Anesthesia management for women with spinal cord injury
Acute spinal cord transection first results in flaccid paralysis with loss of sensation below the level of spinal cord injury.
US Spinal Cord Injury Score:
Grade A indicates complete impairment, i.e., total loss of sensory and motor function below the level of injury, including sacral segments 4-5 (by assessing the tone and sensation of the rectum).
Grade B indicates incomplete impairment, with sensory function below the level of injury, including sacral segments 4 to 5.
Grade C indicates incomplete impairment, i.e., motor function is present below the level of injury, and more than half of the muscles are less than grade 3. Grade D indicates incomplete impairment, i.e., motor function is present below the level of injury, and more than half of the muscles are at grade 3 or higher.
A grade of E indicates normal spinal cord function.
Pathophysiology of spinal cord injury
The extent to which spinal cord injury affects physiological function depends on the level of the spinal cord of the injury, with cervical spinal cord injury causing the most severe physiological dysfunction. A drop in blood pressure is often seen in acute traumatic spinal cord injury, especially if accompanied by cervical spinal cord injury. The decrease in blood pressure is mainly affected by two factors: loss of sympathetic nervous system activity and decreased vascular resistance, and bradycardia due to loss of T1-4 sympathetic innervation of the heart. This hemodynamic disturbance is called spinal shock and usually lasts 1-3 weeks. In patients with cervical and upper thoracic spinal cord injuries, the leading cause of death is alveolar hypoventilation with loss of ability to clear endobronchial secretions. Aspiration of gastric juice and gastric contents, pneumonia, and pulmonary embolism are common risk factors during spinal shock.
Sequelae of chronic spinal cord injury include: impaired alveolar ventilation, autonomic hyperreflexia, chronic respiratory and genitourinary tract infections, anemia, and thermostatias.
Transsection of the spinal cord at or above the 5th cervical vertebra may lead to apnea due to loss of C3-5 innervation of the diaphragm. Denervation of the intercostal and abdominal muscles decreases expiratory volume, and the ability to cough and clear airway secretions is often impaired. Arterial hypoxemia may occur, and optimal arterial oxygenation should be ensured prior to suctioning.
Autonomic hyperreflexia occurs after spinal shock and is initiated by skin or visceral stimulation below the level of spinal cord injury. Dilation of the bladder and rectum, as well as surgical procedures, are common irritants. Due to the presence of spinal cord transection injury, the efferent pathway below the level of injury loses the regulation of higher-level inhibitory impulses, and the impulse through the efferent pathway of the splanchnic nerve causes increased activity of the sympathetic nervous system, resulting in vasoconstriction below the level of spinal cord injury. Hypertension and reflex bradycardia are the main features of autonomic hyperreflexia, with reflex vasodilation above the transverse section of the spinal cord, and nasal congestion as evidence of vasodilation. Severe hypertension can cause headache, blurred vision, bleeding in the brain, retina, and subarachnoid space, and increased intraoperative blood loss. Acute left heart failure due to increased cardiac workload can cause pulmonary edema. Loss of consciousness, seizures, and various arrhythmias may also occur. This reflex is present in approximately 85% of patients with spinal cord transection injury above T6.
Prolonged bed rest can lead to osteoporosis, muscle wasting, pressure ulcers, and deep vein thrombosis. Pathologic fractures may occur at the time of metastasis, and deep vein thrombosis prophylaxis includes varicose vein stockings, low-dose anticoagulation, and venous strainer placement. Chronic urinary tract infections reflect a loss of complete bladder emptying and a tendency to form stones, and kidney failure is one of the common causes of death.
Obstetric management:
Decreased functional residual volume and expiratory volume due to spinal cord injury during pregnancy increases respiratory complications. Pregnancy increases the risk of deep vein thrombosis, pulmonary embolism, and urinary tract infections. Decreased sympathetic tone below the level of injury in pregnant women with spinal cord injury predispose to orthostatic hypotension, resulting in decreased uteroplacental perfusion. Uterine contractions can stimulate autonomic hyperreflexia, and secondary vasoconstriction can lead to fetal hypoxia and bradycardia. Women with T11 lesions or higher are at higher risk of preterm birth and do not have labor pain, and weekly cervical examinations should be noted in the third trimester. Vaginal delivery is preferred, but forceps may sometimes be required due to maternal weakness.
Anesthesia Management:
Cervical spine injuries may be present in patients with neck pain, signs and symptoms of neurologic injury, loss of consciousness, severe head injury, and/or poisoning. To protect the cervical spine, a cervical collar should be used to limit cervical spine movement before the patient is transported, and the first aid provider should use a hard collar to stabilize the cervical spine. The use of a hard collar to immobilize the cervical spine is not conducive to direct laryngoscope placement and endotracheal intubation, so difficult airway management tools (video laryngoscope, flexible bronchoscope, laryngeal mask) should be prepared at the time of intubation. If endotracheal intubation is required, the front of the C-neck collar can be removed while the assistant manually keeps the patient's head and neck in a straight stable position. The assistant can stand beside the patient or kneel at the head of the bed and hold the patient's head from the ear so that the patient's mouth can be opened when the laryngoscope is inserted. Patients with acute spinal cord injury must be intubated endotracheally with minimal neck movement and hypotension to maintain spinal perfusion pressure. Coughing may lead to displacement of the cervical spine, and it is necessary to maintain linear stability of the cervical spine with an assistant at all times during awake endotracheal intubation. Patients with cervical and upper thoracic spinal cord injuries are highly susceptible to significant decreases in blood pressure due to the loss of compensatory sympathetic responses, in the presence of emergency changes in position, blood loss, and positive airway pressure. Invasive arteries are necessary for continuous monitoring of blood pressure changes and rapid volume expansion with intravenous fluids. During acute spinal cord injury, ECG abnormalities are common. Optimal respiratory management is mechanical ventilation. Temperature changes below the cross-section of the spinal cord should be monitored and managed. The goal of anesthesia maintenance is to ensure physiological stability and tolerability of endotracheal intubation.
Anesthetic management of patients with chronic spinal cord transverse injury should focus on preventing autonomic hyperreflexia. Epidural anesthesia can treat autonomic hyperreflexia caused by uterine contractions during labor. Epidural anesthesia is less effective in preventing autonomic hyperreflexia than spinal anesthesia because epidural anesthesia is relatively poor for sacrococcygeal nerve block. In general anesthesia, the use of muscle relaxants facilitates endotracheal intubation and prevents reflex muscle spasm caused by surgical stimulation. Non-depolarizing muscle relaxants are the preferred drug for general anesthesia. Avoid succinylcholine in patients who have had a cervical injury for more than 24 hours, especially for 6 months of spinal cord transection. Haemodynamic changes must be noted, especially with cervical and high thoracic spinal cord injury. Regardless of the type of anesthesia used, vasodilators should always be available to treat sudden hypertension. Patients who have been bedridden for a long time should be highly suspicious of pulmonary embolism. Patients with impaired intercostal muscle function are at high risk of perioperative hypoventilation, decreased cough capacity, and consequent failure to discharge secretions.
Knowledge point collation: Wang Buguo, Department of Anesthesiology, Lintong District Maternal and Child Health Hospital, Xi'an City
Reviewer: Weike Tao, Department of Anesthesiology, University of Texas Southwestern Medical Center, Dallas
Xiangyong Zhou, The Second Affiliated Hospital of Zhejiang University School of Medicine
Bu Bo, Department of Anesthesiology, First Hospital of Traditional Chinese Medicine, Yiyang City, Hunan Province
Bibliography:
1. Ronald D. Miller, ed., translated by Deng Xiaoming, Zeng Yinming, Huang Yuguang, Miller Anesthesiology (8th Edition), Peking University Medical Press, 2017:1983, 2201.
2. Roberta L. Hines, ed., Yu Yonghao, Yu Wenli, Stuting Co-Existing Anesthesiology (6th Edition), Science Press, 2017:241-246.
3. John F. Butterworth, edited by Tianlong Wang, Jin Liu, and Lize Xiong, Morgan Clinical Anesthesiology (6th Edition), Peking University Medical Press, 2020:578.
4. David H. Chestnut, Editor-in-Chief, translated by Lian Qingquan, Chestnut Obstetric Anesthesiology (4th Edition), People's Medical Publishing House, 2013:1005-1006.
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