LA: Chapter 3 reference PDF Flashcards
Benefits of
regional vs. GA w/ opioids
↑ pain control
↑ patient satisfaction (lol idc)
↓ stress response to surgery
↓ intraop & postop blood loss
↓ PONV
↓ logistic requirements
ability of a given local anesthetic to block a nerve is r/t (4)
length of the nerve
diameter
myelination
anesthetic used
T/F
Myelinated nerves need to be blocked only at nodes of Ranvier
True
approximately 3 consecutive nodes
Myelinated nerves require (more/less) anesthetic to block.
less
Differential blockade
pain and temperature block (A-d, C fibers)
while minimizing motor block (A-a fibers)
Most local anesthetics have a pKa (less/greater) than 7.4
greater
How does protein binding increase DoA?
high affinity protein binding
↓
bound to nerve membranes longer
↓
increased doA
T/F
High protein binding increases the risk of primary organ toxicity.
False
binding to serum a1-acid glycoproteins and other proteins decreases the availability of free drug in the blood, reducing the potential
for toxicity in the primary organs
Conditions that increase free fraction of LA in the blood
acidosis
decreased serum protein
↑ potential for toxicity
Initial (inhibitory/excitatory) symptoms of toxicity are manifestations of escalating drug concentration in the CNS, specifically the ___.
excitatory
amygdala
S/S
toxicity
muscular twitching
visual disturbance
tinnitus
light-headedness
tongue/lip numbness
extreme anxiety
screaming
concerns about imminent death
if untreated:
generalized tonic-clonic convulsions
coma
respiratory arrest
death
Which is more resistant to toxicity?
CNS
CV system
CV system
circulatory collapse ratio
relationship between:
LA blood [ ] causing circulatory collapse
&
LA blood [ ] needed to cause convulsions
smaller ratio = ↓ interval btwn convulsions & circulatory collapse
Which has the smaller circulatory collapse ratio?
A) bupivacaine & ropivacaine
B) mepivacaine & lidocaine
smaller ratio: bupivacaine & ropivacaine
more potent, long-acting
Ropivacaine (Naropin)
-pKa of 8.2
-chemically similar to mepivacaine & bupivacaine
-pure levorotatory stereoisomer
-less cardiotoxic than bupivacaine
-“safest” long-acting
caution: CV collapse still possible
racemic mixture
combination of levorotatory and dextrorotatory molecules
Which enantiomer tends to be less toxic?
Levorotatory
dextrorotatory
Levorotatory
Which is less 🩷 toxic?
ropivacaine
bupivacaine
ropivacaine
preferred long-acting for PNB anesthesia for many providers
Bupivacaine (Marcaine)
-pKa of 8.1
-long-acting
-longest onset
-Low [ ] : sensory block > motor (differential sensitivity)
-low-vol infiltration & spinal anesthesia well established
caution: large-volume epidural or peripheral nerve a/w prolonged resuscitation
following accidental IV injection
Mepivacaine (Polocaine)
-pKa 7.6
-intermediate-acting
-rapid onset
-infiltration (similar onset to lido; longer doA)
-one of the least neurotoxic LAs
✅ high-risk cardiac pts
-block success despite suboptimal needle position
-intense motor block (shoulder surgery)
Lidocaine (Xylocaine)
-pKa 7.7 (low)
↓
distribution into the exsanguinated extremity
-low systemic toxicity
-rapid onset
-intermediate acting
-moderate W & L solubility = versatile
-caution: transient neurologic syndrome
most common LA used for intravenous regional anesthesia
Lidocaine 0.5%
Peripheral nerve blocks (PNB)
providers usually prefer ___ acting agents
long
so analgesia lasts well into the postop recovery period
Regional Anesthesia
Deep sedation or general anesthesia is avoided because
pt indicators of toxicity or nerve injury are masked
must balance btwn pt comfort & safety during block placement
Why add epi to LA?
prolongs block
reduced plasma [ ]
marker of IV injection during single injection blocks
What changes in V/S would we see with accidental IV injection of LA w/ epi
↑ heart rate (≥10 beats/min)
↑ SBP (≥15 mmHg)
↓ T-wave amplitude (depression ≥ 25%),
10-15+ μg of IV epi can cause this
addition of opioids to intrathecal LA
prolongs sensory anesthesia w/o prolonging recovery from ambulatory procedures
reduces LA requirements for OB
“walking epidural”
T/F
Clonidine provides analgesia
True
a2-adrenoceptor agonist
analgesia via a nonopioid receptor
Dexamethasone 8 mg as LA additive
enhance the duration of sensory and motor blockade
Pretreatment with ____ to increase the seizure threshold to local anesthetic toxicity
benzodiazepines
Minimize accidental IV injection by injecting ___ ml every 10-15 seconds
5
If seizures occur…
airway maintenance
supplemental O2
propofol (25–50 mg) or thiopental (50 mg)
Preventing IV injection:
Initial injection of test dose containing at least ___ epinephrine
5–15 μg
Is this important? idk
Fiber types and fxn
