Hiccups Overview and Mechanism
A hiccup is a sudden involuntary, contraction of the diaphragm (the muscle that separates the chest and abdominal cavities) and the intercostal muscles. This results in a sudden inspiration followed by an abrupt closure of the vocal cords, thereby producing the characteristic ‘hic’ sound.

The medical term for hiccups (or “hiccoughs”) is singultus, derived from the Latin singult, which means “a gasp” or “a sob.”

Hiccups are usually self-limiting, and go away spontaneously, but may become intractable in a few cases, the longest recorded episode continuing for 68 years.

Typically a “bout” of hiccups refers to an episode that lasts less than 48 hours and has no apparent cause. Hiccups which recur very often, or last for more than 48 hours, may signify an underlying medical problem. Usually, a hiccup involves one side of the diaphragm (hemidiaphragm), left more than right.

Neural Pathway of Hiccup Reflex
It is not clear if there is any “purpose” to a hiccup. They are known to even occur in utero in the third trimester.
The hiccup reflex involves the reflex arc of
1. Phrenic nerve, vagus nerve, sympathetic chain (afferent)
2. Central mediator
The central mediator is believed to involve the respiratory centers, phrenic nerve nuclei, reticular part of brainstem, and hypothalamus.
3. Phrenic nerve, glottis, and intercostal muscles (efferent)

Causes of Hiccups
The most common triggers of hiccups that are self-limiting and last less than 48 hours include

• Consuming aerated drinks
• Excess alcohol consumption
• Overeating
• Excitement or emotional stress
• Sudden temperature changes
• Swallowing too much air, eg while chewing gum

Hiccups that last longer than 48 hours may be caused by any of the following
Although there may be several causes, it is useful to consider lesions involving the reflex arc pathway to rule out underlying disease

? Vagus and phrenic nerve irritation – most common cause.
• Foreign bodies or hair against tympanic membrane can irritate the auricular branch of vagus nerve
• Throat disease (pharyngitis, laryngitis, neck tumors) can stimulate the recurrent laryngeal nerve (branch of vagus).
• Esophageal candidiasis has been known to cause hiccups in AIDS patients.
• Goiters, mediastinal masses, tumors may irritate the phrenic nerve

? Diaphragmatic irritation
• Hiatus hernia
• Gastro-esophageal reflux disease (GERD)
• Subphrenic abscess
• Manipulation during surgery

? CNS disorders – Any lesion that disrupts the inhibitory hiccup reflex.
• Vascular – stroke, hemorrhage
• Infectious – meningitis, encephalitis
• Tumors
• Multiple sclerosis
• Hydrocephalus
• Syringomyelia

? Toxic/metabolic
• Anesthesia
• Diabetes – hypoglycemia, hyperglycemia
• Alcohol
• Uremia
• Electrolyte imbalances – hyponatremia, hypokalemia
• Drug induced – dexamethasone, benzodiazepines, alcohol, opioids, methyldopa

? Psychogenic – Must rule out organic pathology first
• Shock, fear, excitement, attention-seeking behaviour.

Risk Factors of Hiccups
Men are much more likely to get long-term hiccups than women. Other factors that may increase risk of hiccups include

• Mental or emotional issues – Anxiety, stress and excitement have been associated with
some cases of short-term and long-term hiccups.

• Surgery – Following abdominal surgery under general anesthesia

Complications of Prolonged Hiccups
• Mainly psychological due to disruption of life and sleep disturbances
• Gastro-esophageal reflux disease
• Cardiac arrhythmias
• Exhaustion
• Malnutrition and weight loss
• Wound dehiscence
• Aspiration pneumonitis

Investigations of Prolonged Hiccups
Work up is usually reserved for prolonged intractable hiccups.

History – A detailed history asking about drug history, occurrence during sleep suggests an organic cause, history of underlying medical illness

Physical examination – including a complete neurological examination

Blood tests – Complete blood count, electrolytes, renal function tests, blood sugar

Imaging tests – These tests may be able to detect anatomical abnormalities that may be affecting the vagus nerve, phrenic nerve or diaphragm. These include

• Chest X-ray
• Abdominal ultrasound
• Computerized tomography (CT) chest and abdomen
• Magnetic resonance imaging (MRI)
• Fluoroscopy of diaphragm movement

Endoscopy – These procedures use a narrow, flexible tube containing a tiny camera, which is passed down your throat to check for problems in the esophagus (upper GI endoscopy) or windpipe (bronchoscopy).

HICCUPS TREATMENT
Non-drug treatments
Most bouts of hiccups will be self-limiting and will require no treatment. However several remedies have been known to relieve troublesome hiccups. Some of these probably act by interrupting the reflex arc and include the following

• Stimulation of the nasopharynx – sipping iced water, swallowing granulated sugar, chewing on a lemon

• Interruption of normal respiratory function – Valsalva manoeuvre, breathing into a bag, breath holding, inducing sneezing (noxious odors), pulling on the tongue, inducing fright

• Counter-irritation of the diaphragm – leaning forward to compress the chest or pulling the knees up to the chest

Drug treatment
Drug therapy may be considered for hiccups that have lasted longer than two days. These include

• Chlorpromazine – most commonly employed and effective in the majority of cases
• Metaclopramide – particularly if hiccups are caused by gastric stasis and distension
• Baclofen – A recent study reported some benefit in cancer patients and in patients intolerant to other agents
• Anticonvulsants – based on the theory that hiccups occur due to persistent clonic activity of diaphragm. Drugs used to good effect are phenytoin, carbamazepine, sodium valproate and, more recently, gabapentin.
• Lidocaine and ketamine – used for intractable hiccups in a specialist setting
• Others – Quinidine, amitriptyline, marijuana

Miscellaneous treatments

• Acupuncture and hypnotherapy – reported to be beneficial in some cases
• Anesthesia with positive pressure ventilation and muscle relaxants – shown to work in a recent report

Surgery – If All Other Measures Fail
• Surgery to decompress or block the phrenic nerve has been used if all other treatment
modalities fail, but carries significant mortality
• Microvascular decompression of the vagus nerve has been rarely performed if all else fails
• Surgical implant of a battery-operated device to deliver mild electrical stimulation to the vagus nerve has been used to treat epilepsy but has been found to be useful for persistent hiccups
• Transesophageal diaphragmatic pacing has been shown to be useful in certain cases

Prognosis of Hiccups
The outcome for prolonged hiccups for which no obvious medical cause is found is good, most cases responding to medical treatment or remitting spontaneously. The prognosis for patients in which there is an underlying pathology for the hiccups usually depends on the prognosis for that condition.