Motion sickness

Motion sickness is a symptom complex typically involving nausea, often accompanied by vague abdominal discomfort, vomiting, dizziness, and related symptoms; it is caused by repeated angular and linear accelerations and decelerations. Behavior modification and drug therapy may help prevent or reduce symptoms.

Individual susceptibility to motion sickness varies greatly, but is more common in women. The incidence varies from <1% in airplanes to nearly 100% on ships in rough seas and in space weightlessness.

The primary cause of motion sickness is excessive vestibular stimulation by motion. No afferent pathways from the labyrinth to the vomiting center in the medulla have been identified, but motion sickness occurs only when the VII cranial nerve and cerebellar vestibular tracts are intact. Motion during any form of transportation, including boat, car, train, airplane, spacecraft, amusement park rides, or playground play, can cause excessive vestibular stimulation. Motion sickness can also develop when the vestibular, visual, and proprioceptive pathways are in conflict for various reasons; when the nature of the motion is different from what has been previously experienced; or when motion is expected but does not occur (e.g., when seeing motion on a television screen or in a movie). Visual stimuli (eg, a moving horizon), poor ventilation (with fumes, smoke or carbon monoxide) and emotional factors (eg, fear, anxiety) can act simultaneously with movement to trigger an attack of the disease.

In space adaptation syndrome (motion sickness during space flight), weightlessness (zero gravity) is the etiologic factor. This syndrome reduces the efficiency of astronauts during the first few days of space flight, but then adaptation occurs.

Symptoms and diagnosis of motion sickness

Nausea and vague abdominal discomfort are characteristic. Vomiting may also occur. These symptoms may be preceded by yawning, hyperventilation, salivation, pallor, profuse cold sweat, and drowsiness. Other symptoms include aerophagia, dizziness, headache, fatigue, general weakness, and inability to concentrate. Pain, dyspnea, visual and speech disturbances are absent. Adaptation may occur with prolonged exposure to motion. However, symptoms may recur with increased motion or after a short rest.

Prolonged motion sickness with vomiting occasionally leads to dehydration with arterial hypotension, exhaustion, and depression. Motion sickness may be more severe in patients with concomitant pathology.

The diagnosis is based on clinical findings and is usually obvious. In some cases, cerebrovascular events such as stroke or transient ischemic attack may mimic motion sickness.

Motion sickness remedies and treatments

There are several options, but they are more effective for prevention than for treating symptoms once symptoms have developed. People prone to motion sickness should take preventive medications before symptoms appear. Scopolamine is used as a patch or tablets taken orally. The patch is a good choice for longer trips because, when applied behind the ear at least 4 hours before travel (optimally 8-12 hours), it is effective for up to 72 hours; the patch releases approximately 1 mg of the drug. Scopolamine is given orally at a dose of 0.4-0.8 mg 1 hour before travel and then every 8 hours as needed. Side effects, including drowsiness, decreased visual acuity, dry mouth, and bradycardia, are less common with the patch. Accidental contamination of the eye with patch residue may cause persistent, marked pupil dilation. Additional adverse effects of scopolamine in the elderly include confusion, hallucinations, and urinary retention. Scopolamine is contraindicated in people at risk for angle-closure glaucoma. Scopolamine may be used in children over 12 years of age at the same dosages as adults. Use in children <12 years of age is likely safe but not recommended.

As an alternative to the previous method, 1 hour before departure, susceptible individuals can be given over-the-counter dimenhydrinate, diphenhydramine, or meclizine 25 to 50 mg orally 4 times a day (dimenhydrinate for children 2 to 6 years, 12.5 to 25 mg every 6 to 8 hours, maximum 75 mg daily; children 6 to 12 years, 25 to 50 mg every 6 to 8 hours, maximum 150 mg daily); promethazine 25 to 50 mg orally 2 times a day (children < 12 years, 0.5 mg/kg body weight 2 times a day); or cyclizine 50 mg orally 4 times a day (children 6 to 12 years, 25 mg 3 times a day) to minimize vagus-related GI symptoms. However, all of these drugs are anticholinergics and can cause side effects, especially in older people.

In case of vomiting, antiemetics are prescribed, rectally or parenterally for greater effectiveness. If vomiting is prolonged, intravenous fluids and electrolytes may be required to replenish and maintain fluid balance in the body.

Some non-drug methods have not been proven to be effective, but they may be helpful. These include the use of bracelets that perform acupressure or conduct electrical stimulation. Both types are safe for people of all ages. Ginger (1-2 g) can help prevent motion sickness.

Motion sickness prevention

Susceptible people should minimize exposure by sitting where movement is minimal (e.g., in the middle of a boat, close to the water level, near the wings on an airplane). When traveling by car, it is best to sit in the front, as the most favorable positions are the driver and front passenger. Regardless of the mode of transport, positions with your back to the movement should be avoided. The best position is supine or reclining with a headrest. Adequate ventilation also helps prevent symptoms. Reading should be avoided. Keeping the visual axis 45" above the horizon and, if possible, focusing on stationary objects reduce susceptibility to motion sickness. Alcohol and overeating before or during travel increase the likelihood of motion sickness. During a long trip, frequent small sips of liquid and light food are recommended. Some people find dry crackers and carbonated drinks, particularly light beer, more acceptable foods. It is better to abstain from food and drink during a short flight. In case of space adaptation syndrome, movements that provoke symptoms should be avoided.