Blood gas analysis Flashcards
What is the first question to ask in ABG analysis?
How is the patient?
The acidity and alkalinity of blood is determined by what?
What is the normal concentration in the body?
Concentration of hydrogen ions [H+]. Hydrogen ions are acidic.
40 nanomole / L
What is the normal pH of blood?
7.35-7.45
What system is used to eliminate acids and regenerate buffers?
Lungs and kidneys
What is the normal PaCO2
35-45mmHg
What is the primary mechanism by which H+ is regulated?
The lungs through PaCO2
What is the most important buffer made by the kidneys?
What is the normal value?
How long does it take to make?
Bicarbonate at 22-26mmol/L
It takes hours to days to make more bicarbonate
What does vomiting do?
It reduces acidity through the vomit - pushing the body towards metabolic alkalosis
What is the normal Base Excess and what is it?
+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.
What is the normal PaO2?
What is the calculation for supplemental oxygen for normal/expected PaO2?
75-100mmHg
When there is supplemental O2, you expect to see 5x % = 40% x 5 = 200mmHg
What are the steps for VBG analysis?
- How is the patient
- Is the patient hypoxaemic <75 mmHg
- Is the patient acidaemic (pH <7.35) or alkalaemic (ph >7.45)
- What has happened to the PaCO2?
- Alkalosis - Mechanical ventilation, pain - 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
Compensation - How do know which is primary?
Look at which side of 7.4 (pH) and then find the Bicarb or CO2 that matches that side -> this is the primary problem
Which is more reliable in cardiac arrest VBG or ABG?
VBG
What is better for post resus? ABG or VBG
ABG
Lactate levels can guide post resus tissue oxygenation. What is normal values?
0.5-2.0mmol/L
When are VBGs (outside of cardiac arrest useful)?
With monitoring metabolic disturbance where respiratory compromise isn’t that important
Is a tourniquet helpful for VBGs
No, it can alter values
What is the normal O2 level for a VBG?
35-50mgHg
When do SpO2 results become very unreliable?
Below 70%
Presence of other haemoglobins like in carbon monoxide poisoning
Methyl blue
High ambient light levels
Nail varnish
Reduced pulse volume
What O2 levels should you use and when?
In critically unwell with acute low O2 or unobtainable sats -> NRB 15L
Once ROSC has been achieved, aim for 94-98%
