General Anesthetics Flashcards
General anesthesia
Amnesia, analgesia, uncoscnousness, inhibition of sensory and autonomic reflexes, skeletal muscle relaxation
Administered preoperatively (sedation/analgesia), intraoperatively (sedation/regional anesthetics)
GABAa receptor Cl channel, use GABA to inhibit NT at these receptor sites
Develop a working understanding of the pharmacokinetics of inhalational anesthetics
Inspired concentration, transfer of gas to arterial blood, transfer of agent to the brain
Tension of the anesthetic in the alveolus provides driving force to establish therapeutically effective brain tension
The more soluble the agent in the blood, the slower to rise to equilibrium between inspired and alveolar concentration
Discuss how the blood:gas coefficient influence the onset of action (and termination of anesthesia) for inhaled anesthetics
Ratio of anesthetic concentration in blood to anesthetic concentration in gas when the two are in partial pressure equilibrium
The more soluble in blood, the more of it must be dissolved in blood to raise its partial pressure appreciable
Discuss how ventilation rate and pulmonary blood flow influences the onset of action for inhaled anesthetics
Directly dependent on minute ventilation
The partial pressure of a highly soluble anesthetic can be increased by over-ventilation during the induction period
If we increase the heart rate and CO pt will take longer to fall asleep because it takes brain longer to reach drug concentration.
ALSO cerebral blood flow is regulated, increased CO should not bring extra agent to the brain.
In terms of uptake and elimination, describe how blood flow to a tissue influences the tension of an anesthetic’s gas in that tissue
Tissues with high blood flow will have rapid rises in concentration and can take up significant amounts of the agent during early stages of anesthesia
Blood flow to adipose tissue is limited, thus anesthetic gases will be delivered to and taken up by fatty tissues slowly. On the flipside, these tissues will retain a significant amount of agent over a longer period of time because elimination is slower
Explain the minimum alveolar concentration (MAC) and what information it provides about a volatile anesthetic
Is a measure of potency
Minimum concentration at 1 atm that prevents movements to standard stimulus (skin incision) in 50% of humans
Multiply by 1.3 to achieve “nearly” 100% clinical efficacy
Discuss the pharmacokinetic properties of the ultrashort acting hypnotics and explain how these properties make this class of drugs popular general anesthetic agents
Thiopental sodium
Methohexital sodium
Rapid entry into CNS followed by quick redistribution to indifferent tissues
Induce anesthesia within one or two circulation times after their administration b/c quickly achieve high concentration in the CNS
LIPID SOLUBLE and diffuse rapidly through BBB
Propofol
Induction, maintenance, sedation, procedures, ICU
Mechanism: IPSP (GABA)
Decreases intracranial pressure and cerebral metabolic rate
Decreases BP
Vasodilator (preload and afterload reduction)
Respiratory depression
Thiopental
Barbiturate: GABA
Not available in U.S.
Arterial vasoconstrictor
Put brain to sleep, decreases intracranial pressure and cerebral O2 consumption
Ketamine
NMDA receptor antagonist
Dissociate anesthesia: patient looks awake but they are asleep
Induction and short procedure, good for pain control
Doesn’t decrease respiratory drive, good for asthmatic and narcotics users
Increases cerebral consumption of O2, intracranial pressure and cerebral blood flow
Increases BP and HR
Bad dream, salivation, twitchy, contraindicated in pts with mental health history
Etomidate
Least cardiovascular side effects
GABA again
Vasoconstrictor and decreased cerebral metabolic rate of O2
Multiple dosing decreases adrenal gland function, body’s response to stress is decreased, CONTRAINDICATED IN SHOCK.
