Endotracheal Tube Position Monitoring DeviceKeith Duran, Byron Hsu, Brandon Pierquet,Warit Wichakool, Rob Sheridan, and Hongshen MaAbstract— We have developed an accurate, economical, andportable device that helps to locate the position of an en-dotracheal tube (ETT). The device uses an grid array ofmagnetic field sensors to detect an anomaly in magnetic fieldcaused by embedded near the top of an ETT and outputs anintuitive color map of relative magnetic field intensity underthe sensor area. The device provides real-time feedback ofETT position to the clinician, so that corrective measures couldbe taken if the ETT is displaced beyond its normal positionwith respect to the patient body. The device is also equippedwith wireless communications to enable continuous monitoringand automated notification of hospital staff when a potentialproblem is detected.I. INTRODUCTIONThe endotracheal tube (ETT) is a staple of hospital pro-cedures, used to keep the airway of patients open duringanesthesia and many surgical procedures. It is inserted toa specific depth in the trachea through either the mouth ornose, or through an incision in the neck. Properly placingthis tube requires a high level of skill and training, and tubesmisplaced into the esophagus are responsible for numerouscases of mortality and morbidity. Even a proper insertioncan result in later complications, as ETT tubes can becomedisplaced by sudden movements, or the tubes can graduallymigrate over time. Improper position of the ETT can causeserious damage to the patient. As a result, there is a need fora reliable method or device for doctors and nurses to monitorand ensure the position of the ETT for a hours or days.Since there are no simple ways to prevent tube migration,the medical staff must take active measures to prevent tube-loss, which may lead to patient mortality or morbidity. Theusual approach is regular visual inspections of the ETT’sposition. However, due the high pliability of the tube insidethe air passages, a problem may not be externally visible.An X-ray examination can determine the tube’s position,but radiography is time consuming, expensive, and exposesthe patient to unnecessary radiation. Despite these drawbacks, radiography remains the most relied-upon approachfor detecting ETT migration.Few methods for monitoring tube position have been in-vestigated to tackle this problem. An acoustic reflectrometrymethod processes the reflection of the transmitted wave todetermine the location of the tube inside the body [1]–[3]. With this method, the signal processing become muchmore challenging if there is a kink along the tube. A muchmore complex method uses an ultrasonic wave to detectthe location of the ETT [4], [5]. Another technique is tomonitor pulmonary compliance and airway pressures andinfer the position of the ETT [6]. This method requires acomplex supporting systems and may not be as accurateas other methods. A carbondioxide-based device has alsobeen investigated [7]. This device only assists the intubationprocedure but has not been tested for the monitoring purpose.Another ETT position detection includes the use of mag-netic field detection scheme. One method detects the changein the mutual inductance of the sensing device and themagnetic material embedded along the ETT [8], [9]. Amagnetic sensor device has also be developed using a singleHall-effect sensor and two magnet attached to the ETT [10].Above devices use only single magnetic field sensor whichmay be inaccurate for patients with different size.To further improve the accuracy, flexibility, and usability,we have developed another type of magnetic-based ETTposition sensor using a two-dimensional array of magneticsensors with an LCD screen to provide a real-time feedbackfor the user of the current position of the magnet marker ofembedded in the ETT. The location of the sensor is criticalin order for the detection algorithm to work consistently.Our device overcomes this problem by giving the clinician apixelated image of the local magnetic field in two dimentions,which enables detection of the magnetic marker in threedimensions.II. THEORY OF OPERATIONThe Magnetic EndoTracheal Tube Imaging Device (MET-TID) utilizes an array of Giant Magneto-resistance (GMR)sensors to locate the position of a tiny magnet installedpermanently into the ETT, near the sternal notch. As thedevice is moved along the respiratory system, the LCDscreen shows the current magnetic field readings form thesensor array. The region where the magnetic field is strongerwill turn redder so that the user can intuitively interpret thatthe magnet is in the direction of the region with the colorwith warmer tone as shown in Fig. 1.III. SYSTEM DESCRIPTIONA. System architectureThe detection system consists of three main components:a magnetic sensing analog circuit, a micro-controller unit(MCU), and a display unit. The analog circuit amplifiesthe sensor signal and provide signal conditioning methodsappropriate for further signal processing steps. The MCUsamples the signal and processes that data appropriatelyfor the user interface unit. In this case, the output is theLCD screen showing the relative strength of the magnetusing an intuitive color scheme. In addition, the systemcan be configured to transmit data wirelessly to a patientHighLow(a)MagnetMagnetic sensor(b)Fig. 1: LCD color map output example. Hong suggests wemove this figure to Theory of operationsFig. 2: METTID system architecturemonitoring system. This data can be used to warn about thetube migration and to lower the risk of re-intubation or othercomplication. The system architecture is showed in Fig. 2.B. Magnetic sensorThe proposed device uses Giant Magnetoresistive (GMR)to sense a magnetic field created by a small, embeddedmagnet in the modified ETT. A GMR sensor is more sensitivethan a Hall-effect sensor. The module AAH-002 from NVEcorporation has a sensitivity of 11mV/V-G (Guass) mini-mum. With the 3.3V power supply, the minimum sensitivityis approximately 36.3mV/G. The high sensitivity enables theproposed device to detect any small change in magnetic fieldunder the sensing area. As a result, only small magnet isrequired to be embedded with the ETT. In addition, highsensitivity also allows the device to show the relative depthperception in the color scheme as well.Additional advantage of the GMR sensor is the low-poweroperation. The sensor output is proportional to the supplyvoltage. In this case, The system is operational