Place the Bubble Solution with Your Fingertip

To The Editor: We have previously described a “soap bubble” drain tube (DT) test utilizing children’s bubble solution to create a soap membrane on the DT port (1). This method is a useful aid when learning to use the ProSeal™ laryngeal mask airway (PLMA) and is also a valuable technique for routinely monitoring safe PLMA usage. The bubble test can verify that there is zero leak at the PLMA/esophageal seal (1), confirm PLMA location behind the cricoid cartilage (2), detect negative DT pressure and aerophagia with spontaneous ventilation (3), and diagnose potentially dangerous esophageal insufflation during positive pressure ventilation (4). Our original demonstration of the bubble DT test utilized the tennis-racket shaped wand that is supplied within the bottle (1). This method is not optimal because repeated use of the same tennis-racket device with different patients is not aseptic. We now use a simple method shown in Figure 1. A small amount of bubble solution is dispensed into a small cap. The anesthesiologist puts on a new examining glove and wets a fingertip with the solution in the cap. Simply touching the DT port with this fingertip quickly creates a membrane.Figure 1: Bubble solution is dispensed into a small cap. A fingertip is then wetted with the solution within the cap. Touching the drain tube port quickly creates a soap membrane.Use of the fingertip application method allows the anesthesiologist to easily perform DT tests on multiple occasions during a single anesthetic. It is a very neat method (no dripping) and it is aseptic. It is easily performed when signing a case over to a colleague, for confirming PLMA position (2) and verifying zero DT leak with positive pressure ventilation (1). Finally, this is a simple way to perform the bubble test if it is used as part of a research protocol. The bubble method is a logical extension from the DT tests that have been previously published (5–7). The PLMA instruction manual recommends placing 1–2 mL of gel within the DT (5). Drs. Brain, Verghese, and Strube recommend placing 0.5–1 mL within the DT (6). Drs. Brimacombe, Keller and Berry recommend observing the gel meniscus (7). The bubble DT test can be considered an infinitesimally thin version of these published methods. Cornelius J. O’Connor Jr.,, MD Michael S. Stix, MD, PhD