Title:
The time for extubation after stopping infusion of propofol depends on the amount of bolus administration of fentanyl at the end of surgery, but dose not depend on ketamine administered in a surgery with AOPRfK(air-oxygen-propofol-remifentanil-low dose ketamine) anaesthesia.


Background and Goal of Study:
It is well known that AOPFK anaesthesia has an advantage in postoperative analgesia. However, AOPFK anaesthesia sometimes sets up a delay of awareness from anaesthesia. Nowadays, continuous infusion of remifentanil(Rf), instead of fentanyl(F), is very common. However, in AOPRfK anaesthesia, the same phenomenon sometimes sets up. Therefore, we investigated what the main reason of the phenomenon in spinal surgery.

Materials and Methods:
The study style is retrospective.11 patients (male/female=9/2), ASAI-II were included in the study. They were 61±14 (mean±standard deviation) years old.
The induction of anaesthesia was performed with bolus infusion of 1mg midazolam, 2mg/kg propofol(PRO), 50mg rocuronium (Rb), and 0.2μg/kg Rf. In 9 patients, bolus Ketamine(Ket) was administered (0.49±0.11mg/kg) at the induction. In 10 patients, a little amount of sevoflurane was inhaled after intubation, but it was stopped to inhale before a surgery. The maintenance of anaesthesia was performed with 50% oxygen in air, continuous infusion of PRO, Ket(0.48±0.13 mg/kg/h), Rf(0.1-0.3μg/kg/min), and Rb. PRO and Rf infusion rate were adjusted to maintain bispectral index between 40 and 60. When a surgery ended, continuous infusion of PRO, Ket, Rf, and Rb were stopped and bolus 100-200μg F and 50mg flurbiprofen were administered. 10-20mL ropivacaine or revobupivacaine were given as infiltration anaesthesia when the operative wound was closed. The time between stopping PRO infusion and the extubation (Time)(minutes) was recorded. Regression lines were drawn in the amount of F per body weight administered at the end of surgery (μg/kg) vs. Time(RL1), and Ket infusion rate during surgery (mg/kg/h) vs. Time(RL2), and the total amount of Ket administered per body weight (mg/kg) vs. Time(RL3) by using SigmaPlot 11.0.(Sistat Software Inc., San Jose, CA, USA).

Results and Discussions:
Time was 23±9.7 minutes. The total amount of Ket was 1.52±0.61 mg/kg. The coefficient of correlation value of RL1, RL2, and RL3 is 0.4636, 0.0455, and 0.2878 respectively. According to RL1, it is suggested that F less than 2μg/kg dose not set a prolongation of Time. Ket infusion rate and the total amount of Ket administered per body weight do not contribute to the phenomenon with given dose in the study.

Conclusions:
The amount of F given at the end of surgery prolongs Time in a dose dependent manner in AOPRfK anaesthesia.

The time for extubation after stopping infusion of propofol depends on the amount of bolus administration of fentanyl at the end of surgery, but dose not depend on ketamine administered in a surgery with AOPRfK (air-oxygen-propofol-remifentanil-low dose ketamine) anaesthesia