Symposium: respiratory medicine
Paediatric applied respiratory physiology – the essentials

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Abstract

General paediatricians will encounter myriad respiratory abnormalities during their careers. A basic knowledge of essential respiratory physiology, its subsequent derangements due to disease states and how to assess these abnormalities will help in the proper care of children. This paper will begin with an overview of normal respiratory physiology and how to monitor the efficiency of gas exchange. It will also discuss common methods of non-invasive monitoring including pulse oximetry, carbon dioxide monitoring, pulmonary function tests and respiratory impedance plethysmography. Finally, paediatric disease states will be used to illuminate the intersection between pathophysiology, clinical symptoms and monitoring capabilities.

Introduction

Bearing in mind the diversity and prevalence of respiratory illnesses in children, paediatricians should understand the basics of respiratory physiology and how to monitor respiratory function. This discussion will review normal respiratory physiology and explore non-invasive forms of respiratory monitoring. With this foundation, the paediatrician can accurately diagnose and assess the severity of illness.

Section snippets

Muscles of respiration

The most important and powerful muscle during the inspiratory phase of respiration is the diaphragm, a dome-shaped musculofibrous septum that separates the thorax from the abdominal cavity. When the diaphragm contracts, abdominal contents move downward and the lung expands in the vertical and horizontal planes. During normal tidal breathing the diaphragm moves approximately 1 cm, but with forced inspiration and exhalation, it can move up to 10 cm.

During inspiration, external intercostal muscles

Gas exchange

The primary purpose of the respiratory system is gas exchange to maintain cellular homeostasis. The two principal components are delivery of oxygen and removal of carbon dioxide.

Pulse oximetry

Cyanosis is the hallmark clinical sign of hypoxaemia, but it can only be recognized confidently when the oxygen saturation is below 75% and cannot be recognized if the haematocrit is less than 15%. Pulse oximetry allows for non-invasive and continuous monitoring of arterial oxygen saturation (SaO2). The basic principles of pulse oximetry are that oxygenated haemoglobin (HbO2) absorbs mostly infrared light while deoxygenated haemoglobin (Hb) absorbs mostly red light. Pulse oximeters exploit the

Obstructive airways disease

The primary pathological defect in obstructive airways disease is airflow limitation. This limitation can occur during expiration, inspiration or both. Both large airways obstruction (croup, epiglottitis, foreign-body aspiration, laryngomalacia, tracheomalacia) and medium (asthma) and small (bronchiolitis) airways obstruction have hallmark findings on physical examination and in the tests discussed above. Knowledge of these patterns assists the physician to localize the obstruction, determine

Conclusion

There is a wide array of non-invasive tools available to the paediatrician for diagnosis and management of various respiratory diseases. With a basic knowledge of respiratory physiology and how pathophysiological states can be monitored, the clinician can optimize therapeutic interventions and readily track disease progression.

Practice points

  • Pulse oximetry, TCOMs and nasal cannula end-tidal CO2 devices are easy and reliable ways to monitor gas exchange

  • Characteristic changes in pulmonary

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