General Anesthetics Flashcards
Anesthesia
Amnesia, analgesia, muscle relaxation, loss of autonomic responses to noxious stimuli, loss of consciousness
EEG Levels 1 and 2
Stupor
EEG level 3
Surgical plane
EEG level 4
Medullary depression
Do benzos cause anesthesia?
No – stupor
Induction vs maintenance anesthesia
One drug is used to induce anesthesia, and another is used to maintain a patient in the surgical plane
Balanced anesthesia
The use of a combination of drugs to produce the effects of an ideal anesthetic. This allows for lower doses of the anesthetics, which avoids complications. Use of adjuncts
Popular adjuncts
Sedative-hypnotics, opioids, NMJ blockers
Inhalation anesthetics
High potency agents that are halogenated derivatives of ether. Sevoflurane, isoflurane, desflurane. All are volatile liquids at room temperature.
Nitrous oxide
Low potency inhalation anesthetic.
How do inhalation anesthetics work?
Current thinking is that they interact with membrane proteins to affect synaptic transmission. Increasing inhibition, decreasing excitiation
How is amount of inhaled anesthetic described?
By its partial pressure in a mixture, can be expressed as a percentage of atmospheric pressure (=760mmHg). So 15.5mmHg is 2%.
What is the maximum partial pressure that is available for a volatile agent?
Its vapor pressure.
MAC
Minimal Alveolar Concentration
The minimum steady state concentration required to suppress movement in response to an incision.
Given as a % of total pressure. 3% in 760mmHG = 3.0 MAC = 22.8mmHg
Is there variation in a dose response relationship for inhalation anesthetics?
No, 99% of individuals are suppressed at 1.2 MAC.
What happens to total mac when multiple agents are administered
They are additive. Agent 1 at 1 MAC, agent 2 at 2 MAC, total effect is 3 MAC of either.
How much inhalation anesthetics needed to suppress autonomics?
More than that to cause analgesia.
What is predictive of anesthetic potency?
Lipid solubility. Greater oil solubility, lower the MAC.
What is predictive of the number of molecules needed to attain therapeutic dose?
Solubility in blood. More soluble, more molecules needed to increase partial pressure in alveoli, induce more slowly.
Another term for partial pressure?
Tension
How to speed up induction?
Increased ventilation rate, decreased blood solubility.
At what MAC is anesthesia usually maintained?
1.3-1.4 MAC, but higher mac multiple is used if inhalation anesthetic used alone
What quality if inhalation anesthetics predict recovery time?
Low blood solubility -> faster recovery time.
What happens to trapped air spaces when nitrous is administered? Why?
Usually administered at a high concentration (70%), nitrous replaces nitrogen, but nitrogen doesn’t move out as fast as nitrous moves in, because N2O has 35X greater blood solubility. Increases pressure in trapped air spaces.
Diffusion hypoxia
When nitrous is turned off, it floods the alveoli as it moves out of the body. So need to terminate with 100% oxygen
Second gas effect
As nitrous leaves the alveoli it creates a vacuum that increases ventilation rate for any other inhalation anesthetic.
Concentration effect
Rate of equilibration for nitrous increases as the concentration increases due to the second gas effect.
For which drugs is the second gas effect greatest?
For drugs with great blood solubilities.
Cardiovascular effects of inhalation anesthetics
Decrease blood pressure.
Which inhalation anesthetics have minimal effects on cardiac output?
Desflurane and isoflurane
Does nitrous have effects on the heart?
No.
Effect of high potency inhalation anesthetics on renal system?
Decrease renal blood flow and GFR.
Effects of inhalation anesthetics on respiration
All except nitrous oxide cause a dose-dependent depression of spontaneous respiration.
All including nitrous oxide decrease ventilatory response to CO2.
Why must arterial CO2 be measured when spontaneously breathing patients?
Because all inhalation anesthetics decrease respiratory drive to CO2.
Effect of inhalation anesthetics on muscle?
Some muscle relaxing activity, lower doses of neuromuscular blockers are required in the presence of these anesthetics.
Elimination of inhalation anesthetics?
The lung. Metabolism in minimal.
What happens when inhalation anesthetics given with succinylcholine?
Can trigger malignant hyperthermia. Muscle rigidity, tachycardia, high fever, rhabdomyolysis, acidosis. Nitrous is safe
How to treat malignant hyperthermia?
Give Dantrolene (interferes with the release of calcium at the ryanodine receptor)
Propofol
Intravenous anesthetic that is a GABAa potentiator. Most widely used induction agent. Not analgesic.
Negative effects of propofol
Decreases BP more than any other induction agent due to vasodilation, respiratory depression, pain on injection.
How is propofol administered, and how is it metabolized?
Administered as fospropofol, metabolized using phase II reactions. After a bolus, recovery is mainly due to redistribution.
Decline in plasma concentration of propofol?
Two-compartment pharmacokinetics. Rapid phase: distribution to poorly perfused tissues including fat. Slow phase: elimination by hepatic metabolism.
Context sensitive half-life
Additional time required for plasma concentration to drop by 50% after an infusion. So when propofol is given via infusion, its half-life is greater than when given as a bolus.
Etomidate
Like propofol, enhances Gaba A signaling, not analgesic. Reduces myocardial O2 consumption. Minimal decreases in BP, HR, CO. Better for cardiac patients, but causes nausea and vomiting.
Ketamine
NMDA receptor antagonist. Produces a dissociative anesthesia. Analgesic even at sub-anesthetic concentrations.
