Acid - Base regulation

Question 1

What is alkalaemia?

Answer 1

high blood pH

Question 2

What is acidaemia?

Answer 2

low blood pH

Question 3

What is alkalosis?

Answer 3

circumstances that will decrease proton concentration and increase pH

Question 4

What is acidosis?

Answer 4

circumstances that will increase proton concentration and decrease pH

Question 5

What is the equation relating H20, CO2, H2CO3, HCO3- and H+?

Answer 5

H20 + CO2 H2C03 HCO3- + H+

Question 6

What is the buffering capacity of blood and how long does it take to respond to pH change?

Answer 6

Th blood has an enormous buffering capacity that can react almost immediately to pH imbalances

Question 7

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

Answer 7

-log10[H+]

Question 8

What is the equation to calculate [H+] form pH?

Answer 8

10^-pH

Question 9

What are the two sources of acid?

Answer 9

• respiratory acid (CO2)
• metabolic acid (e.g. pyruvate)
  Majority of acid is from CO2

Question 10

What is the Henderson - Hasselbach equation?

Answer 10

pH= pK + log10 ([HCO3-]/[CO2])

Combines the dissociation constant (strength of an acid) to work out pH

Question 11

What is normal blood pH approximately?

Answer 11

7.35 -7.45

Question 12

What are normal values in ABG

Answer 12

[H+] = 40 nmol/L
pC02 = 4.7-6.4 kPa
pO2 = >10kPa
HCO3- = 22-26 mEq/L
BE (B) = -2 to 2

Question 13

What is BE?

Answer 13

The ratio of actual bicarbonate to expected

Question 14

PaO2 - what is normal, mild hypoxaemia, moderate hypoxaemia and severe hypoxaemia?

Answer 14

normal: >10kPa
mild: 8-10 kPa
moderate: 6-8 kPa
severe: <6 kPa

Question 15

What is a compensatory mechanism to counteract changes in pH caused by ventilation changes?

Answer 15

Change in HCO3-/H+ retention/secretion in the kidneys. Slow response

Question 16

What must happen to correct an acidosis and an alkalosis?

Answer 16

acidosis - an alkalosis is needed

alkalosis - an acidosis is needed

Question 17

Which 3 things are affected by pH?

Answer 17

enzyme
hormone
membrane transporter

Question 18

When interpreting ABG what should be questioned?

Answer 18

• what type of imbalance
• aetiology of imbalance (respiratory or metabolic)
• any homeostastic compensation (uncompensated, partially or full compensated)
• oxygenation (hypoxaemia/normoxaemia/hyperoxaemia)

Question 19

What does a wrong BE suggest?

Answer 19

a metabolic problem

Question 20

What is normal ICF, ECF, arterial blood, venous blood and stomach pH?

Answer 20

Intracellular fluid: 7.0.
Extracellular fluid: 7.4.
Arterial blood: 7.4.
Venous blood: 7.36.
Stomach: 2.4.

Question 21

Give two compensatory mechanisms

Answer 21

• Changes in ventilation stimulate a rapid compensatory response to change CO2 elimination and therefore alter pH.
• Changes in HCO3- and H+ retention/secretion in the kidneys can stimulate a slow compensatory response to increase/decrease pH

Question 22

What does a high base excess mean?

Answer 22

A rise in base excess is due to an increase in renal excretion of acid, ingestion/administration of a base or loss of acid from vomiting. The result is a metabolic alkalosis

Question 23

What does a low base excess mean?

Answer 23

A fall in base excess is due to the overproduction of metabolic acids, the ingestion of acid, a reduction/failure of acid excretion by the kidney or excessive loss of alkali from intestines with diarrhoea. The result is a metabolic acidosis.

Question 24

What is uncompensated, partially compensated and full compensated?

Answer 24

uncompensated - no compensation yet
partially - compensation kicked in
fully - stimulus still there but pH normal