However, they may tip a patient with limited respiratory reserve into respiratory failure. Endotracheal intubation bypasses the filtering, humidifying and warming functions of the upper airway allowing the entry of pathogens and the drying of secretions. Volatile anaesthetic agents depress the respiratory response to hypoxia and hypercapnia, and the ability to clear secretions is reduced. Intermittent positive pressure ventilation causes an imbalance in ventilation and perfusion matching in the lung, and necessitates an increase in the inspired oxygen concentration. Excessive fluid therapy can result in pulmonary oedema in patients with cardiac failure.
Neuromuscular blockade is reversed before extubation.
In the recovery room residual effects of anaesthesia depress upper airway muscular tone, and airway obstruction may occur. The intravenous induction agents thiopentone, propofol and etomidate produce an initial transient apnoea. Ketamine preserves respiratory drive and is better at maintaining the airway, although secretions increase. Thiopentone increases airway reactivity. Ether however stimulates respiratory drive and increases minute ventilation.