Introduction

Definition

Paediatric Protocol, 4th Edition:

• Chronic airway inflammation leading to increase airway responsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness and coughing particularly at night or early morning.
• Often associated with widespread but variable airflow obstruction that is often reversible either spontaneously or with treatment.
• Reversible and variable airflow limitation as evidenced by a >20% improvement in PEFR (Peak Expiratory Flow Rate), or a > 12% improvement in FEV1 (Forced Expiratory Volume in 1 second) in response to administration of a bronchodilator.

CPG Management of Childhood Asthma:

• Asthma is a heterogenous condition characterised by paroxysmal or persistent symptoms such as dyspnea, chest tightness, wheezing and cough against a background of chronic persistent inflammation and/or structural changes associated with variable airflow limitation and airway hyper-responsiveness.

Pathophysiology

• Atopy, a genetic predisposition to develop specific immunoglobulin E (IgE) antibodies directed against common environmental allergens.
• An initial allergen exposure causes the production of specific IgE antibodies by plasma cells, with an over-expression of Th2 type T cell response. IgE antibodies binds to mast cells and basophils.
• Early or immediate phase reaction: When an allergen is inhaled and comes into contact with mucosal mast cells, it cross links allergen-specific IgE antibodies on the mast cell surface; this causes rapid degranulation and mediator release. This leads to broncho-constriction within several minutes.
• Late phase reaction: The late phase response is characterised by recruitment of inflammatory and immune cells, particularly the eosinophil, basophil, neutrophil, and helper, memory T-cells to sites of allergen exposure. Asthmatics may experience a recurrence of bronchoconstriction several hours later.
• Mast cell degranulation and mediator release causes the airway smooth muscle to constrict causing obstruction. In asthmatics, there is an unexplained bronchial hyper-responsiveness which may be a consequence of remodeling and structural abnormalities of the airway.
• A variety of genetic, environmental, and infectious factors appear to modulate the progression of asthmatics to more severe disease.

Natural History of Asthma

• Many infants wheeze early in life but 3 out 4 school-aged children will outgrow asthma by adulthood.
• Majority of chronic asthma begins in the first 6 years of life. There exists two groups of children who have wheeze and asthma-like symptoms.
  • Transient wheezers tend to have intermittent symptoms, usually presents with a viral illness. They will likely outgrow it as they age.
  • Persistent wheeers are characterised by atopy, positive family history of asthma and an increased risk for asthma later in life.
• Adult onset asthma may originate from undiagnosed childhood asthma.