Secretion Removal Techniques in People with Spinal Cord Injury through Physiotherapy

Respiratory complications are a leading cause of injury and mortality in people with spinal cord injury (SCI) and are more pronounced in individuals with higher level and complete injuries. A major contributor to respiratory illness in individuals with SCI is secretion retention, particularly among individuals with cervical lesions. Higher levels of SCI result in greater denervation of the ventilatory muscles thereby decreasing both inspiratory capacity and expiratory muscle force and resulting in an impaired cough. The figure shows the innervation of the respiratory muscles. Cervical SCI also denervates sympathetic pathways leading to a state of parasympathetic dominance that may increase mucus production and contribute to airway hyper responsiveness. A diminishing cough combined with mucus hyper secretion can overwhelm mucociliary clearance in people with SCI.

The impact of SCI on normal airway clearance can be exemplified by examining the sequence of a cough. After full inspiration to total lung capacity, the glottis is closed followed by an increasing intrathoracic pressure. Opening of the glottis is followed by a forced, high-velocity expiratory flow, which facilitates propagation of sputum towards the upper airway to expectorate or swallow. The ability to inspire to a normal vital capacity (VC) is progressively hindered with higher levels of SCI due to a greater denervation of inspiratory muscles. Inspiring to a lower VC therefore decreases the inward recoil of the chest wall and lungs that contributes to maximal expiratory flow. Forced expiratory flow is further impaired in people with SCI when the injury affects the abdominals and other expiratory muscles, such as intercostals (thoracic roots), pectoralis, or latissimus dorsi. With high thoracic SCI the VC might only be 30% to 50% of normal, and the cough might be weak and possibly ineffective. Spirometric measures, such as forced vital capacity (FVC), forced expiratory volume in 1 second, and VC, are therefore often valuable predictors of cough strength.

Non-SCI factors such as smoking, chronic obstructive pulmonary disease, asthma, and aging exacerbate increased mucus secretions resulting from cervical SCI. Increasing mucus production combined with a diminishing cough and breathing at a lower lung volume, contributes to micro atelectasis and potential trapping of retained secretions. Ultimately, an ineffective cough, micro atelectasis, and retained secretions increase the risk for both pneumonia and mucus plugs, which may lead to potential lung collapse and consolidation.

Physiotherapy treatment to facilitate airway clearance in people with SCI has included traditional chest physiotherapy techniques of manual percussions and vibrations as well as postural drainage. In addition, techniques to enhance forced expiration, including cough, have been used, such as those that improve inspiratory capacity and strength or increase expiratory flow and strength. Despite these physiotherapy techniques being commonly used there is a scarcity of published evidence to support their effectiveness in SCI. This systematic review was done to answer the question, “Do secretion removal techniques increase airway clearance in people with chronic SCI?” Thus focused on interventional and survey studies within the scope of physiotherapy practice, therefore excluding pharmaceutical interventions. In addition, sequelae associated with this acute phase, such as neurogenic pulmonary edema, unstable fractures, or aspiration pneumonia, would complicate the interpretation of outcomes as the result of airway clearance interventions such as percussion or assisted cough.