Local Anaesthesia Part 1 PDF

Local Anaesthesia Part 1 Lucy Harrison FCSP Key GDC learning outcomes 1.1.5 1.1.8 Describe relevant and 1.1.6 Describe the propertie...

Local Anaesthesia Part 1 Lucy Harrison FCSP Key GDC learning outcomes 1.1.5 1.1.8 Describe relevant and 1.1.6 Describe the properties of appropriate dental, oral, Describe relevant and relevant medicines and craniofacial and general appropriate physiology and therapeutic agents and anatomy and explain their explain its application to discuss their application to application to patient patient management patient management management 1.7.4 Manage patient anxiety and 1.7.5 pain through effective Manage patient pain communication, through the appropriate use reassurance and relevant of analgesia behavioural techniques Aims and Objectives By the end of this session students should be able to:  Describe various types of pain control and justification of using pain control agents  Explain how LA agents work  Explain the systemic effects of LA  Discuss the contra-indications and cautions of LA agents Terminology Analgesia – loss of pain sensation unaccompanied by loss of other forms of sensibility e.g. pressure Anaesthesia – loss of all forms of sensation; pain, touch, temperature, pressure perception Both may be local (only part of body affected) or general (all body affected)​ Pain in dentistry The aim of dental treatment is to contain active disease and prevent its recurrence  Oral tissues are well supplied with nerves which carry sensations to the brain  Some dental treatment is perceived as painful How can we avoid this? Pain Reaction The same stimulus produces different reactions in different people Even the same patient may react in a different way to the same stimulus at different times This is due to the appreciation of pain within the central nervous system Why? Differences in pain reaction are partly explained by the Gate Control Theory Control of Pain Pain can be abolished by interrupting the neural pathways at various levels to produce a permanent or temporary result For dental treatment, removal of the stimulus is not possible. We require reversible pain control at a local level This is achieved by the use of a local anaesthetic which blocks painful impulses being conveyed Don’t forget that because of the gate control theory, the effect of local analgesia can be enhanced by the surgery environment, hypnosis and distraction Local anaesthesia Can be achieved by: 1. Application of cold 2. Application of pressure 3. Use of drugs How does LA Agent work?  This is the headline LA agents work by blocking transmission of impulses in sensory nerves  Action potential revision Electrical impulse produced by a nerve cell Travels in one direction Can only send one message at one speed The frequency or number of pulses can vary Impulse transmission Resting potential High Na+ (extracellular) Low K+ (intracellular) Semi-permeable nerve cell membrane Resting potential (-70mV) Depolarization With a stimulus…  Increased permeability of nerve cell membrane to Na+ ions  Na+ ions rush into nerve cell  Membrane potential becomes +ve (+40mV) Repolarization Brings back the neuron cell to the membrane resting potential  Sodium-potassium pump actively moves Na+ and K+ ions across the nerve cell membrane to restore balance  Membrane potential returns to approximately -70mV  Blocking of nerve conduction LA agents set up a chemical roadblock between the source of the impulse and the brain LA agent acts in two ways: 1. Binds to specific receptors in the sodium channels in the nerve cell membrane blocking the inward movement of Na+ ions during the conduction of an impulse 2. Non-specific expansion of nerve cell membrane causing physical obstruction of the Na+ channels No action potential generated so no impulse conducted to brain Nerve conduction blocked Local Anaesthetic Agents Local anaesthetic agent May be described as a drug which brings about a temporary loss of pain sensation in a limited area of the body The drug acts by making the nerve fibres incapable of transmitting an impulse on stimulation Properties of an ideal LA agent Effective and Diffuse through the reversible action on Not irritate or injure Produce rapid onset lipid membrane of the nerves and nerve the tissues of numbness nerve fibre endings Allow combination Adequate working Isotonic (same pH as High safety margin with a time body) vasoconstrictor Capable of Adequate shelf life sterilization Contents of a dental LA cartridge Analgesic agent For blockade of nerve conduction E.G. Lidocaine, Prilocaine, Articaine, Mepivacaine Vasoconstrictor To increase depth and duration of analgesia E.G. Epinephrine, Felypressin Reducing agent To prevent oxidation of the vasoconstrictor E.G. Sodium metabisulphite Vehicle To carry the above agents and ensure solution isotonic E.G. Sterile saline Ester VS Amide Benzocaine Lidocaine Cocaine Prilocaine Procaine Amethocaine Mepivacaine Articaine Bupivacaine Ropivacaine Levobupivacaine  General features Organic weak bases which are insoluble in water Converted into soluble salts (hydrochlorides) for clinical use 2 chemical forms: un-ionized and ionized forms (weak base) Un-ionized form  Lipid soluble  Able to cross the fatty sheath around the nerve to gain access to nerve fibres Ionized form  Actually blocks nerve conduction  Once solution inside nerve fibres  Amides - Lidocaine Lidocaine 2% with epinephrine 1:80,000 is the gold standard for most dental procedures  Effective  Rapid onset  Useful duration of pulpal and soft tissue analgesia  Low toxicity  Good topical effect Gold standard for most dental procedures Lidocaine topical preparations Xylocaine spray 10mg Lidocaine per spray Xylonor gel Lidocaine 5%, cetrimide 0.15% Onset of action 2-5 min Amides - Prilocaine  As potent as lidocaine  Shorter duration of action  Less vasodilation than lidocaine so can be Citanest 3% + Octapressin (Felypressin) (0.03iu/ml) delivered without a vasoconstrictor  Sometimes combined with felypressin but less vasoconstriction than epinephrine Citanest 4% plain  Rapidly dispersed and cleared (No vasoconstrictor)  Very low incidence of side effects Amides - Mepivacaine  Similar properties to prilocaine  Shorter analgesia if used as infiltration (15-30 minutes) Scandonest 3% Plain Scandonest 2% with epinephrine 1:100,000 Amides - Articaine  Powerful analgesic agent  Rapid onset of action  Longer duration of soft tissue analgesia  Rapidly metabolized in plasma and liver CAN NOT BE GIVEN AS A INFERIOR DENTAL BLOCK Septanest 1:100,000 4% articaine hydrochloride with epinephrine 1:100,000 Septanest 1:200,000 Amides - Bupivacaine  Very long lasting (6-8 hours)  Depresses cardiac activity and causes dysrhythmias  Useful for post-surgery Not available in dental use cartridges- given with standard medical type syringe Form: Marcaine + epinephrine Vasoconstrictors Increase depth and duration of anaesthesia Epinephrine (1:80,000, 1:100,000 or 1:200,000) Occurs naturally in the body More profound analgesia Haemorrhage control Felypressin (0.03 IU/mL) Synthetic octapeptide Not such a profound vasoconstrictor Duration of anaesthesia Preparation Pulpal anaesthesia Soft tissue anaesthesia Lidocaine 2% + 45 minutes 3 + hours epinephrine 1:80,000 Prilocaine 3% + 30–45 min 2 hours felypressin 0.03iu/ml Articaine 4% + 75 min 3-4 + hours epinephrine 1:100,000 Mepivacaine 3% plain 20 min 1 hour Bupivacaine 4 hours 6 –8 hours Maximum safe dosages  Effectiveness of L.A. depends on… Analgesic potency of the agent Concentration of the agent Solubility of the agent in (a) water (b) lipid How long it stays at the injection site (concentration of agent and vasoconstrictor) Rate at which agent is metabolized at injection site Accuracy of technique Amount of spread and diffusion of agent Presence of inflammation and infection General Contraindications and cautions Latex allergy All LA cartridges at Eastman have latex-free bungs Need to check in other dental practices