Upper airway reflexes and anaesthesia.

In this thesis I describe the importance of upper airway reflexes to anaesthesia and discuss the anatomy and physiology relating to normal upper airway function and protective airway reflexes. The measurement of upper airway reflexes has not previously been fully investigated in humans and I describe the background to the measurement of the sensitivity of upper airway reflexes and outline a technique to measure the sensitivity of upper airway reflexes. Using this technique I have explored the changes in the sensitivity of upper airway reflexes that occur due to ageing and following administration of drugs. Smokers are known to have an increased incidence of coughing and laryngospasm on induction of anaesthesia. The effect of cigarette smoking and the changes in the sensitivity of upper airway reflexes which occur on stopping smoking were investigated. Benzodiazepines are commonly used for premedication and intravenously to produce sedation, the effects of these drugs on the sensitivity of upper airway reflexes was examined as well as the effect of the reversal agent flumazenil. Patients who have consumed ethyl alcohol may readily aspirate gastric contents with fatal consequences. The effect of ethyl alcohol on the sensitivity of upper airway reflexes is measured and the relevance to anaesthetists providing emergency anaesthesia is discussed. The inhalation of nitrous oxide and oxygen mixtures is frequently used for analgesic purposes in groups of patients known to have full stomachs and who are at risk from aspiration of gastric contents. I have studied the effects of nitrous oxide and oxygen mixtures on upper airway reflexes. The final chapter of this thesis uses a fibre-optic method of measuring the movements of the vocal cords on induction of anaesthesia, to examine the actions of two commonly used anaesthetic induction agents on the sensitivity of upper airway reflexes.