Hypnic jerks, also known as sleep starts or myoclonic jerks, are sudden, involuntary muscle contractions that commonly occur as a person is falling asleep. These brief muscle twitches can sometimes be strong enough to wake an individual and are typically accompanied by a sensation of falling. Though inducing anesthesia is sometimes colloquially referred to as putting someone to sleep, it has important differences as well as parallels with true sleep. But can these hypnic jerks happen under anesthesia?

While sleep is a natural process that cycles through various stages, anesthesia induces an artificially controlled state. This difference impacts muscle control and the nervous system, typically suppressing involuntary movements like hypnic jerks, though they can occur in specific scenarios.

Hypnic jerks occur due to a complex interaction of the nervous system and muscular response, thought to be a result of physiological shifts as the brain transitions from wakefulness to sleep. The exact cause is not fully understood, but it’s believed to involve a sudden, brief activation of the motor cortex, the area of the brain that controls voluntary movements. Fatigue, stress, or caffeine consumption can increase the likelihood of hypnic jerks. While they are usually harmless, hypnic jerks may startle an individual momentarily before deeper sleep takes over 1–3.

Anesthesia is designed to inhibit the central nervous system, blocking pain, and typically ipreventing patient movement, sometimes through direct blockade of neuromuscular signals. There are several levels of anesthesia, ranging from light sedation, where the patient remains conscious and responsive, to general anesthesia, which is used for major surgeries and renders the patient completely unconscious. In general anesthesia, muscle relaxants are often administered, which further suppress muscle movement and prevent reflexive jerks, twitches, or hypnic jerks 4,5.

In light sedation, the body might occasionally display subtle muscle movements, but they aren’t classified as hypnic jerks. These movements could result from incomplete suppression of motor responses, though they tend to be rare and are usually minimal.

Under general anesthesia, hypnic jerks, which are associated with natural sleep cycles and occur during the transition to sleep, are unlikely to happen. The controlled, artificial state of general anesthesia does not allow the nervous system to operate in the same way as it does in natural sleep, meaning hypnic jerks, which are naturally occurring muscle contractions in sleep, are typically suppressed. However, in rare cases, myoclonic movement (sudden, unintentional twitching of muscles) can be a side effect after general anesthesia. These movements typically last a few days and resolve completely 6,7.

In particular, myoclonus is a known side effect of propofol and can interfere with surgery and possibly precipitate patient injury. In one case of a 23-year-old patient undergoing an osteoblastoma resection, the myoclonus did not improve after deepening anesthesia with propofol, administering opioid boluses, or discontinuing the lidocaine infusion. However, the myoclonus ceased after reducing the propofol infusion and increasing ketamine and opioid infusions 8.

Under anesthesia, hypnic jerks are unlikely due to the suppressed state of the nervous and muscular systems. For patients undergoing surgery, anesthesia’s primary goal is to prevent

involuntary movements and ensure comfort and safety, making hypnic jerks under anesthesia an exceedingly rare occurrence.

References

1. Hypnic Jerks: Why You Twitch In Your Sleep. https://www.sleepfoundation.org/parasomnias/hypnic-jerks.

2. Hypnic Jerks (Sleep Starts): Causes and Treatments. https://www.health.com/hypnic-jerks-8710756.

3. Vetrugno, R. & Montagna, P. Sleep-to-wake transition movement disorders. Sleep Med. 12 Suppl 2, (2011). DOI: 10.1016/j.sleep.2011.10.005

4. Billard, V. & Servin, F. Light or deep general anaesthesia: does it matter and how to assess it? Eur. J. Anaesthesiol. 25, 781–783 (2008).doi: 10.1017/S0265021508004705

5. Types of Anesthesia – Anesthesiology | UCLA Health. https://www.uclahealth.org/medical-services/anesthesiology/types-anesthesia.

6. Budde, A., Freestone-Bernd, M. & Vaida, S. Rhythmic movement disorder after general anesthesia. J. Anaesthesiol. Clin. Pharmacol. 28, 371 (2012). DOI: 10.4103/0970-9185.98347

7. Lee, J. J. et al. Myoclonic movement after general anesthesia: A case report and review of the literature. Medicine (Baltimore). 97, e0141 (2018). doi: 10.1097/MD.0000000000010141

8. Chao, S., Khan, R., Lieberman, J. & Buren, M. Propofol-induced myoclonus during maintenance of anaesthesia. Anaesth. Reports 11, e12253 (2023). DOI: 10.1002/anr3.12253