ABSTRACT
Local anaesthetics block sodium channels, preventing neural transmission. Higher concentrations are required to block motor nerves which have the thickest myelin sheath.
Unmyelinated and lightly myelinated C and A delta pain and temperature fibres are blocked at low concentrations. Autonomic nerves are also blocked; thus, vasodilatation and hypotension are side effects. Intravenous fluid loading and vasopressors are used to combat hypotension. Blockade at the level of cardioaccelerator fibres T1-T4 will cause bradycardia and hypotension.
