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The Cavalier With the Rising Sleeping Respiratory Rate

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The Cavalier With the Rising Sleeping Respiratory Rate

A 10-year-old, 5.2 kg spayed female Cavalier King Charles spaniel is booked for a 10:00 dental scaling and polish. She was diagnosed with myxomatous mitral valve disease two years ago and takes pimobendan 0.25 mg/kg PO BID, furosemide 1 mg/kg PO BID, and enalapril 0.5 mg/kg PO BID. The owner says the dog is "fine," then mentions she has been sleeping more and that she started counting resting breaths last week at the cardiologist's suggestion: 22, 24, 22, 26, and 30 this morning. On presentation: temperature 38.6 °C, heart rate 148/min, respiratory rate 40/min with mild abdominal effort, mucous membranes pink but tacky, capillary refill 2 seconds, grade 5/6 left apical systolic murmur, crackles audible over the left caudal thorax, body condition score 6/9. The dog is sitting in sternal recumbency in the treatment area. The veterinarian is in the back finishing an emergency caesarean and has asked not to be disturbed unless a patient is dying. The kennel staff have already drawn up the clinic's standard premedication: acepromazine 0.02 mg/kg with buprenorphine 0.02 mg/kg.

1. Do you administer the premedication as drawn? Justify your answer using the specific findings in the case.

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No. Do not give the premedication, and do not proceed to induction.

Reasoning

  • The resting (sleeping) respiratory rate is the most sensitive home marker of decompensated heart failure in dogs with mitral valve disease. The accepted target is under about 30 breaths/min; a trend from 22 to 30 over a week, with today's rate of 40 and abdominal effort, crackles in the dependent lung field, and tacky mucous membranes, describes pulmonary oedema, not a stable cardiac patient.
  • This is an elective procedure. There is no clinical justification for anesthetising a dog in incipient or active congestive heart failure for a scaling and polish.
  • The premedication itself is a problem. Acepromazine causes vasodilation and can precipitate hypotension in a volume-overloaded, possibly hypoperfusing patient; more importantly, giving any sedative now removes the veterinarian's ability to examine the dog in her current, uncompensated state.
  • The instruction not to disturb the veterinarian applies to non-urgent matters. A patient who may be developing pulmonary oedema is urgent, and the technician's responsibility is to escalate, not to absorb the problem. Send a clear message with the numbers and ask for a decision.
  • Appropriate immediate actions: keep the dog quiet and minimally handled in sternal recumbency, provide flow-by oxygen, do not place a jugular catheter or take chest radiographs unsupervised with an unstable patient, and prepare to update the owner that the dental will be postponed.
  • The owner also needs to hear the interpretation of her own breathing counts - she collected the data that changed the plan, and acknowledging that reinforces the value of home monitoring.

2. Assume the dog is stabilised over the next two weeks and returns for the dental. Outline an anesthetic plan with the reasoning for each drug choice and each drug avoided.

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Premedication

  • Opioid-based: buprenorphine 0.01–0.02 mg/kg IV/IM, or methadone/hydromorphone for more analgesia. Opioids produce minimal cardiovascular depression and provide the analgesia needed for dental pain.
  • ± Midazolam for muscle relaxation and anxiolysis; it is cardiovascularly kind in a titrated dose.
  • Avoid alpha-2 agonists (dexmedetomidine, medetomidine): vasoconstriction raises afterload, which increases regurgitant fraction and worsens mitral regurgitation, and the accompanying bradycardia is poorly tolerated in a failing heart.
  • Acepromazine at a very low dose is not absolutely contraindicated in cardiac patients, but it is not the first choice in a dog with a history of congestion because of vasodilation and hypotension risk.

Induction

  • Pre-oxygenate 3–5 minutes by mask or flow-by; these dogs desaturate fast.
  • Propofol or alfaxalone titrated to effect in small increments, allowing 60–90 seconds between boluses. A single calculated full dose will cause apnea and hypotension.
  • Avoid ketamine: sympathomimetic, causes tachycardia, increases myocardial oxygen demand and regurgitant volume.

Maintenance and support

  • Isoflurane or sevoflurane in 100% oxygen, kept as low as the patient allows; consider a constant-rate infusion of an opioid to reduce inhalant requirement.
  • Local blocks - maxillary and inferior alveolar nerve blocks with bupivacaine - dramatically reduce the systemic drug burden.
  • No fluid boluses. If fluids are needed, give a maintenance-rate balanced crystalloid and reassess for pulmonary oedema.
  • Continue cardiac medications on schedule; a small sip of water with the morning dose is acceptable if the veterinarian agrees.
  • Ventilate if hypoventilating; these patients have little reserve.

3. List the monitoring parameters you would record for this patient, and explain what each one would tell you in a failing heart.

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Cardiovascular

  • ECG and heart rate: tachycardia worsens mitral regurgitation and raises oxygen demand; bradycardia with hypotension suggests excessive anesthetic depth or a vagal response to traction.
  • Blood pressure (oscillometric or Doppler), every 3–5 minutes: target mean arterial pressure ≥60–65 mmHg. Hypotension in a dog on furosemide and enalapril is common and reduces coronary perfusion.
  • Pulse quality and mucous membrane colour/CRT: the cheapest perfusion monitor in the room.

Respiratory

  • ETCO2 and capnography waveform: hypoventilation, and an abrupt change in waveform may signal a tube problem or a circulatory change.
  • SpO2 and inspired oxygen: a falling saturation on 100% oxygen in this dog means oedema until proven otherwise.
  • Respiratory rate and effort, and lung auscultation at each monitoring interval - crackles may develop during the procedure.

Depth and temperature

  • Reflexes, jaw tone, eye position to keep the inhalant as low as possible.
  • Core temperature - small, old, cardiac patients cool quickly, and hypothermia depresses myocardial contractility and delays recovery.

Procedure-specific

  • Blood loss during extractions, estimated from suction and swabs, with PCV/TS available if loss is significant.
  • Pain scoring in recovery; untreated pain drives tachycardia and hypertension.

Record values with times on the anesthetic chart. The chart is the evidence that monitoring happened, and a trend is worth more than any single number.