Response to nocturnal alarms using a real-time glucose sensor

Abstract

Background: The objective of this study was to determine how subjects responded to alarms for hypo- and hyperglycemia while they were sleeping.

Research design and methods: Twenty subjects with type 1 diabetes (4-17 years old) were admitted to a clinical research center for approximately 24 h. Each subject wore two GlucoWatch G2 Biographers (GW2B) (Cygnus, Inc., Redwood City, CA) and was videotaped using an infrared camera from 9 p.m. to 7 a.m. The videotapes were reviewed to determine if the GW2B alarms were audible on the tape and to document the subject's response to the alarms. Because many alarms can occur surrounding a change in blood glucose, GW2B alarm "events" are defined as a one or more alarms separated from previous alarms by more than 30 min.

Results: Downloaded data from the biographers identified 240 individual alarms, 75% of which occurred while the subject was sleeping. Of the 240 alarms 68% were audible on the videotape. Subjects awoke to 29% of individual alarms and to 66% of alarm events. Subjects 4-6 years old responded to 17% of alarms, 7-11 year olds responded to 20% of alarms, adolescents responded to 53% of alarms, and parents responded to 37% of alarms. Subjects awoke to 40% of the first alarm during the night, but to only 28% of subsequent alarms. There were 11 events when the glucose was confirmed to be < or = 70 mg/dL, and in each case the subject was awoken. Fifty-five percent of alarm events occurred when there was no hypo- or hyperglycemia confirmed by a reference glucose value.

Conclusions: Subjects awoke to 29% of individual alarms and to 66% of alarm events. Subjects awoke during all alarm events when hypoglycemia was confirmed, but there was a high incidence of false alarms.

Figures

Figure

On this night two GlucoWatch biographers were worn (GWB 1 = solid line, and GWB 2 = broken line). Down alarms (▪), and low alarms (♦) are marked on the GlucoWatch plots. Reference (⋄) and Ultra (□) glucose values are plotted as discrete data points. Along the bottom of the graph, alarms that awoke the subject are given as large open circles (○) and alarms that awoke the parent are given as small solid circles (•). Alarm events are denoted by a box.