General anesthetics

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General anesthetics


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General anesthetics

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A 40-year-old woman is brought to the emergency department by local paramedics after a motor vehicle accident. The patient is conscious and can provide a history. Medical history is significant for major depressive disorder and type II diabetes mellitus. Current medications include sertraline and metformin. She does not consume tobacco, alcohol, or illicit substances. Temperature is 37.5°C (99.5°F), pulse is 98/min, respirations are 17/min, and blood pressure is 122/62 mmHg. Radiography reveals a displaced fracture of the left femur. The patient undergoes surgical repair with general anesthesia. Fifteen minutes after the surgery begins, the patient’s temperature is 39.0°C (102°F), pulse is 130/min, respirations are 24/min, and blood pressure is 160/110 mm Hg. Generalized muscle rigidity is noted in all four extremities. Which of the following best characterizes the pharmacological agent used to manage this patient’s condition?  

External References

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Enflurane p. 570

seizures with p. 252

Seizures p. 535

enflurane p. 252


General anesthetics are medications used to induce an anesthetic state in patients who are about to go under surgery.

The anesthetic state refers to a number of conditions that make surgery tolerable for the patient and more manageable for the surgeon.

The conditions include: unconsciousness, where the person isn’t aware of themselves or their environment; sedation, so they don’t move in response to painful stimulation; analgesia, so they don’t feel pain; and amnesia, so they don’t remember the procedure.

Local anesthetics are different in the fact that they only block pain sensation in a specific part of the body, and don’t affect consciousness.

Okay, to achieve the anesthetic state, general anesthetics depress the central nervous system. In other words, they diminish the total amount of action potentials that are constantly firing in the brain. The generation of these action potentials depends on excitatory and inhibitory synapses.

Excitatory, means that the neurotransmitters released into the synaptic space stimulate the postsynaptic neuron to start an action potential.

The main neurotransmitter involved is glutamate, which binds to postsynaptic NMDA receptors, so some general anesthetics work by blocking these receptors.

Inhibitory synapses, on the other side, do the opposite; they release the inhibitory neurotransmitter called GABA, which binds to the postsynaptic neuron and keep it from firing.

So certain anesthetics work by stimulating these GABA receptors or by increasing their sensitivity to GABA.

Moving on, there are two main phases in anesthesia: induction, which is when the patient enters the anesthetic state; and maintenance, when the anesthetic state is prolonged for as long as required.

Some anesthetics are better for induction, while others are better for maintenance.

Now, depending on how they’re administered, there are two classes of general anesthetics: parenteral and inhalational anesthetics.

Parenteral anesthetics are given by injection into a vein. They’re highly lipophilic agents that are commonly used for anesthetic induction in a single intravenous injection, although some of them, in special situations, can be used for maintenance by continuous intravenous infusion.

Once in the bloodstream, these medications travel through the body to highly lipophilic tissues that receive a lot of blood, like the brain and spinal cord. There, they can induce the anesthetic state.


  1. "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
  2. "Rang and Dale's Pharmacology" Elsevier (2019)
  3. "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
  4. "General anesthesia" Anesth Prog (1991)
  5. "General anaesthesia for patients with a history of a contrast medium-induced anaphylaxis: a useful prophylaxis?" The British Journal of Radiology (2017)
  6. "Effects of halothane on GABA(A) receptor kinetics: evidence for slowed agonist unbinding" J Neurosci (2000)
  7. "Muscle relaxation and increasing doses of propofol improve intubating conditions" Canadian Journal of Anesthesia/Journal canadien d'anesthésie (2003)

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