14 / 208
Chapter 1
12
Characteristics of the acute phase of critical illness
The acute phase of critical illness in children is characterised by the requirement of
(escalating) vital organ support. The concomitant stress response, initiated by activation of an
inflammatory cytokine cascade and the central nervous system, is aimed at surviving critical
illness. A conceptual overview of the neuro-endocrine, metabolic and immunologic alterations
is depicted in Figure 1.
Figure 1.
Conceptual overview of the different phases of critical illness with corresponding neuro-
endocrine, immunologic and metabolic changes
EGP, endogenous glucose production; PT, protein turnover; GH, growth hormone; rT3, reverse
triiodothyronine; REE, resting energy expenditure; MPS, muscle protein synthesis; IGF-1, insulin-like
growth factor; T3, triiodothyronine; counter-regulatory hormones are cortisol, catecholamines and
glucagon
Neuro-endocrine response
Despite activation of the hypothalamic-pituitary axis to release the anterior pituitary
hormones corticotrophin (ACTH), thyroid stimulating hormone (TSH) and growth hormone,
concentrations of most peripheral effector hormones, such as triiodothyronine (T3, active
thyroid hormone) and insulin-like growth factor (IGF-1) are low due to inactivation or target
organ resistance
17-19
. In absence of adrenal insufficiency, levels of cortisol rise substantially,
mainly due to reduced metabolism in liver and kidneys
20,21
.