Viren Sunil Kalsekar, Joy Lee, Jenny Qiu, Nicholas Ragosta, Javier Ramos, David Taylor Massachusetts Institute of Technology Cambridge, MA, USA
ABSTRACT Endotracheal tubes (ETT), are used to maintain patient airway access during surgical procedures. The design presented here addresses a current need of the gold standard ETT by allowing for the passage of a larger bronchoscope through the inner lumen of the ETT while keeping outer dimensions constant. This design incorporates a flexible membrane with a wavy geometry to ensure a return to the neutral axis, thus allowing for even ventilation of both lungs. Flow tests simulating surgical ventilation conditions were conducted. These results confirmed that adequate air flow could be obtained independent of any pressure differences across the membrane. Tests of the prototype also confirmed that maximum instrumentation diameter was increased through this design when compared to a commercially available ETT with identical outer dimensions (35 Fr). Finite element analysis was conducted to determine the necessary thickness of the membrane for a safe design. One key design feature of the membrane is that its state of maximum deflection (2.1mm) does not significantly hinder airflow through the smaller lumen. Tests to further evaluate the functional requirements of safety and ease of use are currently under way. Methods of manufacturing this design are also under investigation. Keywords: endotracheal tube, flexible membrane, airway access, neutral axis INTRODUCTION Endotracheal tubes (ETT) are used to maintain patient airway access during surgical procedures. During thoracic surgery it is often necessary to ventilate the lungs separately. This allows one lung to be ventilated, while the other may be deflated.  Predicts the number of US thoracic surgeries in 2013 to be 38,500. Most of these surgeries use a double lumen endotracheal tube (DLT). The size of the DLT is selected for each patient based on their tracheal diameter; the outer diameter of the DLT must be small enough to fit in the patient, but large enough to have a small, easily sealed, gap between the tube and the trachea. During the procedure a bronchoscope is frequently used. It can serve as a guide along which the ETT is inserted down the trachea, it provides visual imaging to confirm correct positioning, and it can be used to remove large secretions. Larger bronchoscopes provide improved image resolution and suctioning.
Figure 1 shows a distribution of patients by tracheal size. A tracheal diameter of 14mm or less corresponds to a recommended DLT size of 35 French (Fr) . While using a 35Fr DLT, the use of a full-sized (4.9mm) bronchoscope is not possible . A tracheal size of 15-16mm corresponds to a recommended DLT size of 37Fr , which makes a full-sized bronchoscope very difficult to use . Impossible Population Hard Easy
Size of Trachea (mm)
Figure 1: Ability to use a full sized (4.9mm) bronchoscope, data based on [2, 3]
Using the patient statistics of  it was estimated that in 26% of patients require a 35Fr or 37Fr DLT and therefore during about 26% of thoracic surgeries full-sized bronchoscopes cannot be used. Using the surgery estimates of , this corresponds to an estimated 10,000 underserved patients per year. The modified double lumen ETT presented here aims to make the use of a full-sized bronchoscope possible even in patients who require a 35Fr sized-DLT. PROBLEM STATEMENT An estimated 10,000 patients per year require the use of a double lumen tube smaller than 39Fr, preventing the easy use of a full-sized bronchoscope. Current double lumen tubes are divided by a rigid wall which limits the size of instrument that can be inserted. To better serve these 10,000 patients per year, it was imperative to develop a new ETT that would allow the use of a full-sized bronchoscope in even the smallest...