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General Anaesthesia
- 1. General Anaesthesia Adityadeb Ghosh B. Pharm Guru Nanak Institute of Pharmaceutical Science and Technology, Kolkata, IN
- 2. Contents 1) INTRODUCTION 2) HISTORY 3) MECHANISM OF ACTION 4) M.A.C 5) PREMEDICATION 6) PROCEDURE 7) STAGES 8) MAINTENANCE AND EMERGENCE 9) CONCLUSION 10) REFERENCES
- 3. 1. What is Anaesthesia? Introduction and history of anaesthesia.
- 4. Introduction General anaesthesia is a medically induced state of unconsciousness with loss of protective reflexes, resulting from the administration of one or more general anaesthetic agents. It is carried out to allow medical procedures that would otherwise be intolerably painful for the patient.
- 5. History Before 19th century, alcohol, opium, cannabis, even concussion and asphyxia were used to prevent surgical pain. In the 19th century, invention of antiseptics and advances in pharmacology and physiology led to massive development in general anaesthesia and pain management. On November 14, 1804, Hanaoka Seishū, a Japanese doctor, performed the first successful surgery using general anesthesia.
- 6. Timeline of Anaesthetics 1884 1846 1956 N2O Ether 1847 Chloroform 1929 Cyclopropane Halothane These were the most popular early anaesthetics. The first I.V. anaesthetic thiopentone was introduced in 1935.
- 7. 2. How it works? Mechanism of action of anaesthesia.
- 8. Mechanism of action ▪ Blocking cation channels of nicotinic cholinergic receptors. ▪ Blocking excitatory NMDA type of glutamate receptor. ▪ Enhancement of inhibitory transmission through GABAA receptor. ▪ Interrupting functions of cerebral cortex, thalamus, reticular activating system, and spinal cord
- 9. Minimum Alveolar Concentration ▪ Lowest concentration of the drug in pulmonary alveoli needed to produce immobility in response to a painful stimulus in 50% individuals. ▪ It is a measure of potency and the capacity of an anaesthetic to enter into CNS and attain certain concentration in neuronal membrane. ▪ Declines with age beyond 50 years.
- 10. 3. How is it done? Procedure, premedication and stages of anaesthesia.
- 12. Premedication ▪ Clonidine - reduces postoperative shivering, nausea and vomiting, and emergence delirium. ▪ Midazolam - reduces preoperative anxiety, including separation anxiety in children. ▪ Melatonin - hypnotic, anxiolytic, sedative, antinociceptive, and anticonvulsant. ▪ β-blockers – reduces postoperative hypertension, cardiac dysrhythmia, or myocardial infarction.
- 13. Procedure Anaesthetic agents may be administered by : Inhalation, injection (intravenous, intramuscular, or subcutaneous), oral, and rectal routes. Once they enter the circulatory system, the agents are transported to their biochemical sites of action in the central and autonomic nervous systems. An example sequence of induction drugs: • Pre-oxygenation to fill lungs with oxygen. • Lidocaine for sedation and systemic analgesia for intubation. • Fentanyl for systemic analgesia for intubation. • Propofol for sedation for intubation. • Switching from oxygen to a mixture of oxygen and inhalational anesthetic.
- 14. STAGES ▪ Stage of analgesia – pain is abolished, patient is awake in a dreamy state. Amnesia imminent. ▪ Stage of delirium – patient may shout, struggle and hold his breath. HR and BP rises, pupils dialate. No procedure done. ▪ Surgical Anaesthesia – 4 planes : ▸Plane 1 – Roving eyeballs, eyelids closed, reflexes present. ▸Plane 2 – Loss of corneal and laryngeal reflexes. ▸Plane 3 – Pupil dialates, light refles lost, H.R rises. ▸Plane 4 – Intercostal paralysis, shallow abdominal respiration. ▪ Medullary Paralysis – Cessation of respiration and potential cardiovascular collapse. This stage is lethal without cardiovascular and respiratory support.
- 15. Fig : Physiological changes during stages of general anaesthesia with ether.
- 16. Maintenance and emergence ▪Anaesthesia is maintained for the required time by continuously applying inhalation or intravenous anaesthetics. ▪Emergence usually takes 1-30 min, when the concentration of the drug falls below a certain level. ▪Symptoms like shivering, confusion, aphasia, dyspnoea and arrhythmia occur during emergence. ▪NSAIDS, Opiates and other pain management drugs are administered to reduce post operative pain.
- 17. CONCLUSION Attempts at producing a state of general anaesthesia can be traced throughout recorded history in the writings of the ancient Sumerians, Babylonians, Assyrians, Egyptians, Greeks, Romans, Indians, and Chinese. Rapid advancement in modern anaesthetic techniques has ensured painless surgeries and eliminated the horrible consequences arising from surgeries performed without anaesthesia.
- 18. Thank You! References: Tripathi K.D.; Essentials of Medical Pharmacology; 7th Edition; Jaypee brothers medical publishers ltd.; 2014. Anesthesiology; August 2007; Volume 107; Issue 2.
- 19. “Alcohol is the anaesthesia by which we endure the operation of life - George Bernard Shaw
Editor's Notes
- the overall aim of anaesthesia is to ensure unconsciousness, amnesia, analgesia, loss of reflexes of the autonomic nervous system, and in some cases paralysis of skeletal muscles. No single anaesthetic provides the optimum level of action with minimum side effects, so a combination of different drugs is used.
- READ 1ST -- Attempts of producing functional anaesthesia has been found in the writings of the ancient Sumerians, Babylonians, Egyptians, Greeks, Romans, Indians, and Chinese. The European Renessance caused significant advances in anatomy and surgical technique. However, despite all this progress, surgery remained a treatment of last resort. Largely because of the associated pain, many patients chose to rather die than undergo surgery.
- N2O – Dr. Horace Wells (dentist) laughing gas – bursts. Ether – Dr. william Morton – myocardial depression Chloroform – Dr. Simpson from Britain – phosgene – liver necrosis, respiratory failure, arrhythmia. Cyclopropane - American anaesthetist Ralph Waters – cyclopropane shock-bp falls – arrhythmia, Halothane – Dr. M. johnstone in Manchester – liver Modern - Desflurane, isoflurane and sevoflurane – inhalation, ketamine, propofol - injection
- The mechanism of action of GAs is not precisely known. Probable mechanisms are – Nicotinic cholinergic – non selective cation channel. NMDA – n methyl d aspartate receptor, ca2+ channel Gaba a – ligand gated ion channel – cl - ligand gated ion channels are the major targets of anaesthetic action. The GABA-A receptor gated Cl¯ channel is the most important of these.
- Same for all species
- READ 1ST - Prior to administration of a general anaesthetic, the anaesthetist may administer one or more drugs that complement or improve the quality or safety of the anaesthetic. Patient's age, body mass index, medical and surgical history, current medications, and fasting time are reviewed. a patient who consumes significant quantities of alcohol or illicit drugs could be undermedicated if s/he fails to disclose this fact; causing anaesthesia awareness.
- Inhalation and injection are most preferred routes. Pre oxygenation is done to allow for longer period of apnea during intubation.
- State of delirium is almost negligible in modern anaesthesia
- mixture of oxygen, nitrous oxide, and a volatile anaesthetic agent, is used to maintain inhalation anases… administering medication (usually propofol) through an intravenous catheter. Constant monitoring of HR, airway management, eye management, and establishing neuromuscular blockade is necessary for maintenance of anaesthesia.