Reviewing these case reports, we were impressed with the long duration of CGM-documented severe hypoglycemia of 2–4 h before a seizure occurred in each of these cases. Two of these records were obtained with the original CGMS, which was reported to have a high frequency of low glucose readings at night (7
); however, in our cases, the validity of the CGMS readings was confirmed by the occurrence of hypoglycemic seizures in conjunction with the low nocturnal CGM readings.
To prevent serious events such as seizures, glucose sensors must both detect hypoglycemia and provide a sufficiently robust alarm to awaken the patient or some other member of the household. Schultes et al. (8
) reported that people with diabetes have an impaired awakening response to hypoglycemia, and only 1 of 16 subjects with type 1 diabetes awoke to induced nocturnal hypoglycemia, whereas 10 of 16 healthy control subjects were awakened. We have previously videotaped the response of children to GlucoWatch alarms while they were sleeping (9
). Although children only awoke to 29% of individual alarms, there were 11 episodes when they were <70 mg/dl, and in each case, they awoke to repeated alarms, indicating that sleeping patients can respond to alarms when they are hypoglycemic. Glucose sensors should have sufficiently robust alarm systems, particularly at night, to insure either the patient or a surrogate is awoken to intervene. Given the likelihood that prolonged or severe hypoglycemia is needed before there is a seizure, hypoglycemia detection algorithms that incorporate the duration of hypoglycemia could have lower false-positive alarm rates and thus be more clinically acceptable. This type of an alarm system may not be applicable during the daytime, where a rapid decrease in blood glucose can result in neurocognitive dysfunction, which can quickly impair performance of important daytime tasks (such as driving).
It is our conclusion that even with the time lag in interstitial glucose readings, there is sufficient time to awaken a patient to prevent a seizure, if they are awoken by the alarm. The alarm systems need to be more effective in awakening subjects. We suggest augmenting the alarm with a bedside device that would turn on a light and transmit the alarm to another location in the house, such as a parent's bedroom.