Greyhound Under Isoflurane: A Cluster of Abnormal Monitors

Reading the cluster: bradycardia (46) plus hypotension (MAP 58) plus hypoventilation (ETCO2 56 with a respiratory rate of 6) plus a flaccid jaw and absent palpebral reflex is a dog that is too deep, with a strong vagal contribution from ovarian pedicle traction. The dry surgical field fits vasodilation and poor cardiac output rather than good haemostasis.

The SpO2 of 96% is the most misleading number on the screen. On 100% inspired oxygen, a healthy dog should sit at 98–100%; 96% with an ETCO2 of 56 suggests real hypoxaemia risk behind the supplemental oxygen. Do not let it reassure you.

Checks before acting: is the ETCO2 trace real (waveform present, sampling line patent)? Is the pulse palpable or Doppler-detectable and does it match the oscillometric reading? Is the tube connected with no leak, the circuit assembled correctly, the vaporiser actually at the set percentage? Is the surgeon's hand or a retractor compressing anything, and is traction the only stimulus? Confirm depth with jaw tone and palpebral reflex. Only then treat - but do not spend five minutes troubleshooting while the MAP is 58.

1. Tell the surgeon to pause traction and tell the veterinarian what the monitors are doing. A technician who silently watches a MAP of 58 is not monitoring.
2. Ventilate by hand or with the ventilator to bring ETCO2 to 40–45 mmHg; six breaths a minute is inadequate and the hypercapnia is worsening the bradycardia and the depth.
3. Turn the isoflurane down - from 2.5% toward 1.5% or lower - and reassess depth. Hypercapnia plus a high vaporiser setting plus opioid is a stack of depressants.
4. Fluid bolus: 10 mL/kg = 280 mL of a balanced crystalloid over 10–15 minutes, reassessed in 5 mL/kg increments. If the dog is already on fluids, check the line, the bag height and the pump before assuming the rate is being delivered.
5. Anticholinergic if vagal bradycardia persists after traction is released and depth is lightened: glycopyrrolate 0.005–0.01 mg/kg IV or atropine 0.02 mg/kg IV, as authorised by the veterinarian.
6. Warm the patient - 37.2 °C is drifting and hypothermia deepens bradycardia and prolongs recovery.

Reassess heart rate, MAP, ETCO2 and depth every 1–2 minutes and record each set of values with the time and the intervention.

Breed points: Greyhounds have low body fat, high muscle mass and different drug handling from other breeds. Lipophilic agents redistribute into muscle and can produce a long, swoony recovery; propofol at 4 mg/kg is a full dose for a dog that could have been co-induced at a much lower dose with a benzodiazepine or opioid. Sighthounds are classically sensitive to thiobarbiturates and should not be treated as generic dogs for anaesthetic dosing.

Protocol points: acepromazine produces vasodilation and can worsen hypotension, and sighthounds are often described as having exaggerated or unpredictable responses to it - a lower dose, or an opioid–benzodiazepine premed, is worth discussing with the veterinarian. A pre-induction crystalloid load (10 mL/kg), an anticholinergic drawn up before a procedure known to cause vagal traction, and a plan for intermittent positive pressure ventilation would all have blunted this event. The vaporiser change from 1.8% to 2.5% in response to a swallow should also be reviewed: a swallow is often lightening, and turning the vaporiser up is not the only option.

Record: drugs with dose, route and exact time; vaporiser settings and every change; heart rate, respiratory rate, ETCO2, SpO2, blood pressure and temperature at least every 5 minutes; every intervention and the response. The record is what allows an honest review, protects the patient next time, and supports the veterinarian's clinical decisions if anyone asks.