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#Delivery of anesthetic agents
- 1. Dr Nisar Ahmed Arain Assistant Professor Anesthesia/Critical care/ER DELIVERY OF GENERAL ANESTHETIC AGENTS
- 2. - General Anesthesia -1-loss of sensation, it renders the patient amnesic— -2-unconscious while causing a little muscle relaxation and suppression of undesirable reflexes
- 3. -Inthe “old days”the following were usedfor anesthesia. a-Alcohol b-Icefor numbing c-Blow to theheadand d-Strangulation -Anesthesia
- 7. -Theories of Anesthesia -Anesthetic potency is closely corelated with Lipid solubility -Postulated interaction with the lipid membrane bilayer -Interaction with Ligand gated membrane ion channels -Most anesthetics enhance the activity of inhibitory GABA – A receptors -Many inhibit activation of excitatory receptors such as Glutamine and Nicotinic acetylcholine receptors
- 8. -STAGES of Anesthetic activity -Stage 1 - Analgesia (Patient is) -Conscious but drowsy -Responses to painful stimuli are reduced -Stage 11 – Excitement -loose consciousness -No longer responds to non painful stimuli -Responds in a reflex fashion to painful stimuli -Stage 111 – Surgical Anesthesia -Movements of patient ceases and respiration becomes regular -Stage 1V – Medullary Paralysis -Respiration and vasomotor control cease -Death ocurs
- 9. -Properties of Ideal Inhalational Anesthetics -Rapid and pleasant Anesthetic induction and Recovery -Rapid changes in Anesthetic depth -Adequate relaxation of skeletal muscles -Wide margin of safety -Absence of toxic effects or other adverse properties in normal doses
- 10. -Mechanism of action (MOA) -Increase neuronal threshold for firing leading to a decrease in neuronal activity -Hyperpolarization of Neuron's via activation of k+ currents
- 11. -Potency -Clinically cant be predicted by chemical structure -Potency correlates with Lipid solubility -It is defined as MAC
- 12. MAC -Minimum Alveolar Concentration -Concentration of Anesthetic agents or gas needed to eliminate movement among 50% of patients challenged by standardized skin incision
- 13. -INVERSE of MAC:- is an index of Potency -The more Lipid soluble the agent Lower the concentrations needed to produce Anesthesia -The lower the MAC, more potent is the Anesthetic agent
- 14. -Highest to lowest MAC --N2O --Ether --Enflurane --Isoflurane --Halothane
- 15. -Solubility in the blood -Based on Blood / Gas partition co-efficient (Lowest to Highest) -NO -Isoflurane -Enflurane -Halothane
- 17. -Individual Anesthetic agents -Nitrous Oxide -It has low potency therefore must be combined with other agents -It has Rapid induction and Recovery -It is Good Analgesic, but WEEK Anesthetic -Risk of bone marrow depression with prolonged administration is there -Known as Laughing Gas -It can retard Oxygen uptake during recovery, thus 20% of Oxygen is always needed
- 18. --Nitrous Oxide cont. -Can cause Hypoxia -Least Hepatotoxic -Safest
- 19. -Halothane -Prototype -It’s a week Analgesic -It’s a very potent Anesthetic agent -Usually co-administered with N2O opioids and local Anesthetics -Metabolized to tissue toxic hydrocarbons (Trifluoroethanol) and bromide ions
- 20. -Halothane cont. -Disadvantages -It reduces Myocardial contractility and causes hypotension specially in higher doses and in standing cases -It may cause arrhythmias
- 21. -Individual Inhalational Anesthetics -Enflurane:- -Halogenated anesthetic similar to Halothane -Less metabolism than Halothane; therefore, there is less toxicity -Faster induction and recovery than Halothane (Less accumulation in Fat) -Some risk of Epilepsy—like seizures. CNS excitation -Metabolized to Flouride ion, and excreted through the Kidney
- 22. -Isoflurane -Does not induce cardiac Arrhythmias and does not sensitize the heart to catecholamines -It has a stable Molecule
- 23. -Isoflurane -Disadvantages -More pungent odor than Halothane -Progressive respiratory depression and Hypotension
- 24. -Individual Inhalational Anesthetics -Desflurane and Sevoflurane -Similar to Isoflurane -Have fester onset and recovery -Lack of respiratory irritation -Commonly used clinically
- 25. -Methoxyflurane -It is a Potent Anesthetic with lipid solubility -Specially used in child birth Its Disadvantages It is metabolized to Flouride ions which causes Respiratory and circulatory depression
- 26. HALOTHANE ENFLURANE ISOFLURANE NITROUSOXIDE ARRHYTHMIA INCREASED SENSITIVITYTO CATHECHOL AMI NES INCREASED SLIGHTINC. CARDI AC OUTPU T DECREASED DECBUT RECOV ERS DECREASED BP DECREASED DECBUT RECOV ERS DECREASED RESPIREFLEX INHIBITED INHIBITED HEPATOTOXICITY HIGHRISK SOMERISK
- 27. -Intravenous Anesthetics -Thiopental -It is Barbiturate with very high Lipid solubility -It is GABA mimetic -Rapid action because of rapid transfer across the blood-Brain barrier -It has short duration (about 5 minutes) because of redistribution, mainly to muscle -Potent anesthetic, with week analgesic effect -Little Muscle relaxation Complications a-Laryngospasm b-Not to be given in Asthma patients c-Avoid in Porphyria patients
- 28. --Thiopental cont. -Onset in 40 seconds -Recovery in 30 minutes -Dose:- 400 to 500 mg I/V for induction -Use it for induction Anesthesia -Toxicity:- Respiratory and Circulatory depressions -Intravenous Anesthetics
- 29. -Intravenous Anesthetics -Etomidate -It’s a Potent, non Barbiturate hypnotic -Its non Analgesic -Its similar to thiopentone but more quickly metabolized -It has less risk of Cardiovascular depression
- 30. -Intravenous Anesthetics -ETOMIDATE:- Disadvantages -May cause involuntary movements during induction of Anesthesia -Possible risk of Adrenocortical suppression -It’s a Hypnotic and Lacks in Analgesia
- 31. -Intravenous Anesthetics -KETAMINE -It is Analogue of Phencyclidine, with similar properties (Psychotic reactions) -Effect on NMDA – type glutamate receptors -Onset of effect is relatively slow (2 to 5 Minutes) -Produces “Dissociative Anesthesia” in which patient may remain conscious and insensitive to Pain -Can increase Intracranial pressure -Causes cardiovascular stimulation but not Respiratory depression
- 32. -Intravenous Anesthetics -Propofol Diprivan) -Rapidly metabolized -Very rapid recovery -Useful for day case surgery -Causes more Respiratory and Cardiovascular depression than Barbiturates -Lowers Intracranial pressure
- 33. -Propofol Diprivan) -Used for maintenance of anesthesia Sedation, or treatment of agitation -Has antiemetic properties -Drowsiness -Respiratory depression -Motor restlessness -Increased Blood Pressure
- 34. -Fentanyl -Extremely Potent Analgesic -Dosage Forms a-I/V (Sublimaze) b-Patch (Duragesic) c-Lozenge (Actiq) for children -Used extensively for open- heart surgery due to lack of cardiac depression
- 35. Summaryof Intravenous Anesthetics Drug Speed of induction and recovery Main unwanted effects Notes Thiopental Fast (cumulation occurs, giving slow recovery) Cardiovascular and respiratory depression Widely used as induction agent for routine purposes Hangover Fast onset, fairly fast recovery etomidate Excitatory effects during induction and recovery Less cardiovascular and respiratory depression than with thiopental Causes pain at injection site Rapidly metabolized Adrenocortical suppression Cardiovascular and respiratory depression propofol Fast onset, very fast recovery Possible to use as continuous infusion Causes pain at injection site Produces good analgesia and amnesia Ketamine Slow onset, after-effects common during recovery Psychotomimetic effects following recovery Postoperative nausea, vomiting and salivation Midazolam Slower than other agents Little respiratory or cardiovascular
- 36. Local Anesthesia -Relieves pain of operation without altering alertness or mental function
- 37. -Mechanism of action of Local Anesthetics -Local Anesthesia -They block sodium channels in Nerves -They provide Analgesia without loss of consciousness
- 38. - Local Anesthesia cont. -Variety of ROUTES -1-TOPICAL ANESTHESIA -2-SUPERFICIAL IJECTION (Infiltration) -3-NERVE BLOCK -4-INTRAVENOUS ANESTHESIA -5-EPIDURAL ANESTHESIA -6-SPINAL ANESTHESIA
- 39. -Route of Administration -Topical rout of Anesthesia a-Spray or Injection -Injection of LA to Nerve routs -Epidural Anesthesia (with LA drugs) -Spinal injection in subarachnoid space a-LA injection in the space -NOTES:- a-It reduces PH of the area of infiltration b-It reduces effectiveness of the nerve routs -Co-administered with vasoconstrictor Epinephrine (1:100,000)
- 40. -ESTERS -They are Hydrolyzed by the blood esterase’s -They have short half life
- 41. -ESTERS cont. These are a—Benzoic acid derivatives and B—P- amino-benzoic acid derivatives
- 44. -AMIDES ----Lidocaine (Xylocaine) ----MEPIVACAINE—(Carbocaine, Mepivastesin) ----BUPIVACAINE (Marcaine—Sensorcaine—Senpivacaine) ----PRILOCAINE (Citanest—Emla) ----ETIDOCAINE (Duranest) ----ROPIVACAINE (Naropin) ----LEVOBUPIVACAINE (Sensibloq) ----ARTICAINE (Ubistesin) -These are all metabolized in the Liver and they have long half—life -They are more stable to Hydrolysis than ESTERS
- 45. -AMIDES Adverse Effects -There is cardiovascular depression Hypotension, -Hepatotoxicity to Halothane -Nephrotoxicity to Enflurane, and Methoxyflurane -Malignant Hyperthermia especially with Succinylcholine SYMPTOMS ARE AS a-Hyperthermia with Muscle rigidity ANTIDOTE B-Dentrolene Injection -There could be arrhythmias due to sensitization of Heart to catecholamines
- 46. -DRAW OVER ANESTHESIA --This system refers to those breathing systems in which an Inhalational anesthetic is vaporized by the patients breathing himself. --These include the original methods of administration of inhalational anesthetics. Where the agent is poured over a PAD or a GAUZE which is then applied to the patients face.
- 47. - DRAW OVER ANESTHESIA
- 48. -CONTINUE FLOW ANESTHESIA -In the developed world, the most frequent type in use is the CONTINUOUS FLOW ANESTHETIC MACHINE or “Boyles Machine” Which is designated to provide an accurate supply of medical gases mixed with an accurate concentration of an anesthetic Vapour, and to deliver this CONTINUOUSLY to the patient at safe pressure and flow
- 50. -TOTAL INTRAVENOUS ANESTHESIA (TIVA) -It is a technique of GENERAL ANESTHESIA which uses a combination of agents given exclusively by the INTRAVENOUS route without the use of Inhalational agents (Gas anesthesia)
- 51. THANK YOU