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The effect of bispectral index monitoring on anaesthetic requirements in target-controlled infusion for lumbar microdiscectomy.

BACKGROUND
Target-controlled infusion (TCI) is used to maintain the desired concentration of a hypnotic drug in the plasma and brain. However, pharmacodynamic variability can cause problems with maintaining the adequate level of anaesthesia. The bispectral index (BIS) is one of only a few parameters that allow an assessment of the depth of anaesthesia. In the present study, we attempted to determine the optimal dosages of drugs used for total intravenous anaesthesia with TCI based on BIS-guided monitoring of depth of anaesthesia.


METHODS
The study was conducted in 60 ASA I patients undergoing elective surgery due to lumbar discopathy. The participants were divided into two groups of 30 individuals. The patients were premedicated with 15 mg oral midazolam. Group I was the control group; group II received BIS monitoring. Anaesthesia was induced with TCI propofol (4 mg mL⁻¹), fentanyl (2 mg kg⁻¹) and vecuronium (0.12 mg kg⁻¹) and maintained with TCI propofol, continuous infusion of vecuronium (0.03 mg kg⁻¹ h⁻¹) and fractionated doses of fentanyl. ECG, HR, MAP, SaO₂, ETCO₂, and the degree of neuromuscular blockade were monitored, specifically at the following time points: T₁ - before induction, T₂ - after induction, T₃ - after intubation, T₄ - after positioning of the patient, T₅-T₁₃ - every 5 min during surgery, T₁₄ - on completion of surgery, T₁₅ - before extubation, T₁₆ - after extubation.


RESULTS
The study groups were comparable in terms of age, body weight, duration of anaesthesia and recovery time. The haemodynamic parameters, such as HR and MAP, did not differ significantly between the groups. In both groups, changes in the mean MAP values were observed between T₁ and T₂, T₂ and T₃, T₃ and T₄ as well as T₁₄and T₁₅. The total dose of fentanyl and the doses of propofol were lower in the group that received BIS monitoring.


CONCLUSION
BIS monitoring reduces the doses of opioids and hypnotics used during total intravenous anaesthesia by TCI.