Chapter 18. Intra-articular and Periarticular Infiltration of Local Anesthetics
Intra-articular injection for postoperative analgesia is best comprised of what type of local anesthetic mixture?
A. High volume, high concentration
B. High volume, low concentration
C. Low volume, high concentration
D. Low volume, low concentration
B is correct. A high volume of injectate is necessary due to the many structures and layers that must be infiltrated. This necessitates a low concentration of local anesthetic to avoid administration of a toxic dose of local anesthetic.
A, C, and D are incorrect. All of the other answer choices involve administration of toxic doses of local anesthetic (A) or inadequate coverage of structures (C, D).
All of the following characteristics of local infiltration analgesia contribute to the safety of the technique except:
A. Use of large volume of local anesthetic
B. Use of dilute local anesthetic concentrations
C. Absence of major blood vessels in articular structures
D. Use of vasoconstricting adjuvants
A is correct. The use of large volume of local anesthetic does not contribute to the safety of the technique. One of the problems with local infiltration analgesia is that many structures and layers must be infiltrated, requiring a large volume of local anesthetic, putting the patient at potential risk for local anesthetic toxicity.
B is incorrect. Use of dilute local anesthetic allows for a large volume of local to be infiltrated without risking delivering a toxic dose of local anesthetic.
C is incorrect. Absence of major blood vessels in articular structures prevents systemic uptake of local anesthetic that can occur with peripheral blockade of nerves that often run with vascular structures.
D is incorrect. Use of vasoconstricting adjuvants, specifically epinephrine, is often added to large volume infiltration solutions to prolong their local action and prevent systemic uptake.
Why is the chondrotoxic effect of bupivacaine not a concern when using it for local infiltration analgesia after a total knee replacement?
A. Toxicity is seen only after prolonged infusions.
B. Adding epinephrine to the bupivacaine mitigates the toxicity.
C. Injecting with a short-bevel needle prevents the associated cartilage damage.
D. All cartilage is removed from the joint during surgery.