General anesthesia.pdf

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. It must be safe ,not threatening or unpleasant to the patient. Allow adequate surgical access to the op...

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. It must be safe ,not threatening or unpleasant to the patient. Allow adequate surgical access to the operative site. Cause as little disturbance as possible to internal homeostatic mechanism. Advantages : Makes no psychological demand of the patient. Allows complete stillness for prolonged periods of time. Facilitate complete control of the airway , breathing & circulation. 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 administered without moving the patient from the supine position , Can be adapted easily to procedures of unpredictable duration or extent. Usually can be administered rapidly. Disadvantages Requires the involvement of an extra set of healthcare providers. Require complex & costly machinery. Require some degree of preoperative patient preparation. Usually associated with some degree of physiological trespass. 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 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 ,hyperkalemia & metabolic acidosis. Determinants of drugs choice & dose patients age & weight Physical status Previous adverse experience with drugs used for preoperative medication. Level of anxiety Tolerance for depressant drugs Allergy Elective & emergency surgery Inpatient & out patient surgery Modern anesthetics Inhalational 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 noxios reflexs. Induce muscular relaxation. Induce smooth onset & recovery. Induce anterograde amnesia. Cause no systemic toxicity. Present no hazard to others. Inhalation Anesthetic original agents were vapours from volatile liquids or gases. Nitrous oxide, ether ,chloroform. Induction of anesthesia using latter two lead to categorization of stages & planes of anesthesia. Inhalation drugs used to maintain depth of anesthesia. modern agents :Halothane, influrane ,isoflurane,desflurane. Indication of inhalational induction Young children Upper airway obstruction eg. Epiglottis Lower airway obstruction with foreign body Bronchopleural fistula or empyema No accessible vien. Disadvantages of inhalational induction: Slow induction of anesthesia Airway obstruction, bronchospasm Laryngospasm , hiccup Environmental pollution MAC- minimum alveolar concentration (as percentage) to induce pain insensate anesthesia. Nitrous oxide (N2O) (laughing gas) Commonly used but least potent MAC for true anesthesia =105% Used as analgesia Few undesirable side effects : Respiration-no irritation ,but risk of hypoxia CVS- non ,no sensitization to catecholamines. Halothane MAC- 0.7% Volatile liquid ,widely used, good control ,smooth induction & recovery Problems : At MAC little involvement of CVS but sensitizes myocardium to to the circulating catecholamines via action beta-adrenocepters. Risk of dysrhythmia , vasodilation & hypotension. Depression of ventilation , increase bronchial secretion. Neuromuscular block (slight) but potentiates gurariform drugs. Risk with halothane Malignant hyperthermia. 20 % of metabolism are toxic products causing hepatic damage with repeated exposure. Risk of spontaneous abortion in pregnant or staff. Enflurane Less chance of dysrhythmia than with halothane. 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. More neromuscular depression. Less liver damage ; 17% dose is metabolized. Nausea on recovery. Occosional seizure like effect. Isoflurane less CV or respiratory depression than enflurane but more so than halothane but is restored by the stimulation of surgery. Cardiac out put is maintained through increase in HR. Minimal liver toxicity since little (