Description
This presentation provides a comprehensive overview of local anesthetics and spinal anesthesia, delivered by Sophia Mwale at the University of Zambia School of Medicine. It begins with the classification of local anesthetics into esters and amides, detailing their metabolism and common examples. The mechanism of action, involving sodium channel blockade to prevent action potential propagation, is clearly explained. The lecture covers various administration techniques, including topical application, infiltration, nerve blocks, and intravenous regional anesthesia, before focusing extensively on spinal and epidural methods. It details the anatomy for spinal needle insertion, patient positioning, and key landmarks like Tuffier's line. Indications for spinal anesthesia, such as lower limb orthopedic surgery, hernia repairs, and caesarean sections, are listed alongside absolute and relative contraindications. The presentation thoroughly addresses local anesthetic systemic toxicity, its clinical features, and emergency management, including the use of lipid emulsion. Complications of spinal anesthesia, such as hypotension, total spinal block, and post-dural puncture headache, are discussed with specific treatment protocols. This resource is designed for medical students and clinical officers seeking foundational and practical knowledge in regional anesthesia for exam preparation and clinical practice. Review this material to strengthen your understanding of safe anesthetic techniques.
What's inside
University of Zambia School of Medicine Local Anaesthetics and Spinal Anaesthesia PRESENTER : SOPHIA MWALE MODERATOR : DR SARA Learning Objectives The classification of local anaesthetics The mechanism of action of local anaesthetics Anatomy of spinal cord Use and indications of spinal anaesthesia Basic principles of epidural anaesthesia Common drugs o Lignocaine o Bupivocaine Complications of spinal anaesthesia and their management Introduction Local anaesthetics are agents that produce localized, reversible block to nerve conduction. - They are administered locally. Classification • • • • Local anesthetics are composed of an aromatic ring linked to an hydrophilic amine group via an intermediate link chain. It is the nature of this linking chain that is used to classify the local anesthetic as either an I . ester or II . amide. Ester Local Anaesthetics • • • Contains several less frequently used local anaesthetics. A good pneumonic to remember the ester LA’: CAPE: Cocaine, Amethocaine, Procaine = Esters Esters are metabolised by hydrolysis by pseudocholinesterases found in the plasma Amide Local Anaesthetics All the amide local anaesthetics contain two i’s: li gnocai ne, bupi vocai ne, pri locai ne, ropi vocai ne They are broken down by hepatic amidases and therefore their metabolism is affected by conditions which affect hepatic blood flow Mechanism of Action • • • • • LA’s act by blocking sodium channels. Sodium channels are found on the lipid bilayer of nerve axons. The aim of using local anaesthetics is typically to prevent the passage of afferent nerve action potentials. The drugs cross the neuronal membrane into the axoplasm. They then block the sodium channel from ‘the inside’. This stabilises the membrane and prevents generation of further action potentials Uses /indications 1. Topical - Can be applied to skin as a cream to reduce pain at venepuncture/cannulation. - Brands include EMLA and typically take 45min-60min to work. - LA’s can also be used topically as eye drops 2. Infiltrative Anaesthesia: Most commonly this is to the skin. Surgeons may infiltrate a wound site at the end of an operation 3. Nerve blocks: Include ring blocks (digital nerves for whole finger), femoral nerve blocks, brachial plexus blocks. 4. Intravenous Blocks (Bier’s Block) - These blocks require local anaesthetic drugs to be given - intravenously whilst a tourniquet is in place inflated. - As such there is a high risk of local anaesthetic toxicity and therefore they should only be undertaken by an experienced doctor. 5. Spinal Anaesthesia - If LA is injected into the cerebrospinal fluid in the lumbar region a dense motor and sensory block below the level of injection can be achieved. - used for obstetric (Csection) and lower limb surgery. -However a greatly reduced dose is required and in overdose the block can travel up the spinal sensory levels. - In very high levels this can affect breathing and level of consciousness – known as a ‘high spinal’ – an anaesthetic emergency 6. Epidural Anaesthesia: - By placing a plastic catheter in the epidural space (the potential space that exists around the dura mater of the spinal cord) the LA can prevent conduction of the nerve roots arising from that level of the spinal. - This creates a band of reduced sensation a the sensory level of the injection (eg thoracic, lumbar). Local Anaesthetic Drugs • • • • Lignocaine Lignocaine is an amide local anaesthetic. It comes as a clear colourless solution and has a shelf life of around two years. It may come as a 1%, 2% or 4% solution so be careful to check. It can be used via a variety of roots: topical, infiltration, intrathecally (spinal), epidurally. Its mechanism of action is to block sodium channels preventing the conduction of action potentials.
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