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Local Anesthetics

 Max DoseOnset of ActionDuration of ActionToxicityAntidote
Lidocaine

(+)Epi = 7 mg/kg

(-)Epi = 5 mg/kg

Shorter

2-4 min

Shorter

3 hrs

Neurotoxicity

Cardiotoxicity

Lipid emulsion
Bupivicaine

(+)Epi = 3 mg/kg

(-)Epi = 2 mg/kg

Longer

5-8 min

Longer

10 hrs

Same

Same

Cocaine1.5 mg/kg1 min30 min – 1 hr

Myocardial ischemia

 

Pharmacokinetics

PotencyDuration of Action

↑ with ↑lipid solubility

(i.e. bupivacaine is more soluble than lidocaine) ​

↑ with ↑protein binding

(i.e. bupivacaine is more protein bound than lidocaine) ​

Calculating Max Dose

Epinephrine

  • All local anesthetics are vasodilatory except cocaine 
  • Rate of absorption of local anesthetic is decreased when injected with a vasoconstrictor drug (i.e. epinephrine) 
    • Allows higher doses of anesthetic,  longer pain relief, less blood in operative field 
  • Vasoconstrictive effect
    • Time to peak effect = 25 min 
    • Duration of effect =  60-90 min 
  • Dosing
    • 3ml/kg of 1:200,000 plain epinephrine q10 min can be given safely to a child 
  • Can use in fingers, toes, arteriovenous malformations (AVMs) 
  • Administer intramuscularly for anaphylaxis 
  • Toxicity 
    • Epinephrine injection into finger (i.e. epi pen) → Observation  + supportive care
      • Elevate extremity 
    • Antidote = Subcutaneous Phentolamine  (if symptoms > 90 min) 

Tumescence

  • Diluted local anesthetic with epinephrine 
    • Results in very slow rate of absorption from subQ tissue 
  • Peak onset varies by body location  
    • 5-6hrs above clavicles 
    • 12hrs for trunk  
    • If combining face/trunk procedures, infiltrate face first so that peak concentrations do not overlap 
  • Up to 35mg/kg of lidocaine in solutions containing epinephrine can be safely infiltrated into the subcutaneous fat 

Topical Anesthetics

EMLA (Eutectic Mixture of Local Anesthetic)

  • Eutectic = lowered boiling point → better penetration 
  • Composition =  lidocaine + prilocaine  
  • Pharmacokinetics 
    • Peak efficacy =  60 min 
  • After applying to affected site → cover with occlusive dressing 
  • Superior method of anesthesia of simple extremity wounds  

Regional Blocks

Bier Block

  • Instillation of local anesthetic into exsanguinated, tourniqueted extremity 
  • Indications: 
    • Short duration surgery  
      • Patients cannot tolerate tourniquet >20-30 minutes (no pain relief at tourniquet site) 
  • Contraindications:   
    • Longer procedures 
    • Raynaud’s 
    • Sickle cell disease 
    • Severe HTN 
    • Uncooperative pts or children 
  • Cannot release tourniquet too early otherwise sudden cardiovascular collapse can occur by releasing local anesthetic into systemic circulation  
  • Complications: 
    • Tourniquet cuff leak → lidocaine toxicity   
      • Risk factors for cuff leak: 
        • Obesity (funnel shaped arms) 
        • HTN  
      • Treatment = Do not deflate tourniquet 
        1. ABCs, supportive care 
        2. Intralipid 

Transversus Abdominis Plane (TAP) Block

  • Anterolateral abdominal wall innervated by T7 – L1 spinal nerves 
    • Intercostal nerves = T7-T11 
    • Subcostal nerve = T12 
    • Iliohypogastric and ilioinguinal nerves = L1 
  • Block of thoracolumbar nerves that innervate anterior abdominal wall  
    • Run between the internal oblique and transversus abdominis muscles 
  • Inject through Petit Triangle landmarks to block T10-L1 dermatomes: 
    • Latissimus dorsi 
    • Iliac crest 
    • External oblique muscle 

Anesthetic Complications

Allergy to Local Anesthetics

  • All local anesthetics are either esters or amides 
    • Esters = “caines”
      • Contain para-aminobenzoic acid (PABA) → cross sensitivity with paraben preservatives 
      • Procaine, benzocaine, chloroprocaine, and tetracaine 
    • Amides = “i-caines”
      • Do not contain or metabolize to PABA  
      • Bupivacaine, etidocaine, lidocaine, and mepivacaine 
  • “I” before “C” is OK for anesthetics  

Lidocaine Toxicity

  • <14hrs from surgery 
    • Time of peak concentration with tumescence 
  • Biphasic symptoms of neurologic or cardiac toxicity 
    • Early (Excitatory) Phase: 
      • Tinnitus (1st sign of toxicity
      • Metallic taste 
      • Perioral numbness  
      • Slurred speech 
      • Muscle twitching, tremors 
      • Restlessness, lethargy, agitation 
      • Cardiac arrhythmias 
    • Later (Depressive) Stage (as the concentrations increase): 
      • Can progress to seizures and cardiac arrest 
  • Treatment  
    • ABCs FIRST → supportive care (ACLS) 
    • Then if +Seizures and/or cardiac arrest = Intralipid (lipid emulsion) 
      1. Bolus intralipid 20% 1.5 ml/kg IV over 1 min (100cc) 
      2. Then infusion of 0.25ml/kg/min (500cc over 30 min) 
      3. Repeat bolus q5min for persistent CV collapse 
      4. Double infusion rate if remains hypotensive 
      5. Continue infusion for 30 min 

Malignant Hyperthermia

  • Hypercatabolic state 
    • ↑Temp, ↑ HR, ↑ RR, ↑ CO2 production/O2 consumption 
    • Acidosis 
    • Muscle rigidity, rhabdomyolysis 
  • Autosomal dominant inheritance pattern with variable penetrance 
  • Do NOT USE: DISH 
    • Desflurane 
    • Isoflurane 
    • Succinylcholine 
    • Halothane 
  • SAFE to Use:  
    • The “roniums” → Vecuronium, rocuronium, and pancuronium 
    • Benzodiazepines, barbiturates,  and opiates 
    • Inductive Agents → Propofol, ketamine, etomidate 
  • Treatment  
    1. Stop the inciting agent 
    2. Give dantrolene 
    3. Cooling maneuvers

Methemoglobinemia

Methemoglobin contains ferric (Fe3+) form of iron → greater affinity for oxygen 

  • Oxygen is not released to the tissues → cyanosis + tissue hypoxia 

Pre-Operative Patient Assessment

ASA Score

1 

Healthy 

2 

Only mild systemic disease 

3 

Severe systemic disease 

4 

Severe systemic disease that is a constant threat to life 

5 

Severely ill, anticipated death within 24 hrs 

6 

Transplant recipient 

Cardiac Evaluation for Non-Cardiac Surgery

  • Need pre-op work-up? 
    1. Emergency → Surgery 
    2. +Cardiac condition → Cardiac work-up 
    3. Low risk procedure (Mohs, ophthalmology) → Surgery  
    4. ≥ 4 METs (climb flight of stairs, heavy house work, moderately strenuous sports) → Surgery 
  • (+)Stent  placed within last 6 months → continue ASA, plavix   
    • Only hold for neurosurgery  

Special Patient Populations

HIV+

CD4+ <200  Increased risk of complications  

Von Willebrand Disease

  • Factor VIII binds to/protects vWf →vWF deficiency = ↓factor VIII 
  • Treatment =  DDAVP 

PRegnant PAtients

Benzodiazapines = teratogenic 

Intra-Op Care & Monitoring

  • Ambient temperature 
    • Maintain at least 70°F (21.1 C)  
    • Maintaining normothermia decreases risk of surgical site infection 
  • Pulse oximetry  
    • Can be altered by hypotension  
  • Oxygenation via nasal cannula  
    • ↑ risk of fire in the OR  

Surgical Complications & Critical Care

Post-Op Nausea/Vomiting

  • Risk Factors:  
    • Most Important = Prior history of postoperative nausea/vomiting/motion sickness 
    • Female  
    • Nonsmoking status 
    • Volatile anesthetics/general anesthesia 
    • Opioid/narcotic use 
    • Facial rejuvenation procedures 
    • Breast surgery  
    • Long duration of surgery 
  • Propofol = Least emetogenic  
  • In children: 
    • IV ketamine is better than IM ketamine 
      • Least emetogenic  
      • Also less laryngospasm + faster onset 
  • Prevention 
    • Aprepitant prior to induction of anesthesia 
      • Long-acting neurokinin 1 (NK1) receptor antagonist → blocks substance P in the chemoreceptor trigger zone 
    • Use adjunct local or regional anesthetics to decrease narcotic and inhaled anesthetic needs 
  • Scopolamine 
    • Anticholinergic side effects
      • Fixed, dilated pupil (mydriasis) if pt rubs eyes  Constriction persists despite instillation of parasympathomimetic (i.e pilocarpine) as local ACh receptors are blocked 

        • If CNIII lesion, will constrict if parasympathomimetic is instilled in eye as there is no dysfunction of muscarinic receptors of iris sphincter muscle 

Hyperkalemia

  • Due to up-regulation of ACh receptors in traumatized muscle 
  • Induced by paralytics in surgery (e.g. succinylcholine = depolarizing agent → keeps ACh receptor open allowing K+ ions out of cells)  
  • Risk Factors 
    • Burn patients  
    • Succinylcholine 
  • Peaked T-waves 
  • Treatment 
    • IV calcium 
    • Insulin, dextrose 

Myocardial Infarction (MI)

(+)Arrhythmia 

  1. Replete electrolytes 
  2. ACLS protocol 

Congestive Heart Failure (CHF)

Can be exacerbated by over-resuscitation in OR if chronic cardiovascular dysfunction present

Tachycardia with a Pulse

  • Unstable → cardioversion 
  • Stable → rate control

Acute Kidney Injury (AKI)

  • Fractional Excretion of Sodium (FENa) = % of filtered sodium in urine 
  •  

[Urine Na×Plasma Cr/Plasma Na×Urine Cr] ×100

 

  • FENa <1% = Pre-Renal → Appropriate filtration of sodium, but insufficient renal perfusion 
  • FENa >2% = Intra-Renal  → Acute tubular necrosis (ATN) 

DVT/PE

  • Initiate IV heparin 

Fat Embolism

  • 24-48hr after surgery 
  • Petechial rash, respiratory dysfunction, neurologic dysfunction 

Shock

Treatment = Fluid resuscitation