INDICATIONS AND CONTRAINDICATIONS

At the most basic level, neuraxial block is indicated when the surgical procedure can be accomplished with a sensory level of anesthesia that does not produce adverse patient outcome. The surgical procedure must include the amount and type of supplemental medications and even capacity for administering "light general anesthesia" to ensure effective sedation and anxiolysis. The level of sensory analgesia required is of prime importance. It is clear that low spinal anesthesia (i.e., T10 or lower sensory level) carries different physiologic impact than a block performed to produce high (T5) spinal anesthesia.^[14]

There are few strong contraindications to neuraxial block. Some of the most important ones include patient refusal; a patient's inability to maintain stillness during the needle puncture, exposing the neural structures to unacceptable risk of injury; and raised intracranial pressure, which theoretically may predispose to brainstem herniation. Relative contraindications that must be weighed against the potential benefits include intrinsic and idiopathic coagulopathy, such as that occurring with administration of Coumadin or heparin; skin or soft tissue infection at the proposed site of needle insertion; severe hypovolemia; and lack of anesthesiologist experience. The often-cited relative contraindication of preexisting neurologic disease (e.g., lower extremity peripheral neuropathy) is not usually based on medical criteria but rather on legal considerations.

When deciding between epidural and spinal anesthesia, a number of variables should be considered. Is the procedure (or surgeon's typical time) of predictable length, minimizing the need to consider a continuous catheter technique? Conversely, is the surgeon's estimate so unpredictable that a combined spinal and epidural technique should be recommended? Is the surgical procedure so short that waiting for the epidural to take effect makes spinal anesthesia more practical? Is the patient a candidate for prolonged postoperative analgesia, making a continuous epidural technique preferred? Can the procedure be equally well handled with spinal or epidural anesthesia, allowing consideration of patient variables affecting headache incidence (e.g., age and gender)? Are there concurrent patient diseases, such as hypertrophic cardiomyopathy, that may be of concern with either technique? Will the patient be traveling a significant distance immediately after the procedure, making epidural blood patch therapy for a postdural puncture headache problematic? These are some of the questions that should be considered when contemplating the risk and benefit of neuraxial blocks.