In Reply:-The experience of Sinha and Dubey involving Carlen's double-lumen tube and stylet supports our view that shearing of the sheath over the stylet is likely to occur at the point of angulation. The force exerted at the proximal end of endotracheal tube during the withdrawal of the stylet is linear in direction. This linear force, while overcoming the curvature at the point of angulation, causes contact and friction between the endotracheal tube and the plastic sheath of the stylet. If this frictional force is greater than the tensile strength of the sheath, shearing occurs. Thin plastic sheath (smaller endotracheal tubes and stylets with thin sheaths are likely to be used together) and increased angulation create conditions ideal for shearing. If these conditions are reproduced in a relatively larger inner-diameter tube, as in the case of the double-lumen tube used by Sinha and Dubey, shearing can take place. We agree with the correspondents that the endotracheal tube stylets should be inspected after each use.
Mukul Bhargava, M.D.
Surya N. M. Pothula, M.D.
Suhasini Joshi, M.D.
Assistant Professors of Clinical; Anesthesiology; New York Medical College; Valhalla, New York;
(Accepted for publication August 31, 1998.)