General anesthesia General anesthesia uses drugs given systemically to render the patient unaware of any think that is being done to or around him or her. General anesthesia uses drugs given systemically to render the patient unaware of any think that is being done to or around him or her. It must be safe,not threatening or unpleasant to the patient. It must be safe,not threatening or unpleasant to the patient. Allow adequate surgical access to the operative site. Allow adequate surgical access to the operative site. Cause as little disturbance as possible to internal homeostatic mechanism. Cause as little disturbance as possible to internal homeostatic mechanism. Advantages : Advantages : Makes no psychological demand of the patient. Makes no psychological demand of the patient. Allows complete stillness for prolonged periods of time. Allows complete stillness for prolonged periods of time. Facilitate complete control of the airway, breathing & circulation. Facilitate complete control of the airway, breathing & circulation. Permits surgery to take place in widely separated areas of the body at the same time. Permits surgery to take place in widely separated areas of the body at the same time. Can be used in cases of sensitivity to local anesthetic agent. Can be used in cases of sensitivity to local anesthetic agent. Can be administered without moving the patient from the supine position, Can be administered without moving the patient from the supine position, Can be adapted easily to procedures of unpredictable duration or extent. Can be adapted easily to procedures of unpredictable duration or extent. Usually can be administered rapidly. Usually can be administered rapidly.

Disadvantages Requires the involvement of an extra set of healthcare providers. Requires the involvement of an extra set of healthcare providers. Require complex & costly machinery. Require complex & costly machinery. Require some degree of preoperative patient preparation. Require some degree of preoperative patient preparation. Usually associated with some degree of physiological trespass. Usually associated with some degree of physiological trespass. Carries the risk of major complications including death,MI & stroke. Carries the risk of major complications including death,MI & stroke. Associated with less serious complications such as nausea, vomiting,sore throat, headache,shivering & delay return to normal mental functioning. Associated with less serious complications such as nausea, vomiting,sore throat, headache,shivering & delay 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 result in acute & potentially lethal temperature rise, hypercarbia, metabolic acidosis & hyperkalemia. Associated with malignant hyperthermia, a rare, inherited muscular condition in which exposure to some (but not all) general anesthetic agents result in acute & potentially lethal temperature rise, hypercarbia, metabolic acidosis & hyperkalemia.

Determinants of drugs choice & dose patient age & weight patient age & weight Physical status Physical status Previous adverse experience with drugs used for preoperative medication. Previous adverse experience with drugs used for preoperative medication. Level of anxiety Level of anxiety Tolerance for depressant drugs Tolerance for depressant drugs Allergy Allergy Elective & emergency surgery Elective & emergency surgery Inpatient & out patient surgery Inpatient & out patient surgery Modern anesthetics Inhalational anesthetics Inhalational anesthetics Intravenouse anesthetics Intravenouse anesthetics  Mostly used in conjunction with each other, seldom alone.  TIVA alone iv  Also administered in combination with other drug classes. (neurolapetic an, analgesia) … opiod, droperidol.

The ideal anesthetic drug will: Cause loss of sensation especially pain. Cause loss of sensation especially pain. Cause loss of noxios reflexs. Cause loss of noxios reflexs. Induce muscular relaxation. Induce muscular relaxation. Induce smooth onset & recovery. Induce smooth onset & recovery. Induce anterograde amnesia. Induce anterograde amnesia. Cause no systemic toxicity. Cause no systemic toxicity. Present no hazard to others. Present no hazard to others. Inhalation Anesthetic original agents were vapours from volatile liquids or gases. original agents were vapours from volatile liquids or gases. Nitrous oxide, ether,chloroform. Nitrous oxide, ether,chloroform. Induction of anesthesia using latter two lead to categorization of stages & planes of anesthesia. Induction of anesthesia using latter two lead to categorization of stages & planes of anesthesia. Inhalation drugs used to maintain depth of anesthesia. Inhalation drugs used to maintain depth of anesthesia. modern agents :Halothane, influrane,isoflurane,desflurane. modern agents :Halothane, influrane,isoflurane,desflurane.

Indication of inhalational induction : Young children Young children Upper airway obstruction eg. Epiglottis Upper airway obstruction eg. Epiglottis Lower airway obstruction with foreign body Lower airway obstruction with foreign body Bronchopleural fistula or empyema Bronchopleural fistula or empyema No accessible vien. No accessible vien. Disadvantages of inhalational induction: Slow induction of anesthesia Slow induction of anesthesia Airway obstruction, bronchospasm Airway obstruction, bronchospasm Laryngospasm, hiccup Laryngospasm, hiccup Environmental pollution Environmental pollution MAC- minimum alveolar concentration (as percentage) to induce pain insensate anesthesia.

Nitrous oxide (N2O) (laughing gas) Commonly used but least potent Commonly used but least potent MAC for true anesthesia =105% MAC for true anesthesia =105% Used as analgesia Used as analgesia Few undesirable side effects : Few undesirable side effects : Respiration-no irritation,but risk of hypoxia Respiration-no irritation,but risk of hypoxia CVS- non,no sensitization to catecholamines. CVS- non,no sensitization to catecholamines.Halothane MAC- 0.3% MAC- 0.3% Volatile liquid,widely used, good control,smooth induction & recovery Volatile liquid,widely used, good control,smooth induction & recovery Problems : At MAC little involvement of CVS but sensitizes myocardium to catecholamines via action beta-adrenocepters. Problems : At MAC little involvement of CVS but sensitizes myocardium to catecholamines via action beta-adrenocepters. Risk of dysrhythmia, vasodilation & hypotension. Risk of dysrhythmia, vasodilation & hypotension. Depression of ventilation, increase bronchial secretion. Depression of ventilation, increase bronchial secretion. Neuromuscular block (slight) but potentiates gurariform drugs. Neuromuscular block (slight) but potentiates gurariform drugs. Risk with halothane Malignant hyperthermia Malignant hyperthermia 20 % of metabolism toxic products causing hepatic damage with repeated exposure 20 % of metabolism toxic products causing hepatic damage with repeated exposure Risk of spontaneous abortion in pregnant or staff. Risk of spontaneous abortion in pregnant or staff.

Enflurane Less chance of dysrhythmia than with halothane. Less chance of dysrhythmia than with halothane. More hypotesion & respiratory depression on induction but recovers with the start of surgery. More hypotesion & respiratory depression on induction but recovers with the start of surgery. Cardiac out put fall slightly with a rise in central venous pressure. Cardiac out put fall slightly with a rise in central venous pressure. More neromuscular depression. More neromuscular depression. Less liver damage ; 17% dose is metabolized. Less liver damage ; 17% dose is metabolized. Nausea on recovery. Nausea on recovery. Occosional seizure like effect. Occosional seizure like effect.Isoflurane less CV or respiratory depression than enflurane but more so than halothane. less CV or respiratory depression than enflurane but more so than halothane. But is restored by the stimulation of surgery. But is restored by the stimulation of surgery. Cardiac out put is maintained through increase in HR. Cardiac out put is maintained through increase in HR. Minimal liver toxicity since little (<0.5%) is metabolized. Minimal liver toxicity since little (<0.5%) is metabolized. Potentiation of non-depolarizing nm blocking agents. Potentiation of non-depolarizing nm blocking agents. Risk of malignant hyperpyrexia. Risk of malignant hyperpyrexia. No convulant EEG oattern. No convulant EEG oattern. Mildly pungent ; bronchail irritation & secretion. Mildly pungent ; bronchail irritation & secretion.

Intravenous anesthetic Mainly selected members of sedative drugs classes, Act by : Potentiating the action of an inhibitory ionophores (GABA recepters). Potentiating the action of an inhibitory ionophores (GABA recepters). Blocking the action of excitatory ionophores (Nicotinic Ach & NMDA recepter). Blocking the action of excitatory ionophores (Nicotinic Ach & NMDA recepter).Advantages rapid onst rapid onst Cotrolled dosage Cotrolled dosage Ease of administraion Ease of administraionDisadvantages Overdose not readily corrected. Overdose not readily corrected. No antagonists or antidotes. No antagonists or antidotes. Prolonged after effects (hangover) Prolonged after effects (hangover)

barbiturates Ultra short acting Ultra short acting Methohexital, Thiopentone, pentobarbital Methohexital, Thiopentone, pentobarbital Very lipid soluble, induce anesthesia (hypnosis) in 1 time circulation Very lipid soluble, induce anesthesia (hypnosis) in 1 time circulation Redistribution ocure at a rate proportional to blood supply i.e brain … lean tissue … fat Redistribution ocure at a rate proportional to blood supply i.e brain … lean tissue … fat Metabolism is slower but slow leaching from stores keeps blood levels low; effect restricted to a hungover Metabolism is slower but slow leaching from stores keeps blood levels low; effect restricted to a hungover Induction often accompanied by coughing, sneezing or laryngospasm : prevent with atropine or scopolamine Induction often accompanied by coughing, sneezing or laryngospasm : prevent with atropine or scopolamine Hypotension is transient unless shock is present Hypotension is transient unless shock is present Barbiturate very alkaline......avoid extravasation Barbiturate very alkaline......avoid extravasation Thrombophlebitis a risk with iv injection Thrombophlebitis a risk with iv injection Respiratory depression marked … mechanical ventilation should be available Respiratory depression marked … mechanical ventilation should be availableContraindications Porpheria Porpheria Status asthmaticus Status asthmaticus

Alkylphenols Propofol (milk of amnesia) Propofol (milk of amnesia) Patient recover more rapidly & fell less hungover Patient recover more rapidly & fell less hungover Contraindicated for sedation in children due to acidosis & possible neurological sequelae Contraindicated for sedation in children due to acidosis & possible neurological sequelae Slightly greater incidence of pain & excitation on induction Slightly greater incidence of pain & excitation on induction Significant but transient fall in blood pressure & a rise in heart rate Significant but transient fall in blood pressure & a rise in heart rateImidazoles Etomidate- used mainly for induction & short duration procedure Etomidate- used mainly for induction & short duration procedure Minimal cardiovascular or repiratory effect Minimal cardiovascular or repiratory effect Rapid onset (seconds) but not analgesia-reflexes present Rapid onset (seconds) but not analgesia-reflexes present High incidence of nausea, vomiting, pain on injection High incidence of nausea, vomiting, pain on injection Single dose-inhibitory effects of steroidogenesis- adrenocortical suppression Single dose-inhibitory effects of steroidogenesis- adrenocortical suppressionBenzodiazepines Midazolam- water soluble but slower in onset than barbiturates Midazolam- water soluble but slower in onset than barbiturates Mainly used preoperativly Mainly used preoperativly Prolonged recovery with amnesia Prolonged recovery with amnesia Flumanezil- receptor antagonist ; used to speed recovery, or act as antidote in over dose Flumanezil- receptor antagonist ; used to speed recovery, or act as antidote in over dose

Cyclohexylamine Ketamine-channel blocking agent related phencyclidine Ketamine-channel blocking agent related phencyclidine Blocks both nicotinic Ach & NMDA (glutamic acid) receptor channels Blocks both nicotinic Ach & NMDA (glutamic acid) receptor channels Dissociative anesthesia – catatonia, amnesia, analgesia but not true surgical anesthesia Dissociative anesthesia – catatonia, amnesia, analgesia but not true surgical anesthesia Cardiovascular stimulation Cardiovascular stimulation Muscle tone maintained Muscle tone maintained Emergence reactions – dream & hallucinations (less in children) (control with diazepam) Emergence reactions – dream & hallucinations (less in children) (control with diazepam) Indicated mainly in out patient procedures,children & burn dressings Indicated mainly in out patient procedures,children & burn dressings Muscle relaxants Depolarizing MR Depolarizing MR Non-depolarizing MR Non-depolarizing MR

Depolarising MR Succinylcholine,(suxamethonium) (scoline) Succinylcholine,(suxamethonium) (scoline) Rapid – onset, act within seconds & last for approximately 5 minutes Rapid – onset, act within seconds & last for approximately 5 minutes Short- acting Short- acting Is the drug of choice when rapid muscle relaxation is needed Is the drug of choice when rapid muscle relaxation is needed Used during induction of anesthesia Used during induction of anesthesia Side effects : Side effects : Histamine release producing a scoline rash Histamine release producing a scoline rash Bradycardia Bradycardia Somatic pain resulting from fasciculation Somatic pain resulting from fasciculation Hyperkalemia Hyperkalemia Persistent NM blockade= scoline apnoea Persistent NM blockade= scoline apnoea Malignant hyperpyrexia Malignant hyperpyrexia Increased intra-ocular pressure Increased intra-ocular pressure Increased gastric pressure Increased gastric pressure

Non-depolarizing MR Competitive antagonism of acetylcholine receptor Competitive antagonism of acetylcholine receptor Have duration of action ranging from 15 minutes to more than 2 hours Have duration of action ranging from 15 minutes to more than 2 hours Generally excreted by the kidney, but some preparation are broken down by plasma enzymes (atracurium)& can be used safely in partial or complete renal failure Generally excreted by the kidney, but some preparation are broken down by plasma enzymes (atracurium)& can be used safely in partial or complete renal failure Pancuronium is still in widespread use because of its low cost & familiarity, especialy in ICU Pancuronium is still in widespread use because of its low cost & familiarity, especialy in ICU Rocuronium, mivacurium, & cisatracurium are more likely to be used by contemporary anesthesiologist Rocuronium, mivacurium, & cisatracurium are more likely to be used by contemporary anesthesiologist Used for muscle relaxation Used for muscle relaxation Need anti-dote Need anti-dote