Anesthesia



Anesthesia


Rachel C. Hooper

Steven C. Haase



TYPES OF ANESTHESIA



  • Local anesthesia (“WALANT”)


  • Local anesthesia plus intravenous sedation (also known as monitored anesthesia care [MAC])


  • Intravenous regional anesthesia (Bier block)


  • Regional nerve block (wrist, elbow, brachial plexus)


  • General anesthesia


GENERAL CONSIDERATIONS



  • Comorbidities and general health



    • Deeper anesthetics result in a greater physiologic stress.


  • Age, temperament, and maturity level



    • Able to keep still, follow directions?


    • Sedation may be difficult to titrate in children.


  • Anxiety, attitude, and emotional status



    • Anxious patients may require sedation even for small procedures.


  • Anatomic site and duration of procedure (need for tourniquet?)



    • Awake patients generally tolerate brachial tourniquet for 20 minutes or less.


    • Forearm tourniquet may be more comfortable for longer periods.


    • Finger tourniquets cause negligible discomfort if digit is blocked.


KEYS TO SUCCESS



  • Patient education—discuss anesthesia options in detail before surgery


  • Teamwork—work with anesthesia colleagues to obtain most comfortable situation for your patient



LOCAL ANESTHETICS1



  • Mechanism of action—reversibly block nerve impulses by reducing cells’ permeability to sodium



    • Formulated as water-soluble hydrochlorides


    • Must transition to lipid-soluble form to enter cells and take effect


    • Acidic environment (infection/inflammation) favors water-soluble form and decreases efficacy


  • Two basic types—amides and esters



    • Tip—Amides contain an “i” in the name before the “-caine.” Esters do not!


    • Amides (eg, lidocaine, bupivacaine)—most common class


    • Esters (eg, procaine, tetracaine)—used less often


  • Duration of action/maximum safe dose—vary based on lipid solubility as well as addition of epinephrine



    • Epinephrine reduces drug diffusion/absorption, prolonging duration of action and increasing maximum safe dose.


    • Calculating maximum safe dose depends on patient weight, drug volume, and drug concentration.


    • Tip—Move the decimal one place to the right to convert % to mg/mL (1.0% = 10 mg/mL)


    • For rapid onset plus long duration, consider using a 1:1 mixture of lidocaine + bupivacaine!


  • Allergies—true allergies to local anesthetics are rare



    • More often, “reactions” are related to syncope or epinephrine-related palpitations.


    • True allergic reactions may occur in response to:



      • Para-aminobenzoic acid (PABA)—metabolite of methylparaben, a preservative included in multidose vials to prevent microbial growth


      • Sulfites—inorganic compounds included in epinephrine-containing products to prevent oxidation of the vasopressor



      • The Drug Itself—amides and esters can both provoke allergies



        • Esters may be more common, because procaine metabolizes to PABA


    • In case of a true allergy:



      • If drug is known—OK to use a different drug (amide or ester); cross-reactivity is rare


      • If drug is unknown—patient may require allergy testing


  • Resistance2



    • True “resistance” to local anesthetics is also rare, and usually anecdotal:



      • Patients with Ehlers-Danlos syndrome—several reports of failed regional blocks


      • Patients with exposure to scorpion venom (affects sodium channels)—anecdotal reports


      • Patients/families with genetic mutation in SCN5A gene (responsible for opening and closing sodium channels)


  • Toxicity—all local anesthetics are central nervous system depressants and may potentiate other depressants



    • Early symptoms (serum > 5 µg/mL)—perioral numbness, facial tingling, restlessness, vertigo, tinnitus, slurred speech


    • Life-threatening symptoms (serum > 10 µg/mL)—tonic-clonic seizures, coma, respiratory arrest, cardiovascular collapse


    • Treatment



      • ABCs—airway, breathing, circulation


      • Seizures—treat with thiopental or diazepam


      • Cardiac toxicity



        • Bupivacaine has greater potential for direct cardiac toxicity than other agents.


        • Antidote = lipid emulsion (20%)—bolus 1.5 mL/kg over 1 minute, then infuse at 0.25 mL/kg/min


      • Anaphylaxis—diphenhydramine, subcutaneous epinephrine, intravenous steroids
















































Generic name


Brand name


Type


Speed of onset


Duration


Max safe dose without epinephrine


Max safe dose with Epinephrine


Lidocaine


Xylocaine


Amide


Rapid


1-2 h


5 mg/kg


7 mg/kg


Bupivacaine


Marcaine


Amide


Slow


8-12 h


2.5 mg/kg


3 mg/kg


Procaine


Novocain


Ester


Rapid


0.25-0.5 h


8 mg/kg


10 mg/kg


Tetracaine


Tetravisc


Ester


Slow


2-3 h


1.5 mg/kg


2.5 mg/kg



LOCAL ANESTHESIA (“WALANT”)3

May 7, 2019 | Posted by in ORTHOPEDIC | Comments Off on Anesthesia
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