Ultrasound view of the groin area at the level of the inguinal crease
Figure 59.1 image is obtained from a patient (80yo M, 60 kg) in the PACU after a repeat femoral peripheral nerve block for postoperative pain of a knee arthroplasty. The patient received a total of 30 cc of 0.5% bupivacaine and 20 cc of 0.5% ropivacaine. Patient is complaining of persistent pain in the area of the surgery.
What are the structures labeled a, b, and c?
What are the possible causes of persistent postoperative pain?
Would you repeat the block?
If the patient develops seizures how would you treat him?
If the patient develops hypotension and asystole how would you treat him?
What other options are available to treat this patient’s pain?
a, femoral vein; b, femoral artery; c, femoral nerve.
Persistent pain might be due to:
Inadequate distribution of the local anesthetic in the correct plane, possibly due to difficult and distorted anatomy after multiple attempts
Lack of coverage of the sciatic nerve area on the back of the knee or the obturator nerve on the medial aspect of the thigh
This patient has received a large amount of local anesthetic after the two attempts; a repeat one is inadvisable as we are over the maximum safe dose for local anesthetic.
In this patient, the maximum safe dose of ropivacaine (3.5 mg/kg) is 280 mg and bupivacaine (2 mg/kg) is 160 mg.
In the case of combined local anesthetics, the proportional maximum dose of each agent should be calculated, and the sum should not exceed 100%.
This patient has received 100 mg of ropivacaine and 150 mg of bupivacaine.
The proportion of the maximum safe dose per agent is calculated as follows:
In this patient the proportion for each agent is calculated as follows: