Principles of Anesthesia Practice I Unit I Flashcards
What are the clinical indications for neuraxial anesthesia?
Surgical procedures involving the lower abdomen, perineum, and lower extremities, Orthopedic surgery, Vascular surgery on the legs, Thoracic surgery (adjunct to GETA)
What are the benefits of neuraxial anesthesia?
Decreased narcotic usage, less bleeding, lower respiratory complications, lesser chance of PONV, decreased thromboembolic events and less chance of post-op ileus
What are the “other” neuraxial anesthesia benefits listed in lecture?
Better/faster mental alertness, less urinary retention (can vary based on the patient), quicker to eat/void/ambulate, avoid unexpected admission to hospital d/t GA, quicker PACU DC (variable based on hospital policy), blunts stress response from surgery and pre-emptive analgesia/anesthesia
What are some relative contraindications to neuraxial anesthesia?
Deformities of spinal column
Spinal stenosis, kyphoscoliosis, ankylosing spondylitis
Preexisting disease of the spinal cord
Exacerbate a progressive, degenerating disease like MS or post polio syndrome
Chronic headache/backache
Inability to perform SAB/Epidural after 3 attempts
What are absolute contraindications to neuraxial anesthesia?
Coagulopathy (INR greater than 1.5, platelets less than 100,000 or PT/PTT x2 from baseline), coagulation disorder or on anticoagulants, patient refusal, evidence of dermal site infection, severe valvular disease, HSS (idiopathic hypertrophic subaortic stenosis), surgery duration greater than duration of LA, increased ICP, severe CHF (EF less than 30-40% and/or preload dependence)
What is the pneumonic to remember the intrinsic/extrinsic pathways?
E: for 37 cents you can purchase this pathway (factors 3 and 7)
I: you can’t buy the intrinsic pathway for 12$, but you can buy it for 11.98 (factors 8, 9, 11 and 12)
What is the pneumonic to remember the common pathway?
The common pathway can be purchased at the five and dime for one or two dollars on the 13th of the month (factors 1, 2, 5, 10 and 13)
At what mean valve area is aortic/mitral valvular disease severe? Critical?
Severe = 0.7 - 1.0 cm sq
Critical = less than 0.7 cm sq
in general, if less than 1.0 cm sq, it is severe disease and a contraindication to anesthesia
Describe the onset, spread, nature of block, motor block and chances of hypotension with spinal vs epidural
Spinal: Rapid onset, higher spread, dense/more profound nature of block and motor block with likely hypotension
Epidural: Slow onset, more controlled spread (reliant on volume of LA), the nature of the block is segmental with minimal motor block and less chance of hypotension than spinal
What type of neuraxial anesthesia is limited to the L3-S1 region?
Spinal
What type of neuraxial anesthesia requires more skill to place?
Epidural
What type of neuraxial anesthesia is dose based?
Spinal
What type of neuraxial anesthesia is volume based?
Epidural
What type of neuraxial anesthesia is dose based? Volume base?
Dose = spinal
Volume = epidural
Describe the difference in concentration of an LA with spinal vs epidural
Spinal = concentrated and fixed
Epidural = varies
Describe the incidence rate LA toxicity (in general terms) of spinal vs epidural
Spinal = little to no chance of LA toxicity
Epidural = carries risk of LA toxicity
How does gravity influence a spinal? Epidural?
Spinal = depends on the baricity of the LA
Epidural = depends on the patient position
How would you manipulate the dermatome spread of an epidural vs spinal?
Spinal = the baricity, patient position and dose to dictate spread
Epidural = incremental dermatome spread based on volume, generally 1-2 ml per segment
How many vertebrae are there? Describe how many are at each level
33
Cervical = 7
Thoracic = 12
Lumbar = 5
Sacral = 5
Coccyx = 4 total
What drug can mitigate epidural related hypotension?
Zofran
The symptoms of severe valvular disease include angina, syncope and heart failure/SOB, which are correlated with what survival lengths?
Angina = 5 year survival
Syncope = 3 year survival
Failure/SOB = 2 year survival
What structures link the the anterior/posterior segments of the vertebrae?
The lamina and pedicle
What space houses the spinal cord, nerve root and the epidural space?
The vertebral foramen made up by the connections between each vertebrae
What is the primary spinal landmark used in neuraxial anesthesia?
The spinous process
Which vertebrae have a caudal orientation? Horizontal?
Caudal = cervical and thoracic
Horizontal (ish) = lumbar
In relation to the intervertebral foramen, what makes up the anterior/posterior aspects?
Anterior = vertebral body and intervertebral disc
Posterior = facet joints
What occurs with disc degeneration?
Narrowing of the foramen which can press on the spinal nerves causing pain/weakness/NT
At what level is the vertebral prominens?
C7
At what level is the root of spine of scapula (spinous process of scapula)?
T3
At what level is the inferior angle of the scapula?
T7
At what level is the superior aspect of the iliac crest?
L4
At what level is the posterior superior iliac spine?
S2
At what level does the intercristal line usually occur in adults? Infants?
Adults = L4
Infants = L5-S1
What is the caudal access point for neuraxial anesthesia?
The Sacral Hiatus
What is the incomplete part of the sacrum bridged only by ligaments?
S5
What landmarks help guide accessing the sacral hiatus for caudal anesthesia?
The sacral cornu
Where does the spinal cord originate and end?
Originates in the medulla and ends at the conus medullaris, roughly about L1 or L2
Per lecture, where does the spinal cord end in adults? Infants?
Adults = L1
Infants = L3
Describe the origin and endpoint of the cauda equina
Origin = tip of the conus medullaris and ends around S5 after the dural sac has ended
What levels would you find the cauda equina?
L2 - S5
What makes up the cauda equina?
Nerve roots and the coccygeal nerve
What is the end point of the dural sac in adults? Infants?
Adults = S2
Infants = S3
Where does the subarachnoid space end?
At the end of the dural sac (so S2 in adults, S3 in infants)
Describe the filum terminale
A continuation of the pia mater that extends from the conus medullaris to the tail bone and anchors the spinal cord in place
Describe the internal and external filum terminale
Internal = begins at the conus medullaris and extends to the dural sac (L1 or L2 to S2)
External = starts from the dural sac and extends into the sacrum (S2 to S5)
What is the primary blood supply for the motor function of the cord?
Anterior spinal artery
What is the primary blood supply for the sensory function of the cord?
The posterior (2 of them) spinal arteries
What do most of the anterior/posterior spinal arteries originate from?
Vertebral arteries
Why are the posterior spinal arteries more resistant to ischemia?
The have much more collateral circulation than the anterior spinal artery (from the subclavian and intercostal arteries)
Where is the anterior spinal artery most likely to receive additional branches of blood vessels from?
the intercostal and iliac arteries
What are common causes of spinal cord ischemia?
Profound hypotension, mechanical blockage, blood vessel disease (vasculopathy) and bleeding
What crucial connection helps supply blood to the lower 2/3 of the spinal cord?
The great radicular artery (artery of adamkiewicz)
Where can the great radicular artery emerge from?
Anywhere from the T9 - L2 regions, highly variable throughout the population
Starting from out to in, list the spinal ligaments
Supraspinous, interspinous, ligamentum flavum, posterior longitudinal and anterior longitudinal
What layers are skipped when using a paramedian approach?
the supraspinous and interspinous ligaments
List the layers traversed during a midline insertion
Skin -> subQ fat -> supraspinous -> interspinous -> ligamentum flavum -> dura mater -> subdural space -> arachnoid mater -> subarachnoid space
Common indication for a paramedian approach?
When the interspinous ligament is calcified or the patient cannot flex their spine
What angle is ideal for a paramedian approach?
15 degrees off midline, 1 cm lateral and 1 cm below the vertebrae
List the meningeal layers from outer to inner
Dura mater, arachnoid layer and pia mater
Where is the epidural space?
In between the dura mater and the ligamentum flavum
Per lecture, what 2 medications are contraindicated in spinals?
Reglan and zofran
What type of neuraxial anesthesia can be placed at any level?
Epidural
What angle would you anticipate needing to use for accessing T6/7?
about 40 degrees or a cephalad approach
What do spinal nerves exit from?
Intervertebral foramina
Per lecture, what is a good anatomic location for thoracic anesthesia (give level and anatomic landmark)?
T7, the inferior angle of the scapula
What are the 2 names for the horizontal line drawn across from L4?
Intercristal line or Tuffier line
What ligament connects the coccyx and sacrum and covers the sacral hiatus?
Sacrococcygeal ligament
In an adult, what is the lowest level you could find CSF? Infant?
Adult = S2
Infant = S3
Piercing what ligament indicates entry into the epidural space?
Ligamentum flavum
List the layers you want to pierce if you are doing a spinal?
Skin -> subQ fat -> supraspinous ligament -> interspinous ligament -> ligamentum flavum -> dura mater -> subdural space -> arachnoid mater -> then you are in the subarachnoid space
What approach is most common with thoracic neuraxial axis?
Paramedian
What supplies blood to the anterior 2/3 of the spinal cord?
Anterior spinal artery
What is the name for the epidural veins? What distinguishes them from other veins?
Batson’s plexus. They are valveless and form a plexus that drains blood from the cord and its linings. Their density increases laterally
What do conditions like pregnancy or obesity do to Batson’s plexus?
They engorge the veins, increasing the risk of needle puncture
What anatomic feature may explain the presence of a unilateral block related to an epidural insertion?
Plica mediana dorsalis
What layer would you pierce during a spinal if you kept advancing the needle after entering the sub-arachnoid space?
Pia mater
What effects would occur with a spinal vs an epidural if administered in the subdural space?
Spinal = a failed block
Epidural = it can cause a “high spinal” effect, meaning the medication would have a greater than intended effect
Of the 3 meningeal layers, which is the most vascular?
Pia mater
List how many nerves each group of vertebrae (groups being cervical, thoracic etc) have
Cervical = 8
Thoracic = 12
Lumbar = 5
Sacral = 5
Coccyx = 1
What dermatome(s) innervate the anterior and inner surface of lower limbs?
L1 - 4
What dermatome(s) innervate the foot?
L5 - S1
What dermatome(s) innervate the medial side of the great toe?
L4
What dermatome(s) innervate the posterior and outer surface of lower limbs?
L5 - S2
What dermatome(s) innervate the lateral margin of the foot and little toe?
S1
What dermatome(s) innervate the perineum?
S2 - 4
What dermatome(s) innervate the umbilicus?
T10
What dermatome(s) innervate the inguinal region?
T12
What dermatome(s) innervate the clavicles?
C5
What dermatome(s) innervate the lateral parts of the upper limbs?
C5 - 7
What dermatome(s) innervate the medial sides of the upper limbs?
C8 - T1
What dermatome(s) innervate the thumb?
C6
What dermatome(s) innervate the hand?
C6 - 8
What dermatome(s) innervate the ring and little fingers?
C8
What dermatome(s) innervate the level of the nipples?
T4
What supplies the sensory innervation to the face?
CN V (trigeminal nerve), of that nerve, it has 3 branches, the ophthalmic nerve (V1), maxillary nerve (V2) and the mandibular nerve (V3)
What is the desired dermatome level for a perianal surgery or saddle block?
S2-S5
What is the desired dermatome level for a foot/ankle surgery?
L2
What is the desired dermatome level for a thigh/lower leg/knee surgery?
L1
What is the desired dermatome level for a vaginal delivery/uterine/hip/tourniquet/TURP?
T10
What is the desired dermatome level for a scrotal surgery?
S3
What is the desired dermatome level for a penile surgery?
S2
What is the desired dermatome level for a testicular surgery?
T8
What is the desired dermatome level for a urologic/gynecologic/lower abdominal surgery?
T6
What is the desired dermatome level for a C-section/upper abdominal surgery?
T4
What is the site of action in a spinal vs epidural?
Spinal = subarachnoid space acting on the myelinated preganglionic fibers of the spinal nerve roots. Also inhibits neural transmission in the superficial layers of the spinal cord
Epidural = diffuses through the dural cuff to reach nerve roots (it can also leak into the para-vertebral area)
What factors can affect the spread of a spinal? Which do not?
Affect = baricity, patient position, dose and site of injection, volume of CSF, increased intra-abdominal pressure (obese, pregnant), age
Does not affect = barbotage (repeated aspiration and reinjection of CSF), speed of injection, orientation of bevel, addition of vasoconstrictor and gender
What factors significantly affect the spread of an epidural? small effect on spread? No effect?
Significant = LA volume, level of injection and dose, pregnant, old age
Small = LA concentration, position, height
No effect = additives (they can change onset or duration but not spread), direction of the bevel, speed of injection
How would a spinal injection most likely spread from the lumbar region? thoracic? cervical?
L = spreads mostly cephalad
T = balanced in both cephalad and caudad direction
C = spreads caudad
List the nerve fibers in order of block onset
B -> C -> A delta -> A gamma -> A beta -> A alpha
If the level of T8 is blocked what would be the level of motor blockade? Sympathetic blockade?
Motor = T10
Sympathetic = T2 - 6
How many levels higher may the sympathetic block be from a spinal?
Sympathetic = 2 - 6 levels higher
What nerve fibers blocks first and recovers the slowest?
Beta fibers (sympathetic)
What nerve fibers block last and recover fastest?
A-alpha (motor function, proprioception)
List the sensations in order of blocked first to last
Temperature is blocked first, followed by pain then touch/pressure
What scale is used to evaluate patient movement after a spinal block?
modified bromage scale
What are the general CV effects from a spinal?
Everything decreases, pre/afterload, CO, HR
note that CO initially increases after a spinal d/t the reflex of losing vascular tone, but CO is only briefly increased, it quickly drops
What is the Bezold-Jarisch reflex? What nerve mediates this reflex?
It’s a response to ventricular underfilling; it causes significant bradycardia. The vagus nerve
What drug can help mediate the Bezold-Jarisch reflex?
Zofran
What reflex, other than Bezold-Jarisch, can cause bradycardia after a spinal?
The reverse bainbridge reflex
What population is sudden cardiac arrest most likely to occur in after a spinal? Onset?
Young adults with high parasympathetic tone, and generally occurs 20 - 60 minutes after a spinal
What are the choice vasopressors in treating spinal related hypotension?
Ephedrine (if bradycardic) or Neo (if tachycardic)
In general, what are the spinal effects on the pulmonary system?
Minimal to no effects. There may be a small decrease in ERV that may cause patients to feel short of breath
What positions may be used with a paramedian approach?
Sitting, lying, or face down (there are far more viable positions for a paramedian approach than a midline approach)
What is the cranial and caudal border of the epidural space?
Cranial = the foramen magnum
Caudal = Near the the sacrococcygeal ligament
Describe the anterior, lateral and posterior borders of the epidural space
Anterior = the posterior longitudinal ligament
Lateral = on the sides near the vertebral pedicles
Posterior = the ligamentum flavum and close to the vertebral lamina
How many paired spinal nerves are there?
31
Which blockade requires a greater concentration of LA; sensory or autonomic?
Sensory, as sensory would be either C fibers or a subset of A fibers, they block later than the autonomic (pre-ganglionic B-fibers) which block first.
What receptors mediate the Bezold-Jarisch reflex? Where would you find them?
5-HT3 receptors in the vagus nerve and the ventricular myocardium
What information does the efferent and afferent aspects of the PNS of the GI tract transmit?
Afferent = transmits sensations of satiety, distension and nausea
Efferent = tonic contractions, sphincter relaxation, peristalsis, and secretion
At what level does sympathetic innervation to the GI tract originate?
T5 - L2
What information does the efferent and afferent aspects of the SNS of the GI tract transmit?
Afferent = visceral pain
Efferent = inhibits peristalsis and gastric secretion, vasoconstriction and sphincter contraction
What occurs to the sympathetic and parasympathetic activity of the GI system when neuraxial anesthesia is administered?
Due to sympathectomy, the SNS is decreased which allows the PNS to take over/become more dominant (causes more rest and digest rather than fight or flight)
Due to the sympathectomy from neuraxial anesthesia, what GI effects would you expect to occur?
Sphincters relax, increased peristalsis, smaller contracted gut with active peristalsis, increased chance (20%) of N/V, increased GI blood flow and reduced chance of ileus
At what level is sympathetic blockade of the bladder affected?
Above T10
How do neuraxial opioids cause urinary retention/incontinence?
They decrease detrusor contraction and increase bladder capacitance, combined allow for retention and incontinence (this is why foley’s are generally indicated with neuraxial anesthesia)
When is the best time to administer neuraxial anesthesia in order to take advantage of the maximal benefit of suppressing the neuroendocrine surgical response from surgery?
Before surgical stimulus
What dictates LAs onset? Potency? Duration?
Onset = pKa
Potency = lipid solubility
Duration = %protein bound
What is the relationship of pKa and physiologic pH in regards to onset?
The closer you are to physiologic pH, the faster the onset should be as more of the LA remains in the nonionized state
List the routes of administration that have the least to most plasma concentration of an LA
Subq -> Sciatic -> Brachial -> Epidural -> Paracervical -> Caudal -> Intercostal -> Tracheal -> IV
If supine, where would you expect to find and iso/hypo/hyperbaric LA?
Iso = same level of injection with some caudal and cephalad movement
Hypobaric = rises above the point of injection or, rather, it floats
Hyperbaric = sinks within the CSF moving below the point of injection
If supine, where would you expect to find the greatest concentration of a hyperbaric anesthetic? Hypobaric?
Hypobaric = floats and goes to highest points, so C3 and L3
Hyperbaric = sinks and goes to lowest points, T6 and S2
Describe the metabolism/elimination of sub-arachnoid LAs
No metabolism occurs in the CSF, in order for elimination to occur they must be re-uptaken via vessels in the pia mater
Do lipophilic or hydrophilic LAs have a faster reuptake rate after a spinal?
Hydrophilic are faster, lipophilic are slower because they have a high affinity for the fat
Chloroprocaine has a fairly high pKa, yet has a very fast onset in epidurals (common to use this drug in OB), why is this?
They overcome the higher pKa by having a high concentration of 2-3% to overcome the high pKa (bupivacaine for example has a concentration of 0.5 - 0.75%)
How does the dose, in general, of a spinal change from a T10 dose to a T4 dose?
A T4 dose is higher than a T10 dose
How much does the inclusion of epi increase the duration of a SAB?
20 - 50% increase in duration
What metabolizes 2-3 Chloroprocaine? Is it an amide or ester?
Metabolism = plasma cholinesterase and it is an ester
remember the trick from pharm, one I is an ester, two I’s is an amide
Describe how Epi can be used as a biomarker to determine if you are in an ideal place for an epidural
You use it to check if you are in an vein or not, if you give a small dose of epi, and have no change in HR, you can reasonably say you are not in a vein. If you give the epi, and have an increase in HR, you are likely in or near a vein
Why do you use incremental dosing when starting an epidural?
To avoid accidental high spinal (such as if you are in the subdural space) or hypotension from rapid autonomic blockade. It also mitigates LA toxicity concerns
What is the ratio of Bicarb and LA for appropriate alkalinization?
1 mEq of bicarb per 10 mL of LA
How does alkalization affect LA pharmacokinetics?
It increases the concentration of non-ionized free base, the rate of diffusion and the speed of onset
What is the relationship of concentration of an LA to onset/duration of an epidural?
In general, the higher the concentration the faster the onset and shorter duration. The lower the concentration, the slower the onset and the longer the duration
How much should the top-up dose be for an epidural? When do you administer it?
50 - 75% of the initial dose, and you give it before the block decreases more than 2 dermatomes
How does the degree of spread of an LA compare from the thoracic vs lumbar space?
The thoracic area is smaller which correlates to greater spread whereas the lumbar region is larger and correlates with with lesser spread