roman empire dating system Neuraxial analgesia and non sedating antihistamines

In increasing order, the small postganglionic sympathetic fibres are blocked most readily, followed by sensory and finally motor fibres.

The lipid solubility and shape of the molecule are the most important factors that effect the passage of opioids across the dura.The CSF solubility should be poor, to allow rapid elimination from this compartment.Lipid-soluble drugs penetrate the spinal cord rapidly and are poorly soluble in the CSF, but may be extensively absorbed into the circulation.Total spinal anaesthesia caused by excessively high spread of local anaesthetic may occur following a 'dural tap'.Morphine, initially the most commonly used opioid in the epidural space, produces unpredictable late respiratory depression.

This led researchers to use lipid-soluble opioids, partial agonist-antagonist opioids, opioid local anaesthetic combinations and, most recently, alpha agonists such as clonidine.The ideal opioid must cross the dura rapidly and enter the spinal cord, where it should bind with strong affinity to the opioid receptors in the substantia gelatinosa.This is inadequate for postoperative pain relief, but indwelling catheters, which allow repeat dosing or infusions overcome this problem.Concentrations of 0.125-0.25% bupivacaine have been used as continuous infusions at rates of 6-10 ml per hour.Side effects and analgesia both increase as the dose of local anaesthetic is increased.Hypotension is the most common problem; it is caused by sympathetic blockade and its severity is related to the segmental height of the block and whether an adequate preload has been administered.