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Background and Aims Delirium is being increasingly acknowledged as a significant adverse event that occurs postoperatively in elderly surgical patients. Upon establishing the diagnosis, the primary objective of delirium therapy is to identify crucial, potentially life-threatening, treatable organic causes responsible for this syndrome.

Methods We present a case of a 70-year-old woman, history of Hypertension, Diabetes Mellitus and hyperlipaemia who was submitted to an uneventful left total knee arthroplasty under general anaesthesia because she had history of previously failed spinal anaesthesia.

Results After admission to the PACU, she started to report knee pain NPS 9/10. Multimodal intravenous analgesia was initiated. Soon after patient started to become delirious, experiencing confusion, disorientation and maintaining repetitive speech about unbearable pain. Other pathophysiological causes of delirium beyond pain were excluded. None of the systemic analgesia strategies resulted in pain relief. So, a different approach based on regional analgesia were applied. We performed an Adductor Canal nerve block ultrasound-guided with ropivacaine. After a few minutes, resolution of the cognitive symptoms was archived, and the patient reported a pain score of NPS 2/10.

Conclusions Early diagnosis is the key to the effective treatment for early postoperative delirium and every patient admitted to the PACU should be screened. Risk factors assessment and effective strategies to prevent it should be implemented by routine. If established, treat of causes should be aimed. Pain can be a trigger for delirium and multimodal analgesia with peripheral nerve block can be used even in patient where neuraxial anaesthesia may be difficult.