<prompt> Least useful in Treatment of local anesthetic induced convulsionsseizures?Phenytoin sodiumThiopentone sodiumMidazolamPropofol  <response>: Ans. a Phenytoin sodium Ref. Katzung pharma, 9thChapter 26; Anaesthesia by Ajay Yadav 3rdpg. 111When local anesthetic-induced seizures occur, hypoxia, hypercarbia and acidosis develop rapidly. ABC Airway, Breathing and Circulation is the mainstay of treatment. Administration of O2 by mask, or ventilation support by bag and mask, is often all that is necessary to treat seizures. If seizures interfere with ventilation, benzodiazepines, small dose propofol or thiopental can be used. The use of succinylcholine effectively facilitates ventilation and, by abolishing muscular activity, decreases the severity of acidosis. However neuronal seizure activity is not inhibited and therefore, cerebral metabolism and oxygen requirements remain increased.LOCALANAESTHETICSMechanism of action of local anesthetics Diffusion of the unionized base form across the nerve sheath and membrane Re-equilibration between the base and cationic forms in the axoplasm Binding of the cation to a receptor site inside of the Na channel, resulting in its blockade and consequent inhibition of Na conductance.Order of blockade: small fibre large fibres; myelinated fibres unmyelinated fibres. Modality blocked: autonomic and pain touchpressure motor. There are two main classes: amides and esters.Local anesthetic potencyAgentLipid SolubilityRelative PotencyProteinDuration Binding pKaOnset TimeProcaine115Short8.9Slow2-Chloroprocaine13-Short9.1Very QuickquickMepivacaine11.575Medium7.7QuickLidocaine3265Medium7.8QuickBupivacaine28895Long8.1ModerateTetracaine80895Long8.4SlowEtidocaine140895Long7.9QuickRopivacaine14894Long8.1ModerateLocal anaesthetic Toxicity:The following are accepted plasma levels of selected local anesthetics, above which systemic effects are expected in humans: Lidocaine 5 mcgmL; mepivacaine 5 mcgmL; bupivacaine 1.5 mcgmL; ropivacaine 4 mcgmL.A. CNS Toxicity Lightheadedness, tinnitus, perioral numbness, confusion especially known with Lignocaine Muscle twitching, auditory and visual hallucinations Tonic-clonic seizure, unconsciousness, respiratory arrest Benzodiazepines or rapidly acting barbiturates administered intravenously are the drugs of choice for both the prevention and arrest of convulsions. Transient neurological symptoms is side-effect of LIGNOCAINE Seizures induced by local anesthetics can also be treated with small doses given intravenously of thiopental 1-2 mg kg, propofol 0.5-1 mgkg, midazolam 2-4 mg total dose, or diazepam 0.1 mgkg.B. Cardiotoxicity Hypertension, tachycardia,can occur or Decreased contractility and cardiac output, Sinus bradycardia, ventricular dysrhythmias, circulatory arrest Bretylium tosylate is drug of choice for lignocaine-induced arrhythmias.C. Methemoglobinemia Prilocaine doses of more than 600 mg are needed to produce clinically significant methemoglobinemia. Depending on the degree, methemoglobinemia can lead to tissue hypoxia. 02Hb curve shifts to left P50 27 mmHg. Rx:Methylene blue l-2mgkg of 1 solution over 5 min or less successfully with ascorbic acid 2 mgkg.Educational points:Ropivacaine Ropivacaine is a new amide local anesthetic that is structurally and behaviorally similar to bupivacaine. Like bupivacaine, it is highly protein bound and has a lengthy duration of action. It is, however, less cardiotoxic. With ropivacaine, sensory anesthesia may be provided without a significant degree of motor blockade. These characteristics may make ropivacaine an ideal anesthetic for use in obstetric procedures. 