inhalation Agents UPDATED ACTUAL
Exam Questions and CORRECT
Answers
Nitrous Oxide - CORRECT ANSWER - Nitrous oxide is a low-molecular-weight, odorless to
sweet-smelling nonflammable gas of low potency and poor blood solubility
(blood:gas partition coefficient 0.46) that is most commonly administered in combination with
opioids or volatile anesthetics to produce general anesthesia. Although nitrous oxide is
nonflammable, it will support combustion.
Physical Properties - CORRECT ANSWER - •Volatile agents are either gases or liquids with a
vapor pressure high enough so that they can be used by inhalation
•Vapor Pressure
[The pressure exerted by the molecules of a liquid as they bump into each other and the sides of
their container]
•Chief reason that agents like ether are not used anymore [flammability]
-All agents used in US today are non-flammable
Pharmacokinetics - CORRECT ANSWER - - Object of general anesthesia is to produce a
brain anesthetic partial pressure sufficient for surgery
•Gas delivery from the machine to the brain
[depends upon a series of partial pressures]
•We indirectly regulate brain Pp by adjusting vaporizer
•We indirectly monitor brain Pp by monitoring alveolar Pp with respiratory gas
spectrophotometer
-Bispectral Index monitoring (BIS)
•
How quickly patients go to sleep depends upon several factors: - CORRECT ANSWER --
Machine
, [The anesthesia circuit must be filled with gas before it can get to the patient]
- Rate at which this happens can be calculated using time constants
t = volume of container / flow into it
-20 L circuit with O2 flow rate of 10 LPM should take 2 minutes to fill the circuit (VACUUM)
the Time Constant - CORRECT ANSWER - = capacity / flow
-or-
= vol of container/ flow into it
1T = time to a 63% change
Explain how to calculate 1T to fill a container to 63% capacity - CORRECT ANSWER - -2x
(t) = 86% 3x (t) = 95% 4x (t) = 98%
-Therefore it takes 8 minutes to fill the circuit with approximately 100% of new gas [4x (t)]
-Or use the O2 flush valve at 35-75 L/min to cut time to under a minute
Machine Patient's airway (FI/FD ratio) - CORRECT ANSWER - **Machine to Patient's
airway (FI/FD ratio)**
- FD (what the vaporizer delivers) is affected by the characteristics of the anesthesia circuit
-Carrier flows, valve placement
-Solubility of the agent in the machine parts
[Plastics, soda lime, etc.]
- FD to FI gradient narrows with a non-rebreathing system (high carrier gas flows; decrease tau)
[Widens with absorption by the machine]
Patient's airway to Lungs (FA/FI ratio) - CORRECT ANSWER - **Patient's airway to Lungs
(FA/FI ratio)**
Exam Questions and CORRECT
Answers
Nitrous Oxide - CORRECT ANSWER - Nitrous oxide is a low-molecular-weight, odorless to
sweet-smelling nonflammable gas of low potency and poor blood solubility
(blood:gas partition coefficient 0.46) that is most commonly administered in combination with
opioids or volatile anesthetics to produce general anesthesia. Although nitrous oxide is
nonflammable, it will support combustion.
Physical Properties - CORRECT ANSWER - •Volatile agents are either gases or liquids with a
vapor pressure high enough so that they can be used by inhalation
•Vapor Pressure
[The pressure exerted by the molecules of a liquid as they bump into each other and the sides of
their container]
•Chief reason that agents like ether are not used anymore [flammability]
-All agents used in US today are non-flammable
Pharmacokinetics - CORRECT ANSWER - - Object of general anesthesia is to produce a
brain anesthetic partial pressure sufficient for surgery
•Gas delivery from the machine to the brain
[depends upon a series of partial pressures]
•We indirectly regulate brain Pp by adjusting vaporizer
•We indirectly monitor brain Pp by monitoring alveolar Pp with respiratory gas
spectrophotometer
-Bispectral Index monitoring (BIS)
•
How quickly patients go to sleep depends upon several factors: - CORRECT ANSWER --
Machine
, [The anesthesia circuit must be filled with gas before it can get to the patient]
- Rate at which this happens can be calculated using time constants
t = volume of container / flow into it
-20 L circuit with O2 flow rate of 10 LPM should take 2 minutes to fill the circuit (VACUUM)
the Time Constant - CORRECT ANSWER - = capacity / flow
-or-
= vol of container/ flow into it
1T = time to a 63% change
Explain how to calculate 1T to fill a container to 63% capacity - CORRECT ANSWER - -2x
(t) = 86% 3x (t) = 95% 4x (t) = 98%
-Therefore it takes 8 minutes to fill the circuit with approximately 100% of new gas [4x (t)]
-Or use the O2 flush valve at 35-75 L/min to cut time to under a minute
Machine Patient's airway (FI/FD ratio) - CORRECT ANSWER - **Machine to Patient's
airway (FI/FD ratio)**
- FD (what the vaporizer delivers) is affected by the characteristics of the anesthesia circuit
-Carrier flows, valve placement
-Solubility of the agent in the machine parts
[Plastics, soda lime, etc.]
- FD to FI gradient narrows with a non-rebreathing system (high carrier gas flows; decrease tau)
[Widens with absorption by the machine]
Patient's airway to Lungs (FA/FI ratio) - CORRECT ANSWER - **Patient's airway to Lungs
(FA/FI ratio)**
