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UW-Madison BME 200 - Endotracheal Tube Cuff Pressure Indicator

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Endotracheal Tube Cuff Pressure Indicator Michael Alexander, Team Leader Samantha Bergh, Communications Claire Edlebeck, BWIG Tyler Lark, BSAC Lucas Vitzthum, Graphics BME 200/300 Department of Biomedical Engineering University of Wisconsin-Madison October 25, 2006 Client Lester Proctor, M.D Department of Anesthesiology, UW-Hospital Advisor Krystin Masters, Ph.D, Professor Department of Biomedical Engineering2 Abstract Endotracheal intubation is required for most invasive surgeries. The current tubes used in adults have a cuff attached at the end of the tube that when inflated, creates an air tight seal inside the trachea to prevent aspiration. However, this cuff system is not suitable for pediatric intubations since it can cause injury and scarring to the tissue of the trachea if over inflated. The goal of the new design is to modify the existing tube-cuff-valve system to indicate, for the purposes of regulation, pressure in the cuff so that it may be safely utilized in pediatric cases.3 Table of Contents Page Abstract 2 Table of Contents 3 Problem Statement 4 Background Information 4 Current Devices 6 Design Constraints 6 Design 1: Electrical 7 Design 2: Mechanical 9 Design 3: Relief Valve 12 Design Matrix 13 Future Work 15 References 17 Appendix A: Current Patents 18 Appendix B: Project Design Specifications 204 Problem Statement Our client, Dr. Lester Proctor, has charged us with the task of designing an endotracheal tube cuff system that would indicate the cuff pressure for purposes of regulation. Dr. Proctor is a practicing anesthesiologist and professor working in the University of Wisconsin hospitals. One of the duties he must perform is the intubation of patients undergoing invasive surgical procedures. Normally, he uses a cuffed endotracheal tube for the intubation, but for all the advantages the cuff provides there are several risks associated with it that make it unsafe for use with pediatrics. The smaller diameter endotracheal tube used in pediatric cases traditionally does not even have a cuff at its end. Accordingly, Dr. Proctor would like us to design an endotracheal tube that is also cuffed so in future procedures the child will benefit from all the advantages of a cuffed tube, without the possibility of harm due to excess cuff pressure. Background Information Every year the UW hospital system performs upwards of 20,000 operations. 25% of those procedures are on children over the age of five, and 75% of those children are intubated using an uncuffed endotracheal tube (Proctor, 2006). When an adult patient is intubated, a cuffed endotracheal tube is used. In this process, a plastic tube is inserted into the patient’s trachea, past the larynx (Figure 1), where it will serve to provide oxygen and other various medical gasses to the anesthetized patient. A cuff at the posterior end of the endotracheal tube is then inflated with air. The cuff is a simple balloon that encircles the end of the endotracheal tube which, when inflated, pushes against the tracheal wall. This provides several advantages to the doctors and patients. First, it5 anchors the endotracheal tube in the trachea. This is important in the progression of the surgery, so that the tube does not become accidentally dislodged. Second, the cuff creates an airtight seal between the respiratory machine and the lungs. The seal allows for more accurate delivery of oxygen at lower pressures, as well as prevents pollution of the air from medical gasses. Finally, the cuff prevents patient aspiration. Aspiration occurs when foreign matter, be it bacteria laden mucous or vomit, enters the lungs (Spray et al., 1976). Normally, the foreign matter would be dispelled from the lungs via an involuntary reflex, usually coughing, but the anesthetized patient is unable to cough due to the various paralyzing agents used in surgery. Foreign matter that remains in the lungs for an extended period of time can ultimately cause infection and pneumonia. Adults receiving mechanical ventilation have an incidence of Ventilator Associated Pneumonia of up to 60% with an attributed death rate of 27% (Fagon et al., 1993). The cuff is inflated with air via a one-way valve attached to the cuff through a separate tube that runs the length of the endotracheal tube. A syringe is inserted into the valve and depressed until a suitable intracuff pressure is reached. Sengupta et al., (2004) has shown that cuff pressure is highly variable among patients. 27% of their sample population had endotracheal tube cuffs inflated past 40 centimeters H2O. Overinflation of Figure 1: Endotracheal Tube Placement [Source: http://connection.lww.com/]6 the cuff past the optimal range of 20 – 30 centimeters H2O is associated with the risk of Ischemia in the trachea. Ischemia is a shortage of blood supply to an organ or tissue (Wikipedia, 2006), in this case due to pressure exerted on blood vessels in the tracheal wall. Extended shortages of blood supply can lead to necrosis in the area, scarring, and even closure of the trachea. Children are particularly susceptible to ischemia, which is why anesthesiologists use the uncuffed endotracheal tube. Current Devices Several patents with ideas for intracuff pressure-regulating systems exist as well, although none have been seriously marketed. Most of the patented ideas consist of designs that include either bulky, expensive, electronic components or non-disposable components. The goal of this semester’s project is to produce a working prototype that is inexpensive, and easy to use. (A summary of current patents can be found in Appendix A.) Currently one product exists on the market with a pressure-regulating system designed for the endotracheal tube cuff. This is the Hi-Lo® Tracheal Tube With Lanz® Pressure Regulating Valve. It is not suitable for use in pediatrics, however. Design Constraints This semester’s design must adhere to several requirements that have been specified by the client. Singularly most important among the design specification is that any modification cannot negatively impact the performance of the existing endotracheal tube. FDA approval for use in human pediatrics is required in order to


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UW-Madison BME 200 - Endotracheal Tube Cuff Pressure Indicator

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