Acquired acute resistance to local anaesthetics in a patient of total knee replacement - A case report

A 72-year-old female patient weighing 80 kg underwent right total knee replacement (TKR) under successful subarachnoid block (SAB) and continuous femoral nerve block (cFNB). Five days later, SAB failed twice for left TKR, with no sensorimotor block observed. The patient refused general anaesthesia on the first day but underwent surgery under general anaesthesia the next day. Postoperative analgesia via ultrasound-guided cFNB was inadequate. This unusual sequence of events, involving differential success of SAB and nerve blocks during two surgeries with different drugs and techniques, suggests acquired acute resistance to local anaesthetics. While technical failure is a common cause of SAB failure, genetic variations in sodium channels, potentially acquired over time, may explain this phenomenon. Such resistance is rare and challenging to diagnose, highlighting the need for further investigation into molecular mechanisms and genetic testing in similar cases.