Epileptiform EEG Patterns During Induction of General Anaesthesia With Sevoflurane Compared to Those With Propofol

The aim of the study was to assess the influence of volatile induction of general anaesthesia with sevoflurane using two different techniques and intravenous anaesthesia with propofol on the possible presence of epileptiform electroencephalograph patterns during the induction of general anaesthesia. We aimed to verify whether presence of epileptiform patterns (EPs) defined as polispikes (PS), rhytmic polispikes (RPS), periodic epileptiform discharges (PED) on Electroencephalographs (EEGs) influence the behaviour of values of the Bispectral Index (BIS), State (SE) and Response (RE), A-line Auto Regressive Index (AAI) derived from middle latency auditory evoked potentials (MLAEP) during the induction of general anaesthesia using abovementioned techniques and such variations may be useful in detection of presence of EPs.

Both sevoflurane and propofol are considered safe and potent anaesthetics and are used for induction or coinduction of general anaesthesia. During all stages of general anaesthesia, both agents may induce seizure-like movements or seizures (clinically manifested events and confirming electroencephalographic pattern) accompanied by haemodynamic instability. Their proconvulsant activity should be verified and assessed.

The aim of the additional analysis was to identify whether observance of the variations of values displayed on different depth of anaesthesia monitors (DOA monitors) reliably reflect the actual depth of general anaesthesia during presence of epileptiform patterns (EPs) in EEGs during VIGA with sevoflurane using two different techniques and intravenous induction of general anaesthesia with single dose of propofol.

We performed standard 30-minute initial EEG recordings for all patients participating in the study to exclude any pre-existing epileptic EEG patterns. We took the initial EEG recordings in a dark quiet room for 5 minutes as a baseline, followed by three eye opening and closing sequences of 10 seconds each and photostimulation lasting 10 minutes (flash stimuli at frequencies of 3/6/9/12 Hz- alpha; 15/18/21/24 Hz- beta). Then we obtained another baseline reading and we asked the patients to achieve a state of hyperventilation by taking 20 forceful breathes per minute for five minutes. Finally, we obtained another baseline reading.

Throughout the induction of anaesthesia and the surgery, standard monitoring procedures were utilised to pay close attention to the vital parameters such as non-invasive arterial pressure (BP), heart rate (HR), standard electrocardiography (ECG) II, arterial oxygen saturation (SaO2), fraction of inspired oxygen in the gas mixture (FiO2), facial electromyography (fEMG), fraction of inspired sevoflurane (FiAA), fraction of expired sevoflurane (FeAA), exhaled carbon dioxide concentration (etCO2), minimal alveolar concentration of sevoflurane (MAC).

Eligibility Criteria:
Inclusion Criteria:

* an American Society of Anaesthesiologists (ASA) score I-II
* written informed consent to undergo general anaesthesia

Exclusion Criteria:

- history of epilepsy, medical treatment that might interfere with the EEG (e.g., tranquilizers, antiepileptic drugs), pregnancy, drug or alcohol abuse, history of neurological disease or a neurosurgical operation that would impair EEG or BIS monitoring, history of pulmonary disease, or the presence of signs predicting difficult mask ventilation or intubation. any pre-existing epileptic EEG patterns in standard 30-minute initial EEG recordings performed in all the patients participating in the study.