Sedation will be started by 10-15 mcg/kg Alfentanil and 0.4 mg/kg Propofol, or by 0.2-0.3 mg/kg Ketamine and 0.4 mg/kg Propofol. It will be maintained by additional boluses of Propofol (aliquots of 10-50 mg) or by additional boluses of Propofol (aliquots of 10-50 mg) and/or Ketamine (aliquots of 5-25 mg).