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22
Q
A

Uncompensated respiratory acidosis with severe hypoxaemia.

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23
Q

What are the 4 summaries the respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalisis?

  • pH
  • PaCo2
  • PaO2
  • HCO3
  • Condition
A
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24
Q

What is the cause of respiratory acidosis?

A

Carbon dioxide is retained when ventilation is depressed. Eg. Overdose, acute respiratory failure, upper airway obstruction.

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25
Q

What are 5 clinical manifestations of respiratory acidosis?

A
  1. restlessness, apprehension
  2. lethargy
  3. muscle twitching, tremors, seizures
  4. warm peripheries, vasodilation
  5. tachycardia.
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26
Q

Eg. pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg

Is the pH in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

pH > 7.45 => Alkalosis

pH is alkalotic, as it is greater than 7.45.

27
Q

Eg. pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg

Is the PaCO2 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

PaCO2 < 35 => Respiratory alkalosis

  • PaCO2 is alkalotic, as it is less than 35mmHg.
28
Q

pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg

Is the HCO3 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

HCO3 22-28 => Normal range

  • HCO3 is within normal range, as it is between 22 and 28.
29
Q

pH 7.49 = Alkalotic

PaCO2 27mmHg = Alkalotic

HCO3 25 = Normal

PaO2 110mmHg

Which of PaCO2 or HCO3 agrees with pH?

  • PaCO2
  • HCO3
A

The PaCO2 and pH are both alkalotic

  • It is the PaCO2 that is alkalotic and therefore agrees with pH.
30
Q

pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg

What are 3 steps to look at for compensation?

A
  1. Is the other system (metabolic in this case) trying to compensate for the disruption to pH?
  2. Look at the pH
    1. is it within normal range?
    2. is it outside normal range?
  3. Look at the other system – HCO3 in this case
    1. is it within normal range?
    2. Is it outside normal range?

It is important to look at the pH and the HCO3 to see if there is any compensation occurring.

31
Q

pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg

  • pH 7.49 = Alkalotic (outside normal range)
  • PaCO2 50 mmHg = Alkalotic
  • HCO3 25 (within normal range)
  • PaO2 110 mmHg

Look at the pH and HCO3 values above. Is there any compensation?

  • Complete
  • Incomplete
  • No compensation
A

No compensation

  • There no compensation, as the pH is OUTSIDE normal limits, but HCO3 is within normal range.
32
Q

pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg

Hypoxaemia:

  • PaO2 80 - 100 mmHg = Normal levels
  • PaO2 < 80mmHg = Hypoxaemia
  • PaO2 < 60mmHg = Severe hypoxaemia

Look at the PaO2 levels. Is there any hypoxaemia?

  • Hypoxaemia
  • Severe hypoxaemia
  • No hypoxaemia
A

PaO2 > 100mmHg = normal range

  • PaO2 > 100mmHg, therefore greater than normal range
33
Q

What do the values indicate?

A

Uncompensated respiratory alkalosis.

34
Q

What is the cause of respiratory alkalosis?

A

occurs when there is alveolar hyperventilation and hypocapnia.

  • Eg. mechanical ventilation, anxiety, hypoxaemia, pneumonia, pulmonary embolus, fever, pain
35
Q

What are 4 clinical manifestations of respiratory alkalosis?

A
  1. confusion, dizziness
  2. paresthesia
  3. seizures and coma
  4. nausea and vomiting
36
Q

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg

Is the pH in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

pH < 7.35 => Acidotic

  • The pH is acidotic, as it is less than 7.35.
37
Q

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg

Is the PaCO2 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

PaCO2 35-45 => Within normal range

  • The PaCO2 is within normal range, as it is between 35 and 45mmHg.
38
Q

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg

Is the HCO3 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

HCO3 < 22 => Metabolic acidosis

  • The HCO3 acidotic, as it is less than 22.
39
Q
  • pH 7.21 = Acidotic
  • PaCO2 35mmHg = Normal
  • HCO3 19 = Acidotic
  • PaO2 96mmHg

Which of PaCO2 or HCO3 agrees with pH?

A

The HCO3 and pH are both acidotic

  • It is the HCO3 that is acidotic and therefore agrees with pH.
40
Q

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg

  • pH 7.21 = Acidotic (outside normal range)
  • PaCO2 35mmHg = Normal (within normal range)
  • HCO3 19 = Acidotic (outside normal range)
  • PaO2 60mmHg

Is there any compensation occurring?

  1. Complete
  2. Incomplete
  3. No compensation
A

No compensation

  • pH is within normal range, no attempt by respiratorynsystem to compensate (PaCO2 35).
41
Q

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg

  • PaO2 80 - 100 mmHg = Normal levels
  • PaO2 < 80mmHg = Hypoxaemia
  • PaO2 < 60mmHg = Severe hypoxaemia

Is there any hypoxaemia?

  1. Hypoxaemia
  2. Severe hypoxaemia
  3. No hypoxaemia
A

PaO2 80 – 100 mmHg = Normal

  • PaO2 is between 80 to 100 mmHg, therefore within normal levels.
42
Q

What do these valves indicate?

A

Uncompensated metabolic acidosis.

43
Q

What is the loss of base in metabolic acidosis?

A

such as in cases of severe diarrhoea

44
Q

What is the gain of metabolic acids in metabolic acidosis?

A

Anaerobic metabolism; drug overdose (e.g.salicylates); renal failure; diabetic ketoacidosis

45
Q

What 6 clinical manifestations of metabolic acidosis?

A
  1. headache and lethargy
  2. warm flushed skin
  3. agitation, seizures, mental confusion
  4. nausea, vomiting and diarrhoea
  5. hyperkalemia (shift of acid to the ICF and K+ to the ECF)
  6. cardiac dysrhythmias
46
Q

pH 7.50, PaCO2 39mmHg, HCO3 32, PaO2 98mmHg

Analysis of the above ABGs show:

  1. Compensated respiratory alkalosis with hypoxaemia
  2. Uncompensated respiratory alkalosis
  3. Partially compensated metabolic alkalosis
  4. Uncompensated metabolic alkalosis
A
  • pH = 7.50 Alkalosis
  • PaCO2 = 39 mmHg Within normal range
  • HCO3 = 32 mEq/L Alkalosis
  • PaO2 = 98 mmHg Within normal range

The answer is uncompensated metabolic alkalosis, as PaCO2 is within normal range and pH is alkalotic.

47
Q

What is the loss of metabolic acids in metabolic alkalosis?

A

such as in cases of prolonged vomiting or gastrointestinal suctioning.

48
Q

What is the gain of base in metabolic alkalosis?

A

an increased intake of bicarbonate.

Diuretics (e.g. furosemide) can cause sodium, potassium, and chloride excretion more than bicarbonate excretion.

49
Q

What are 3 clinical manifestations of metabolic alkalosis?

A
  1. general weakness, muscle cramps, hyperactive reflexes
  2. shallow and slow respirations
  3. confusion and seizures may occur in severe cases
50
Q

What are 4 characteristics of compensation?

A
  1. Until now, the case examples have involved mainly uncompensated blood gases. That is, there is no attempt by the respiratory or metabolic system to compensate for a primary problem.
  2. If primary problem exists for long enough the lungs or kidneys will compensate.
  3. You need to work out which was the initial or primary problem, as often both PaCO2 and HCO3 will be abnormal.
  4. pH may be back in normal range or slightly out of range. If it is still out of range the patient is said to be partially compensated.
51
Q

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg

Is the pH in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

pH 7.35 – 7.45 => Within normal range

  • Note: pH 7.35 – 7.40 : Acidotic side of normal
  • pH 7.40 – 7.45 : Alkalotic side of normal

Correct, the pH is within normal range, however, it is between 7.35 – 7.40 and is considered to be on the acidotic side of normal. Click to continue the analysis.

52
Q

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg

Is the PaCO2 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

PaCO2 > 45mmHg => Acidotic

  • The PaCO2 is acidotic, as it is greater than 45mmHg.
53
Q

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg

Is the HCO3 in the example:

  1. Acidotic
  2. Alkalotic
  3. Within normal range
A

HCO3 > 28 => Metabolic alkalosis

  • The HCO3 alkalotic, as it is greater than 28.
54
Q
  • pH 7.35 : Normal (but acidotic side)
  • PaCO2 50mmHg = Acidotic
  • HCO3 30 = Alkalotic
  • PaO2 65mmHg

Which of PaCO2 or HCO3 agrees with pH?

A

The PaCO2 and pH are both acidotic

  • It is the PaCO2 that is acidotic and therefore agrees with pH. Therefore the PaCO2 or respiratory system is the primary change.
55
Q

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg

  • It is important to look at the pH and the HCO3 to see if there is any compensation occurring.

Is the other system (metabolic in this case) trying to compensate for the disruption to pH?

A
  1. No compensation = pH outside normal range + other system within normal range
  2. Partial compensation = pH outside normal range + other system outside normal range
  3. Complete compensation = pH within normal range + other system outside normal range
56
Q

What is complete compensation for metabolic?

A
  1. Other system outside normal range AND pH within normal range
  2. Need to check is the pH one side of normal?
  3. pH 7.35 – 7.40 => Acidotic side, check for acidotic changes to PaCO2 or HCO3 for primary change.
  4. pH 7.40 – 7.45 => Alkalotic side check for alkalotic changes to PaCO2 or HCO3 for primary change.
  5. This will help to determine which was the initial or primary problem/change.
57
Q

What is incomplete/partial compensation for metabolic?

A
  1. Other system outside normal range
  2. pH outside normal range
  3. The initial or primary problem will be the system that caused the change in pH.
58
Q
A
59
Q
  • pH 7.35 : Normal (but acidotic side)
  • PaCO2 50mmHg : Acidotic
  • HCO3 30 (Other system) : Alkalotic
  • PaO2 65mmHg

Is there any compensation occurring?

  1. Complete
  2. Incomplete
  3. No compensation
A

Complete compensation by metabolic system

  • There is complete compensation, as the pH is INSIDE normal limits, and the HCO3 is outside normal limits.
60
Q

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg

  • PaO2 80 - 100 mmHg = Normal levels
  • PaO2 < 80mmHg = Hypoxaemia
  • PaO2 < 60mmHg = Severe hypoxaemia

Is there any hypoxaemia?

  1. Hypoxaemia
  2. Severe hypoxaemia
  3. No hypoxaemia
A

PaO2 < 80mmHg = hypoxaemia

  • PaO2 < 80mmHg, therefore the patient is hypoxaemic
61
Q

What do these values indicate?

A

Compensated respiratory acidosis with hypoxaemia.

62
Q

What are 5 clinical features of compensated respiratory acidosis?

A
  1. Common in COPD, sleep apnea, obesity
  2. Morning headache, daytime somnolence
  3. PaCO2 rises slowly over a number of years
  4. The carotid bodies become accustomed to a high PaCO2
  5. Increased bicarbonate reabsorption
63
Q

Case 1

A patient is admitted to the hospital and is being prepared for a craniotomy. The client is very anxious and scared of the impending surgery. He begins to hyperventilate and becomes very dizzy.

  • pH = 7.45
  • PaCO2 = 27 mmHg
  • HCO3 = 19 mEq/L
  • PaO2 = 112 mmHg

Analysis of the above ABGs show:

  1. Compensated respiratory alkalosis
  2. Uncompensated respiratory alkalosis with hypoxaemia
  3. Partially compensated respiratory alkalosis
  4. Uncompensated metabolic alkalosis
A

Compensated respiratory alkalosis, as HCO3 is outside normal range and pH is within normal range. The respiratory alkalosis is the primary change and metabolic acidosis a compensatory change.

Compensated respiratory alkalosis can occur in pregnancy, asthma, chronic anxiety, mechanical ventilation with high minute ventilation.

64
Q

Case 2

An infant, three weeks old, is admitted to the Emergency Room. The mother reports that the infant has been irritable, difficult to breastfeed and has had diarrhoea for the past 4 days.

The results from the ABGs come back from the laboratory and show:

  • pH = 7.34
  • PaCO2 = 29 mmHg
  • HCO3 = 17 mEq/L

Analysis of the above ABGs show:

  1. Compensated respiratory acidosis
  2. Uncompensated respiratory acidosis
  3. Partially compensated metabolic acidosis
  4. Compensated metabolic acidosis
A

Partially compensated metabolic acidosis. pH is acidotic and HCO3 is acidotic (primary change) reflecting metabolic acidosis. However, the PaCO2 (other system) is alkalotic (compensatory change), and although is unable to return pH to normal values, it demonstrates partial compensation.

PHTY3250 (20 decks)

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