CONSIOUSNESS (WEEK 4) Flashcards
(14 cards)
What are the 3-5 main components of anesthesia?
- analgesia = pain relief
- amnesia = loss of memory
- immobilization
- hypnosis = loss of consciousness “sleep” (not in all sources)
- muscle relaxation (optional)
How is anesthesia administered?
vaporizer machine -> breathing circuit -> patient’s trachea -> lungs -> pulmonary blood -> brain
IV anesthesia is another route
Factors affecting anesthetic uptake?
- anesthetic solubility in blood (if anesthetic too soluble in blood, has high concentration in blood at the start and low concentration in the brain at the start - > takes longer to equilibrate the two b/c brain concentration has to also be higher to reflect high blood solubility (and it takes a while for blood to be filled to its maximum capacity) -> takes a while to reach that; so high blood solubility increases t for brain to uptake)
- partial pressure difference between alveoli and pulmonary venous blood (bigger difference, more drug uptake)
- alveolar ventillation -> better diffusion -> better brain transport
how is solubility of inhaled anesthetic expressed?
via partition coefficient - the higher the blood/gas solubility the higher the blood/gas partition coefficient -> the longer it takes for equilibrium to be reached between alveoli and blood -> slower rate of induction (introduction)
NO/desflurane - lowest partition coefficient - fastest
isoflurane/halothane - highest partition coefficient - longest to reach equilibrium in brain
What is the general idea of how anesthetics work?
Facilitation of inhibition
↑ GABA A receptor-mediated transmission (Cl- in, hyperpolarizes cell)
↑ Background (“leak”) K+ conductance
— Inhibition of excitation
↓ Glutamate & ACh receptor-mediated transmission
what are some S/E of anesthetic metabolism (inhaled), how is toxicity related to blood solubility?
higher blood solubility -> higher metabolism -> higher potential of organ damage when metabolized and eliminated - > hepatotoxicity and nephrotoxicity (double whammy - less availability to brain and higher toxicity (think higher concentration in the blood - more chances to hurt kidneys and liver)
How is concentration of inhaled anesthetics measured?
MAC = minimal alveolar concentration = concentration of an inhaled anesthetic IN THE ALVEOLI at 1 atm that prevents movement in response to painful stimulus in 50% of patients
1 MAC not enough, usually 1.2 MAC prevent movement in 95% of patients
but… low therapeutic index LD50/ED50 = 2-3 (twice the therapeutic dose can be fatal)
What are factors that decrease anesthetic’s MAC (minimal alveolar concentration)?
age (as age decreases, need less anesthetic)
pregnancy (progesterone increase is a natural anesthetic)
decrease in core temperature (hypothermia is anesthetic)
opioids (likewise)
What are organ effects of inhaled anesthetics? CNS CV Resp Kidneys MSK Uterus
remember vasodilation in most systems…
CNS - decrease in cerebral metabolic rate (decreased oxygen consumption)
cerebral vasodilation
CV - decrease in arterial blood pressure, halothane can cause ventricular arrhythmias
Resp - respiratory depression
but also decreases airway resistance (last resort treatment for asthmatics)
Kidneys - reduction in renal blood flow (vasodilation, so less blood to kidneys) -> decreased GFR and urinary output
MSK - skeletal muscle relaxation
Uterus - uterine relaxation (think that it is also a muscle), can lead severe blood loss at birth due to prolonged relaxation - general anesthesia not recommended, spinal done
examples of inhaled anesthetics?
halothane, sevoflurane, isoflurane, desflurane, NO (nitrious oxide)
examples of Iv anesthetics?
propofol, ketamine, etomidate
Propofol: MOA and S/E
Propofol: sedation, maintenance of anesthesia; smooth, pleasant dreams, head clear on awakening
Propofol: facilitates inhibition via GABAA receptors
Propofol: metabolized in liver
Propofol: no analgesic potential
Propofol: risk of hypotension, respiratory depression and apnea (stop of breathing), potential for sepsis b/c bacteria love its formulation -> must be used fast
Ketamine: MOA and S/E
Ketamine = PCP: dissociative anesthesia - patient conscious but unable to process or respond to sensory input (+ amnesia +analgesia)
Ketamine: minimal resp depression and airway reflexes maintained
Ketamine: still bronchodilator
Ketamine: unpleasant dreams
Good for trauma or shock b/c no change in pressure of battlefield surgery
works by blocking glutamate
Etomidate (imidazole derivative): S/E & MOA?
etomidate: minimal effects on hemodynamics - good for unstable patients
etomidate: no analgesia
etomidate: MOA similar to proposal
