Anesthetic effects of ketamine–medetomidine–hydromorphone in dogs during high-quality, high-volume surgical sterilization program under field conditions

Objective   To describe the anesthetic and adverse effects of an injectable anesthetic protocol in dogs as part of a high-volume sterilization program under field conditions in Belize. 

Study design  Prospective, observational, field study. 

Animals  A total of 23 female and eight male dogs (14.2 ± 7.7 kg; age ≥ 8 weeks). 

Methods  Using a volume per kg-based dose chart, dogs were administered ketamine (4.5 mg kg⁻¹), medetomidine (0.04 mg kg⁻¹) and hydromorphone (0.09 mg kg⁻¹) intramuscularly. After induction of anesthesia, an endotracheal tube was inserted and dogs were allowed spontaneous breathing in room air. Monitoring included peripheral oxygen saturation (SpO₂), mean arterial pressure (MAP), heart rate (HR), respiratory rate, rectal temperature and end-tidal carbon dioxide (PE′CO₂). Meloxicam (0.2 mg kg⁻¹) was administered subcutaneously after surgery. Data were analyzed with linear models and chi-square tests (p < 0.05). 

Results  Onset of lateral recumbency (3.4 ± 2 minutes) was rapid. Desaturation (SpO₂ < 90%) was observed at least once in 64.5% of dogs and was more frequent in large dogs (p = 0.019). Hypercapnia (PE′CO₂ ≥ 50 mmHg; 6.7 kPa) was observed in 48.4% of dogs. MAP was 111 ± 19 mmHg, mean ± standard deviation. Hypertension (MAP ≥ 120 mmHg), bradycardia (HR ≤ 60 beats minute⁻¹) and tachycardia (HR ≥ 140 beats minute⁻¹) were observed in 45.2%, 16.1% and 3.3% of dogs, respectively. Hypotension and hypothermia were not observed. Sex was not significantly associated with any complication. Return of swallowing reflex and time to standing were 71 ± 23 and 152 ± 50 minutes after injection, respectively. Return of swallowing was significantly longer in large dogs. 

Conclusions and clinical relevance  At the doses used, ketamine–medetomidine–hydromorphone was effective in dogs for high-volume sterilization. In this field setting, adverse effects included hypoventilation, hypoxemia and prolonged recovery.