Chapter 12: Respiratory care, CPR and blood transfusion
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Anatomy and physiology
The mucosa of the respiratory tract is lined with pseudostratified columnar epithelial cells, which are covered in hair‐like structures known as cilia. Mucous secreted by goblet cells in the mucosa traps inhaled particles and pathogens, and the mucous is swept by the cilia from the distal to the proximal airways to be either swallowed or coughed up. Airway mucous therefore defends the airways and forms part of our innate immune system (Tortora and Derrickson [272]).
Normal room air has an approximate temperature of 22°C with a relative humidity of 50% and a water content of 10 mgH2O per litre. For effective gas exchange to occur in the lungs, the air needs to be at a temperature of 37°C with 100% humidity and a water content of 44 mgH2O per litre by the time it reaches the bifurcation in the trachea (McNulty and Eyre [154]). This is referred to as the ‘isothermic point’. In normal circumstances, inspired air is mainly conditioned (optimally heated and humidified) in the nose and oropharynx (Doctor et al. [67]).
