Comparison of upper airway properties during dexmedetomidine and propofol sedation

INTERVENTION: A randomised cross over study design will be employed. 20 healthy volunteers will participate in two daytime anaesthesia studies during which they will receive light or deep sedation with intravenous dexmedetomidine or propofol in randomized order on two separate days. Study days are separated by at least 1 week. Airway collapsibility (pharyngeal critical pressure; Pcrit and pharyngeal closing pressure; Pclose), neuromuscular responsiveness derived from genioglossus EMG (EMGgg), and sedation depth (Observer’s Assessment of Alertness/Sedation (OAAS) Scale, Richmond Agitation Sedation Scale (RASS), University of Michigan Sedation Scale (UMSS) and processed EEG/EMG (Bispectral Index Score; BIS)) will be assessed at light and deep levels of sedation. Pclose will also be assessed at 2 minute intervals following cessation of drug infusion. EEG (O1,C3,F3,M2), End‐tidal CO2 (EtCO2), transcutaneous CO2 (TcCO2) and oesophageal pressure (Pes) will be monitored continuously. Drug dosing involves a bolus dose (10 minutes at 0,6 microg/kg (DEX) or 4,5 mg/kg/h (= 75 microg/kg/min)(Propofol)) followed by a maintenance infusion aiming for light sedation (DEX: 0,5 microg/kg/h; Propofol 2,5 mg/kg/h (= 42 microg/kg/min)) then deep sedation (DEX: 1,5 microg/kg/h; Propofol 5 mg/kg/h (= 83 microg/kg/min)). At each level of sedation 20 mins is allowed for attainment of steady state prior to beginning measurements. Venous blood samples will be collected at baseline and completion of measurements at light and deep sedation levels for determining drug plasma concentrations. The first measurement will be made at completion of the 30min bolus/steady state period and sedation will not extend beyond 75 mins from the time of the start of the first measurement. CONDITION: anaesthesia safety PRIMARY OUTCOME: Airway collapsibility ; 1. pharyngeal critical pressure technique (Pcrit) where applied nasal pressure is lowered during early expiration for 5 breaths to a pressure eliciting flow limitation and then returned to the holding pressure. Following a recovery period to allow all physiological measurements to stabilise nasal pressure is again lowered to induce a different degree of flow limitation. A minimum of three pressure reductions inducing variable degrees of flow limitation (identified from no further increase in flow despite 3cmH2O increase in negative pressure as assessed by Pes) are required to produce a single Pcrit measurement from the relationship between airflow and pressure. Pcrit is the pressure at which flow would be zero. Any breaths associated with arousal or variations in sleep stage are excluded. ; 2. airway collapsing pressure (Pclose) technique where airflow is abruptly occluded with a pneumatic balloon valve for a maximum of 5 inspiratory efforts. The mask pressure (Pmask) at which the point of divergence between Pmask and Pes the Pclose. SECONDARY OUTCOME: Apneas, mean frequency and duration as identified from the pneumotach‐dervied airflow signal will be reported. Bispectral Index (BIS), mean, maximum and minimum values arousability (sedation depth), OASS, RASS, UMSS neuromuscular responsiveness (genioglossus EMG; EMGgg), phasic and tonic EMGgg INCLUSION CRITERIA: healthy volunteers