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Spinal Anesthesia

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General
Spinal needles
Specific catheters
Specific techniques
Factors affecting level of block
Spinal anesthetic agents

General
-blocks nerve roots located within the subarachnoid, intrathecal space
-spinal subarachnoid space spans from the foramen magnum to S2 (adults) and S3 (children)
-spinal anesthesia = intrathecal anesthesia = subarachnoid anesthesia

spinal needles
-precicely made without any surface defects or abnormalities
-prevention of epithelial cells tracking from skin into subarachnoid space by use of a tightly fitting removable stylet
available in different:
-sizes (16-30 gauge)
-lengths
-bevel designs
-tip designs (sharp tipped vs. blunt tipped)
ex. Quinke needle, Whitacre needle, and Sprotte needle

Quinke needle: cutting needle with end injection
Whitacre needle: pencil point needle with rounded points containing side injection
Sprotte needle: long opening needle containing side injections

spinal catheters
-currently not approved by the USFDA due to the catheter association with cauda equina syndrome

specific techniques
-midline approach
-paramedian approach
-prone approach

Spinal needle advanced from the skin through the deeper structures containing:
-skin
-supraspinous ligament
-interspinous ligament
-ligamentum flavum
-dura-arachnoid mater
first resistance (pop): ligamentum flavum
second resistance (pop): dura:arachnoid mater
-successful dural puncture is confirmed by free flowing CSF when the stylet is removed

factors affecting level of block

Major determinants:
-baricity of anesthetic (hyperbaric vs hypobaric solution)
-position of patient (during injection and immediately after injection)
-dosage of anesthetic (greater the dosage of agent,the higher the level of anesthesia obtained)
-site of injection (higher the site of injection, the higher the level of anesthesia obtained)

Hyperbaric solution: local anesthetic agent is denser than the CSF (ex. addition of dextrose to anesthetic agent)
isobaric solution: local anesthetic agent is same density as the CSF
hypobaric solution: local anesthetic agent is lighter than the CSF (ex. addition of sterile water to the anesthetic agent)

Minor determinants:
patient height, age, curvature of spine, volume of drug, increased intra-abdominal pressure ex. pregnancy, direction of needle

spinal anesthetic agents
-only preservative free local anesthetics are used for spinal anesthesia
-addition of vasoconstrictors and opiods greatly help to enhance the quality and duration of spinal anesthesia with local anesthetics

Spinal anesthetic agents consist of:
Procaine 10% solution
Bupivicaine 0.75% in 8.25% dextrose
Tetracaine 1% in 10% dextrose
Lidocaine 5% in 7.5 % glucose
Ropivacaine 0.2-1% solution