General anesthesia Dr. Pond Flashcards
What are the factors that need to be fulfilled for anesthesia?
-hypnosis - sleep state
-analgesia - pain relief
-amnesia - no memory
-muscle relaxation - no muscle response to pain
-homeostasis - still intact (breathing, heartbeat, life supporting functions)
-> Usually IV or inhalation as a mixture of these
What are the stages of anesthesia?
- analgesia: pain relief and patient has memory
- excitement/delirium: respiration might be irregular, vomitting may occur if the patient is stimulated
- surgical anesthesia: respiration gets back to normal, all 5 factors of anesthesia are met
- medullary depression: too much -> severe depression of vasomotor center and respiratory center -> can cause death
Examples of complete anesthetics
Halothane
Enflurane
Isoflurane
Sevoflurane
Desflurane
What is the Minimal Alveolar Concentration MAC?
the alveolar concentration that prevents purposeful movement in 50% of subjects in response to pain stimulus (surgery)
-> need to give 1.2 or 1.3x the MAC
MACs can be additive between drugs -> so if a patient is using an opioid we will need a lower concentration of an anesthetic
What is the MAC of newborns?
1.2x the MAC of an adult (30y)
6 month old baby: 1.5x the MAC
What affects the uptake and distribution of inhaled anesthetics in the brain?
-Solubility of anesthetic
-Its concentration in inspired air
-The volume of pulmonary ventilation
Which agent will equilibrate the fastest?
EXAM Q
the one with the lower blood gas partition coefficient -> less soluble in blood and able to move to the brain, the ones with higher blood/gas coefficient will stay longer in the blood (quicker onset with the lower coefficient)
-infervsley related
How does elimination work compared to uptake and distribution?
blood/gas coefficient and elimination are proportional
-> the lower the blood/gas coefficient the slower the elimination???
-mainly eliminated through exhalation
What is the theory about anesthestics introduced by Meyer and Overton?
relationship between lipidsolubility (hydrophobicity) and anesthetic potency
in general: the more hydrophobic the more potent
-> theory: anesthetics incorporate into the plasmamembran (lipid bilayer) and stabilize ion fluxes across the membrane (less ion flux -> less action potential firing)
How is Isoflurane thought to affect neuronal activity?
in a frequency-dependent manner
-neurons that fire at a higher frequency are more affected by anesthetic action
-cognition and movement require high-frequency action potential neurons
-life supporting functions tend to require low-frequency action potential neurons
How does Isoflurane cause the decrease in neuronal activity?
MOA
decrease activation in voltage-gated Ca2+channels on neuron terminals
-> decreased vesicle docking and NT release
How do anesthetics affect mean arterial pressure (MAP)?
all anesthtis (except N2O, incomplete anesthetic) decrease the mean arterial pressure
Which chamber of the heart is affected by anesthetics?
-inhaled anesthetics increase right atrial pressure bc the heart is not able to pump out blood as much
-> greatest increase with halothane
arryhtmias can occur in patients with cardiac disease
How do anesthetics affect respiratory function?
-all (except N2O) decrease tidal volume (amount of intake per breath)
-increase in respiratory rate
-overall decrease in minute ventilation (Tidal volume x respiratory rate)
-> increase in pCO2
How does the body respond to hypoxia that is induced by anesthetics?
0.1 MAC: 50-70% decrease in response to hypoxia
at 1.1 MAC: no response to hypoxia
-> we usually use 1.2-1.3x
How do anesthetics affect the pressure in the brain?
increase in intercranial pressure
-blood flow is driven by metabolic activity of the brain -> in the case of CNS depression the brain is not as active but the blood supply is still high -> causing an increase in intracranial blood pressure
-> also seen with opioids
-some agents have a risk for seizure:
Enflurane
Sevoflurane
Which anesthetics have a risk for seizure?
Enflurane
Sevoflurane
Which anesthetic drugs are converted to trifluoroacetate causing hepatoxicity?
-Halothane
-desflurane
-isoflurane
Which anesthetic drug can cause Nephrotoxicity?
Methoxyflurane
-> produces flouride ions when metabolized
Sevoflurane
-> reacts with CO2 absorbents to form “compound
A” -> nephrotoxic
Which drug can cause malignant hyperthermia?
succinylcholine (muscle relaxant), also anesthetic drugs
-> due to a genetic disorder (regulating Ca2+ release in muscle cells)
-prolonged muscle contraction -> RIGIDITY
-increase in metabolic activity -> Hyperthermia and acidosis
What are the symptoms of malignant hyperthermia?
-rapid onset of tachycardia and hypertension
-muscle rigidity
-hyperthermia
-acidosis
How to treat malignant hyperthermia
-dantrolene
-reduce body temp
-restore acid-base balance
How does dantrolene work?
MOA
it blocks the Ryanodine receptor
-> ryanodine receptor is responsible for Ca2+ influx in muscle cells from the sarcoplasmic reticulum
Anesthetic function of Barbiturates
-Rapid onset
-sedation, anxiolytic
-With continuous infusion,
decrease MAP and CO (cardiac output)
ADE - Barbiturates and respiratory depressants
-transient apnea
-lowered sensitivity to pCO2
Anesthetic function of Benzos
-sedation
-anxiolytic
-amnestic properties
-No analgesia
-insufficient muscle relaxation
Which drug can be used to cause sedation, and reduce anxiety and amnesia?
Benzos
Diazepam (t1/2 = 43 hr)
midazolam (t1/2= 2 hr)
No analgesia, insufficient muscle relaxation
Which drug is used to accelerate recovery from Benzodiazepines?
Flumazenil
-> Benzodiazepine antagonist
Which drug is used to produce an analgesic effect in anesthesia?
opioids
-Morphine
-fentanyl
-sufentanil
-No muscle relaxation
-No amnesia
mu receptor agonists
Role of Etomidate
-Non-barb. hypnotic
-rapid action
-> sedation
-> No analgesia
-Minimal cardiovascular and respiratory depression
-> beneficial in patients with CV disease
Which receptor is targeted by Etomidate?
acts on GABA(A) receptor -> increases frequency of Cl(-) channel opening -> INHIBITORY
ADE Etomidate
-myoclonic activity (muscle jerks)
-nausea after surgery
-avoid prolonged sedation due to adrenal steroidogenesis inhibition
Which receptor is targeted by Propofol/Fospropofol?
-act on GABA(A) receptor
-Rapid action with more rapid recovery
How does Propofol affect BP and respiratory function?
-reduces BP by dcreasing vascular resistance
-causes respiratory depression
How does Propofol affect cerebral blood flow and intracranial pressure?
-reduces cerebral blood flow
-reduces metabolic rate
-decrease intracranial pressure
Which drug can cause Adrenal steroidogenesis inhibition with prolonged use?
Etomidate
Which receptor is targeted by Ketamine?
NMDA receptor -> acts as an agonits
may also target opioid receptors
How does Ketamine affect cardiac function?
-increases HR, MAP, and CO
(stimulation of the sympathetic nervous system)
How does Ketamine affect cerebral blood flow and intracranial pressure?
increase in cerebral blood flow
increase in intracranial pressure
How does Ketamine affect respiratory function?
decrease in respiratory rate
