Ketamine potentiates the sedative effect of propofol, while propofol blunts the emergence 'terror' response to ketamine.
Propofol is a non-barbiturate sedative hypnotic with minimal direct analgesic properties. A relatively large total dose would be needed for effective sedation during a potentially painful procedure. Propofol dosage is limited by its potential to depress the respiratory drive, and to cause hypotension.
Ketamine is a 'dissociative' agent, blocking conscious awareness by interrupting communication between the thalamic and limbic brain regions. Respiratory drive is preserved. Patients receiving ketamine at any dose may experience the release of vivid (comforting or frightful) imagery upon emergence.
Propofol and ketamine used in combination is more effective than either one used alone. A single dose of ketamine (0.5 to 1 mg/kg) is followed by multiple small (0.25 mg/kg) doses of propofol, titrated to effect: analgesia with intact respiratory drive. Unpleasant ketamine emergence reactions are rare, as awareness of disinhibition is blunted by the residual effects of propofol; a benzodiazepine is therefore not needed.
Arora S. Combining Ketamine and Propofol (“Ketofol”) for Emergency Department Procedural Sedation and Analgesia: A Review. West J Emerg Med 2008
Akin A, Esmaoglu A, Tosun Z, et al. Comparison of propofol with propofol-ketamine combination in pediatric patients undergoing auditory brainstem response testing. Int J Pediatr Otorhinolaryngol 2005