Transcatheter aortic valve implantation (TAVI) is now the standard procedure for elderly patients with severe aortic stenosis. This patient group is characterised by increased frailty, multiple comorbidities and limited physiological reserve, exposing them to an increased risk of intraoperative complications.

The majority of TAVI procedures are now performed under conscious sedation, in order to limit the risks associated with general anaesthesia and to promote a faster recovery. However, this strategy carries a risk of intraoperative respiratory events, notably bradypnoea, oxygen desaturation and airway obstruction, particularly in elderly patients with comorbidities.

The anaesthetic strategy, and in particular the type of sedation used, is likely to influence intraoperative respiratory and haemodynamic tolerance. Traditionally used agents, such as propofol combined with opioids, can induce dose-dependent respiratory depression. Conversely, dexmedetomidine, an α2-adrenergic receptor agonist, has a distinct pharmacological profile, characterised by sedation with a theoretically limited respiratory impact.

However, comparative data regarding the impact of different sedation strategies on intraoperative respiratory tolerance during TAVI remain limited, justifying the conduct of this study.

Dexmedetomidine is a selective α2-adrenergic receptor agonist, used in anaesthesia and intensive care for its sedative and anxiolytic properties. It induces what is known as 'cooperative' sedation, characterised by the maintenance of relative alertness, the possibility of interacting with the patient and, above all, a limited impact on spontaneous breathing.

Physiologically, dexmedetomidine differs from conventional sedatives, such as propofol and opioids, in causing less respiratory depression, making it a particularly attractive option for conscious sedation. This property is essential in elderly and comorbid patients, particularly during procedures such as TAVI, where maintaining spontaneous ventilation is a major concern.

Several clinical studies, particularly in procedural sedation and interventional cardiology, suggest that the use of dexmedetomidine is associated with better respiratory tolerance, with a reduction in episodes of desaturation, bradypnoea and the need for airway interventions, compared with strategies based on propofol and opioids.

However, data specific to the context of TAVI under conscious sedation remain limited, particularly regarding the prospective and standardised assessment of intraoperative respiratory events.

This study therefore aims to address this knowledge gap by assessing the effect of dexmedetomidine, compared with standard sedation using propofol-remifentanil, on intraoperative respiratory tolerance in patients undergoing TAVI under conscious sedation.

Inclusion Criteria:

• -aged 60 or over,
• undergoing transfemoral TAVI,
• treated under sedation without general anaesthesia,
• having given their written informed consent,
• with sufficient command of French to undertake cognitive tests.

Exclusion Criteria:

• whose first language is not English,
• who have a contraindication to dexmedetomidine,
• who require conversion to general anaesthesia during the procedure,
• or who present with major haemodynamic instability (shock, uncontrolled arrhythmia).

The anaesthetist and the investigator will know which group the patient has been allocated to (dexmedetomidine sedation versus propofol-remifentanil sedation). The pumps used to administer these drugs will be concealed from the patient and the interventional cardiologist.

The interventional cardiologist and the patient will not know which group the patient has been allocated to.