Grade III/VI Murmur on the Dental Schedule
A 9-year-old male neutered Labrador retriever weighing 41 kg (BCS 7/9) is admitted for a dental prophylaxis and extractions. Preoperative auscultation reveals a grade III/VI left basilar systolic murmur; heart rate is 112, femoral pulses are fair, mucous membranes are pink, and the owner reports the dog "slows down on walks more than he used to" but has no cough or syncope. Bloodwork: PCV 44%, TS 7.2 g/dL, BUN 28 mg/dL, creatinine 1.7 mg/dL, ALT 92 U/L, glucose 105 mg/dL. The veterinarian's standing protocol is acepromazine 0.05 mg/kg plus butorphanol 0.2 mg/kg IM, then ketamine 5 mg/kg with diazepam IV for induction, maintained on isoflurane. Stock includes isoflurane, sevoflurane, propofol, alfaxalone, hydromorphone, methadone, fentanyl, midazolam, dexmedetomidine, atropine, and glycopyrrolate. There is no local cardiologist; an echocardiogram is a 40-minute drive and costs about $450. The owner has approved a $700 dental estimate and asks whether the murmur "is a big deal."
1. Evaluate the standing anesthetic protocol for this dog and propose an alternative, including whether to proceed at all.
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The protocol is not automatically wrong, but it is poorly matched to this dog. Ketamine raises heart rate, blood pressure, and myocardial oxygen demand, and in an unstaged murmur it muddies the ability to interpret any cardiovascular change during the procedure. Acepromazine produces vasodilation and can deepen hypotension in a dog with questionable cardiac reserve. Dexmedetomidine would be worse - vasoconstriction and increased afterload are exactly what an outflow obstruction or a failing myocardium tolerates badly.
A more defensible plan: hydromorphone 0.05–0.1 mg/kg or methadone 0.3–0.5 mg/kg IM with midazolam 0.2 mg/kg, preoxygenate by mask for 3–5 minutes, induce with propofol or alfaxalone titrated to effect (to intubation, not to a fixed volume), and maintain on isoflurane at the lowest concentration that holds a surgical plane, adding a fentanyl or lidocaine CRI if needed. Avoid ketamine and alpha-2 agonists.
The larger judgement call is whether to proceed. A grade III/VI murmur with reduced exercise tolerance in a 9-year-old Labrador deserves an echocardiogram before an elective dental. Offer the $450 option, document the owner's decision, and record that the risks were explained - proceeding without it is defensible only after that conversation.
2. Mid-procedure at 2% isoflurane, MAP falls to 55 mmHg and heart rate to 55 beats/min. Walk through your response in order.
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MAP 55 with a heart rate of 55 in a dog at 2% is a depth-and-volume problem until proven otherwise.
Check the monitor first: cuff size and placement, Doppler versus oscillometric, and whether the number matches the palpated pulse and mucous membrane color. Then, in order: turn the vaporizer down to 1.25–1.5% and assess depth (jaw tone, palpebral reflex, eye position) - if the dog is too deep, that alone may fix it. Give a crystalloid bolus of 10 mL/kg (410 mL) over 10–15 minutes and reassess.
Consider the surgical stimulus: traction on the eye or a dental elevator can produce vagal bradycardia - if rate and pressure rise after reducing stimulation, that is your answer, and glycopyrrolate 0.005–0.01 mg/kg IV is reasonable if bradycardia persists. Check temperature; a cold dog responds poorly to fluid boluses. Recheck MAP every 3–5 minutes. If MAP stays below 60 after depth, volume, and vagal causes are addressed, escalate - colloid, a vasopressor, or abandon the procedure and recover the dog.
3. Six hours after recovery the dog is at 150 beats/min, 40 breaths/min, 39.4°C, and restless. How do you decide whether this is pain, and what do you do?
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In a dog that just had extractions, pain is the most likely explanation, but you cannot assume it. Score pain with a validated tool (Glasgow CMPS-SF or Colorado) and read the whole picture: panting, trembling, reluctance to move the head, guarding the mouth suggests pain; disorientation, paddling, and hypersensitivity to sound suggest dysphoria. Check SpO2, blood pressure, temperature trend, and glucose. A temperature of 39.4°C is mild and can reflect pain or excitement, but combined with tachycardia and tachypnea it needs an explanation.
If the pain score is high, treat - hydromorphone 0.05–0.1 mg/kg IV or methadone - and confirm an NSAID was given if renal values allow - then reassess in 15–20 minutes. If the dog is dysphoric rather than painful, more opioid makes it worse: reduce stimulation, quiet the cage, and consider a lower opioid dose with a dexmedetomidine microdose.
If the dog remains painful despite an opioid, call the veterinarian and examine the extraction sites for swelling, hemorrhage, or a fractured tooth fragment - do not simply wait until morning.