(Ch 21) Local and General Anesthetics Flashcards
Anasthetic Agents / General Anesthetics
Cause what type of Physical Changes ?
General anesthesia involves the physiological changes:
- Reversible loss of response to painful stimuli, loss of consciousness and loss of motor and autonomic reflexes.
- Loss of consciousness is associated with inhibition of the activity of reticular formation.
Type of effects Anesthetic agents have on the CNS?
Anesthetic agents depress the central nervous system, causing a loss of consciousness (except for local and regional anesthetic agents) and relieving pain.
Anesthetic agents are classified as:
Anesthetic agents are classified as:
- Local Anesthetic:* Block specific nerve pathways in a region and result in temporary analgesia and paralysis but no loss of consciousness.
- General Anesthetic:* A general anesthetic used for surgery consists of one medication or a combination that causes a temporary loss of consciousness.
General Anesthetic: are classified into 2 based on their ROA as ” Inhilation and Itravenous anesthetics”
Name the 2 Routes in which General anesthetics are administered:
1. inhalation or 2. intravenous routes.
They are classified into 2 on the basis of their route of administration as inhalation and intravenous anesthetics.
General anesthetics ROA
Inhalation anestetics:
Name 4 main Agents
- Halothane
- Nitrous Oxide
- Enflurane
- Ether
Halothane:
Halothane:
Is the most widely used agent, highly lipid soluble, potent. It causes arrhythmia, hangover and the risk of liver damage is high if used repeatedly.
Nitrous oxide:
Nitrous oxide:
Oderless and colourless gas. It is rapid in action and also an effective analgesic agent. Its potency is low, hence must be combined with other agents. It is a relatively free of serious unwanted effects.
Enflurane:
Enflurane:
Halogenated ether (similar to halothane). Poorly metabolized in the liver, thus less toxic than halothane. It is faster in its action, less liable to accumulate in the body fat compared to halothane. It causes seizure during induction and following recovery from anaesthesia.
Ether:
Ether:
Has analgesic and muscle relaxant properties. It is highly explosive, causes respiratory tract irritation, postoperative nausea and vomiting. It is not widely used currently.
Describe Intravenous anesthetics
Use:
Intravenous anesthetics act much more rapidly, producing unconsciousness in about 20 seconds, as soon as the drug reaches the brain from the site of its injection.
These agents used for induction of anaesthesia followed by inhalation agent.
The main induction agent in current use is: thiopentone, etomidate, propofol, ketamine and short acting benzodiazepine (midazolam).
Agents used for induction of anaesthesia followed by inhalation agent.
The main induction agent in current use:
Name 5
- thiopentone
- etomidate
- propofol
- ketamine
- short acting benzodiazepine (midazolam).
Thiopentone: (IV)
Thiopentone:
- a barbiturate with very high lipid solubility.
- After intravenous administration the drug enters to tissues with a large blood flow (liver, kidneys, brain, etc) and more slowly to muscle.
- Uptake into body fat occurs slowly because of the low blood flow to this tissue, which may cause prolonged effect if given repeatedly.
- It causes cardiovascular depression.
Etomidate: (IV)
Etomidate:
It is more quickly metabolized and the risk of cardiovascular depression is less compared to thiopentone.
Etomidate suppresses the adrenal cortex, which has been associated with an increase in mortality in severely ill patients.
Propofol (Diprivan) (IV agent)
Propofol is a nonbarbiturate hypnotic agent and the most recently developed intravenous anesthetic.
- Its rapid induction and short duration of action are identical to thiopental, but recovery occurs more quickly and with much less nausea and vomiting.
- Rapidly metabolized in the liver and
- -Can be used for long durations of anesthesia, *unlike thiopental.
- Propofol is rapidly replacing thiopental as an anesthetic agent.
Ketamine: (IV)
Ketamine:
- acts more slowly than thiopentone and produces a different effect, known as dissociative anaesthesia in which there is a marked sensory loss and analgesia, as well as amnesia and paralysis of movement, without actual loss of consciousness. -
Ketamine causes dysphoria, hallucinations during recovery.
Benzodiazepines
Provide example
Use
Benzodiazepines
(diazepam, lorazepam, midazolam)
- are used in general anesthetic procedures.
- Compared with intravenous barbiturates, benzodiazepines produce a slower onset of central nervous system effects.
- Benzodiazepines prolong the postanesthetic recovery period but also cause a high incidence of amnesia for events occurring after the drug is administered.
The benzodiazepines are useful in anesthesia as premedication and intraoperative sedation
Opioid analgesic anesthesia:
Opioid analgesic anesthesia:
Opioid analgesics can be used for general anesthesia, in patients undergoing cardiac surgery and fentanyl and its derivates are commonly used for these purposes.
Preanesthetic medication:
Preanesthetic medication:
- It is the use of drugs prior to the administration of anaesthetic agent with the important objective of making anaesthesia safer and more agreable to the patient.
- The drugs commonly used are, opioid analgesics, barbiturates, anticholinergics, anti emetics and glucocorticoids