ABGs

Question 1

What is a normal anion gap?

Answer 1

12 +/ - 4

Question 2

How do you calculate the delta gap

Answer 2

Change Anion gap/Change HCO3-

(AG - 12)/ (24 - HCO3)

Question 3

What is the anion gap corrected for albumin?

Answer 3

Albumin/4 + 1.5 x phosphate

the normal anion gap depends on serum phosphate and serum albumin

albumin is the major unmeasured anion and contributes almost the whole of the value of the anion gap.
every 1g/L decrease in albumin will decrease anion gap by 0.25 mmoles
a normally high anion gap acidosis in a patient with hypoalbuminaemia may appear as a normal anion gap acidosis.
this is particularly relevant in ICU patients where lower albumin levels are common

Question 4

How do you correct sodium for glucose?

Answer 4

= Na + (glucose - 5)/3

Question 5

What does delta gap of 0.4 to 0.8 mean?

Answer 5

Normal anion gap acidosis +
High anion gap acidosis

Question 6

What does a delta gap of <0.4 mean?

Answer 6

Pure normal AG metabolic acidosis

Question 7

What does a delta gap of 0.8 - 2 mean?

Answer 7

Pure high anion gap acidosis

Question 8

What is the age adjusted A-a gradient?

Answer 8

Age/4 + 4

Question 9

What does a delta gap of > 2 mean?

Answer 9

Metabolic acidosis +
Metabolic alkalosis

Question 10

What is the expected pCO2 in a metabolic acidosis?

Answer 10

1.5 x HCO3 + 8 (+/- 2)

Question 11

What is the expected HCO3- in ACUTE respiratory acidosis?

Answer 11

24 + (pCO2 - 40)/10

Question 12

What is the expected HCO3 in CHRONIC respiratory acidosis?

Answer 12

24 + (pCO2 - 40)/10 x 4

Question 13

What is the expected pCO2 in metabolic alkalosis?

Answer 13

0.7 x HCO3 + 20 (+/- 5)

Question 14

What is the expected HCO3- in ACUTE respiratory alkalosis?

Answer 14

24 - (40 - pCO2)/10 x 2

Question 15

What is the expected HCO3- in CHRONIC respiratory alkalosis?

Answer 15

24 - (40 - pCO2)/10 x5

Question 16

What is the expected K+ in acidosis?

Answer 16

5 + (0.5 x1 for every 0.1 unit change below 7.4)

K+ exchanges with H+ intracellularly to correct for acidosis. More K+ will become extracellular

Question 17

What is the expected K+ in alkalosis?

Answer 17

5 - (0.5 x 1 for every 0.1 unit change above 7.4)

Question 18

What does an elevated Aa gradient suggest?

Answer 18

VQ mismatch
- APO
- LRTI
- PE
- Aspiration
- ARDS
- membrane disease

Question 20

What is the “saturation gap”

Answer 20

Difference between paO2 on ABG sats from a pulse oximeter.
If it is greater than 5%, the hemoglobin may be abnormal:
- carbon monoxide poisoning
- methemoglobinemia
- sulfhemoglobinemia

sats 85% = 50
Sats 92% = 64
Sats 99% = 100