What Is Neurogenic Shock?

The spine is a part of our body that plays an imperative role; it carries precious cargo (in the shape of electrical messages) that helps us to engage in day-to-day activities, like riding a bike, eating and pulling our hand back from a hot object. Furthermore, it helps to regulate our body’s temperature, blood pressure and heart rate, which requires careful maintenance to make sure the body is ready for any situation.

As the name suggests, neurogenic shock has something to do with the neurons in the spine. Neurogenic shock is a disorder that can occur in any individual who has had a spinal injury.

Neurogenic shock causes dysregulation of the autonomic nervous system. This can result in sudden changes to the heart rate, blood pressure and temperature, which can be life-threatening.

Overview

Neurogenic shock is a secondary condition as it is preceded by an initial acute spinal cord injury (SCI). Usually, the injury is more likely to occur in the cervical section of the spine rather than in the thoracic section (see diagram below).¹

Neurogenic shock is a life-threatening condition because traumatic injury to the spinal cord results in damage to the central nervous system. The initial trauma leads to a disruption in the function of the autonomic nervous system, the part of the nervous system that helps to regulate the body’s unconscious processes and which consists of the sympathetic and parasympathetic systems. Upon spinal cord injury, the balance between the two opposing systems can become tipped.  This causes the loss of sympathetic tone (signals), allowing the parasympathetic nervous system (vagal tone) to overpower the sympathetic nervous system, manifesting as a neurogenic shock. ² The loss of tone in the sympathetic nervous system occurs in two steps. Primary injury is the direct damage that occurs to the nerve after trauma.  Physical damage can result in excitotoxicity and leakage of all sorts of nerve cell components. After hours or days, secondary injury can appear, which is when the body tries to repair the nerve damage, and in the process, the controlled and uncontrolled killing of these spinal cord nerve cells occurs. Both primary and secondary injury leads to a loss of sympathetic tone. When the parasympathetic system dominates in the body, parameters such as blood pressure, body temperature and heart rate are not effectively regulated. Neurogenic shock is a serious condition that requires immediate management and treatment to avoid complications.^{1, 2} Neurogenic shock is not to be confused with spinal shock, as the latter denotes a loss of reflex, motor and sensory functions below the area of spinal injury. This means that in spinal shock, a person’s reflex response (like the knee jerk reflex), the ability to sense touch, and the ability to make voluntary movements are lost. If the injury is not too severe and there is no permanent damage, a person can recover from spinal shock with extensive rehabilitation and physical therapy. Neurogenic shock can occur simultaneously with spinal shock.³ 

Causes of neurogenic shock

Neurogenic shock most commonly occurs due to an acute spinal cord injury above the 6th thoracic column of the spine.¹
Other causes include:

• Guillain Barre syndrome
• Autonomic nervous system toxins (of plant or animal origin)
• Down syndrome (genetic cause)
• Spinal anaesthesia (such as epidural anaesthesia administered during childbirth)
• Transverse myelitis (a neuroimmune spinal cord disorder that can lead to neurogenic shock in extremely rare cases). 
• Skeletal dysplasia (improper development of bones)

These conditions can disrupt pathways of the autonomic nervous system, thus resulting in a loss of sympathetic tone. This can lead to decreased vascular resistance and changes in the vagal tone.^{4, 5}

Signs and symptoms of neurogenic shock

The sympathetic nervous system is responsible for regulating vital body functions, such as blood pressure, heart rate, and body temperature. In cases of neurogenic shock, the sympathetic nervous system is compromised, so these functions are dysregulated. This reduces the flow of oxygen-rich blood throughout the body, lowering blood pressure drastically. Temperature dysregulation manifests as a loss of heat, causing a person to feel cold. Finally, neurogenic shock causes the heart rate to fall, which can lead to serious complications, resulting in signs and symptoms.¹ 

Hypotension is where the systolic blood pressure is lower than 90 mmHg and/or the diastolic blood pressure is lower than 60 mmHg. This can happen when the blood vessels dilate (vasodilation), especially in the skin, because the surface area increases and the pressure on blood vessel walls decreases. It also gives a feeling of warmth and a flushed appearance to the skin, even if the patient does not have a  fever. Bradycardia is defined as a heart rate that is below 60 beats per minute when at rest. The heart slows down, and the force used to push the blood also weakens, ultimately reducing blood pressure. Reductions in body temperature happen due to vasodilation of blood vessels close to the surface of the skin. When blood flows closer to the skin, heat can more easily escape.  Thus, body temperatures drop. Although the person may seem warm to the touch, their core temperature will have been reduced. 

Below are symptoms that the patient may also experience:

• Fatigue
• Nausea
• Confusion
• Weakness
• Blurred vision
• Confusion
• Poor concentration
• Dizziness and fainting 

All these occur as a result of the previously mentioned hypotension, bradycardia and temperature dysregulation.^{6, 7} 

These three parameters need to be properly regulated, which is why three types of nervous systems coordinate and tune them. There are hormones that the brain secretes in response to environmental stimuli (such as one that causes you to feel fear), which can cause local effects, somewhat compensating for the lack of sympathetic tone in neurogenic shock. Adrenaline is a hormone that causes your heart to beat faster and harder, which combats the bradycardia and low blood pressure that arise in people affected by neurogenic shock. It can also promote metabolism, leading to more heat being produced, which compensates for the lowered body temperature. However, the effects of adrenaline are temporary, so when there is a drop in the hormone level, the counter effect to the parasympathetic nervous system is rapidly lost.

Management and treatment for neurogenic shock

Neurogenic shock is a medical emergency that needs treatment immediately. Initially, the treatment involves stabilising patients’ blood flow (haemodynamics). One of the most important factors that need to be treated is low blood pressure (hypotension), as this endangers all parts of the body, especially the brain, which needs oxygen-rich blood to supply neurones in the brain that try to keep the rest of the body alive and functioning properly. The first line of treatment is to increase the volume of fluid in the body, which is done by giving a patient fluid intravenously (IV). As vasodilation can cause blood pressure to fall, medications that constrict blood vessels (vasoconstriction) can be used, although with caution, as complications can arise. The mean arterial blood pressure needs to be kept between 85 to 90 mmHg for optimum recovery. Other medications can be used for the treatment of bradycardia to counteract the vagal tone. In acute injuries, the neck needs to be immobilised once it is determined that there is no heavy bleeding to avoid further damage to the spinal cord. Surgery can be performed to reduce the pressure on the spine. Symptoms of neurogenic shock may last for up to 5 weeks.^{1, 8, 9, 10, 11}

Diagnosis

Neurogenic shock was difficult to diagnose in times when screening instruments were not as advanced as today. It would always get associated with spinal injury and would be diagnosed as spinal cord injury without radiological abnormality (SCIWORA). Yet, technological advances have made diagnosis easier. With the support of computed tomography (CT) and magnetic resonance imaging (MRI) scans, injuries to the spinal cord can be accurately identified. When diagnosing neurogenic shock, multiple parameters need to be considered and constantly monitored to get an accurate diagnosis. Those parameters include data collected by radio imaging, like the CT and MRI scans, bloodwork, and  clinical examination.^{12, 13}

FAQs

How can I prevent neurogenic shock?

To prevent neurogenic shock, spinal cord injuries need to be avoided. This can be done by refraining from activities that put you at risk of serious accidents, such as drinking and driving, and extreme sports, like horse riding. To avoid accidents, only drive when sober and always wear a seatbelt. Try to avoid extreme sports that can cause damage to the spine, such as cliff diving, or educate yourself on the equipment and protocols which are needed to engage in these activities safely. 

How common is neurogenic shock?

In a research study, 19.3% of 490 patients with spinal cord injuries were found to have classic symptoms of neurogenic shock.¹⁴

How long does neurogenic shock last?

The symptoms can last up to 5 weeks, but for those with extensive nerve damage in the spine, it may last even longer.

Who is at risk of neurogenic shock?

Patients that have suffered a spinal cord injury (SCI).

When should I see a doctor?

When you develop any of the symptoms mentioned in this article, and you have experienced an injury to your neck, head or back, immediately see your doctor.

Summary

Neurogenic shock is a serious medical emergency that needs to be dealt with immediately. It can happen after an injury to the spine, particularly to the neck. It manifests as bradycardia, temperature dysregulation and hypotension. It is a serious condition with a high risk of death. Hence, prompt treatment needs to stabilise the patient’s body parameters and address the lack of sympathetic tone by administering IV fluids and giving appropriate medication.