Blood gas analysis

Question 1

What is the first question to ask in ABG analysis?

Answer 1

How is the patient?

Question 2

The acidity and alkalinity of blood is determined by what?

What is the normal concentration in the body?

Answer 2

Concentration of hydrogen ions [H+]. Hydrogen ions are acidic.

40 nanomole / L

Question 3

What is the normal pH of blood?

Answer 3

7.35-7.45

Question 4

What system is used to eliminate acids and regenerate buffers?

Answer 4

Lungs and kidneys

Question 5

What is the normal PaCO2

Answer 5

35-45mmHg

Question 6

What is the primary mechanism by which H+ is regulated?

Answer 6

The lungs through PaCO2

Question 7

What is the most important buffer made by the kidneys?
What is the normal value?
How long does it take to make?

Answer 7

Bicarbonate at 22-26mmol/L

It takes hours to days to make more bicarbonate

Question 8

What does vomiting do?

Answer 8

It reduces acidity through the vomit - pushing the body towards metabolic alkalosis

Question 9

What is the normal Base Excess and what is it?

Answer 9

+2 to -2mmol/L

more negative than -2 is metabolic acidosis

a base excess greater than +2 is in metabolic alkalosis

This is a measure of the amount of excess acid or base is in the blood as a result of a metabolic derangement.

Question 10

What is the normal PaO2?

What is the calculation for supplemental oxygen for normal/expected PaO2?

Answer 10

75-100mmHg

When there is supplemental O2, you expect to see 5x % = 40% x 5 = 200mmHg

Question 11

What are the steps for VBG analysis?

Answer 11

1. How is the patient
2. Is the patient hypoxaemic <75 mmHg
3. Is the patient acidaemic (pH <7.35) or alkalaemic (ph >7.45)
4. What has happened to the PaCO2?
   - Alkalosis - Mechanical ventilation, pain
5. If pH is < 7.35 and base deficit < -2 or bicarb < 22 -> acid
   if pH is >7.45 and BE > +2 or bicarb > 26 -> alkalosis

Question 12

Compensation - How do know which is primary?

Answer 12

Look at which side of 7.4 (pH) and then find the Bicarb or CO2 that matches that side -> this is the primary problem

Question 13

Which is more reliable in cardiac arrest VBG or ABG?

Answer 13

VBG

Question 14

What is better for post resus? ABG or VBG

Answer 14

ABG

Question 15

Lactate levels can guide post resus tissue oxygenation. What is normal values?

Answer 15

0.5-2.0mmol/L

Question 16

When are VBGs (outside of cardiac arrest useful)?

Answer 16

With monitoring metabolic disturbance where respiratory compromise isn’t that important

Question 17

Is a tourniquet helpful for VBGs

Answer 17

No, it can alter values

Question 18

What is the normal O2 level for a VBG?

Answer 18

35-50mgHg

Question 19

When do SpO2 results become very unreliable?

Answer 19

Below 70%

Presence of other haemoglobins like in carbon monoxide poisoning

Methyl blue

High ambient light levels

Nail varnish

Reduced pulse volume

Question 20

What O2 levels should you use and when?

Answer 20

In critically unwell with acute low O2 or unobtainable sats -> NRB 15L

Once ROSC has been achieved, aim for 94-98%