This ‘lesson of the week’ article describes how exposure of an insulin pump to heat and sunlight led to insulin degradation, with a resultant hospital admission due to diabetic ketoacidosis.

The patient was an 11 year old girl with type 1 diabetes (diagnosed aged 7), who had been using an insulin pump for 11 months, and had reasonable control of her condition (HbA1c of 7.9%).  When she presented with ketoacidosis, she was wearing her insulin pump (Medtronic 522) and the pump was delivering at the programmed rate. 

Two days prior to admission she had disconnected her pump so she could go swimming, and had left it by the side of the pool – the pump was therefore exposed directly to the sun at up to 35°C (an Australian summer’s day).  Her blood glucose began to rise when the pump was reconnected later in the day; she therefore administered an additional dose of insulin via injection and altered the rate of insulin infusion from the pump, but the insulin in the reservoir was not changed.  She presented with ketoacidosis 48 hours after the incidence.

The author proposes that ‘by exposure to high temperatures through being left in direct sunlight, the insulin in the pump reservoir was destabilised and made ineffective’.  He recommends that if an insulin pump is disconnected during exercise activities, it should be placed away from sunlight and extreme temperatures.  If hyperglycaemia occurs despite a corrective dose of insulin and changing the infusion set, then the insulin in the reservoir should also be changed.