Resp 12 - Acid-base regulation

Question 1

What are typical blood gases values (PaO2, SaO2, PaCO2) in oxygenated and deoxygenated circulations?

Answer 1

Oxygenated
PaO2 = >10 kPa
SaO2 = 95%
PaCO2 = 4.7-6.4 kPa

Deoxygenated
PaO2 5.3 kPa
SaO2 ~75%
PaCO2 6.1 kPa

Question 2

Define
Alkalaemia
Acidaemia
Alkalosis
Acidosis

Answer 2

Alkalaemia Refers to high-than-normal pH of blood
Acidaemia Refers to lower-than-normal pH of blood
Alkalosis Describes circumstances that will decrease [H+] and increase pH
Acidosis Describes circumstances that will increase [H+] and decrease pH

Question 3

What is the equation to calculate pH (sorensen equation)?

Answer 3

pH = -log[H+]

Question 4

What is the equation to get [H+] out of pH?

Answer 4

10^-pH=[H+]

Question 5

Where can acid come from?

Answer 5

Respiratory acid +++++++++

Metabolic acid

Question 6

What is the equation to calculate the dissociation constant Ka (Henderson equation)?

Answer 6

Ka = [H+] x [HCO3-] / [CO2]

Question 7

From Soresen’s and Henderson’s equations, what is another way of calculating pH (Henderson-Hasselbach equation)?

Answer 7

pH = pKa + log [HCO3-]/[CO2]

Indeed
Ka = [H+] x [HCO3-] / [CO2]
so pKa = -log ([H+] x [HCO3-] / [CO2])
= -log[H+] - log [HCO3-] / [CO2]
= pH - log[HCO3-] / [CO2]

So pH = pKa + log [HCO3-] / [CO2]

Question 8

What are the basic guidelines for PaO2?

Answer 8

Basic guidelines for PaO2
>10 kPa is normal
8-10 kPa is mild hypoxaemia
6-8 is moderate hypoxaemia
<6 kPa is severe hypoxaemia