Using Magnetic Field Tracking to Confirm Nasogastric Tube Placement at Point of Care

In order to address the clinical need for the localization of nasogastric tube (NGT) at point-of-care, Nanyang Technological University, Tan Tock Seng Hospital and Woodlands Health Campus co-developed the prototype of a medical device that consists of a guidewire attached to a gold-plated Neodymium magnet to be used with a T-shaped body-worn sensors connected to a laptop. The magnetic-tipped guidewire is compatible with 14Fr or larger Ryles tubes. The sensors are passive and are designed to fit on the patient's sternum beginning at the level of the second intercostal space or xiphisternum. These sensors can track the changes in magnetic flux density real-time as the magnetic-tipped guidewire is inserted into the lumen of an NGT. The tracking may be done during NGT insertion or before feeding if confirmation of its location is required. The changes in magnetic flux density will be used to determine the location of the magnet in relation to the sensors. The result of these computations will be displayed on the computer screen as a trajectory of the magnet's movement inside the NGT. At full insertion of the guidewire, the trajectory should correspond to the actual location of the NGT in the patient.

This device is currently not in use but the investigators have notified the Health Science Authority of Singapore for its use as a Clinical Research Material.

The investigators aim to recruit 12 adult patients from both gender (6 each) who would already have had NGT placement and confirmation of its position by CXR within 48 hours of NGT insertion. These patients may have a variety of body habitus and will be screened according to a detailed list of exclusion criteria that rules out a recent medical history of oesophageal or gastric surgery, cardiac stent, pacemaker, implantable defibrillator or ferromagnetic implants in the neck, thorax, abdomen, pelvis or spine.

The investigators plan to test the following hypotheses and safety parameters.

• Concordance of our tracking with the trajectory of the NGT seen on chest X-ray
• The vertical and horizontal range of tracking
• The ability to detect a leftward deviation from the midline inferior to the xiphisternum
• Test-retest reliability
• Adverse events related to the magnetic-tipped guidewire or the sensors

Inclusion criteria

• Patients from the general ward or the Otorhinolaryngology clinic of Tan Tock Seng Hospital who had an NGT inserted within the last 10 days and chest X-ray confirming its correct placement

• The NGT inserted is a Ryles tube size Fr 14 or 16
• COVID negative or not deemed to be infective as judged by the prevailing policies at the time of recruitment
• Age > or = 21 years
• BMI < 35
• Height < 1.9m
• Mentally competent for informed consent

Exclusion criteria

• • Radiological:

• On chest X-ray, the length of the NGT distal to the gastroesophageal junction is less than 12cm, or the side-holes of the NGT can be visualized in the esophagus.
• The NGT is kinked within 10cm of its tip
• The chest X-ray is rotated such that the thorax is not oriented in the frontal plane
• The NGT cannot be visualized in the mediastinum
• The second intercostal space cannot be visualized on chest X-ray

• Medically unstable:
• Heart rate >=100 or <60
• Systolic blood pressure >=160 or <100
• SpO2 <92% in patients with chronic lung disease and <95% in patients without chronic lung disease
• Temperature >= 38 degrees Celsius

• Chest wall deformity:
• Patients with pectus carinatum or excavatum, defined by physical examination

• Patients with the following implants
• Pacemaker
• Automatic cardioverter defibrillator
• Ferromagnetic coronary stents or heart valves
• Ferromagnetic implants of the cranium, face, spine, sternum or ribs
• Ferromagnetic surgical clips or implants in the head, neck, thorax, abdomen or pelvis

• Following conditions within the last 30 days
• Upper gastrointestinal bleeding
• Oesophageal or gastric surgery
• Stroke
• Myocardial infarction
• Aortic dissection
• Ruptured aortic aneurysm

• Allergy to neodymium, gold, epoxy or nitinol
• Not able to understand English, Chinese, Malay or Tamil
• Women whose last menstrual period commenced more than 4 weeks before recruitment unless they have a negative urinary or serum pregnancy test during their current admission.