Caloric irrigators: air, open-loop water and closed-loop water.

Abstract

Selective stimulation of the semicircular canal system of one ear by establishing a temperature gradient is still widely used in the clinic in the caloric test. The results obtained are noted for their imprecision and variability. This is, in part, due to a lack of uniformly applied standardized test protocols, as well as difficulties in applying a precise stimulus. The relative merit of the three types of irrigation are reviewed. Whilst some authors argue that both the closed-loop and air irrigators produce even more variability of response than open water systems, the present author believes that intratest replication studies indicate that the closed-loop irrigation stimulus is the least variable and best tolerated by the patient. In perhaps one-fifth of patients, response to the first irrigation is much stronger than subsequent stimulus applications. It is suggested that there may therefore be a case for routinely performing five irrigations in the bithermal caloric test, including a replication of the first irrigation. It is assumed that psychological factors, especially anxiety, may explain the phenomenon of enhanced initial response, and some of the variability of caloric test responses in general. Use of the closed-loop irrigator is advocated for ease of use, reduced routine maintenance and to minimize patient distress, thereby reducing anxiety and result variability.