You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Outcome", "Participant", "Intervention"].

Please return the output as a JSON object of the format: {"Participant" : ["patients with COPD", ...], "Intervention" : ["Atenolol", ...], "Outcome" : ["blood pressure", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Injection pain with propofol . Reduction with aspiration of blood . A randomised , controlled , single-blind study was performed on 100 patients to investigate a new method of reducing pain on propofol injection . Aspiration of 2 ml of the patient 's blood into a syringe of propofol immediately before injection was compared with the addition of lignocaine 20 mg or normal saline 2 ml to the propofol before injection . The addition of blood was significantly more effective in reducing pain on injection than the addition of saline ( p < 0.001 ) , but was not significantly more effective than the addition of lignocaine .
{"Intervention": ["lignocaine 20 mg", "propofol", "2 ml to the propofol before injection", "propofol .", "normal saline"], "Outcome": ["pain", "reducing pain on injection", "effective", "Injection pain"], "Participant": ["100"]}