Magnetic resonance safety of the Freestyle Libre glucose monitoring system
The Freestyle Libre glucose monitoring system (Abbott Diabetes Care, Witney, UK) was introduced locally for many of our diabetic patients in 2017, offering them an alternative to regular finger-prick capillary blood glucose measurements. The Freestyle system measures interstitial blood glucose through a small sensor on the skin, storing up to 8 h of data, which can be ‘read’ using a device placed in close proximity to the sensor (Fig. 1). The sensors each last 14 days and are waterproof 1.
The system consists of a small fibre which pierces the skin into subcutaneous interstitial fluid, and an electrochemical reaction between an enzyme and glucose in this fluid then occurs, which is converted into a blood glucose reading, and stored in the sensor. A ‘reader’ device is passed over the sensor and the last 8 h of readings can be transferred to the reader.
Locally, our early adopters of the new system are now starting to appear for surgery. After some background reading in the product literature, we noted that the user manual states that the device must be removed before magnetic resonance imaging (MRI) 2. The reason for this is twofold: firstly, the sensor contains a small battery, and there is risk of malfunction of the sensor; and, secondly, magnetic fields may cause heating of the electrical components of the sensor, with a risk of burns to the patient.
However, both the patient information 3 and the product safety information on the Abbott website 4 state that the sensor should also be removed for computed tomography (CT) or diathermy procedures and that the patient should inform their healthcare provider that they are using the sensor.
We are aware that this device is relatively new and that information concerning its use in the peri-operative environment is not widespread. We plan to brief this to colleagues at a departmental meeting and also disseminate this information to key members of the peri-operative team including the pre-assessment department. We would recommend a similar approach for colleagues in their own institutions.
This device has been demonstrated to be accurate when used within critical care units 5, and the potential benefits to patient safety and good glycaemic control of regular monitoring of glucose levels during surgery are clear, although we can find no published study of this application.
This device is clearly of great benefit to diabetic patients in self-management of their condition. It is, however, important that all staff involved in the care of these patients are aware of the potential associated risks.
