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 :
C i.e. Systemic toxicity of Local Anaesthetics Systemic 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 d/t: - 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 palsy Nerve injury d/t tight bandage or cast.
Crush injury to the hand and lacerated nerves
A tight cast or dressing
Systemic toxicity of local anaesthetics
Tourniquet pressure