<prompt> A 25 year old male with roadside accident underwent debridement and reduction of fractured both bones right forearm under axillary block.On the second postoperative day the patient complained of persistent numbness and paresthesia in the right forearm and the hand. The commonest cause of this neurological dysfunction could be all of the following except :Crush injury to the hand and lacerated nervesA tight cast or dressingSystemic toxicity of local anaestheticsTourniquet pressure  <response>: C i.e. Systemic toxicity of Local AnaestheticsSystemic toxicity of LA include - CNS toxicity, cardiovascular system, methemoglobinemia Allergies.CNS is paicularly vulnerable to toxicity is the site of premonitory signs of overdose in awake patients. Coical inhibitory pathways are most susceptible resulting in excitatory motor phenomenon in initial stages of LA toxicity.Hypercapnia, respiratory metabolic acidosis exacerbates CNS toxicityQ. Increased PaCO2 increases cerebral blood flow delivering greater dose of LA more rapidly to brain. And decreased intracellular pH ours formation of non diffusable cationic protonated form of LA, which is trapped within neuron. Finally plasma protein binding of LA is decreased in acidic environment resulting in increased availability of free drug for diffusion into brain.But the involvement of the peripheral nerve is characterized by parathesies, numbness, hypaesthesia, pain and neurological dysfunction.So, this patient is having peripheral nerve injury. It could have happened dt:- Open crush injury 1 t laceration of nerves. As the patient underwent debriment, so he is a case of open injury.Nerve injury during debriment.Nerve injury during reduction manipulation.Tourniquet pressure palsyNerve injury dt tight bandage or cast. 