A slideshow on how general anaesthesia works and its history, modern usage and procedure. This slide gives a concise and comprehensive review on General 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.
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.