Catheter occlusion can occur as the result of several etiologies and the cause of the occlusion will help drive the appropriate interventions. Therefore, a thorough assessment of the catheter is a key initial step. Assessment should include whether the occlusion is partial (able to flush but not withdraw blood) or complete (unable to flush or withdraw blood), if the patient has any risk factors for occlusion (e.g. history of venous thromboembolism, specific cancer types such as lung, history of recent surgery), and if there is any pain or edema. Repositioning of the patient (e.g. lay flat, raise lateral arm, take deep breaths) should be attempted. Diagnostic testing and treatment will depend on the symptoms and cause of the occlusion. The Access Device Standards of Practice for Oncology Nursing contain algorithms for both partial and complete occlusions and the assessment, testing, and treatment recommended (pages 87-88). 

References:  

Camp-Sorrell, D., & Matey, L. (Eds.). (2017). Access device standards of practice for oncology nursing. Pittsburgh, PA: Oncology Nursing Society