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8. End points
This approach balances risk and benefit, but should event rates exceed those experienced in the literature
and stated above, consideration should be given to discontinuing any programme that permits certification
of Type 2 diabetic insulin-treated applicants. Any significant hypoglycaemia during the period of
certification, i.e. requiring the help of another, is likely to result in a long term unfit assessment for the
individual and may cast doubt on the feasibiliy of extension of the programme. ICAO would like to hear
of any State that permits insulin-treated applicants to operate and has run into any significant flight safety
problems.
The approach is highly specific and an estimate of the numbers likely to be included is difficult to predict.
In the United Kingdom approximately 1-2 professional pilots/20,000 per annum show failure of treatment
with oral hypoglycaemic agents and require insulin, and it is likely that similar numbers may occur within
the jurisdiction of other Authorities.
PROTOCOL DEVELOPMENT FOR CERTIFICATION OF APPLICANTS
WITH TYPE 2 DIABETES
Achieving and sustaining near normal glycaemia is a central target in the management of patients with
both Type 1 and Type 2 diabetes mellitus whose microvascular complications are then reduced (DCCT
[1993], UKPDS [1995, 1998, 2000]). However, the clinical consequence of improving glycaemic control
is an increase in the frequency of hypoglycaemia (UKPDS [1998], DCCT [1997]) which is a concern in
the risk assessment of diabetic aircrew. The relative risk of severe hypoglycaemia (requiring the
assistance of another) is greater for intensively treated (to achieve lower HbA1c levels) patients with
Type 1 diabetes (about 27 per cent per year according to the Disease Control and Complications Trial
(1997) than for those with Type 2 (approximately 2 per cent per year) according to the UK Prospective
Diabetes Study (1998), despite similar glycaemic control.
Several factors may explain why patients with Type 2 diabetes are less prone to severe hypoglycaemia.
Normally, as plasma glucose concentrations fall, there is a hierarchy of defence responses. The first is an
ICAO Preliminary Unedited Version — March 2010 III-4A-7
increase in the release of counter-regulatory hormones as plasma glucose falls to approximately
3.8 mmol/L, which is designed to prevent glucose concentrations from falling further. The second is an
awareness of warning symptoms, predominantly autonomic (sweating, hunger, anxiety, tachycardia, etc.),
which begin as plasma concentration decreases to approximately 3.4 mmol/L. In patients well educated
in diabetic management, such symptoms will prompt preventive steps, i.e. ingestion of carbohydrate,
which will prevent neuroglycopaenia, which commences at approximately 3.0 mmol/L.
In people who have had Type 1 diabetes for over five years, counter-regulatory hormone responses to
hypoglycaemia are generally impaired. Initially, most patients lose their glucagon response to
hypoglycaemia, thereby becoming dependent on catecholamine responses to prevent or reverse
hypoglycaemia. Sometimes even that response becomes impaired and the risk of severe hypoglycaemia
increases several fold. Additionally, episodes of mild hypoglycaemia, even if symptomless, can further
impair glucose counter regulation and may reduce ß-adrenergic sensitivity leading to a situation of
“hypoglycaemic unawareness”. In this situation, patients may not recognize impending hypoglycaemia
until it is too late to institute preventive measures (Gerich J F, 2000).
The situation is somewhat different in Type 2 diabetes. Firstly, although glucagon responses are
commonly impaired, catecholamine responses are usually normal or increased. Secondly, the patients are
insulin resistant; and thirdly, they have persistent ß-cell function. The ability to modulate insulin secretion
can act as a buffer, since endogenous insulin secretion will decrease as plasma glucose falls. This
opportunity is not available in Type 1 patients whose insulin availability is pre-determined by the amount
already injected. Fourthly, most Type 2 patients are not on intensive insulin regimes so they are less at
risk of hypoglycaemic unawareness as a result of insulin induced hypoglycaemia.
This differing rate of hypoglycaemia has been confirmed by Heller et. al (2007) who found no
differences in the rate of severe hypoglycaemia in Type 2 diabetic patients treated with sulphonylureas or
insulin for less than 2 years (0.1 and 0.2 episodes per subject – year) and this frequency was far less than
that encountered in Type 1 diabetes (< 5 years 1.1; > 15 years 3.2 episodes per subject – year).
From a number of studies including Akram et. al (2006)., the risk factors for severe hypoglycaemia
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Manual of Civil Aviation Medicine 1(139)
