A BIS-guided study of sevoflurane requirements for adequate depth of anaesthesia in Caesarean section.
Caesarean section carries a high risk of awareness, especially in the period prior to neonatal delivery. We investigated the concentration of sevoflurane required to maintain bispectral index (BIS) < 60 until delivery occurred. We enrolled 23 parturients into an up-down sequential allocation study. The median effective end-tidal concentration (EC(50)) of sevoflurane was defined as that which maintained BIS < 60 between skin incision and delivery in 50% of patients. This was calculated using Dixon and Massey's method. Receiver operating characteristic curve analysis was used to establish BIS response probability thresholds. The EC(50) for sevoflurane was 1.22% (1.08-1.33, 95% CI). The probability of maintaining BIS < 60 was < 55% at a concentration of < 1.1%; this increased to 80% at concentrations of 1.2-1.3%. We conclude that sevoflurane concentrations of at least 1.2-1.3% should be administered in uncomplicated Caesarean section, so as to minimise the risk of awareness and recall.
Department of Anaesthesia, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Republic of Singapore. gasgenie@yahoo.co.uk
K J
KJ
Chin
S W
SW
Yeo
D000328:Adult; D000769:Anesthesia, Inhalation / Q000379:methods*; D000773:Anesthesia, Obstetrical / Q000379:methods*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D001364:Awareness / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D002585:Cesarean Section; D004334:Drug Administration Schedule; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D011939:Mental Recall / Q000187:drug effects; D008738:Methyl Ethers / Q000008:administration & dosage*; D016343:Monitoring, Intraoperative / Q000379:methods; D011247:Pregnancy; D011446:Prospective Studies; D000077149:Sevoflurane
D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane