Neuraxial Anesthesia- physiologic changes and Techniques Flashcards
What are the Cardiovascular effects of neuraxial anesthesia?
Treatment?
- Sympathecomy causes vasodilation below level of blockade, decreasing SVR (15-20%) leading to decreased preload and therefore CO (10-15%)
- venous dilation > arterial dilation
- If blockade is at or above T1-T4 the cardiac accelerators are blocked, leading to bradycardia
- Can result in profound hypotension
- Treatment:
- vasopressors
- volume load (15 ml/kg)- if pt can tolerate
- +/- vagolytic drug to treat bradycardia
What are the pulmonary effects of neuraxial anesthesia?
- Low levels of blockade will have minimal effect on MV, TV, RR, and dead space
- As the block ascends, accessory muscles to breathing will become paralyzed, causing the pt to feel like they can’t breath. Also decreases the ability to cough and protect the airway
- No direct respiratory effects excep those related to positioning unless high block
- Phrenic nerve at C3-C5
- Profound hypotension may cause ischemia of the central respiratory centers leading to respiratory arrest.
What are the GI effects of neuraxial anesthesia?
Renal?
- N/V (20%)- usually due to low BP
- Hyperparistalsis d/t unopposed parasympathetic activity
- Liver bloodflow depends on BP- maintain BP to avoid liver damage
- Renal bloodflow is autoregulated, no major effects
- bladder dysfunction
- urinary retention
- In no foley is present, avoid excessive fluids
What are the endocrine/metabolic effects of neuraxial anesthesia?
- blocks the stress response to surgery
- good for pts with CAD (must maintain perfusion)
- Catecholamine release may be blocked from the adrenal medulla
- Cortisol secretion is delayed
- shivering/altered thermoregulation with vasodilation
- important to keep pt warm!
What are the neurological effects of neuraxial anesthesia?
- CBF is maintained unless MAP <60 mmHg
- Manifested by N/V and if sufficiently decreased, will cause apnea and hypoxia
- decreased signals to Reticular activating System (RAS) will cause drowsiness
How do you position your patient for SAB or epidural?
- Lateral decubitus
- forehead to the knees
- thighs flexed to abdomen
- Sitting
- good for lower lumbar or sacral block
- improved midline anatomy
What do you do to get ready for a SAB or epidural?
- have pt hooked up to appropriate monitors
- suction
- oxygen delivery
- fluid bolus (500-1000 ml)
- Equipment for airway management and resuscitation are available
- emergency drugs drawn and available
- consider sedation prior to procedure
- identify landmarks
What are the common landmards for an epidural?
SAB?
- Epidural- see pic
- SAB- below level of spinal cord (L2-L5 interspaces)
What are the two different approach/techniques you can use when placing an epidural or SAB?
- Median (most common)
- the needle or introducer is placed midline, perpendicular to spinous processes, aiming slightly cephalad
- Paramedian approach
- indicated in pts who cannot adequately flex because of pain or whose ligaments are ossified
- the spinal needle is placed 1.5 cm laterally and with a slight cephalad direction to the center of the selected interspace
What layers do you go through when doing the midline approach?
***this WILL be a question!!
- Tripple S- I Love Epidurals
- skin
- subcutaneous tissue
- supraspinous ligament
- interspinous ligament
- ligamentum flavum
- epidural space
- dura mater
- subdural space
- arachnoid mater
- subarachnoid space
- pia mater
- spinal cord
How is the paramedian approach different from the median approach as far as what layers it doesn’t go through?
When is it useful?
- Misses the supraspinous and interspinous ligaments
- unable to use the spinous process as a guide
- Useful in thoracic epidurals or patients with narrow vertebral openings
What are the different types of needles that can be used for SAB?
- Pencil point needles (sprotte/Whitacre)
- designed to spread the dural fibers and help reduce the occurence of post dural puncture headache
- you will feel a distinct “pop” as it penetrated the dura
- better tip strength to minimize bending or breakage
- Side hole enables directional flow of anesthetic and reduces the possibility of straddling the dura
- tracks straight when advancing through the dura
- Cutting needles (Quinke)
- dural “pop” less obvious
- increased risk of wet tap
- introducer may not be necessary depending on pt size
- bevel mist be facing left/right in sitting position and up/down in lateral position to decrease risk of wet tap
What is the procedure for a SAB?
- identify anatomic landmarks
- clean area starting at center and moving out
- apply drape, wipe iodine from site with sterile gauze
- use 2 cc of 1% lidocaine to make wheal at selected space. Use this needle to feel around for spinous processes
- Pass a 17g introducer through wheal site, angled slightly cephalad, stopping in the ligamentum flavum. Ensure bevel is parallel to longitudinal fibers
- 25g choice needle inserted into introducer, passing through arachnoid and stopping when CSF is noted
- if no CSF flowing, rotate 90 degrees
- CSF is aspirated into syringe with LA
- dose is slowly injected, aspirate again after instillation
- all needles removed, patient repositioned
What interspace matches with the Superior illiac crests?
L4
What is the procedure for a paramedian approach for a SAB?
- Identify the edge of the superior spinous process
- skin wheal 1 cm lateral and 1 cm caudad to that point
- insert needle aimed 10-15 degrees medial and slightly cephalad
- if lamina contacted needle, walk needle off in a medial and cephalad direction
- After CSF obtained, coninue same technique as median approach
What is density?
specific gravity? of CSF?
Baracity?
What are the different ratios of LA:CSF?
- Density- the weight in grams of 1 cc of solution at a specified temperature
- Specific gravity- the ratio of the density of a solution to the density of water (temp constant)
- Specific gravity of CSF = 1.004-1.008
- Baricity- the density of a solution to the density of another substance
- LA:CSF
- hyperbaric- LA has higher density than CSF
- hypobaric- LA has lower density than CSF
- Isobaric- LA has same density as CSF
- LA:CSF