ANAESTHETICS

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Anesthetics divided into 2 classes:

Anesthetics divided into 2 classes

Mechanism of Action :

Mechanism of Action Interaction with protein receptors Volatile A – increase GABA and Glycine ( inhibitory neurotransmitters)

MAC(minimum alveolar concentration):

MAC(minimum alveolar concentration) A measure of potency of inhaled anesthetics MAC is the concentration necessary to prevent responding in 50% of population.

Pathway for General Anesthetics:

Pathway for General Anesthetics

Pharmacokinetics of Inhaled Anesthetics :

Pharmacokinetics of Inhaled Anesthetics Amount that reaches the brain Indicated by oil:gas ratio (lipid solubility) Solubility of gas into blood The lower the blood:gas ratio, the more anesthetics will arrive at the brain

General Actions of Inhaled Anesthetics:

General Actions of Inhaled Anesthetics Respiration Depressed respiration and response to CO2 Kidney Depression of renal blood flow and urine output Muscle High enough concentrations will relax skeletal muscle

Cont’:

Cont’ Cardiovascular System Generalized reduction in arterial pressure and peripheral vascular resistance. Isoflurane maintains CO and coronary function better than other agents Central Nervous System Increased cerebral blood flow and decreased cerebral metabolism

Nitrous Oxide:

Nitrous Oxide widely used Potent analgesic Produce a light anesthesia Do not depress the respiration/vasomotor center Used as adjunct to supplement other inhalationals Inhaled Anesthetics

Halothane:

Halothane non-flammable 20% metabolism by P450 induction of hepatic microsomal enzymes Myocardial depressant (SA node), sensitization of myocardium to catecholamines - arrhythmia Inhaled Anesthetics

Halothane:

Halothane Transient hepatic damage Liver necrosis In repeated exposure Immunosensititation Inhaled Anesthetics

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Malignant hyperthermia (MH) is a pharmacogenetic hypermetabolic state of skeletal muscle induced in susceptible individuals by inhalational anesthetics and/or succinylcholine (and maybe by stress or exercise). Malignant Hyperthermia

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Signs: tachycardia, tachypnea, metabolic acidosis, hyperthermia, muscle rigidity, sweating, arrhythmia May be fatal Treated with dantrolene Malignant Hyperthermia

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Enflurane Rapid, smooth induction and maintenance 2-10% metabolized in liver Introduced as replacement for halothane Inhaled Anesthetics

Isoflurane:

Isoflurane smooth and rapid induction and recovery very little metabolism (0.2%) no reports of hepatotoxicity or renotoxicity most widely employed Inhaled Anesthetics

Intravenous Induction Agents:

Intravenous Induction Agents Commonly used IV induction agents Propofol Thiopental sodium Ketamine

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Intravenous Anesthetics Most exert their actions by potentiating GABA A receptor GABAergic actions may be similar to those of volatile anesthetics, but act at different sites on receptor

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Most decrease cerebral metabolism and intracranial pressure Most cause respiratory depression May cause apnea after induction of anesthesia Organ Effects

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Barbiturates, benzodiazepines and propofol cause cardiovascular depression. Cardiovascular Effects

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Thiopental sodium rapid onset (20 sec) short-acting

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Effect terminated not by metabolism but by redistribution repeated administration or prolonged infusion approached equilibrium at redistribution sites Build-up in adipose tissue = very long emergence from anesthesia Thiopental sodium

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Side effects Hypotension apnoea airway obstruction Thiopental sodium

Propofol:

Propofol Short-acting agent used for the induction maintenance of GA and sedation Onset within one minute of injection

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It is highly protein bound and is metabolised by conjugation in the liver Side-effect pain on injection hypotension transient apnoea following induction Propofol

Ketamine:

Ketamine usually stimulate rather than depress the circulatory system.

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Analgesic dissociative anesthesia Cataleptic appearance, eyes open, reflexes intact, purposeless but coordinated movements Ketamine

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Stimulates sympathetic nervous system Psychomimetic – “emergence reactions” vivid dreaming extracorporeal (floating "out-of-body") experience misperceptions, misinterpretations, illusions may be associated with euphoria, excitement, confusion, fear Ketamine

Induction:

Induction

Maintenance:

Maintenance Inhaled agents are supplemented by intravenous anaesthetics, such as opioids (usually fentanyl or morphine)

What is Balanced Anesthesia?:

What is Balanced Anesthesia? Use specific drugs for each component 1. Sensory N 2 0, opioids, ketamine for analgesia 2. Cognitive Produce amnesia, and preferably unconsciousness inhaled agent IV hypnotic (propofol, midazolam, diazepam, thiopental) 3. Motor Muscle relaxants

Simple Combinations:

Simple Combinations Morphine Propofol N 2 O Sevoflurane Relaxant of choice

Simple Combinations:

Simple Combinations Fentanyl Thiopental sodium N2O Halothane Relaxant of choice

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