GA Flashcards
what does GA aim to do
unconsciousness
amnesia
analgesia
relaxation of skeletal muscle
loss of autonomic NS reflex
What are the stages of anesthesia
- analgesia
- excitement
- surgical anesthesia
- medullary depression
What happens during the surgical anesthesia stage of anesthesia
loss of eye movement, eye reflexes, regular respiration recurs followed by apnea
What are the types of anesthetic
Inhaled, IV
for Inhaled, there are gas and liquid
for IV, there are inducing agents, dissociative anesthesia, and neurolept analgesia
When would inhaled analgesic be considered effective in terms of absorption
need to achieve a brain concentration of inhaled anesthetic
what affects the rate at which therapeutic brain concentration is achieved
- solubility ( low solubility in blood, can transfer into brain faster), reach high arterial tension rapidly
- anesthetic concentration in inspired air
- rate and depth of pulmonary ventilation
- pulmonary blood flow( higher blood flow, rate of rise of anesthetic tension in blood and brain decreases)
- arteriovenous concentration gradient( concentration gradient depend on uptake of anesthetic by tissue, which is high. high concentration gradient increases time to achieve equilibrium with brain)
What is the rate of metabolism of GA dependent on
a.solubility in blood
b. duration of exposure
What is the pharmacokinetics of the inhaled anesthetics
- modify ion channels by direct interactions with multiple members of the ligand-gated ion channel family
for eg GABAa, nicotinic, glycine receptors
also act on the sensitivty of specific neurons and pathway like the spino-thalamic tract and reticular activating system
Which inhaled GA causes a decrease in systemic resistance
isoflurane , sevoflurane
List examples of inhaled liquid GA
isoflurane sevoflurane, ester, halothane, enflurane, desflurane, methoxyflurane
What inhaled GA causes a reduction in cardiac output
halothane and enflurane
what are the action of inhaled GA on the organ system
- CVS decreases mean arterial pressure, depression of the myocardial function
- Respiratory, decrease in minute ventilation, reduced response to hypercapnia, increase apnoeic threshold, depression of mucociliary function, bronchodilation
- brain, increased cerebral blood flow by decreasing cerebral vascular resistance
- renal, reduced renal blood flow
- Liver
- Uterus, halogenated anesthetics are potent uterine muscle relaxants
What inhaled GA causes bronchodilation
halothane and sevoflurane
What are some toxic effects of inhaled GA
- hepatic ( some exposed to halothane may develop hepatitis), may initiate immune mediated response
- Renal–> renal dysfunction following methoxyflurane due to release of fluoride during metabolism
- Malignant hyperthermia
an autosomal dominant skeletal muscle disorder. GA in suceptible individuals trigger hypertension, tachycardia, severe muscle rigidity, hyperthermia, acidosis. Increase muscle cell calcium.
What is malignant hyperthermia treated with
dantrolene to reduce release calcium and supportive measure
what does halothane do
used to maintain anesthesia and also can be used for induction most commonly in children
- relaxes skeletal muscle and potentiate skeletal muscle relaxants
- decrease blood pressure due to depression of cardiac output with little change in systemic vascular resistance. may cause bradycardia and arrythmia
- may rarely cause halothane hepatitis, sudden and sever liver necrosis, usually develop several days after anesthesia
What is the limitation of Nitrous oxide
even at maximum dose nitrous oxide cannot give complete unconciousness or surgical anesthesia. Used as an adjunct with other inhaled anesthetics. Analgesic agent for labour pain
What is the difference between IV anesthetics and inhaled anesthetics
onset of action is faster and hence commonly used for induction.
most IV lack analgesic properties, can be supplemented with local or inhaled anesthetics
What are some examples of IV GA
- inducing agents
thiopentone,propofol, etomidate - dissociative anesthesia like ketamine
- neurolept analgesia like fentanyl+Droperidol
how does barbiturates act to achieve anesthesia
Binds to Gabaa receptors, facilitate action of GABA by increasing duration of GABA gated chloride channel opening.
Act on AMPA receptor to depress glutamate mediated excitation, non synaptic membrane efect
Why is thiopental commonly used for induction
- rapidly distributes out of blood and brain to muscle and fat due to high lipid solubility
- rapidly crosses blood brain barrier, produces loss of consciousness quickly when sufficient doses given
What is the benzodiazepine antagonist, whats the dose required
flumazenil, short duration of action (<90mins), may require multiple doses
How does benzodiazepine compare with barbiturates
Benzodiazepine have a slower onset of CNS depressant effects, it also reaches a plateau inadequate for surgical anesthesia
How does propofol potentiates its action of anesthetic
it potentiates GABAa receptor activity, slowing the channel closing time; sodium channel blocker; endocannabinoid system activity
What is the most popular IV anesthetic and why
Propofol; has a rapid rate of onset of action and also recovery is more rapid than barbiturates. Also used for induction and maintenance of anesthesia as a part of total IV or balance anesthesia
how does propofol decrease BP
Decrease peripheral arterial resistance, venodilation, negative inotrope
What kind of IV GA is ketamine, how does it work
produces dissociative amnesia( no loss of consciousness) . It is a lipophilic drug that is rapidly distributed to the brain. Metabolised by liver, excreted by kidney and in the bile.
It is the only IV with both anesthetic and analgesic properties
stimulates Central sympathetic NS and inhibit reuptake of noradrenaline, useful in those with cardiogenic or septic shock. Increase cerebral blood flow, oxygen consumptio and intracranial pressure
WHat is the side effect of ketamine
associated with post operative disorientation, illusions and dreams
What kind of alternative to GA are there
balanced anesthesia, monitored anesthesia, conscious sedation
what does balanced anesthesia entail
- use both iv and inhaled anesthesia, IV for induction, inhalation for maintenance. Can also use LA to provide pre or peri operative analgesia, CvS drugs to control transient autonomic responses to noxious surgical stimuli
