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KEY CONCEPTS
Neuraxial anesthesia greatly expands the anesthesiologists’ armamentarium, in many cases providing alternatives to general anesthesia. Neuraxial anesthesia may also be used simultaneously with general anesthesia or afterward for postoperative analgesia. Neuraxial blocks can be performed as a single injection or with a catheter to allow intermittent boluses or continuous infusions.
Performing a lumbar (subarachnoid) spinal puncture below L1 in an adult (L3 in a child) usually avoids potential needle trauma to the spinal cord.
The principal site of action for neuraxial blockade is believed to be the nerve root, at least during initial onset of block.
Differential blockade typically results in sympathetic blockade (judged by temperature sensitivity) that may be two segments or more cephalad than the sensory block (pain, light touch), which, in turn, is usually several segments more cephalad than the motor blockade.
Interruption of efferent autonomic transmission at the spinal nerve roots during neuraxial blocks produces sympathetic blockade.
Neuraxial blocks typically produce variable decreases in blood pressure that may be accompanied by a decrease in heart rate.
Deleterious cardiovascular effects should be anticipated and steps undertaken to minimize the degree of hypotension. However, volume loading with 10 to 20 mL/kg of intravenous fluid in a healthy patient before initiation of the block has been shown repeatedly to fail to prevent hypotension (in the absence of preexisting hypovolemia).
Excessive or symptomatic bradycardia should be treated with atropine, and hypotension should be treated with vasopressors.
Major contraindications to neuraxial anesthesia include lack of consent, coagulation abnormalities, severe hypovolemia, elevated intracranial pressure, and infection at the site of injection.
For epidural anesthesia, a sudden loss of resistance (to injection of air or saline) is encountered as the needle passes through the ligamentum flavum and enters the epidural space. For spinal anesthesia, the needle is advanced through the epidural space and penetrates the dura–subarachnoid membranes, as signaled by freely flowing cerebrospinal fluid.
Continuous epidural anesthesia is a neuraxial technique offering a range of applications wider than single dose spinal anesthesia. An epidural block can be performed at the lumbar, thoracic, or cervical level.
Epidural techniques are widely used for surgical anesthesia, obstetric analgesia, postoperative pain control, and chronic pain management.
Epidural anesthesia is slower in onset (10–20 min) and may not be as dense as spinal anesthesia, a feature that can be useful clinically.
The quantity (volume and concentration) of local anesthetic needed for epidural anesthesia is larger than that needed for spinal anesthesia. Toxic side effects are almost guaranteed if a “full epidural dose” is injected intrathecally or intravascularly.
Caudal epidural anesthesia is a common regional technique in pediatric patients.
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Spinal, caudal, and epidural blocks were first used for surgical procedures at the turn of the twentieth century. These central blocks were widely used worldwide until reports of permanent neurological injury appeared, most prominently in the United Kingdom. However, a large-scale epidemiological study conducted in the 1950s proved that complications were rare when these blocks were ...