Arterial Blood Gases

Question 1

What are the five causes of hypoxia?

Answer 1

1) Altitude (low atmospheric O2)
2) Hypoventilation
3) Diffusion limitations
4) V/Q mismatch
5) Shunt

Question 2

Which hypoxia causes have normal A-a gradients?

Answer 2

Altitude and hypoventilation.

Diffusion, V/Q mismatch, and shunt cause a high (>15) gradient

Question 3

What is respiratory acidosis?

Answer 3

Increase in PACO2, caused by hypoventilation (central or NM disorer) or hypercapneic respiratory failure.
Compensation by kidney bicarbonate conservation.

Question 4

What is respiratory alkalosis?

Answer 4

Decrease in PACO2, Caused by hyperventilation, altitude, neurological disorders, chronic salicylate (aspirin) toxicity, pain or anxiety.
Compensation by kidney bicarbonate excretion,

Question 5

What is metabolic acidosis?

Answer 5

Primary acid addition. 1) Anion-gap: caused by MUDPILES, (AG=Na-Cl-HCO3, 12 normal) and 2) Non Anion-gap: GI or renal losses
Compensation by hyperventilation. Winters formula determines if compensated properly.

Question 6

What are the MUDPILES?

Answer 6

Methanol, Uremia, DKA, Propylene glycol, Isoniazid, Lactate, Ethylene glycol, Salicylates

Question 7

What is metabolic alkalosis?

Answer 7

Base increase or acid loss (vomiting, hypovolemia or excess antacid).
Compensated by hypoventilation.

Question 8

What is the typical ABG for respiratory acidosis/alkalosis?

Answer 8

Low pH
High/normal PACO2

High pH
Low/normal PACO2

Question 9

What is the typical ABG for metabolic acidosis/alkalosis?

Answer 9

Low pH
Low PACO2

High pH
High PACO2

Question 10

What ABG value determines chronicity?

Answer 10

HCO3- normal in acute, high in chronic