ILP 3: CAL 1 ABGs

Question 1

What are normal values for:

• pH
• PaCO2
• HCO3
• PaO2

Answer 1

• 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.

Question 2

What are the 3 components of ABGs?

Answer 2

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.

Question 3

What is pH as a component of ABGs?

Answer 3

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).

Question 4

What is PaCO2 as a component of ABGs?

Answer 4

PaCO2 is influenced by respiration.

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

Question 5

What is HCO3 as a component of ABGs?

Answer 5

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.

Question 6

What are the 6 steps to analyse ABGs?

Answer 6

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?

Question 7

What is pH is acidosis VS alkalosis?

Answer 7

• pH < 7.35 => Acidosis
• pH > 7.45 => Alkalosis

Question 8

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

Is the pH in the example:

1. Acidotic
2. Alkalotic
3. Within normal range

Answer 8

pH < 7.35 => Acidosis

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

Question 9

What PaCO2 is respiratory acidosis VS alkalosis?

Answer 9

• PaCO2 > 45 => Respiratory acidosis
• PaCO2 < 35 => Respiratory alkalosis

Question 10

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

Is the PaCO2 in the example:

1. Acidotic
2. Alkalotic
3. Within normal range

Answer 10

PaCO2 > 45 => Respiratory acidosis

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

Question 11

What HCO3 is metabolic acidosis VS alkalosis?

Answer 11

• HCO3 < 22 => Metabolic acidosis
• HCO3 > 28 => Metabolic alkalosis

Question 12

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

Is the HCO3 in the example:

1. Acidotic
2. Alkalotic
3. Within normal range

Answer 12

HCO3 22-28 => Normal range

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

Question 13

pH 7.23 = Acidotic

PaCO2 50mmHg = Acidotic

HCO3 24 = Normal range

PaO2 60mmHg

Which of PaCO2 or HCO3 agrees with pH?

Answer 13

The PaCO2 and pH are both acidotic

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

Question 14

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

What is important to look at (for compensation)?

Answer 14

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.

Question 15

What are 3 types of compensation in the ABG analysis?

Answer 15

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.

Question 16

What are 3 characteristics of complete compensation in ABG analysis?

Answer 16

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.

Question 17

What are 3 characteristics of incomplete compensation in ABG analysis?

Answer 17

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.

Question 18

What are 3 characteristics of no compensation in ABG analysis?

Answer 18

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

Question 19

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?

Answer 19

No compensation

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

Question 20

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

Answer 20

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

Question 21

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

Is there any hypoxaemia?

1. Hypoxaemia
2. Severe hypoxaemia
3. No hypoxaemia

Answer 21

PaO2 < 60mmHg = Severe hypoxaemia

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

Question 22

Answer 22

Uncompensated respiratory acidosis with severe hypoxaemia.

Question 23

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

• pH
• PaCo2
• PaO2
• HCO3
• Condition

Answer 23

Question 24

What is the cause of respiratory acidosis?

Answer 24

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

Question 25

What are 5 ***clinical manifestations*** of **respiratory acidosis**?

Answer 25

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

Question 26

Eg. pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg Is the pH in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 26

pH \> 7.45 =\> Alkalosis pH is alkalotic, as it is greater than 7.45.

Question 27

Eg. pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg Is the PaCO2 in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 27

PaCO2 \< 35 =\> Respiratory alkalosis * PaCO2 is alkalotic, as it is less than 35mmHg.

Question 28

pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg Is the HCO3 in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 28

HCO3 22-28 =\> Normal range * HCO3 is within normal range, as it is between 22 and 28.

Question 29

pH 7.49 = Alkalotic PaCO2 27mmHg = Alkalotic HCO3 25 = Normal PaO2 110mmHg Which of PaCO2 or HCO3 agrees with pH? * PaCO2 * HCO3

Answer 29

The PaCO2 and pH are both alkalotic * It is the PaCO2 that is alkalotic and therefore agrees with pH.

Question 30

pH 7.49, PaCO2 27mmHg, HCO3 25, PaO2 110mmHg What are 3 steps to look at for **compensation**?

Answer 30

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.

Question 31

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

Answer 31

No compensation * There no compensation, as the pH is OUTSIDE normal limits, but HCO3 is within normal range.

Question 32

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

Answer 32

PaO2 \> 100mmHg = normal range * PaO2 \> 100mmHg, therefore greater than normal range

Question 33

What do the values indicate?

Answer 33

Uncompensated respiratory alkalosis.

Question 34

What is the ***cause*** of **respiratory alkalosis**?

Answer 34

occurs when there is alveolar hyperventilation and hypocapnia. * Eg. mechanical ventilation, anxiety, hypoxaemia, pneumonia, pulmonary embolus, fever, pain

Question 35

What are 4 ***clinical manifestations*** of **respiratory alkalosis**?

Answer 35

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

Question 36

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg Is the pH in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 36

pH \< 7.35 =\> Acidotic * The pH is acidotic, as it is less than 7.35.

Question 37

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg Is the PaCO2 in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 37

PaCO2 35-45 =\> Within normal range * The PaCO2 is within normal range, as it is between 35 and 45mmHg.

Question 38

pH 7.21, PaCO2 35mmHg, HCO3 19, PaO2 96mmHg Is the HCO3 in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 38

HCO3 \< 22 =\> Metabolic acidosis * The HCO3 acidotic, as it is less than 22.

Question 39

* pH 7.21 = Acidotic * PaCO2 35mmHg = Normal * HCO3 19 = Acidotic * PaO2 96mmHg Which of PaCO2 or HCO3 agrees with pH?

Answer 39

The HCO3 and pH are both acidotic * It is the HCO3 that is acidotic and therefore agrees with pH.

Question 40

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

Answer 40

No compensation * pH is within normal range, no attempt by respiratorynsystem to compensate (PaCO2 35).

Question 41

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

Answer 41

PaO2 80 – 100 mmHg = Normal * PaO2 is between 80 to 100 mmHg, therefore within normal levels.

Question 42

What do these valves indicate?

Answer 42

Uncompensated metabolic acidosis.

Question 43

What is the ***loss of base*** in **metabolic acidosis**?

Answer 43

such as in cases of severe diarrhoea

Question 44

What is the ***gain of metabolic acids*** in **metabolic acidosis**?

Answer 44

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

Question 45

What 6 ***clinical manifestations*** of **metabolic acidosis**?

Answer 45

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

Question 46

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

Answer 46

* 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.

Question 47

What is the ***loss of metabolic acids*** in **metabolic alkalosis?**

Answer 47

such as in cases of prolonged vomiting or gastrointestinal suctioning.

Question 48

What is the ***gain of base*** in **metabolic alkalosis**?

Answer 48

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

Question 49

What are 3 ***clinical manifestations*** of **metabolic alkalosis**?

Answer 49

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

Question 50

What are 4 characteristics of **compensation**?

Answer 50

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.***

Question 51

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg Is the pH in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 51

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.

Question 52

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg Is the PaCO2 in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 52

PaCO2 \> 45mmHg =\> Acidotic * The PaCO2 is acidotic, as it is greater than 45mmHg.

Question 53

pH 7.35, PaCO2 50mmHg, HCO3 30, PaO2 65mmHg Is the HCO3 in the example: 1. Acidotic 2. Alkalotic 3. Within normal range

Answer 53

HCO3 \> 28 =\> Metabolic alkalosis * The HCO3 alkalotic, as it is greater than 28.

Question 54

* pH 7.35 : Normal (but acidotic side) * PaCO2 50mmHg = Acidotic * HCO3 30 = Alkalotic * PaO2 65mmHg Which of PaCO2 or HCO3 agrees with pH?

Answer 54

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.

Question 55

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?

Answer 55

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

Question 56

What is ***complete compensation*** for metabolic?

Answer 56

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.

Question 57

What is ***incomplete/partial compensation*** for metabolic?

Answer 57

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.

Question 59

* 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

Answer 59

Complete compensation by metabolic system * There is complete compensation, as the pH is INSIDE normal limits, and the HCO3 is outside normal limits.

Question 60

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

Answer 60

PaO2 \< 80mmHg = hypoxaemia * PaO2 \< 80mmHg, therefore the patient is hypoxaemic

Question 61

What do these values indicate?

Answer 61

Compensated respiratory acidosis with hypoxaemia.

Question 62

What are 5 ***clinical features*** of **compensated respiratory acidosis**?

Answer 62

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

Question 63

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

Answer 63

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.

Question 64

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

Answer 64

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.