Hypotension and VPCs During Splenectomy
A 10-year-old castrated male Rottweiler weighing 45 kg is scheduled for splenectomy after a 2-week history of lethargy and a splenic mass. Preoperative PCV is 32%, total protein 5.8 g/dL, BUN 28 mg/dL, and creatinine 1.4 mg/dL. An ECG shows roughly 8 ventricular premature complexes per minute without pulse deficits. The anesthesia plan is acepromazine 0.02 mg/kg and hydromorphone 0.05 mg/kg IM, propofol to effect, and isoflurane maintenance. Fifteen minutes after induction, the heart rate is 58 beats/min, oscillometric blood pressure is 70/40 mmHg, SpO2 is 96%, and the ECG shows a short run of ventricular premature complexes. The surgical team has just begun a midline celiotomy; the dog is pale, and the splenic mass feels fluid-filled. The technician notes that the isoflurane vaporizer is at 2.5% and the dog has not received a fluid bolus.
1. List the most likely contributors to the hypotension and arrhythmia, and state which you would address first. Justify your priorities.
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The hypotension is likely multifactorial: acepromazine produces alpha-adrenergic blockade and vasodilation; isoflurane at 2.5% causes dose-dependent vasodilation and myocardial depression; the splenic mass may be bleeding, causing hypovolemia; and the dog may be painful or hypoventilating. The VPCs are probably secondary to hypoperfusion, hypoxia, or myocardial irritation from the splenic mass rather than a primary arrhythmia. Address perfusion and oxygenation first: reduce isoflurane to 1.0–1.5%, deliver 100% oxygen, check the airway and ventilation, and give a crystalloid bolus of 10–20 mL/kg IV while reassessing. Check PCV/TS, lactate, and blood loss; if the dog remains hypotensive or is actively bleeding, start a colloid or blood product. Bradycardia with hypotension may respond to glycopyrrolate, but fluids and reducing anesthetic depth are more important. Do not reflexively give an antiarrhythmic; treat the trigger and recheck the ECG.
2. How would you revise the premedication and induction plan for a dog with a splenic mass and VPCs if surgery were delayed 24 hours?
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For a dog with a splenic mass and VPCs, I would avoid acepromazine because of vasodilation and hypotension. Premedicate with an opioid (hydromorphone or methadone) plus midazolam for anxiolysis and muscle relaxation. Preoxygenate, place a large-bore IV catheter, and induce with etomidate, which is relatively cardiovascular-stable, or a ketamine-midazolam combination; avoid a large propofol bolus in a hypovolemic dog. Maintain with isoflurane at the lowest effective concentration plus a fentanyl CRI for analgesia. Have crossmatched blood available, monitor ECG, blood pressure, EtCO2, SpO2, temperature, and lactate, and keep the surgeon informed. If the dog deteriorates, convert to a balanced anesthetic protocol and support perfusion.
3. What postoperative monitoring is essential, and what signs would prompt you to call the veterinarian immediately?
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Postoperative monitoring should include continuous ECG, heart rate and rhythm, blood pressure, respiratory rate and effort, SpO2/EtCO2 if sedated, CRT, mucous membrane color, temperature, PCV/TS, lactate, urine output, and pain score. Watch the incision for swelling or bleeding and monitor for arrhythmias, which are common after splenectomy. Call the veterinarian immediately for sustained tachycardia, new arrhythmia, hypotension, pale or muddy gums, prolonged CRT, oliguria, distended abdomen, uncontrolled pain, or signs of sepsis. Also report any seizure-like activity or profound sedation.