Respiratory impairment in SCI

Author(s): Heather Asthagiri, MD, Justin Weppner, DO, Sara Raiser, MD, and Justin Albright, MD

Originally published:11/05/2012

Last updated:03/27/2017

1. DISEASE/DISORDER:

Definition

Spinal cord injury (SCI) commonly results in some degree of respiratory dysfunction due to weakness or paralysis of the respiratory muscles, reduced vital capacity (VC), ineffective cough, reduction in lung and chest wall compliance, and increased oxygen cost of breathing due to respiratory system impairment. The range of respiratory complications following SCI includes dyspnea, respiratory failure, pulmonary thromboembolism, atelectasis, pneumonia, sleep disordered breathing, and dysphonia. The more rostral the level and the more complete the SCI, the more likely the injury will affect ventilation. Respiratory dysfunction is a major cause of morbidity and mortality in patients with SCI.1

Etiology

Normal respiration requires coordination between somatic control of the respiratory muscles and autonomic control of the bronchopulmonary tree.2 Inspiratory muscle impairment prevents deep breaths, leading to atelectasis and abnormalities of gas exchange and lung compliance.  Expiratory muscle dysfunction results in impaired cough and secretion clearance, increased airway resistance, and persistence of infection when it occurs.1 Loss of sympathetic autonomic signaling to the bronchopulmonary tree results in changes in mucus production and airway tone. The level and completeness of the SCI determine the severity of the respiratory dysfunction; greater impairment occurs with higher and more complete injuries.2 Patients with complete, high cervical injuries may be unable to sustain spontaneous ventilation. Those with lower or incomplete injuries typically demonstrate restrictive impairments and a weakened cough.

Epidemiology including risk factors and primary prevention

The incidence of respiratory complications varies, depending on the SCI population being studied. Not surprisingly, the incidence of respiratory dysfunction is higher in patients with cervical SCI. It has been shown to occur in 70% of cases with complete, cervical SCI and in 26.8% of cases with incomplete, cervical SCI.3 Pneumonia, atelectasis, and other respiratory complications reportedly occur in 40-70% of patients with tetraplegia, and are the leading cause of mortality in these patients.4 Other predictors of respiratory dysfunction in those with acute SCI include a history of trauma, advanced age, and prior cardiopulmonary disease.3 Independent risk factors for respiratory dysfunction include a lower forced expiratory volume in one second (FEV1) and a history of pneumonia or bronchitis since the SCI occurred. Patients with a history of smoking or chronic obstructive pulmonary disease (COPD) are also at increased risk for respiratory dysfunction. 5-7

Pathoanatomy/physiology

The degree of respiratory dysfunction associated with a traumatic injury to the spinal cord depends on the level of the spinal cord lesion.  Functional impairment worsens as the level of the injury moves more rostral. An injury classified as American Spinal Injury Association (ASIA) score A results in greater functional impairment than an incomplete injury in the ASIA score B–D categories.

Respiratory dysfunction in tetraplegia and high thoracic paraplegia results from compromise to the somatic and autonomic nervous systems.2

Somatic nervous system

  • The phrenic nerve, originating from C3-5, innervates the diaphragm, which is the primary muscle of inspiration. As such, preservation of the C3-C5 spinal cord segments is critical for maintaining spontaneous respiration.2 Patients with complete lesions at C1 and C2 cannot maintain effective spontaneous ventilation.8
  • Patients with incomplete or lower cervical SCI typically maintain spontaneous respiration, but due to partial or complete paralysis of other inspiratory muscles, often demonstrate more restrictive impairment than patients with thoracolumbar SCI.2
  • In neurologically intact individuals, maximal VC is achieved through contributions from the intercostal and scalene muscles. Abdominal muscle dysfunction limits the patient’s ability to raise abdominal pressure during inspiration, impairing optimal diaphragmatic contraction.
  • Loss of control of the abdominal and intercostal muscles impairs expiratory function including the ability to generate a forceful cough for airway clearance.2 To compensate, patients with tetraplegia may recruit the clavicular portion of the pectoralis major muscle to deflate the rib cage during expiration.8

Autonomic nervous system

  • Sympathetic: The cell bodies of preganglionic sympathetic neurons are located in the lateral grey column of the spinal cord from T1-L2/3. These neurons synapse with postganglionic neurons in paravertebral ganglia.
  • Parasympathetic: The cell bodies of the parasympathetic nervous system are located in the brainstem (CN III, VII, IX, X) or the sacral spinal cord (S2-S4).  The vagus nerve provides parasympathetic innervation to the lungs.
  • In acute, severe cervical and high thoracic SCI, much of the sympathetic tone is lost, leaving the parasympathetic nervous system to provide the dominant autonomic control of the bronchopulmonary system.2
  • Loss of sympathetic modulation of the parasympathetic outflow tract likely contributes to unopposed bronchoconstriction.2
  • In the acute phase of injury, airway secretions are produced in large volumes due to unopposed vagal tone in patients with cervical SCI.8 The secretions contribute to acute respiratory distress, hypoxemia, worsening hypercapnia, and the need for intubation for ventilatory support and airway suctioning. These events may be avoided when the expiratory muscles are assisted to help eliminate secretions.8

Disease progression including natural history, stages of disease, and disease trajectory (changes in clinical features over time)

Acute

  • Respiratory failure following acute SCI may occur because of partial or complete respiratory muscle paralysis, fatigue of remaining intact muscles, or in association with pleuropulmonary pathology.8 In addition, flaccid paralysis of the intercostal muscles worsens vital capacity, with the rib cage moving inward with diaphragm contraction.
  • Common respiratory complications during the first month after SCI include atelectasis, pneumonia, edema, pulmonary embolism, and aspiration. These account for the increased mortality rate during this time.3

Subacute

  • Improvements in respiratory function over time may be due to enhanced neurologic function in the cord segments at or above the level of injury with improved diaphragm function as tone increases, providing a more rigid rib cage and better lever arm for the diaphragm to work against.8
  • Studies have shown a significant improvement in VC within the first 5 weeks after SCI, with doubling of VC occurring within 3 months of the injury.3

Chronic

  • The severity of the SCI and a past history of tobacco smoking predict lung function impairment in chronic SCI.1
  • In the year following SCI, improvements may be seen in both FEV1 and VC. This has been attributed to an improvement in diaphragm performance, reflex activity in the abdominal and intercostal muscles, enhanced performance of the accessory muscles of the neck, and improvement in the diaphragm neural supply.1

Terminal

  • Respiratory dysfunction is the most common causes of death in the SCI population.8

Specific secondary conditions and complications

  1. Sleep-disordered breathing: There is a high prevalence of sleep-disordered breathing in patients with tetraplegia. Most demonstrate an obstructive sleep apnea (OSA) pattern thought to be related to neurologic deficits, obesity, and medications used for management of SCI. Polysomnography is the gold standard for OSA diagnosis. A machine that provides continuous positive airway pressure (CPAP), or in some cases bilevel positive airway pressure (BiPAP), can be helpful in managing OSA.4
  2. Aspiration and dysphagia: Risk factors for aspiration in the SCI population include: supine position, spinal shock, gastric reflux, inability to turn the head to spit out regurgitated material, medications that decrease GI motility or cause nausea and vomiting, recent anterior cervical spine surgery, presence of a tracheostomy, and advanced age. The presence of a tracheostomy is the strongest predictor of dysphagia in this population.4

2. ESSENTIALS OF ASSESSMENT

History

When assessing a patient’s risk of respiratory dysfunction, one should consider:4

  • Relevant past medical history, including a history of smoking and prior lung disease
  • Current medications, with particular attention being paid to bronchodilators, deliriogenic agents, and those that may impair respiratory drive such as opioids
  • Neurologic impairment, the strongest predictor of respiratory dysfunction after SCI
  • Coexisting injuries, such as a traumatic brain injury, rib fractures, and acute lung injury all of which influence a patient’s respiratory status

Physical examination

Signs of deteriorating respiratory function that may indicate the development of atelectasis and pneumonia include:4

  • Fever and other constitutional symptoms
  • Dyspnea and increasing respiratory rate
  • Increasing anxiety
  • Increased volume and tenacity of secretions
  • Declining oxygen saturation
  • Declining VC: VC < 15 cc/kg may indicate impending an need for assisted ventilation
  • Declining peak expiratory flow rate (especially during cough)

Functional assessment

Serial determination of VC, peak expiratory flow rate, negative inspiratory force (NIF), and oxygen saturation of blood should be performed.4 Signs of impending respiratory failure include hypoxia coupled with a rising respiratory rate, VC < 15 cc/kg, NIF < 20 cm H2O, hypercapnia, fatigue, and tachycardia.9 If any of these changes are noted, a chest radiograph should be performed.4

Laboratory studies

Following acute SCI, the initial assessment should include:4

  • Arterial blood gas
  • Routine laboratory analysis (CBC, BMP, coagulation profile, urinalysis, toxicology screen, cardiac enzymes)
  • Electrocardiogram
  • Chest radiographs

Imaging

  • Diaphragm fluoroscopy may be used to assess diaphragm movement.4 Phrenic nerve conduction studies can be used to assess phrenic nerve function.1
  • Chest radiographs can be used to identify atelectasis, pneumonia, or effusion.4
  • Pulmonary CT angiography (CTA) can be used to diagnose pulmonary emboli.

Supplemental assessment tools

Periodic assessments of respiratory function should include:4

  • Physical examination of the respiratory system
  • Chest imaging as appropriate
  • Continuous pulse oximetry
  • Assessment of respiratory muscles function, including VC and NIF
  • FEV1 or peak cough flow
  • Neurologic status and extent of impairment
  • Polysomnography

Early predictors of outcome

Mechanical ventilation is likely indicated if there is:

  1. One or more signs of respiratory distress9
  2. Hypercarbia with PaCO2 > 50 mmHg9
  3. Hypoxia with PaO2 < 50 mmHg that is unresponsive to oxygen therapy9
  4. The inability to handle oral secretions9
  5. A decline in VC to < 10-15cc/kg of ideal body weight (approximately 1000cc for the average 80 kg person)4

Life expectancy for any age or level of SCI is reduced if the patient remains ventilator-dependent.10

Environmental

Ventilator-dependent patients and their caregivers must plan in advance for emergencies. This includes maintenance of portable ventilators, ancillary respiratory equipment, power generators, and emergency call systems.4

When tetraplegic patients are traveling by air, meticulous advanced planning is required. Patients with respiratory compromise at ground level may require supplemental oxygen to avoid the hypoxemia that can develop at altitude. In addition, mucous plugging can be particularly problematic if the patient breathes dry air cycled from outside the aircraft. To combat mucous plugging, inspired air should be humidified when possible and suctioning equipment should be readily accessible during transport.11

Social support system

Important things to consider when treating patients with respiratory dysfunction due to SCI include:4

    • Establishing an effective communication system
    • Ensuring that family and caregivers receive adequate training
    • Assessing for possible concomitant traumatic brain injury
    • Assessing the patient’s adjustment to SCI
    • Considering the impact of medication side effects

Professional Issues

Given the quality of life issues that can arise in cases of ventilator-dependent tetraplegia, the presence of advance directives can help the treatment team formulate a clinical plan. In the rare situation where a patient wishes to withdraw treatment, it is important to address the medical as well as social factors that contribute to the patient’s expressed wishes. Specific procedures may involve assessing the patient’s capacity to make such decisions and the consistency of the decision, exposing the patient to other similarly injured individuals, consulting with the institutional ethics committee, and ensuring a humane end of life.4

3. REHABILITATION MANAGEMENT AND TREATMENTS

Current treatment guidelines

Consortium for Spinal Cord Medicine Clinical Practice Guidelines are available for respiratory management following spinal cord injury.4

At various disease stages

Ventilatory support:

  1. Glossopharyngeal breathing: performed by rapidly “gulping” a series of mouthfuls of air, forcing the air into the lungs, and then exhaling the accumulated air.1
  2. CPAP and BiPAP: may be used to rest the non-intubated patient and to give the patient a deep breath to help manage secretions.1
  3. Intermittent positive-pressure breathing: can be administered with mechanical devices or with a bag valve mask. It assists lung expansion by introducing large volumes of air. The pressure should be set at 10–15 cmH2O then gradually increased, never to exceed 40 cmH2O.4
  4. Phrenic nerve pacing: requires intact phrenic nerve function and allows for at least part-time freedom from mechanical ventilation.1
  5. Intramuscular diaphragm pacing: often requires a period of gradually increasing stimulation (reconditioning period) due to diaphragm atrophy.1

Secretion management/cough:

  1. Assisted cough: requires another person forcefully applying pressure to the abdomen to enhance expiratory flow and mobilize secretions.1
  2. Postural drainage: if the patient is immobilized, passive positioning techniques using gravity can facilitate the movement of secretions.1
  3. Suction catheter: applies negative pressure at the mouth or tracheostomy site.1
  4. Mechanical insufflation-exsufflation: involves maximal insufflation followed immediately by a decrease in pressure of about 80 cmH2O.1
  5. Bronchoscopy: the most effective method for secretion clearance; reserved for when other methods have been inadequate.1
  6. Bronchodilators: effective adjuncts to prevent atelectasis, decrease sputum production, and stimulate the secretion of surfactant. Beta-2-adrenergic medications improve expiratory pressures which may in turn translate to a more effective cough.9
  7. Mucolytic: medications such as guaifenesin used in combination with adequate oral hydration may thin pulmonary secretions and thereby increase their mobilization.9

Ventilator weaning:

  1. The parameters used to best determine if the patient is ready to be weaned from the ventilator include: values derived from arterial blood gas or capnography, vital capacity, the effectiveness of the cough, and the results of diaphragmatic electromyography.12
  2. Data suggests that cautious implementation of higher ventilator tidal volumes may treat atelectasis and contribute to a reduced time for ventilator weaning.4
  3. Weaning protocols described in the literature for cervical and high thoracic SCI suggest gradually increasing periods of ventilator-free breathing.13
  4. When weaning a patient with a complete cervical SCI, trials are more successful with the patient in a Trendelenburg position. In this position, the diaphragm is higher in the chest secondary to pressure from the abdominal contents. This improves diaphragmatic contraction since the higher the diaphragm is in the chest, the more effective is its contraction.14

Health maintenance:

  1. Recommend annual influenza and regular pneumococcal vaccinations.
  2. Encourage cessation of smoking and avoidance of second-hand smoke.

Coordination of care

Care of patients with SCI requires a multidisciplinary team including rehabilitation and pulmonary physicians, respiratory therapists, nurses, physical and occupational therapists, and speech and language pathologists (SLP). For patients requiring assisted ventilation, SLP is particularly important in aiding vocalization.

Patient & family education

Patients and their families must be well educated on the symptoms of respiratory dysfunction and know how to provide prompt assistance.

Emerging/unique interventions

Periodic spirometry (to assess VC, NIF, FEV1, peak cough flow) and polysomnography are recommended to evaluate for changes in pulmonary function and the development of OSA.4

Translation into practice: practice “pearls”/performance improvement in practice (PIPs)

Abdominal binders:

  1. Increase abdominal pressure and place the diaphragm in a more efficient position when upright, helping to increase tidal volume.1
  2. Improve speech in patients with cervical SCI who demonstrate low volume (due to impaired alveolar pressure-generation capability) and short phrases (due to small tidal volume).1

Speech generation:

  1. For ventilator-dependent patients with a tracheostomy, the tracheostomy tube cuff must be deflated for speaking. This often requires a coordinated increase in ventilator-delivered tidal volume to compensate for air loss through the larynx.1
  2. Tracheostomy-ventilation speech is often characterized by short phrases, long pauses, poor voice quality, and variable loudness. Modifying ventilator settings or using a one-way inspiratory valve may improve speech.1

4. CUTTING EDGE/EMERGING AND UNIQUE CONCEPTS AND PRACTICE

Cutting edge concepts and practice

Spinal cord stimulator cough assist: An emerging technique that produces vigorous abdominal muscle contraction via direct stimulation of the spinal cord by epidural electrodes.1

5. GAPS IN THE EVIDENCE-BASED KNOWLEDGE

Gaps in the evidence-based knowledge

Controversy remains about the optimal volume for ventilation of SCI patients. Further research aimed at determining the incidence of barotrauma and establishing ventilator weaning protocols is needed.

REFERENCES

  1. Brown R, DiMarco AF, Hoit JD, Garshick E. Respiratory dysfunction and management in spinal cord injury. Respir Care. 2006;51(8):853-68;discussion 869-70.
  2. Krassioukov A. Autonomic function following cervical spinal cord injury. Respir Physiol Neurobiol. 2009;169(2):157-164. doi: 10.1016/j.resp.2009.08.003 [doi].
  3. Casha S, Christie S. A systematic review of intensive cardiopulmonary management after spinal cord injury. J Neurotrauma. 2011;28(8):1479-1495. doi: 10.1089/neu.2009.1156 [doi].
  4. Respiratory management following spinal cord injury: A clinical practice guideline for health-care professionals. consortium for spinal cord medicine clinical practice guidelines. Washington, DC: Paralyzed Veterans of America; 2005:1-22.
  5. Stolzmann KL, Gagnon DR, Brown R, Tun CG, Garshick E. Risk factors for chest illness in chronic spinal cord injury: A prospective study. Am J Phys Med Rehabil. 2010;89(7):576-583. doi: 10.1097/PHM.0b013e3181ddca8e [doi].
  6. Stolzenberg D, Siu G, Cruz E. Current and future interventions for glenohumeral subluxation in hemiplegia secondary to stroke. Top Stroke Rehabil. 2012;19(5):444-456. doi: 10.1310/tsr1905-444 [doi].
  7. Waddimba AC, Jain NB, Stolzmann K, et al. Predictors of cardiopulmonary hospitalization in chronic spinal cord injury. Arch Phys Med Rehabil. 2009;90(2):193-200. doi: 10.1016/j.apmr.2008.07.026 [doi].
  8. Baydur A, Sassoon C. Respiratory dysfunction in spinal cord disorders. In: Lin V, Bono C, Cardenas D, et al, eds. Spinal cord medicine: Principles and practice. 2nd ed. New York, NY: Demos Medical Publishing; 2010.
  9. Bryce T, Ragnarsson K, Stein A. Spinal cord injury. In: Braddom R, Buschbacher R, Chan L, eds. Physical medicine and rehabilitation. 3rd ed. Philadelphia, PA: Elsevier; 2007:1322.
  10. DeVivo MJ, Ivie CS,3rd. Life expectancy of ventilator-dependent persons with spinal cord injuries. Chest. 1995;108(1):226-232. doi: S0012-3692(16)38621-4 [pii].
  11. Armitage JM, Pyne A, Williams SJ, Frankel H. Respiratory problems of air travel in patients with spinal cord injuries. BMJ. 1990;300(6738):1498-1499.
  12. Chiodo AE, Scelza W, Forchheimer M. Predictors of ventilator weaning in individuals with high cervical spinal cord injury. J Spinal Cord Med. 2008;31(1):72-77.
  13. Arora S, Flower O, Murray NP, Lee BB. Respiratory care of patients with cervical spinal cord injury: A review. Crit Care Resusc. 2012;14(1):64-73.
  14. Gutierrez CJ, Stevens C, Merritt J, Pope C, Tanasescu M, Curtiss G. Trendelenburg chest optimization prolongs spontaneous breathing trials in ventilator-dependent patients with low cervical spinal cord injury. J Rehabil Res Dev. 2010;47(3):261-272.

Original Version of the Topic

Deborah A. Crane, MD, MPH. Respiratory impairment with spinal cord injury. 06/07/2013.

Author Disclosure

Heather Asthagiri, MD
Nothing to Disclose

Justin Weppner, DO
Nothing to Disclose

Sara Raiser, MD
Nothing to Disclose

Justin Albright, MD
Nothing to Disclose

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