The Anuric Cat After a Bite Wound
A 6-year-old male castrated domestic shorthair is presented 36 hours after a dog bite to the right flank. He is depressed, tachycardic (200/min), and tachypneic (36/min). Temperature 36.2°C. Mucous membranes pale, CRT 3 seconds. The wound is a 2 cm puncture with surrounding bruising and crepitus. He has not produced urine in the last 12 hours despite being given fluids at home. Blood work: BUN 88 mg/dL, creatinine 4.2 mg/dL, K+ 6.8 mmol/L, Na 148 mmol/L, Cl 118 mmol/L, ionized Ca 0.9 mmol/L, glucose 180 mg/dL. PCV 48%, TS 6.0 g/dL. Venous pH 7.18, HCO3 12 mmol/L. ECG shows peaked T waves and a widened QRS.
1. Identify the life-threatening abnormalities and explain the pathophysiology of the hyperkalemia in this patient.
Read the worked answer
The life-threatening abnormalities are severe hyperkalemia (K+ 6.8 mmol/L) with ECG changes - peaked T waves and a widened QRS indicate impending ventricular fibrillation or asystole - plus severe metabolic acidosis (pH 7.18, HCO3 12) and acute kidney injury (BUN 88, creatinine 4.2, anuria). The hyperkalemia has multiple contributors: acute kidney injury with reduced excretion, tissue trauma/necrosis from the bite releasing intracellular potassium, acidosis shifting potassium out of cells, and hypoperfusion with possible rhabdomyolysis. The widened QRS is the critical finding - it means the myocardium is already affected and the patient can arrest at any moment. The hypothermia (36.2°C) and tachycardia further reflect shock. The combination of trauma, AKI, and hyperkalemia is a crush/trauma-induced AKI picture, and the acidosis worsens potassium cardiotoxicity.
2. Outline the emergency treatment of the hyperkalemia and acidosis, in order of priority.
Read the worked answer
Step 1 - Stabilize the myocardium: Give 10% calcium gluconate 0.5–1 mL/kg IV slowly over 10–15 minutes (or calcium chloride 10 mg/kg) with ECG monitoring. This does not lower potassium but protects the heart; effect lasts 30–60 minutes. Repeat if ECG changes persist.
Step 2 - Shift potassium intracellularly: Give regular insulin 0.1–0.2 U/kg IV with dextrose 1–2 g/U (e.g., 0.5 g/kg dextrose) to drive K+ into cells; monitor glucose every 30 minutes for hypoglycemia. Alternatively, sodium bicarbonate if acidosis is severe (pH <7.2) - give 1–2 mEq/kg slowly IV, but only with adequate ventilation and calcium already given, as it can worsen hypocalcemia and paradoxical CNS acidosis.
Step 3 - Remove potassium: Fluid therapy with balanced crystalloid to restore perfusion and urine output; consider furosemide if producing urine, or dialysis if anuric and refractory. Do not give potassium-containing fluids.
Step 4 - Treat the cause: Address the bite wound (debridement, antibiotics), treat shock, and monitor ECG continuously. Recheck K+ and glucose frequently. The order matters: calcium first for cardiac protection, then insulin/dextrose and bicarbonate for shifting, then fluids/dialysis for removal.
3. The cat remains anuric after fluids and calcium. What are your options, and how do you counsel the owner about prognosis?
Read the worked answer
If the cat remains anuric despite adequate fluid resuscitation and correction of hyperkalemia, the options are limited and time-sensitive: renal replacement therapy (dialysis) if available, which is the definitive treatment for refractory anuria and hyperkalemia; continuous renal replacement or peritoneal dialysis as alternatives; and supportive care with careful fluid balance to avoid volume overload while awaiting renal recovery. Furosemide may convert oliguria to diuresis in some cases but is unlikely to help true anuria. Dopamine or mannitol are not recommended for AKI. If dialysis is unavailable, the prognosis is grave - anuric AKI with hyperkalemia carries a high mortality, and euthanasia is a reasonable discussion if the cat deteriorates.
Counseling: Be honest that anuria after trauma indicates severe renal injury, and recovery is possible but uncertain; some cats recover renal function over days to weeks with dialysis support. Discuss costs, the need for referral, and quality-of-life. Monitor for volume overload (pulmonary edema), uremic complications (pericarditis, encephalopathy), and ongoing hyperkalemia. The key point is to refer early for dialysis rather than waiting until the patient is refractory, and to have an open conversation about goals of care.