General Anaestics Flashcards
What are the 5 goals of Anesthesia?
1) Unconsciousness
2) Amnesia
3) Analgesia
4) Inhibition of Autonomic reflexes
5) Skeletal Muscle relaxation
MOA - unknown but may include
- GABA chloride channels (inhibitor)
- Potassium channels (inhibitory)
- Ach (excitatory)
- Glutamate (excitatory
Types of (inhaled) Anesthetics: Volatile - they have high boiling points and liquid at RT (all the ranes)
halothane
enflurane
isoflurane
sevoflurane
Gaseous Anesthetics:
Low bowling points and gas at Rt
Nitrous Oxide (blue cylinder) Xenon
Guedal’s Stages of Anesthesia
(a) Stage I Analgesia, initially analgesia without amnesia (decrease awareness of pain but fully awake)
(b) Stage II Excitement (Disinhibition), delirious and vocalizing but amnesic [we want to get through this phase as fast as possible]
(c) Stage III Surgical Anesthesia, pupil size used to determine plane of this stage - unconscious, no reflexes, loss response to stimuli [where you want to keep the pt]
(d) Stage IV Medullary Depression, CNS depression, death ensues
Pharmacokinetics:
the concentration of inhaled anesthetic gas is proportional to its partial pressure (also called tension) - concentration at the site of action is a critical parameter
Factors Controlling Gas Uptake into the CNS
1) Alveolar concentration of the gas.
***(2) Solubility in the blood, high blood
solubility, slow induction. Poor solubility,
rapid induction. The blood: gas partition
coefficient. Nitrous oxide 0.47 rapid (prefers the fat of the brain), halothane 2.3 slow.
**(3) Cardiac Output. Changes in pulmonary
blood flow.
4) Alveolar-Venous Blood Partial Pressure Difference: change rate of ventilation, increase the concentration in the blood.
what is the induction of anesthesia by gas control? 1
1) solubility of gas in the blood is called the blood: gas partition coefficient – slow onset stays in blood longer and enters the brain like Halothane
what is the induction of anesthesia by gas control? 2
2) Inspired gas partial pressure. Increase the partial pressure (%) in inspired air of gas to increase rate of transfer into the brain (overcome solubility issues).
Elimination of the drugs
Is limited by biotransformation in the lover (varies with gas)
- limited biotransformation in the kidneys
- MAC - Minimum Alveolar Anesthetic Concentration - measurement for potency
Alveolar concentration required to eliminate the response of surgical incision in 50% of the patient population
- derived from quantal dose-response curve
- 5 MAC = mild amnesia
- 0 MAC = obtundation deepens
- 3 MAC = no response to the surgery 99% patients immobile at 1.3 MAC
Pharmacodynamics: what is the primary target of gas anesthetics?
GABAa chloride channel
- most inhaled gas anesthetics enhance GABA mediated chloride neuron inhibition
- the gases may also hyperpolarize neurons through activation of potassium channels
- gases may also block the excitatory actions of Ach at nicotinic receptors
major sites of action for inhalation anesthetics?
1) GABAa receptors (Cl- influx, hyperpolarization)
2) glycine receptors (ligan gated channel, influx of Cl-)
3) Potassium channels
what is malignant hyperthermia?
a disease that causes a fast rise in body temperature and severe muscle contractions when someone with the MH gets general anesthesia. MH is passed down through families. an autosomal dominant genetic disorder
- occurs with sime pts on gas plus succinylcholine
what are some results of malignant hyperthermia?
hyperthermia, HTN, muscle rigidit, hyperkalemia, acidosis - causes by too much release Ca from the SR of the muscle
how do you treat malignant hyperthermia?
dantrolene (Dantrium®)
which blocks the release of calcium from SR.
What are the gas anesthetics?
Desflurane • Enflurane • Halothane • Isoflurane • Nitrous oxide (blue cylinder) • Sevoflurane
IV anesthetics
- used in addition to inhaled anesthetics and alone
- faster induction of anesthesia compared to inhaled agents
- rapid recovery
- potency adequate for use in short surgical procedures
Barbiturates - not used that often act by blocking GABA channels and Na channels
(a) thiopental, methohexital
(b) readily cross BBB (lipid soluble) and rapidly induce anesthesia
Thipoental - what is it used for?
- induction of anesthesia, induce unconsciousness in less than 30 seconds.
- Actions through GABAa receptors and Na+ gated ion channels.
- Contraindicated in acute intermittent porphyria (genetic disorder of heme metabolism)
Benzodiazepines
(a) diazepam, lorazepam, midazolam used for preanesthesia medication
(b) sedative, anxiolytic, amnestic inducing
(c) medazolam drug of choice for iv administration
Opioid Analgesics
- used with benzos to induce anesthesia
IV morphine
Fentanyl (and derivitaves)
PROPOFOL (Diprivan®) - gas + iv drug
(a) most popular iv anesthetic (think Michael Jackson)
(b) reduced incidence of nausea and vomiting with rapid recovery at termination of iv infusion
(c) used for both induction and maintenance of anesthesia
(d) fospropofol, prodrug that reduces the incidence of injection site pain
Ketamine (Ketalar®)
(a) sold on the streets by junkies as “Special K”
(b) drug produces dissociative anesthetic state, which includes catatonia, amnesia, analgesia with or without loss of consciousness
(hypnosis) .
(c) drug blocks excitatory neurotransmitter glutamic acid at NMDA receptors
(d) only iv anesthetic with both analgesic and anesthetic properties
(e) drug often induces emergence phenomena following use as an anesthetic (perceptual illusions, vivid dreams)
(f) diazepam or midazolam reduces incidence of emergence phenomena
(g) useful in low dose because of lack of respiratory depression
