Class is in Session

You gon learn today son!

Abg interpretation; the core of Icu rotation and even medicine as well. pH, pO2/CO2, HCO3-, Compensation So we need to ask ourselves, is the pH normal, acidotic or alkalotic?

Acidotic: pH <7.35

Normal: pH 7.35 – 7.45

Alkalotic: pH >7.45

Type 1 vs type 2 respiratory failure

Type 1 respiratory failure involves hypoxaemia (PaO2 <8 kPa) with normocapnia (PaCO2 <6.0 kPa).

Type 2 respiratory failure involves hypoxaemia (PaO2 <8 kPa) with hypercapnia (PaCO2 >6.0 kPa).

So we need to ask ourselves:

1. Is the HCO3– normal or abnormal?

2. If abnormal, does this abnormality fit with the current pH (↓HCO3– and acidosis)

3. If the abnormality doesn’t make sense as the cause for the deranged pH, it suggests the cause is more likely respiratory (which you should have already seen from the CO2)

ECG- Rate, Rhythm, Axis. Then all the special stuff

Step 1 – Heart rate

Heart rate can be calculated using the following method (if regular):

Count the number of large squares present within one R-R interval

Divide 300 by this number to calculate the heart rate

Step 2 – Heart rhythm

The heart rhythm can be regular or irregular.

Irregular rhythms can be either:

Regularly irregular (i.e. a recurrent pattern of irregularity)

Irregularly irregular (i.e. completely disorganised)

Mark out several consecutive R-R intervals on a piece of paper, then move them along the rhythm strip to check if the subsequent intervals are the same.

Step 3 – Cardiac axis

Cardiac axis describes the overall direction of electrical spread within the heart.

In a healthy individual the axis should spread from 11 o’clock to 5 o’clock.

To determine the cardiac axis you need to look at leads I,II and III.

Then move to St segments, Pr intervals etc. Looking for pathology throughout.

One thing not discussed here is the causes for these conditions. We pointed out the features, you need to know why.