Respiratory assessment

The optimal position for assessing acute respiratory function is supine, as this position reduces the work of breathing and allows access for a range of assessments and interventions.

Ideally, head elevation should remain less than 30 degrees to minimise the risk of sacral skin shearing, while cases involving abdominal distension, obesity, or chronic spinal cord injury, a modified supine position with slight head elevation may be required.

Consider whether any of the following may affect capacity to be managed in supine:

• spinal alignment or other medical/orthopaedic precautions
• risk of aspiration in supine
• areas of skin breakdown.

Complete general observations of key clinical signs and note:

• blood gases and respiratory rate, within the context of any supplemental oxygen and/or ventilation supports
  • continuous pulse oximetry for at least 48-72 hours and beyond, until signs of spinal shock resolve and respiratory function stabilises
  • regular arterial blood gas and capnography monitoring, as pulse oximetry will not be sufficient to detect early signs of respiratory deterioration
• hypotension, bradycardia, or hypothermia, which is often secondary to ANS dysfunction
• pyrexia/fever, which may indicate respiratory complications such as pulmonary embolism or pneumonia
• pain, including capacity to manage normal tidal breathing versus higher inspiratory volumes and cough
• consciousness, particularly capacity to manage sputum and saliva clearance, follow instructions and communicate.

Auscultate all lung fields, with particular attention to the bases and note:

• the degree and symmetry of air entry
• the presence of any added sounds (e.g. crackles or wheezes), especially if aspiration is suspected
• the presence of additional tactile fremitus and external respiratory sounds.

Lung volume augmentation with a positive pressure breathing device may assist auscultation further. 

 

Spirometry, also known as respiratory function tests (RFTs) provide objective measures of respiratory muscle strength, lung capacity and forced expiratory flow rates.

Spirometry is valuable to:

• monitor respiratory function deterioration or improvement
• guide use of ventilation support, including weaning and decannulation
• evaluate the effectiveness of interventions, including lung volume augmentation and secretion management
• educate on strategies such as abdominal binder use in sitting to support diaphragm function.

Following SCI, changes from predicted spirometry values typically correlate with the neurological level of injury (NLI) and the degree of motor completeness.

The diagram below highlights the overall reduction in lung volumes following SCI, particularly at a cervical NLI.

These changes commonly reflect a restrictive lung pattern.

For a full description of spirometry measures, refer to Normal respiratory function: Measures of air volume and flow rate.

Spirometry trends

Cervical SCI: VC may be reduced to 20–60% of predicted values.

Thoracic SCI: VC may be reduced to 80–90% of predicted values.

Respiratory pattern: FEV₁ is typically reduced in proportion to FVC, consistent with a restrictive lung pattern (with the FEV₁/FVC ratio >0.7).

However, this pattern can become mixed due to any pre-existing chronic airway diseases or autonomic nervous system (ANS) disruption—such as bronchospasm or increased sputum production—which causes obstruction (FEV₁/FVC ratio <0.7).

Impact of time: Respiratory dysfunction usually improves over time as spinal shock resolves, along with the positive effects of neural plasticity and rehabilitation. Factors contributing to this improvement were discussed earlier.

Spirometry indicators

Spirometry predictive values for a person with SCI are dependent on many factors such as sex, age, height, weight and ethnicity, so the following is only a guide.

Spirometry should be used to identify respiratory function trends to inform management, rather than just capturing absolute values in isolation. Results should be considered in the context of a holistic assessment, including the potential risks of acute or chronic respiratory complications.

The following spirometry values are not prescriptive in the acute or chronic management of a person with SCI. Rather they are indicative, reflecting evidence-based values reported in the literature relevant to acute neuromuscular disease management, including SCI.

MIP < -30 cmH₂0 indicates significant reduction in inspiratory muscle strength and likely increased work of breathing: there is a high risk of impending respiratory fatigue and failure—ventilation support may be indicated.

FVC < 15-20 mL/kg indicates significant reduction in lung volumes and respiratory muscle strength: there is a high risk of impending respiratory fatigue and failure—ventilation support may be indicated.

PCF < 270 L/min indicates reduction in lung volumes and respiratory muscle strength: there is a high risk of developing retained secretions—use of a manual or mechanical assist cough may be indicated.

PCF < 160 L/min indicates significant reduction in lung volumes and respiratory muscle strength: there is a high risk of developing retained secretions, even with a manual assisted cough—use of a mechanical assisted +/- manual cough may be indicated.

MEP < 40 cmH₂0 indicates significant reduction in expiratory muscle strength: cough is ineffective and there is a high risk of developing retained secretions, even with a manual assisted cough—use of a mechanical +/- manual assisted cough may be indicated.

The diaphragm, intercostal, and abdominal muscles are the primary respiratory muscles to assess, along with a range or accessory muscles. For more information, refer to Respiratory muscles.

A holistic assessment of respiratory muscle function should involve a neurological assessment, breathing pattern analysis, inspiratory and expiratory muscle palpation, along with a review of the work of breathing.

Neurological assessment

For information, refer to Respiratory Predictive Factors.

Breathing pattern analysis

Altered breathing patterns may be caused by factors such as pain inhibition, altered consciousness etc. However, it may also indicate impaired respiratory muscle function, while highlighting the risk of hypoventilation and respiratory fatigue.

Paradoxical breathing pattern

Palpate the anterior rib cage while observing the intercostal spaces and abdominal rise during quiet and forced inspiration.
• Anterior chest wall collapse and intercostal recessions with excessive abdominal rise typifies paradoxical breathing, including flaccid muscle paralysis of the intercostal and abdominal muscles.

For more information, see Respiratory Changes: Paradoxical breathing.

Inspiratory muscle assessment

Diaphragm palpation

Qualitative diaphragm movement can be assessed when viewing the patient in the supine position from the foot end of the bed to assess symmetry on quiet and deep inspiration.

Bilaterally palpate the upper abdomen during quiet and deep inspiration.
• Poor abdominal rise may indicate diaphragm weakness or abdominal restriction (e.g. paralytic ileus).
• Excessive abdominal rise is a feature of paradoxical breathing, indicating flaccid muscle paralysis of the abdominal muscles and loss of positioning support of the diaphragm.
• Asymmetry of abdominal rise may suggest hemidiaphragm dysfunction.

Intercostal muscle palpation

Bilaterally palpate the lower lateral ribcage during quiet and deep inspiration.
• Poor expansion may indicate intercostal weakness.
• Collapse of the anterior chest wall and intercostal recessions are features of paradoxical breathing, indicating flaccid muscle paralysis of the intercostal muscles.

Accessory muscle palpation

Palpate the scalene, sternocleidomastoid, and upper trapezius muscles during quiet and deep inspiration.
• Significant activity during quiet breathing indicates increased work of breathing, risk of respiratory fatigue, and potential for hypoventilation.

Expiratory muscle assessment

Abdominal muscle palpation

Palpate the abdomen bilaterally during forced expiration and cough versus a huff.
• Low-volume exhalation or cough indicates abdominal muscle weakness or paralysis (in addition to reduced inspiratory capacity). Determine if cough is effective, noting that ineffectiveness may relate to expiratory muscle weakness and/or fatigue, but also mucous viscosity.
• Reduced voice projection may indicate loss of transdiaphragmatic pressure generation from significant abdominal muscle paralysis (in addition to reduced inspiratory capacity).

The presence of any increased work of breathing, along with any progressive worsening, heightens the risk for respiratory fatigue and possibly respiratory failure. Any of the following signs and symptoms constitutes an increased work of breathing:

• paradoxical breathing
• increased airway/inspiratory resistance e.g bronchospasm, atelectasis, sputum retention
• any compensatory responses to declining ventilation e.g. increased respiratory rate, recruitment of accessory muscles in speech or quiet breathing
• activities related to personal and acute medical care

For more information, refer to Work of breathing.

In addition to mobilising sputum from peripheral airways into the mouth, it is also important to determine if there are particular care needs related to sputum and/or saliva clearance from the mouth. This may be due to reduced consciousness, spinal precautions, impaired upper limb function or dysphagia etc.

Ineffective sputum and/or saliva clearance from the mouth can not only be distressing for the person with SCI, it can become a risk for aspiration or choking. This risk may be compounded by other factors such as reduced consciousness, pain etc.

Sputum and saliva productivity

Identify whether the person’s cough and huff is dry or moist, and also whether the person’s mouth is similarly dry or moist.

Note the volume of sputum and saliva production, as well as colour and thickness; also whether both are being effectively cleared from the mouth, either by swallowing or other strategies.

The risk of vomiting or reflux should also be considered in the context of managing oral clearance.

Oral care plan

Observation and treatment notes, along with swallowing assessments should inform an oral care plan and may include:

• positioning in side-lying to reduce risk of aspiration and improve clearance
• regular mouth suctioning and hygiene via nursing care, plus yankeur suction unit within the person with SCI’s reach
• speech pathology referral for swallowing and oromotor assessment
• appropriate medication to reduce sputum and saliva production, or vomiting and reflux
  • anti-cholinergic medications
  • antibiotic therapy
  • antiemetic medications
• appropriate humidification, hydration and mucolytic agents to aid sputum clearance
• physiotherapy referral for additional treatment to aid sputum clearance
• regular monitoring including auscultation, to detect any signs of aspiration, desaturation or respiratory distress.

Dysphagia

A person with high-level cervical SCI should have an early swallow and voice assessment, especially following extubation or cervical spinal surgery (e.g. anterior cervical discectomy and fusion).

For more information on swallowing dysfunction, refer to Dysphagia.

Voice and phonation

A review of a person with SCI’s voice and phonation may highlight the risk of respiratory fatigue, as well as highlight the need for additional nurse call and communication systems.

When spirometry is not immediately available following an acute SCI, timed sustained phonation also offers a simple method to estimate lung capacity, flow rates, and respiratory muscle strength.

A common approach involves asking the individual to sustain the vowel sound “a” at a normal pitch and volume. Typical sustained phonation times for adults range from 15 to 35 seconds, with males generally achieving longer durations.

During the rehabilitation phase following SCI, voice and phonation tasks can serve dual purposes:
• as a functional assessment of respiratory support needed for speech to promote communication (e.g. ventilation settings, lung volume augmentation techniques)
• as an intervention for respiratory muscle training.

For example, following a maximal inhalation or air stacking using a lung volume recruitment (LVR) bag, the number of words spoken in one breath can be counted to assess augmented lung volume for expiratory control.

A range of medical investigations may be used to assess changes in respiratory function and identify the onset of secondary complications following SCI. These investigations may include:

Blood pathology

• arterial blood gas analysis to assess gas exchange and ventilation status
• screening for infection and electrolyte imbalances.

Hypoventilation develops when ventilation is inadequate, resulting in insufficient removal of CO₂ from the blood and potentially insufficient O₂ intake. 

If sustained and significant, hypoventilation is associated with

• hypercapnia, which is a build-up of CO₂ in the blood (PaCO₂ to levels >45 mmHg)
• hypoxaemia, which is a deficiency of especially O₂ in the blood, which worsens during sleep (PaO₂ <60 mmHg).

Sputum pathology

• screening for infection.

Radiological lung imaging

• chest x-ray to detect any lung consolidation or collapse as well as check diaphragm positioning, including any hemidiaphragm abnormalities
• diaphragm ultrasound to evaluate diaphragm function, although it is less effective than spirometry for assessing performance and quantifying improvements
• computed tomography pulmonary angiogram (CTPA) to investigate suspected pulmonary embolism.

Other respiratory function tests

• comprehensive spirometry (e.g. plethysmography, flow-volume loops)
• investigations for sleep-disordered breathing (e.g. overnight oximetry, polysomnography).

• poor positioning
• insufficient ventilation support, lung volume augmentation and secretion management
• development of respiratory/medical complications
• combination of above contributing to respiratory fatigue and failure.

• stabilised cardiovascular function
• early and optimal ventilation support
• prevention and treatment of secondary respiratory complications
• resolution of spinal shock, leading to a transition from flaccid to spastic tone of respiratory muscles, resulting in:
  • reduced abdominal and chest wall compliance, improving diaphragm function
  • reduced breathing effort, especially when sitting upright
• reduction of inflammation and oedema around the spinal cord and secondary injury sites (e.g. chest wall), along with neural plasticity
• general muscular strengthening and training, improving recruitment of the diaphragm and other respiratory muscles from neural plasticity and rehabilitation interventions
• improved cardiopulmonary fitness through mobilisation, rehabilitation and engagement in activities of daily living.