Sinus Tachycardia Following Administration of Naloxone in a Dog During Anesthetic Recovery.

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 in the teaching hospital due to acute right facial swelling. To further evaluate the swelling in the ER, 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, the dog was placed under general anesthesia to evaluate the recurrent facial swelling and undergo a dental procedure. After 55 min of discontinuation of isoflurane, no swallowing reflex was observed, making extubation not possible. Naloxone (0.01 mg/kg) was administered IV to reverse the effects of fentanyl. 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.