Emergency management of hyperkalemia in dogs and cats - Part 1: Pathophysiology and etiology.

Objective: Hyperkalemia is a frequent, life-threatening emergency in dogs and cats. It disrupts neuromuscular function and cardiac conduction. Clinicians need a clear physiologic framework to recognize risk and act quickly. Animals and procedure: Part 1 of this 2-part review explains potassium homeostasis and the main causes of hyperkalemia in small animals. The article draws on peer-reviewed veterinary studies and core physiology, with direct patient-side relevance. Results: Most body potassium is intracellular; small extracellular shifts alter membrane excitability and electrocardiogram patterns. Two systems control plasma potassium: transcellular control through insulin, β Conclusion and clinical relevance: Evaluate hyperkalemia in the full clinical context. In dogs, common causes include hypoadrenocorticism, acute kidney injury, and urinary tract obstruction or rupture. In cats, urethral obstruction and advanced renal failure predominate, whereas iatrogenic potassium load and severe metabolic acidosis are additional concerns. A firm grasp of both pathophysiology and etiology improves differential diagnosis and early decisions. Part 2 of this review will build on this foundation and outline diagnosis and treatment.