Observations on sensory and sympathetic function during intrathecal analgesia

Area of Science:

• Neuroscience
• Anesthesiology
• Human Physiology

Background:

• Local anesthetics like procaine are used to block nerve conduction.
• Understanding the differential susceptibility of various nerve fiber types to local anesthetics is crucial for clinical applications.

Purpose of the Study:

• To investigate the differential effects of procaine on various sensory modalities in humans.
• To identify the specific nerve fiber types responsible for transmitting pain, temperature, and tactile sensations.

Main Methods:

• Administration of dilute procaine solution via slow lumbar thecal drip to induce differential nerve block.
• Systematic observation and recording of changes in skin vasodilatation, pain, warmth, cold, and tactile sensibility in lower limbs.
• Correlation of sensory changes with the degree of nerve block.

Main Results:

• Vasodilation consistently preceded sensory changes.
• Loss of pain and warmth sensation occurred simultaneously or with one modality more affected than the other.
• Cold sensation was altered, sometimes perceived as non-thermal sensations.
• Tactile sensibility remained intact even when pain, warmth, and cold fibers were blocked.
• Pre-ganglionic B fibers demonstrated the highest susceptibility to procaine.
• Piloerection and spontaneous itching were observed under specific block conditions.

Conclusions:

• Nerve fibers signaling warmth are likely smaller delta or non-myelinated fibers.
• Fibers signaling cold utilize a similar delta range as warmth fibers, with some larger delta fibers involved.
• The contribution of smaller delta and non-myelinated fibers to tactile sensibility in humans is insignificant.
• Pre-ganglionic B fibers are the most susceptible nerve fibers to local anesthetics.