LA 1 And 2 Flashcards
Duration of anesthesia of PNB is dependent on
Type of block (uptake)
Drug used
Concentration
Adjuncts
Onset of PNB
Can take up to _____ to determine if block failed
10 minute onset
- 15 for Ropivacaine and Bupivacaine
Up to 30 minutes to determine if failed
Most single shot blocks _____ duration when combined with adjunct
16-24 hours
Decadron or epinephrine
Which is longer?
Analgesic time or surgical anesthetic time
Analgesic time much longer
Motor block will wear off but analgesia will continue
3 reasons for rescue blocks
Done when primary block
- failed or has nerve sparing properties
- ineffective in providing analgesia or doesn’t cover appropriate dermatome
- duration of LA has been exceeded
If primary block has failed or has nerve sparing properties
Supplemental distal blocks
Redo primary block targeting location of missed nerves
Primary block is ineffective in providing analgesia or doesn’t cover appropriate dermatome
Surgeon operated on unanticipated area
Pain originates outside block coverage
When duration of LA has been exceeded
Usually at 16-24 hour mark when pain is still moderate-severe in nature
Rescue blocks are done by
Single shot
Single shot with catheter placement
Uptake of LA based on Regional Anesthetic Technique
Highest blood concentration to lowest
IV Tracheal Intercostal Caudal Paracervical Epidural Brachial Sciatic Subcutaneous
(In Time I Can Please Everyone But Sally and Susan)
Pathophysiology of LAST
LA affect SNS and PNS
Profound arterial vasodilation and smooth muscle relaxation
Slows rate of depolarization, blocking fast Na channels
Very high doses dampen SA pm cells = bradycardia and sinus arrest
Dose dependent inotropic depression from negative modulation of Ca release from SR
Hypercapnia, acidosis, hypoxia increase negative inotropic and chronotropic effects of LA
BB, Ca channel blockers, and dig decrease threshold for cardiac toxicity
3 classes of drugs that decrease the threshold for cardiac toxicity
Beta blockers
Calcium channel blockers
Digoxin
LA with Lower safety margin and resuscitation if more difficult in event of LAST
Bupivacaine
LA that accounts for significant portion of LAST events
Lidocaine
Ropivacaine
4 things that are more predictive of high plasma levels of LA than body weight or BMI
Block site
Total LA dose
Test dosing
Pt comorbidities
7 events in LA toxicity
First to last
Drowsiness
Parentheses in mouth and tongue
Tinnitus, auditory hallucination
Muscular spasm
Seizure
Coma
Respiratory arrest
Cardiac arrest
Systemic intoxication by LA
Cardiocirculatory increasing degree of intoxication
HTN, tachycardia
Bradycardia, extrasystoles, hypotension
Asystole
Cerebral systemic intoxication s/s by degree of intoxication
Psychically “abnormal”
Confusion, dizziness, tinnitus, metallic taste
Seizure
Bupivacaine, levobupivacaine, ropivacaine
Which requires lower dose for toxic effects of LA
Bupivacaine
Levobupivacaine
Ropivacaine
Systemic presentations of LAST
CNS only
CV only
CNS and CV
CNS only 43%
CV only 24%
CNS and CV 33%
Spectrum of CV presentations with LAST
Dysrhythmia 34%
Conduction delay 27%
Cardiac arrest 23%
Bradycardia/hypotension 16%
Spectrum of CNS presentations of LAST
Seizure 47%
Loss of consciousness 36%
Prodromes 11%
Agitation 6%
The changing slop of trend lines suggest that contemporary LAST presentations are becoming
More delayed as compared with previous years
Due to the variability in presentation of LAST pt should be monitored for at least
30 minutes after injection
Immediate (<60sec) presentation of LAST suggests
IV injection of LA with direct access to brain
Presentation of LAST delayed 1-5 minutes suggests
Intermittent IV injection, lower extremity injection, or delayed tissue absorption
4 basic steps of treatment of LAST
Get help
Initial focus
- airway mgmt - HYPERVENTILATE
- seizure suppression
- Alert nearest facility with CPB
Mgmt of cardiac arrhythmia
- BLS and ACLS
- avoid vasopressin, BB, Ca channel blockers, LA
- reduce epi dose to <1mcg/kg
Lipid emulsion therapy
Drugs to avoid in management of cardiac arrhythmias with LAST
Vasopressin
Calcium channel blockers
Beta blockers
LA (lidocaine)
Lipid emulsion therapy dosage
20% therapy
Bolus 1.5mg/kg (lean body mass) over 1 minute
Infusion 0.25ml/kg/min (at least 30min)
- double rate if BP remains low
Repeat bolus up to 2 times of CV collapse
Max 10-12 ml/kg over first 30 minutes
Seizure control in LAST
Benzodiazepines
Small doses of propofol (avoid if CV collapse)
Small doses of succ or NMB to minimize acidosis and hypoxemia
Epinephrine dosage during cardiac arrest due to LAST
<1mcg/kg
If ventricular arrhythmias develop
Treatment of choice
Amiodarone
Avoid lidocaine and procainamide
Pt with significant CV event should be monitored for
At least 4-6 hours
If event is limited to CNS symptoms that resolve quickly they should be monitored for
At least 2 hours
Steps to prevent IV injection
Slow injection
Multiple needle redirections and small injection 2-3ml
Aspirate for blood every 5 ml
Awake and monitored pt
US
Epi 2.5-5mcg/ml vascular marker
Vigilant monitoring
Dose of LA is product of
Volume X concentration
IV injection of epi s/s
> 10bpm increase in HR
> 15mmHg increase in BP
S/S IV injection of epi are masked in
Beta blocked pt
Active labor
Advanced age
General/neuraxial anesthesia
To decrease risk of LAST associated with truncal blocks
Use lower concentration
Dose on lean body weight
Adjunctive epi
Observe at least 30-45 minutes
Myotoxicity of LA
IM injection of LA causes muscle damage and necrosis
Myotoxicity of LA causes
Increase intracellular Ca
Myotoxicity of LA
Which causes most damage
Bupivacaine
Why use adjuncts of LA
Increase block duration
Post op analgesia
Which blocks is epi for duration excluded
Sciatic
Digit blocks
Adjuncts to LA examples
Epi
A2 agonist (precedex, clonidine)
Decadron
(Tramadol, buprenex, mag investigational)
First liposomal, bupivacaine encapsulated drug
Exparel
Exparel is a _____% solution
1.3%
Max dose of Exparel
266 mg
Dilution of exparel
Diluted to 0.89 mg/ml with NS or LS
Use within 4 hours
FDA approved use of exparel
TAP blocks
If exparel has been used. Don’t give bupivacaine for
96 hours
Increased risk of toxicity
Obstacles in regional block anesthesia
Surgeon resistance
2 man procedure, stress staff resources
Risk of persistent parethesia, nerve injury, paralysis
Neurotoxicity from LA
IV injection
Key to IV injection
Prevention
Early recoginition
Dose of Decadron
IV
PNB
10mg IV after GETA induction
2mg per block
LA works by
Blocking NA gated voltage channels
Form of LA that is active
Protonated
Ionized
Lipid insoluble
To speed the onset of LA you can add HCO3
MOA
More unprotonated from to cross the lipid bilayer
1MeQ of NAHCO3 for every 10 ml of LA
First to disappear with LA blockade
B sympathetic fibers
Then Fast pain (Type A delta fibers)
Most resistant fiber to LA
Slow pain (Type C fiber)
Order of common LA from vasodilatory properties to vasoconstricitive properties
Tetracaine
Lidocaine
Bupivacaine
Mepivacaine
Ropivacaine
LA onset/duration from fastest to slowest
Lido
Mepivacaine
Ropivacaine
Bupivacaine
Levobupivacaine
Exparel
LA are only pharmacologically active in
Free, unbound state
Rationale behind hyperventilating patient when suspect LAST
Pushes pH more alkaloid so more LA bound to protein so less free for CV and CNS toxicity
