AUTHOR – DR.Gururaj Arakeri

DEFINITION:

Wendell Holmen coined the word anaesthesia in 1847.

General anaesthesia implies absence of all sensations including consciousness. “General anaesthesia is reversible state of unconsciousness from which a person cannot be aroused by external stimuli. There is partial or complete loss of protective reflexes including the ability to maintain airway independently. Normally laryngeal reflexes and cardiovascular functions are not depressed.

General anaesthetics are the agents, which bring about loss of all modalities of sensation, particularly pain along with reversible loss of consciousness.

HISTORICAL ASPECT:

           Ancient carvings/paintings are the facts that shows that the dental treatment were among man earliest treatments. How very early humans use to relive their pain is not known. Around 25 to 40 thousand years ago medicine man attempted to remove pain by having victim’s intake smoke produced by burning various therapeutic agents.

Intoxicating effects of juices of the poppy Mandragara henbane and Indian hemp were among the next generation of general anaesthetics. First record of evidence of alcohol ingestion for unconsciousness found in the bible genesis IX: 21, where Noah drank an excess of grape wine.

Serivonius in 47 AD advocated that the nose of the patient should be rubbed with known sugar ivy & green oil. And the patient is advised to hold his breath, a stone is then placed between his teeth and he is made to close his mouth forcefully, the fluid which causes the pain is seem to flow through mouth and then tooth is extracted.

          Galen, a Greek physician in165AD used strong vinegar as an anaesthetic agent for tooth removal.

First truly modern experimental note was found in 1799. Davy published an account of his research and experiment with various vapours of gases. Davy observed that pain caused by erupting wisdom tooth was reduced upon inhaling nitrous oxide; he also termed it as a laughing gas. However Davy was not impressed by idea of surgical anaesthesia.

           On December 10 1844, Horace wells, a young Hartford dentist attended a lecture on chemical phenomenon by Gardner. The idea of inhalation anaesthesia crystallized in his mind. The following day, Wells the man officially recognized by both ADA & AMA as discoverers of anaesthesia, painlessly extracted a tooth under a influence of N2O

Another dentist, Morton received the idea of inhalation from one of well’s demonstration. In 1846 he presented demonstration of ether and was first to manufacture anesthesia equipment.

In 1847, Simpson discovered the use of chloroform for anaesthesia. From 1850 to 1860, chloroform was being used for dental as well as major surgical procedures. Vaporization of topically applied chloroform was used as a means for refrigerant anaesthesia.

Edward Andrew in 1868 added inhalation of 20% of O2 to nitrous oxide to make anaesthetics mixture safe and more pleasant than any other. In late 1890`s two German dentists Carlson and Thieving working independently discovered that while spraying ethyl chloride into oral cavity in an attempt to produce local anaesthesia they noticed that several patients lost consciousness, this was used in many hospitals for major surgeries

In 1924 Charles Dodd a dentist reported 100 successful dental cases carried out under ethylene chloride anaesthesia. Attempts to reduce flammability increase potency and hasten induction and recovery periods resulted in production of different agents like vinyl ethyl ether divinyl oxide, tri-chloroethylene.

In 1951 C.W.Suckling of Manchester synthesized halothane; and in 1966, ketamine was used clinically by corssen and domino in U.S.A

ADVANTAGES -

1.     Patient cooperation is not absolutely essential for the success of general anaesthesia.

2.     the patient is unconscious

3.     the patient does not respond to pain

4.     amnesia is present

5.     the onset of general anaesthesia is usually quite rapid

6.     unlimited operating time

7.     Caters for all degrees of surgical complexity.

DISADVANTAGES:

1.     very costly

2.     protective reflexes are depressed

3.     vital signs are depresses

4.     advanced training is required

5.     unsafe for elderly and medically compromised patients

6.     intra and post operative complications

CLASSIFICATION–

I. Inhalation General Anaesthetics/Volatile General Anaesthetics

a)     Volatile liquids:

Chloroform, Ethyl Chloride, Diethyl ether, Trichloroethylene, Halothane, Enflurane, isoflurane, desflurane, sevoflurane.

b)    Gases:

Cyclopropane, Nitrous oxide

II. Non volatile General Anaesthetics (I.V. Anaesthesia)

a)     Inducing agents:

Thiopentone sodium, methohexitone sodium, propofol, etomidate

b)    Slower acting drugs:

Benzodiazepines, dissociative anesthesia, neurolept analgesia

STAGES OF ANAESTHESIA: -

Guedel  in 1920, using ether, divided stages of anaesthesia into 4 stages, of which 3^rd stage is subdivided into 4 planes.

Stage 1:

Also known as stage of analgesia.  It lasts from beginning of anaesthesia to loss of consciousness.  Consciousness and sense of touch are retained and sense of hearing increased.  Sensation of pain is absent and gradual depression of cortical centre in this stage is manifested by sensation of remoteness, falling, suffocation, individuals may experience a feeling of warmth.

Stage 2:

(Stage of Delirium/excitement)

Loss of consciousness to beginning of surgical anaesthesia.  It is characterised by onset of automatic breathing.  Associated with excitement, increased motor activity, breath holding, tachy apnea and hyperventilation, vomiting, struggling (patient may shout, become violent)

Stage 3:

From the onset of regular breathing to cessation of respiration. It is characterised by loss of reflexes, regular respiration, relaxation of skeletal muscle, reflex activity is lost.

Plane 1:

From the onset of automatic respiration to cessation of eyeball movements.

·        Pupils are normal in size and eyeballs are roving. The pupils will dilate in response to surgical stimulation.

·        Respiration is full regular and deep thoraco-lumbar in character.

·        Normal pulse and BP, skeletal muscle incompletely relaxed.

·        Lid reflex, swallowing and vomiting get abolished.

·        Corneal reflex is present but the conjunctival reflex lost.

·        Secretion of tears present.

Plane 2:

It is from cessation of eyeball movements to commencement of inter costal paralysis.

·        The pupils begin to dilate.

·        Respiration is regular, the volume (amplitude) diminished.  Respiratory response to surgical trauma disappears.

·        Corneal reflexes abolished and endotracheal intubation performed.

Plane 3:

Commencement to completion of intercostal paralysis.

·        Tidal volume is reduced, inspiration shorter than expiration.

·        BP falls, asynchrony between thoracic and abdominal respiratory movement.

·        Respiration increases, the pupillary light reflex is abolished as well as conjuctival.

·        Muscular relaxation is complete.

Plane 4:

Complete intercostal paralysis to diaphragmatic paralysis.

·        Respiration is paradoxical, tracheal tug is evident as the trachea moves down with each inspiration.

·        The pupils are dilated, do not respond to light, muscles are flaccid and BP is low.

·        The secretions are progressively reduced from plane 1 onwards and are completely abolished in plane 4

Stage 4: (Medullary Paralysis)

Severe depression of vital medullary centres. This stage is characterised by diaphragmatic paralysis to apnoea and death.  All reflex activity is lost, pupils are widely dilated. The respiratory arrest is accompanied by vasomotor collapse and heart ceases to beat.

Mode of Action: (Unknown):

Several mode action, mainly on the brain, primarily on the mid brain reticular activating system and the cortex – Principal site of action seems to be along the neuronal lipid bilayer membrane so that cation (Na, K) movement through the protein pores which are associated with action potential are obstructed.

PATIENT ASSESSMENT;

This has to be determined by both surgical and anaesthetic point of view. The surgeon must initially access the patient for operating procedure, types, duration, airway etc.

Pre anaesthetic evaluation is the responsibility of an anaesthetist. Surgeon should also evaluate the patient. This is categorized into physiological, pathological and drug induced problems.

Physiological:

1) Age: metabolic rates in infants and children are higher than adults. In the older persons functioning of the body becomes less efficient. Effect of any complication may be magnified in infants or old people. In this it is biological age, which is important, and not chronological age.

2) Pregnancy:

 First trimester; it is especially important in the formation of foetus and       placenta. This process may be disturbed by externally evoked stimulus. Drugs proven safe should be used.

Second trimester; no contra indication since fetal organs development is complete and fetus is yet not large enough to significantly affect the venous return. But adequate oxygen should be supplied

Third trimester; foetus may obstruct venous return from legs by extending pressure on lower part of abdomen and therefore decreased venous return, this causes decreased cardiac output. Anaesthesia in supine position is not advised; patient should be in head down in lateral position, upward pressure may also cause delayed gastric emptying. In pregnancy maternal blood volume increases by 20% therefore increased dose of anaesthesia is necessary

Pathological/ systemic problems: 

1)    CVS

Cardiac diseases can be suspected by patient’s history of chest pain, medications he is receiving, cyanosis, clubbing, swelling of ankles, engorgement of jugular vein. Patient with angina should be advised to suck glycerol trinitrate before treatment and should be exposed to minimum stress. Patient with valvular diseases present potential problems during anaesthesia. Change in B P is induced by anaesthetic agents and is tolerated in healthy individual. In cardiac diseases patient may present with large fluctuation in CVS. Any patient with diastolic pressure greater than 90 mmhg should be referred to physician for treatment of high B P.

2)    Respiration:

 In upper respiratory tract infection (i.e. above vocal cord), common cold is most common. Lower respiratory infection commonly includes slight bronchitis’s in winter. Cough, laryngospasm, bronchospasm can produce a frighteningly quick deterioration in patients well being. The anaesthetists should consider amount and type of airway, obstruction- presence of local secretions, and effect of disease on blood gas exchange. In patients with Ludwig’s angina IV sedation is contraindicated. Here inhalation anaesthesia can be given. In acute respiratory tract infection,    G A is postponed. In chronic conditions, refer to physician.

3)    Haematological disorders:

All anaemia’s affect general anaesthesia but special significance is in sickle cell anaemia and thalassemia that should be referred to hospital for treatment. Other haematological disorders may affect WBC and platelets. Problem of prolonged bleeding and delayed healing of wound must be considered. In patients with clotting disorders, injections should be avoided. In patients with haemophilia and thrombocytopenia, correct treatment either locally or systemically is the only way to prevent blood loss. It should be remembered that death is caused by 30% of acute blood loss.

 4) Endocrine/metabolic disturbances:

 In diabetes mellitus patient should be starved before anaesthesia and this is bound to upset the stability of blood glucose level. In hospital patient may be observed with modern electronic and computerized aids and blood glucose is controlled.

5) Diseases of thyroid/ parathyroid:

These patients should be stabilized before they are anaesthetized, there is a little risk to a well-stabilized patient while reverse is for hyper/hypo thyroid or parathyroid, therefore patient should be hospitalised. In hyperthyroid there is persistent tachycardia, atrial fibrillation. In hypothyroid there is bradycardia, mental retardation.

6) Diseases of adrenal glands:

These may lead to dangerous complications. Here the response to stress is suppressed, and there may be secondary insulin resistant diabetes. Oedema and increased blood pressure may result.

7) Diseases of kidney and liver:

In disorders of kidney, a response to drug may be increased or decreased. In kidney diseases, patient’s appearance of good health may hide serious problems, which with injudicious handling could become a crisis. Impairment of liver may be result of infective, atrophic or neoplastic change, occasionally damage is due to toxic drugs and repeated use of certain anaesthetics agents. Such patients should be referred for medical fitness before general anaesthesia.

Drug induced problems:

 There is no real contra indication to a patient on anti-coagulant for general anaesthesia but it is necessary to reduce dose to allow homeostasis after surgery. Great care should be taken for patients on psychiatric treatment. Two types of anti depressants are given

1.     The tri cyclic group of compounds and

2.     Mono amino oxidase inhibitor.  

The risk of general anaesthesia is greater for patients with mono amino oxidase inhibitor particularly when opiate derivatives are used.

9) OTHER PROBLEMS: patient with history of difficult previous anaesthesia

PHARMACOLOGY OF ANESTHETIC DRUGS:

INHALATIONAL ANAESTHETICS:

The preferred inhalation agents are those that are minimally irritant and non-inflammable and comprise nitrous oxide and fluorinated hydrocarbon like halothane and its allies. 

Pharmacokinetics:

          The level of anaesthesia is dependent on the development of a series of tension gradients from high partial pressure delivered to the alveoli and decreasing through blood to brain and other tissues.  These gradients are dependent upon physical properties of anaesthetic and the tissues as well as physiological function.

Few points:

1.     An anaesthetic that has high solubility in blood, if given at a steady concentration provide a slow induction.

2.     Agents that have low solubility in the blood provide rapid induction.

3.     During induction of anaesthesia the blood is taking up anaesthetic gas selectively and rapidly and the resulting loss of volume in the alveoli leads to a flow of gas in to lungs that is independent of respiratory activity.

4.     Diffusion hypoxia is most common in with gases relatively insoluble in the blood, for they will diffuse out most rapidly when the drug is no longer inhaled i.e., just as a induction is faster, so is elimination.  Highly blood soluble agents will diffuse out more slowly, so that recovery will be slower just as induction is slower and with them diffusion anoxia is insignificant.

NITROUS OXIDE (1844)

Non-flammable, nor explosive, has a slightly sweetish odour.  It produces light anaesthesia without demonstrably depriving the respiratory vasomotor centre provided that normal oxygen tension maintained.  It is known as “laughing gas” (since it is administered along with air produces a stage of excitement of delirium and also produces amnesia).

Advantages:

1.     Rapid induction and recovery  (1 – 4 min)

2.     Safest anaesthesia agent (has no effect on circulation, respiration, liver and kidney)

3.     Because of analgesic action it is used in sub anaesthetic concentration, Nitrous oxide is employed for tooth extraction, for obstetrical analgesic, changing of dressing of burns, cleaning and dressing of wounds and cauterisation.

Disadvantages:

1.     It is expensive to buy and transport.  It must be used in conjunction with more potent anaesthetic and muscle relaxants to produce full surgical anaesthesia.

2.     Excitement may be violent.

3.     CO2 accumulation and hypoxia may develop during prolonged Nitrous oxide anaesthesia, especially when supplemented with skeletal muscle relaxants.

4.     A special form of apparatus is necessary to control its administration.

5.     An increase in spontaneous abortion has been noted in wives of surgeons

Uses:

1.     Maintenance of surgical anaesthesia in combination with other anaesthetic agents (halothane, ether, thiopentone/ketamine) and muscle relaxants.

2.     In sub anaesthetic doses it is used to provide analgesia for obstetric practice, for emergency management of injuries, during postoperative physiotherapy and for refractory pain in terminal illness.

3.     It is used to measure cerebral coronary blood flow by Fick’s principles.

Dosage: For analgesia 50% O₂ + 50₂ N₂O₂

For maintenance of anaesthesia N₂O₂ combined with at least 30% oxygen.

 Plane2 of surgical anaesthesia is reached with an N₂O_{2 and oxygen} 80: 20.

Contraindications:

In patients with demonstrable collections of air in the pleural, pericardial or peritoneal space, intestinal obstruction; occlusion of the middle ear: arterial air embolism decompression sickness, chronic obstructive airway disease or emphysema.

Precautions:

Continuous administration of oxygen may be necessary during recovery especially in elderly patients.

Adverse affects:

The incidence of nausea and vomiting increases with the duration of anaesthesia. Prolonged and repeated exposure may be associated with bone marrow depression and a teratogenic risk.

Storage:

Nitrous oxide supplied under pressure cylinders, which must be kept below 25^O C. Cylinders containing premixed oxygen 50% and nitrous oxide 50% (Entonox) are available for analgesia.

HALOTHANE:

Colourless, volatile, non-irritant liquid with sweet odour.  It is neither flammable nor explosive.

Advantages:

1.     Induction is smooth and pleasant, rapid and surgical anaesthesia can be produced in 2 – 5 min., rapid recovery time and incidence of past operative nausea and vomiting is low.

2.     Halothane inhibits laryngeal and pharyngeal reflexes in upper planes of surgical anaesthesia to certain extent.  It also relaxes the masticatory muscles and inhibits salivation (Hence tracheal intubation much easier).

Disadvantages:

1.     Severe hepatitis (1:50,000 incidence)

-         More common in pregnancy and individuals with hepatic disease. Halothane should not be repeated at intervals less than 3 months to avoid liver toxicity.

2.     Muscle relaxants are additionally required to prepare the patient for abdominal surgery.

3.     It causes cardio vascular depression; severe hypertension is main draw back. Halothane sensitises heart to the dysrhythmic effects of catecholamines.

4.     Recovery of mental function takes several hours after halothane general anaesthesia.

5.     Halothane raises intra-cranial pressure due to cerebral vasodilation.

Contraindications:

1.     A history of unexplained jaundice following previous exposure to halothane.

2.     A family history of malignant hyperthermia.

3.     Increased CSF pressure.

Precautions:

          Proper history to reveal previous reactions to halothane e.g.: unexplained fever and jaundice. At least 3 months should be allowed to elapse between each re-exposure to halothane.

Adverse effects:

          Cardiac dysrhythnias may be induced. Hepatic damage occurs in small proposition of exposed patients.

Drug interaction:

          Halothane potentiates response to antihypertensive drugs.  Pre-medication with atropine reduces the risk of hypotension and bradycardia. Interaction occurs with adrenaline.

INTRAVENOUS ANAESTHETICS:

THIOPENTAL/ THIOPENTONE:

          It is very short acting barbiturate, which administered parenterally, rapidly induces hypnosis and anaesthesia without analgesia.  It is bound to plasma albumin, initially distributed to highly vascularised organ, subsequently diffuses selectively into fatty tissue.  It is slowly, almost entirely metabolised in liver.

Uses:

1.     Induction of general anaesthesia prior to administration of inhalational and other anaesthetics.

2.     As anaesthetic agent for operation of short duration. E.g. in fracture reduction, dilatation, curettage and certain dental procedure.

3.     As anticonvulsant in emergency treatment of convulsions.

Advantages:

1.     Anaesthesia is induced rapidly, pleasantly and without any excitement and speedy recovery after small dose.

2.     Quiet respiration, no sensitisation of the myocardium to adrenaline.

3.     Low incidence of post-anaesthetic complications.

Disadvantages:

1.     It has insignificant analgesic action.

2.     Muscular relaxation with thiopental is usually adequate.

3.     It depresses respiratory centre, vasomotor centre and myocardium.  It should be used carefully in patients with cardiac diseases, because rapid injection may produce hypotension and cardiac arrhythmias.

4.     The stages of anaesthesia may be reached very quickly and consistent supervision is necessary to prevent an over dosage.

Contra indications:

          It should not be used if there is doubt that a clear airway can be maintained, allergy to barbiturate, severe CVS diseases, obstructive respiratory diseases; status asthmatics; Addision’s disease, hepatic dysfunction, myxoedma, acute intermittent porphyria.

Precaution:

1.     Whenever possible thiopentone should be administered under supervision of specialist anaesthetist.

2.     Equipment for CPR and endo tracheal intubation should be immediately available and ready for use.

3.     Concentration  > 25mg/ liable to cause thromboplebhitis.

4.     Intra-arterial injection causes intense pain and results in arteriospasm.

Adverse effects:

          Rapid injection may result in severe hypotension and hiccoughs. Coughing, sneezing or laryngeal spasm may occur during induction.      Over dosage results in respiratory depression.

          Doses = 3.5mg/kg given by slow i.v injection over 10 – 15 seconds and repeated if necessary after 20 – 30 seconds.  Dosage requirements vary; they are reduced in elderly, in hypovolemic patients and in patients with heavily premedicated with narcotics/with the cerebral depressants.

KETAMINE:

          It is a phencyclidine derivative produces a transient like state known as “dissociative anaesthesia”.

Advantages:

1.     Anaesthesia lasts for about 15 min. after single i.v.injection and profound analgesia lasts for about 40 min.

2.     It can be used as a sole agent in diagnostic and minor surgical interventions.

3.     It is less likely to induce vomiting.

4.     Airway is at less risk compared to other general anaesthesia technique since laryngeal and pharyngeal reflexes are only slightly impaired.

5.     It is of particular value in children and poor risk patients and also in asthmatic patients.

Disadvantages:

1.     It produces no muscular relaxation

2.     It tends to raise heart rate and intracranial and intraoccular pressure.

3.     In hypertensive patients it may raise BP unduly.

4.     Hallucinations may occur during recovery.

Uses:

1.     In procedures of short duration such as dressing of burns, radio therapeutic procedures, bone marrow sampling and minor orthopaedic procedure to provide analgesia, sub anaesthetic dose of ketamine is used.

2.     It is used for induction of anaesthesia prior to administration of inhalational anaesthetics.

3.     Maintenances of short lasting diagnostic and surgical interventions, including dental procedure that does not require skeletal muscle relaxation.

4.     It is of particular value for children requiring frequent repeated anaesthesia.

Dosage and Administration:

·        Ketamine administration should always be preceded by premedication with atropine to reduce salivary secretions.

·        Pre-medication with diazepam reduces subsequent requirement for ketamine and the incidences of emergence reactions.

Induction:

I.V rate – 1 – 2mg/kg – slow injection over a period of 60 seconds.

          Dose of 2mg/kg produces surgical anaesthesia within 1 – 2 min, which may be expected to last 5 to 10 min.

          1M route: – 6 – 8 mg/kg by deep intra muscular injection.  This dose produces surgical anaesthesia within 3 – 5min. and may be expected to last up to 25 min.

Maintenance:

          Following induction, serial doses of 50% of the original intravenous dose as 25% of intra muscular dose are administered as required.

          As an analgesic à 500 mg/kgi.m /i.v.followed if necessary by a dose of 250µgm/kg

Recovery:

          Return to consciousness is gradual.  Emergence reaction with delirium may occur, avoided by unnecessary disturbance of patient during recovery and administration of diazepam preoperatively and supplemented by 5 – 10 mg of diazepam i.v at the end of the procedure.

Contra indications:

          Moderate to severe hypertension, CHF, a history of cerebrovascular accident, alcohol intoxication, cerebral trauma, increased intracranial pressure, eye injury, increased IOP, psychiatric disorders such as schizophrenia, acute psychoses.

Precautions:

·        Pulse and BP should be closely monitored.

·        Mechanical stimulation of pharynx avoided unless muscle relaxants are used.

PROPOFOL

-         Non barbiturate IV general anaesthetic agent.

-          In lower doses it can also be used to induce either conscious sedation/deep sedation.

-         Rapid onset of action

-         Short duration of action (5 min)

-         Effect on CVS à it depends on mean arterial blood pressure, with   no effect on heart rate.

·        Hypotensive effects are dose and rate dependants, are transient and rarely require pharmacological correction.

·        Propofol is respiratory depressant, the extent of which is dose and rate depressant à Apnoea

·        It does not release histamine and therefore should be safe for use in asthmatic.

·        Most frequent adverse effect is pain from injection.

·        It has anti emetic property as well as antipruritic properties. There is no analgesic effect.

·        Propofol’s major advantage is extremely rapid recovery with more clear headed when compared with other agents.

DISSOCIATIVE ANAESTHESIA:

          It is a state of analgesia and light hypnosis (eyes may remain open). Ex; Ketamine.

1.     It is particularly useful where modern equipment and necessary trained staff are lacking.

2.     Also used at scenes of major accidents and wars.

NEUROLEPTANALGESIA:        

Patient is in a state of analgesia, but is cooperative.

                   Droperidol (Combination of neuroleptic)

                             +

                   Fentanyl (High efficiency opoid analgesic)

It is also used to supplement general anaesthesia e.g., with N2O2 (Neuroleptoanaesthesia).

Sedation and amnesia without analgesia is provided by diazepam and midazolam i.v.  They can be used alone for procedures causing discomfort but not pain. E.g.; endoscopy. It can be supplemented with general anaesthesia where pain is expected. E.g. removal of impacted 3^rd molar.

Disadvantages:

          Respiratory depression and apnoea can occur with the above especially in the elderly with cerebral atherosclerosis. Laryngeal reflexes are not spared and inhalation of oral secretions or dental debris can occur.

Patient controlled analgesia:

          E.g. N2O2/O2 mixtures are effective for brief procedures.  Apparatus to allow patient to control i.v. analgesics has been developed.

MUSCLE RELAXANTS:

          A muscle relaxant is to facilitate tracheal intubation at the start of anesthesia. During the maintenance of anesthesia muscle relaxation may be required to facilitate surgery and intermittent positive pressure ventilation (ippv).

          Muscle relaxant can be either of the following:

Depolarising:  Depolarizes the neuromuscular end plate: ex suxamethonium (scoline). Depolarising muscle relaxant does not require reversal agent. It gets metabolised with pseudocholine esterase enzyme and its effects wears off. It is rapidly acting and has short duration of action.

 Non depolarizing:  competitive antagonism at neuro muscular junction e.g. pancuronium, vacuronium, atracurium and rocuronium. Non depolarizing muscle relaxant requires reversal with anti choline esterase drugs.

REVERSAL OF ANAESTHESIA:

 The only component of anaesthesia that is truly reversible at the conclusion of general anaesthesia is the effect of the non depolarizing muscle relaxant.

          The timing of the last dose of the muscle relaxant is important and if it is too near to the conclusion of surgery, adequate time must be allowed before reversal is attempted.

          Non depolarising muscle relaxant is reversed by anti choline esterase drugs . e.g. neostigmine sulphate (0.05- 0.07 mg/ kg). atropine sulphate (anticholinergic) is given along with this to prevent the muscarinic effects of neostigmine like bradycardia, profuse salivation and bronchospasm.

ANAESTHETIC EQUIPMENT:

          The anaesthetic equipment can be conveniently described sequentially from the supply of the gases to a point of delivery to the patient.

This sequence is as follows:

1)    Supply of gases:

a)     From outside the operating theatre

b)    From cylinders within the operating theatre, together with the connections involved

2)    the anesthetic machine

a)     unions

b)    cylinders

c)     reducing valves

d)    flowmeters

e)     vapourizers

3)    safety features of the anaesthetic machine

4)    anaesthetic breathing systems

5)    ventilators

6)    apparatus used in the scavenging waste anaesthetic gases

7)    apparatus used in interfacing the patient to the anaesthetic breathing system

a)     laryngoscopes

b)    tracheal tubes

8)    accessory apparatus for the airway

a)     anaesthetic masks and airways

b)    forceps

c)     laryngeal sprays

d)    bougies

e)     mouth gags

f)      stilletes

g)     catheter mounts

9)    suction apparatus

PRACTICAL CONDUCT OF ANAESTHESIA

Planning the conduct of anaesthesia starts normally after details concerning the surgical procedure and the medical condition of the patient have been ascertained at the preoperative visit.

PREPARATION FOR ANAESTHESIA:

Before starting the anaesthesia, consideration should be given to the induction and maintenance of anaesthesia, the position of the patient on the operating table, the equipment necessary for monitoring, the use of intravenous fluids or blood for infusion and the post operative care and recovery facilitates that will be required.

                     The anaesthetic machine to be used must be tested for leaks, misconnections and proper function.

EQUIPMENT REQUIRED FOR TRACHEAL INTUBATION

1.     Correct size of laryngoscope and spare {in case of light failure}

2.     Tracheal tube of correct size & an alternative small size.

3.     Tracheal tube connector.

4.     Wire stilette.

5.     Gum elastic bougies.

6.     Magill forceps.

7.     Cuff inflating syringe.

8.     Artery forceps.

9.     Securing tape or bandage.

10.                        Catheter mounts.

11.                        Local anaesthetic spray- 4% lidocaine.

12.                        Cocaine spray or gel for nasal intubation.

13.                        Tracheal tube lubricant.

14.                        Throat packs.

15.                        Anaesthesic breathing system & face masks treated with oxygen to ensure no leaks present.

INDUCTION OF ANAESTHESIA :

         Anesthesia is induced using one of the following techniques:-

1.     Inhalation induction.

2.     Intravenous induction.

(A)INHALATION INDUCTION:

INDICATIONS:

1.     Young children.

2.     Upper airway obstruction. Ex:- Epiglottitis.

3.     Lower airway obstruction with foreign body.

4.      Bronchopleural fistula or empyema.

5.     No accessible veins.

EQUIPMENTS:-

 Anaesthesia face masks to administer oxygen & anaesthetic gases & to ventilate the non intubated patient.

TECHNIQUE:- 

The mask is gradually introduced to the face from the side, it is held with one hand. The fingers should be kept on the bone rather than soft tissues because the latter position may cause discomfort in the awake patient & can cause airway obstruction if such pressure sufficiently raises the base of the tongue.

 Ventilation with a mask requires a tight fit that involves downward displacement of the mask with the thumb & first finger & upward displacement of the mandible with other three fingers {jaw thrust}

Mandibular displacement along with upper cervical extension & chin lift, all tend to pull the tongue & soft tissues up off the posterior pharyngeal wall & relieve the upper airway obstruction that occurs in the anaesthetized or unconscious patient. This may require holding the mask with two hands & vigorously pulling the mandible upward {jaw thrust}. A two-handed mask grip requires an assistant to provide manual ventilation.

Mask ventilation may be extremely difficult for patients with problems such as obesity, tumours, infection and inflammatory disorders.

 After placing the mask on the patients face the anesthetist encourages the patient to breathe normally. All patients should be pre oxygenated to whatever extent possible. This provides a buffer to tolerate an inability to ventilate or intubate for several minutes.

        Then initially nitrous oxide 70% in oxygen is used and anesthesia is deepened by gradually introduction of increments of a volatile agent. e.g;-Halothane 1-3%.

 Maintenance concentrations are then used when anesthesia has been established. Ex. Halothane 1-2%.

Observation of the colour of the patient’s skin and pattern of ventilation, palpation of the peripheral pulse, ECG & SPO2 monitoring & measurement of arterial pressure are important. Insertion of an oropharyngeal airway, a laryngeal mask airway or a tracheal tube may be considered when anaesthesia has been established.

 COMPLICATIONS AND DIFFICULTIES WITH INHALATIONAL ANAESTHESIA:

1.     Slow induction of anaesthesia.

2.     Problems particularly during stage2.

3.     Airway obstruction, bronchospasm.

4.     Laryngeal spasm, hiccups.

5.     Environmental pollution.

(B)  INTRAVENOUS INDUCTION:

Induction of anaesthesia with an i.v agent is suitable for most routine purposes & avoids many of the complications, associated with the inhalation technique. It the most appropriate method of rapid induction for the patient undergoing emergency surgery, in whom there is a risk of regurgitation of  gastric contents during induction.

All drugs which may be required at induction should be prepared and a cannula inserted into suitable vein before starting. Monitoring should be commenced before induction and pre-oxygenation may be started, using a close-fitting face mask & 100% oxygen delivered for approximately 5min.

Induction doses of the common i.v agents are shown below

1)    Thiopental 3-5mg/kg,

2)    Methohexital 1-1.5 mg/kg

3)    Etomidate 0.3 mg/kg

4)    Propofol 1.5-2.5 mg/kg

5)    Ketamine 2mg/kg

The induction dose varies with the patient’s weight, age, state of nutrition, circulatory status, premedication & any concurrent medication. Slow injection is recommended in the aged & in those with a slow, circulation time {ex- shock, hypovolaemia, cardiovascular diseases} while the effects of the drug on the CVS & RS are monitored.

 A rapid sequence induction technique is indicated for patients undergoing emergency surgery & for those in whom vomiting or regurgitation is a potential problem. After i.v induction, a rapid transition to stage3 is achieved; this is maintained by the introduction of inhalation agent or by repeated bolus injections or a continuous infusion of an i.v   anaesthetic agent.

COMPLICATION AND DIFFICULTIES WITH INTRAVENOUS INDUCTION:

1.     Regurgitation & vomiting.

2.     Intra arterial injection of thiopental.

3.     Peri venous injection.

4.     Cardiovascular depression.

5.     Respiratory depression.

6.     Histamine release.

7.     Porphyria {thiopentone, methohexital,etc}

8.     Pain on injection {methohexital, Propofol, etc}

POSITION OF PATIENT FOR SURGERY

  After induction of anaesthesia, the patient is placed on the operating table in a position appropriate for the proposed surgery. When positioning the patient, the anesthetist should take into account surgical access, patient safety, anaesthetic technique, monitoring and position of i.v line, etc.

MAINTENANCE OF ANAESTHESIA

Anaesthesia may be continued using inhalation agents or i.v opoids either alone or in combination. Tracheal intubation with or without muscle relaxants may be used.

INHALATION ANAESTHESIA WITH SPONTANEOUS VENTILATION

 This is an appropriate form of maintenance for superficial operations, minor procedures which produce little reflex or painful stimulation & operation for which profound muscle relaxation is not required.

DELIVERY OF INHALATION AGENTS: – AIRWAY MAINTENANCE

Airway maintenance can be done by delivering inhalation agents via a face mask, a LMA or a tracheal tube.

(1) FACEMASK: 

The face mask is used in current practice only before tracheal intubation or insertion of the LMA or during short non invasive procedure. ex:- Dental anaesthesia & orthopedic manipulations, to ensure potency of airway, other adjuvant like oral & nasal  airway may be used.

(2) LARYNGEAL MASK AIRWAY

(3) TRACHEAL INTUBATION

INDICATIONS:-

1.     Airway protection.

2.     Maintenance of patent airway.

3.     Pulmonary toilet.

4.     Application of positive-pressure ventilation.

5.     Maintenance of adequate oxygenation.

CONTRA-INDICATIONS:

           There are few contraindications. In emergency situations, hypoxemia must be relieved if at all possible before insertion of a tracheal tube.

EQUIPMENT

1. Endotracheal tube.

2. Laryngoscope.

3. Oxygen source.

4. Bag & mask.

5. Airways.

6.     Stylet.

7.     Lubricant.

8.     Tape.

9.     Reliable suction.

 TECHNIQUES OF TRACHEAL INTUBATION:

        Tracheal intubation may be performed under L.A {awake intubation} or under G.A.  The usual intubation sequence includes the administration of a rapidly acting induction agent {ex:- thiopental}, demonstration of adequate mask ventilation, administration of a rapidly acting neuromuscular blocking agent{ex:- succinyl choline}, perform laryngoscopy & direct vision intubation & then to maintain anaesthesia via the tracheal tube with spontaneous or controlled ventilation.

     The critical decision is whether to administer muscle relaxants or not. If there is sufficient doubt before induction with regard to the patient’s airway, a conscious intubation with sedation & topicalization is indicated.

Endotracheal intubation during anaesthesia:

         After it has been decided that the patient can be safely anaesthetized for intubation, a variety of methods can be used to achieve acceptable intubating conditions.

Anaesthetics and muscle relaxants:

          Intubation may be accomplished with intravenous or inhalation anaesthetics without relaxants, but this approach also possesses difficulties such as the potential for laryngospasm & a lesser degree of muscle relaxation to improve laryngoscopic conditions. In practice most clinicians employ muscle relaxant to facilitate intubation.

          The most commonly employed relaxant for intubation is succinyl choline, but the non depolarizing relaxants in appropriate doses may be used.

           The side effects of succinyl choline include- masseter spasm, malignant hyperthermia, and hyperkalaemia after burns, Neurologic injury & trauma, as well as increases in intraocular and intracranial pressure.

            The great advantage is that it produces excellent intubating conditions, usually within a minute or slightly longer if pre-treatment with a small amount of non depolarizing relaxant is employed to diminish fasciculation & post-op throat & skeletal muscle soreness.

Succinyl choline maintains the advantage of rapid offset of action by ester hydrolysis. If the airway cannot be secured, the patients own ventilation & airway maintenance will return much more quickly than with of any of the currently available non depolarizing relaxants.

           When a muscle relaxant is to be employed in a difficult or potentially difficult airway, succinyl choline appears to be the relaxant of choice unless there are contraindications to its use, such as risk of hyperkalaemia.

          The use of non-depolarizing relaxants for intubation has increased with the availability of short acting compounds like Rocuronium.

NASAL VERSUS ORAL ROUTE:

 In the operating room, nasal intubation is performed

1.     When surgery in the oral cavity or on mandible is performed.

2.     If the mouth is to be wired {IMF}.

    Contraindications to the nasal intubation includes:-

1.     Coagulopathy

2.     Severe intra-nasal disorders.

3.     Basilar skull fractures.

4.     CSF leaks.

          Nasal intubation is also used in the operating room in difficult airway situations. These include blind or fibreoptic intubation in the topicalised, sedated patients.

          Unlike oral intubation, nasal intubation may produce a bacteremia & appropriate endocarditis prophylaxis should therefore precede it.

 ORAL ENDOTRACHEAL INTUBATION:

          It is the usual method of intubation in the O.T. The position of the patient’s head & neck is important. The neck should be fixed & the head extended with the support of a pillow, thus the oral pharyngeal & tracheal axes are brought into alignment.

          The laryngoscope is held in the left hand while the fingers of the right hand are gently used to open the mouth. The laryngoscope blade is inserted into the right side of the patient’s mouth to avoid the incisor teeth & enable the flange of the blade to keep the tongue to the left.  Pressure on the teeth, gums or lips is avoided. The length of the blade is passed over the contour of the tongue. The laryngoscope is lifted upwards & forwards avoiding a levering movement which can damage the upper teeth. Using a straight blade, the tip is passed posterior to the epiglottis, which is lifted anteriorly the vocal cords are seen. With a curved blade, the tip is inserted into the vallecula & pressure on hyoepiglottic ligament moves the epiglottis to expose the vocal cords.  

        BURP maneuver, which includes backward, upward & right lateral displacement of the thyroid cartilage, may aid in laryngeal vision,

CONDUCT OF INTUBATION:

After laryngeal visualization, the supraglottic area & cords may be sprayed, if required, with L.A {lidocaine 4%}. The tracheal tube is passed from right side of the mouth between the open vocal cords under direct vision till the cuff is below the vocal cords.

         In men, the tube is generally inserted to about 23cms at the lips to position the tube, with the tip an appropriate 4cms above the carina. For women, the distance is about 21cm.Tubes inserted too far can cause endobronchial intubation {usually right}, where as that are not far enough may be difficult to seal because of cuff protrusion through the larynx & carry a higher risk of accidental extubation. In children the distance {in cms} at the lips can be estimated by the formula: – 12 + (age/2).

          The tube cuff is inflated sufficiently to abolish audible gas leaks on inflation of the lungs. The correct position of the tube must now be confirmed.  Finally the tube is secured with cotton tape, bandage or sticking plaster strips.

NASAL ENDOTRACHEAL INTUBATION:

            When nasal intubation is chosen solely for the purposes of surgical convenience, anaesthesia may be induced before intubation.

             A vasoconstrictor {cocaine 4% or phenylephrine 0.25-1.0% nose drops} should be applied before nasal instrumentation.

          After anaesthesia is induced and mask ventilation is established, the endo tracheal tube is introduced into the nose in a plane that is roughly perpendicular to the face. The tube is passed along the floor of the nose and advanced gently into the pharynx, avoiding excessive force. Laryngoscopy takes place and the tube is advanced into the trachea by manipulation of the proximal end or by grasping the distal tip with magill’s intubating forceps to pass it between the cords.

          Packing the throat may be used after intubation, especially for oropharyngeal operations. The moist gauze pack is introduced using the laryngoscope and magill forceps. The pharynx should be packed on each side of the tracheal tube. The pack should be applied gently to avoid abrasion of the mucosa. A tail of the pack is left protruding from the mouth and the anesthetist must accept the responsibility for the removal of the pack before extubation.

WHEN INTUBATION FAILS:

          Difficult intubation may be unanticipated. The prevalence of difficult laryngoscopy appears to be approx 1-4%.

          In 1984, cormack and lehane have graded the difficulties in laryngoscopy:

          Grade 1- no difficulty

          Grade 2- only posterior extremity of the glottis visible

          Grade 3- only epiglottis seen

          Grade 4- no recognizable structures

Patients of grade 4 and many of grade 3 are likely to present difficulties and may be even impossible to intubate

When an initial attempt at intubation fails, mask ventilation should be resumed while the situation is reassessed. As long as mask ventilation can be maintained, the problem is not emergent. Head position and laryngoscopy technique need to be examined.

If repeated laryngoscopy by an experienced practitioner is unsuccessful, a decision branch point is reached if short acting drugs (ex: thiopental, inhalational anesthetic, succinyl choline) have been used. The patient may be allowed to awaken for an attempt at intubation with topical anaesthesia or the case may even be postponed if non emergent. If long acting drugs have been used (ex: high dose narcotic, non depolarizing, relaxant) mask ventilation must be maintained until reversal is possible.

          If intubation cannot be accomplished, and the decision has been made to keep the patient anaesthetized for intubation (or long acting drugs have been used), a variety of other techniques can be used. First help should be obtained, if possible. The assistant may provide laryngeal displacement such as BURP maneuver, which is likely to improve glottic exposure. An anti cholinergic should be administered to reduce the secretions that often accumulate in this situation.

          The next approach can be use of gum elastic bougie, if the arytenoids or epiglottis can be visualized.

          Fibreoptic bronchoscopy can be an option and should be best attempted immediately before the field is obscured with blood and edema.

          Other options include:

a)     blind nasotracheal intubation

b)    blind orotracheal intubation

c)     laryngeal mask airway

d)    combitube

If multiple attempts fail and the case is not of emergent nature, it is best to simply ventilate the patient until the drugs can be reversed, because edema and blood may produce serious airway obstruction, preventing even mask ventilation.

WHEN MASK VENTILATION AND INTUBATION ARE IMPOSSIBLE:

          This situation presents a brain and life threatening emergency. It is critical to institute one of the following interventions before irreversible cardiac arrest or brain damage has occurred.

1)    If only short acting drugs have been used and the patient has been adequately pre oxygenated, adequate spontaneous ventilation may resume before further intervention is required

2)    The next intervention can be the laryngeal mask airway, the combitube is an alternative

3)    Transtracheal jet ventilation (TTJV) should be instituted if the above two methods fail.

Successful TTJV should be followed with provision of a definite airway by tracheostomy, endotracheal intubation, or wake up and resumption of the normal airway.

  CONCIOUS (AWAKE) INTUBATION

After appropriate sedation, topical anaesthesia & nerve blocks, conscious intubation can be performed with minimal discomfort in the conscious patient.

Conscious intubation is performed when the clinician believes that it is the safest way to insert an endotracheal tube.

INDICATIONS

1.     History of difficult intubation.

2.     Findings on the history or physical examination that can make intubation difficult & severe risk for aspiration or hemodynamic instability.

DRUGS FOR INTUBATION:

1. SEDATION:-

 Narcotic analgesics ex-Fentanyl, provide mild sedation, analgesia & reduction of airway reactivity that may result in cough & bronchospasm. The dose ranges from 25-500ug & the drug should be administered slowly in small increments. The greatest advantage of narcotics, especially Fentanyl, is the ease of reversibility by Naloxone, if an undesired degree of respiratory depression results.

 If awake intubation is performed because of a severe risk of aspiration, Narcotics & other i.v sedatives must be given separately.

To afford more sedation than a moderate dose of narcotics provides, a second drug is usually given. Droperidol provides adequate sedation without respiratory depression {dose=1.25-5mg i.v}. But higher doses may cause

a.     Akathisia.

b.     Dyspluria.

c.      Prolonged state of sedation {upto 24 hrs}.

Droperidol is contraindicated in Parkinsonism.

 Other clinicians prefer to add a benzodiazepine to the narcotic effect. Midazolam is preferred because of rapid onset & offset of action & the production of anterograde amnesia. The disadvantage of using benzodiazepines includes

a.     Increased respiratory depression in presence of narcotics.

b.     Decreased level of consciousness that results in loss of verbal contact with the patient, who in such situations must respond to commands especially to breathe.

2. ANTICHOLINERGICS & TOPICAL ANAESTHESIA:-

                 Glycopyrrolate {0.2-1mg i.v} is recommended to improve visualization during laryngoscopy by reducing secretions.

                 Anaesthesia of the nares & nasopharynx should be accompanied by vasoconstriction to widen the available passage & decrease bleeding.

Ex:-Cocaine 4% sol. or Phenylephrine 0.25-1% nose drops. The solution may be instilled through a 16 or 18 gauge plastic catheter inserted deep into the nose or on long cotton tipped applicators.

              The tongue & oropharynx may be anaesthetized with 10%lidocaine spray. The patient can also gargle & expectorate viscous lidocaine to produce topical anaesthesia of the tongue & pharynx.

               The larynx can be sprayed additional lidocaine directly on the visualized glottis.

               The trachea can be anaesthetized by a laryngotracheal application of 2-3ml of lidocaine through the cricothyroid membrane.

 NERVE BLOCKS:

           a. Glossopharyngeal  nerve block à posterior 1/3^rd of the tongue.

            b. Superior laryngeal nerve block à epiglottis, aryepiglottic fold,         

                                                                                               False cords.

              The Superior laryngeal nerve block can be blocked by an external approach using a 23 gauge needle and 3ml syringe to inject 2-3ml of 1% lidocaine between the greater cornu of the hyoid bone & the thyroid cartilage.

              The Superior laryngeal nerve may also be blocked by the application {for about a minute per side} of lidocaine soaked gauze pads with Krause angle forceps held in piriform fossa.

 CHOICE OF TECHNIQUE:

The choice of technique for conscious intubation depends on preference for oral or nasal tube placement, experience & availability of equipment. If one technique fails, other is usually tried.

1. CONSCIOUS ORAL INTUBATION WITH DIRECT                  LARYNGOSCOPY:

      Preparation for conscious & oral intubation involves use of the drying agents, sedation, topical anaesthesia & nerve blocks.

 The laryngoscope must be inserted gently but with firm manipulation when required.

Superior laryngeal block & Transtracheal anaesthesia are not generally used if there is concern for aspiration of gastric contents.

2. CONSCIOUS ORAL INTUBATION WITH INDIRECT LARYNGOSCOPY.

          The Bullard laryngoscope, an instrument for indirect laryngoscopy, is inserted much like a routine laryngoscope. The handle is then rotated from the horizontal to vertical as the blade slides around the tongue.

3. BLIND ORAL INTUBATION

          When there is minimal visualization of the laryngeal structures during direct laryngoscopy, a blind or semi-blind technique for intubation may be attempted in the conscious or anaesthetized patient. A blade is helpful to pull up the tongue & thereby open up & maintain the airway. An endotracheal tube with a curved stylet is then guided in the presumed direction of the glottis, where the tube is then slid off, ideally into the trachea.

4.  NASAL INTUBATION IN A CONSCIOUS PATIENT  

         Conscious nasal intubation is useful for urgent intubations outside the operating room when mouth opening or neck movement is limited or prohibited & when a nasal endotracheal tube is required but anaesthesia & paralysis are thought to be too risky.

           Sedation, topical anaesthesia & nerve blocks are given. The tube is passed into the larynx during inspiration.

5.  RETROGRADE ENDOTRACHEAL INTUBATION

          Retrograde endotracheal intubation involves passage of a wire or plastic Stylet through the cricothyroid membrane that is then coughed out of the larynx & into the oropharynx by the patient. This may be done in the anaesthetized or conscious patient. In the conscious patient it should be preceded by topicalization.

 A kit with a j-wire can be used to insert endotracheal tubes as small as 4mm internal diameter. If a nasal tube is desired & the wire or catheter comes out of the mouth, the tip can be secured to a nasally passed catheter & then pulled up & out through the nose.

The endotracheal tube is then inserted into the larynx over the wire, which is held with mild tension.

The tip of the tube may catch on the anterior commissure & therefore not pass. Turning the tube, loosening the wire or threading the tube onto the wire by means of Murphy eye may facilitate passage. The use of a catheter rather than a wire as a guide {as in the cook kit} may be helpful in allowing the tube passage.

COMPLICATION OF TRACHEAL INTUBATION

          Complication may be mechanical, respiratory or cardiovascular & may occur early or late.

Early complications

1.     Trauma to the lips & teeth.

2.     Jaw dislocation.

3.     Aretynoid dislocation.

4.     Damage to larynx & vocal cords, during intubation.

5.     Nasal intubation may produce epistaxis, trauma to the pharyngeal wall or dislodgement of adenoid tissue.

6.     Obstruction or kinking of the tube can occur or bronchial intubation may take place if the tube is too long.

7.     Laryngeal trauma may produce post-op croup, bronchospasm or laryngospasm, especially in children.

8.     Immediate post-op or respiratory complications may be minimized by humidification of inspired gases.

9.     Cardiovascular complications of intubation include arrhythmias & hypertension, especially in untreated hypertensive patients.

Late complications:

More common after long term intubation.

1.     Tracheal stenosis – rare

2.     Trauma to vocal cords may result in ulceration or granulomata which may require surgical removal.

3.     Cord trauma may be more common in the presence of an upper respiratory tract infection

  EXTUBATION:

Extubation of the trachea may be performed while the patient is deeply anaesthetized or is nearly fully awake.

Deep or more precisely, anaesthetized extubation is performed after muscle relaxants have been fully reversed & the patient is maintaining an acceptable respiratory rate & depth.

 A difficult mask airway, difficult intubation, risk of aspiration, or surgery that may produce airway edema or maintenance problems are contraindications to such extubation. Adequate recovery of the ability to maintain & protect the airway must be demonstrated after the use of neuro muscular relaxant.

 A sustained {5sec} head lift is an excellent way to assess clinically adequate reversal. If head lift is contraindicated or painful, leg lift or sustained tongue protrusion can be similarly assessed.

 As the anaesthetic level diminishes, the patient is suctioned, & the tube is removed after a positive pressure breath has been given with the anaesthesia bag to allow subsequent expulsion or secretions out of the glottis.

As the patient awakens, laryngospasm & cough may occur anyway. Because there is no way to entirely avoid such coughing after an anaesthetic, many physicians regard deep extubations merely as premature extubations.

When such extubations in the anaesthetized are contraindicated, awake extubation is essential. The patient is not extubated until judged ready to maintain & protect the airway. The patient who is unresponsive to verbal stimuli, has deviation of the eyes, or  is breath holding is not ready for extubation & is prone to laryngospasm, which is most likely to occur when patients are extubated in between awake & anaesthetized states.

              Coughing & bucking probably indicate the ability to protect the airway, but the timing of awake extubation remains a matter of clinical judgment.

              After extubation, the patient may be maintained in the supine or lateral position.

CAUSES OF DIFFICULT EXTUBATION INCLUDE:-

1.     Leaving the endotracheal cuff inflated.

2.     Fixation of the endotracheal tube by a k-wire or a suture during head & neck surgery.

3.     A tangled nasogastric tube.

4.     Swollen or tense vocal cords.

5.     A barb accidentally cut on the endotracheal tube can interfere with extubation.

COMPLICATIONS OF TRACHEAL EXTUBATION:

     1.   Airway obstruction.

2. Laryngospasm.

       3. Aspiration / regurgitation.

  4. Vocal cord paralysis.

  5. Difficult extubation.

COMPLICATIONS OF GENERAL ANESTHESIA:

          GA should never be taken lightly for a complication or an emergency may occur at any time. The anaesthetists should be aware of any of the possibility.

DEFINITION:

An anaesthetic complication may be defined as deviation from the normally expected physiological pattern during or after the administration of anaesthesia.

          An anaesthetic emergency may be defined as any unforeseen combination of circumstances requiring immediate treatment. Though all are not severe some immediate treatment is required.

          In general anaesthesia as compared to regional anaesthesia a much greater percentage of the complication are emergency in nature that is they require immediate treatment. A seemingly minor complication may become a serious emergency if it is neglected.

CLASSIFICATION:

Immediate or secondary,

Mild or severe,

 Permanent or transient,

Mortality rate for anaesthesia in OMFS

·        ASOS symposium 1966 – 1 in 3,15,000

·        ASOS survey 1972 – 1 in 3,49,408

·        SCSOMFS 1975 – 1 in 8,60,000

·        SCSOMFS 1988 1 in 6,33,000

Most common anaesthetic emergency by occurrence rate is

1.     Laryngospasm

2.     Dysrhythmia

3.     Respiratory depression

4.     Allergy

5.     Seizures

6.     Bronchospasm

Studies in medical anaesthesiology indicates mortality rate that varies widely from 1 in 10,000 to 1 in 2,00,000.

The important complications include:

I.       Airway complications

-         Hypoventilation and apnoea

-         Obstruction and restrictive problems

-         Upper airway obstruction

-         Laryngospasm

-         Brochospasm

-         Pulmonary oedema

-         Emesis

II.      Cardiovascular complications

-         Angina

-         Dysrhythmia

III.     Allergic and anaphylactic reaction.

IV.     Malignant Hyperthermia

V.      Peripheral venous complications

The anaesthetic complications can also be classified as those occurring during pre operative period, during operative period and those occurring in the post operative period.

1) Pre op period:  related to prior dug therapy.

2) During operation: these may include:

a)     coughing

b)    wheezing

c)     cyanosis

d)    cardiac arrhythmias

e)     fluctuations in blood pressure

f)      hypoxaemia

g)     hyper/ hypo carbia

h)    changes in body temperature (hypothermia, hyperthermia, malignant hyperthermia)

i)       laryngospasm

j)       upper airway obstruction

k)    pulmonary aspiration

l)       cardiac arrest

m)  severe drug reactions

3) Post op complications:

n)    post op nausea and vomiting

o)    post op hypertension

p)    post op respiratory inadequacy

q)    failure to wake ups

r)      post op infection

s)     post o restlessness

t)      respiratory obstruction