💊 Do Muscle Relaxants Stop the Heart During Anesthesia?🫀😨

♦️ Why Do We Use Muscle Relaxants?

🔷 Introduction

During anesthesia and surgery, sedatives and analgesics are administered, but muscle relaxants are often added as well. While it’s easy to understand the need to induce sleep and relieve pain, why do we also deliberately paralyze skeletal muscles?

The main reasons include:

In Japan, the most commonly used agent in routine clinical practice is rocuronium (brand name Esmeron®/Eslex® in Japan).
In other countries, rocuronium, vecuronium, cisatracurium, atracurium, and succinylcholine are frequently used depending on the clinical situation.

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🔷 During Tracheal Intubation

Although not required for every procedure, most general anesthetics involve tracheal intubation. This means inserting a breathing tube into the trachea through the vocal cords in order to secure the airway and provide controlled ventilation.

Imagine trying to open the mouth of a sleeping person, inserting a laryngoscope, and pushing a tube into the throat — the patient would reflexively resist!😅
Even if unconscious, patients may tense up, clench their jaw, or bite down on the laryngoscope, making intubation difficult and potentially traumatic. In addition to sedatives and opioids, muscle relaxants are given to ensure safer and smoother intubation.

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🔷 During Surgery

When adequate anesthesia and analgesia are maintained, patients usually do not move during surgery. Therefore, muscle relaxants are not always essential. For example, in limb surgery or superficial procedures, relaxants may be used only at the time of intubation.

They become especially important in abdominal or laparoscopic surgery. Although surgery is possible without full relaxation, unexpected movements or abdominal wall tension can obscure the surgical field.
In laparoscopy, where surgeons work within a narrow space, inadequate relaxation increases the risk of accidental organ or vessel injury.

For these reasons, adequate neuromuscular blockade is generally maintained throughout such procedures☝️.

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♦️ But the Heart Is Also a Muscle — Why Doesn’t It Stop?

The short answer: it doesn’t stop. And it absolutely must not stop! If it did, the operation would be over immediately.

The reason lies in the physiology of different muscle types.

Neuromuscular blocking agents act only on skeletal muscle contraction mechanisms. They have no effect on cardiac or smooth muscle, which rely on different molecular pathways.
This is why the heart keeps beating during anesthesia, even when the rest of the body is fully paralyzed.

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A Side Note: Misrepresentation in Japanese TV Dramas😅

In an old TV drama, the protagonist was injected with a muscle relaxant through clothing, supposedly subcutaneously or intramuscularly. The character collapsed instantly with eyes wide open. In reality, it doesn’t work like that:

• Intramuscular or subcutaneous injection would take several minutes, not seconds.
• Even intravenous administration takes a short delay before onset.
• Yes, neuromuscular blockers cause paralysis with eyes open, but the “instant collapse” trope is exaggerated.
• And if the drug was strong enough to knock someone down immediately, it would likely be a fatal overdose.

So, while dramatic, the portrayal was physiologically inaccurate. Well, dramas and movies often exaggerate things or skip over the finer details just to make the story more entertaining. 😅

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📝 Summary : Take Home Message

• Neuromuscular blocking agents are among the most potent and high-risk drugs used in medicine. Because of this, their use and storage are strictly regulated by hospital pharmacies, and occasional reports of missing vials make the news.
• Clinicians must remain vigilant and handle these agents with the utmost care.

📚 References & Further reading