Lecture 54: General Anesthetics Flashcards
General anesthesia is used
For procedures that require loss of consciousness; immobility despite painful stimulation
What is the surgical plane and one goal of anesthesia
Surgical plane = Level III EEG; goal is to minimize time at levels I & II
What four things would an ideal anesthetic do? What do we have to do to achieve these effects?
- Loss of consciousness, 2. Analgesia, 3. Paralysis, 4. Amensia; no ideal anesthetic, must blend drugs = balanced anesthesia
What drugs as used as adjuncts in anesthesia?
Sedative-hypnotics, opioids, NM blockers
Advantage of an inhaled anesthetic
Rapidly titrate depth of anesthesia
Advantage of intravenous anesthetic
Better tolerated at induction (no mask)
Three examples of high potency inhaled anesthetics we need to know (+ one from LC) and the molecule they’re derived from
Sevolurane, isoflurane, desflurane* (halothane**); ether
One example of low potency inhaled anesthetic
N2O*
How are inhaled anesthetics thought to work (2)
Enhance inhibitory ligand-gated channels (GABAa, glycine in SC) and inhibit excitatory ligand-gated channels (AMPA, NMDA, nAChR)
What is the limit on volatile anesthetic concentration?
Vapor pressure of the liquid
Define MAC; how is MAC expressed and how would you describe a certain dose?
Minimum Alveolar Concetration: median value of the minimum effective concentration to suppress movement in standardized incision, expressed a % and dose given as MAC multiples
Describe lipid solubility and anesthetic potency. What key drug has the highest oil:gas ratio?
Oil : gas partition coefficient –> greater oil solubility (larger coefficient), lower the MAC; Isoflurane
Higher blood solubility means you need more/less molecules to get anesthetic to brain
More
Describe blood solubility and rate of equilibrium. What drug has very low solubility?
Lower the solubility, the faster the induction; N2O
What is the effect of ventilation on induction rate? Biggest effect on what type of anesthetic?
Increased ventilation speeds induction; those w/ high solubility
Anesthesia is maintained at what MAC multiple? What if its used for induction?
1.3 - 1.4x MAC; higher MAC (maybe 3-4x MAC)
Name and describe two considerations for NO (one when NO is turned on and one when it’s turned off)
- Turn on: Trapped air space, due to N2O moving into blood faster than N2 leaves; 2. Turn off: Diffusion hypoxia, due to N2O flooding alveoli, terminate with 100% O2
Why would you want to deliver NO with other inhaled anesthetics. Name the effect.
Second gas effect: N2O creates alveolar “vacuum” which increases respiration, quickening induction of all inhaled anesthetics
All high-potency agents do what to blood pressure, GFR, pCO2?
Decrease; decrease; increase
Describe N2O’s BP/pCO2 effects
N2O does not decrease BP and is less likely to increase pCO2
When used with what, what SE of inhaled anesthetics can occur? Treatment?
Malignant hyperthermia; Dantrolene
What is the most widely used induction agent. Receptor? Advantage? SEs?
Propofol*; GABA; rapid onset; decreases BP/respiratory depression
Explain why Propofol’s half life increases with length of administration
Obeys two-compartment kinetics: the fast phase involves distributing the drug into poorly perfused tissues and the slow phase involves hepatic elimination; injection favors fast phase while infusing favors slow phase
Name another common infused anesthetic and its advantage over Propofol
Etomidate*; does not cause cardiopulmonary SEs
What is the mechanism of ketamine? What state does it produce? SEs?
Inhibits excitatory glutamate signaling via NMDA receptors; dissociated anesthetic state; sympathetic: increased HR/BP/bronchodilation
