Curved rigid laryngoscope: missing link between direct suspension laryngoscopy and indirect techniques?

Microlaryngoscopy is the standard procedure for endolaryngeal surgery. The advantages are a steady operating field, bimanual handling and stereoscopic view in high-resolution magnification. The major drawback is that the oropharyngeal structures have to be brought into an unnatural position by the straight rigid laryngoscope with considerable forces occurring. These forces can lead to tissue injuries or even make a microlaryngoscopic operation impossible. To overcome these disadvantages, a few case studies using curved rigid laryngoscopes are published. However, there is still a lack of information to what extent curved rigid laryngoscopes could actually improve the endolaryngeal exposure with less forces occurring. It was the aim of this study to gain basic data on the forces that are needed for endolaryngeal exposure with a prototype of a curved rigid laryngoscope and to compare the occurring forces with straight laryngoscopes. In 30 consecutive patients scheduled for routine microlaryngoscopic procedures the curved laryngoscope was inserted and occurring forces were measured by a tension spring balance in four different head positions. A standard straight laryngoscope was inserted afterwards and measurements were taken again. Our results showed that the occurring forces could be reduced significantly in each head position when compared with a standard straight laryngoscope. Similarly, the anterior commissure could be exposed in a significantly higher percentage with the curved laryngoscope. In conclusion, we could show that even with a moderate-curved rigid laryngoscope a significant reduction of the forces to the oro-pharyngeal tissues can be obtained and that endolaryngeal exposure is possible in virtually all patients. Bimanual precise operations should be possible in the common way like in standard microlaryngoscopy with the only difference of not using a microscope, but operating via a monitor. We do not think that traditional microlaryngoscopy with straight instruments can or should be replaced by curved laryngoscopes, but these techniques could bridge the gap to indirect techniques in particular in specialised institutions dealing frequently with difficult patients and situations.