A 3 year old, male castrated domestic shorthair cat is presented by his very worried owner. He has been missing for the last 2 nights and came home this morning. He ate well when he came home but has been sleeping since then, and doesn’t want to play games.
On physical examination the cat is bright, alert, and interactive. He is interested in investigating the exam room including trying to get into cabinets and playing with the paper towel roll. Aside from being a bit overweight, his physical examination is completely unremarkable.
T 100.4F P 170 R 36 mm pink CRT 1.5s BCS 7/9 Weight 6.8kg BP 124/88 (100mmHg)
At the owner’s insistence you perform blood work. The CBC and serum chemistry are normal. Interpret the blood gas:
Step 1: Evaluate the pH
This patient’s pH is 7.36, which is in the normal range. A normal pH can indicate a normal blood gas status, OR it can indicate a mixed acid-base disturbance. The most common error people make when interpreting the blood gas is to see a normal pH and assume there is no acid-base disturbance. The only way to know if this is a normal blood gas or not is to assess the metabolic and respiratory components and correlate those findings to the patient.
Step 2: Determine the primary disturbance/evaluate the metabolic and respiratory components
Next we look at the pCO2 and HCO3. We see the pCO2 is 42 (normal) and the bicarbonate is 21 (also normal).
Step 3: Does the ‘normal’ blood gas result fit with the patient’s clinical picture?
This is a very important question to ask yourself when you have a ‘normal’ blood gas.
It is possible on rare occasions for a very sick patient with multiple (mixed) acid-base disturbances have a ‘normal’ pH, pCO2, and HCO3. This occurs because of the complex interactions of multiple disturbances and the body’s compensations for them. For this reason you should always ask ‘knowing what I know about my patient, does it make sense for the blood gas to be normal?’ If the answer is ‘no’ then further investigations such as applying semi-quantitative acid-base analysis, the strong ion difference, or other blood-gas analysis techniques need to be performed.
In this case we have a cat who seems to be quite okay on physical examination and blood work – he probably just needs to sleep off his night(s) on the town. So, in this case the ‘normal’ blood gas indicates there is no acid-base disturbance occurring.
Want to learn about reading blood gases? You’ve come to the right place. Every week a new blood gas case will be posted. The scenario will post on Monday and the solution will post on Wednesday.
New to blood gasses? Check out the quick guide to acid-base interpretation here.
