Neurogenic shock is acute circulatory failure that results from the sudden loss of sympathetic tone and vascular tone when the nervous system is damaged. The most characteristic signs of pathology are hypotension, relative bradycardia, hyperemia, and hyperthermia of the skin of the extremities. Severe shock is accompanied by impaired breathing and consciousness, neurological disorders. Diagnostics are carried out according to the data of clinical examination, blood tests, hemodynamic monitoring, CT, and MRI of the affected areas. Shock relief is carried out using intensive therapy; an important place is given to early surgical correction.
The epidemiology of neurogenic shock is difficult to assess as it is based on limited statistical data and depends on the clinical criteria used. Compared to other types of circulatory failure, this type of shock is considered the rarest. With injuries of the cervical spinal cord, an emergency condition is recorded in 19-29% of patients, exceeding the thoracic and lumbar regions (7 and 3%, respectively). The frequency of neurogenic shock in intracranial disorders remains unknown. The gender-age structure usually corresponds to spinal injuries; half of all cases occur between the ages of 16 and 30, with an 8-fold predominance in men.
Causes of neurogenic shock
The development of neurogenic shock is mediated by acute damage to the central nervous system, either primary or secondary. Hemodynamic changes usually occur with lesions of the craniospinal tract above the Th6 level, including the brainstem. The primary process is associated with direct destruction of the nerve pathways; the secondary is due to vascular and electrolyte changes, edema. Thus, shock reactions are caused by two groups of reasons:
- Organic. A common cause of neurogenic shock is severe damage to the spine and spinal cord (automobile, sports, gunshot). Cerebral disorders include traumatic brain injury, stroke, subarachnoid hemorrhage. Other factors include severe cerebrospinal fluid hypertension, transverse myelitis, Guillain-Barré syndrome, and other peripheral neuropathies.
- Functional. In some cases, circulatory disorders are due to functional disorders. Shock can occur against the background of deep anesthesia, epidural anesthesia, and intense pain. The role of toxic damage to the vegetative system, the influence of certain medications, and severe psychoemotional trauma are noted. Hypothalamic-pituitary-adrenal insufficiency is recognized as a separate cause.
Specific risk factors have been described for the pediatric population. Insufficient blood circulation is the result of birth trauma or child abuse. Shock-related fractures and dislocations of the upper cervical segments of the spinal cord are more common in patients with Down syndrome, skeletal dysplasia, and juvenile idiopathic arthritis.
Classification of neurogenic shock
According to the development mechanism, neurogenic shock is a type of distributive shock in which relative hypovolemia is noted. Considering the prevailing processes, it proceeds in three pathogenetic variants: vasodilatory, cardiogenic, and neuroendocrine. The generally accepted clinical classification of shock includes several degrees of severity:
- I degree. Perfusion of vital organs is maintained. The general condition of moderate severity, clear consciousness, the patient is slightly inhibited. Systolic blood pressure exceeds 100 mm Hg.
- II degree. There is a gradual depletion of compensatory capabilities. The patient’s condition is serious; they experience lethargy, and the skin is pale. Blood pressure drops to 90-80 mm Hg; breathing becomes more frequent, becomes shallow.
- III degree. Compensatory mechanisms cannot maintain adequate perfusion. The condition is severe; weakness is characteristic, the level of consciousness is stupor. The skin is pale; acrocyanosis is present. The blood pressure level drops below 70 mm Hg; the pulse is threadlike, it is determined only on the main arteries. Anuria develops.
- IV degree. Damage is irreversible; multiple organ failure is typical. The patient is in a terminal state; the skin is grayish with a marble pattern and stagnant spots. BP is below 50 mm Hg or not detected, pulse and breathing are barely noticeable. Pupils dilate, reflexes and reactions to painful stimuli are absent.
Symptoms of neurogenic shock spinal cord
The localization of the primary defect largely determines the clinical picture and severity of the pathology. Circulatory failure can occur against the background of complete or partial neurological deficits. The lesion above the Th1 segment disrupts the sympathetic regulation of many internal organs, with a decrease in the level of damage, the severity of the violations decreases.
The hemodynamic profile of the vasodilator variant of neurogenic shock is considered warm and dry:
- peripheral vasodilation is complemented by hypotension with increased pulse pressure
- relative bradycardia
- warming the skin of the limbs.
After spinal cord injuries, it is possible to notice a difference in the tone of the vascular network above and below the affected segments. Orthostatic hypotension without reflex tachycardia is common when moving from a prone to an upright position. Priapism is diagnosed in men.
The cardiogenic form of shock is manifested through:
- heart palpitations
- bradycardia in such a situation is extremely rare.
Peripheral vessels narrow, systemic venous resistance increases, and the skin become cold and moist. Myocardial dysfunction is accompanied by decreased cardiac output, a drop in stroke volume, dizziness, and pallor. Central venous pressure is normal or elevated.
Arterial hypotension with neurological shock responds poorly to vasopressor infusion. Hemodynamic signs of vascular insufficiency are decreased CVP and peripheral resistance, stroke volume, and cardiac output. Low baseline cortisol levels can be considered a hallmark. The corticotropin stimulation test often leads to an increase in its concentration, but this does not exclude the presence of shock.
Neurogenic disorders can persist for 1-6 weeks. Autonomic dysreflexia, low resting blood pressure, and orthostatic hypotension are not uncommon during the chronic phase aftershock reactions that have been successfully resolved. Vegetative instability is often manifested by episodic hypertension, skin flushing, sweating, and tachycardia.
Diagnostics neurogenic shock
Taking into account the potential danger of pathology, an urgent examination of the patient is carried out in the intensive care unit. Prior to establishing the diagnosis of neurogenic shock, it is recommended to exclude other causes of circulatory failure, especially in the presence of severe progressive refractory hypotension. The following methods of laboratory and instrumental control help in this:
- General and biochemical blood tests. Get a detailed picture of peripheral blood, coagulogram data, plasma electrolyte composition. Determine the concentration of cortisol, markers of myocardial necrosis (troponins, myoglobin, creatine phosphokinase). Evaluation of arterial and venous blood gases is crucial, according to the results of which hypoxemia, hypercapnia, acidosis are detected.
- Hemodynamic monitoring. It is possible to study hemodynamic parameters by non-invasive or invasive methods. Non-invasive methods include blood pressure measurement, pulse oximetry, ECG, and plethysmography. Cardiac output is measured by Doppler echocardiography, thermodilution-based techniques. Tissue perfusion is judged by the amount of urine output. Invasive monitoring is done through a central venous or arterial catheter.
- Tomographic methods. They are necessary to establish the causes of hemodynamic instability, to detect concomitant injuries that pose a danger to the patient. CT scan allows you to assess the condition of the spine, brain, and internal organs. MRI diagnostics are more informative for spinal injuries. In patients with shock reactions, imaging should be performed under close supervision.
Diagnostic lumbar puncture with cerebrospinal fluid analysis, neurophysiological studies (encephalography, neuromyography) are of great importance. A neurologist differentiates vascular insufficiency from hypovolemic, hemorrhagic, obstructive shocks. Therefore, patients need urgent advice from a traumatologist and neurosurgeon.
Cases of severe neurogenic shock caused by spinal cord or cerebral injury with a complete neurological deficit are life-threatening. Delays in surgical correction worsen an already severe prognosis. Even after hemodynamic stabilization of the patient, autonomic dysregulation persists for a long time. There is a risk of secondary complications and a decrease in the quality of life; preventative measures are reduced to the timely diagnosis of neurological pathology, early and complete therapy of systemic disorders.