Ketamine‑Induced Muscle Tone and Safety Profile

Mechanism of Muscle Tone Effects

Ketamine produces a trance‑like cataleptic state characterized by normal or slightly increased skeletal muscle tone, which is fundamentally different from the pathological rigidity seen with other anesthetics【1】【2】【3】.
The drug’s effect on muscle tone is mediated by NMDA‑receptor antagonism combined with indirect sympathomimetic activity, leading to functional dissociation between limbic (stimulated) and cortical/thalamic (depressed) brain regions【1】【5】.

Patients retain normal pharyngeal‑laryngeal reflexes during ketamine sedation, unlike many other sedatives【1】【2】.
Cataleptic posturing is a typical manifestation of the dissociative state rather than true rigidity【6】【3】.

Even at doses 5–100 times the intended therapeutic range, ketamine does not depress airway or cardiovascular reflexes, making its modest increase in muscle tone clinically manageable【1】【2】【6】.
Chest‑wall rigidity that can impede ventilation is a known adverse effect of high‑dose fentanyl, but this phenomenon is not observed with ketamine【4】.

Enhanced muscle tone after ketamine administration resolves spontaneously and does not require specific pharmacologic intervention【1】【2】.
The dissociative state, including any motor manifestations, typically lasts 10–15 minutes after an IV dose, with full recovery occurring within 15–30 minutes【2】【3】.
If severe rigidity does appear, clinicians should evaluate for concurrent high‑dose opioid use or other causative agents rather than attributing it to ketamine alone【4】.
Co‑administration of a benzodiazepine (e.g., midazolam) can lessen emergence reactions and any concerning motor phenomena, although it does not specifically target the modest increase in muscle tone【1】【5】【2】.