Sinus Tachycardia Following Administration of Naloxone in a Dog

A 7-year-old, 38.3 kg, male neutered Labrador retriever presented to the Teaching Hospital for a consultation of Comprehensive Oral Health Assessment and Treatment. Nine months prior to the consultation, the patient presented to the ER service due to acute right facial swelling. To further evaluate the swelling, the patient was sedated by IV administration of dexmedetomidine and fentanyl, and ventricular premature contractions (VPCs) were confirmed. The facial swelling subsided afterward, but it recurred. Therefore, a dental procedure under general anesthesia was scheduled. Although norepinephrine CRI was initiated to treat the hypotension perioperatively, VPCs were noticed a few minutes after norepinephrine CRI. After the dental procedure, a prolonged recovery was observed, and naloxone (0.01 mg/kg) was administered IV to reverse the effects of fentanyl. Before administration of naloxone, the HR was 80 bpm. Within one minute of administering naloxone, the patient was extubated. However, the HR surged to 240 bpm, and sinus tachycardia was observed. Ninety minutes after naloxone IV, the HR was 105 bpm with normal sinus rhythm, gradually approaching the pre-anesthesia HR level (110 bpm). Veterinarians should recognize that administration of naloxone could induce arrhythmias. Therefore, continuous monitoring of ECG, pulse, and blood pressure is imperative when administering naloxone.