Anesthetic Plan for a Geriatric Golden Retriever with a Limb Mass
Riley is a 9-year-old, 32 kg, castrated male Golden Retriever scheduled for excision of a 3 cm mast cell tumor on the right lateral thigh. Preoperative physical examination: HR 104 bpm, RR 32 with mild panting, T 38.4°C, BCS 6/9, and a grade II/VI systolic murmur heard best over the left apex. Bloodwork: PCV 46%, TS 7.4 g/dL, BUN 24 mg/dL, creatinine 1.3 mg/dL, ALT 96 U/L, glucose 108 mg/dL, albumin 3.4 g/dL. The owner reports that Riley becomes extremely excitable and difficult to handle in the clinic. He has been fasted since 10 pm the previous night and has no previous anesthetic history. The veterinarian asks you to prepare a premedication and induction plan and to draw up the drugs in advance. Stock includes hydromorphone 2 mg/mL, acepromazine 10 mg/mL, midazolam 5 mg/mL, propofol 10 mg/mL, meloxicam 5 mg/mL, and isoflurane. Surgery should last about 45 minutes with 2 cm margins.
1. Give your premedication recommendation with the dose in mg/kg, the calculated dose in mg, and the volume in mL using the stock concentrations above. Justify each drug for this specific patient, and name one drug or class you would avoid and explain why.
Read the worked answer
Recommended premedication (IM if no catheter yet; IV once access is confirmed):
- Hydromorphone 0.1 mg/kg → 0.1 × 32 = 3.2 mg → 3.2 ÷ 2 mg/mL = 1.6 mL. The opioid provides sedation, pre-emptive analgesia for the tumor excision, and lowers isoflurane MAC, which matters in a dog with a murmur. At this dose, respiratory depression is mild and reversible with naloxone.
- Midazolam 0.2 mg/kg → 0.2 × 32 = 6.4 mg → 6.4 ÷ 5 mg/mL = 1.28 mL. A benzodiazepine adds muscle relaxation and anxiolysis for a dog that is hard to handle, with minimal cardiovascular depression, and is reversible with flumazenil if sedation overshoots.
- Meloxicam 0.2 mg/kg IV → 0.2 × 32 = 6.4 mg → 6.4 ÷ 5 mg/mL = 1.28 mL, given after IV access and only with adequate perfusion. It improves postoperative comfort but compounds renal risk if the dog becomes hypotensive intraoperatively, so MAP must be supported and creatinine rechecked the next day.
Avoid acepromazine. Alpha-1 blockade causes vasodilation and hypotension that lasts for hours and cannot be reversed; in a geriatric dog with a newly noted murmur and unknown cardiac reserve, that is an unnecessary gamble when opioid/benzodiazepine sedation will work. Dexmedetomidine would be a similarly poor first choice for cardiovascular reasons. Preoxygenate by mask for 3-5 minutes while the premed takes effect.
2. Calculate the propofol dose at 4 mg/kg and describe exactly how you would induce Riley, including what you would do if he will not allow IV catheter placement.
Read the worked answer
Total propofol at 4 mg/kg: 4 × 32 = 128 mg = 128 ÷ 10 mg/mL = 12.8 mL.
That 12.8 mL is a ceiling, not a target. Draw it up, then give roughly a quarter to a third (3-4 mL) over 30-60 seconds, assess jaw tone, palpebral reflex, and eye position, and titrate in 1-2 mL increments until intubation is possible. After opioid/benzodiazepine premed, the true induction requirement is often closer to 2-4 mg/kg. Rapid boluses of the full calculated volume cause apnea and hypotension because propofol produces vasodilation and myocardial depression; preoxygenation buys several minutes of safe apnea time, and intubation equipment plus a working suction should be at hand before the first milliliter goes in.
If IV access is impossible: the premed should make catheter placement feasible, and that is the preferred fix. Mask induction with isoflurane in an excitable dog is a poor option (struggling, breath-holding, room pollution). A reasonable fallback is ketamine 5 mg/kg + midazolam 0.25 mg/kg IM = 160 mg (1.6 mL of 100 mg/mL) + 8 mg (1.6 mL), which should allow catheter placement, while accepting that the airway cannot be secured immediately if the dog reacts.
3. Fifteen minutes into surgery at 1.5% isoflurane, MAP is 52 mmHg, HR is 128 bpm, ETCO2 is 38 mmHg, SpO2 is 98%, and the surgeon reports minimal stimulation. Outline your actions in the order you would take them.
Read the worked answer
Do not treat the number until you trust it, and do not reach for a vasopressor first.
- Confirm the reading - cuff size and position (width ≈ 40% of limb circumference), transducer zeroed at heart level, tubing not kinked, no fluid leak.
- Deepen the assessment, then lighten the anesthetic - check jaw tone and palpebral reflex. If the dog is adequately deep, reduce isoflurane to 1.0-1.25% and reassess MAP in 3-5 minutes. Isoflurane causes dose-dependent vasodilation and myocardial depression, so this is often the single most effective step.
- If the dog is light (the low MAP may reflect inadequate analgesia and a high catecholamine state), top up with hydromorphone 0.05 mg/kg IV (= 1.6 mg = 0.8 mL) and reduce the vaporizer rather than pushing more inhalant.
- Volume - give a crystalloid bolus of 10-20 mL/kg = 320-640 mL over 15-20 minutes, and estimate blood loss; if loss exceeds ~10% of blood volume, check PCV/TS and consider a colloid.
- Check the machine - O2 flow, canister, circuit connections, and that the vaporizer is actually delivering what the dial says.
- Temperature - hypothermia depresses cardiac output; apply active warming.
- Escalate - if MAP remains below 60 mmHg after the above, call the veterinarian and start dopamine 5-10 µg/kg/min or dobutamine 2-5 µg/kg/min, and document every intervention and response.