7.1 Spinal anesthesia (mechanism of action and use): 

Local anesthetics administered in the subarachnoid space block sensory, autonomic, and motor impulses as the anterior and posterior nerve roots pass through the cerebro spinal fluid (CSF) by which loss of sensation and paralysis produced reversibly. It is mainly indicated for lower abdominal, gynecologic, urologic and lower extremity procedures.

7.1.1 Advantages of spinal anesthesia:

 When compared with general anesthesia spinal anesthesia has the following advantage.

• Spinal anesthesia produces few adverse effects on the respiratory system as long as unduly high blocks are avoided.
• Maintain Patent airway: There is a reduced risk of airway obstruction or the aspiration of gastric contents. This advantage may be lost if too much sedation is given.
• For diabetic patients: There is little risk of unrecognized hypoglycemia in an awake patient. Diabetic patients can usually return to their normal food and insulin regime soon after surgery as they experience less sedation, nausea and vomiting.
• Decreased incidence of nausea and vomiting
• Decreased blood loss
• Improved mobility following major lower extremity procedure
• Less immunosuppression
• An alternative for patient's that may not tolerate a general anesthetic
• Less cognitive impairment (especially in the elderly)
• Easy to perform for well trained
• Reliable and provides excellent operating conditions for the surgeon
• Less costly than general anesthesia
• Normal gastrointestinal function returns faster with spinal anesthesia compared to general anesthesia
• Decreased incidence of deep vein thrombosis and pulmonary emboli formation compared to general anesthesia

7.1.2 Disadvantages of Spinal Anesthesia

• Risk of failure even in skilled hands. Always be prepared to induce general anesthesia.
• Normal alteration in the patient's hemodynamic. It is essential to place the spinal block in the operating room, while monitoring the patient's ECG, blood pressure, and pulse oximetry. Resuscitation medications should be available.
• The operation could outlast the spinal anesthetic. Alternative plans (i.e. general anesthesia) should be prepared in advance.

7.1.3 Contraindication

• Absolute Contraindications:
Inability to guarantee sterility of medications/equipment
Infection at the site of injection
Bleeding problem(low platelet count)
Severe hypovolemia. Hypovolemia should be corrected prior to spinal anesthesia. A spinal anesthetic in a severely hypovolemic patient may lead to cardiac arrest.
Increased intra-cranial pressure (i.e. brain tumor or recent head injury)
Severe aortic stenosis and severe mitral stenosis
Severe uncorrected anemia
An allergy to local anesthetics.

• Relative Contraindications:
Sepsis (may spread infection to subarachnoid/epidural space)
Uncooperative patient (dementia, psychosis, emotional instability)
Preexisting neurological deficits (hard to differentiate natural progression versus neurological trauma related to neuraxial blockade)
Severe spinal deformity