Evaluation of bispectral index monitorization (BIS) findings at different anesthesia protocols in cats

General anesthesia; is a CNS-controlled and reversible state of unconsciousness in which the patient is unable to perceive nociceptive or other stimuli. In the patient under general anesthesia, these three criteria, called the components of anesthesia, including unconsciousness, suppressed reflexes and analgesia, must be fulfilled. The degree of CNS depression created depending on the effect and concentration of the applied general anesthetic agents is expressed as depth of anesthesia. Anesthesia should not be excessively deep or superficial, as its purpose is to provide the patient with unconsciousness, pain relief, amnesia, and immobility. Therefore, monitoring the patient's level of consciousness and depth of anesthesia throughout the surgical procedure is essential. The observation or monitoring of vital functions during anesthesia application is referred to as monitoring, and various monitoring methods are often employed to enhance patient safety. Bispectral Index Monitorization (BIS) is a specialized monitoring system based on electroencephalography (EEG) that enables the monitoring of the central nervous system (CNS) and provides an objective assessment of anesthesia depth. BIS transforms EEG signals into a numerical value ranging from 0 to 100 using a specific algorithm. During general anesthesia, the BIS value should ideally be within the range of 40 to 60. In this PhD study; between 2018 and 2022, 100 VBO operations were performed using 86 cats that were brought to Istanbul University-Cerrahpaşa Faculty of Veterinary Medicine, Department of Surgery, Ear Nose and Throat Clinic, and as a result of the examinations, Ventral Bulla Ostectomy (VBO) was indicated, and BIS findings were evaluated in the perioperative period. The patients were randomly divided into 4 groups of 25 each. Patients in groups 1 and 2 received medetomidine HCl in induction; Ketamine HCl was used in the 1st group, and propofol was used in the 2nd group. Dexmedetomidine HCl was used in the patients in the 3rd and 4th groups, ketamine HCl was used in the patients in the 3rd group, and propofol was used in the patients in the 4th group. Preemptive analgesia was planned for each patient, and butorphanol was administered preventively, while ketamine was used as an adjuvant for intraoperative analgesia. After sedation, self-adhesive sensors were placed on the frontal region in a specific configuration for measurement. BIS values and conventional monitor findings were recorded at 12 predefined time points. Physical examination findings such as palpebral reflex, corneal reflex, pupillary size, which are subjective indicators of the depth of anesthesia, and findings indicating tissue perfusion such as CRT and MMC, were evaluated with BIS monitoring findings at different times. Although the hemodynamic response is considered an indicator of anesthesia depth, our study revealed a limited correlation between BIS and hemodynamic responses. In the first 8 time points, a statistically significant positive relationship was observed between BIS and body temperature. During the anesthesia, which was maintained under the control of BIS monitoring, it was determined that the anesthesia was maintained by providing surgical anesthesia at a dose lower than the specified MAC of isoflurane in cats. Contrary to existing literature knowledge, the study indicated that ketamine reflects a true hypnotic state based on the anesthesia protocols employed. Although ocular reflexes are widely used to evaluate the depth of anesthesia, we believe that objective CNS monitoring methods, especially BIS, should be used in patients with eye problems. In our findings, we consider that the average MAC percentage being below normal limits is associated with the use of a balanced anesthesia technique. The BIS findings also support this idea. In conclusion; although sources state that BIS monitorization does not reflect anesthetic depth in cats and shows lower BIS values compared to humans, our findings have proven that BIS monitorization is a reliable method that can be used to monitor the depth of anesthesia in cats and the BIS scale used in humans is also accurate in cats. BIS monitorization allows realtime monitoring of the true hypnotic state, ensuring rapid awakening and recovery with minimal drug usage tailored to individual patient differences. Keywords: Anesthesia, Cat, Depth of Anesthesia, Bispectral Index Monitoring (BIS), Monitoring