User evaluation of the 'free style Navigator continuous glucose monitoring system

Optimal glycaemic control is an important goal in the treatment of patients
with diabetes mellitus. Optimal glycaemic control decreases the risk of
developing chronic organ complications. In addition, prevention of acute
hypoglycaemic and hyperglycaemic episodes is an important goal. Measuring the
blood glucose level is an essential method to improve glycaemic control.
Patients measure the blood glucose levels themselves in capillary blood
obtained by finger stick. With these values a daily glucose profile can be made
and this profile, in combination with factors like nutrition and physical
exercise, is used to adjust the treatment with glucose-lowering drugs like
insulin.

Glucose profiles comprise generally of two to seven measurements during the
day. These measurements give however only a 'snapshot' picture of glucose
control and there is a desire to obtain more detailed information on the
glucose levels in order to improve glucose control. This is even more important
in those patients who can not be treated satisfactorily at all with the
current, classic methods to construct glucose profiles.

Continuous subcutaneous glucose monitoring is a recently developped technique
using an subcutaneously inserted needle, impregnanted with a glucose-measuring
enzyme, allowing frequent glucose determinations in the interstitial fluid
compartment. Levels are given every 5 minutes. On the basis of these frequent
levels, a detailed picture of daily glucose control is provided. With first
devices, glucose levels could only be displayed 'off line' after disconnecting
the device and downloading the data. Although the analysis of the detailed
glucose profile has a great educational effect, there is a need for devices
that can display directly, 'on line' the glucose results. The 'free style
navigator continuous glucose monitoring system' is such a 'on line' device. In
addition to 'on line' display there is the possibility to set threshold alarms:
the device warns with an auditory and vibration signal when the glucose level
falls below or surpasses the individually-set lower or the upper threshold,
respectively. The most innovative feature of the 'Navigator' is the dynamic
alarm function. This means that the alarms go off with a change in glucose
level in a specific period of time above an individually-set threshold. For
example, an alarm can be set at a change of more than 5 mmol/l per 10 minutes.
This is irrespective of the absolute glucose level. In practice, both specific
absolute and dynamic thresholds are used. These innovations can in theory
provide a method to further extend the methods to measure glucose levels in
order to improve glucose control.

The objective of the study is the assessment of the effect of the use of the
'free style navigator continuous monitoring system' on the glucose variability
in patients with type 1 diabetes mellitus. This assessment is combined with the
analysis of the patient experiences with this devices.

This is a study that comproses two sequential periods. During the first period
of 20 days the devices is worn but the glucose levels are not displayed. During
the next second period of 40 days, the device is worn and the device displays
'on line' the glucose levels.

The intervention is the use of the 'free style navigator continuous glucose
monitoring device' with an number of facilities:
1: 'On line' display of the glucose level in the insterstitial fluid every 5
minutes
2: Alarm features with fixed, individually set glucose upper and lower
thresholds
3: Alarm features using a dynamic threshold, that is an individually set
change in glucose level in a specific time period

Before the start of the intervention (Day 0) and after the end of the
intervention (Day 60) a blood sample will be drawn to determine HbA1c and
fructosamine (both indices of longer term glycaemic control). Frustosamine
gives a reflection of glycaemic control during the last 2 tot 3 weeks HbA1c
during the last 2 months.

The burden and risk associated with the study are firstly wearing the device
and inserting the sensor (measuring device) into the subcutaneous tissue.
Insertion takes places every 5 days; insertion is done with a little, specially
designed device. The sensor is basically similar to the sensor that is used
with the 'off line' glucose monitoring system. With insertion, a little
bleeding can occur and pain can be experienced. After some days, the insertion
place can become red as a consequence of an inflammatory reaction. In that case
the sensor is removed and a new one inserted at another place.
Secondly, patients are confronted with actual glucose results, alarms outside
fixed glucose levels and alarms outside a fixed change in glucose level over a
period of time. This may mean a certain mental burden. In practice this has not
be proven to be a problem and in depth assessment of one's own glucose profile
is part and parcel of the study as well as normal practice.