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Local anaesthesia
 

Local anaesthesia

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    Local anaesthesia Local anaesthesia Presentation Transcript

    • Local Anaesthesia DEFINITION: Local anaesthesia is drug-induced reversible local blockade of nerve conduction in a specific part of the body that does not alter consciousness.
    • Prosperities of ideal LA Reversible action. Non-irritant. No allergic reaction. No systemic toxicity. Rapid onset of action. Sufficient duration of action. Potent. Stable in solutions. Not interfere with healing of tissue. Have a vasoconstrictor action or compatible with VC. Not expensive
    • structural classification of local anaesthetics•Examples ofamides includelidocaine,bupivacaine andprilocaine.Examples of estersinclude cocaine,procaine andamethocaine.
    • Esters vs Amides The ester linkage is more easily broken so the ester drugs are less stable in solution and cannot be stored for as long as amides. Amide anaesthetics are also heat-stable. The metabolism of most esters results in the production of para-aminobenzoate (PABA) which is associated with allergic reaction. Amides, in contrast, very rarely cause allergic phenomena. For these reasons amides are now more commonly used than esters.
    • The mechanism of action of local anaesthetics Disruption of ion channel function via specific binding to sodium channels, holding them in an inactive state. Disruption of ion channel function by the incorporation of local anaesthetic molecules into the cell membrane .
    • Demonstrating video
    •  Small nerve fibres are more sensitive than large nerve fibres Myelinated fibres are blocked before non-myelinated fibres of the same diameter. Thus the loss of nerve function proceeds as loss of pain, temperature, touch, proprioception, and then skeletal muscle tone. This is why people may still feel touch but not pain when using local anaesthesia.
    • LA and pH All local anaesthetic agents are weak bases, meaning that they exist in two forms: unionised (B) and ionised (BH+). The pKa of a weak base defines the pH at which both forms exist in equal amounts. As the pH of the tissues differs from the pKa of the specific drug, more of the drug exists either in its charged or uncharged form.
    • Local anaesthetics and infection The relevant feature of infected tissue is that it tends to be a more acidic environment than usual. As the pH is reduced the fraction of unionised local anaesthetic is reduced and consequently the effect is delayed and reduced. Infected tissue may also have an increased blood supply and hence more anaesthetic may be removed from the area before it can affect the neurone.
    • Physicochemical characteristics of a local anaesthetic affect its function The aromatic ring structure and hydrocarbon chain length determine the lipid solubility of the drug. The more lipid soluble drug penetrates the cell membrane more easily to exert its effect. Thus bupivacaine – which is highly lipid soluble – is approximately four times more potent than lidocaine.
    • The duration of action The duration of action of the drug is also related to the length of the intermediate chain joining the aromatic and amine groups. Protein binding , Procaine is only 6% protein bound and has a very short duration of action, wherease bupivacaine is 95% protein bound. bupivacaine have a longer duration of action .
    • Absorption and distribution Some of the drug will be absorbed into the systemic circulation: how much will depend on the vascularity of the area to which the drug has been applied. The distribution of the drug is influenced by the degree of tissue and plasma protein binding of the drug. the more protein bound the agent, the longer the duration of action as free drug is more slowly made available for metabolism.
    • Metabolism and excretion Esters (except cocaine) are broken down rapidly by plasma esterases to inactive compounds and consequently have a short half life. Cocaine is hydrolysed in the liver. Ester metabolite excretion is renal. Amides are metabolised hepatically by amidases. This is a slower process, hence their half-life is longer and they can accumulate if given in repeated doses or by infusion.
    • Adverse Effects CNS: excitation followed by depression (drowsiness to unconsciousness and death due to respiratory depression. Cardiovascular System: bradycardia, heart block, vasodilation (hypotension) Allergic reactions: allergic dermatitis to anaphylaxis (rare, but occur most often by ester-type drugs).
    • Mechanism•Block nerve conduction reversibly. Two groups amideProcaine,chloroprocaine,tetracaine Lidocaine,prillocaine,mepivocaine,bubi vacaine,ropivacaineLess common More commonPlasma cholinestrase Metabolized at liverMore side effect less
    • Uses: Local anesthesia. Ventricular arrhythmia. Decrease haemodynamic response to tracheal intubation also decrease cough. Treatment of epileptic fits.
    • Advantage of using adrenaline:•Epinephrine vasoconstricts arteries reducing bleeding and also delays theresorption of lidocaine, almost doubling the duration of anaesthesia.•Bupivacaine has caused several deaths when the epidural anaesthetichas been administered intravenously accidentally.
    • Treatment of overdose: lipid rescue There is animal evidence that Intralipid, a commonly available intravenous lipid emulsion, can be effective in treating severe cardiotoxicity secondary to local anaesthetic overdose.
    • Contraindications Heart block, second or third degree (without pacemaker) Severe sinoatrial block (without pacemaker). Serious adverse drug reaction to lidocaine or amide local anaesthetics. Concurrent treatment with quinidine, flecainide, disopyramide, procainamide (Class I antiarrhythmic agents). Prior use of Amiodarone hydrochloride.
    •  Hypotension not due to Arrhythmia. Bradycardia. Accelerated idioventricular rhythm.
    • Six Placement SitesSurface/topical Local infiltration Peripheral nerve anesthesia block Bier block (IV Epidural Spinal anesthesia regional anesthesia anesthesia)
    • Topical/Surface anesthesia For Application to mucous membranes: Nose- Mouth- Esophagus- Tracheobronchial tree- Genitourinary tract. Commonly used drugs:  Cocaine (4%-10%).  > 50% of rhinolaryngologic cases (USA).  Unique pharmacological property: produces localized vasoconstriction as well as anesthesia.  Localized vasoconstriction:  less bleeding.  improved surgical field visualization.
    • Cocaine substitution: lidocaine (Xylocaine) -oxymetazoline (Afrin) combinations. tetracaine (pontocaine)- oxymetazoline (Afrin) combinations. Tetracaine (pontocaine) (1%-2%). Lidocaine (Xylocaine) (2%-4%).Ineffective agents: Procaine (Novocain) & chloroprocaine (Nesacaine): poor mucous membrane penetration.
    •  Nebulized lidocaine (Xylocaine)-- surface anesthesia • Upper & lower respiratory tract prior to bronchoscopy or fiber- optic Laryngoscope. • Treatment for intractable cough. • Normal subjects: No effect on airflow resistance (they produce some bronchodilation). • Patients with asthma: nebulized lidocaine (Xylocaine) may increase airflow resistance (bronchoconstriction)-- concern if bronchoscopy is intended for this patient group.
    •  Systemic concentration following nebulized lidocaine (Xylocaine)  Following mucosal absorption: systemic.  concentration may be similar to IV injection. Reasons:  Large surface area.  Significant vascularity of tracheobronchial region.
    • Skin Surface ApplicationBarrier: keratinized skin layer  Higher local anesthetic concentrations required: o 5% lidocaine (Xylocaine)- prilocaine (Citanest) cream {2.5% lidocaine (Xylocaine) & 2.5% prilocaine (Citanest)}  no local irritation.  even absorption.  no systemic toxicity.
    • Combination of local anesthetic:Definition: eutectic mixture of local anesthetics (EMLA) .General definition: eutectic--said of a mixture which has the lowest melting point which it is possible to obtain by the combination of the given components.Melting point of combined drug is lower then either lidocaine (Xylocaine) or prilocaine (Citanest) alone.
    • Clinical uses of EMLA applications-- pain relief for:  Venipuncture  Lumbar puncture  Arterial cannulation
    • Special uses  In combination with nitroglycerin ointment -- makes venous cannulation easier by causing vasodilation.  EMLA use in blood sampling: no effect on blood analysis.Factors affecting EMLA analgesia time to onset, duration of action, & efficacy  Skin blood flow.  Epidermal/girl thickness.  Application duration.  Presence of pathology.
    • Contraindications/Concerns  EMLA cream not recommended for mucosal application due to faster lidocaine (Xylocaine)/prilocaine (Citanest) absorption.  EMLA cream not recommended for application to skin wounds (wound infection risk, increased)  EMLA cream: contraindicated in patients are allergic to amide local anesthetics
    • Local Infiltration Definition: Extravascular placement of the local anesthetic in the region to be anesthetized.  Example: subcutaneous local anesthetic injection in support of intravascular cannula placement. Preferred local anesthetics for local infiltration:  Most common: lidocaine (Xylocaine).  Other choices: 0.25% Ropivacaine (Naropin) or Bupivacaine (Marcaine) (effective for pain management at inguinal operative location),
    •  Duration of action:  Duration extended by 2x using 1:200,000 epinephrine.  Caution: Epinephrine-containing local anesthetic solution should not be injected intracutaneously (intradermal) or into tissues supplied by "end-arteries" such as ears, nose, fingers because vasoconstriction may be sufficiently severe to produce tissue ischemia and gangrene.
    • Peripheral Nerve Block Procedure: local anesthetic injection into tissues around individual nerves or nerve plexuses (e.g. brachial plexus). Mechanism:  Local anesthetic diffusion path: nerve outer surface (mantle) to the nerve core [driving force: concentration gradient].  Anesthetized first: mantle fibers (innervating more proximal structures).  Anesthetized last: core fibers (innervating more distal anatomy)  Explanation of why anesthesia develops proximately first.  Recovery in the opposite direction (sensation returns proximally first; lastly the distal anatomy).
    • •The median nerve is blockedby inserting the needlebetween the tendons of thepalmaris longus and flexorcarpi radialis. The needle isinserted until it pierces thedeep fascia. Three to 5 mL oflocal anesthetic is injected.Although the piercing of thedeep fascia has been describedto result in a fascial "click", it ismore reliable to simply insertthe needle until it contacts thebone. The needle is thenwithdrawn 2-3 mm and thelocal anesthetic is injected.
    •  Mixed peripheral nerves: (motor/sensory)  Sequence of onset & recovery (motor anesthesia first or sensory anesthesia first): dependent on anatomical locations within the nerve fiber. Not recommended: Tetracaine (pontocaine): slow onset & more likely to cause systemic toxicity; not recommended for peripheral nerve block or for local infiltration.
    • Duration of action-dependencies • Prolongation of drug effect: safer with added vasoconstrictor (e.g. epinephrine) than by increasing local anesthetic dose.  Example: bupivacaine (Marcaine) + epinephrine: peripheral nerve block may last 14 hours (in some reports).
    • Intravenous Regional Anesthesia (Bier Block)Procedure: Local anesthetic injection into an extremity isolated by tourniquet. Result: rapid anesthesia onset; skeletal muscle relaxation.Duration of anesthetic action: Dependent on how long the tourniquet is kept inflated. Following tourniquet deflation: rapid recovery as blood dilutes local anesthetic concentration.Probable Mechanism: Drug action on nerve endings & nerve trunks.
    • Lidocaine Prilocaine Higher lower plasma prilocaine (Citanest) concentrations following tourniquet deflation, compared to lidocaine Less SaferAgents not recommended:  Chloroprocaine (Nesacaine) -- High incidence of thrombophlebitis.  Bupivacaine (Marcaine) -- More likely than other local anesthetic to cause cardiotoxicity upon tourniquet deflation.  Ropivacaine (Naropin)-Might also cause cardiotoxicity upon tourniquet deflation (less likely than with bupivacaine (Marcaine)).
    • Indications for local anesthesia Most frequent use: regional anesthesia. Analgesic espescially post operative pain. Lidocaine (Xylocaine) also reduces blood pressure response to direct laryngoscopic tracheal intubation, an effect probably secondary to generalized cardiovascular depression. Treatment of intractable cough.
    • 1-Causes.2-Factors reducing toxicity.3-Signs and symptoms.4-Treatment of toxicity.
    • Causes : Accidental rapid intravenous injection Rapid absorption, such as from a very vascular site ie mucous membranes. Overdose .
    • Factors reducing toxicity: Decide on the concentration of the local anaesthetic that is required for the block to be performed. Calculate the total volume of drug that is allowed according to the table below
    •  Use the least toxic drug available Use lower doses in frail patients or at the extremes of ages Always inject the drug slowly (slower than 10ml /minute) and aspirate regularly looking for blood to indicate an accidental intravenous injection Injection of a test dose of 2-3ml of local anaesthetic containing adrenaline will often (but not always) cause a significant tachycardia if accidental intravenous injection occurs
    •  Add adrenaline (epinephrine) to reduce the speed of absorption. The addition of adrenaline will reduce the maximum blood concentration by about 50%. Usually adrenaline is added in a concentration of 1:200,000, with a maximum dose of 200 micrograms. Make sure that the patient is monitored closely by the anaesthetist or a trained nurse during the administration of the local anaesthetic and the following surgery.
    • Signs and Symptoms of Local Anaesthetic Toxicity:1-CNS toxicity : Early or mild toxicity: light-headedness, dizziness, tinnitus, circumoral numbness, abnormal taste, confusion and drowsiness. Severe toxicity: tonic-clonic convulsion leading to progressive loss of consciousness, coma, respiratory depression, and respiratory arrest.
    • 2-CVS toxicity: Early or mild toxicity: tachycardia and rise in blood pressure. This will usually only occur if there is adrenaline in the local anaesthetic. If no adrenaline is added then bradycardia with hypotension will occur. Severe toxicity: Usually about 4 - 7 times the convulsant dose needs to be injected before cardiovascular collapse occurs. Collapse is due to the depressant effect of the local anaesthetic acting directly on the myocardium.
    • Essential Precautions: Secure intravenous access before injection of any dose that may cause toxic effects Always have adequate resuscitation equipment and drugs available before starting to inject.
    • Treatment of Toxicity:Treatment is based on the A B C D of Basic Life Support : A. Ensure an adequate airway, give oxygen in high concentration if available B. Ensure that the patient is breathing adequately. Ventilate the patient with a self inflating bag if there is inadequate spontaneous respiration. Intubation may be required if the patient is unconscious and unable to maintain an airway.
    • C Treat circulatory failure with intravenous fluids and vasopressors such as ephedrine (10mg boluses) if hypotension occurs. Adrenaline may be used cautiously intravenously in boluses of 0.5 - 1ml of 1:10,000 (1mg in 10ml) if ephedrine is either not available or not effective in correcting the hypotension. Treat arrhythmias
    • D Drugs to stop fitting such as Diazepam 0.2-0.4mg/kg intravenously slowly over 5 minutes repeated after 10 minutes if required, or 2.5mg - 10 mg rectally. Thiopentone 1-4 mg/kg intravenously may also be used in theatre Treatment of local anaesthetic toxicity is likely to have a good outcome if toxicity is recognised and basic resuscitation is started early. Monitor patients closely when using local anaesthetics. If a reaction occurs.
    • Advantages of local anaesthesia Non inflammable. Excellent muscle relaxant effect. During local anesthesia the patient remains conscious. It requires less skilled nursing care as compared to other anesthesia like general anesthesia. Maintains his own airway.
    •  Less pulmonary complication.s Aspiration of gastric contents unlikely. Less nausea and vomiting. Contracted bowel so helpful in abdominal and pelvic surgery. Postoperative analgesia. There is reduction surgical stress. Earlier discharge for outpatients.
    •  Suitable for patients who recently ingested food or fluids. Local anesthesia is useful for ambulatory patients having minor procedures. Ideal for procedures in which it is desirable to have the patient awake and cooperative. Less bleeding. Expenses are less.
    • Disadvantages of local anaesthesia There are individual variations in response to local anesthetic drugs. Rapid absorption of the drug into the bloodstream can cause severe, potentially fatal reactions. Apprehension may be increased by the patients ability to see and hear. Some patients prefer to be unconscious and unaware.
    •  Direct damage of nerve. Post-dural headache from CSF leak. Hypotension and bradycardia through blockade of the sympathetic nervous system. Not suitable for extremes of ages. Multiple needle bricks may be needed.
    • Introduction Spinal anesthesia also called spinal analgesia or sub-arachnoid block (SAB), is a form of regional anesthesia involving injection of a local anesthetic into the subarachnoid space, generally through a fine needle.
    • Difference from epidural anesthesia Epidural anesthesia is a technique whereby a local anesthetic drug is injected through a catheter placed into the epidural space. This technique has some similarity to spinal anesthesia, and the two techniques may be easily confused with each other.
    • Differences include: The involved space is larger for an epidural, and consequently the injected dose is larger, being about 10– 20 mL in epidural anesthesia compared to 1.5–3.5 mL in a spinal. In an epidural, an indwelling catheter may be placed that avails for additional injections later, while a spinal is almost always a one-shot only. The onset of analgesia is approximately 15–30 minutes in an epidural, while it is approximately 5 minutes in a spinal.
    • Injected substances Bupivacaine (Marcaine) is the local anaesthetic most commonly used, although lignocaine (lidocaine), tetracaine, procaine, ropivacaine, levobupivicaine and cinchocaine may also be used. Sometimes a vasoconstrictor such as epinephrine is added to the local anaesthetic to prolong its duration.
    • Mechanism Regardless of the anesthetic agent (drug) used, the desired effect is to block the transmission of afferent nerve signals from peripheral nociceptors. Sensory signals from the site are blocked, thereby eliminating pain. The degree of neuronal blockade depends on the amount and concentration of local anesthetic used and the properties of the axon.
    • Limitations Spinal anesthetics are typically limited to procedures involving most structures below the upper abdomen. To administer a spinal anesthetic to higher levels may affect the ability to breathe by paralyzing the intercostal respiratory muscles, or even the diaphragm in extreme cases (called a "high spinal", or a "total spinal", with which consciousness is lost).
    • Indications This technique is very useful in patients having an irritable airway (bronchial asthma or allergic bronchitis), anatomical abnormalities which make endotracheal intubation very difficult (micrognathia), borderline hypertensives where administration of general anesthesia or endotracheal intubation can further elevate the blood pressure, procedures in geriatric patients.
    • Contraindications Non-availability of patients consent, local infection or sepsis at the site of lumbar puncture, bleeding disorders, space occupying lesions of the brain, disorders of the spine and maternal hypotension.
    • OperationsAll surgical interventions below the umbilicus, is the general guiding principle: Abdominal & vaginal hysterectomies Laparoscopy Assisted Vaginal Hysterectomies (LAVH) combined with general anesthesia Caesarean sections Hernia (inguinal or epigastric) Piles fistulae & fissures orthopaedic surgeries on the pelvis, femur, tibia and the ankle nephrectomy
    • Complications Can be broadly classified as immediate (on the operating table) or late (in the ward or in the P.A.C.U. post-anesthesia care unit): Spinal shock. Cauda equina injury. Cardiac arrest. Hypothermia. Broken needle. Bleeding resulting in hematoma, with or without subsequent neurological sequelae due to compression of the spinal nerves.
    •  Infection: immediate within six hours of the spinal anesthetic manifesting as meningism or meningitis or late, at the site of injection, in the form of pus discharge, due to improper sterilization of the LP set. PDPH: Post dural puncture head ache or post spinal head ache.
    • Epidural anesthesia
    • Mechanism Direct action on nerve roots and spinal cord following local anesthetic diffusion across the dura. Diffusion of local anesthetic into paravertebral region.
    •  Onset of action:15-30 minute delay . Choice of local anesthetics:  Lidocaine (Xylocaine): frequently used; diffuses well for tissues.  Bupivacaine (Marcaine) & Ropivacaine (Naropin) (0.5%-0.75%).
    • Epidural anathesia Spinal anathesiaSite of injection In the epidural space Subarachnoid spaceOnset and duration Slow onset and continous duration Rapid onset and limited (use catheter) durationadvantages Can be used in analgesia Not usedNeedle Curved,longand blunt (touhy) Small and sharpdose 10_30ml 1_4mlspace Any space usually lumber lumberQuality of sensory less More liableand motor nerveblocktoxicity Hypotention gradual Sudden total spinal +++ + systemic toxicity +++ +
    •  Indications: 1-Pain relief: a)Post operative b)Labour pain c)Cancer 2-Operations in perineum lower limb lower abdomen. 3-Expected difficult intubation. An epidural injection may be performed anywhere along the vertebral column (cervical, thoracic, lumbar, or sacral).
    • Contra indications: A)absolute: 1-Hypovolemia. 2-Refusal of patient. 3-Coagulopathy. 4-Local and systemic sepsis. B)relative: - Increase intra cranial pressure deformity of vertebral column.
    • ComplicationsA)during operation: 1)Hypotension 2)Bradycardia 3)Cardiac arrest 4)Nausea ,vomiting 5)Failed spinal 6)Total spinal 7)Broken needle 8)Hypothermia
    •  B)Post operative: 1)Post dural puncture headache. 2)Back pain. 3)Meningitis and neurological sequalae. 4)Haematoma. 5)Urine retention.