DM1 Pt4-3 Volatile Agents Flashcards
What are the advantages of using volatile agents for maintenance of anesthesia?
- Easy control of anesthesia depth by changing the vaporizer concentration.
- Rapid recovery since volatile agents are expelled via expiration, not metabolism.
Why is recovery from anesthesia fast with volatile agents?
Volatile agents are expelled predominantly through exhalation rather than metabolized, meaning minimal drug accumulation occurs even with prolonged use.
What are the disadvantages of using volatile agents for maintenance of anesthesia?
- Requires an anesthetic machine, vaporizer, and oxygen as a carrier gas, unsuitable for field conditions.
- Requires intubation for safe delivery.
- Volatile agents pose health hazards for humans if not properly scavenged.
How do volatile agents produce anesthesia?
Volatile agents are absorbed into the bloodstream through the lungs and distributed to body tissues. Their lipophilic nature allows them to cross the blood-brain barrier, though the exact mechanism of action remains unknown.
How does the blood
partition coefficient affect anesthesia induction and recovery?
Agents with higher blood solubility (higher blood
partition coefficient) have slower induction and recovery due to the need to saturate a larger tissue reservoir before reaching an effective brain concentration.
Which modern volatile agent has the lowest solubility in blood?
Sevoflurane has the lowest solubility in blood, leading to the fastest induction and recovery from anesthesia, followed by isoflurane and then halothane.
What is the Minimal Alveolar Concentration (MAC), and what does it represent?
MAC is the alveolar concentration of an anesthetic at 1 atmosphere required to prevent movement in response to a supramaximal stimulus in 50% of patients. It is used to compare the potency of different volatile agents.
How does MAC relate to the potency of volatile anesthetic agents?
Agents with lower MAC values are more potent. For example, halothane has a MAC of 0.9%, making it more potent than isoflurane (MAC 2.1%) and sevoflurane (MAC 2.6%).
What are the haemodynamic effects of halothane compared to isoflurane and sevoflurane?
Halothane causes myocardial depression and hypotension, and sensitizes the heart to catecholamine-induced arrhythmias. Isoflurane and sevoflurane are more cardiovascularly stable, causing vasodilation and dose-dependent hypotension.
How are modern volatile agents metabolized by the liver?
Halothane has significant liver metabolism (30%), which can lead to hepatic dysfunction with repeated exposure. Isoflurane and sevoflurane have minimal liver metabolism.
Why is sevoflurane considered more suitable for faster recovery from anesthesia than halothane and isoflurane?
Sevoflurane has the lowest blood
partition coefficient (0.6), leading to the quickest induction and recovery times compared to isoflurane and halothane.
How is the MAC value used to determine the concentration of volatile agents for anesthesia?
Typically, 1.5 times MAC is required to maintain anesthesia during surgery. However, the use of other anesthetic and analgesic drugs can reduce the MAC value, allowing for a lower volatile agent concentration.
How do alpha-2 agonists affect the concentration of volatile agents?
Alpha-2 agonists significantly reduce the concentration of volatile agents required, allowing lower concentrations to be used during anesthesia.
What factor can cause a difference between the dialed concentration and delivered concentration of volatile agent in a rebreathing system?
In a rebreathing system, the concentration of volatile agent in the patient’s lungs may initially be lower than the dialed concentration due to uptake by the lungs and tissues. High gas flow rates are used to stabilize the concentration.
Why are high flow rates used at the beginning of anesthesia with volatile agents?
High flow rates (3-4 liters/min) are used for the first 10-15 minutes to ensure the volatile agent concentration in the breathing system stabilizes and matches the dialed concentration.
