Calculating weight in critically ill paediatric patients with a special smartphone for drug dosing

Knowing child weight is critical while managing paediatric emergencies because dosing resuscitation drugs are generally based on weight. However, in many out-of-hospital and emergency department settings the child weight is unknown to the treating team and often it is not possible to weight the patients. Some of the conditions which make challenging to obtain a rapid and reliable measurement of the weight include on-going cardiopulmonary resuscitation, spinal immobilization, emergency airway management, and emergency delirium or agitation. Calculation of emergency drug doses, choosing the most appropriate equipment size and defibrillation energy level requires knowing or accurately estimating the child weight.

For this reason, various weight estimation techniques were developed. Current techniques include visual estimation by parents or healthcare providers and estimation from child age or length. Despite poor accuracy, more than twenty age-based formulae were created with some of this requiring relatively complex arithmetic calculations increasing the risk for errors in a stressful resuscitation setting. Moreover, resuscitation guidelines suggest using a body-length tape subdivided in colour zones with pre-calculated doses if the child’s weight is unknown. Each zone estimates the 50th percentile weight for length and thus represents the ideal body weight.

Concerned by the risk derived by drug dosing errors in critically ill children we developed the first smartphone app that estimates child weight using the smartphone camera and augmented reality (AR) by implementing a virtual 3D tape.

The app is very simple to use. After launching it, the smartphone camera is activated with a yellow marker in the centre of the screen, and AR software tracks a correspondence between the real world and the virtual space. After the completion of this process, the app is ready to measure child height. The first step is pointing and tapping the marker over the head of the child. As a result, a virtual tape anchored to the head is displayed and its length will increase as the smartphone moves heading toward the foot. To complete the measurement the user has to point and tap the marker over the foot. At this point, the measured length and the colour corresponding to the weight zone are displayed in the bottom of the screen with the ability to consult medications dose, route of administration and notes, equipment sizes and other critical calculations. In order to obtain accurate measures, users must be aware of lighting conditions and quality of smartphone camera.

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