الفهرس 
ANATOMY OF THE VERTEBRAL COLUMNOnly 14 pages are availabe for public view
 |  | from | 141 |  |  |
| | | from | 141 | | |
Abstract
Spinal (intrathecal) anaesthesia is generally regarded as one of the most reliable regional block methods.
Most experienced practitioners would consider the incidence of failure with spinal anaesthesia to be extremely low, perhaps less than 1%. However, a figure as high as 17% has been reported.
In general terms, block failure is usually ascribed to one of three aspects:
1- Clinical technique.
2- Lack of clinical experience.
3- Failure to select a meticulous approach
Inability to obtain CSF, sometimes referred to as a ‘dry tap’, is the only cause of failure which is immediately obvious.A needle with a lumen blocked at the outset is a theoretical possibility, but is most unlikely with modern equipment.
Proper positioning is essential for a successful block.There are three positions used for the administration of spinal anesthesia: lateral decubitus, sitting, and prone.
The appearance of CSF in the needle hub is an essential pre-requisite for spinal anaesthesia, but it does not guarantee success, which also requires that a fully effective dose is both chosen and actually deposited in the CSF.
The three most important factors for determining spread of local anesthesia in the subarachnoid space are baricity of the local anesthetic solution, position of the patient during and just after injection, and dose of the anesthetic injected.
The mixing of two different pharmaceutical preparations also raises the possibility of ineffectiveness as a result of interaction between local anaesthetic and adjuvant.Local anaesthetics seem to be compatible with most of the common opioids, but there has been little formal study of the effects of mixing them, and the situation is even less definitive with other adjuvants such as clonidine, midazolam, and other more extreme substances.
Very rarely a failed spinal anaesthetic has been attributed to physiological ‘resistance’ to the actions of local anaesthetic drugs.
Option For Managing An Inadequate Block Include:
1- Repeating the injection especially in response to a poor quality block, may lead to excessive spread, so it may be argued that a lower dose should be used to reduce the risk of this possibility.
2- Manipultion of the patient’s posture to encourage wider spread of the injected solution.
3- Supplementation with local anaesthetic infiltration by the surgeon use of systemic sedation or analgesic drugs.
4- Recourse to general anaesthesia:
There are many ways in which an inadequate block might be ‘rescued’, but there is a limit to how much discomfort or distress an individual patient can tolerate, so general anaesthesia must be considered if one or two simple measures have not rectified matters.