Differential sensorial nerve blockage occur as a result of
different degree blockage of A-β, A-δ and C fibers and also
different recovery profiles
7,8. During spinal anesthesia
pinprick, touch and cold stimulation commonly used to
determine the differential sensory blockage dermatomal level
that each of them activate different fiber population.
Touch sensation mediated via A-β, pinprick sensation
mediated via A-δ and cold sensation mediated via C fibers 1.
Lui et al 8 showed quantitively that touch, pinprick and cold
sensations return correlated by A-β, A-δ and C fibers
functional recovery.
Both surgical pain and touch sensation mediated by A-β
fibers. The studies made by using transcutaneous electrical
stimulation for monitoring anesthesia zone with regional
anesthesia showed that, there is correlation between tolerance
loss to electrical stimulus that is equal to the surgical incision
and surgical anesthesia time and also A-β fiber functional
recovery 8,9. Rocco et al 7 monitored the sensorial
blockage differential levels of pinprick, touch and cold
sensations during whole spinal anesthesia in 50 patients to
determine the variations of initial, plato and regression spread
degrees. They showed that there were significant differences at
pinprick, touch and cold sensation loss dermatomal levels and
also touch sensation loss begin later and regress faster. Authors
found the level of touch sensation as the sign of spinal
anesthesia zone limits.
Hughes et al 6 found that gas jet delivered at room
temperature compared favorably with ethyl chloride and
pinprick, but not as well as with touch sensation. Another
study with warm air sensation which was compared with cold
sense from ethyl chloride spray showed that block level
assessment results after spinal anesthesia was similar with both
methods. This study showed that each method can be used
interchangeably 10. Larson et al 11 used pupillary
responses to electrical stimulation for the assessment of
sensory block level during combined epidural/general
anesthesia. They administered noxious electrical stimulation to
dermatomal levels and measured pupillary dilatation as
response to stimulation (predicted block level). Then measured
the actual block level with pinprick test. This study concluded
that the level predicted by pupillary responses was within two
dermatomal segments of the actual level in all the patients.
Another study with different concentrations of lidocaine (1%
or 2%) for the quantitative and selective assessment of sensory
block level during lumbar epidural anesthesia showed that the
dose of lidocaine affected intensity of sensory block.
Cutaneous current perception device and also touch, cold and
pinprick modalities were used to determine block level.
Beyond the effect of lidocaine dose differential neural block levels were associated with differential effect on nerve fibers
of different sizes 12.
Russell 13 determined that there is a two segmental
median difference between pinprick, touch and cold sensations
differential blockage level, however cold and pinprick
blockage level were 1-3 segment upper than touch block level.
Our findings showed that pinprick, touch and cold sensation
loss dermatomal level are different and also both pinprick and
cold sensation loss dermatomal level is greater than the
dermatomal levels of touch stimulation. These findins are
harmonized with literature discussed above 7,13.
The stimulus type applied to the unblocked skin,
repetition, and the extension of application zone effect the
sensorial level 1. However in our study we used a narrow
zone, avoid from repetition and sensorial test applied only at
5th and 20th min. So we thought that temporal and spatial
summation minimised.
As a conclusion, it may be beneficial to use the noninvasive
and painless method touch stimulation instead of
pinprick test for the assessment of block level at spinal
anesthesia.