Pupil
Dilation Testing And Epidural Analgesia In Thoracic Surgery
Huybrechts
I, Engelman E, Schmartz D, Ducart A, Cappello M, Barvais L
Anesthesiology Department, Erasme hospital, ULB, Belgium
The aim of the study was to relate the sensitivity to cold at the emergence of propofol TCI anaesthesia combined with a continuous ropivacaine epidural analgesia technique with pupil dilation in response to a painful stimulus in the same metamer after thoracic surgery.
After informed consent, 14 patients scheduled for thoracotomy were selected. An epidural catheter was inserted at the Th3-Th4 level. A test dose of 3 ml lidocaine 2% + epinephrine was injected, followed by a continuous variable infusion of ropivacaine 0.5% Epidural analgesia was supplemented by propofol TCI anaesthesia. During surgery, ropivacaine flow rate (0-8ml/h) was adapted to abolish any pupil dilation to a 100 Hz tetanic stimulus (TET) applied in the Th4 metamer using a neuromuscular stimulator. At the end of surgery, TET was applied at the Th2 and Th4 metameric levels. A TET stimulus in the ulnar nerve area was used as a reference. The pupil diameters before and after TET were measured, using an infrared portable pupillometer (OASIS, Colvard). At emergence from anaesthesia, the same metameric levels were tested for their sensitivity to cold. The patient’s responses to cold were characterized as cold, medium or nothing. The pupil dilation measurements were divided in 2 groups ( 0, > 0 mm change)and 1 subgroup(≥ 1mm). All the pupil dilatation measurements were pooled together by category of response to cold and were compared to the mean pupil diameter variations following TET at the 3 sites (Th2, Th4, ulnar) using a one-way ANOVA test.
Mean amplitude of the pupil dilation (mm) following TET at the 3 sites
|
Ulnar area |
Th2 |
Th4 |
|
|
1.04 ± 0.54 |
0.5 ± 0.68 * |
0.21 ± 0.54 ** |
P=0.0026 |
Mean amplitude of pupil dilation (mm) following TET for the 3 cold levels
|
Cold |
Medium |
Nothing |
|
|
1.00 ± 0.58 |
0.69 ± 0.70 |
0.17 ± 0.48 * ## |
P=0.0005 |
Proportion of patient’s answer to a cold test stimulus according to the size of pupil dilation
|
0 mm = (N=20) |
2 = cold |
10% |
|
|
3 = medium |
15% |
|
|
15 = nothing |
75% |
|
> 0 mm (N=22) |
14 = cold |
63.6% |
|
|
5 = medium |
22.7% |
|
|
3= nothing |
13.6% |
|
³ 1 mm (N=17) |
12 = cold |
70.6% |
|
|
4 = medium |
23.5% |
|
|
1 = nothing |
5.9% |
A significant relation between pupil dilation following a painful 100 Hz tetanic stimulation at Th2 and Th4 and cold sensitivity in the same area was evidenced after epidural ropivacaine analgesia during thoracic surgery. At the emergence of propofol TCI anaesthesia combined with epidural analgesia, the lack of pupil dilation at Th2 and Th4 helps to predict that a cold stimulus in the same metameric area is blocked and that good analgesia is obtained.