During apnoeic oxygenation there is a continuous raise in carbon dioxide with subsequent respiratory acidosis. The hypercapnia and respiratory acidosis have several dose-related effects on both the systemic and the pulmonary circulation and the heart that ultimately, if unrecognised, can result in cardiovascular collapse and fatal arrhythmias. In our knowledge, no studies have investigated the haemodynamic effects of apnoeic oxygenation with HFNO. The general purpose of this project is to investigate haemodynamic alternations during apnoeic oxygenation with HFNO compared to mechanical ventilation in relatively healthy patients under general anaesthesia during laryngeal surgery.