Anesthesiology
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Anesthesiology Anesthesia – is a reversible condition of comfort, quiescence and physiological stability in a patient before, during and after performance of a procedure. General anesthesia – for surgical procedure to render the patient unaware / unresponsive to the painful stimuli.

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Anesthesiology l.jpg
Anesthesiology

  • Anesthesia – is a reversible condition of comfort, quiescence and physiological stability in a patient before, during and after performance of a procedure.

  • General anesthesia – for surgical procedure to render the patient unaware / unresponsive to the painful stimuli.


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Anesthesiology

Original in the Royal College of Surgeons of England, London.


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Anesthesiology

  • Surgical stress – evokes HPA axis and sympathetic system.

  • Tissue damage during surgery induces coagulation factors and activates platelets leading to hypercoagulability of blood.

  • Anesthesia decreases the components of surgical stress response.


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Anesthesiology

Anesthetics are associated with

  • Decrease in systemic blood pressure – myocardial depression and direct vasodilatation.

  • Blunting of baroreceptor control and decreased central sympathetic tone.


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Anesthesiology

Hallmark of anesthesia:

  • Amnesia / unconsciousness

  • Analgesia

  • Muscle relaxation

    General anesthetics have therapeutic indices of about 2 - 4.


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Anesthesiology

Preanesthetic medication:

It is the use of drugs prior to anesthesia to make it more safe and pleasant.

  • To relieve anxiety – benzodiazepines.

  • To prevent allergic reactions – antihistaminics.

  • To prevent nausea and vomiting – antiemetics.

  • Toprovide analgesia – opioids.

  • To prevent bradycardia and secretion – atropine.


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Anesthesiology

Stages of anesthesia:

  • Stage I : Analgesia

  • Stage II : Excitement, combative

    behavior – dangerous state

  • Stage III : Surgical anesthesia

  • Stage IV : Medullary paralysis –

    respiratory and vasomotor

    control ceases.


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Anesthesiology

Molecular mechanism of the GA :

  • GABA –A : Potentiation by Halothane,

    Propofol, Etomidate

  • NMDA receptors : inhibited by Ketamine


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Anesthesiology

The main target of inhalation anesthetics is the brain.


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Anesthesiology

There are two types of anesthetics :

  • Inhalational --- for maintenance

  • Intravenous --- for induction and short procedures

    Inhalation anesthetics:

  • Advantage of controlling the depth of anesthesia.

  • Metabolism is very minimal.

  • Excreted by exhalation.


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Anesthesiology

Inhalational anesthetics :

Non-halogenated gas:

  • Nitrous oxide

    Halogenated hydrocarbons:

  • Halothane

  • Enflurane

  • Isoflurane

  • Desflurane

  • Sevoflurane

  • Methoxyflurane – nephrotoxicity.


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Anesthesiology

The important characteristics of Inhalational anesthetics which govern the anesthesia are :

  • Solubility in the blood (blood : gas partition co-efficient)

  • Solubility in the fat (oil : gas partition co-efficient)


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Anesthesiology

Blood : gas partition co-efficient:

  • It is a measure of solubility in the blood.

  • It determines the rate of induction and recovery of Inhalational anesthetics.

  • Lower the blood : gas co-efficient – faster the induction and recovery – Nitrous oxide.

  • Higher the blood : gas co-efficient – slower induction and recovery – Halothane.



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Anesthesiology

Blood gas partition co-efficient affecting rate of induction and recovery


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Agents with low solubility in blood quickly saturate the blood. The additional anesthetic molecules are then readily transferred to the brain.

BLOOD GAS PARTITION COEFFICIENT


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Anesthesiology blood. The additional anesthetic molecules are then readily transferred to the brain.


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Anesthesiology blood. The additional anesthetic molecules are then readily transferred to the brain.

Oil: gas partition co-efficient:

  • It is a measure of lipid solubility.

  • Lipid solubility - correlates strongly with the potency of the anesthetic.

  • Higher the lipid solubility – potent anesthetic. e.g., halothane


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Anesthesiology blood. The additional anesthetic molecules are then readily transferred to the brain.

  • MAC value is a measure of inhalational anesthetic potency.

  • It is defined as the minimum alveolar anesthetic concentration ( % of the inspired air) at which 50% of patients do not respond to a surgical stimulus.

  • MAC values are additive and lower in the presence of opioids.


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OIL GAS PARTITION CO-EFFICIENT blood. The additional anesthetic molecules are then readily transferred to the brain.

Higher the Oil: Gas Partition Co-efficient lower the MAC . E.g., Halothane

0.8

1.4

220


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Inhalational anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Nitrous oxide:

  • Safest inhalational anesthetic.

  • Weak anesthetic but a good analgesic.

  • No toxic effect on the heart, liver and kidney.

  • Caution about diffusional hypoxia megaloblastic anemia.


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Inhalational anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Halothane:

  • It is a potent anesthetic.

  • Induction is pleasant.

  • It sensitizes the heart to catecholamines.

  • It dilates bronchus – preferred in asthmatics.

  • It inhibits uterine contractions.

  • Halothane hepatitis and malignant hyperthermia can occur.


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Inhalational anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Enflurane:

  • Sweet and ethereal odor.

  • Generally do not sensitizes the heart to catecholamines.

  • Seizures occurs at deeper levels –contraindicated in epileptics.

  • Caution in renal failure due to fluoride.


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Inhalational anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Isoflurane:

  • It is commonly used with oxygen or nitrous oxide.

  • It do not sensitize the heart to catecholamines.

  • Its pungency can irritate the respiratory system.


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Inhalational anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Desflurane:

  • It is delivered through special vaporizer.

  • It is a popular anesthetic for day care surgery.

  • Induction and recovery is fast, cognitive and motor impairment are short lived

  • It irritates the air passages producing cough and laryngospasm.


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Inhalational anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Sevoflurane:

  • Induction and recovery is fast.

  • It is pleasant and acceptable due to lack of pungency.

  • It do not cause air way irritancy.

  • Concerns about nephrotoxicity.


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Anesthesiology blood. The additional anesthetic molecules are then readily transferred to the brain.

Parenteral anesthetics (IV):

  • These are used for induction of anesthesia.

  • Rapid onset of action.

  • Recovery is mainly by redistribution.

  • Also reduce the amount of inhalation anesthetic for maintenance.

  • E.g., includes thiopental, midazolam propofol, etomidate, ketamine.


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Anesthesiology blood. The additional anesthetic molecules are then readily transferred to the brain.

Thiopental (Pentothal):

  • It is an ultra short acting barbiturates.

  • Consciousness regained within 10-20 mins by redistribution to skeletal muscle.

  • It do not increase ICT.

  • It is eliminated slowly from the body by metabolism and produce hang over.

  • It can be used for rapid control of seizures.


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Intravenous anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Propofol (Diprivan):

  • Most commonly used IV anesthetic.

  • Unconsciousness in ~ 45 seconds and lasts ~15 minutes.

  • Anti-emetic in action.

  • Suited for day care surgery - residual impairment is less marked.


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Intravenous anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Etomidate:

  • It is a short acting anesthetic.

  • It suppress the production of steroids from the adrenal gland and no repeated injections.

  • It is a pro-convulsant and emetic.

  • CVS stability is the main advantage over anesthetics.


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Intravenous anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Ketamine : Dissociative anesthesia

  • Produce - profound analgesia, cataleptic state, immobility, amnesia with light sleep.

  • Acts by blocking NMDA receptors

  • Heart rate and BP are elevated due to sympathetic stimulation.

  • Respiration is not depressed and reflexes are not abolished.


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Intravenous anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Ketamine:

  • Emergence delirium, hallucinations and involuntary movements occurs in 50% cases during recovery.

  • It is useful for burn dressing and trauma surgery.

  • Dangerous for hypertensive and IHD.


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Intravenous anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Neuroleptanalgesia :

  • It is characterized by general quiescence, psychic indifference and intense analgesia without total loss of consciousness.

  • Combination of Fentanyl and Droperidol as Innovar


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Intravenous anesthetics blood. The additional anesthetic molecules are then readily transferred to the brain.

Neuroleptanalgesia :

  • It is associated with decreased motor functions, suppressed autonomic reflexes, cardiovascular stability with mild amnesia.

  • It causes drowsiness but respond to commands.

  • Used for endoscopies, angiography and minor operations.


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