From the Guidelines
Yes, trismus (jaw muscle rigidity) can occur after administration of succinylcholine, as it causes an initial increase in muscle tone, most evident in the jaw muscles, which can lead to resistance to mouth opening within the first 60–90 s after administration. Succinylcholine, a depolarizing neuromuscular blocking agent commonly used for rapid sequence intubation, initially causes muscle fasciculations before paralysis. In some patients, these fasciculations can lead to masseter muscle rigidity or trismus, making mouth opening and intubation difficult. This reaction is more common in children than adults, with an incidence of approximately 0.3-1% in adults and up to 14% in children. The mechanism involves the depolarizing effect of succinylcholine on muscle membranes, causing sustained contraction of the masseter muscles. This reaction may be more pronounced in patients with underlying myopathies, particularly malignant hyperthermia susceptibility, as noted in the study published in Anaesthesia in 2021 1. When trismus occurs after succinylcholine, it should raise concern for possible malignant hyperthermia, a rare but potentially fatal hypermetabolic condition. Clinicians should be prepared with alternative airway management strategies if trismus develops and should monitor for other signs of malignant hyperthermia such as hyperthermia, tachycardia, and hypercarbia.
Some key points to consider:
- The incidence of trismus after succinylcholine administration is higher in children than adults.
- The reaction is more pronounced in patients with underlying myopathies, particularly malignant hyperthermia susceptibility.
- Clinicians should be prepared with alternative airway management strategies if trismus develops.
- Monitoring for other signs of malignant hyperthermia is crucial when trismus occurs after succinylcholine administration.
The most recent and highest quality study, published in Anaesthesia in 2021 1, provides the strongest evidence for the occurrence of trismus after succinylcholine administration. Other studies, such as those published in 2020 1 and 2018 1, also support the use of succinylcholine and its potential side effects, but the 2021 study provides the most up-to-date and relevant information on the topic. Additionally, guidelines for the management of tracheal extubation, published in 2012 1, provide recommendations for the treatment of laryngospasm, which can be related to trismus. However, the primary concern is the potential for malignant hyperthermia, and clinicians should prioritize monitoring for this condition when administering succinylcholine.
From the FDA Drug Label
Malignant hyperthermia frequently presents as intractable spasm of the jaw muscles (masseter spasm) which may progress to generalized rigidity, increased oxygen demand, tachycardia, tachypnea and profound hyperpyrexia Jaw rigidity
Succinylcholine administration can cause Trismus (lockjaw), as it may lead to malignant hyperthermia, which frequently presents with intractable spasm of the jaw muscles (masseter spasm), and jaw rigidity is also reported as an adverse reaction 2, 2.
From the Research
Succinylcholine Administration and Trismus
- Succinylcholine administration can cause trismus, also known as masseter muscle rigidity or lockjaw, as reported in several studies 3, 4, 5.
- Trismus is a rare but potentially life-threatening complication of succinylcholine-induced neuromuscular blockade, requiring prompt intervention 3, 5.
- The condition can present as masseter spasm, sometimes referred to as "jaws of steel," and may progress to malignant hyperthermia if not properly managed 4, 5.
- The pathophysiology, diagnosis, and treatment of malignant hyperthermia, which can be associated with trismus, have been reviewed in the literature 5.
Clinical Implications
- Despite the risks, succinylcholine is still used in some clinical settings, such as rapid sequence induction and procedures requiring brief muscle relaxation 6.
- However, some studies suggest that the use of succinylcholine for endotracheal intubation should be limited or discontinued due to the availability of alternative muscle relaxants with fewer side effects 6, 7.
- New muscle relaxants and reversal agents, such as gantacurium and calabadion, are being developed and tested, which may offer safer alternatives to succinylcholine in the future 7.