• Elaheh Allahyary, Farid Zand, and Hamid Reza Tabatabaee.
• Department of Anesthesiology, Namazi Hospital and Department of Biostatistics and Epidemiology, School of Health, Shiraz University of Medical Sciences, Shiraz, Iran.
• Acta Anaesthesiol Taiwan. 2008 Mar 1;46(1):16-24.

BackgroundOne of the hazards of general anesthesia for cesarean section (C/S) is the risk of intraoperative awareness with or without recall of the event. We examined the relationship between auditory evoked potential index (AAI), end-tidal isoflurane concentration and hemodynamic parameters to evaluate the adequacy of our routine general anesthetic technique in C/S.MethodsThis study was carried out in 70 parturients undergoing elective C/S. A standardized anesthetic technique was applied, including thiopentone and suxamethonium for induction, and O2, N2O and isoflurane for maintenance of anesthesia. AAI, heart rate, blood pressure, end-tidal isoflurane concentration and any clinical signs of inadequate depth of anesthesia such as movement, lacrimation and coughing or jerking were continuously monitored and recorded at 17 fixed time points during surgery and anesthesia.ResultsMean arterial pressure and heart rate increased at intubation, but did not show a positive correlation with the AAI values during this time. The AAI subsequently changed in the same manner as the hemodynamic parameters. There were median AAI values of 43, 37 and 27 respectively during laryngoscopy, skin incision and the time of delivery. An Emax pharmacodynamic model of AAI and end-tidal isoflurane concentration showed an r2 of 0.35 (95% CI, 0.35-0.53). According to AAI values, the majority of patients (range, 48.5-61%) had a light level of anesthesia in the time from laryngoscopy up to uterine curettage and after that they experienced an adequate (surgical or deep) level of anesthesia (range, 62.3-80%).ConclusionOur current general anesthetic technique appears to provide an inadequate depth of anesthesia, especially before uterine closure as a milestone. Also, we found a moderate correlation between AAI and end-tidal isoflurane concentration and, to a lesser extent, with heart rate and mean blood pressure during isoflurane-N2O anesthesia for C/S.

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