Why Anesthetics Aren't Effective for Long Cases

A DOCS Education member has been using the same anesthetics successfully for years. But recently two four to six hour restoration cases have required more anesthetic than usual and the clinician hasn't been able to do the final adjustments. DOCS Education faculty members, and another doctor member, weigh in.

A DOCS Education Member inquires:

I am on a recent streak of long cases that I have had difficulty keeping patients numb. These are all NON sedation cases and all ASA I. Both cases required significant carpules of anesthetic over a four to six hour period of time; by the end of each session I was unable to do any final adjustments that required any air or water. Both were full arch restorative cases bonding porcelain restorations. Although we were able to comfortably remove the temps, within an hour and a half the patients needed some level of reinjection. Each time we administered local anesthetic it appeared as if the patient would metabolize it faster until it was no longer effective.

One case was a mandibular case which we did bilateral blocks with both mepivacaine and lidocaine 1/100 with Septocaine® infiltrations and long buccals as needed. We used the same anesthetics for the maxillary case.

I have done many of these cases with the same anesthetics over the years without much incidence. I've never needed to go to bupivacaine and because of that I had none in the office. Expiration dates were all current.

Suggestions?

Dr. Jerome Wellbrock, DOCS Education faculty member, responds:

I have had great success with Septocaine 4% with 1:100,000 Epi. If I need longer anesthesia, I would consider Marcaine®. You may find greater success with your local anesthetic if you are sedating the patient, even if dental fear or anxiety is not an issue; you will have a far more comfortable patient who will react less to any invasive procedures.

The member follows up:

What is the physiologic reaction that is occurring preventing the patient from being anesthetized after having success the first two hours and then ultimately metabolizing it so quickly it is ineffective?

Dr. Jerome Wellbrock, DOCS Education faculty member, responds:

Obviously, every patient is different. I can only guess that the vasoconstriction of the blood vessels began to wear off and the local anesthetic was more rapidly absorbed into the circulation. Hence, the anesthetic effect rapidly faded.

Another member responds:

My initial thought is, that's a long time (I think you said four to six hours) to ask a person to sit in the chair without OCS. In my experience, it's much easier and more predictable to keep patients numb when they're sedated and relaxed. My personal "time limit" for using OCS is any procedure that will take three hours or more. It's so much less stressful on everyone—especially me!

Dr. Anthony S. Feck, DOCS Education Dean of Faculty, responds:

The loss of efficacy of the medication is most likely occurring as a result of the vasoconstrictor wearing off, and the medication being carried away from the local area. Higher volumes of local anesthetic and vasoconstrictor, along with local anesthetics that last longer will give you longer duration of action. Reinjecting local anesthetic doesn't work as well as the tissue injury from previous injections causes a lower pH environment that makes the local anesthetic not as effective.

Patients who are a challenge to numb and/or keep numb for longer appointments are best off being sedated.