Skip to main content
UploadLanguage (EN)Support
BusinessMobileSocial MediaMarketingTechnologyArt & PhotosCareerDesignEducationPresentations & Public SpeakingGovernment & NonprofitHealthcareInternetLawLeadership & ManagementAutomotiveEngineeringSoftwareRecruiting & HRRetailSalesServicesScienceSmall Business & EntrepreneurshipFoodEnvironmentEconomy & FinanceData & AnalyticsInvestor RelationsSportsSpiritualNews & PoliticsTravelSelf ImprovementReal EstateEntertainment & HumorHealth & MedicineDevices & HardwareLifestyle
Mayur Chaudhari, profile picture
Uploaded byMayur Chaudhari
10,580 views

General anaesthesia

This document discusses general anaesthetics. It begins by defining general anaesthetics as drugs that produce reversible loss of consciousness and sensation, including pain, reflexes, and mobility. It then covers various topics related to general anaesthetics, including historical uses, mechanisms of action, stages of anaesthesia, inhalational agents like ether, nitrous oxide, and halothane, and intravenous agents like thiopentone sodium. The ideal properties of anaesthetics are discussed. Inhalational agents have advantages like rapid induction but also risks like flammability, while intravenous agents allow rapid induction and recovery but are only suitable for short procedures.

Health & Medicine◦
General Anaesthetics DR. MAYUR CHAUDHARI ASSISTANT PROFESSOR DEPARTMENT OF PHARMACOLOGY GOVERNMENT MEDICAL COLLEGE, SURAT
Objectives  Terminologies  Stages of anaesthesia  Inhalational Anaesthetics  Intravenous Anaesthetics  Preanaesthic Medication
General Anaesthetics  Drugs Which Produce Reversible Loss of consciousness and all sensation  Loss of sensation – Pain  Unconsciousness and amnesia  Immobility and Muscle relaxation  Loss of reflexes
Historical Aspects
Some Strange Methods  Strangulation  Cerebral Concussion  Applying Cold or compression  Alcohol  Plants
Time Line  1799 – Davy  1818 – Michael Faraday  1844 – Horace wells  1846 – William TG Morton  1847 – John Snow and John Sympson  1956 – Charles Suckling
Mechanism of action  Main Sites of action are Cortex, Thalamus and Hippocampus.  Can also act at Peripheral Sensory Nerves, Spinal Cord, Brain Stem
Molecular Mechanism  Chloride Channel GABA-A Receptor Complex  Glycine gated chloride channel  Neuronal Nicotinic receptors  Antagonizing NMDA receptors
Minimum Alveolar Concentration (MAC)  Measure of Potency of inhalational General anaesthetic agent  Lowest Concentration in alveoli  To produce immobility in 50 % subjects  In response to painful stimuli.  Correlation with oil/gas partition Coefficient  Reflect capacity of anaesthetic to enter into CNS
MAC : Practically  Alveolar concentrations can be monitored continuously by measuring end-tidal anesthetic concentration using spectrometry  End point (immobilization) – can me measured.  Other end points – Verbal commands or memory etc.
MAC  Premedication with CNS depressant lowers MAC  When combination is used MAC is additive  DRC of inhaled anesthetic is steep  Concentration exceeding 1.5 MAC are not used  2-3 MAC is lethal  Patient wakes up when concentration falls to 0.4 MAC
Guedel’s Stages of Anaesthesia  Guedel in 1920 described with ether  Descending depression of CNS.  Higher to lower areas of brain are involved.  Vital centers located in medulla are paralyzed last.  In spinal cord lower segments are affected earlier than the higher segments.
Stage I – Analgesia  Starts with inhalation up to loss of consciousness  Can Hear, See and Dream like state  Reflexes and respiration normal  Minor Operations can be carried out
Stage II - Excitement  Delirium and combative behavior  Rise and irregularity in BP and Respiration  Chance of laryngospasm  Pupils dilated  No procedure is carried out in this stage
Stage III – Surgical Anaesthesia  Onset of regular respiration to cessation of spontaneous breathing  Phase1: Roving eyeballs.  Phase2: Loss of corneal and laryngeal reflexes.  Phase 3: Pupil starts dilating and light reflex is lost.  Plane 4: Intercostal paralysis, shallow abdominal respiration, dilated pupil.  Muscle tone decreases, BP falls, HR increases with weak pulse, respiration decreases
Stage IV – Medullary Paralysis  Cessation of breathing to failure of circulation  Death.  Dilated Pupil, Flabby muscles  Thready or imperceptible Pulse  Low BP
Observations  Eyelash reflex and swallowing movement present – Stage I  Loss of response to painful stimuli – Stage III  Light Anaesthesia – Reflex increase in respiration, BP on Incision,  Resistance to intubation, Coughing, Vomiting, Laryngospasm  Deep Anaesthesia - Fall in BP, Cardiac and respiratory depression
Phases of Anaesthesia  Induction: Beginning of administration of anaesthesia to the development of surgical anaesthesia  Maintenance: Sustaining the state of anaesthesia.  Recovery: At the end of surgical procedure administration of anaesthetic is stopped and consciousness regains
Pharmacokinetics
Pharmacokinetics  Depth of anaesthesia depends on Potency of the agent (MAC) and Partial Pressure (PP) attained in the brain.  Induction and recovery depends on rate of change of PP in brain.
Factors affecting PP of anaesthetic
1. PP of anaesthetic in the inspired gas  Higher the inspired gas tension more anaesthetic will be transferred to the blood.  Induction can be hastened by administering the GA at high concentration in the beginning.
2.Pulmonary Ventilation  Delivery of GA to alveoli depends on ventilation  Hyperventilation – More delivery per minute  Hypoventilation – Opposite effect
3. Alveolar Exchange  The GAs diffuse freely across alveoli, but if alveolar ventilation and perfusion are mismatched the attainment of equilibrium between alveoli and blood delayed  Induction and recovery both are slowed.
Solubility of anaesthetic in blood  Determined by Blood: Gas Partition coefficient  Lower the blood : gas co-efficient – faster the induction and recovery – Nitrous oxide.  Higher the blood : gas co-efficient – slower induction and recovery – Halothane.
5. Solubility of anaesthetic in tissues  It determines its concentration in that tissue equilibrium.  Most of GAs are equally soluble in tissue as in blood  Lipid soluble more rapidly enter and slowly leave adipose tissue
6. Cerebral blood flow  Highly perfuse so quick entry,  Hasten by CO2 inhalation (cerebral vasodilatation)  CO2 causes hyperventilation
Elimination  Mostly through lungs in unchanged form.  Channel of absorption (lungs) become channel of elimination  Enter and persists in adipose tissue for long periods – high lipid solubility and low blood flow.  They are not metabolized except Halothane
Second gas effect  The ability of the large volume uptake of one gas (first gas) to accelerate the rate of rise of the alveolar partial pressure of a concurrently administered companion gas (second gas) is known as the second gas effect.
Diffusion Hypoxia  Diffusion hypoxia is a decrease in PO2 usually observed as the patient is emerging from an inhalational anesthetic where nitrous oxide (N2O) was a component.  The rapid outpouring of insoluble N2O can displace alveolar oxygen, resulting in hypoxia.  All patients should receive supplemental O2 at the end of an anesthetic and during the immediate recovery
Ideal Anaesthetic
Ideal For Patient  Pleasant, nonirritating, no nausea or vomiting.  Induction and recovery should be fast with no after effects
Ideal for Surgeon  Adequate analgesia, immobility and muscle relaxation.  Noninflammable and nonexplosive
Ideal for Anaesthetic  Easy, Controllable and Versatile  Wide margin of safety.  Potent so that low concentrations are needed.  Rapid adjustments in depth of anaesthesia should be possible.  Cheap, stable and easily stored.  Not react with rubber tubing or soda lime.
Classification  Inhalational  Gas  Volatile Liquid  Intravenous  Faster Acting  Slower Acting
Inhalational  Gas – Nitrous Oxide  Volatile Liquids  Ether  Halothane  Isoflurane  Desflurane  Sevoflurane
Intravenous  Faster Acting  Thiopentone Sodium  Methohexitone  Propofol  Etomidate  Slower Acting  Diazepam  Lorazepam  Ketamine  Fentanyl
Ether  Colorless, highly volatile liquid with a pungent odor. Boiling point – 35ºC  Produces irritating vapors and are inflammable and explosive.  85 to 90 percent is eliminated through lung and remainder through skin, urine, milk and sweat.  Can cross the placental barrier.
Ether: Advantages  Can be used without complicated apparatus.  Potent anaesthetic and good analgesic.  Muscle relaxation.  Wide safety of margin.  Respiratory stimulation and Broncho dilatation.  Does not sensitize the heart to adrenaline  Can be used in delivery.  Less likely hepatic or nephrotoxicity.
Ether: Disadvantages  Inflammable and explosive.  Slow induction and unpleasant -atropine.  Slow recovery – nausea & vomiting  Cardiac arrest.  Convulsion in children.  Cross tolerance – ethyl alcohol.
Ether: Precaution  Should not be used in Hot environment  Electro cautery should not be used
Nitrous Oxide  Non inflammable, nonexplosive, colorless and odorless gas  Weak and low efficacy anaesthetic  Produces Light anaesthesia
Nitrous Oxide: Advantages  Quick and pleasant induction and recovery  Strong analgesic action even at low concentration  Requirement of toxic anaesthetic agent can be reduced  No Nausea and vomiting  Non toxic to liver kidney and brain
Nitrous oxide: Disadvantages  Costly  Supplementation required  No muscle relaxation  Diffusion Hypoxia
Nitrous Oxide: Use  As an adjuvant with other agents  Obstetrics and terminal illness – 50% + O2  Maintenance anaesthesia – 30 to 60%
Nitrous Oxide: Precautions  Should always be used with 30% Oxygen  Should be avoided in patient with collection of air in pleural, pericardial or peritoneal space.  On Prolonged use – Bone marrow depression  Megaloblastic Anaemia
Halothane  Fluorinated volatile liquid with sweet odour, non-irritant non- inflammable and supplied in amber coloured bottle.  Potent anaesthetic, 2-4% for induction and 0.5-1% for maintenance.  Boiling point - 50ºC  60 to 80% eliminated unchanged. 20% retained in body for 24 hours and metabolized.
Halothane: Advantages  Quick and pleasant induction and recovery  Non Inflammable – Electro cautery safe  Non Irritant – No effect on secretion, Bronchospasm, Nausea and vomiting  Potent bronchodilator – Preferred in asthmatics  Do not react with Soda lime
Halothane: Disadvantages  Costly, Special Apparatus required  Poor Analgesic and Poor muscle relaxant  Sensitize heart to CAs – arrhythmias  Cerebral vasodilator – Increase ICT  induces Microsomal enzymes in patients and exposed persons
Halothane on Uterus  Relaxation of uterine smooth muscle  Useful for manipulation of position of foetus in perinatal period  Helpful in delivery of placenta postnatally  Not useful as analgesic or anaesthetic during labour
Halothane: Adverse effects  Halothane Hepatitis ( 1:10000)  Malignant Hyperthermia  Patient with abnormal RyR1 calcium channel at SR.  Massive Ca++ released – Persistent Muscle contraction, Heat.  Treatment – Rapid Cooling, Bicarbonate, 100% O2 + IV dantrolene
Halothane: Precaution  Proper History regarding exposure  Repeated use should be avoided
Enflurane  Causes Hypotension with minimal effect on heart  Does not sensitize to CAs  Significant Muscle relaxation  Respiratory depression is more  ↑ ICT, ↓ O2 consumption of cerebrum, Produce convulsions  Less chances of hepatotoxicity  Can produce malignant hyperthermia  Same effect on uterus
Isoflurane  Isomer of Enflurane and have similar properties but slightly more potent.  Intermediate onset induction
Isoflurane: Advantages  Rapid induction and recovery  Good muscle relaxation  Good coronary vasodilatation  Less Myocardial depression No renal or hepatotoxicity  Low nausea and vomiting  No dilatation of pupil and no loss of light reflex in deep anaesthesia  No seizure and preferred in neurosurgery  Uterine muscle relaxation
Isoflurane: Disadvantages  Pungent and respiratory irritant  Special apparatus required  Respiratory depression  Maintenance only, no induction  ß adrenergic receptor stimulation  Costly
Sevoflurane  Rapid induction and recovery  Non irritant and Pleasant – Children  Bronchodilator – Asthmatics  Hypotension without tachycardia- MI or IHD patients  Weak muscle relaxant
Intravenous Anaesthetic Agents
Thiopentone Sodium  Ultrashort acting Barbiturate – 5to 10 minutes  Onset with in arm to brain circulation time – 12 seconds  Dose – 3-5mg/kg , repeated as per requirement (Max – 1gm)  T1/2 – 9 hours
Thiopentone: Redistribution
Thiopentone: Advantages  Rapid induction, rapid Recovery  No CNS Excitement  Patient Directly goes into Surgical anaesthesia
Thiopentone: Disadvantages  No Analgesic, rather Hyperalgesic  No Muscle Relaxant Action  Ultrashort – Short procedure only
Thiopentone: Adverse Effects  Apnoea, Hypotension  Pain, Necrosis and gangrene if accidently injected into artery  Shivering  Delirium during recovery
Thiopentone: Contraindications  Acute Intermittent porphyria –LMN Paralysis  Poor GC, Shock  Crush injury  ↑ ICT, IOT, Eye injury  Psychiatric patient
Thiopentone: Use  For Induction and ET intubation with muscle relaxant  Endoscopies with short acting muscle relaxant  ECT  Short Surgical procedures  Status epilepticus
Objective  Intravenous general Anaesthetics  Administration of drugs for anaesthesia  Preanaesthetic Medication  Complication of General anaesthesia
Etomidate  Wide safety margin  Preferred in patient with poor cardiac function  Duration of action – 5 to 10 minutes  Metabolized in liver , excreted through kidney and bile
Etomidate: Advantages  Rapid induction  Does not sensitize myocardium to adrenaline  No nausea and vomiting  Non-explosive and non-irritant  Short operations (alone)
Etomidate: Disadvantages  Involuntary movements during induction  Post operative Nausea and Vomiting  On Prolonged use- Suppression of adrenal cortex, Hypotension, electrolyte imbalance and oliguria  Not used in Status epilepticus – Proconvulsant  Poorly soluble in water- Solution prepared in Propylene Glycol
Propofol  Rapid Induction and Rapid recovery  One Dose – 4 minutes, t1/2 45 minutes  Recovery after multiple dose is much faster  Extensively metabolized  88% of an administered dose appears in the urine  Metabolized by hepatic conjugation of the inactive glucuronide metabolites
Propofol: Advantages  Inducing agent, Maintenance Agent  Suppression of laryngeal reflex – Endotracheal intubation  Antiemetic and anticonvulsant action  Safe in pregnancy, can cross placenta  Suitable for OPD Anaesthesia
Propofol: Disadvantages  Induction Apnoea  Hypotension  Bradycardia  Dose dependent respiratory depression  Pain during injection: local anaesthetic combination
Benzodiazepines  PAM, Induction, Maintenance and Supplementation  Conscious Sedation  Produce Sedation, Amnesia, and Unconsciousness in 5 minutes  No Respi/ CVS Depression.  Preferred for Endoscopies, Cardiac Catheterization, Angiographies, Local/ regional Anaesthesia, Fracture Setting  Balanced Anaesthesia
Ketamine  Dissociative anaesthesia  Commonly used as IV, IM, Oral, Rectal can also be given  Induction, Maintenance  Large Volume of Distribution, rapid Clearance  Metabolized in liver and excreted through Kidney and Bile
Ketamine: Advantages  Effect of single dose last for 15 minutes  No Vomiting, No Hypotension  Little impairment of pharyngeal and laryngeal reflex  Bronchodilator – Asthmatics  Suitable for patient who lost circulatory volume due to dehydration, Hemorrhage or burns  Poor risk and geriatric patient, Poor GC  Children – IM, rectal
Ketamine: Disadvantages  No Muscle relaxation  ↑ BP, ↑ Cerebral blood flow, ↑ O2 Consumption, ↑ ICT, ↑ IOT  Hallucinations, Disorientation, Sensory and perceptual illusions during recovery  Involuntary movements
Ketamine and Pregnancy  Contraindicated in pregnancy  Oxytocic actionm  Dangerous in eclampsia and preeclampsia  Can be used for assisted vaginal delivery – Less Foetal and neonatal depression
Fentanyl  Opioid analgesic, given at the start of painful procedures  Supplements Anaesthetics in balanced anaesthesia  In combination with BZDs – Diagnostic, Angiography and minor procedures in poor risk patients
Fentanyl: Advantages  Patient is conscious- Patient cooperation can be asked  Smooth onset and rapid recovery  Suppression of vomiting and coughing  Less fall in BP and no sensitization to adrenaline
Fentanyl: Disadvantages  Respiratory depression  Increase tone of chest muscle  Nausea, vomiting and itching during recovery
Administration of Drugs in Anaesthesia  Minimize deleterious effects – Preanaesthetic medication  Maintain Physiological homeostasis  Better Post anaesthetic outcome
Preanaesthetic Medication  To relieve patients anxiety and apprehension  To produce amnesia  To prevent and control nausea and vomiting  Supplement analgesic, Less anaesthetic required  Decrease secretions and Vagal Stimulation  Decrease acidity and volume of gastric juice
Selection of preanaesthetic drug  Patient’s mental makeup  Anaesthetic agent to be used  Type of surgery  Presence of preoperative problems
Antimuscarinics Drugs: Atropine, Glycopyrollate, Hyoscine  Decrease salivary and bronchial secretions  Prevents laryngospasm, bronchospasm, Nausea and Vomiting  Prevent Vasovagal attack, Prevent Bradycardia, Hypotension, Cardiac arrhythmia and arrest  Hyoscine – Sedation, amnesia, Antiemetic  They ↑ body temperature  Produce Pupillary dilation – alter pupil sign
Benzodiazepines: Diazepam, Lorazepam, Midazolam  Anxiolytic  Perioperative amnesia  Sedative  Smooth induction
Opioid Analgesics: Morphine, Pethidine, Fentanyl √ Good perioperative analgesic √ Sedation and Hypnotic effects x Respi. Depression, Hypotension, Post op Nausea, Vomiting x Constipation, Urinary retention x Asthma can be precipitated x Pupil constricted – Pupillary sign altered
Neuroleptics: Chlorpromazine, Haloperidol √ Sedation, √ Antianxiety √ Antiemetic x Hypotension x Extrapyramidal Side effects
Antiemetics: Metoclopramide, Domperidone  Prevent Gastric reflux and aspiration pneumonia  Antiemetic action in perioperative period  Metoclopramide – EP Side effects  Promethazine- Antiemetic+ Sedative+ Anticholinergic  Promethazine reverses EP Side effects
Antacids, H2 Blockers, Proton Pump Inhibitors  Antacids neutralize gastric acidity, H2 Blockers and Proton Pump Inhibitors decrease acid secretion  Useful for emergency surgeries, Prolonged surgeries, CS, Obese Patients  Given night before and in the morning  Prevent stress ulcers
Induction and Maintenance  Induction: Thiopentone/ other IV agent  Maintenance: 1. N2O + O2+ Ether 2. N20 + O2 + Halothane + SM Relaxant 3. O2 + Halothane + SM relaxant + Analgesic  Prevent/ Treat undesired side effects:  Anticholinergics, Antiemetics, Analgesics
After Anaesthesia  Oxygen: Prevent Diffusion Hypoxia  Neostigmine: Reverse effect of SM relaxant  Analgesic: Pain relief postoperatively  Antiemetic: to Control vomiting
Complication of Anaesthesia
During Anaesthesia  Bradycardia, Cardiac arrhythmia, Cardiac arrest  Hypotension  ↑ Salivary and bronchial secretion  Respiratory depression, Hypercapnia  Aspiration pneumonia  Delirium, Convulsions  Hypoxia  Awareness and recall of events  Fire and explosion
After Anaesthesia  Nausea and Vomiting  Delayed recovery, Persistent sedation  Atelectasis and pneumonia  Liver and Kidney damage  Delirium  Nerve palsy
Drug Interactions  Patient on antihypertensive: fall in BP  Neuroleptics, Opioids, Clonidine and MAO Inhibitors potentiate Anaesthetics  Halothane sensitize heart to adrenaline  Insulin need of diabetic increased
Summary  Stages of Anaesthesia  Ether, Nitrous Oxide  Second Gas Effect, Diffusion Hypoxia  Enflurane, Sevoflurane, Desflurane  Thiopentone, Propofol, Ketamine  Preanaesthetic Medication