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Excerpt
We thank Dr. Koscielniak-Nielsen for his interest in our case report describing anxiety, vocalization, and agitation following peripheral nerve block with ropivacaine.1 We wish to apologize for not previously acknowledging Dr. Koscielniak-Nielsen's case report2 in our recent manuscript. Dr. Koscielniak-Nielsen raises several concerns regarding our report. He notes that mepivacaine with epinephrine can cause similar symptoms of “anxiety, agitation, and loss of consciousness” as we observed with ropivacaine. Second, he questions how the recommended doses of ropivacaine with epinephrine used in our three cases could result in toxic levels. In addition, he believes that any local anesthetic containing epinephrine injected intravascularly will result in the described symptom profile. Dr. Koscielniak-Nielsen also questions our use of epinephrine for peripheral nerve block with ropivacaine.
In the discussion of our case report, we previously emphasized that local anesthetics other than ropivacaine can cause unusual central nervous system (CNS) symptoms such as euphoria and aggressive behavior if injected intravascularly. We also stated that epinephrine itself, if injected intravascularly, can cause patient apprehension and anxiety and thus explain part of the observed symptomatology. In addition, we also noted that it is possible to have a successful block and still unintentionally inject part of the local anesthetic solution into the systemic system.
We don't agree with Dr. Koscielniak-Nielsen that toxic levels of ropivacaine were unlikely to be reached in any of our patients. In fact, all evidence supports the contrary conclusion. It is certainly possible to achieve toxic local anesthetic concentrations even with recommended dosages. This may occur, for example, from an intra-arterial injection. Direct intra-arterial injections, for example during interscalene block, require much smaller amounts of local anesthetic to produce CNS symptoms. It should be noted that patient #2 eventually became completely unresponsive and patient #3 developed clonic movements. These are classic symptoms of local anesthetic toxicity and cannot be attributed to epinephrine.
Our three cases differ from the one described in Dr. Koscielniak-Nielsen's report because they involved the use of long-acting amide local anesthetics. CNS symptoms as described in our report to our knowledge have not been described before with a long-acting amide local anesthetic. We would like to emphasize that we do not “blame” ropivacaine or necessarily believe it is a “culprit” as Dr. Koscielniak-Nielsen suggests. Rather, we believe it may act differently than other long-acting amide local anesthetics. We can only speculate that the unique Senantiomer may confer less CNS toxicity (a broader safety/toxicity profile) and, hence, demonstrate symptoms that are clinically similar to lidocaine or mepivacaine.
The addition of epinephrine to local anesthetics is standard care at our institution when performing peripheral nerve blocks. We are certainly aware that the addition of epinephrine does not significantly alter the pharmacokinetic profile of ropivacaine. However, we use it because it functions as an intravascular marker.
