IV Anesthetics

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Pharmacology

Summary

The realm of IV anesthetics is intricate, with no single drug able to accomplish all the desirable effects of anesthesia: unconsciousness, amnesia, analgesia, inhibition of autonomic reflexes, and skeletal muscle relaxation. The use of these drugs often involves combinations to cater to different stages of general anesthesia: induction, maintenance, and recovery. Central to the understanding of their action is the GABA-A receptor, with most IV anesthetics potentiating its neuro-inhibitory effects. Propofol, a standout among IV anesthetics, is frequently employed in anesthesia induction due to its swift onset and brief duration of action. However, it's associated with challenges such as significant hypotension, respiratory depression, elevated serum triglycerides, and potential anaphylactic reactions from its egg and soy constituents. The profile of etomidate shines for its ability to maintain cardiovascular stability, making it a valuable choice for patients with fragile hemodynamics, even as it may induce adrenocortical suppression. Ketamine diverges by targeting the NMDA receptor, ushering in 'dissociative anesthesia' that maintains both consciousness and respiratory function, while augmenting cardiovascular activity. Briefly, benzodiazepines serve their role as perioperative anxiolytics and sedative-hypnotics, while barbiturates, historically pivotal in anesthesia induction, are now infrequently utilized.

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FAQs

What IV anesthetics are commonly used for the induction of anesthesia and how do they generally function?

Propofol, etomidate, ketamine, benzodiazepines, and barbiturates are the primary IV anesthetics used for anesthesia induction. The majority operate by enhancing the chloride current via the GABA_A receptor complex, leading to a reduction in central nervous system activity.

What are the unique characteristics and potential side effects of propofol?

Propofol is characterized by its rapid onset due to its high lipophilicity, enabling quick distribution to high-perfusion, lipophilic tissues like the brain. Its action is brief, attributed to its swift redistribution to less vascularized areas like muscles and fat. Beyond induction, propofol is effective for anesthesia maintenance and extended ICU sedation. Some adverse effects include elevated serum triglycerides, anaphylactic reactions due to its egg and soybean-based lipid solution, pronounced vasodilation resulting in hypotension, and marked respiratory depression. Notably, it lacks analgesic properties.

What are the unique characteristics and side effects associated with the use of etomidate?

Etomidate, unlike other IV anesthetics, preserves cardiovascular stability and is hemodynamically neutral, exerting minimal effects on blood pressure, heart rate, and cardiac output. However, etomidate inhibits 11-beta hydroxylase, which hinders cortisol synthesis and can lead to adrenocortical suppression.

What are the unique characteristics and adverse effects associated with the use ketamine?

Ketamine obstructs the NMDA receptor complex, resulting in a dissociative anesthesia that includes amnesia. Ketamine has strong analgesic properties and perserves respiratory function, making it ideal for conscious sedation. However, patients may encounter disturbing emergence reactions like vivid dreams or hallucinations. Additionally, it provokes cardiovascular stimulation due to catecholamine release, a factor that also triggers bronchodilation.

What roles do benzodiazepines and barbiturates play in anesthesia?

Benzodiazepines offer anxiolytic and sedative-hypnotic benefits, making them suitable for preoperative use and conscious sedation during minor procedures, such as colonoscopies. IV barbiturates, like thiopental, were once popular for anesthesia induction but are now infrequently used. Thiopental distinguishes itself as a rapid-onset, lipid-soluble barbiturate with a fleeting duration of action.

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