Anesthetics A Short History of Anesthesia Before anesthesia surgery was butchery Dr William T G Morton first demonstrated the use of either as an anesthetic in either dome of MGH Two advances made modern surgery possible o Germ theory and antiseptic techniques o Treatment of shock from blood loss Balanced Anesthesia minimal doses Balanced Anesthesia uses combination of drugs to maximize effects with Different combinations of drugs may be used for different operations o Depend on patient and type of operation Stages of General Anesthesia Stage 1 analgesia Stage 2 excitement can be blocked by premedication Stage 3 surgical anesthesia o Plane 1 regular breathing o Plane 2 longer expiration o Plane 3 shallow breathing o Plane 4 diaphragm only Stage 4 breathing and heart stops toxic o Must take steps to resuscitate patient Inhalational General Anesthetics Nitrous Oxide laughing gas used as an adjunct with other anesthetics Protoype Isoflurane o Enflurane o Desflurane o Sevofluane o Ether strong irritant of respiratory system flammable In general the newer fluranes are similar differing primarily in onset and duration of action Anesthetic Potency Oil and Potency concentration or Potency measured as MAC minimal alveolar the concentration which half of the patients show no signs of pain when a standardized incision is made The more soluble in oil the more potent the anesthetic Rate of Onset and Recovery Rate of onset and recovery from inhaled anesthetics is controlled by solubility in blood The lower the solubility the faster the onset and recovery and vice versa Side Effects and Drug Interactions of Anesthetics Side Effects ADRs o Hypotension o Decreased temperature o Respiratory and cardiovascular depression o Malignant Hyperthermia muscles contract forcefully and burn energy shooting up body temperature Post Operative Effects o Delirium o Shivering o Hallucination o Confusion o Increased excitability Drug Interactions stimulated by EP with increased pressure Cardiovascular and Respiratory Effects o Inhaled anesthetics predispose the heart to arrhythmias when Many anesthetics increase intracranial pressure contraindicated in patients IV Anesthetics Barbiturates thiopental I V Anesthetics often used to induce anesthesia Benzodiazepines midazolam diazepam lorazepam Hypnotics etomidate o Prototype Drug propofol Opiates fentanyl alfentanil Dissociative Anesthetics pain is dissociated from patient slight consciousness o Ketamine cause hallucinations during recovery Neuroleptics patient retains consciousness during an operation when need patient to respond to something o Droperidol o Droperidol plus fentanyl is precompounded as innovar Propofol Diprivan Prototype intravenous anesthetic Contraindicated during pregnancy use caution with patients with seizures cardiac disease or high intracranial pressure Common adverse effect is nausea and vomiting most serious apnea or anaphylaxis Pre Anesthetics and Adjuncts Opioids o Fentanyl Sedative hypnotics and anti anxiety drugs to calm the patient o Examples benzodiazepines barbiturates Anti Emetics to prevent vomiting o Promethazine blocks vomiting center in the brain Anti muscarinic to block excess secretions in mouth and trachea Nicotinic antagonists to relax skeletal muscles o Vecuronium blocks nicotinic receptors in skeletal muscle to cause o Atropine paralysis o If non depolarizing blocker is used common to use an anticholinesterase such as Neostigmine during the recovery period to move muscle block o Succinylcholine nicotinic agonist to provide short term muscle depolarizing blockade Vecuronium tubocurarine is the classical drug Nicotinic antagonist and nondepolarizing neuromuscular blocker Blocks nicotinic receptors in muscle and in autonomic ganglia at higher doses Indication used in surgery to produce long lasting muscle paralysis extending for more than a few minutes used IV only Adverse Response prolonged muscle weakness paralytics effects can be reversed by anticholinesterases e g neostigime Uses with extreme caution in patients with myasthenia gravis Tubcurarine can release histamine causing anaphylactic shock but Effects are enhanced with some antibiotics inhalational and local anesthetics vecuronium is much less risky ketamine or magnesium salts Succinylcholine Nicotinic agonist and depolarizing neuromuscular blocker Over stimulates nicotinic receptors causing paralysis Indications used in surgery to produce a relatively short paralysis used IV or IM only prevent convulsions during electroconvulsive shock therapy o Setting a bone intubating a patient Adverse Effects broken down by plasma cholinesterases some patients have abnormal plasma cholinesterase leading to prolonged apnea o Histamine release can lower BP or cause anaphylactic shock Succinylcholine initially causes muscle contractions before paralysis sets in therefore often cause postoperative aches and pains Very rare when used with halotheme or isoflurane can cause malignant hyperthermia due to excessive muscle contractions o Treated with ice and dantrolene Local Anesthetics Prototype Lidocaine Xylocain Used to block pain perception in awake conscious patients Local anesthetics are applied to nerves Block conduction of action potentials by blocking sodium channels Smaller pain conducting nerve fibers are usually blocked first higher doses will cause muscle paralysis as well Administration Topical relief of pain or itching in skin or conjunctives Infiltration minor surgery Block dental and limb surgery Spinal Block subarachnoid abdominal surgery surgery in lower extremities muscle relaxation saddle block for labor Differences in Local Anesthetics Cocaine Procaine Tetracaine Benzocaine Prototype Lidocaine Bupivicaine Use with EP esters metabolized to para amino benxoic acid PABA can cause drug allergy Vasodilation by local anesthetics can be prevented by co administration of avasoconstrictor EP This can prolong the local anesthetic effect Caution do not use EP with local anesthetics in end artery areas toes fingers penis Can cause ischemia and gangrene