 |
Motion sickness is a symptom complex that usually includes nausea, often accompanied by vague abdominal discomfort, vomiting, dizziness, and related symptoms; it is caused by repetitive angular and linear acceleration and deceleration. Behavioral change and drug therapy can help prevent or control symptoms.
Individual susceptibility to motion sickness varies greatly. However, motion sickness is more common among women, and incidence ranges from < 1% on airplanes to nearly 100% on ships in rough seas and upon becoming weightless during space travel.
Etiology
Excessive stimulation of the vestibular apparatus by motion is the primary cause. Afferent pathways from the labyrinth to the vomiting center in the medulla are undefined, but motion sickness occurs only when the 8th cranial nerve and cerebellar vestibular tracts are intact. Movement via any form of transportation, including ship, motor vehicle, train, plane, spacecraft, and playground or amusement park ride, can cause excessive vestibular stimulation.
The trigger may involve conflicting vestibular, visual, and proprioceptive inputs. For example, visual input that indicates being stationary may conflict with the sensation of movement (eg, looking at an apparently unmoving ship cabin wall while sensing the ship rolling). Alternatively, moving visual input may conflict with lack of perception of movement (eg, viewing a rapidly moving slide with a microscope or watching a virtual reality game while sitting still). Another possible trigger is a pattern of motion that differs from the expected pattern (eg, in a zero gravity environment, floating instead of falling).
Risk factors:
Factors that may increase the risk of developing motion sickness or increase the severity of symptoms include the following:
In space adaptation syndrome (motion sickness during space travel), weightlessness (zero gravity) is an etiologic factor. This syndrome reduces the efficiency of astronauts during the first few days of space flight, but adaptation occurs over several days.
Symptoms and Signs
Nausea and vague abdominal discomfort are characteristic. Vomiting may also occur. These symptoms may be preceded by yawning, hyperventilation, salivation, pallor, profuse cold sweating, and somnolence. Other symptoms include aerophagia, dizziness, headache, fatigue, weakness, and inability to concentrate. Pain, shortness of breath, and visual and speech disturbances are absent. With prolonged exposure to motion, patients often adapt. However, symptoms may recur if motion increases or if motion resumes after a short respite from the inciting trigger.
Prolonged vomiting due to motion sickness may rarely lead to dehydration with hypotension, inanition, and depression.
Diagnosis
The diagnosis is suspected in patients with compatible symptoms who have been exposed to typical triggers. Diagnosis is clinical and usually straightforward. However, the possibility of another diagnosis (eg, CNS hemorrhage or infarction) should be considered in some people, particularly the elderly and patients with no prior history of motion sickness or those with risk factors for CNS hemorrhage or infarction, who develop acute dizziness and vomiting during travel. Patients with focal neurologic symptoms or signs, significant headache, or other findings atypical of motion sickness should be further evaluated.
Treatment
People prone to motion sickness should take prophylactic drugs and use other preventive measures before symptoms start; interventions are less effective after symptoms develop. If vomiting occurs, an antiemetic, given rectally or parenterally, can be effective. If vomiting is prolonged, IV fluids and electrolytes may be required for replacement and maintenance.
Scopolamine:
Scopolamine, an anticholinergic drug, is effective for prevention, but efficacy in treatment is uncertain. Scopolamine is available as a prescription transdermal patch or in oral form. The patch is a good choice for longer trips because after being applied behind the ear at least 4 h before travel (optimally 8 to 12 h), it is effective for up to 72 h as it releases about 1 mg. The oral form of scopolamine is given as 0.4 mg to 0.8 mg 1 h before travel and then q 8 h as needed.
Adverse effects, which include drowsiness, blurred vision, dry mouth, and bradycardia, occur less commonly with patches. Inadvertent contamination of the eye with patch residue may cause a fixed and widely dilated pupil. Additional adverse effects of scopolamine in the elderly can include confusion, hallucinations, and urinary retention. Scopolamine is contraindicated in people who are at risk of angle-closure glaucoma.
Scopolamine can be used by children > 12 yr in the same dosages as for adults. Use in children ≤12 yr may be safe but is not recommended due to the higher risk of adverse effects.
Antihistamines:
The mechanism of action for antihistamines is probably anticholinergic. These drugs can be effective for prevention and possibly treatment. Beginning 1 h before departure, susceptible people may be given nonprescription dimenhydrinate, diphenhydramine, or meclizine 25 to 50 mg po qid (dimenhydrinate for children 2 to 6 yr, 12.5 to 25 mg po q 6 to 8 h, maximum 75 mg/day; for children 6 to 12 yr, 25 to 50 mg po q 6 to 8 h, maximum 150 mg/day), or cyclizine 50 mg po qid (for children 6 to 12 yr, 25 mg tid) to minimize vagally mediated GI symptoms. However, anticholinergic adverse effects may be troublesome, especially in the elderly. Nonsedating antihistamines do not appear to be effective.
Antidopaminergic drugs:
Promethazine (25 to 50 mg po 1 h before departure and then bid; for children < 12 yr, 0.5 mg/kg po 1 h before departure and then bid) appears to be effective for prevention and treatment; adding caffeine may increase efficacy. Metoclopramide may also be effective, but evidence suggests it is less so than promethazine.
Nondrug measures:
Susceptible people should minimize exposure by positioning themselves where motion is the least (eg, in the middle of a ship close to water level, over the wings in an airplane). Also, they should try to minimize the discrepancy between visual and vestibular stimuli. If traveling in a motor vehicle, driving or riding in the front passenger seat, where vehicle motion is most evident, is best. When traveling on a ship, viewing the horizon or land masses is usually better than viewing a cabin wall. Whatever the form of transportation, reading and rear-facing seats should be avoided. A supine or semirecumbent position with the head supported is best.
Adequate ventilation helps prevent symptoms. Consuming alcoholic beverages and overeating before or during travel increase the likelihood of motion sickness. Small amounts of fluids and bland food consumed frequently are preferred to large meals during extended travel; some people find that dry crackers and carbonated beverages, especially ginger ale, are best. If travel time is short, food and fluids should be avoided.
In space adaptation syndrome, movement, which aggravates the symptoms, should be avoided.
Alternative therapies:
Some alternative therapies are unproved but may be helpful. These alternative therapies include wristbands that apply acupressure and wristbands that apply electrical stimulation. Both can be safely used by people of all ages. Ginger (0.5- to 1-g dose, which can be repeated but should be limited to 4 g/day) may help prevent motion sickness.
Last full review/revision August 2009 by Thomas V. Jones, MD, MPH
Content last modified February 2012
| |
|
