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.
Chin
K J
KJ
Department of Anaesthesia, Tan Tock Seng Hospital, 11 Jalan Tan Tock Seng, Singapore 308433, Republic of Singapore. gasgenie@yahoo.co.uk
Yeo
S W
SW
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