regional anesthesia pharmacology and therapeutics

Regional Anesthesia Pharmacology and

TherapeuticsEdwin Perez, MD, BS, High School

Director-Acute PainNewark Beth Israel

(not the one in New York :(

Objectives

Types-Amides vs EstersSpread of LocalPharmacokineticsUse of VasoconstrictorsToxicity

Objectives

key points about all blocks in generalwhen to use themrisks/benefitsultrasound versus landmark/stim techniqueLAST

Amides And Esters

All local Anesthetics (LA) have a hydrocarbon chain connected to a lipophilic portion. This is done by either an ester (-CO-) bond or amine (-HNC-) bond. amides are metabolized in liveresters are metabolized in plasma by

pseudocholinesterase

Rule of iEsters AmIdesprocaine lIdocainechloroprocaine bupIvacainetetracaine mepIvacainecocaine ropIvacaine

Do you have any allergies?

Extremely unlikely-1% of ADR are caused by Local anestheticsMost likely seeing systemic toxicityesters are the culprit more than amides-think PABAwhen linked to amides usually due to preservative-methylparaben

Max single-shot doseEsters-

procaine-1000mg in 70kg malechloroprocaine-800mg in 70kg male 1000mg in 70kg male w/epi

tetracaine-20mg in 70kg maleAmides

Lidocaine- 3 or 5mg/kg depending on epiBupivacaine/Ropivacaine 3mg/kg

Spread (rules are different for peripheral)

Pharmacology 101:its gotta get inside

LA bind to sodium channels on the inside of the channel

They also obstruct the outsidemaintains them in inactivated-closed state

Pharmacokinetics

pKa of local anesthetics makes them such that only 0.5% is already in a nonionized form.It must be nonionized to cross (abscess)Intrinsic vasodilator-lidocaineesters safer except in pseudocholinesterase deficiency

Toxicity

1) #1 casue is accidental intravascular placement

2) Then from absorptionintercostal>caudal>epidural> sciatic

CNSScale of effects

A) AnalgesiaB) Lightheadedness, tinnitus, numb tongueC) SeizuresD) ComaE) Then cardiovascular depression

Cardiac

Hypotensionincreased P-R and wide QRSarrythmiabupivacaine is fast in/slow out

Other effectsTRICauda equina syndrome

Why BlocksSignificant improvement in analgesia

Significant improvement in patient satisfaction

Sometimes decreased LOS

Decreased opioid requirements by 50% or more

BlocksChronic vs Acute Pain Blocks (diag vs ther)contraindicationsperipheral blocks only work on peripheryblock effect timesnerve sparing and the compartment syndrome situationadjuvant therapy (fem/sciatic controversy)how long do blocks actually last

LAST Rectus Sheath Block

Checklist for Treatment of Local Anesthetic Systemic Toxicity

The Pharmacologic Treatment of Local Anesthetic Systemic Toxicity (LAST) is Different from Other Cardiac Arrest Scenarios❑ Get Help ❑ Initial Focus❑ Airway management: ventilate with 100% oxygen ❑ Seizures uppression: benzodiazepines are preferred; AVOID propofolin patients having signs of cardiovascular instability ❑ Alert the nearest facility having cardiopulmonary bypass capability❑ Management of Cardiac Arrhythmias ❑ Basic and Advanced Cardiac Life Support (ACLS) will requireadjustment of medications and perhaps prolonged effort❑ AVOID vasopressin, calcium channel blockers, beta blockers, or local anesthetic❑ REDUCE individual epinephrine doses to <1 mcg/kg ❑ Lipid Emulsion (20%) Therapy (values in parenthesis are for 70kg patient)❑ Bolus 1.5 mL/kg (lean body mass) intravenously over 1 minute (~100mL)❑ Continuous infusion 0.25 mL/kg/min (~18 mL/min; adjust by roller clamp)❑ Repeat bolus once or twice for persistent cardiovascular collapse❑ Double the infusion rate to 0.5 mL/kg/min if blood pressure remains low❑ Continue infusion for at least10 minutes after attaining circulatory stability❑ Recommended upper limit: Approximately 10 mL/kg lipid emulsion over the first 30 minutes❑ Post LAST events at www.lipidrescue.org and report use of lipid to www.lipidregistry.org

BibliographyDang, Charles;The value of adding sciatic block to continuous femoral block for analgesia after total knee replacement; Regional Anesthesia and Pain Medicine; Volume 30, Issue 2, March–April 2005, Pages 128–133

Benzon, Honorio, Essentials of Pain Medicine and Regional Anesthesia, 2005

Neal, Joseph;ASRA Practice Advisory on Local Anesthetic Systemic Toxicity; Regional Anesthesia & Pain Medicine; March/April 2010; Vol 35 Issue 2; pp152-161

Stoelting, Robert; Basics of Anesthesia; 2000