ANAESTHESIA: INDUCTION, MAINTENACE & REVERSAL

Learn about anaesthesia

1. INDUCTION,MAINTENCE & REVERSAL OF ANAESTHESIA PRESENTED BY ALEX LAGOH SUPERVISED BY DR. SARPONG

2. Anesthesia??? Anesthesia is a pharmacologically induced reversible state of amnesia, analgesia, loss of responsiveness, loss of skeletal muscle reflexes and decreased stress response

3. Components of anaesthesia Analgesia Amnesia Unconsciousness Akinesia Abolition of autonomic reflex

4. Components of anaesthesia Analgesia Amnesia Unconsciousness Akinesia Abolition of autonomic reflex

5. Stages Of Anaesthesia Stage I: the stage of analgesia . Stage II: stage of excitement . Stage III: surgical anaesthesia . Stage IV: stage of impending respiratory and circulatory failure . ( Medullary Paralysis)

6. Stages of Anaesthesia Anaesthesia performed with general anaesthetics occurs in four stages which may or may not be observable because they can occur very rapidly:   Stage One : Analgesia. The patient experiences analgesia or a loss of pain sensation but remains conscious and can carry on a conversation.   Stage Two : Excitement. The patient may experience delirium or become violent. Blood pressure rises and becomes irregular, and breathing rate increases. This stage is typically bypassed by administering a barbiturate, such as sodium pentothal, before the anaesthesia.

7. Stages of Anaesthesia Stage Three : Surgical Anaesthesia. During this stage, the skeletal muscles relax, and the patient's breathing becomes regular. Eye movements slow, then stop, and surgery can begin.   Stage Four : Medullary Paralysis. This stage occurs if the respiratory centres in the medulla oblongata of the brain that control breathing and other vital functions cease to function. Death can result if the patient cannot be revived quickly. This stage should never be reached. Careful control of the amounts of anaesthetics administered prevent this occurrence.

8. Induction of Anaesthesia It refers to transition from an awake to an anaesthetized state through the administration of a drug or combination of drugs at the beginning of an anaesthetic procedure. . Induction aims at achieving the triad of Anaesthesia Loss of Consciousness: IV or Inhalational Muscle relaxation: using muscle relaxants Analgesia

9. How is Induction Done? 1. Inhalational route Gaseous –N2O Volatile liquid (halothane, isofurane , sevoflurane , desflurane , ether) 2. Intravenous Propofol Thiopentone Etomidate Ketamine Midazolam Fentanyl 3. Intramuscular route 4. Rectal route

10. Indications For Inhalational Induction Young children Upper airway obstruction . eg epiglottitis Lower airway obstruction eg . Foreign body Bronchopulmonary fistula Inaccessible veins

11. Complications and Difficulties Assoc. with Inhalational Induction Slow induction of anesthesia Problems with second stage of anesthesia Airway obstruction eg . Bronchospasm Laryngospasm and hiccups Environmental pollution

12. Intravenous induction of anaesthesia Induction by IV agents is the commonest and can be done for ALL patients, but there are indications for induction using Inhalational agents . This is most frequently achieved in adults by the IV injection of a drug. Consciousness is lost rapidly as the concentration of the drug in the brain rises very quickly. The drug is then redistributed to other tissues and the plasma concentration falls; this is followed by a fall in brain concentration and the patient recovers consciousness, that’s why maintenance is important.

13. INDUCTION CONT’D Preparation in theatre - Check anaesthetic equipment – Machines & Monitors - Check tracheal intubation trolley - Check emergency drugs - Draw drugs for anaesthesia -ATTACH MONITORS AND RECORD BASELINE READING -IV ACCESS -PRE-OXYGENATION -INDUCTION: IV OR INHALATIONAL

14. Rapid Sequence Induction Used where the risk of aspiration is high pre-oxygenate with 100% oxygen for 3-5 minutes Sellick’s manoeuvre on induction. Firm backward pressure on cricoid cartilage occluding the oesophagus to prevent gastric reflux into the larynx Short-acting muscle relaxant is given immediately after induction The trachea is then intubated and the cuff of the endotracheal tube inflated Once the ET tube is correctly positioned, cricoid pressure maybe released and maintenance of anaesthesia continues Give a longer-acting muscle relaxant when the shorter acting one wears off

15. MUSCLE RELAXANTS Mild muscle relaxation can be attained by increasing the depth of general anesthesia with potent inhalational agents but the amount required for useful muscle relaxation is too high to be practical Muscle relaxation often desired during surgical procedures for various reasons facilitate intubation prevent muscle stretch reflex and suppresses muscle resting tone facilitate controlled ventilation allow access to the surgical field ( intracavitary surgery)

16. NEUROMUSCULAR BLOCKING AGENTS These drugs fall into two groups: DEPOLARIZING BLOCKING AGENTS : These agents act by depolarizing the plasma membrane of the skeletal muscle fiber. This persistent depolarization makes the muscle fiber resistant to further stimulation by ACh . eg Suxamethonium NON-DEPOLARIZING BLOCKING AGENT : These agents constitute the majority of the clinically-relevant neuromuscular blockers. They act by competitively blocking the binding of ACh to its receptors. - Benzylisoquinolinium compounds – eg Atracurium , Cisatracurium , Mivacurium - Aminosteroidal compounds – eg Vecuronium , Rocuronium , Pancuronium

17. MAINTENANCE OF ANAESTHESIA The duration of action of IV induction agents is generally 5 to 10 minutes, after which time spontaneous recovery of consciousness will occur. In order to prolong anaesthesia for the required duration (usually the duration of surgery), anaesthesia must be  maintained Either be by i nhalational or by TIVA

18. Maintenance of Anaesthesia Gauging the depth of anaesthesia will involve monitoring the following parameters Heart rate Blood pressure Lacrimation Pupil size Movement

19. Minimum Alveolar Concentration This is the minimum alveolar concentration that produces no movement to standard surgical stimulus for 50% of patients. This allows for comparison with other agents and gives us an idea of the depth of anaesthesia . Compounds with high MAC – low potency( desflurane ) Compounds with low MAC – High potency(halothane)

20. Minimum Alveolar Concentration The effect of inhalational anaesthetic are additive therefore the values for MAC are often quoted as the value in oxygen and the value when given with a stated percentage of nitrous oxide(which has its own MAC) which will be clearly less

21. FACTORS THAT AFFECT MAC INCREASES MAC Decreasing age (infants) Pyrexia Chronic alcohol ingestion Thyrotoxicosis Presence of ephedrine or amphetamine Chronic drug abuser

22. FACTORS THAT AFFECT MAC REDUCES THE MAC Increasing age(the elderly) Hypotension Hypothermia Hypothyroidism Pregnancy Current use of Opiods

23. Maintenance Cont’d Maintenance of the airway is important if you will maintain anesthesia by inhalational facemask , laryngeal mask airway (LMA ) or a tracheal tube . Can be used.

24. TOTAL INTRAVEENOUS ANAESTHESIA (TIVA) When IV drugs are given to induce and maintain anesthesia the term TIVA is used eg ketamine, propofol Anaesthesia is maintained by infusion or intermittent I.V injection

25. TIVA For a drug to be of use in maintaining anaesthesia , it must be rapidly eliminated or metabolised to inactive substance to prevent accumulation and delayed recovery and have no unpleasant side effects. Currently an infusion of propofol is the most common and widely used technique

26. TIVA USING PROPFOL With this technique an approximate brain concentration of propofol must be achieved and maintained to prevent awareness and any response to surgery The simplest way is to give the usual IV induction dose followed by repeated injections at intervals depending on the patients response

27. TIVA USING PROPFOL Advantages The potential toxic effect an inhalational anaesthetic are avoided The problem associated with nitrous oxide is also avoided A better quality of recovery May be beneficial esp in neurosurgery Pollution is reduced

28. TIVA USING PROPFOL Disadvantages Secure reliable iv access is required Risk of awareness if the iv infusion fails Cost of electronic infusion pumps May cause profound hypotension

29. REVERSAL OF ANAESTHESIA " Paralysis" or temporary muscle relaxation with a neuromuscular blocker is an integral part of modern anaesthesia . The first drug used for this purpose was curare, introduced in the 1940s, which has now been superseded by drugs with fewer side effects and generally shorter duration of action. Muscle relaxation allows surgery within major body cavities, eg . Abdomen and thorax without the need for very deep anaesthesia , and is also used to facilitate endotracheal intubation. 

30. Reversal of Anaesthesia These drugs fall into two groups: Non-depolarizing blocking agent : These agents constitute the majority of the clinically-relevant neuromuscular blockers. They act by competitively blocking the binding of ACh to its receptors. Depolarizing blocking agents : These agents act by depolarizing the plasma membrane of the skeletal muscle fiber. This persistent depolarization makes the muscle fiber resistant to further stimulation by ACh .

31. Reversal of Anaesthesia Acetylcholine, the natural neurotransmitter substance at the neuromuscular junction, causes muscles to contract when it is released from nerve endings. Muscle relaxants work by preventing acetylcholine from attaching to its receptor. The effects of muscle relaxants are commonly reversed at the termination of surgery by anticholinesterase drugs

32. Anticholinesterase This inhibit the accumulation of the enzyme acetylicholinesterase resulting in an increase in acetyl choline at the neuromuscular junction(nicotinic effect). Anticholinesterase also function at the parasympathetic nerve endings (muscarinic effect) causing bradycardia, Spasm of the bowel, bladder and bronchi and increased bronchial secretions

33. Anticholinesterase Therefore they are always admistered with a suitable dose of atropine or glycopyrolate to block the unwanted muscarinic effect Most commonly used anticholinesterase is neostigmine(a dose of 0.05mg/kg iv is used in adults) and its maximum effect is seen in approx 5mins and last 20-30mins. Atropine 0.02mg/kg or glycopyrolate 0.5mg

34. Assessing neuromuscular blockage This can be achieved either by clinical or by using a peripheral nerve stimulation

35. Clinical Assesment This requires a conscious, co-operative patient to perform a sustained activity and therefore limited in its application Test commonly used include Lifting of the head off the pillow for 5seconds A hand grip for 5sec The ability to produce vital capacity breath >10ml/kg

36. Clinical Assesment Inability to perform this task and/or the presence of ‘see-saw’ or ‘paradoxical’ respiration suggest a degree of residual neuromuscular block. A further dose of neostigmine and an anticholinesterase may be required

37. Peripheral nerve stimulation A peripheral nerve supply a discrete muscle group is stimulated transcutaneously with a current of 20mA. The resulting contractions are observed and measured