Mannitol enhances IAN effectiveness

Adding mannitol increases the effectiveness of inferior alveolar nerve (IAN) block anesthesia, according to a new study in Anesthesia Progress (Winter 2011, Vol. 58:4, pp. 157-165).

The most commonly used local anesthetic injection for lower teeth is IAN block. However, failure rates ranging from 10% to 39% have been reported, noted the study authors, from Ohio State University.

They tested the efficacy of adding a solution of mannitol -- a sugar alcohol that occurs naturally in fruits and vegetables and is quickly excreted by the kidneys -- to the anesthetic typically used in IAN blocks.

The researchers compared the effectiveness of the standard anesthetic, lidocaine with epinephrine, with the effectiveness of two different volumes of lidocaine with epinephrine plus 0.5 M mannitol.

Forty adult subjects participated in the study, receiving an IAN block at each of three appointments that were at least one week apart. After injections of the IAN block solutions, patients' pain levels were measured by an electric pulp test of their mandibular teeth at four-minute intervals for 60 minutes.

"Adding 0.5 M mannitol to lidocaine with epinephrine formulations significantly improved effectiveness in achieving a greater percentage of total pulpal anesthesia compared with a lidocaine formulation without mannitol for IAN block," the study authors wrote.

Though its impact is short-lived, mannitol has the positive effect of opening the perineurial membrane. In cases of IAN block failure, it is believed that the perineurial barrier around the nerve does not allow complete diffusion of the anesthetic into the nerve trunk. The addition of mannitol apparently allows enhanced permeability, increasing the success of an IAN block when administered concurrently, according to the researchers.