Flashcards in Lecture 5 - Volatile Anesthetics Deck (17):
what are the inhaled anesthetics?
which is a gas at room temp? which are liquids?
What can they reliably be used for?
what desired effect is not achieved ?
liquids at room temperature -- Sevoflurane, Desflurane, Isoflurane
Gas at room temperature -- N2O
Reliable for: Unconsciousness, Amnesia, Immobility
They are not analgesics
Patients body will still respond to the pain (eg tachycardia and HTN)
what is monitored when the patient is under anesthesia ?
which levels allow for monitoring concentrations in the brain?
Vital Signs: ECG, HR, BP, O2 Sats,
Spontaneous Respiration -- if the patient is breathing on their own
(tachypnic would indicate pain)
Movement in response to surgery
Levels of Exhaled gases --
O2, CO2, N2O, volatile anesthetics
Correlate with levels in the brain
what are the mechanisms behind:
-CNS depression -
Poorly understood overall
Immobility -- acting on the spinal cord
Amnesia - hippocampus, amygdala, cerebral cortex
Enhance inhibitory NTs -- GABA and Glycine
Block Excitatory -- NMDA
what is Minimum Alveolar Concentration (MAC)
what is the goal MAC for surgical anesthesia ?
which of the inhaled anesthetic agents cannot achieve this goal on its own?
Definition: Concentration of anesthetic required to suppress movement to surgical stimulus in 50% of patients
Goal MAC = 1 - surgical anesthesia
N2O Max MAC = .7; must be used in combination with other drugs
what are 5 important characteristics to know about inhaled anesthetics
The dose needed to achieve MAC = 1
(lowest to highest -- Isoflurane < Sevoflurane < Desflurane < N2O)
Blood Gas Partition Coefficient (solubility of the gas in the blood) (most soluble to least -- Iso > Sevo > N20 > Des)
Blood brain coefficienct (measure of brain solubility)
(Sevo, Iso, Des, N2O
Oil Gas partition coefficient -- lipid solubility
(Iso> Sevo> Des> N20)
% Metabolized -- clinically insignificant
Isoflurane -- charactersitic profile
whats the significance of its solubility?
the most lipid and blood soluble --- Longer emergence;
second most brain soluble ---
Least dose needed for MAC = 1 --- most potent
○ Not very expensive --- used a lot
Sevoflurane characteristic profile
• Medium solubility- good for longer cases and obese patients
• Medium potency
• Not very expensive
Used for inhaled induction in pediatrics - (for kids woh hate needles; can knock them out first)
Desflurane characteristic profile
• Least soluble- good for longer cases and obese patients
• Least potent- highest dose needed to achieve 1 MAC, so have to use a lot of it
Most expensive compound --- therefore not used that often
N2O Characteristic profile
• N2O: Not used much
○ Increases n/v
○ Not good for surgeries on spaces/organs that contain air (bowel, lungs ear) → will cause distension because diffuses faster into air filled space than nitrogen can leave
○ Cannot achieve 1 MAC alone, so have to use in combination with another agent
○ In pediatrics, can use for inhalation induction along with sevoflurane
Not very expensive
equilibriation between what three partial pressures?
how long does it take P(brain) to equilibriate wiht PA
how is Pbr measured?
• PA ↔ Pa ↔ Pbr
• Alveolar arterial brain partial pressure
• Uptake from alveoli into systemic circulation
• Uptake from circulation into brain- site of action of anesthetics
• Redistribution of anesthetic throughout body
6-12 minutes for Pbr to equilibriate with PA
• P alveolar mirrors Pbr -- can't measure the Pbr directly
§ P-alveolar -- also measure of rate of induction and recovery from anesthesia; also a measure of potency
Factors Determining PA:
Solubility -- want to be less solubule in blood than it is in lipid and brain (N2O
Inspired anesthetic partial pressure (PI)
Alveolar Ventilation -- Increased ventilation accerlates induction by more rapidly increasing PA
Cardiac Output -- Low CO = faster induction; high CO = harder to load up quickly
Emergence From Anesthesia ---
what happens when the gas is turned off?
at what MAC does a patient awake?
Partial pressure gradient is reversed
• Stored anesthetic in tissues diffuses down its concentration gradient into the blood and is exhaled
wake up; MAC = .2-.3
Factors for Emergence --
• Solubility of agent
• Less soluble agents will allow faster emergence
• Depends on alveolar ventilation
• More ventilation allows faster emergence
• Depends on cardiac output
• Lower CO (slower moving train) allows faster emergence; can offload all of the gas into the Alveoli, which then gets exhaled and the patient emerges faster; but this plays a very small role
Inhaled anesthetics --
effects on the Circulatory system (MAP, HR, other)
which can prolong QT interval?
VA -- the volatile anesthetics cause vasodilation and decrease MAP and SVR
N20 = no change
HR -- Small increase (Iso>des); Small Decreased (N2O and sevo)
VAs are cardioprotective (ischemic preconditioning)
VA(esp Sevo) may prolong QT
Inhaled anesthetics --
which drugs are best for inhalation induction? why?
why must patients be intubated on these drugs?
Increase respiratory rate and decrease TV
Decrease in FRC --
Increase in dead space
Inhalation induction using sevo and N2O because are nonpungent
Depression of pharyngeal and laryngeal reflexes ---- and must intubate
Inhaled anesthetics: CNS effects
which has some mild analgesic properties?
All cause cerebral vasodilation
Increased cerebral blood flow (CBF)
Increased intracranial pressure (ICP)
Uncoupling effect -- paradoxically increased CBF but decrased Cerebral metabolic rate
analgesic: N2O has some mild analgesic properties