Assessing the severity of a respiratory problem in children is not entirely straightforward. Guidelines attempt to categorise according to specific parameters however it is not uncommon for the category given to contradict our gut feel. Sometimes the answer suggested by the guideline seems to be contradicted by the appearance of the child in frontof us. Why is that? What weight can we put on our gut feel? When should we be worried?
To understand any severity system and to explore the nuances, I would ask the question, “What is the correlation between the words (mild/ moderate/ severe) and the clinical state of the patient?”
The clinical state of the patient could be categorised as follows:
- Normal physiology
- Fully compensating
- Partially compensating
- Decompensating
Normal physiology
In a normal physiological state, circulation and respiration are unaffected. The child’s activity and interaction are normal. This normal behaviour is evidence of end-organ function – the brain is well perfused, hydrated and nourished.
Fully compensating
When a child becomes unwell, physiology alters to compensate for the illness. For example, a baby with mild bronchiolitis will breathe faster and heart rate will increase to mitigate the effect of the viral illness on their lungs. If this compensation is fully effective, activity and interaction will be unaffected. In this context, the infant is often referred to as a “happy wheezer”. Thus happy wheezer is not a diagnosis, but rather a clinical evaluation.
Partially compensating
As the effects of an illness become more significant, physiological compensation increases but there reaches a point where it is no longer fully effective. The brain is a sensitive organ and the early effects of reduced perfusion, hydration and respiration are usually apparent in the gross neurology of a child. Activity and interaction becomes reduced as an early sign that compensatory physiology is no longer fully effective.
Decompensating
If physiological compensation begins to fail, the child’s clinical state deteriorates rapidly. If the problem is primarily respiratory, the deleterious effects on the central nervous system and the respiratory muscles create a vicious cycle: tired muscles and a dysfunctioning brain are unable to continue driving the compensatory mechanisms. Respiration is further impeded which in turn reduces the oxygen delivery and CO2 clearance so badly needed for the child’s physiology to compensate.
If the problem is primarily circulatory the point of decompensation leads to reduced cerebral, cardiac, hepatic and renal perfusion. This accelerates the effects of poor perfusion through a combination of worsening cardiac output and biochemical changes that impair the metabolic functions needed to cope.
In either case, the effects of decompensation are dramatic. Conscious level is affected and the child is likely to be pale and look seriously unwell. Do not mistake a falling heart rate or respiratory rate for clinical improvement. What is happening is quite the opposite. The child’s physiology is failing – impending cardiorespiratory arrest is inevitable without critical care support.
