TP 13312

•	Foreword
•	Section 1
•	Section 2
•	Neurology
•	Cardiovascular
•	Diabetes
•	Asthma
•	Other Policies
•	Contacts
•	Alternate Formats

Guidelines

One of the major considerations in medically certifying diabetics who are insulin treated or who require oral hypoglycemics agents, is the risk of subtle or sudden incapacitation. In the diabetic person this would be most likely caused by hypoglycemia. Let us therefore consider the metabolic condition of hypoglycemia.

Hypoglycemia:

Hypoglycemia is usually considered to be a blood glucose concentration in the range below the level at which symptoms could be expected to occur. In the person without diabetes, blood glucose is kept within a fairly narrow range by a homeostatic mechanism regulated by glucose intake and storage, insulin, glucagon, catecholamines, cortisol and growth hormone. In insulin treated diabetes mellitus (ITDM) insulin is provided from an exogenous
source so fine control of this delicate homeostasis has been compromised. Hypoglycemia may result from too much insulin, too little glucose, an over–expenditure of energy or any combination of the above.

Diabetes specialists officially define hypoglycemia as being either:

1. when the plasma glucose falls below 2.8 mmol/L (50 mg./dl) or
2. when symptoms of hypoglycemia occur. 

   The symptoms and signs of hypoglycemia can be broken down into two main groups:

   1. Neurogenic
      • Weakness
      • Palpitations
      • Tremor
      • Sweating
      • Hunger
   1. Neuroglycopenic
      • Cognitive impairment
      • Mental status changes
      • Abnormal behaviour
      • Irritability
      • Seizure activity

Results from the multicentred Diabetes Control and Complications Trial revealed that among an intensive insulin treated group of patients with diabetes, the incidence of hypoglycemic reactions is relatively common. Severe hypoglycemia is definitely related to the degree of glycemia control and the effectiveness of the physiological counter regulatory mechanisms.

Studies have also demonstrated that patients with diabetes who are poorly controlled tend to recognize hypoglycemia at higher blood glucose levels than do intensively insulin treated diabetic individuals, who may not recognize the hypoglycemic reaction until their blood glucose level is much lower. This is a result of blunting of the counter regulatory mechanisms. This situation which exists among the intensively treated group is termed by diabetologists hypoglycemia unawareness. 

It is apparent then that the unpredictability of hypoglycemia could be a major aviation safety hazard in the cockpit or the air traffic control worksplace. 

As in many other areas of risk assessment in aviation medicine, (e.g. cardiovascular, neurological), a level at which the degree of risk can be considered acceptable must be sought. This degree of risk should not be much in excess of the risk of the same condition occurring in a completely healthy person. Most recently in Canada, for conditions such as coronary events or seizure following head injury, a risk of 2% per annum or less has been considered acceptable.

Table 1 attempts to address the question of risk of hypoglycemia. Those Insulin treated diabetics who fell into the high risk group would not be considered for any form of licence, whereas those falling in the low risk group could be considered. 

With this in mind the conference group has proposed the following guidelines for the medical certification of pilots, air traffic controllers and flight engineers with diabetes. It must be understood that these are only guidelines and that each case will be reviewed individually by the Aviation Medicine Review Board.  Of particular concern are the neuroglycopenic effects of hypoglycemia and the effect they have on information processing, which is an extremely important aspect of both piloting and air traffic controlling tasks.

Table 1 - Hypoglycemia Risk Among Insulin Users