Regional Anaesthesia

"DXM is a nonselective α2 agonist. Alpha2 adrenoreceptors, the overall response to α2 adrenoreceptors agonists is related to the stimulation of α2 adrenoreceptors located in the CNS and spinal cord. These receptors are involved in the sympatholysis, sedation, and antinociception effects of α2 adrenoreceptors.~DEXMEDETOMIDINE (DXM) DXM shows a high ratio of specificity for the α2 receptor (α2/α11600: 1) compared with clonidine (α2/α1 200: 1), making it a complete α2 agonist. (76) DXM belongs to the imidazole subclass of α2 receptor agonists, similar to clonidine. It is freely soluble in water."

Neostigmine is an indirect cholinomimetic agent. It produces its primary effects by inhibiting the action of AChe, which hydrolyzes acetylcholine (ACh) to choline and acetic acid. By inhibiting AChe, the indirect-acting drug increases the concentration of spinal endogenous ACh. This drug is, in effect, amplifiers of endogenous ACh and act primarily where ACh is physiologically release. It combines reversibly with AChe by the formation of an ester linkage, which lasts about 30 minutes. The pharmacokinetic of neostigmine administered by bolus injection is linear with respect to bolus injection.

"The onset of sensory blockade following spinal block with bupivacaine is very rapid (within one minute); maximum motor blockade and maximum dermatome level are achieved within 15 minutes in most cases.~The conduction of nerve impulses along nerve fibers is related to changes in the electrical gradient across the nerve membrane and movement of predominantly sodium ions (but also potassium ions) from intracellular to extracellular fluid and vice versa. Bupivacaine work by reversibly blocking specific areas of the nerve cell membrane, known as sodium channels. It contains a mixture of ionized and un-ionized particles which, when injected into body tissues, make more un-ionized particles available, which are lipid soluble and able to penetrate the nerve cell membrane."