Nausea, an unpleasant sensation often preceding vomiting, is a common experience following a physical injury. Understanding the body’s various triggers for this feeling can help clarify why a simple sprain or a more severe accident might lead to stomach distress.
The Body’s Generalized Stress Response
Intense pain and the shock of a sudden injury initiate an immediate, involuntary activation of the body’s defense mechanisms. This “fight or flight” response is governed by the sympathetic nervous system, which rapidly releases stress hormones, such as adrenaline (epinephrine) and cortisol, from the adrenal glands. The surge of adrenaline redirects blood flow away from non-essential functions, including digestion, toward the major muscles, heart, and brain to prepare for immediate action.
The reduced blood flow to the gastrointestinal (GI) tract slows down normal digestive movement, known as decreased GI motility. This disruption can lead to discomfort and nausea. Additionally, the intense pain signal activates the nervous system, triggering an excessive autonomic response that contributes directly to the sensation of nausea.
Pain signals are transmitted to the brainstem, interacting with centers that regulate vomiting. Inflammation at the injury site releases chemical messengers, such as prostaglandins and cytokines, which circulate and sensitize the brain’s nausea centers. The vagus nerve also transmits sensory information from the distressed GI tract back to the brainstem, further amplifying the nausea signal.
When the Injury Affects the Brain
Nausea and vomiting are common following head trauma, from a mild concussion to a severe traumatic brain injury (TBI). This is often a direct result of neurological disturbance. A primary mechanism involves an increase in intracranial pressure (ICP) caused by brain tissue swelling or internal bleeding.
Elevated ICP directly stimulates the chemoreceptor trigger zone (CTZ), a specialized region in the brainstem. The CTZ monitors the blood and cerebrospinal fluid for imbalances. When stimulated by pressure or inflammatory chemicals released after injury, the CTZ signals the vomiting center, leading to nausea and vomiting.
Disruption to the vestibular system is another common neurological cause of post-injury nausea, especially with concussions. The vestibular system, located in the inner ear, is responsible for processing balance and spatial orientation. Trauma can disrupt the signals sent from the inner ear to the brain, causing a mismatch in sensory information that the brain interprets as motion sickness, resulting in dizziness and nausea. Persistent vomiting after a head injury should prompt immediate medical attention, as it can indicate worsening ICP or a developing complication like an intracranial hemorrhage.
Nausea Caused by Circulatory Shock
Nausea can signal a life-threatening complication, such as circulatory or hypovolemic shock. This results from a significant reduction in circulating blood volume, often due to massive blood loss. To compensate, the body activates the sympathetic nervous system, constricting peripheral blood vessels to maintain pressure to vital organs like the heart and brain.
This mechanism diverts blood away from non-essential organs, reducing blood flow (perfusion) to the gastrointestinal tract. The stomach and intestinal tissues become deprived of oxygen, causing ischemia. This tissue distress triggers signals sent to the vomiting center in the brainstem, initiating nausea.
A patient experiencing nausea with shock may also exhibit signs of inadequate tissue perfusion, such as a rapid heart rate, cool skin, paleness, confusion, or lack of urine output. Nausea alongside these symptoms necessitates immediate emergency medical care, as it reflects a systemic failure to deliver oxygen to the tissues.
Medications and Other Contributing Factors
External factors like pain medication and psychological stress contribute to post-injury nausea. Opioid pain medications, often prescribed for severe injuries, are a major cause of nausea and vomiting. Opioids stimulate mu-opioid receptors, including those in the chemoreceptor trigger zone (CTZ) in the brain, directly triggering nausea.
Opioids also slow gut movement by inhibiting peristalsis. This reduced motility can lead to constipation and pressure in the intestines, which signals the brain and results in nausea. Additionally, general anesthesia used during surgery can linger and stimulate CTZ receptors, contributing to post-operative nausea.
Intense emotional distress, such as fear or anxiety following an accident, can independently activate the body’s stress response. This psychological trigger activates the sympathetic nervous system, releasing hormones that disrupt digestion. Even the psychological shock of an injury can be powerful enough to induce stomach distress.