Topic Discussion: OUCH!! Should Anesthesia Hurt??

“It will burn for a few seconds, then become numb…” Sound familiar? That’s how I describe the local infiltration of lidocaine to patients. In order to decrease the pain associated with the administration of lidocaine, our interventional radiology department has taught nephrologists to use lidocaine buffered with sodium bicarbonate (1 part NaHCO3 for 9 parts lidocaine) during local anesthesia in preparation for ultrasound guided kidney biopsies. A quick literature search reveals much support for this technique. One hypothesis is that the buffered solution has less protonated molecules which are lipophilic and can more readily enter the myelin sheath resulting in a more rapid onset of action. A second idea is that the buffered solution has less associated discomfort simply because it has a more physiologic pH.

On the other hand, one study showed that the administration rate of lidocaine may have more influence on the perceived pain associated with injection than does buffering. Slow, unbuffered injections were associated with less perceived pain than rapid, buffered injections. (http://www.annemergmed.com/article/S0196-0644(98)70278-1/abstract)