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Hypoalgesia following intrathecal morphine: a segmental dependent effect.
L Arendt-Nielsen1, E Anker-Møller, P Bjerring
1Department of Medical Informatics, Aalborg University, Denmark.
Acta Anaesthesiologica Scandinavica
|July 1, 1991
Summary
Intrathecal morphine onset causes segmental hypoalgesia, primarily affecting spinal mechanisms. This study used laser-induced pain to assess the localized pain relief effects of morphine.
Area of Science:
- Neuroscience
- Pharmacology
- Pain Research
Background:
- Intrathecal morphine is used for pain management.
- Understanding the onset and spread of its analgesic effects is crucial.
- Segmental versus widespread effects require differentiation.
Purpose of the Study:
- To assess the onset phase of hypoalgesia after intrathecal morphine.
- To determine the segmental spread of morphine-induced analgesia.
- To investigate the underlying mechanisms of early hypoalgesia.
Main Methods:
- Administered 0.4 mg intrathecal morphine at L3-L4 in nine patients.
- Utilized argon laser-induced pain to measure pain thresholds.
- Monitored pain-evoked brain potentials in S1, L1, and C7 dermatomes for 2 hours.
Main Results:
- Hypoalgesia was observed in the S1 (5 min) and L1 (15 min) dermatomes.
- No hypoalgesic effect was detected in the C7 dermatome.
- No changes in brain potential latency indicated no conduction delay.
Conclusions:
- Early hypoalgesia from intrathecal morphine is predominantly segmental, mediated by spinal mechanisms.
- Laser-induced pain is a valuable quantitative tool for assessing analgesic onset and spread.
- Findings suggest localized spinal action rather than a generalized systemic effect.