Exam 1- Neuraxial Principles (6/1/23) Flashcards
What adjunct agents are lipophilic in spinal blocks and rapidly spread to the spinal cord?
- Fentanyl and Sufentanil
- Early respiratory depression
Besides respiratory depression, an overdose of opioids can cause what adverse effects?
- Muscle rigidity
Which opioids are the best adjunct agents for spinal anesthesia in an outpatient setting?
- Fentanyl and sufentanil
- Quicker onset of respiratory depression
What does ERAS stand for?
- Enhance Recovery After Surgery
ERAS attempts to minimize the use of opioids to improve patient outcomes.
What were the three main side effects of neuraxial opioids discussed in the lecture?
- Pruritus
- Respiratory Depression
- PONV
What is the incidence of pruritis from neuraxial opioids?
- 30-100%
What are the treatments for pruritus from neuraxial opioids?
- Benadryl 25-50 mg IV
- Naloxone 0.1 mg IV (best)
- Buprenex (mixed agonist/antagonist)
Although Naloxone is the best treatment for pruritus, it will also reverse the analgesic properties of the opioid resulting in the patient being in pain.
What are prophylactic managements for pruritus from neuraxial opioids?
- Minimize the dose of morphine to < 300 mcg
- Ondansetron 4 mg IV
- Nubain 2.5-5.0 mg IV
__________ opioids will have delayed respiratory depression and a cephalad spread.
- Hydrophilic (Morphine)
__________neuraxial opioids will have early/ immediate respiratory depression.
- Lipophilic (Fentanyl/Sufentanil)
Neuraxial opioids can be reversed with what medication?
- Naloxone 0.1-0.2 mg
What does this graph show?
- Respiratory depression quickly peaks when the patient receives fentanyl/ sufentanil (1 hour).
- Repression depression peak is delayed when the patient receives morphine (6-7 hours).
PONV from neuraxial opioids is very dose-dependent. What is the recommended neuraxial dose of morphine?
- < 300 mcg
- At less than 100 mcg of morphine, N/V will almost be absent
What is the treatment for PONV from neuraxial opioids?
- Ondansetron (5 HT antagonist) 4-8 mg
- Naloxone 0.1 mg
- Phenergan 12.5- 25 mg IM
What is the incidence rate of urinary retention from neuraxial opioids?
- 30-40%
Since foleys are rarely placed in the OR, it is important to remind PACU nurses to use a bladder scanner/ ultrasound to check for urinary retention.
What is the dose for an “epi wash”?
What is the dose for a “neo wash”?
- Epinephrine 0.2 - 0.3 mg
- Neosynephrine 2-5 mcg
What LA will have a profound effect if vasoconstrictors are added to it?
- Tetracaine
Bupivacaine and Lidocaine will have variable increases.
What is the prophylactic management of hypotension from alpha 2 adrenergic agonst like precedex or clonidine?
- Give fluids (250-500 cc bolus)
If a craniotomy requires a trans-ethmoidal approach, what medication can be given to prevent the Five and Dime (VX) Mechansim?
- Glycopyrrolate (Rubinol) (↑ HR)
α2-adrenergic agonist neuraxial dosage:
Clonidine
Dexmedetomidine
Clonidine 15-45 mcg
Dexmedetomidine 3 mcg
Opioid neuraxial (spinal) dosage:
Morphine
Fentanyl
Sufentanil
Morphine 0.1-0.4 mg
Fentanyl 10-25 mcg
Sufentanil 2.5-10 mcg
Vasoconstrictor neuraxial dosage
Epinephrine
Phenylephrine
Epinephrine 0.2-0.3 mg
Phenylephrine 2-5 mcg
What are the factors affecting the uptake of LA in the neural space?
- Concentration of the LA in the CSF. ( ↑ Concentration, ↑ uptake)
- Surface Area of neural tissue (↑ SA, ↑ uptake)
- Lipid content of the nerve (↑ Lipid content, ↑ uptake)
- Blood flow of the nerve (↑ blood flow, ↑ uptake)
__________ is the clinical phenomenon referring to the temporal blockade of autonomic, sensory, and motor nerve fibers when using neuraxial local anesthetics.
- Differential Block
B fibers are blocked first (sympathectomy), followed by sensory loss (C and A-delta fibers), and lastly motor loss. (motor fibers)
What is the clinical progression of the differential blockade?
When assessing for sensory after performing neuraxial anesthesia. Is it better to assess pain or temperature?
- Be nice and assess temperature with a cold alcohol swap or a cold teaspoon.
For zones of differential blocks, the sympathetic level is ___ to ___, higher than the sensory level.
- 2 to 6 levels
If the sensory level is T10, the sympathetic level could be as high as T4.
For zones of differential blocks, the sensory level is _____ levels higher than the motor level.
- 2 levels
What function will return that indicates the patient is starting to recover from neuraxial anesthesia?
- Return of motor function (wiggling toes)
All LAs used in neuraxial anesthesia are eliminated by ______.
- Reuptake (reabsorption) by vessels in the pia mater
What is the clinical relevance of isoflurane when used for outpatient anesthesia?
- Because isoflurane is lipophilic, the drug will have a slower reuptake d/t the high affinity for fat.
- Therefore, turn isoflurane off earlier.
For spinals, what are the most important drug factors that affect the LA distribution and block height?
- Dose
- Baricity
What are the most important patient factors that affect the LA distribution and block height?
- CSF volume
- Advance age
- Pregnancy
What are the most important procedure factors that affect the LA distribution and block height?
- Patient position
- Epidural injection post-spinal (Epidural volume extension)
What is an epidural injection post-spinal?
- Epidural block performed after a spinal block.
- This is also known as epidural volume extension
- Usually reserved for longer cases (or new surgical residents)
Volume x Concentration =
- Dose
What is the most reliable determinant of local anesthetic spread (block height) when compared with either volume or concentrations for isobaric and hypobaric LA solution?
- The Dose
_______ is defined as the relationship between the densities of local anesthetics and the density of CSF
- Baracity
Define Isobaric
- “Stays where you put it”
- LA has the same density or specific gravity as CSF
- Normal Saline
Define Hypobaric
- “Floats” up
- LA has a density or specific gravity that is less than CSF
- Sterile Water
Define Hyperbaric
- Settles to the dependent aspect of the subarachnoid space
- LA has a density or specific gravity that is greater than CSF
- Dextrose
What type of LA would you want to use for a hip or knee procedure (Iso/Hypo/Hyperbaric solution)?
- Isobaric
What type of LA anesthetic would you want to use for a C-section procedure (Iso/Hypo/Hyperbaric solution)?
- Hyperbaric
What type of LA would you want to use for a hemorrhoidectomy (Iso/Hypo/Hyperbaric solution)?
- Hypobaric
Dosing of Hyperbaric SAB in Non-Obstetric Patient
T4:
T10:
Sacral Level:
Dosing of Hyperbaric SAB in Non-Obstetric Patient
T4: 2 mL (usually 0.75% bupivacaine)
T10: 1.5 mL
Sacral Level: 1 mL
The estimated ED50 of hyperbaric bupivacaine with or without opioids ranged from _____ to _____.
- 4.7 mg to 9.8 mg.
The calculated ED95 of hyperbaric bupivacaine with or without opioids ranged from _____ to ____.
- 8.8 mg to 15 mg.
How can a hyperbaric solution control dermatome spread?
- Dose
- Positioning
What physical characteristic is seen with a hyperbaric solution as the needle is aspirated to check for CSF and placement?
- Swirl
The isobaric solution is difficult to get a level above ________.
- T10
Small CSF volume correlates to ________ spread of LA in intrathecal space.
- extensive
Peak of the block is higher with lower CSF.
What is barbotage?
- A method of spinal anesthesia injects a small amount of anesthetic into the subarachnoid space, followed by the withdrawal of cerebrospinal fluid into the syringe.
- Found not effective
What are the physiological responses of a SAB?
CV:
Pulmonary:
GI/GUT:
Thermoregulation:
- CV - sympathectomy
- Pulmonary - resp depression
- GI and GUT - can be a mess
- Thermoregulation: shivering
Preganglionic B fibers that maintain arterial and venous tone are blocked FIRST by neuraxial anesthesia. A ↓ sympathetic tone results in:
- Arterial and Venous dilation
- Decrease in venous return
- Decrease in cardiac output
- Increase in venous capacitance (venous pooling)
- HYPOTENSION
- Bradycardia
What are the mechanisms that will cause bradycardia with autonomic blockade?
- Inhibition of Bainbridge reflex
- Bezold-Jarisch reflex
- T1-T4 cardio accelerator block
What drug can inhibit Bezold-Jarisch Reflex?
- Ondansetron (Zofran)
What fluids are used to prevent hypotension secondary to neuraxial anesthesia?
- Isotonic fluids (NS, Osmolyte A, LR)
- Preload with 1 L
- Co-loading is giving fluid during the procedure
- Make sure the fluids are warm
Fluids with dextrose will pull fluids and increase urination, contributing to hypotension.
How low can you let a patient’s HR go in the OR?
- No lower than 50 bpm
What is given to manage the BP if severe hypertension occurs from ephedrine or phenylephrine?
- Vasodilators
- Narcotics
- Anxiolytics
What happens to vital capacity and abdominal muscles with a T4 thoracic level dermatome spread of LA?
- Small decrease in vital capacity
- Loss of abdominal muscle contraction in forced expiration
High thoracic blockade can result in the blockade of ___________ muscles of respiration.
- Accessory (can be pronounced with COPD patients)
What is the treatment for a patient when they start experiencing exhalation issues from neuraxial anesthesia?
- Oxygen
- Position
- Reassurance
Oftentimes with neuraxial anesthesia, ______ and _______ precedes hypotension and bradycardia.
- Nausea
- Vomiting
Sympathetic outflow originates from what levels?
- T6 to L1
Sympathetic blockade above ________ affects bladder control.
- T10 (urinary sphincter tone relaxed)
How does neuraxial anesthesia affect thermoregulation?
- Shivering d/t LA effect on the central thermoregulation center of the brain.
What medication can be given to prevent shivering from neuraxial anesthesia?
- Ondansetron 4-8 mg