Local Anesthetics

Anesthesia, Chapter 15

1. List the local anesthetics (LA's) that are esters. Where/how are they metabolized?

2. List the LA's that are amides. Where/how are they metabolized?

3. You are asked to place an epidural for an arthroscopy. The surgeons are in a huge hurry to get started. Your plan, prior to seeing the patient, is to use chloroprocaine in an effort to speed the onset of your anesthetic. When you preop the patient, he mentions that he hurt himself water skiing in Florida. You notice a resolving rash over the sun-exposed portion of his body and ask him in passing about its origin. He indicates that he believes a sunscreen he was using caused him to break out. Will you alter your anesthetic plan? If so, how?

4. True or false? Hydrophobicity is a primary determinant of potency of LA's in vivo.

5. Which of the following has the greatest lipid solubility at physiologic pH?

• Mepivacaine
• Lidocaine
• Bupivacaine
• Tetracaine
• Etidocaine

6. True or false? Local anesthetics primarily have their effect by specifically inhibiting currents through voltage-activated Na+ channels.

7. Each of the following is true except:

• The amount of LA deposited near a nerve that actually penetrates the nerve depends on tissue binding, removal by the circulation, and local hydrolysis of aminoesters.
• Potent, long-acting hydrophobic agents are more protein bound than more hydrophilic agents.
• LA's diffuse across the nerve sheath and membrane in the base form, but act on receptors in the cationic form.
• The rates of LA onset and recovery are governed by the rate of drug binding to and dissociating from ion channels.
• Binding of LA to sites on voltage-gated Na+ channels prevents opening of the channels by inhibiting conformational changes.
  
  

Local Anesthetics

8. Which LA will exist with the greatest proportion in the ionized (cationic) form at physiologic pH?

• Etidocaine e) Chloroprocaine
• Mepivicaine f) Lidocaine
• Tetracaine g) Bupivacaine
• Prilocaine h) Procaine

9. Each of the following is true except:

• Differential nerve block is a result of inversely proportional susceptibility of nerve fibers with respect to their diameter.
• In vivo, the concentration of a LA plays a major role in its onset.
• The duration of action of a LA in vivo is significantly influenced by the LA's inherent vascular effects.
• Local infiltration of an infected area may result in delayed or inadequate anesthesia.
• All LA's (except cocaine) have a biphasic effect on vascular smooth muscle: at low concentrations they cause vasoconstriction, and at clinical concentrations they cause vasodilation.

10. You are asked to provide anesthesia for an arthroscopy. The surgeon requests an epidural with a differential block so that she can observe the dynamics of the patient's knee mechanics. What agent will you use? What concentration?

11. The highest peak serum LA concentration would occur after injection via:

• Intercostal > brachial plexus > lumbar epidural > subcutaneous
• Intercostal > lumbar epidural > subcutaneous > brachial plexus
• Lumbar epidural > intercostal > brachial plexus > subcutaneous
• Intercostal > lumbar epidural > brachial plexus > subcutaneous
• Subcutaneous > brachial plexus > lumbar epidural > intercostal

12. Epinephrine significantly prolongs duration of anesthesia with all of the following except:

• Lidocaine
• Tetracaine
• Etidocaine
• Prilocaine
• Bupivacaine

13. True or false? Addition of epinephrine may deepen and prolong epidural blockade when using low concentrations ( < 0.25%) of bupivacaine.

Local Anesthetics

14. You are placing a labor epidural at HCMC. The patient has greeted you at the door by calmly indicating "I don't care about anything. Just give me my damn epidural." What options are available to accelerate the onset of the block and restore her composure?

15. It has been suggested that 1 - 1.5 cc of LA should be administered per spinal segment to achieve a desired level of anesthesia. Assume the patient in #14 has developed arrested labor and is demanding a C-section. Would you expect to use more, less, or the recommended dose to provide a given level when compared to a similar, non-pregnant patient?

16. Assume the patient in #14 needs an emergent C-section for fetal distress. Will you use epinephrine as a component of your anesthetic agent? Why/why not?

17. Each of the following is acceptable for use in a Bier block except:

• 0.5% lidocaine
• 0.5% mepivacaine
• 0.5% procaine
• 0.5% prilocaine
• 0.25% bupivacaine

18. You are planning a brachial plexus block for an upper extremity case. The surgeons are in a hurry to get started and indicate that the case will be quick. Your experience suggests that the term "quick" is metaphorical, so you intend to use an agent that will have a long duration. You are also interested in rapid onset since your tolerance for surgical whining is low today. What agent(s) will you use and why?

19. In your haste to move the case in #18 along, you neglect to aspirate prior to injecting LA. The patient complains of tingling lips and numbness of tongue. List other symptoms and signs of CNS toxicity for which you would be immediately watchful.

20. You are on call in the SICU and are hurriedly placing a PA catheter in a preop tune patient, fully mindful that time spent doing this is time away from the platoon of ultra-sickies you're responsible for tonight. You prep the neck and inject 3cc of 2% lidocaine with a 1.5 inch 21 guage needle. The patient promptly seizes. Can you suggest a possible explanation?

21. You are (still) PAR dog and are summoned to a code called by the pulmonologists. Upon your arrival the patient is unresponsive and not breathing. You deftly take control of the airway and learn that things were going well with bronchoscopy until the patient appeared to have a seizure. They are puzzled because the patient has no seizure history, was oxygenating and ventilating well just before his seizure, and had received only versed 2 mg IV and topical 4% lidocaine for his bronchoscopy. What can you add to your colleagues' differential regarding why this patient may have seized and gone on to respiratory arrest?

22. Why is bupivacaine significantly more cardiotoxic than lidocaine?

23. List the thresholds for CNS symptoms in humans for the following:

• Procaine
• Chloroprocaine
• Tetracaine
• Lidocaine
• Mepivicaine
• Prilocaine
• Bupivacaine
• Etidocaine

24. Matching

• Methemoglobinemia
• Procaine
• Bupivacaine
• Chloroprocaine
• Sodium metabisulfite
• Prilocaine

• May cause neurotoxicity
• May cause severe cardiac arrhythmias, including ventricular fibrillation
• May cause re-entrant arrhythmias similar to torsades des pointes
• Blood level producing circulatory collapse may be decreased in pregnancy
• Lowest systemic toxicity on a mg/kg basis.
• May cause cyanosis at total doses greater than 500 mg
• Responds to treatment with methylene blue when caused by local agent
• Primary site of metabolism is serum.