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
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LOCAL ANESTHESIA (“WALANT”)3
Wide Awake Local Anesthesia No Tourniquet (WALANT) is a term increasingly used
No intravenous (IV) sedation
No anesthesiologist, no anesthesia charges
No need to be NPO for surgery
Select patients may drive themselves home
Able to talk with patient during procedure:
Improved patient education/understanding
Able to elicit active motion to test intraoperative function
Need a cooperative patient
Need to inject local anesthesia without sedation
To reduce pain of injection:
▲ Inject slowly (eg, 10 mL over 5-10 minutes)
▲ Use a small needle (25- to 30-gauge)Related posts:
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