C.E. Mutty replies:
The first and most pointed question raised by Mr. Rogers and Mr. Rang is whether we should be doing nerve blocks at all in patients with an acute lower-extremity injury. The risk-benefit ratio of the use of a femoral nerve block to manage pain caused by a femoral fracture was carefully examined prior to the start of our study. Trauma patients in the emergency department are in a unique category. These patients often have severe, multiple injuries. To adequately manage the pain of a fractured femur would require a level of intravenous opioid analgesia that could alter subtle clues to the trauma team that additional, potentially life-threatening conditions could be present or developing. Perhaps an improved protocol for systemic analgesia that does not diminish the trauma team's ability to monitor the patient can be designed.
In the meantime, we should evaluate all of the tools currently available for improving the inadequate management of fracture-related pain. The femoral nerve block has shown itself to be a very effective method for controlling pain related to a femoral fracture. Use of the block does require an increased awareness of the development of compartment syndrome and, as stated in the article, we do not recommend use of the block in patients at increased risk for this complication. Twenty-one of the thirty-one patients in the study who received the block had sustained the fracture through a high-energy mechanism (most commonly a motor-vehicle accident). These fractures were AO-OTA type 32 (diaphyseal) or 33 (distal). The majority of the diaphyseal fractures were subtype A (simple) or B (wedge), but there were several subtype-C (complex) patterns. The distal fractures were either subtype A (extra- articular) or C (complete articular), and some degree of comminution was present in both subtypes. No compartment syndromes developed, and all patients were followed around the clock by orthopaedic house staff. While the fracture pattern is important in that it helps to indicate the degree of energy imparted to the soft tissues, it appears that it should not be the sole determinant of which patients are appropriate candidates for the block.
We used a threshold minimum nerve stimulation current of 0.8 mA to produce a quadriceps muscle twitch. Experience demonstrated that this current level provided a reliable patellar twitch. As suggested by Mr. Rogers and Mr. Rang, optimizing needle placement by adjusting the current downward to <0.5 mA while maintaining a patellar twitch may have resulted in improved pain scores in the few patients who received the block but continued to report high pain levels. Ultrasound is being increasingly used for nerve localization in patients receiving peripheral nerve blocks and is available in our emergency department. The peripheral nerve stimulator technique for nerve localization was quickly mastered by the orthopaedic house staff and could be performed efficiently in the trauma setting. However, as more experience is gained with ultrasound techniques, its use for this indication will be evaluated and the results will be compared with those achieved with the stimulator technique.
While cardiotoxicity has not been reported with the use of our femoral nerve block protocol, this remains a concern as there is a risk of intravascular injection with improper technique. Levobupivacaine and ropivacaine are prepared in an almost pure L-isomer form, whereas bupivacaine is a racemic mixture of the D and L isomers. Levobupivacaine and ropivacaine reportedly have less cardiotoxicity than bupivacaine because they contain almost none of the D-isomer form. Levobupivacaine is five times more expensive and ropivacaine is eight times more expensive than bupivacaine1. The real-world difference in cost is approximately $10 for our application, and I agree that either of these agents is probably a better choice given their improved side-effect profile.
Finally, the importance of explaining the risks and benefits of any procedure cannot be overstated. Obtaining informed consent in the acute trauma setting is a major challenge, but it must be done appropriately before proceeding with any intervention.
These letters originally appeared, in slightly different form, on . They are still available on the web site in conjunction with the article to which they refer.