7th lecture - general anesthetics Flashcards
General anaesthesia is a condition characterised by
a loss of sensation,
loss of consciousness,
loss of some reflexes and/or control of them,
absence of muscle tone,
all whilst vital functions are maintained.
is a reversible phenomenon.
'’Narcosis’ is also used in reference to medical general anaesthesia.
Generalized CNS depression, the degree of depression is described as depth of anesthesia.
During narcosis or gen. anesthesia, the cell membrane permeability to
Na+ ions is reduced, the same applies to K+ and Ca2+ ions.
Postsynaptic membrane stabilisation will occur. The capability of neurons to generate impulses in response to stimulus is reduced.
General anaesthesia (narcosis) is based on
the inhibition of synaptic transmission mechanisms.
The exact molecular and cellular mechanisms of action of inhalation anesthetics remains unknown.
gen.anesthetics are divided into 2 main groups:
Inhalation general anaesthetics
Parenteral (injectable) general anaesthetics
Inhalation general anaesthetics are divided into 2 further groups:
Volatile and gaseous
though gaseous aren’t really used in vet med today
Name min. 3 volatile Inhalation general anaesthetics
Halothane
Isoflurane, enflurane and sevoflurane
Methoxyflurane
The aim in administering an inhalation anesthetic is to achieve
an adequate partial pressure of anesthetic in the CNS to cause a desired level of anesthesia.
Main Components of general anesthesia: (4)
loss of consciousness,
amnesia,
analgesia,
immobility
(and suppression of autonomic reflexes)
General inhalation anesthetic effect on the resp. system
All inhalation anesthetics depress alveolar ventilation.
Airway irritaion is not generally recognized as a problem associated with anesthesia in animals.
Inhalation anesthetic effect on the cardiovascular system (4)
Drug specific and dose related effects.
All volatile anesthetics decrease cardiac output; depress myocardial contractility.
Decrease in arterial blood pressure.
Inhalation anesthetics, especially halothane, may sensitize the heart to arrhythmogenic effects of catecholamines.
inhalation anesthetic effect on the liver
Hepatocellular injury – a consequence of a reduction in hepatic blood flow or direct toxicity.
inhalation anesthetic effect on the kidneys
All volatile anesthetics reduce renal blood flow and glomerular filtration.
During anesthesia even healthy animals produce small volumes of concentrated urine.
In most cases the effects are rapidly reversed after anesthesia.
what does volatile mean when speaking of general anesthetics?
The volatile anesthetics (halothane, isoflurane, desflurane, and sevoflurane) are liquids at room temperature and require the use of vaporizers for inhalational administration.
(And e.g. the gaseous anesthetic Nitrous Oxide is already a gas under normal conditions of temperature and pressure)
describe Halothane (5)
Clear, volatile liquid.
Does not irritate the respiratory tract.
Depresses CNS in a dose-related manner.
Skeletal muscle relaxation.
Cerebral blood fow usually increases, this may result in an increase in cerebrospinal fluid pressure.
Some drowsiness remains evident for several hours after halothane anesthesia.
Halothane effect on the heart
strongly negative inotrope, chronotrope an dromotrope, blood pressure decreases, the sensitivity of the organism to blood loss increases.
Some anesthetics may increase (xylazine, thiopental) and others may decrease (acepromazine, lidocaine) the arrhythmogenic dose of epinephrine during halothane anesthesia.
Halothane effect on resp. system
Halothane depresses respiration
(dose-related)
Halothane effect on liver and kidneys
Hepatic blood flow is decreased.
Hepatic dysfunction that may occur following inhalation anesthesia is most often associated with halothane.
Nefrotoxic.
Isoflurane and enflurane are what to each other?
structural isomers.
Isoflurane effect on resp. tract
It slightly irritates the respiratory tract.
Depresses respiration.
Isoflurane cerebral and pressure effects
Causes less cerebral vasodilation than halothane.
Blood pressure drops, there is a risk that arrhythmia may develop.
Isoflurane affects cardiac output less than
halothane does.
Isoflurane effect on liver and kidneys
Risk of liver damage, but blood flow to the liver is altered less than by halothane.
Effects on kidney similar to halothane - nefrotoxic.
More potent to enhance the neuromuscular blocking effect.
describe Desflurane
Causes dose-related depression in the CNS.
Does not predispose the heart to ventricular arrhythmias, sensitizes to arrthymogenic effects of epinephrine.
Desflurane general effects are similar to
isoflurane.