Ohg. Wildersmith et al., SENSORY CHANGES AND PAIN AFTER ABDOMINAL HYSTERECTOMY - A COMPARISON OF ANESTHETIC SUPPLEMENTATION WITH FENTANYL VERSUS MAGNESIUM OR KETAMINE, Anesthesia and analgesia, 86(1), 1998, pp. 95-101
Drugs interacting with opioid or N-methyl-D-aspartate (NMDA) receptors
may have differing effects on post surgical sensory changes, such as
central inhibition or spinal excitation. We compared the effect of sup
plementing isoflurane/N2O/O-2, anesthesia with an opioid agonist (fent
anyl [n = 15]) or two drugs inhibiting the NMDA system differently (ma
gnesium, ketamine [n = 15 in each group]) on sensory changes after abd
ominal hysterectomy. Electric sensation, pain detection, and pain tole
rance thresholds were determined (preoperatively and 1, 4, 24h, and 5
days postoperatively) in arm, thoracic, incision, and leg dermatomes t
ogether with pain scores and cumulative morphine consumption. Threshol
ds relative to the arm were derived to unmask segmental sensory change
s hidden by generalized changes. Absolute thresholds were increased 1-
24 h, returning to baseline on Day 5, without overall differences amon
g drugs. Fentanyl thresholds were lower Ih and higher 5 days postopera
tively compared with magnesium and ketamine; thresholds were lower at
24 h for magnesium versus ketamine. Relative thresholds increased comp
ared with baseline only with fentanyl (1-4 h); none decreased. Pain sc
ores and morphine consumption were similar. Thus, all adjuvants suppre
ssed spinal sensitization after surgery. Fentanyl showed the most, and
magnesium the least, central sensory inhibition up to 5 days postoper
atively, with different patterns of inhibition directly postsurgery ve
rsus later. Differences in sensory processing were not reflected in cl
inical measures. Implications: We studied the effects on postsurgical
sensory processing of general anesthesia supplemented by drugs affecti
ng opioid or N-methyl-D-aspartate receptors using sensory thresholds.
Generalized central sensory inhibition, differently affected by the dr
ugs, predominated after surgery. All drugs suppressed spinal excitatio
n. Clinical pain measures did not reflect sensory change.