Spinals and Epidurals Flashcards
(41 cards)
Describe the vertebrae
33, building blocks of the spine 7 cervical 12- thoracic 5 lumbar 5 sacral (fused) high curves: C5 L3 Low curves: T5 S2
Ligaments of the spine
Purpose is to stabilize vertebral body
- Supraspinous- think
- Interspinous- touches the tips of spinous processes
- Ligamentum flavum- thick and deep right before ED space
- Longitudinal- behind vertebral body
- Ligamentum nuchae
Describe Ligamentum flavum
Extends from the foramen magnum to the sacral hiatus, extends down entire back, tough ligament made of elastin, thickest at midline L3, 3-5mm, “yellow ligament” Varies in thickness down spine
Describe the spinal meninges
Protective membranes continuous with cranial meninges
Arachnoid, dura, pia
Describe the Dura Mater
Thickest meningeal tissue
begins at foramen magnum and ends at S2
Abuts the arachnoid mater (subdural space)
Arachnoid mater
Primary physiological barrier for drugs to cross epidural to spinal cord
Abuts the pia mater (subarachnoid space)
Subarachnoid space
Contains CSF, where we deliver “spinal”, continuous with the cranial CSF to reach brain, houses the spinal nerve roots and rootlets
Pia mater
Adheres to the spinal cord
Describe the spinal cord
Foramen magnum to conus medullaris, L1-L2, gives rise to 31 pairs of spinal nerves, roots (sensory and motor) roots comprised of rootlets. We try to hit posterior root (sensory) but we get motor. Dorsal roots are very large, greater surface area, easier blocked. Anterior motor root smaller.
Dural sac ends at S2
What are dermatomes?
Portion of spinal cord that gives rise to rootlets of a single spinal nerve is called segment. Dermatomes is the skin area innervated by a spinal nerve and its segment.
T4 (nipple), t6 (xiphoid), T8 (last rib), T10 (umbilicus)
Describe the physiology of a neural blockade
Local anesthetic bathes the nerve roots in that space.
Subarachnoid (spinal) local anesthetic into CSF
Epidural (or caudal)- LA injected into epidural or caudal space
Overall goal is sensory blockade, we get inadvertent motor
*blockade can occur at an point and all points along neural pathway. from site of drug admin to interior of cord.
Describe the physiology of a neural blockade PART 2
Blocks all impulses regardless of fiber type: nociceptive, motor, proprioceptive, autonomic
Autonomic is also blocked, but goal is to do nociceptive fibers
Benefits of neuroaxial blockade
decreased metabolic stress to surgery or anesthesia compared with GA
avoids airway instrumentation
Decreases post op N/V
less intraop sedation required
Post-op pain relief
Allows patient to remain awake during C section
Disadvantages of neuroaxial blockade
Hypotension, slower case start if placement is difficult, failure rate depends on experience, urban legends
Considerations for choosing a regional technique
Anatomy: scoliosis, contractures, BMI
Age: affects dose, increased age means lower dose req.
Pregnancy- reduced volume in epidural space, compression of vena cava can decrease CO
pathophysiology: valve disease
Indications for SAB vs Epidural
sensory level of anesthesia required vs. adverse physiological effects of regional anesthesia, ex. severe COPD, needs muscles to expire (thoracic)
Consider length of surgery, post-op analgesia needs, co-existing diseases; combined SAB with CLE, or combo GA/RA (major abdominal cases, lower extremity vascular cases); used for analgesia postop or for L and D.
Absolute contraindications for spinal block
Patient refusal infection at injection site coagulopothies severe hypovolemia/hemorrhage CNS disease or meningitis Hysteria Bactermia or septicemia
Cardiovascular effects
effects depend on spread and blockade of the ANS. Venous dilation > arterial
SVR (15-25 %) and CO (10-15%) decreases
HR decreases as T1-T4 contain cardioaccelerators, unopposed vagal and decreased atrial baroreceptors.
MAP decreases
Pulmonary effects
low levels of blockade have minimal effect
As block ascends, accessory muscle paralysis occurs. No direct effect unless a high blockade, C3-C5 is phrenic.
With profound hypotension might see ischemia of central respiratory centers causes respiratory arrest
GI/Renal effects
N/V, hyperperistalsis, flow to liver is BP dependent so must maintain MAP, renal blood flow is auto regulated tho, bladder urinary retention, avoid excessive IV fluids
Metabolic/Endocrine effects
Blocks the stress response to surgery, catecholamine release blocked from adrenal medulla, cortisol secretion delayed, shivering, altered thermoregulation with vasodilation
Positioning
Positioning is crucial
Lateral decubitus- forehead to knees, thighs flexed to abdomen
Sitting: low lumbar sacral block, improves midline anatomy
R hip fracture, R hip down for gravity’s effects
Spinal anesthesia needle types
Pencil point needles (sprout)- designed to help spread the fibers and reduce PDPH, feel a pop as point punctures dura, increased tip strength Cutting needle (Quincke)- dural pop is less likely, increased risk of PDPH d/t trauma to dura
What are the needle approach techniques?
Median- most common approach needle or introducer is placed midline, perpendicular to spinous process, slightly cephalid*
Paramedian- indicated in patients who cannot flex, needle placed 1.5cm laterally and slightly caudad.*
