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The Relationship of Depth of Anaesthesia With Blink Reflex in Cats
Özlem Şengöz Şirin1, Ayşe Nihan Elvan2
1Department of Surgery, Faculty of Veterinary Medicine, Burdur Mehmet Akif Ersoy University, Burdur, Turkey.
Background:
The blink reflex is a neurological response characterised by eyelid movements and can provide important data on the state of anaesthesia. Sevoflurane is a commonly used inhalation anaesthetic agent in cats and evaluation of eye reflexes under this agent may help to better understand the depth of anaesthesia.
Objectives:
The aim of this study was to evaluate the relationship between the blink reflex and the depth of anaesthesia in cats and to evaluate the parameters that can be obtained from the blink reflex in addition to its effect in determining the depth of anaesthesia.
Methods:
All cats were premedicated with midazolam 0.1 mg kg-1 and butorphanol 0.4 mg kg-1. Propofol at a dose of 4 mg kg-1 was administered for the induction of anaesthesia. Following this, anaesthesia was maintained with sevoflurane. Anaesthesia was maintained at a minimum alveolar concentration (MAC) value of 2.9, which is the end-tidal MAC value that provides deep anaesthesia for cats. Following the end of the operation, electrical stimulation was given to the supraorbital nerve for each 0.1 for each decreasing MAC value starting from the end-tidal MAC value of 2.9, and blink parameters were recorded from the orbicularis oculi muscle. In this study, the mean latency, amplitude and duration values in sevoflurane anaesthesia in cats were determined.
Results:
In cats, only two blink responses, R1 and R2, were found in all MAC values. At the same time, a very strong positive correlation was found between R1 latency and MAC, and a moderate negative correlation was found between R2 latency and MAC. There was a very strong negative correlation between R1 amplitude and MAC and a moderate positive correlation between R2 amplitude and MAC. There was a moderate negative correlation between R1 duration and MAC and a weak negative correlation between R2 duration and MAC. When the relationship between anaesthesia stages and MAC was compared, R1 amplitude and R2 amplitude were found to be significant only between stage II and awake stage. In all other stages, R1 latency, R2 latency, R1 amplitude and R2 amplitude were not significant. All cats woke up with an average MAC value of 0.43 ± 0.20.
Conclusions:
In this study, mean latency, amplitude and duration values in cats under sevoflurane anaesthesia were determined. It was demonstrated that it was possible to elicit blink parameters in cats under sevoflurane anaesthesia with a short stimulus sequence to the supraorbital nerve. Only two blink responses, R1 and R2, were elicited at all MAC values.
