Abstract: ObjectiveOur study was to analyze the effect and safety of micro-dose ketamine plus fentanyl in patient-controlled intravenous analgesia (PCIA) for advanced cancer. MethodsEighty advanced cancer pain patients required were randomly divided into fentanyl group (group F) (n=20) and ketamine plus fentanyl groups (FK) (n=60). FK group included three groups of equal number,ie. FK1 Group(100 μg/ml fentanyl+ 1 mg/ml ketamine), FK2 Group(100 μg/ml fentanyl+ 2 mg/ml ketamine) and FK3 Group(100 μg/ml fentanyl+ 3 mg/ml ketamine). Analgesic consumption score, sedation score, respiratory depression, delirium and other complications were recorded during analgesia. ResultsIn non-load condition, the onset time of analgesia in group FK2, FK3 was shorter than that in group F and group FK1. Fentanyl consumption in group F showed obviously increasing trend. Fentanyl consumption in group FK was constant during treatment and lower than that in group F. Group FK2 patients had better effect, almost did not need to regulate analgesia pump. Fentanyl consumption in FK3 was significant lower than that in other three groups, although with increased incidence of excessive sedation. No respiratory depression, hallucinations, delirium and other symptoms were observed. ConclusionMicro-dose ketamine could significantly reduce fentanyl consumption through protection of anti-opioid receptor, improve fentanyl tolerance, and enhance the quality of fentanyl PCIA analgesia in patients with advanced cancer. 0.006 μg/kg. fentanyl plus (1.3 ±0.02) μg/kg ketamine was an ideal combination.