Neurogenic shock is a distributive type of shock resulting in

hypotension Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is ...

(low blood pressure), often with

bradycardia Bradycardia, also called bradyarrhythmia, is a resting heart rate under 60 beats per minute (BPM). While bradycardia can result from various pathological processes, it is commonly a physiological response to cardiovascular conditioning or due ...

(slowed heart rate), caused by disruption of

autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

pathways. It can occur after damage to the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain, spinal cord and retina. The CNS is so named because the brain integrates the received information and coordinates and influences the activity o ...

, such as

spinal cord injury A spinal cord injury (SCI) is damage to the spinal cord that causes temporary or permanent changes in its function. It is a destructive neurological and pathological state that causes major motor, sensory and autonomic dysfunctions. Symptoms of ...

and

traumatic brain injury A traumatic brain injury (TBI), also known as an intracranial injury, is an injury to the brain caused by an external force. TBI can be classified based on severity ranging from mild traumatic brain injury (mTBI/concussion) to severe traumati ...

. Low blood pressure occurs due to decreased

systemic vascular resistance Vascular resistance is the resistance that must be overcome for blood to flow through the circulatory system. The resistance offered by the systemic circulation is known as the systemic vascular resistance or may sometimes be called by another ter ...

resulting from loss of sympathetic tone, which in turn causes blood pooling within the extremities rather than being available to circulate throughout the body. The slowed

heart rate Heart rate is the frequency of the cardiac cycle, heartbeat measured by the number of contractions of the heart per minute (''beats per minute'', or bpm). The heart rate varies according to the body's Human body, physical needs, including the nee ...

results from a vagal response unopposed by a

sympathetic nervous system The sympathetic nervous system (SNS or SANS, sympathetic autonomic nervous system, to differentiate it from the somatic nervous system) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous sy ...

(SNS) response. Such

cardiovascular In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart a ...

instability is exacerbated by hypoxia, or treatment with endotracheal or endobronchial

suction Suction is the day-to-day term for the movement of gases or liquids along a pressure gradient with the implication that the movement occurs because the lower pressure pulls the gas or liquid. However, the forces acting in this case do not orig ...

used to prevent

pulmonary aspiration Pulmonary aspiration is the entry of solid or liquid material such as pharyngeal secretions, food, drink, or stomach contents from the oropharynx or gastrointestinal tract, into the trachea and lungs. When pulmonary aspiration occurs during ea ...

. Neurogenic shock is a potentially devastating complication, leading to

organ dysfunction Organ dysfunction is a condition where an organ does not perform its expected function. Organ failure is organ dysfunction to such a degree that normal homeostasis cannot be maintained without external clinical intervention or life support. It is ...

and death if not promptly recognized and treated. It is not to be confused with spinal shock, which is not circulatory in nature.

Signs and symptoms

* Instantaneous hypotension due to sudden, massive

vasodilation Vasodilation, also known as vasorelaxation, is the widening of blood vessels. It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. Blood vessel wa ...

and decrease in blood

oxygen saturation Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is Dissolution (chemistry), dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the g ...

* Warm, flushed skin due to vasodilation and inability to constrict blood vessels. * Priapism, also due to vasodilation * The patient will be unable to mount a tachycardic response, and often becomes bradycardic * If the injury is below

cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...

C5, the patient will exhibit

diaphragmatic breathing Diaphragmatic breathing, abdominal breathing, belly breathing, or deep breathing, is a breathing technique that is done by contracting the Thoracic diaphragm, diaphragm, a muscle located horizontally between the thoracic cavity and abdominal cav ...

due to loss of nervous control of the

intercostal muscle The intercostal muscles comprise many different groups of muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle ...

s (which are required for thoracic breathing). * If the injury is above C3, the patient will go into

respiratory arrest Respiratory arrest is a serious medical condition caused by apnea or respiratory dysfunction severe enough that it will not sustain the body (such as agonal breathing). Prolonged apnea refers to a patient who has stopped breathing for a long period ...

immediately following the injury, due to loss of nervous control of the diaphragm.

Causes

Neurogenic shock can result from severe central nervous system damage (

brain injury Brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating trauma-induced damage. A common ...

, cervical or high

thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main ...

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

). In simple terms, the trauma causes a sudden loss of background SNS stimulation to the blood vessels. This causes them to relax (vasodilation) resulting in a sudden decrease in blood pressure (secondary to a decrease in peripheral vascular resistance). Neurogenic shock results from damage to the spinal cord above the level of the 6th thoracic vertebra. It is found in about half of people who have a spinal cord injury within the first 24 hours, and usually persists for one to three weeks. Neurogenic shock may be caused by severe brain injury. However, in case of increased

intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury ( mmHg) and at rest, is normally 7–15 mmHg for a supine adu ...

, according to the Cushing triad, blood pressure will be ''increased'' (unless decreased from

hypovolemia Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss ...

), respirations will be irregular and bradycardia will also be a feature.

Pathophysiology

Neurogenic shock is diagnosed based on a person's symptoms and blood pressure levels. Neurogenic shock's presentation includes: * Warm and pink skin * Labored breathing * Low blood pressure * Dizziness * Anxiety * History of trauma to head or upper spine * If the injury is to the head or neck, hoarseness or difficulty swallowing may occur. Symptoms of neurogenic shock are differentiated from other forms of shock by the lack of signs of the compensatory mechanisms triggered by the SNS, usual in other forms of shock. 'This SNS response is effected via release of

epinephrine Adrenaline, also known as epinephrine, is a hormone and medication which is involved in regulating visceral functions (e.g., respiration). It appears as a white microcrystalline granule. Adrenaline is normally produced by the adrenal glands a ...

and

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic compound, organic chemical in the catecholamine family that functions in the brain and human body, body as a hormone, neurotransmitter and neuromodulator. The ...

, and signs of these

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

s' activity are typically absent where shock is of neurogenic origin. Those signs - in non-neurogenic shock - would include: tachycardia (increased heart rate),

tachypnea Tachypnea, also spelt tachypnoea, is a respiratory rate greater than normal, resulting in abnormally rapid and shallow breathing. In adult humans at rest, any respiratory rate of 1220 per minute is considered clinically normal, with tachypnea b ...

(increased breath rate), sweating, and adaptive

vasoconstriction Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vesse ...

, which serves in other forms of shock to shunt blood away from the extremities and to the vital organs. In neurogenic shock, the body loses its ability to activate the SNS so that only parasympathetic tone remains. The resulting loss of sympathetic tone, which plays a major role in other forms of shock, is responsible for the unique and atypical features mentioned above.

Treatment

Dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. It is an amine synthesized ...

(Intropin) is often used in combination with other vasopressors. Dopamine is not the best first-line vasopressor as it increases the chance of arrhythmias. *

Vasopressin Mammalian vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the ''AVP'' gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It ...

(antidiuretic hormone, ADH) is another vasopressor often used in combination with norepinephrine *Certain vasopressors (

ephedrine Ephedrine is a central nervous system (CNS) stimulant and sympathomimetic agent that is often used to prevent hypotension, low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred ...

). Norepinephrine (Levophed) is the most common first-line vasopressor for people who don't respond well to other hypotension treatments such as fluid resuscitation. *

Atropine Atropine is a tropane alkaloid and anticholinergic medication used to treat certain types of nerve agent and pesticide poisonings as well as some types of slow heart rate, and to decrease saliva production during surgery. It is typically give ...

is administered for bradycardia. It acts on the vagus nerve so it's not effective in heart transplant patients as the vagus nerve is severed during the transplant.

References

External links

{{shock types Neurological disorders