Acid Base

Question 1

normal blood pH

Answer 1

7.35-7.45

Question 2

FiO2

Answer 2

fraction of inspired oxygen.

at any altitude the FiO2 of air is 0.21, often described as 21%

Question 3

PaO2

Answer 3

Partial pressure of oxygen in arterial blood.
normal at room air is 12.5 - 13.0 kPa(95-100mmHg)
past 65 years of age drops to around 11 kPa

the PaO2 does not reveal how much oxygen is in the blood but only the pressure exerted by the dissolved O2

Question 4

PaCO2

Answer 4

partial pressure of carbon dioxide in arterial blood. normal is 5.3kPa

Question 5

HCO3-

Answer 5

bicarbonate concentration 22-24 mmol/l

Question 6

BE

Answer 6

base excess - the quantity of strong acid or base required to restore pH to 7.4
normal is +/-2 mmol/l
positive value indicates base excess, negative indicates acid excess (deficit of base)

Question 7

the difference between the PO2 in the inspired gas at the mouth and the arterial PO2 is a healthy person

Answer 7

10 kPa, ie when breathing 21% oxygen, a person with normal lungs should have a PaO2 > 11kPa

Question 8

steps to interpret ABG

Answer 8

1. assess oxygenation?
   is the patient hypoxic? is there a significant alveolar-arterial gradient?
2. determine status of pH, i.e. acidemia or alkalemia
3. determine respiratory component
   paCO2 > 6.0kPa - respiratory acidosis (or respiratory compensation of metabolic alkalosis)
   paCO2 26 mmol/l - metabolic alkalosis (or renal compensation for respiratory acidosis)