Trismus

Description

Trismus is defined as the complete inability to open the mouth and can result from a number of causes ranging from preexisting pathology to acute intraoperative pathology
Perioperatively, trismus may result in difficulty with securing the airway or as a precursor of malignant hyperthermia (MH).

Epidemiology

Incidence

Seen in 1–4% of general anesthetic cases

Prevalence

More common in pediatrics; 40–50% of cases are seen in patients less than 10 years of age.

Morbidity

Associated with MH. 40–50% of trismus patients have a positive halothane contracture test.

Mortality

Death in less than 1% from lost airway
One to five percent mortality from treated MH.

Etiology/Risk Factors

Pediatrics <10 years of age
- Patients with an increased association for MH such as Duchenne's muscular dystrophy, central core disease, osteogenesis imperfecta, and King–Denborough syndrome.
- Strabismus surgery has a slight increased risk.
Preexisting pathologic processes
- Peritonsillar abscesses
- Temporomandibular disorder (TMD)
- Bruxism
- Pericoronitis
- Tetanus
- Radiation or surgery to the head or neck
Medications such as amphetamines

Physiology/Pathophysiology

Trismus describes a common end-point of an inability to open the mouth.
MH. Trismus is a feared predecessor of MH; it has a demonstrated association. MH is a pharmacogenetic disorder of the ryanodine receptor. It is characterized by the triggering of acute skeletal muscle hypermetabolism with increased oxygen consumption and carbon dioxide production.
Peritonsillar abscess from tonsillitis
Temporal mandibular joint disorders
Bruxism (grinding of teeth) is often seen in patients in a coma and can lead to trismus. It may be relieved by botulin toxin injection.
Pericoronitis describes inflammation around the crown of a tooth resulting from an infection.
Tetanus can result from the bacteria Clostridium tetani and describes the toxicity to nerves that leads to muscle rigidity or "lock jaw."
Radiation or surgery to the head and neck
Medications
- Injection of local anesthetics can cause injury to the temporalis and medial pterygoid muscles causing trismus.
- Amphetamines and phenothiazines are thought to cause motor disturbances of the trigeminal nerve and spasm of masticatory muscles leading to bruxism and possible trismus.

Preventative Measures

In patients with a known history or family history of MH, avoid triggering agents such as succinylcholine and volatile agents. Use of a total IV anesthetic or regional technique should be utilized.
Carefully assess for a difficult airway with preexisting trismus
- A mouth opening <3 finger breaths or 20 mm is considered significant.
Treatment for preoperative trismus includes NSAIDS, muscle relaxants, heat, exercises, and range of motion devices.

Diagnosis ⬆ ⬇

The inability to open the mouth despite an abolition of twitches after neuromuscular relaxation is administered.
MH; signs include trismus, total body rigidity, tachycardia, mixed respiratory and metabolic acidosis, hypercarbia (early sign), increased temperature (late sign), and myoglobinuria.

Differential Diagnosis

Masseter muscle rigidity (MMR) describes difficulty with opening the mouth, but not the complete inability.
Inadequate depth of anesthesia or neuromuscular relaxation
Neuroleptic malignant syndrome
Etomidate myoclonus

Treatment ⬆ ⬇

Trismus after induction
- Bag mask ventilation possible
  - Asleep nasal or oral fiberoptic intubation
  - Light wand
  - Retrograde wire-assisted intubation
  - Awaken patient
- Bag mask ventilation difficult/impossible
  - Blind nasal intubation
  - Awaken patient and perform a nasal or oral fiberoptic intubation.
  - Surgical airway
Pre-existing trismus
- Bag mask ventilation appears possible
  - Awake or asleep nasal or oral fiberoptic intubation
  - Advanced airway technique after induction: Light wand, retrograde wire-assisted intubation
- Bag mask ventilation appears difficult/impossible
  - Awake nasal or oral fiberoptic intubation
  - Surgical airway
If patient appears "light," resulting in an inability to open the mouth, increase the depth of anesthetic.
If MH is suspected, discontinue the surgery and anesthetic.
- If an emergency case, change anesthetic to nontriggering MH agents and monitor for signs of MH.
- MH treatment
  - Discontinue triggering agents (volatile agent)
  - Hyperventilate, with 100% oxygen at high flow
  - Start dantrolene at 2.5 mg/kg, repeat every 5 minutes until symptoms improve or up to 10 mg/kg (maximum dose may need to be exceeded in some cases). Consider continuing dantrolene at 1 mg/kg for up to 24 hours
  - Send arterial blood gases and treat metabolic acidosis with bicarbonate 1–2 mEq/kg to maintain pH
  - Monitor CK, electrolytes, and myoglobin until normalized. Check hepatic function
  - Consider placing arterial or central venous line
  - Treat hyperkalemia with calcium, glucose/insulin, and bicarbonate.
  - Maintain adequate urine output with hydration and consider mannitol for renal protection
  - Cool patient's core body temperature to 37–39°C

Follow-Up ⬆ ⬇

If trismus is the result of pre-existing conditions, consider labeling the patient as a "Difficult Airway."
If MH is suspected, admit the patient for 24 hours to monitor for manifestations. Discuss workup (caffeine test, muscle biopsy).

References ⬆ ⬇

Glahn KPE , Ellis FR , Halsall PJ , et al. Recognizing and managing a malignant hyperthermia crisis: Guidelines from the European Malignant Hyperthermia Group. Br J Anaesth. 2010;105(4):417–420.
Litman RS , Rosenberg H. Malignant hyperthermia. JAMA. 2005;293(23):2918–2924.
Rosenburg H. Trismus is not trivial. Anesthesiology. 1987;67(4):453–455.
Schwartz L , Rockoff MA , Koka BV. Masseter spasm with anesthesia. Anesthesiology. 1984;61(6):772–775.
Shulman DH , Shipman B , Willis FB. Treating trismus with dynamic splinting: A cohort case report. Adv Ther. 2008;25(1):9–16.
Van der Spek AF , Fang WB , Ashton-Miller JA , et al. The effects of succinylcholine on mouth opening. Anesthesiology. 1987;67(4):459–465.

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Basics ⬇

Incidence

Prevalence

Morbidity

Mortality

Diagnosis ⬆ ⬇

Treatment ⬆ ⬇

Follow-Up ⬆ ⬇

References ⬆ ⬇

Additional Reading ⬆ ⬇

Codes ⬆ ⬇

Clinical Pearls ⬆ ⬇

Author(s) ⬆