Residency · Residency · Physical Medicine Rehabilitation
Respiratory Management in Cervical SCI
Overview
Respiratory complications are the leading cause of morbidity and mortality in acute and chronic cervical SCI. Pulmonary embolism and pneumonia are the top causes of death in the first year after SCI. Respiratory impairment severity directly correlates with injury level and completeness. Understanding respiratory muscle innervation is essential for predicting deficits and guiding management.
Respiratory Muscle Innervation
Diaphragm: C3, C4, C5 (phrenic nerve) - primary inspiratory muscle (60-80% of tidal volume). Accessory inspiratory muscles: Sternocleidomastoid: CN XI (spinal accessory). Scalenes: C3-C8.
Trapezius: CN XI, C3-C4. Intercostals: External intercostals (inspiratory): T1-T11. Internal intercostals (expiratory): T1-T11.
Abdominal muscles (primary expiratory/cough): Rectus abdominis: T6-T12. External obliques: T7-T12. Internal obliques: T7-L1. Transversus abdominis: T7-L1.
Respiratory Impairment by Injury Level
C1-C2 (Above Phrenic Nucleus)
Complete diaphragm paralysis. Total ventilator dependence. No volitional cough. Consider diaphragmatic pacing if phrenic nerve intact.
C3-C5 (Phrenic Nucleus Level)
Variable diaphragm function depending on completeness. C3: usually ventilator dependent initially, some may wean. C4: partial diaphragm function, may achieve ventilator-free breathing. C5: diaphragm usually intact, accessory muscles variably preserved. No intercostal or abdominal muscle function. Severely impaired cough.
C6-C8
Intact diaphragm. No intercostal function (C6-C7) to partial (C8). No abdominal muscle function. Impaired cough, reduced vital capacity (50-70% predicted). Paradoxical breathing pattern may be present.
T1-T6
Intact diaphragm. Progressive intercostal function. Absent or minimal abdominal muscle function. Moderately impaired cough.
T7-T12
Intact diaphragm and intercostals. Progressive abdominal muscle recovery. Mildly impaired to near-normal cough. Respiratory function approaches normal by T12.
| Injury Level | Diaphragm | Intercostals | Abdominals | Cough | Ventilator Need |
|---|---|---|---|---|---|
| C1-C2 | Paralyzed | Absent | Absent | None | Dependent |
| C3-C5 | Variable | Absent | Absent | Severely impaired | Variable; may wean |
| C6-C8 | Intact | Absent/partial | Absent | Impaired | Usually not needed |
| T1-T6 | Intact | Progressive | Absent/minimal | Moderately impaired | Not needed |
| T7-T12 | Intact | Intact | Progressive | Mildly impaired → normal | Not needed |
<image>Respiratory muscle innervation levels and predicted respiratory function by spinal cord injury level</image>
Acute Respiratory Management
Initial Assessment
Vital capacity (VC): most important bedside measure. VC < 15-20 mL/kg: consider intubation. VC < 10 mL/kg: intubation usually required. Negative inspiratory force (NIF): < -20 cmH2O suggests inadequate spontaneous breathing.
Peak cough flow (PCF): < 160 L/min = ineffective cough. Serial monitoring essential (respiratory function may worsen in first 3-5 days due to ascending edema). ABG monitoring for hypercapnia.
Ascending Injury Pattern
Cervical SCI may demonstrate worsening respiratory function over 48-72 hours. Cord edema can ascend 1-2 levels. Vital capacity should be monitored every 4-6 hours initially. Declining VC trend is more important than absolute value.
Intubation and Mechanical Ventilation
C1-C3 complete: nearly always require intubation. C4-C5: variable - close monitoring with low threshold for intubation. Preferred: orotracheal intubation with in-line stabilization. Avoid succinylcholine after 48 hours post-injury (hyperkalemia risk from denervation).
Secretion Management
Impaired cough is the primary contributor to respiratory complications. Secretion retention leads to atelectasis, mucus plugging, pneumonia.
Techniques
Assisted cough (quad cough): manual abdominal thrust timed with expiratory effort. Caregiver places hands below diaphragm and pushes inward and upward during cough. Mechanical insufflation-exsufflation (MI-E / CoughAssist): Delivers positive pressure (insufflation) followed by rapid negative pressure (exsufflation).
Simulates normal cough mechanism. Typical settings: +40/-40 cmH2O. First-line device for cough augmentation in SCI. Chest physiotherapy: percussion, vibration, postural drainage.
Suctioning: nasotracheal or via tracheostomy as needed. Nebulized bronchodilators and mucolytics: as adjuncts. Adequate hydration: prevents mucus thickening.
<image>Secretion management techniques in cervical SCI including assisted cough and mechanical insufflation-exsufflation</image>
Ventilator Weaning
Prerequisites for Weaning
Hemodynamic stability. Absence of active infection/sepsis. Adequate nutrition. Resolution of spinal shock. FiO2 ≤ 40%, PEEP ≤ 5 cmH2O. Baseline VC assessment.
Weaning Protocols
Progressive ventilator-free breathing (PVFB): Preferred method in SCI. Gradual increase in time off ventilator (sprinting). Start with 5-15 minutes off ventilator, increase progressively.
Monitor VC and SpO2 during trials. Rest on ventilator overnight initially. Weaning success is possible even in high cervical injuries if diaphragm has partial function. Average weaning time: days to months depending on injury level.
C1-C2 complete: unlikely to wean fully. C3-C4: may achieve partial to full ventilator independence with diaphragm recovery. C5 and below: most achieve full ventilator independence.
Predictors of Successful Weaning
Injury level (lower = better). Incomplete injury (AIS B-D better than A). VC > 15 mL/kg. Younger age. Absence of chest wall/lung injury. Good nutritional status.
Tracheostomy
Indications: prolonged ventilator dependence (typically after 7-14 days of intubation). Benefits: improved comfort, oral hygiene, speech (with speaking valve), easier suctioning. Timing controversy: early (< 7 days) vs. late (> 14 days) tracheostomy. Recent evidence suggests early tracheostomy may reduce ICU stay and pneumonia rates.
Speaking valves (Passy-Muir): allow phonation during exhalation, improve swallowing, enhance quality of life. Decannulation criteria: ventilator independence, adequate cough, manageable secretions, tolerate capping trial.
Diaphragmatic Pacing
Electrical stimulation of phrenic nerve to produce diaphragmatic contraction. Requirements: intact phrenic nerve and diaphragm (nerve conduction study to confirm). Types: Surgical phrenic nerve electrode placement (thoracoscopic).
Intramuscular diaphragmatic pacing (laparoscopic). Benefits: ventilator independence, improved speech quality, portability, reduced infection risk. Not suitable for lower motor neuron phrenic nerve injuries (C3-C5 anterior horn cell destruction). Progressive conditioning over weeks to months.
Sleep-Disordered Breathing in SCI
Prevalence of obstructive sleep apnea: 25-60% in SCI (higher than general population). Risk factors: supine positioning, medications (opioids, baclofen, benzodiazepines), obesity, neck anatomy. Central sleep apnea also occurs, especially in cervical injuries. Screening: Epworth Sleepiness Scale, STOP-BANG. Diagnosis: polysomnography. Treatment: CPAP/BiPAP, positional therapy, medication adjustment, weight management.
<image>Diaphragmatic pacing system components and surgical electrode placement on the phrenic nerve</image>
Abdominal Binder
External support for paralyzed abdominal muscles. Improves diaphragm mechanics by maintaining abdominal contents in position. Increases vital capacity by 10-15% in upright position. Most beneficial in upright/seated position.
Should be loosened or removed when supine (may restrict diaphragm). Standard of care for cervical and high thoracic SCI.
Clinical Pearls
Respiratory function may worsen in the first 3-5 days after cervical SCI due to ascending cord edema - never assume initial assessment reflects final respiratory status. The vital capacity trend is more informative than a single measurement - serial monitoring every 4-6 hours is essential in acute cervical SCI. Mechanical insufflation-exsufflation (CoughAssist) is the single most important device for secretion management in cervical SCI. An abdominal binder should be applied when patients with cervical/high thoracic SCI are upright, as it substitutes for paralyzed abdominal muscles and improves vital capacity. Always check phrenic nerve function (nerve conduction studies) before considering diaphragmatic pacing - intact lower motor neurons are required.
References
- Berlowitz DJ, et al. Respiratory management of people with spinal cord injuries. In: Eng JJ, et al., editors. Spinal Cord Injury Rehabilitation Evidence. Version 7.0. 2020.
- Galeiras Vázquez R, et al. Respiratory management in the patient with spinal cord injury. BioMed Res Int. 2013;2013:168757.
- DiMarco AF. Phrenic nerve stimulation in patients with spinal cord injury. Respir Physiol Neurobiol. 2009;169(2):200-209.
- Berlly M, Shem K. Respiratory management during the first five days after spinal cord injury. J Spinal Cord Med. 2007;30(4):309-318.
- Cifu DX, et al. Braddom's Physical Medicine and Rehabilitation. 6th ed. Elsevier; 2020.
