A previously healthy, 2 year old, spayed female cat is presented with 2-day history of vomiting and diarrhea. She is drinking large volumes of water and has no interest in food. She is noted to be about 8% dehydrated with an otherwise unremarkable physical examination.
T 101.1P 198R 38mm pinkCRT 1.5s BCS 4/9Weight 3.3kg BP 118mmHg (doppler)
Blood is obtained for analysis. Interpret the blood gas:
Acidemia can be caused by high pCO2 or low bicarbonate. This patient has both normal bicarbonate and normal pCO2. We cannot determine a primary process using our usual approach to acid-base.
At first glance we see the pCO2 is trending up to the high end of the range, which may lead us to think there is a respiratory acidosis – possible, but a pH of 7.30 is too low to be all respiratory with the CO2 still in the normal range. We have enough information on this blood gas and electrolyte report to calculate the anion gap:
AG = [Na + K] – [Cl + HCO3]
AG = [156 + 4.8] – [117+20.6]
AG = 23.2
The normal anion gap for a cat is 12-16 (reference: table inside front cover of Silverstein & Hopper Small Animal Critical Care Medicine). This patient’s anion gap is 23, suggesting there is likely a metabolic acidosis present.
Previously in BGOTW #15 we talked about the GOLDMARK mnemonic for high anion gap metabolic acidosis (you can review here). The “L” stands for Lactate. This cat has an ever so slightly elevated lactate could this be the cause? Probably not. Lactate is reported on mmol/L, so we can add it to the anion side (the chloride and bicarbonate side) of the AG equation:
AG = [Na + K] – [Cl + HCO3 + Lactate]
AG = [156 + 4.8] – [117+20.6 + 2.1]
AG = 21.1
So even accounting for the lactate the AG is still elevated. So, we should head to our GOLDMARK differentials to continue our diagnostic evaluation.
