Anesthesia Clerkship

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The Anesthesia rotation is a 10-day bit in the middle of your surgical subspecialty rotation. It is generally regarded as a pretty light rotation, as most students will find themselves finishing before noon on most days. It is also an excellent opportunity to get a lot of hands-on procedures including obtaining IV access, placing an arterial line and a central line (you will need to be proactive and ask your attending to see if they will let you try these, but most are receptive). However, the most important skill to master will be how to effectively administer bag-mask ventilation. The residents and staff are outstanding pretty much anywhere you are placed, so this will really be a “what you want to make of it” type of rotation. If you want to just get out early, you can probably do that. If you want to stick around and get extra procedures, there’s definitely the possibility to do that as well.

Your grade comes 90% from the exam at the end of the rotation, which is about 30 questions, home grown, almost exclusively from the study guide provided. The most important thing to study to do well on this rotation would be the study guide written by Dr. Emhardt. The study guide goes through various case scenarios and provides questions similar in content to what you will see on the exam. The other 10% is your clinical performance evaluation, which unless you really rub someone the wrong way, you will do well on.

Resources

Drug Review

IV Anesthetics

Propofol

  • Used often for induction due to rapid onset and recovery.
  • Can cause burning/stinging feeling when injected into small veins
  • SBP decreases
  • HR no change or decrease
  • Ventilation decreases (dose dependent)
  • Can decrease nausea and vomiting (n/v)

Barbiturates

*You don't need to know much about these, just know that thiopental belongs to this class.

  • Disadvantage: can have residual drug conc and effects hours after

infusion (rarely seen in doses used for induction)

  • SBP decreases / HR increases
  • Ventilation decreases

Etomidate

  • SBP unchanged or decreases
  • HR unchanged or decreases- may be used in pts with compromised myocardial contractility
  • Ventilation decreases
  • May cause adrenocortical suppression (via inhibition of 11 -beta-hydroxylase)

Ketamine

  • May cause "dissociative anesthesia" where pt eyes are open but analgesia,

amnesia is present.

  • SBP increases (only IV drug that increases SBP) acts like sympathetic stim
  • HR increases
  • No depression of ventilation
  • May have emergence delirium- visual, auditory, proprioceptive, and confusional illusions. May blunt this by pre-treatment with midazolam.
  • Remember this drug causes sympathetic stimulation: the bronchodilatation may be helpful in asthmatics, but the cardiac stimulation requires caution when using in pts with CAD

Benzos:

  • Includes midazolam, diazepam, lorazepam
  • Causes anterograde amnesia 
  • HR no change / SBP may decrease or no change
  • *minimal depression of ventilation
  • used perioperatively (esp in kids) for amnesia, calming and sedative effects

Opioids

Produce analgesia without loss of touch, proprioception, of consciousness. Basically, the pain is still there, but your threshold is raised to where you don't perceive it as pain. All can cause side effects including pruritus (this is why your pts wake up scratching their neck, face eyes etc), n/v, urinary retention, depression of ventilation.

  • Includes morphine, meperidine, fentanyl, sufentanil, alfentanil, and remifentanil,
  • Naloxone is the pharmacological antagonist (used to reverse overdose).

Morphine

  • This is the prototypical opiate
  • May cause orthostatic hypotension
  • SBP decreased due to histamine release

Fentanyl

  • 75-125 times more potent than morphine

Remifentanil

  • Structurally unique ester linkage. Susceptible to hydrolysis by plasma and tissue esterases.
  • Good to use for a short time, but tolerance will develop even with continuous infusion.

Local Anesthetics

Injected adjacent to nerve to produce reversible blockade of neural impulses. Progressive increases in concentration of drug can cause autonomic nervous system blockade, sensory anesthesia, and skeletal muscle paralysis. Usually reverses spontaneously and completely.

Includes:

  • esters (procaine, choloroprocaine, tetracaine, cocaine) [all contain 1 letter "i"]
  • amides (lidocaine, mepivacaine, bupivacaine, etidocaine, prilocaine, ropivacaine) [all contain 2 letter "i"]

Addition of epinephrine or phenylephrine to local anesthetic causes vasoconstriction which decreases systemic absorption, and increases duration of action (because the anesthetic stays near the nerve longer). DO NOT add epi or phenylephrine if local is to be used near fingers, toes, penis or nose. These areas may lack collateral blood flow distally. Additional contraindications include unstable angina, dysrhythmias, HTN, uteroplacental insufficiency, IV regional anesthesia.

Cocaine

  • Unique because it produces vascoconstriction and topical anesthesia, this can be beneficial during nasotracheal intubation (decrease nasal hemorrhage) and ENT and eye surgeries.

Toxicity:

  • CNS: increasing plasma concentrations have CNS manifestations including restlessness, vertigo, tinnitus, slurred speech, tonic clonic seizures. Treat seizures with diazepam.
  • CV: Bupivacine has potential for cardiotoxicity! (Pregnancy increases

sens to cardiotoxicity) Prilocaine

  • In high doses may cause accumulation of metabolite capable of converting hemoglobin to methemoglobin. Pt will appear cyanotic, blood will appear chocolate colored.

Toxicity:

  • NEURO: Cauda equina syndrome may occur with diffuse injury to lumbo-sacral plexus as with spinal anesthesia. Pt will have sensory anesthesia, bowel and bladder dysfunction, and paraplegia.         
  • ALLERGIC: True allergic rxns to locals are rare. Esters are more likely than amides to produce allergic reactions (due to PABA metabolite).

Neuromuscular Blockers

Depolarizing NMB

Succinylcholine (SCh)

This is the only depolarizing NMB used.

  • Advantages: rapid onset of skeletal muscle paralysis, which only lasts 5–10 minutes. Elimination due to hydrolysis by plasma cholinesterase (pseudocholinesterase). Used to facilitate tracheal intubation.
  • Disadvantages: Never give SCh to burn victims, anyone who has skeletal muscle denervation (paraplegics, quadriplegics, DMD, BMD) because they may get hyperkalemic.

The greatest disadvantage is the potential of malignant hyperthermia (tx with dantrolene).

  • Other side effects include cardiac dysrhythmias, myoglobinuria, increased intraocular pressure, increased intragastric pressure, allergic rxn, trismus.
  • Remember there is a period of fasciculations that can lead to muscle soreness afterwards. This can be minimized by using a small "defasciculating" dose of a non-depolarizing NMB, some anesthesiologists still don't use SCh in young people because of their muscle mass and potential for myalgia. 
  • Also potential for young males to have unrecognized muscular dystrophy and they go into cardiac arrest.
  • Atypical pseudocholinesterase cannot hydrolyze ester bonds in SCh, then the skeletal muscle paralysis effects of SCh are prolonged (> 1 hr). Unfortunately you don't know who has atypical pseudocholinesterase until you've given the SCh.

Nondepolarizing NMB

  • Long acting: Pancuronium (60-90 min)
    • Pancuronium side effects = increased HR and CO (caution in pt w/ CAD)
  • Intermediate acting: Vecuronium, Rocuronium, Atracurium, Cisatracurium
    • Atracurium: clearance by Hoffmann elimination (spontaneous nonenzymatic degradation at norm body temp and pH) and ester hydrolysis. Therefore good in pts with renal or hepatic failure. Can cause transient increases in plasma histamine concentrations (parallel transient increases in HR, and BP decrease).
    • Cisatracurium: isolated from 1 of 10 stereoisomers of atracurium, so also undergoes Hoffmann Elimination, but not hydrolyzed by plasma esterases. Also safe in hepatic or renal failure pts. No histamine release.
  • Short Acting: Mivacurium, Rapacuronium
    • Rapacuronium: rapid onset most comparable to SCh. "histamine related phenomena" may occur at high doses.
    • Mivacurium: duration is increased in pts with atypical pseudochonnesterase. Rapid administration can cause histamine release.