Comparison of pupil reflex dilation after 100Hz tetanos at the end of surgery and postoperative pain under a stable remifentanil concentration.
G Michiels, A Verleije, E Engelman, B Ickx, L Barvais.
Anaesthesia department, Erasme hospital, ULB, Brussels, Belgium.
Painful stimuli dilate the pupil; this reflex is called pupil reflex dilation (PRD). Opiate drugs such as remifentanil reduce PRD. Our goal was to assess the relationship between PRD in anaesthetised patients at the end of surgery and postoperative pain in order to improve the postoperative pain management during the transition after a remifentanil TCI anaesthesia.
Nineteen ASA 1/2 patients undergoing gynaecological surgery were anaesthetised with propofol and remifentanil. At the end of surgery, target effect site concentration (CeT) of remifentanil was titrated down to 1.5 ng/ml and maintained at this level during the whole awakening period. Propofol TCI was maintained at the appropriate level to study PRD with an infrared pupillometer at rest and in response to four electrical tetanic stimulation at 100Hz (TET100) on the ulnar nerve during 10 seconds, applied randomly at 20, 40, 60, 80 mA.
Thereafter, propofol was stopped and VAS at rest was evaluated under constant remifentanil CeT of 1.5 ng/ml.
Fifteen women showed acceptable VAS less or equal to 3. Four women had a VAS greater than 3 with one having a VAS at 8. This patient was the only one showing a PRD greater than 1 mm at a low tetanic stimulation of 40 mA. However, no significant statistical difference was found in the mean PRD values at the different TET100 intensities between women with a VAS value under or over a value of 3.
|
Intensity of TET100 |
20 mA |
40 mA |
60 mA |
80 mA |
|
PRD ± SD of women with VAS ≤ 3 at awakening |
0.28 mm ± 0.27 |
0.58 mm ± 0.34 |
0.76 mm ± 0.40 |
0.93 mm ± 0.54 |
|
PRD ± SD of women with VAS > 3 at awakening |
0.50 mm ± 0.40 |
0.75 mm ± 0.86 |
0.92 mm ± 0.78 |
1.42 mm ± 0.43 |
PRD testing at several intensities of tetanic stimulation under stable remifentanil concentration does not help the anaesthetist to predict pain in young healthy women undergoing low abdominal surgery.