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Anesthesia and it's Classification

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Anesthesia and it's Classification

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In this document i tried to discuss about anesthesia,it's classification,Purpose and biochemical mechanism, Stages of anesthesia, Risk,Complication, Side effects of anesthesia, Advantages & Disadvantages of anesthesia with Some Commonly used medication for anesthesia.

In this document i tried to discuss about anesthesia,it's classification,Purpose and biochemical mechanism, Stages of anesthesia, Risk,Complication, Side effects of anesthesia, Advantages & Disadvantages of anesthesia with Some Commonly used medication for anesthesia.

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Anesthesia and it's Classification

  1. 1. Anesthesia
  2. 2. Contents :  Introduction to anesthesia.  Definition of anesthesia.  Classification of anesthesia.  General Anesthesia.  Purpose & Biochemical M/A of general anesthesia.  Stages of general anesthesia.  Risks of general anesthesia.  Complication of General anesthesia.  Side effects of general anesthesia.  Advantages & disadvantages of general anesthesia.  Local & regional anesthesia.  M/A of local anesthesia.  Classification of local anesthesia.  Methods of administration.  Side-effect/Complication of local anesthesia.  Advantages & disadvantages of local anesthesia  Commonly used medications.  Conclusion.
  3. 3. Introduction to anesthesia The word anesthesia is coined from two Greek words: "an" meaning "without" and "aesthesis" meaning "sensation". There are various types of anesthesia. Throughout their lives, most people will undergo anesthesia either during the birth of their baby or for a surgical procedure, which could range from relatively short, simple surgery on a day-stay basis through to major surgery requiring complex, rapid decisions to keep them safe. Many of today's operations are made possible as a result of developments in anesthesia and training of specialist anesthetists. Patients having anesthesia will have an anesthetist with them all the way from the preoperative assessment of their medical conditions and planning of their medical care, to closely monitoring their health and wellbeing throughout their procedure to ensure a smooth and comfortable recovery. Relief of pain and suffering is central to the practice of anesthesia. Despite an increase in the complexity of surgical operations, modern anesthesia is relatively safe due to high standards of training that emphasis quality and safety. In addition, there have been improvements in drugs and equipment. Increased support for research to improve anesthesia has resulted in best patient safety records in the world. Anesthesia Anesthesia refers to the practice of administering medications either by injection or by inhalation (breathing in) that block the feeling of pain and other sensations, or that produce a deep state of unconsciousness that eliminates all sensations, which allows medical and surgical procedures to be undertaken without causing undue distress or discomfort.
  4. 4. Classificationofanesthesia Classified into 2 major types. They are : 1. General anesthesia. 2. Local & regional anesthesia. 1. GeneralAnesthesia General anesthesia is a medically induced state of unconsciousness with loss of protective reflexes, resulting from the administration of one or more general anesthetic agents. It is carried out to allow medical procedures that would otherwise be intolerably painful for the patient or where the nature of the procedure itself precludes the patient being awake. A variety of medications may be administered, with the overall aim of ensuring unconsciousness, amnesia, analgesia, loss of reflexes of the autonomic nervous system, and in some cases paralysis of skeletal muscles. The optimal combination of drugs for any given patient and procedure is typically selected by an anesthetist, or another provider such as a physician assistant or nurse anesthetist (depending on local practice), in consultation with the patient and the surgeon, dentist or other practitioner performing the operative procedure. Purpose Purpose of General anesthesia has includes: 1. Analgesia (loss of response to pain) 2. Amnesia (loss of memory) 3. Immobility (loss of motor reflexes) 4. Hypnosis (unconsciousness) 5. Paralysis (skeletal muscle relaxation)
  5. 5. Biochemicalmechanismof action Biochemical mechanism of action of general anesthetics is not well understood. To induce unconsciousness, anesthetics have myriad sites of action and affect the CNS at multiple levels. Common areas of the central nervous system whose functions are interrupted or changed during general anesthesia include the-  Cerebral cortex,  Thalamus,  Reticular activating system  & Spinal cord. Current theories on the anaesthetized state identify not only target sites in the CNS but also neural networks and loops whose interruption is linked with unconsciousness. Potential pharmacologic targets of general anesthetics are-  GABA -(Halothane has been found to be a GABA agonist)  Glutamate-activated ion channels,  NMDA receptor families -(ketamine is an NMDA receptor antagonist)  Voltage-gated ion channels,  Glycine & Serotonin receptors. Stages ofgeneralanesthesia Guedel's classification, introduced by Arthur Ernest Guedel in 1937 describes four stages of anesthesia. Despite newer anesthetic agents and delivery techniques, which have led to more rapid onset of – and recovery from – anesthesia (in some cases bypassing some of the stages entirely), the principles remain. Stage 1 Stage 1, also known as induction, is the period between the administration of induction agents and loss of consciousness. During this stage, the patient progresses from analgesia without amnesia to analgesia with amnesia. Patients can carry on a conversation at this time. Stage 2 Stage 2, also known as the excitement stage, is the period following loss of consciousness and marked by excited and delirious activity. During this stage, the patient's respiration and heart rate may become irregular. In addition, there may be uncontrolled movements, vomiting, suspension
  6. 6. of breathing, and pupillary dilation. Because the combination of spastic movements, vomiting, and irregular respiration may compromise the patient's airway, rapidly acting drugs are used to minimize time in this stage and reach Stage 3 as fast as possible. Stage 3 In Stage 3, also known as surgical anesthesia, the skeletal muscles relax, vomiting stops, respiratory depression occurs, and eye movements slow and then stop. The patient is unconscious and ready for surgery. This stage is divided into 4 planes: 1. The eyes roll, then become fixed. 2. Corneal and laryngeal reflexes are lost. 3. The pupils dilate and light reflex is lost. 4. Intercostal paralysis and shallow abdominal respiration occur. Stage 4 Stage 4, also known as overdose, occurs when too much anesthetic medication is given relative to the amount of surgical stimulation and the patient has severe brainstem or medullary depression, resulting in a cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support. Risks ofgeneralanesthesia Overall, general anesthesia is very safe. Even particularly ill patients can be safely anesthetized, it is the surgical procedure itself which offers the most risk. Modern general anesthesia is an incredibly safe intervention. However, older adults and those undergoing lengthy procedures are most at risk of negative outcomes. These outcomes can include postoperative confusion, heart attack, pneumonia and stroke. Some specific conditions increase the risk to the patient undergoing general anesthetic:  Obstructive sleep apnea - a condition where individuals stop breathing while asleep  Seizures  Existing heart, kidney or lung conditions
  7. 7.  High blood pressure  Alcoholism  Smoking  History of reactions to anesthesia  Medications that can increase bleeding - aspirin, for example  Drug allergies  Diabetes  Obesity or overweight. Death due to general anesthetic does occur, but only very rarely - roughly 1 in every 100,000- 200,000. Complication of General anesthesia Unintended intra-operative awareness Unintended intra-operative awareness refers to rare cases where patients report a state of awareness during an operation, after the point at which the anesthetic should have removed all sensation. Some patients are conscious of the procedure itself and some can even feel pain. Unintended intra-operative awareness is incredibly rare, affecting an estimated 1 in every 19,000 patients undergoing general anesthetic. Because of the muscle relaxants given alongside anesthesia, patients are unable to signal to their surgeon or anesthetist that they are still aware of what is happening. Unintended intra-operative awareness is more likely during emergency surgery. Patients that experience unintended intra-operative awareness can suffer long-term psychological problems. Most often, the awareness is short-lived. According to a recent large-scale investigation of the phenomenon, patients experienced "tugging, stitching, pain, paralysis and choking," among other sensations.
  8. 8. Because unintended intra-operative awareness is so infrequent, it is not clear exactly why it occurs. The following are considered to be potential risk factors:  Heart or lung problems  Daily alcohol use  Emergency surgery  Cesarean section  Anesthesiologist error  Use of some additional medications  Depression.  Pre-surgical evaluation Side effects of generalanesthesia Side effects of general anesthesia include -  Confusion and memory loss - (more common in the elderly)  Dizziness  Difficulty passing urine.  Bruising or soreness from the IV drip.  Nausea and vomiting (Most common)  Shivering and feeling cold.  Sore throat (due to the breathing tube).
  9. 9. Advantages of generalanesthesia  Reduces intra-operative patient awareness and recall.  Allows proper muscle relaxation for prolonged periods of time.  Facilitates complete control of the airway, breathing, and circulation.  Can be used in cases of sensitivity to local anesthetic agent.  Can be administered without moving the patient from the supine position.  Can be adapted easily to procedures of unpredictable duration or extent.  Can be administered rapidly and is reversible. Disadvantagesofgeneralanesthesia  Requires increased complexity of care and associated costs.  Requires some degree of preoperative patient preparation.  Can induce physiologic fluctuations that require active intervention.  Associated with less serious complications such as nausea or vomiting, sore throat, headache, shivering, and delayed return to normal mental functioning.  Associated with malignant hyperthermia, a rare, inherited muscular condition in which exposure to some (but not all) general anesthetic agents results in acute and potentially lethal temperature rise, hypercarbia, metabolic acidosis, and hyperkalemia. 2. Local& regional anesthesia Local anesthesia is the reversible loss of sensation in a defined area of the body and is achieved by the topical application or injection of agents that block the generation and/or journey of nerve impulses in tissue. Regional anesthesia is essentially local anesthesia but covering a larger area of subcutaneous tissue or larger peripheral nerves. Chemically they are weak bases formed of lipophylic group connected to ionizable hydrophilic group by an intermediate chain.
  10. 10. Local anesthesia is used in many dermatological procedures and surgical operations. The aim is to minimise pain and suffering and maximise patient comfort. Mechanismof action localanesthesia - They act from inside the nerve & inhibit Na influx (membrane stabilization) - Fibers are affected in this sequence (Sensory, cold, touch, pressure & lastly motor) & unmyelinated before myelinated. - Recovery occurs in the reverse direction. Classificationoflocalanesthesia According to their chemical structure they are classifiedinto2 types, (i) Amides  Lidocaine (most frequently used)(effective, acts rapidly)  Dibucaine  Prilocaine  Mepivacaine  Bupivacaine (ii) Esters  Cocaine  Procaine  Tetracaine  Benzocaine
  11. 11. According to their solubility and therapeutic application they are classifiedinto3 types, (i) Soluble L.A suitable for injection:  Lidocaine  Dibucaine  Procaine  Tetracaine All these can produce surface anesthesia except Procaine which is effective only by injection. (ii) Soluble L.A used only topically:  Cocaine  Phenacaine  Butacaine Mainly used to produce topical anesthesia of the Eye. (iii) Insoluble L.A:  Benzocaine  Orthoform Used as surface anesthetics in the form of powders and ointments for wounds. Methods of administration 1. Surface anesthesia - By direct application for skin & mucous membrane 2. Infiltration anesthesia - By S.C injection to reach fine nerve branches and sensory nerve terminals. 3. Nerve block anesthesia - By injection close to the appropriate nerve trunks (Brachial plexus) to produce a loss of sensation peripherally.
  12. 12. 4. Sympathetic block - It is injected around sympathetic ganglion. 5. Para vertebral block - It is injected around spinal roots as they emerge from the paraverterbal foramina. 6. Epidural anesthesia - The LA is injected in the epidural space,between the dura & bony spinal canal containing fat & connective tissue. - It can be performed in sacral hiatus (Caudal anesthesia) 7. Spinal - The LA is injected in the subarachnoid space in the lumbar region - The level of spinal anesthesia depends upon: i. Posture of the patient. ii. Specific gravity of the injected solution. Modification Adrenaline (epinephrine) is sometimes added to local anesthetic formulations. It is used to:  Prolong duration of anesthesia.  Reduce systemic absorption.  Reduce surgical bleeding.  Increase the intensity of blockade.
  13. 13. Can anyone be allergic to localanesthetics? True allergy to local anesthetics is rare, the estimated rate of allergic reactions caused by these agents is less than 1%. Often an adverse reaction is the result of the rapid rise in circulating local anesthetic, or the absorption of adrenaline, or an allergy to the preservative (most local anesthetics contain parabens preservative). Aminoesters are more allergenic than aminoamides because of their cross-reactivity to other drugs of the para-aminobenzoic acid ester type. Patients with a history of allergy to benzocaine, sulphonamides, paraphenylenediamine or other para-type substances should avoid using aminoester local anesthetics. Prior exposure to parabens or para-aminobenzoic acid may sensitize you to local anesthetics containing these substances. In such cases, preservative-free aminoamide local anesthetics such as lignocaine (lidocaine) can be used. Side effects / Complications of local anesthetic Local side effects such as bruising and a temporary sensation of stinging or burning are common. When administered correctly the chances of more serious side effects occurring are minimal. Signs and symptoms of systemic toxicity include:  Severe numbness or tingling  Dizziness and drowsiness  Tinnitus (ringing in the ears)  Slurred speech  Metallic taste in mouth  Mental status change  Muscle twitching
  14. 14. Which localanesthetic is right for us? The choice of which anesthetic to use depends on a number of factors:  Patient factors  Age  Pregnancy status  History of allergies  Other medical conditions such as renal or hepatic failure, cardiac problems  Current medications  Procedure being performed  Consider site  Consider area involved  Consider duration of operation  Doctor's own preference and experience. Advantages of Local anesthetic  During local anesthesia the patient remains conscious.  Patient maintains own airway.  Aspiration of gastric contents unlikely.  Recovery is smooth as it requires less skilled nursing care as compared to other anesthesia like general anesthesia.  Postoperative analgesia.  There is reduction surgical stress.  Earlier discharge for outpatients.  Expenses are less.
  15. 15. DisadvantagesofLocalanesthetic  Sometimes patient may prefer to be asleep.  It needs a practiced and skilled person for the best results.  Some blocks require up to 30 min or more to be fully effective.  It is also possible that analgesia may not always be totally effective. May be the patient requires additional analgesics, IV sedation, or a light general anesthetic.  Sometimes toxicity may occur if the local anesthetic is injected intravenously or if the overdose is given Operation like thoracotomies is not suitable for local anesthetics. Commonly used medications Volatile anesthetics  All are bronchodilators, except for desflurane which is irritating and may cause bronchospasm. Administered alone (i.e., without narcotics), inhaled anesthetics increase respiratory rate but decrease tidal volume.  Except for halothane, inhaled anesthetics are not metabolized by the body and are eliminated by ventilation.  All volatile anesthetics (but not nitrous oxide) are capable of triggering malignant hyperthermia (MH).  While in many cases volatile anesthetics are used for maintenance of anesthesia, in some circumstances these drugs may be chosen to induce anesthesia such as in pediatrics cases in which the child may not tolerate IV placement awake. Halothane PRO Cheap, nonirritating so can be used for inhalation induction CON Long time to onset/offset, Significant Myocardial Depression, Sensitizes myocardium to catecholamines, Association with Hepatitis
  16. 16. Isoflurane PRO Cheap, excellent renal, hepatic, coronary, and cerebral blood flow preservation CON Long time to onset/offset, irritating so cannot be used for inhalation induction Desflurane PRO Extremely rapid onset/offset CON Expensive, Stimulates catecholamine release, Possibly increases postoperative nausea and vomiting, Requires special active-temperature controlled vaporizer due to high vapor pressure, Irritating so cannot be used for inhalation induction Sevoflurane PRO Nonirritating so can be used for inhalation induction. Extremely rapid onset/offset. CON Expensive. Due to risk of “compound A” exposure must be used at flows > 2 L/min. Theoretical potential for renal toxicity from inorganic fluoride metabolites. Nitrous Oxide PRO Decreases volatile anesthetic requirement, Dirt cheap, Less myocardial depression than volatile agents CON Diffuses freely into gas filled spaces (bowel, pneumothorax, middle ear, eye, Decreases Fi02, Increases pulmonary vascular resistance
  17. 17. Iv anesthetics Most sedative hypnotics work through the inhibitory gamma-aminobutyric acid (GABA) neurotransmitter system in which increased chloride conductance leads to neuronal inhibition. Most IV induction agents bind to a specific site called GABAA for this inhibitory effect, and they have a rapid onset due to lipophilic properties which allow them to quickly partition into the highly perfused lipophilic brain and spinal cord. They also have short duration of action, with their termination of effect due to redistribution into less perfused tissues such as muscle and fat. Barbiturates (e.g., thiopental) Decrease ICP by decrease in cerebral oxygen consumption. Since cerebral perfusion is preserved, desirable drug for neurosurgery cases. Causes respiratory and cardiac depression. PRO Excellent brain protection, Stops seizures, Cheap CON Myocardial depression, Vasodilation, Histamine release, Can precipitate porphyria in susceptible patients Propofol In adults, induction dose 1.5 to 2.5 mg/kg while continuous infusion of 100 to 200 micrograms/kg/min maintains unconsciousness. These values differ for children and for the elderly. PRO Prevents nausea/vomiting, Quick recovery if used as solo anesthetic agent CON Pain on injection, Expensive, Supports bacterial growth, Myocardial depression (the most of the four), Vasodilation, cross reactivity in patients with egg allergy.
  18. 18. Etomidate Minimal depression of cardiovascular and pulmonary function. Ideal for patients with CVD or hemodynamic instability. Induction dose of 0.2 to 0.4 mg/kg that causes pain on injection and myoclonus. Suggested that it may suppress cortisol synthesis. PRO Least myocardial effect of IV anesthetics CON Pain on injection, Adrenal suppression (? significance if used only for induction), Myoclonus, Nausea/Vomiting Keratin Works via antagonism of the N-methyl-D-aspartate receptor channel complex. Minimally depresses the cardiorespiratory system. Induction dose of 1 to 2 mg/kg in adults. Directly stimulates SNS and increases BP and heart rate. Increasing demand on the heart and is not a good choice for CAD patients. PRO Works IV, PO, PR, IM - good choice in uncooperative patient without IV, Stimulation of SNS → good for hypovolemic trauma patients, often preserves airway reflexes CON Dissociative anesthesia with postop dysphoria and hallucinations, Increases ICP/IOP and CMR02, Stimulation of SNS → bad for patients with compromised cardiac function, increases airway secretions Dexmedetomidine Selective alpha-2 adrenergic agonist, which is used in the operating room as an adjunct to general anesthesia, or to provide sedation for awake fiberoptic intubation or for regional anesthesia. It is generally given as a loading dose of 0.5-1 mcg/kg over 10 minutes, followed by an infusion of 0.2 to 0.7 mcg/kg/hr. It produces sedative-hypnotic and analgesic effects without causing respiratory depression.
  19. 19. Benzodiazepines (BDZ) Usually provided as premedication for sedation and anxiolysis before general anesthesia. Properties include anxiolytic effects to sedation and unconsciousness at higher doses. Midazolam (Versed) induction dose of 0.1 to 0.2 mg/kg and infusion rates of 0.25 to 1 microgram/kg per minute. BDZs produce respiratory, cardiovascular, and upper airway reflex depression and in the presence of hypovolemia, may cause significant hypotension. Reversal of the sedative action of these compounds with the competitive antagonist, flumazenil. Opioids Morphine Depresses breathing principally by impairing the medullary response to CO2. Also trigger the chemoreceptor trigger zone (CTZ) which may lead to nausea, and may in turn stimulate the vomiting center and produce emesis. Also, morphine decreases GI motility and propulsion, produces urinary retention, and releases histamine by stimulating basophils in the lungs and mast cells in the skin. In the CVS, morphine may produce vascular dilation, decrease SVR, and overall hypotension. It is long acting & renally excreted → active metabolite has opiate properties, therefore beware in renal failure Demerol Euphoria, stimulates catecholamine release, so beware in patients using MAOI’s, renally active metabolite associated with seizure activity, therefore beware in renal failure
  20. 20. Conclusion In conclusion we can say that for healthy patients undergoing a planned operation, general anesthesia is about as dangerous as pregnancy in a healthy woman. In other words, general anesthesia is very safe. However, the poorer the health of a person, the older they are, and the higher the risk of the operation - the greater the chance of dying as a result of anesthesia and surgery. There are actually very few conditions where anesthesia is likely to be lethal for a patient, e.g. extremely severe aorta stenosis, major coronary artery stenosis, someone in deep shock, etc. Fortunately, these conditions occur very seldom. In general, for nearly all people, as the discussion above clearly demonstrates, anesthesia is very safe and far less dangerous than the effects of surgery.
  21. 21. Reference : 1. Book : "Anesthesiology Advanced Clinical Rotation Handbook" 2. http://www.bu.edu/orccommittees/iacuc/policies-and-guidelines/anesthesia-and-analgesia-in- research-animals/commonly-used-anesthetics-and-analgesics/ (Accessed on 11-11-2016) 3. http://emedicine.medscape.com/article/1271543-overview (Accessed on 11-11-2016) 4. http://www.slideshare.net/cetdmgh/types-of-anesthesia (Accessed on 11-11-2016) 5. http://images.slideplayer.com/19/5919481/slides/slide_15.jpg (Accessed on 11-11-2016) 6. https://en.wikipedia.org/wiki/Anesthetic (Accessed on 11-11-2016) 7. https://en.wikipedia.org/wiki/General_anaesthesia (Accessed on 11-11-2016) 8. https://en.wikipedia.org/wiki/Anesthesia (Accessed on 11-11-2016) 9. http://aelberry.kau.edu.sa/files/0053626/researches/28929_18-%20anesthesia.pdf (Accessed on 09-11-2016) 10. https://www.drugs.com/drug-class/general-anesthetics.html (Accessed on 09-11-2016) 11. http://emedicine.medscape.com/article/873879-overview (Accessed on 09-11-2016) 12. http://www.anzca.edu.au/patients/what-is-anaesthesia (Accessed on 09-11-2016) 13. https://en.wikipedia.org/wiki/Local_anesthesia (Accessed on 09-11-2016) 14. http://www.altiusdirectory.com/Lifestyle/local-anesthesia-advantages.html (Accessed on 09- 11-2016) 15. http://www.anesthesiaweb.org/risk.php (Accessed on 11-11-2016)

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