Paediatrics: Respiratory distress

Respiratory distress

Respiratory distress is defined as increased work of breathing that causes a sense of altered well-being. The hallmarks are use of accessory muscles and tachypnoea. Distress can be caused by disorders of gas exchange (O₂ absorption, or CO₂ elimination), respiratory drive, neuromuscular disease, and infection.

Box 5.1 Differential diagnosis of respiratory distress

Nasopharynx

·   Nose: choanal atresia, stenosis

·   Oropharynx: tonsillar hypertrophy

·   Tongue: glossomegaly

·   Pharynx: peritonsillar abscess, retropharyngeal abscess, diphtheria

Upper airway obstruction

·   Larynx: vocal cord dysfunction, laryngomalacia, papilloma, haemangioma, croup

·   Epiglottis: epiglottitis, foreign body

Lower airway disorder

·   Trachea: tracheitis, tracheobronchomalacia, foreign body, pulmonary artery sling

·   Bronchi: bronchitis, bronchomalacia

·   Bronchioles: asthma, bronchiolitis, pertussis

Disordered gas exchange

·   Haemoglobin: carbon monoxide poisoning, methaemoglobinaemia, acidosis

·   Shunt: pulmonary oedema, haemorrhage, atelectasis, or embolism

·   Dead space ventilation: asthma, bronchiolitis, pulmonary hypertension

·   Other: sickle chest syndrome, pneumonia, pneumothorax

Respiratory drive

·   Hyperventilation: psychogenic, brainstem tumour

·   Hypoventilation: apnoea, drugs

Neuromuscular

·   Respiratory muscle weakness: Duchenne muscular dystrophy, spinal muscle atrophy, central nervous system (CNS) depression

Other

·   Pleural: pneumothorax, chylothorax, haemothorax, pleural effusion, empyema

·   Chest wall: flail chest, rib fractures

Definitions

Broadly, we can define the two major causes of respiratory distress as follows.

Respiratory failure

·Hypoxaemia despite high FiO₂: arterial oxygen tension (PaO₂) <8kPa in previously well child.

·Acidosis: pH <7.25; no specific arterial carbon dioxide tension (PaCO₂) since the child may have a chronic ‘compensated’ problem.

·Increasing fatigue, or absence of improvement with therapy: based on your observations on child’s breathing and mental state.

Neuromuscular weakness

·Clinical: bulbar dysfunction with poor or absent cough, gag, swallow, or chest wall weakness of neurological or muscular origin.

·  Physiological: use spirometry to assess vital capacity <12mL/kg, or manometry to assess maximum inspiratory force <–20mmHg.