• After participating in this lecture, you will be able to:- Define the benefits of complementary foods for infants- Describe the types of complementary foods available for infants- Describe methods and timing for introduction of complementary foods for infants- Describe 4 most common problems in introduction of complementary foods for infants and best methods to resolve theseproblems• This educational package looks briefly at the history of theanaesthetic machine and then covers the basic principlesinvolved in the safe use of anaesthetic machines.• The module is intended to be a reminder of best practiceand will provide all users with a better understanding ofwhy procedures need to be followed, the value of recordkeeping and the possible pitfalls with cutting corners.
Introduction• General anaesthetics (GAs) are drugs which produce reversible loss of all sensation andconsciousness. The cardinal features of general anaesthesia are:• Loss of all sensation, especially pain• Sleep (unconsciousness) and amnesia• immobility and muscle relaxation• Abolition of somatic and autonomic reflexes. "• In the modern practice of balanced anaesthesia, these modalities are achieved by usingcombination of inhaled and i.v. drugs, each drug for a specific purpose; anaesthesia hasdeveloped as a highly specialized science in itself.
STAGES OF ANAESTHESIA• Stage of analgesia• Stage of delirium• Surgical anesthesia• Modularly paralysis
Fig. 27.1: Stages of general anaesthesiaSTAGES OF ANAESTHESIA
STAGES OF ANAESTHESIA• I) Stage of analgesia– Starts from beginning of anaesthetic inhalation and lasts up to the loss of consciousness.– Pain is progressively abolished. Patient remains conscious, can hear and see, and feels a dream likestate; amnesia develops by the end of this stage.– Reflexes and respiration remain normal. Though some minor operations can be carried out duringthis stage, it is rather difficult to maintain use is limited to short procedures.
STAGES OF ANAESTHESIA• II) Stage of delirium– From loss of consciousness to beginning of regular respiration.– Apparent excitement is seen patient may shout, struggle and hold his breath; muscletone increases, jaws are tightly closed, breathing is jerky; vomiting, involuntarymicturation or defecation may occur.– Heart rate and BP may rise and pupils dilate due to sympathetic stimulation.– No stimulus should be applied or operative procedure carried out during this stage. Thisstage is inconspicuous in modern anaesthesia.
STAGES OF ANAESTHESIA• III. Surgical anesthesia Extends from onset of regular respiration to cessation ofspontaneous breathing. This has been divided into 4 planes which may be distinguished as:– Plane 1 Roving eyeballs. This plane ends when eyes become fixed.– Plane 2 Loss of corneal and laryngeal reflexes.– Plane 3 Pupil starts dilating and light reflex is lost.• As anesthesia passes to deeper planes, progressively—muscle tone decreases, HR increaseswith weak pulse, respiration decreases in depth and later in frequency also— thoracic laggingbehind abdominal.
STAGES OF ANAESTHESIA• IV. Modularly paralysis– Cessation of breathing to failure of circulation and death.– Pupil is widely dilated, muscles are totally flabby, pulse is Already or imperceptible andBP is very low.– Many of the above indices have been robbed the use of atropine (pupillary, heart rate)morphine (respiration, pupillary), muscle relaxants (muscle tone, respiration, eyemovements, reflexes) etc. and the modem anaesthetist has to depend several otherobservations to gauge the depth of anaesthesia
TECHNIQUES OF INHALATION OF ANAESTHETICS• Different techniques are used according to facility available, agentused, condition of the patient, type and duration of operation.Open drop method:– Liquid anaesthetic is poured over a mask with gause and their vapor isinhaled with air. A lot of anaesthetic vapor escapes in the surroundingsand the concentration of anaesthetic breathed by the patient cannot bedetermined. It is wasteful—can be used only for cheap anaesthetics.– Some breathing does occurred in this method. However, it is simplerequires no special apparatus.– Ether is the only agent used by this method, especially in children.
TECHNIQUES OF INHALATION OF ANAESTHETICSThrough anaesthetic machines• Use is made of gas cylinders, specialized graduated vaporizers, flow meters7~uriidtrectionalvalves, corrugated rubber tubing and reservoir bag. The gases are delivered to the patientthrough a tightly fitting face mask or endotracheal tube. Administration of the anaestheticcan be more precisely controlled and in many situations its concentration determined.Respiration can be controlled and assisted by the anesthetists.• (a) Open system:– the exhaled gases are allowed to escape through a valve and fresh anaesthetic mixture is drawn ineach time. No rebreathing his allowed flow rates are high more drug is consumed. However, inhaledO2 and anaesthetic concentration can be accurately delivered.• (b) Closed system:– the patient re-breaths the exhaled gas mixture after it has circulated through soda lime whichabsorbs CO2. Only as much O2 and anaesthetic as have been taken up by the patient are added tothe circuit.– The flow rates are low; especially useful for expensive and explosive agents (little anaestheticescapes in the surrounding air) e.g. halothane, enflurane, isoflurane.
Properties of an ideal anaesthetic• For the patient It should be pleasant, non-irritating, should not cause nausea orvomiting. Induction and recovery should be fast with no after effects.• For the surgeon It should provide adequate analgesia, immobility and musclerelaxation.• It should be non inflammable and non explosive• For the anesthetists its administration should be easy, controllable and versatile.• Margin of safety should be wide, no fall in BP.• Heart, liver and other organs should not be affected.• It should be potent so that low concentrations are needed and oxygenation of thepatient does not suffer.• Rapid adjustments in depth of anaesthesia should be possible.• It should be cheap, stable and easily stored.• It should not react with rubber tubing or soda
Nitrous oxide (N2O)• Nitrous oxide , or laughing gas, was discovered in 1772 by Joseph Priestley, Nitrous oxide was firstused as an anaesthetic in 1845. Unfortunately, the patient woke during the procedure and so its usewas abandoned• It is a colorless, odorless, heavier-than air, noninflammable gas Supplied under pressure in steelcylinders. It is non-irritating but low potency anaesthetic;• It is a poor muscle relaxant; neuromuscular-blockers are often required. Onset of N2O actions isquick and smooth (but thiopentone is often used for induction), recovery is rapid: both because ofits low blood solubility. Second gas effect and diffusion hypoxia occur with N2O only. Post-anaesthetic nausea is not marked.• Unconsciousness cannot be produced in all individuals without concomitant hypoxia: MAC is 1 Q5%.• Implying that even pure N2O cannot produce adequate anaesthesia at 1 atmosphere pressure.Patients maintained on 7 0 % N2O -1- 3 0 % O; along with muscle relaxants of ten recall theevents during anaesthesia, but some lose awareness completely.• Nitrous oxide is a good analgesic; even 2 0 % produces analgesia equivalent to that produced byconventional doses of morphine.
Nitrous oxide (N2O)• Nitrous oxide is generally used as a carrier and adjuvant to other anaesthetics. A mixture of 70 % N2 6 + 2 5 -3 0 % O; + 0 . 2-2 % another potent anaesthetic is employed for mostsurgical procedures. ln this way concentration of the other anaesthetic can be reduced to 1/3for the same level of anaesthesia. Because N2Ohas little effect on respiration, heart and BP:breathing and circulation are better maintained with the mixture than _with the potentanaesthetic given alone in full doses. However, N2O can expand pneumothorax and otherabnormal air pockets in the body.• As the sole agent, N2O ( 5 0 % ) has been used with02 for dental and_ obstetric analgesia. Itis nontoxic to liver, kidney and brain. Metabolism of N2O does not occur; it is quicklyremoved from body by lungs. It is cheap and very commonly used
Ether (Diethyl Ether)• It is a highly volatile liquid, produces irritating vapors which are inflammable andexplosive. (C2H5-O-C2H5)• Ether is a potent anaesthetic, produces good analgesia and marked musclerelaxation by reducing ACh output from motor nerve endings dose of competitiveneuromuscular blockers should be reduced to about 1 / 3 . And unpleasantwith struggling, breath-holding, salivation and marked respiratory secretions(atropine must be given as premedication to prevent the patient from dro w ningin his o w n secretions.• Recovery is slow; post-anaesthetic nausea, vomiting and retching are marked.
Ether (Diethyl Ether)• BP and respiration are generally well maintained because of reflex stimulation and highsympathetic tone. It does not sensitize the heart to Adr, and is not hepatotoxic.• Ether is not used now in developed countries because of its unpleasant and inflammableproperties. However it is still used in developing countries, particularly in peripheral areasbecause it is cheap, can be given by open drop method (though congestion of eye, sorenessof trachea and ether bums on face can occur) without the need for any e quipment, and isrelatively safe even inexperienced hands.
Halothane• It is a potent anaesthetic—precise control of administered concentration is essential.• For induction 2- 4 % and for maintenance 0. 5 -1 % is delivered by the use of a specialvaporizer.• It is not a good analgesic or muscle relaxant; however, it potentiates competitiveneuromuscular blockers.• Halothane causes direct depression of myocardial contractility by reducing intracellular Ca2+concentration.• Cardiac output is reduced with deepening anesthesia. BP starts falling early and parallels thedepth.
Halothane• Halothane causes relatively greater depression, of respiration; breathing isshallow and rapid—PP of CO2 in blood rises if respiration is not assisted.• Pharyngeal and laryngeal reflexes are abolished early and coughing issuppressed while bronchi dilate—preferred for asthmatics.• It inhibits intestinal and uterine contractions. This property is utilized forassisting external or internal version during late pregnancy. However, itsuse during labor can prolong delivery and increase post portal blood loss.• Urine formation is decreased during Halothane anaesthesia primarily dueto low g.f.r. as result of fall in BP.
Isoflurane (SOFANE)• It is a later introduced 1 9 8 1 isomer of enflurane; has similar properties, butmore potent, more volatile and less soluble in blood.• It produces relatively rapid induction and recovery, and is administeredthrough a special vaporizer; 1.5 - 3 % induces anaesthesia in 7-10 min, and 1-2% is used for maintenance.• Magnitude of fall in BP is similar to halothane, but is primarily due tovasodilatation while cardiac output is well maintained. Heart rate is increased.• These cardiovascular effects probably result from stimulation of P adrenergicreceptors, but it does not sensitize the heart to adrenergic arrhythmias.Coronary circulation is maintained: safer in patients with myocardial ischemia.Respiratory depression is prominent and assistance is usually needed to avoidhypercardia. Secretions are slightly increased. Uterine and skeletal musclerelaxation is similar to halothane.
Isoflurane (SOFANE)• Metabolism of isoflurane is negligible. Renal and hepatic toxicity has not beenencountered. Post-anaesthetic nausea and vomiting is low. Pupils do not dilate andlight reflex is not lost even at deeper levels.• Though slightly irritant, isoflurane has many advantages, i.e. better adjustment ofdepth of anaesthesia and low toxicity.• It is a good maintenance anaesthetic, but not preferred for induction. It does notprovoke seizures and is preferred for neurosurgery.• Isoflurane has become the routine Anaesthetic, but use may be restricted due tocost.
Desflurane• It is a newer all fluorinated congener of isoflurane which has gained• Popularity as an anaesthetic for out patient surgery in western countries. Though itis highly thermostatically special vaporizer is used to deliver a preciseconcentration of pure desflurane vapor in the carrier gas (N2O + O2) mixture.• Its distinctive properties are lower oil: gas partition coefficient and very lowsolubility in blood as well as in tissues, because of which induction and recoveryare very fast.• Depth of anaesthesia changes rapidly with change in inhaled concentration. Postanaesthetic cognitive and motor impairment is short lived patient can bedischarged a few hours after surgery.
Desflurane• Desflurane is less potent than isoflurane; higher concentration has to be used forinduction irritates air passage may induce coughing, breath-holding and laryngospasmbecause of somewhat pungent odour making it unsuitable for induction.• Rapid induction sometimes causes brief sympathetic stimulation and tachycardia.Degree of respiratory depression, muscle relaxation, vasodilatation and fall in BP, as wellas maintained" cardiac contractility and coronary circulation are like isoflurane.• Lack of seizure provoking potential or arrthyhmogenicity and absence of liver as well askidney toxicity are also similar to isoflurane.• It is exhaled unchanged, but more rapidly.• As such, desflurane can serve as a good alternative to isoflurane for routine surgery aswell, especially prolonged operations.
Desflurane• Sevoflurane This new polyfluorinated anaesthetic has properties intermediate betweenisoflurane and desflurane. Solubility in blood and tissues as well as potency is less thanisoflurane but more than desflurane.• Induction and emergence from anaesthesia are fast and rapid changes in depth can beachieved. Absence of pungency makes it pleasant and administrable through face mask.Unlike desflurane, it poses no problem in induction; acceptability is good even bypediatric patients. Recovery is smooth; orientation, cognitive and motor functions areregained almost as quickly as with desflurane. Sevoflurane is suitable both foroutpatient as well as inpatient surgery.
Desflurane• Sevoflurane does not cause sympathetic stimulation and airway irritation evenduring rapid induction. Fall in BP is due to vasodilatation as well as modest cardiacdepression. Respiratory depression, absence of seizure and arrthymia precipitatingpropensity are similar to isoflurane" About 3% of absorbed sevoflurane ismetabolized, but the amount of fluoride liberated is safe for kidney and liver.However, it is degraded by soda lime—not recommended for use in closed circuit.
• INTRAVENOUS ANAESTHETICS INDUCING AGENTS
Thiopentone sod.• It is an ultra short acting thiobarbiturate, highly soluble in water yielding avery alkaline solution, which must be prepared before Injection.• Extravasations of the solution or inadvertent intra arterial injectionproduces intense pain necrosis and gangrene may occur. Injected i.v. (3-5mg/kg) as a 2.5% solution, it serum consciousnessJrLl5=2Q sec.• Its undissociated form has high lipid solubility-enters brain almostinstantaneously. Initial distribution depends on organ blood flow braingets large amounts. However, as other less vascular tissues (muscle, fat)gradually Jake up the drug, blood concentration falls and it back diffusesfrom the brain: consciousnesses regained in 6-10 min (Iv distributionphase is 3 min).
Thiopentone sod.• On repeated injection, the extra cerebral sites are gradually filled up lower dosesproduce anaesthesia which lasts longer.• Its ultimate disposal_ occurs mainly by the hepatic metabolism (elimination it is 7-12 hr), but this is irrelevant for termination of action of a single dose.• Residual CNS depression may persist for 12 hr. The patient should not be allowedto leave the hospital without an attendant before this time. Thiopentone is a pooranalgesic.• Painful procedures should not be carried-Out under the influence unless anopioids or N2Ohas-been given; otherwise, the patient may struggle, shout andshow reflex .changes in BP and respiration.
Methohexitone sod.• It is similar to thiopentone,• 3 times more potent,• has a quicker and briefer (5-8 min) action.• Excitement during induction and recovery is more common.• It is more rapidly metabolized (VA 4 hr) than thiopentone:patient may be roadworthy more quickly.
• SLOWER ACTING DRUGS
Benzodiazepines (BZDs)• In addition to preanaesthetic medication, BZDs are now frequently usedfor inducing, maintaining and supplementing anaesthesia as well as forconscious sedation.• Relatively large doses (diazepam 0.2-0.3 mg/kg or equivalent) injected i.v.produce sedation, amnesia and then unconsciousness in 5-10 min.• If no other anaesthetic or opioids is given, the patient becomes responsivein 1 hr or so due to redistribution of the drug (distribution tic of diazepamis 15 min), but amnesia persists for 2-3 hr and sedation for 6 hr or more.Recovery is further delayed if larger doses are given.• BZDs are poor analgesics: an opioids or N2O is usually added if theprocedure is painful.
Benzodiazepines (BZDs)• By themselves, BZDs do not markedly depress respiration, cardiaccontractility or BP, but when opioids are also given these functions areconsiderably compromised.• BZDs decrease muscle tone by central action, but require neuromuscularblocking drugs for muscle relaxation of surgical grade. They do notprovoke postoperative nausea or vomiting. Involuntary movements arenot stimulated.
Ketamine• It is pharmacologically related to the hallucinogen phencyclidine; induces a socalled dissociative anesthesia characterized by profoundanalgesia, immobility, amnesia with light sleep and feeling of dissociation fromones own body and the surroundings.• The primary site of action is in the cortex and sub cortical areas; not in thereticular activating system (site of action of barbiturates).• Respiration is not depressed, airway reflexes are maintained, muscle toneincreases; limb movements occur and eyes may remain open.
• Heart rate, cardiac output and BP are elevated due to sympathetic stimulation. Adose of 1-3 (average 1.5) mg/kg i.v. or 5 mg/kg i.m. produces the above effectswithin a minute, and recovery starts after 10-15 min, but patient remains amnesicfor 1-2 hr.• Ketamine has been used for operations on the head and neck, in patients whohave bled, in asthmatics (relieves bronchospasm), in those who do not want tolose consciousness and for short operations. It is good for repeated use;particularly suitable for burn dressing.• Combined with diazepam, it has found use in angiographies, cardiaccatheterization and trauma surgery.
Fentanyl• This short acting (30-50 min) potent opioids analgesic related to pethidineis generally given i.v. at the beginning of painful surgical procedures.• Reflex effects of painful stimuli are abolished.• It is frequently used to supplement anaesthetics in balanced anaesthesia.This permits use of lower anaesthetic concentrations with betterhemodynamic stability.• Combined with BZDs, it can obviate the need for inhaled anaesthetics fordiagnostic, endoscopic, angiographic and other minor procedures in poorrisk patients, as well as for bum dressing. Anaesthetic awareness withdreadful recall is a risk.
Dexmedetomidlne• Activation of central ofc adrenergic receptors has been known to causesedation and analgesia.• Clonidine (a selective α 2 agonist antihypertensive) given before surgeryreduces anaesthetic requirement.• Dexmedetomidlne is a centrally active selective agonist that has beenrecently introduced for sedating critically ill/ventilated patients inintensive care units.• Analgesia and sedation are produced with little respiratory depression,amnesia or anaesthesia. It is administered by i.v. infusion. Side effects aresimilar to those with clonidine, viz. hypotension, bradycardia and drymouth.
A. During anaesthiesia• Respiratory depression and hypercarbia.• Salivation, respiratory secretions- less now as nonirritant anaesthetics aremostly used.• Cardiac arrhythmias, a systole.• Fall in BP• Aspiration of gastric contents: acid pneumonitis.• Awareness: dreadful perception and recall of events. During surgery byuse of light anaesthesia -1- analgesics and muscle relaxants.• Delirium, convulsions and other excitatory effects are generally seen withi.v. anaesthetics especially if phenothiazines or hyoscine have been givenin premedication. These are suppressed by opioids.• Fire and explosion rare now due to use of non-inflammable agentsCOMPLICATIONS OF GENERAL ANAESTHESIA
B. After anaesthesia• Nausea and vomiting.• Persisting sedation: impaired psychomotor function• Pneumonia, atelectasis.• Organ toxicities: liver, kidney damage.• Nerve palsies due to faulty positioning.• Emergence delirium.• Cognitive defects: prolonged excess cognitive decline has been observedin some patients, especially the elderly, who have undergone generalanaesthesia, particularly of long duration.COMPLICATIONS OF GENERAL ANAESTHESIA
DRUG INTERACTIONS• Patients on antihypertensive given general anaesthetics—BP may fall markedly.• Neuroleptics, opioids, clonidine and monoamine oxidase inhibitors potentiateanesthetics.• Halothane sensitizes heart to Adrenaline• If a patient on corticosteroids is to be anaesthetized, give 100 mg hydrocortisoneintraoperatively because anaesthesia is a stress can precipitate adrenalinsufficiency and cardiovascular collapse.• Insulin need of a diabetic is increased during GA: switch over to plain insulineven if the patient is on oral hypoglycemic.
PREANAESTHETIC MEDICATIONPreanaesthetic medication refers to the use of drugs before anaesthesia to make itmore pleasant and safe. The aims are:1 . Relief of anxiety and apprehension preoperatively and to facilitate smoothinduction2. Amnesia for pre- and postoperative events.3. Supplement analgesic action of anaesthetics and potentiate them so that lessanaesthetic is needed.5. Decrease secretions and vagal stimulation caused by anaesthetics.6. Antiemetic effect extending to the postoperative period.7. Decrease acidity and volume of gastric juice so that it is less damaging ifaspirated.
Sedative-antianxiety drugs• Benzodiazepine-pines like– Diazepam (5-10 mg oral) or lorazepam (2 mg or 0.05 mg/kg i.m. 1 hour before)have become popular drugs for preanaesthetic medication because theyproduce tranquility and smoothen induction;– There is loss of recall of perioperative events (especially with lorazepam) withlittle respiratory depression or accentuation of postoperative vomiting. Theycounteract CNS toxicity of local anaesthetics and are being used along withpethidine/fontanels for a variety of minor surgical and endoscopic procedures.– Midazolam is a good amnesic with potent and shorter lasting action; it is alsobetter suited for i.v. injection, due to water solubility. Promethazine (50 mgi.m.) is an antihistaminic with sedative, antiemetic and Anticholinergicsproperties. It causes little respiratory depression.
Opioids• Morphine (10 mg) or pethidine (50-100 mg), i.m.– allay anxiety and apprehension of the operation– produce pre and postoperative analgesia,– smoothen induction,– reduce the dose of anaesthetic required and supplement poor analgesic(thiopentone, halothane) or weak anaesthetics (Nfl).– Postoperative restlessness is also reduced.– Disadvantages:– They depress respiration– interfere with pupillary signs of anaesthesia,– may cause fall in BP during anaesthesia, can precipitate asthma and tend to delay recovery.– Other disadvantages are lack of amnesia, flushing, delayed gastric emptying and bleary spasm.Some patients experience dysphoria.– Morphine particularly contributes to postoperative constipation, vomiting and urinaryretention. Tachycardia sometimes occurs when pethidine has been used.
Anticholinergics• Atropine or hyoscine (0.6mg i.m. /i.v.) have been used, primarily toreduce salivary and bronchial secretions.• Need for their use is now less compelling because of the increasingemployment of non-irritant anaesthetics.• However, they must be given before hand when ether is used.• The main aim of their use now is to prevent vagal bradycardia andhypotension (which occur reflex due to certain surgical procedures),and prophylaxis of laryngospasm which is precipitated byrespiratory secretions.
Anticholinergics• Hyoscine, in addition, produces amnesia and antiemetic effect, but tendsto delay recovery. Some patients get disoriented; emergence delirium ismore common.• They dilate pupils, abolish the pupillary signs and increase chances ofgastric reflux by decreasing tone of lower esophageal sphincter (LES). Theyshould not be used in febrile patients.• Dryness of mouth in the pre- and postoperative period may be distressing.• Glycopyrrolate (0.1-0.3 mg i.m.) is a longer acting quaternary atropinesubstitute. It is a potent antisecretory and antibradycardiac drug; actsrapidly and is less likely to produce central effects.
Neuroleptics• Chlorpromazine (25 mg), triflupromazine (10 mg) or haloperidol (2-4 mg)i.m. are infrequently used in premedicahon.• They allay anxiety, smoothen induction and have antiemetic action.• However they potentiate respiratory depression and hypotension causedby the anesthetics and delay recovery.• Involuntary movements and muscle dystonias can occur, especially inchildren.
H2 blockers• Patients undergoing prolonged operations, caesarian section and obesepatients are at increased risk of gastric regurgitation and aspirationpneumonia.• Ranitidine (150 mg) or famotidine (20 mg) given night before and in themorning benefit by raising pH of gastric juice; may also reduce its volumeand thus chances of regurgitation.• Prevention of stress ulcers is another advantage.• They are now routinely used before prolonged surgery.• The proton pump inhibitor omeprazole/ pantoprazole are an alternative.
Antiemetic• Metoclopramide 10-20 mg i.m. preoperatively is effective in reducing postOperative vomiting. By enhancing gastric emptying and tone of LES, it reduces thechances of reflux and its aspiration. Extra pyramidal effects and motor restlessnesscan occur. Combined use of metoclopramide and H2 blockers is more effective.• Domperidone is nearly as effective and does not produce extra pyramidal sideeffects.• After its success in cancer chemotherapy induced vomiting, the selective 5-HT3blocker Ondansetron (4-8 mg i.v.) has been found highly effective in reducing theincidence of post anaesthetic nausea and vomiting.