Blood gases

Question 1

What is the purpose of obtaining blood gas values in neonates?

Answer 1

To determine adequate ventilation and perfusion

Blood gas values also facilitate analysis of oxygenation and acid-base status.

Question 2

What are the normal arterial blood gas values for pH?

Answer 2

7.35 – 7.45

Question 3

What is the normal range for pCO2 in arterial blood gas values?

Answer 3

35 – 45

Question 4

What is the normal range for pO2 in arterial blood gas values?

Answer 4

50 – 100

Question 5

What is the normal range for HCO3 in arterial blood gas values?

Answer 5

22 – 26

Question 6

What does an elevated pH (> 7.45) indicate?

Answer 6

Alkalosis

Question 7

What does a pH < 7.35 indicate?

Answer 7

Acidosis

Question 8

What does PaO2 measure?

Answer 8

The amount of O2 dissolved in the serum

Question 9

What is the reliability of capillary PaO2 compared to arterial specimens?

Answer 9

Lower reliability

Question 10

What does PaCO2 indicate?

Answer 10

How well the infant is ventilating

Question 11

What happens to pH when there is an increase in PaCO2?

Answer 11

Decrease in pH (respiratory acidosis)

Question 12

What is HCO3 and its role in acid-base balance?

Answer 12

Bicarbonate; it is a base

Question 13

How does increased bicarbonate affect pH?

Answer 13

Causes the pH to rise (metabolic alkalosis)

Question 14

What is respiratory alkalosis characterized by?

Answer 14

PaCO2 < 35; pH > 7.45

Question 15

What is metabolic alkalosis characterized by?

Answer 15

HCO3 > 26; pH > 7.45

Question 16

What are some causes of respiratory alkalosis?

Answer 16

• Iatrogenic – excessive mechanical ventilation
• Hypoxemia
• CNS irritation
• Aspirin overdose

Question 17

What are the causes of metabolic alkalosis?

Answer 17

• Gastric suction/vomiting
• Diuretic therapy
• Iatrogenic – administration of HCO3

Question 18

What causes acidosis?

Answer 18

Decreased pH < 7.35 due to decreased base (HCO3) or increased acid (CO2, lactic acid)

Question 19

What is respiratory acidosis characterized by?

Answer 19

PaCO2 > 45; pH < 7.35

Question 20

What is metabolic acidosis characterized by?

Answer 20

HCO3 < 22; pH < 7.35

Question 21

What are some causes of respiratory acidosis?

Answer 21

• CNS depression
• Decreased V/Q ratio
• Decreased lung compliance
• Injury to the thorax

Question 22

What are some causes of metabolic acidosis?

Answer 22

• Decreased tissue perfusion
• Hypoxia
• Sepsis
• Renal failure
• Diarrhea

Question 23

What is the first rule of blood gas evaluation?

Answer 23

Think of carbon dioxide (CO2) as an acid

Question 24

What is the second rule of blood gas evaluation?

Answer 24

Think of bicarbonate (HCO3) as a base

Question 25

What does it indicate if the pH is normal?

Answer 25

The blood gas is normal or full compensation has occurred

Question 26

What does it mean if the pH is low?

Answer 26

The blood gas is uncompensated secondary to metabolic acidosis or respiratory acidosis

Question 27

What are the three questions to ask when evaluating blood gases?

Answer 27

* Is the pH normal? * Is the pCO2 normal? * Is the HCO3 normal?

Question 28

What is the organ of oxygen exchange for the fetus?

Answer 28

The placenta

Question 29

What does umbilical cord compression lead to?

Answer 29

Intermittent fetal hypercarbia

Question 30

What is the normal pH for umbilical vein blood?

Answer 30

7.35 +/- 0.05

Question 31

What is the normal pH for umbilical artery blood?

Answer 31

7.28 +/- 0.05

Question 32

When should cord blood gases be done?

Answer 32

Any time the newborn condition is depressed or has significant risk factors

Question 33

What does a low pH in umbilical arterial gases indicate?

Answer 33

Metabolic acidosis

Question 34

How quickly does metabolic acidosis develop with complete occlusion of the cord?

Answer 34

pH falls ~ 0.04/minute

Question 35

What does the difference in arterial and venous pH values indicate in respiratory acidosis?

Answer 35

CO2 is cleared rapidly