Deep procedural sedation has seen an increased use indication over the last couple of years aided by the introduction of high flow nasal oxygen therapy (HFNOT) during these procedures. However, this level of deep sedation does come with the increased risk of examining whether a patient is adequately ventilated during this procedure.

The definition of deep sedation is: 'a drug-induced depression of consciousness during which patients cannot be easily aroused but respond purposefully following repeated or painful stimulation. The ability to independently maintain ventilatory function may be impaired. Patients may require assistance in maintaining a patent airway, and spontaneous ventilation may be inadequate. Cardiovascular function is usually maintained.' As the definition showed there may be an insufficient ventilation during deep sedation. Therefore, HFNOT is used to ensures that the peripheral oxygen saturation is sufficient. However, there are two potential disadvantages. HFNOT can mask the presence of an insufficient respiratory minute volume and an insufficient gas exchange, which can lead to high arterial CO2 (paCO2) levels. Another risk associated with HFNOT is the fact that high oxygen levels are toxic, and prolonged exposure to high partial oxygen pressures, can cause oxidative damage to cell membranes, collapse of the alveoli in the lungs, retinal detachment, and seizures. Most of this damage can be explained by hyperoxia that increases the 'leak' of electrons from the mitochondrial electron transport chain and the resulting increased generation of reactive oxygen species (ROS). Low paCO2 levels and hyperoxia cannot be examined using standard monitoring techniques therefore, this study will use the transcutaneous carbon dioxide (tcPCO2) a proven technique which correlates well to the arterial CO2 (paCO2) to evaluate whether there is an adequate level of ventilation during deep procedural anesthesia with HFNOT. Moreover, the cutaneous mitochondrial oxygenation (mitoPO2) will be monitored to determine the effects that deep procedural sedation with HFNOT has on the cellular oxygenation.

Inclusion Criteria:

• Age over 18 years
• Acceptable proficiency of the Dutch language
• Scheduled for a procedure requiring deep procedural sedation with HFNOT.

Exclusion Criteria:

• Porphyria
• Known intolerance to components of the ALA plaster
• Presence of mitochondrial disease
• Pregnancy/lactation
• Patients with skin lesions on the measurement location which impede measurements
• Incapability to provide inform consent, due to a mental condition interfering with the ability to understand the provided information

The study population will be composed of patients undergoing procedures which require deep procedural sedation with HFNOT.