A 2 year old, 67kg, intact male mastiff mix is presented for assessment and care after crashing through a plate glass window in pursuit of a squirrel. He has an approximately 10cm laceration on the left lateral thorax that is not actively bleeding, as well as probable injuries on his feet that are oozing a small amount of blood. The dog is significantly fear aggressive and is lunging at everyone who walks past. He is otherwise a healthy dog with no prior medical concerns.
The owner, who appears to weigh less than the dog, places a muzzle on the dog and you are able to perform a very cursory evaluation of the patient. The laceration on the thorax involves a large dead-space pocket, and he will not permit you to evaluate his feet.
T (not obtained)P 86R panting & growlingmm pinkCRT (probably has one) BCS 5/9Weight 67kg BP (good enough to lunge without syncope)
You briefly fantasize about having your friend at the local zoo come over and dart the dog with a lot of drugs, then get on with sedating the dog to evaluate and repair the wounds. Once the dog is sedated IV access is established, blood is collected for analysis, and a new complete set of vitals are obtained (all normal). Interpret the blood gas:
This patient’s pH is 7.40, which is the middle of 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
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.
The dog’s PCV was 48% and total solids 6.9g/dL – both quite normal, and the owner reports minimal bleeding from the wounds.
In this case we have a dog who has bled a little bit, but apparently not too badly. The lactate is up a bit but the dog was terrified and trying to fight his way free, so that’s not so that’s not too surprising. So, in this case the ‘normal’ blood gas indicates there is no acid-base disturbance occurring.
Can you have a high lactate without a metabolic (lactic) acidosis, or does that elevated lactate indicate there is a mixed disturbance occurring that we otherwise didn’t detect?
High lactate does not necessarily cause a metabolic acidosis. As lactate rises it is buffered by the body’s buffer systems. Acidosis will only occur when the buffer systems are overwhelmed. This is a young otherwise healthy dog who has a good reason to have a high lactate (fight-or-flight response, and unable to escape = big adrenalin surge = increase lactate production). While a high lactate (and 4 is significant) should always prompt us to ask the question ‘why’ in this case there is a reasonable physiologic explanation, and very importantly there is NOT evidence of hypovolemia, shock, sepsis, etc.
It would be very reasonable to recheck the lactate once the wound has been addressed to be sure it is returning to normal.
