UC Davis

Objective

To describe the semiquantitative acid-base status of dogs with untreated naturally occurring typical hypoadrenocorticism and to compare this to the status determined by traditional acid-base analysis.

Design

Retrospective study.

Setting

University teaching hospital.

Animals

Thirty-three dogs with newly diagnosed typical hypoadrenocorticism between 2000 and 2017.

Interventions

None.

Measurements and main results

Dogs were included if they had newly diagnosed hypoadrenocorticism, post-ACTH stimulation serum cortisol concentration <2 μg/dL, and blood collected within 6 hours of presentation for acid-base, electrolyte, and serum biochemical assays. Dogs were excluded if the Na⁺ :K⁺ ratio was ≥28 or the dog had received a mineralocorticoid-containing corticosteroid medication within the preceding month. Traditional acid-base analysis identified normal acid-base status in 1 dog, simple respiratory acid-base abnormalities in 2 of 33 dogs, and simple metabolic acidosis in 14 of 33 dogs. A mixed disorder was most common, noted in 16 of 33 dogs. The semiquantitative approach identified metabolic abnormalities in all cases. All dogs had ≥1 acidifying process, and 29 of 33 had both acidifying and alkalinizing processes. Acidosis attributable to excess free water was present in all dogs, and an acidifying phosphate effect was present in 27 of 33. Hyperlactatemia contributed to the acidosis in 8 of 33 dogs, with a median (range) lactate concentration of 1.5 mmol/L (13.5 mg/dL) (0.3-4.2 mmol/L [2.7-37.8 mg/dL]).

Conclusions

Dogs with untreated Addison's disease have complex acid-base derangements. The semiquantitative approach to acid-base analysis provides greater insight into the underlying mechanisms of metabolic acid-base abnormalities in these dogs, particularly because lactic acidosis appears to be a minor influence in most cases.