11

22

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Anesthesia:

• Loss of bodily SENSATION with or without loss of consciousness

Analgesia:

• Absence of the sense of PAIN without loss of consciousness

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• 1772: Joseph Priestly discovered Nitrous Oxide NO

• 1800: Humphry Davy picked up on Priestly's work and tested on animals

• 1844: Dr. Horace Wells saw a public demo of Nitrous Oxide at a carnival and started using it for dental treatment

• Under the influence of Nitrous Oxide, he extracted his own infected tooth with the help of his colleague

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Techniques of Anesthesia from the past:

• Soporifics and narcotics marijuana, belladonna & jimsonweed

• Healers induce a psychological state of anesthesia by mesmerism or hypnosis

• Distracting patients rubbing them with counter-irritants as stinging nettles (broad coarsely toothed leaves with copious stinging hairs)

• Simply knocking out the patient with blows to the jaw

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• Before 1846, Surgery was a last and desperate resort

• 1846: Analgesic agents, alcohol and opium, were used during surgery

• Side Effects of Alcohol nausea; vomiting; DEATH instead of sleep

• Downside of Opium not powerful enough to completely blunt a surgical stimulus

• The use of Hey’s Saw to make an aperture in the skull to relieve pressure on the brain

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1. General

2. Regional

3. Local

4. Sedation

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General Anesthesia:

• Affects brain cells:

• loss of consciousness (brain-stem reticular activating system)

• Amnesia (cerebral cortex)

• Analgesia

• Relaxation of muscle & immobility (spinal cord)

• Allows general surgery and other painful procedures to be carried out with the patient “asleep” (e.g. heart surgery)

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Regional Anesthesia:

• Affects large bundle of nerves to a PARTICULAR area of the body

• Lose sensation without losing consciousness

• During childbirth, women given anesthetics, loses sensation of lower body (legs)

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Local Anesthesia:

• Numbing a small area

• Injection made right under the skin of incision area (e.g. Injection of anesthetics to gums for tooth extraction)

• Blocks nerve impulses by decreasing permeability of nerve membranes to sodium ions

• Eutectic Mixture of Local Anesthetics (EMLA) cream, can be placed on for numbing effect for up to an hour. Usually used before injections and superficial splinter removals

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Sedation:

• A small dose of general anesthesia is able to produce a “twilight sleep”

• A state of depression of the central nervous system

• Verbal contact with the patient is maintained throughout the period of sedation

• Sedation alone will not produce analgesia (pain control), so a local anaesthetic may also be used

• Widely used as a mean of reducing anxiety during dental procedures

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1. Inhalation

2. Intravenous Injection

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Inhalation:

• Mask over mouth and nose, release sedative agents or anesthetics

• Commonly used Anesthetics

• Sevoflurane – easy to inhale

• Halothane – easy to inhale, heart rate decreases, blood pressure decreases

• Desflurane – irritating to inhale, shorter duration time

• Nitrous Oxide – easy to inhale, but not strong enough to complete general anesthetic

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Inhalation (cont.):

• Gas is inhaled to lungs and blood carries the gas to CNS cells

• Rate depends on:

• Concentration of gas

• Rate flow of gas from anesthesia machine

• Solubility of gas in blood

• Rate and depth of breathing

• Cardiac output

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Inhalation (cont.):

• Anesthesia is a reversible process

• When gas is turned off, bloodstream brings gas back to the lungs and it is exhaled

• Least soluble anesthetics take longest to take effect

• Measurement of potency - Minimum Alveolar Concentration (MAC):

• Alveolar partial pressure of a gas that prevents movement in response to a standard painful stimulus (surgical incision) in 50% of subjects

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Intravenous Injection:

• Liquid anesthetics injected directly into bloodstream through intravenous catheter

• Common injected Anesthetics:

• Barbiturates (powerful soporific effect, e.g. sodium thiopental)

• Propofol

• Ketamine (causes hallucination in large doses)

• Etomidate

• Narcotics (e.g. morphine)

• Benzodiazepines (valium-like drugs)

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Intravenous Injection (cont.):

• Factors which affect the rate of the injected drug:

• Volume or dosage of drug injected in body

• Fat solubility of the drug (fat soluble drugs react quicker)

• Rate at which body eliminates the drug

• Example:

• Sodium thiopental is fat-soluble and acts very quickly

• When asked to count down from 100, most people will not remember past 95

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• Spinal Anesthesia: Causes loss of sensation in lower body

• Epidural Anesthesia: Injection into epidural space just outside the spinal canal

• Axillary Block: Injection in the armpit that will block sensation to hand, forearm and elbow

• Interscalene Block: Injection to the side of the neck, made after sedation or general anesthesia. Blocks sensation to arm and shoulder

• Bier Block: Procedures under 40 minutes. Blocks sensation to hand, forearm & wrist

• Ankle Block: Blocks sensation to foot. 3-4 injections of local anesthetics around the ankle (http://www.nysora.com/techniques/ankle_block/)

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Ankle Block Axillary Block

Bier Block

Interscalene Block

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1. Intravenous lines inserted/started

2. Sedation may be given

3. In operating room, machines monitors breathing, heart and blood pressure

4. Anesthetics is then given through the IV line

5. Wake up in the recovery room (perhaps a little confused?)

6. Pain medications may be given through IV if needed

7. Transferred to hospital room or able to head home

2121

1. Intravenous Line injected/started

2. Sedation given

3. Monitoring instruments placed on patient

4. Patient placed sitting or in lateral position

5. Sterilize back and local anesthetics given

6. Spinal needle inserted into lower back into the subarachnoid space

7. Patient lies down

8. More sedation given throughout procedure as needed

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Subarachnoid

SpaceEpidural Space

Spinal Cord cross-section

2323

1. Intravenous line injected/started

2. Sedation given

3. Numbing skin with local anesthetics

4. Insert needle into the epidural space

5. Insertion of catheter through the epidural needle and the needle is removed

6. Catheter taped to the person’s back

7. Medicine is injected through catheter

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Sodium Ion (Na+) Channels:

• Shifted the activation of the Na+ conductance to more positive potentials

• Reduced the maximum value attained

• Sped up the rate of switching on the inactivation

Conclusion:

• Resultant effect reduce macroscopic* Na+ current

• Different anesthetic classes affect different factors controlling the amplitude and time course of the macroscopic Na+ current

*The macroscopic current arises from summation of minuscule currents through many independent channels

2525

Calcium Ion (Ca2+) Channels:

• Decreased the macroscopic Ca2+ current peak amplitude

• Enhanced its rate of decay

Hypothesis:

• Many anesthetics depress the release of transmitter

• Propose that this is due to a reduction of Ca2+ entry through voltage-gated Ca2+ channels

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When using anesthetics, the anesthesiologist must monitor the following vital signs closely with the following monitors:

• Oxygen Analyzers – confirms that O2 is being delivered to body

• Pulse Oximeter – measures hemoglobin saturation

• Capnography – measures exhaled CO2

• Ventilation Monitors

• Temperature Monitor

• ECG – records electrical voltages in the heart in the form of a continues strip graph

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• Lose ability to protect lungs from inhaling foreign particles

• Instructed not to eat before surgery

• When awake, swallowing mechanism involves a reflex that results in the epiglottis sealing off the larynx to the lungs

• When anesthetized, food from stomach may come up from esophagus and enter lungs

• Nitrous Oxide:

• High doses may cause nausea

• Does not work for 10% of patients

• Cannot be used effectively for people who are claustrophobic or have blocked nasal passages

2828

• How Anesthesia Works <www.howstuffworks.com/anesthesia.htm>• General Anesthesia <www.lcanesthesia.com/expect.html>• Basic Anesthetic Monitoring

<www.wramc.amedd.army.mil/departments/surgery/anesthesiology/monitors.htm>• Surgery Before Anesthesia

<http://nerosourgery.mgh.harvard.edu/history/beforeth.htm>• New York School or Regional Anesthesia <www.nysora.com/techniques>• E.B. Smith & S. Daniels, Gases in Medicine Anaesthesia: 8th BOC Priestley

Conference; The Royal Society of Chemistry, 1998.• Guyton & Hall, Textbook of Medical Physiology, 10th Ed., W.B. Saunders Company,

2000.