Projectile vomiting is defined by the sheer force with which stomach contents are expelled from the mouth, often traveling a distance of several feet. This is markedly different from typical vomiting, which is usually less forceful and preceded by nausea. The mechanism behind this forceful expulsion, known as emesis, involves a coordinated physiological reflex. This reflex is driven not by the stomach muscles, but by intense, sustained contractions of the abdominal muscles and the diaphragm. These contractions generate immense pressure inside the abdomen, forcefully compressing the stomach and propelling the contents outward with great velocity.
Structural Blockages in Infants
In infants, a common and serious cause of projectile vomiting is a physical obstruction that prevents the normal flow of food from the stomach into the small intestine. When the stomach cannot empty, it contracts forcefully to push contents past the blockage, resulting in the characteristic forceful ejection.
The primary condition is Hypertrophic Pyloric Stenosis (HPS), which affects the pylorus, a muscular valve at the bottom of the stomach. In HPS, the circular muscle of the pylorus thickens abnormally (hypertrophy), narrowing the channel (stenosis). This narrowing blocks the passage of breast milk or formula into the duodenum, the first part of the small intestine.
Symptoms typically begin when the infant is between three and six weeks old, as the muscle gradually thickens after birth. Vomiting progresses from simple regurgitation to the classic projectile form shortly after feeding. Despite the forceful vomiting, babies with HPS often remain hungry, indicating the food is not reaching the intestines for nutrient absorption.
The blockage causes contents to build up, and the stomach develops stronger contractions to overcome the obstruction. These powerful contractions generate the high abdominal pressure needed for projectile vomiting. While HPS is the most common structural cause, other congenital issues like intestinal malrotation can also lead to obstruction and similar symptoms.
Acute Gastrointestinal Illnesses
Acute illnesses that cause severe irritation or inflammation of the digestive tract can trigger the forceful vomiting reflex. The body responds to a perceived toxic threat, such as an ingested pathogen, by attempting to purge the stomach contents quickly.
Gastroenteritis, often called the stomach flu, is a common culprit caused by viral infections (like Norovirus) or bacterial infections (like Salmonella or E. coli). The infection causes intense inflammation and irritation of the stomach and intestinal lining, sending powerful signals to the brain’s vomiting center.
Food poisoning, resulting from ingesting toxins or large amounts of bacteria, also prompts the body to rapidly clear the stomach. While most vomiting from gastroenteritis is not projectile, severe cases of irritation or toxic exposure can provoke the maximum force response.
Neurological System Involvement
The cause of projectile vomiting sometimes originates in the central nervous system rather than the digestive tract. The brain contains the vomiting center, located in the medulla oblongata, which coordinates the entire reflex. This center can be directly stimulated by issues affecting the brain itself.
The most common neurological trigger is an increase in Intracranial Pressure (ICP), which occurs when there is excessive fluid or mass within the rigid confines of the skull. Conditions that increase ICP, such as hydrocephalus, severe traumatic brain injury, brain tumors, or meningitis, exert pressure on the brainstem. This pressure mechanically irritates the vomiting center or the adjacent chemoreceptor trigger zone, initiating the reflex.
Vomiting caused by increased ICP often lacks preceding nausea, meaning the forceful expulsion can occur suddenly without warning. It may also occur in the early morning, as ICP can naturally increase while a person is lying down and sleeping. Furthermore, this type of emesis is typically “non-bilious,” meaning it does not contain bile, because the central nervous system trigger bypasses gastrointestinal distress.
Recognizing Warning Signs
Regardless of the underlying cause, certain accompanying symptoms signal a potentially serious medical emergency requiring immediate attention. The frequency of projectile vomiting significantly increases the risk of severe dehydration, especially in infants and young children. Signs of dehydration include:
- Reduced urination.
- A lack of tears when crying.
- Lethargy.
- A sunken soft spot (fontanelle) on a baby’s head.
The appearance of the vomitus itself is also a significant red flag. The presence of blood, which may look bright red or resemble dark “coffee grounds,” can indicate a tear in the esophagus or stomach lining. Green or yellow-green vomit suggests the presence of bile, which can be a sign of a critical intestinal blockage, particularly in newborns, and requires urgent medical evaluation.
Other concerning signs that necessitate prompt medical consultation include a high fever, a stiff neck, a severe headache that is different from previous ones, or any sign of altered consciousness or confusion. Persistent vomiting lasting more than 24 hours in a child, or for any duration in an infant, also warrants immediate medical advice to prevent complications like electrolyte imbalance and severe dehydration.