Bloqueadores Neuromusculares | Aula 13 | Farmacologia rápida e fácil | Flavonoide

Summary

In this pharmacology video lecture, the focus is on neuromuscular blockers, explaining their mechanisms of action, classification, and clinical uses. The lecturer begins by discussing nicotinic receptors, their roles in the neuromuscular junction, and how blockers affect skeletal muscle contraction. The historical context of neuromuscular blockers, originating from indigenous Amazonian practices, is also covered. The video elaborates on non-depolarizing blockers (antagonists) and depolarizing blockers (agonists), particularly suxamethonium. Key differences in their effects, uses in anesthesia, and adverse reactions, including potential risks of prolonged apnea and hyperkalemia, are explored, along with their impact on various receptors in the autonomic nervous system.

Takeaways

• 😀 Blockers of neuromuscular function are primarily used in anesthesia to relax skeletal muscles during surgeries and procedures.
• 😀 Neuromuscular blockers have their origins in the Amazon, where indigenous people used curare in hunting to paralyze prey without immediate death.
• 😀 Curare affects muscles in a specific order: first the facial muscles, followed by the limbs, neck, and lastly the diaphragm, leading to asphyxiation.
• 😀 Neuromuscular blockers can be divided into two categories: non-depolarizing (antagonists of nicotinic receptors) and depolarizing (agonists of nicotinic receptors).
• 😀 Non-depolarizing blockers prevent the activation of nicotinic receptors, which results in no muscle contraction and no depolarization.
• 😀 Non-depolarizing blockers vary in the speed of action and duration. Some, like mivacurium, have a rapid effect, while others, like pancuronium, have a long duration.
• 😀 Non-depolarizing blockers can be reversed with medications like neostigmine or edrophonium, which inhibit acetylcholinesterase.
• 😀 Depolarizing blockers, such as succinylcholine, act in two phases: initially causing muscle fasciculations and later leading to muscle paralysis through receptor desensitization.
• 😀 Succinylcholine has a rapid onset of action (about 1 minute) and is mainly used for quick procedures like endotracheal intubation.
• 😀 Succinylcholine can have side effects like prolonged apnea in patients with atypical acetylcholinesterase or high potassium levels, leading to serious complications.
• 😀 The effect of neuromuscular blockers is specific to the NM receptors at the neuromuscular junction, so they don’t affect autonomic receptors, ensuring targeted action.

Q & A

What are the two types of nicotinic receptors mentioned in the script, and where are they located?

The two types of nicotinic receptors are NN and NM. NN receptors are located on the postganglionic neurons of the autonomic nervous system (both sympathetic and parasympathetic), while NM receptors are located on the skeletal muscle tissue, specifically at the neuromuscular junction.

What is the role of acetylcholine in muscle contraction, according to the script?

Acetylcholine is released from vesicles in the somatic neuron at the neuromuscular junction. It binds to the nicotinic receptor, causing it to open and allow sodium to enter, which generates a new action potential. This leads to the depolarization of the muscle membrane, triggering the release of calcium from the sarcoplasmic reticulum, which causes muscle contraction.

What is the historical origin of neuromuscular blockers mentioned in the script?

Neuromuscular blockers have their origins in the Amazon, where indigenous people used mixtures of plants to create poisons, known as curare. These poisons were used on arrows or blow darts for hunting and paralyzed animals by affecting their rapid muscle contractions before eventually causing respiratory paralysis.

How do neuromuscular blockers help in anesthesia and surgical procedures?

Neuromuscular blockers are used as adjuncts in anesthesia to relax skeletal muscles during surgeries. This helps prevent muscle contractions, makes intubation easier, reduces the amount of anesthesia needed, and allows for faster recovery. They also help decrease respiratory depression during surgery.

What is the reverse order of recovery for muscle function after using neuromuscular blockers?

The recovery from neuromuscular blockers occurs in the reverse order of paralysis. The first muscles to recover are the respiratory muscles (diaphragm), followed by the neck muscles, limbs, and finally the eye and facial muscles.

Why can't neuromuscular blockers be taken orally?

Neuromuscular blockers cannot be taken orally because they do not have oral bioavailability. They are typically administered intravenously as they are not absorbed effectively through the gastrointestinal tract.

What are the two main categories of neuromuscular blockers, and how do they differ?

Neuromuscular blockers are divided into two categories: non-depolarizing and depolarizing blockers. Non-depolarizing blockers are antagonists that prevent the receptor from opening, while depolarizing blockers are agonists that initially activate the receptor before causing a sustained block.

What is the mechanism of action of non-depolarizing neuromuscular blockers?

Non-depolarizing neuromuscular blockers act by binding to nicotinic receptors without activating them. This prevents sodium from entering the muscle cell, thus preventing muscle contraction.

How does suxamethonium (succinylcholine) work as a depolarizing neuromuscular blocker?

Suxamethonium is a depolarizing neuromuscular blocker that first binds to the nicotinic receptor and opens it, allowing sodium to enter and depolarize the muscle. However, unlike acetylcholine, suxamethonium stays bound to the receptor, leading to prolonged depolarization, causing muscle fasciculations followed by a flaccid paralysis.

What are the potential adverse effects of suxamethonium?

Suxamethonium can cause prolonged apneic episodes if the patient has atypical acetylcholinesterase or deficiencies in acetylcholinesterase. It can also lead to hyperkalemia, which is dangerous for patients with existing high potassium levels, such as those with burns or extensive tissue damage.