Electroencephalographic power dynamics as early indicator of reduction in depth of anesthesia in a dog

This case report describes the electroencephalographic (EEG) power changes that preceded clinical signs of inadequate depth of anesthesia (DoA) in a dog during a minimally invasive procedure under general anesthesia. A 6-month-old Golden Retriever (14.1 kg) was anesthetized for fluoroscopy-guided cystoscopic ablation of bilateral ectopic ureters. Anesthetic premedication consisted of subcutaneous dexmedetomidine. General anesthesia was induced with intravenous midazolam and propofol and maintained with isoflurane alongside lumbosacral epidural analgesia with bupivacaine-morphine. Physiologic variables, including invasive arterial blood pressure, were monitored together with a single-channel prefrontal EEG, recorded via needle electrodes. Real-time EEG activity and its spectrogram were continuously evaluated using dedicated software. A stable anesthetic plane, confirmed clinically and by EEG features, was present with an end-expired fraction of isoflurane between 0.9 and 1.0%. After 99 minutes from anesthesia induction, the EEG spectrogram showed a marked reduction in delta [0.5-4 hertz (Hz)] and theta (4-8 Hz) power with a simultaneous increase in beta (12-25 Hz) and gamma (25-35 Hz) power. At this time and for the following 2-3 minutes, the dog's palpebral reflex, eye position, jaw tone, cardiovascular, and respiratory variables remained unchanged. Four minutes later, the dog exhibited movements of both thoracic limbs, which were accompanied by the reappearance of the palpebral reflex and an increase in arterial blood pressure. A propofol bolus was administered and the isoflurane concentration was increased. No further complications occurred and recovery was uneventful. In the present case, EEG power dynamics signaled a reduction in DoA several minutes before the appearance of clinical or cardiovascular indicators. Although EEG patterns associated with anesthetic depth are not yet standardized in veterinary patients, real-time spectrogram assessment may offer an additional and sensitive tool to detect early changes in cortical activity and guide anesthetic agent titration.