Evidence-based respiratory management strategies required to prevent complications and improve outcome in acute spinal cord injury patients

Abstract

Spinal injuries without neurological damage have little effects on respiratory function unless associated with injury to the chest wall. Early verticalisation or mobilisation of these patients is safe and likely to improve vital capacity. Spinal injury with cord damage has a profound effect on the mechanics of respiration and on respiratory function particularly in cervical cord injuries. Around 40% of spinal cord injuries occur in the cervical spine, a trend that is steadily increasing, with respiratory causes being responsible for death in over 20% of individuals. Loss of lung volumes and relative hypoxemia contribute to global hypoxaemia, exacerbating cord ischaemia in the acute period. Respiratory compromise results in the loss of muscle strength generation capacity and reduced lung volumes and in particular vital capacity, of up to 70%, ineffective cough and secretion clearance abilities; reductions in both lung and chest wall compliance and an additional oxygen cost of breathing due to changes in respiratory mechanics, with obstructive sleep apnoea evident in over 50% of acute tetraplegics. While some countries have specialist spinal centres to manage such catastrophic trauma with a demonstrable improvement in health outcomes attributed to their contribution, many individuals are initially admitted to local hospitals where healthcare professionals are less likely to fully appreciate the significant and continued vulnerabilities of such individuals. This article aims to provide a basic understanding of the causes and identification of the main principles of the respiratory management strategies required to maintain pulmonary health for cervical spinal cord injury patients during the initial and early post trauma phase.

Keywords

Spinal cord injuries respiratory management complication

Introduction

Spinal injuries without neurological damage have little effects on respiratory function unless associated with injury to the chest wall. Early verticalisation/mobilisation of these patients is safe and likely to improve vital capacity (VC).

Spinal injury with cord damage (SCI) has a profound effect on the mechanics of respiration and on respiratory function particularly in cervical cord injuries. Early mobilisation of patients with high thoracic and cervical cord injuries especially during the stage of spinal shock is likely to cause further reduction in VC-added morbidity.^1,2 Respiratory complications are the leading cause of morbidity and death after SCI.^3–5 The degree of respiratory dysfunction depends on pre-existing pulmonary status, the level of SCI, any associated chest wall or lung injuries as well as on the quality of the management of the physiologically impaired respiratory functions. The more rostral and complete the damage to the spinal cord, the greater the likelihood of major respiratory impairment.

The impact of spinal shock on respiratory function following acute SCI can be severe necessitating a transient need for an artificial airway and mechanical ventilatory assistance. As spinal shock resolves the flaccid paralysis of the chest wall muscles is replaced by spasticity. The chest wall becomes rigid with loss of compliance while the abdomen is hypercompliant. These factors both contribute to the reduction in tidal volume in the sitting posture resulting in impaired respiratory function particularly during inspiration.⁶ Additionally, pulmonary function may be altered in SCI due to the loss of ventilatory muscle function from denervation, concomitant lung injuries such as pneumothorax, haemothorax or pulmonary contusion, and decreased central ventilatory drive that is associated with head injury or the effects of alcohol and drugs.

Around 40% of SCIs occur in the cervical spine, a trend that is steadily increasing, with respiratory causes being responsible for death in over 20% of individuals.⁷ Loss of lung volumes and relative hypoxemia contribute to global hypoxaemia, exacerbating cord ischaemia in the acute period.^7–11 Respiratory compromise results in the loss of muscle strength generation capacity and reduced lung volumes and in particular VC of up to 70%, ineffective cough and secretion clearance abilities;^7–11 reductions in both lung and chest wall compliance and an additional oxygen cost of breathing due to changes in respiratory mechanics, with obstructive sleep apnoea evident in over 50% of acute tetraplegics.¹²

While some countries have specialist spinal centres to manage such catastrophic trauma with a demonstrable improvement in health outcomes attributed to their contribution,¹³ many individuals are initially admitted to local hospitals where healthcare professionals are less likely to fully appreciate the significant and continued vulnerabilities of such individuals. This article aims to provide a basic understanding of the causes and identification of the main principles of the respiratory management strategies required to maintain pulmonary health for cervical SCI patients during the initial and early post trauma phase.

Respiratory mechanics

Individuals with SCI exhibit reduced lung volumes and expiratory flow rates as a result of respiratory muscle weakness. These features have been investigated in relation to the combined effects of injury level and posture. Supine values of forced VC and forced expiratory volume in 1 s were repeatedly and consistently shown to be larger in recumbence compared with the seated posture.^14–17

Early mobilisation of patients with spinal neural tissue injury is associated with a reduction of VC and a potential drop of oxygen saturation (SaO₂) and/or postural hypotension. Individually or in combination, these may further impair cord functions. The tetraplegic and high paraplegic patient’s ability to cough is markedly impaired due to the loss of motor function in the abdominal and expiratory muscles. It is more difficult to get rid of bronchial secretions with assisted coughing against gravity than when patients are in recumbence.

Complete injuries above the mid-thoracic region will result in loss of the major respiratory muscle groups for both inspiration and expiration and thus an inability to either fully aerate the lungs or to clear pulmonary secretions, resulting in major vulnerabilities toward pulmonary collapse and infection. The higher the cord lesion, the greater the loss of muscle function.

Intercostal and abdominal muscle paralysis results in paradoxical chest wall motion, i.e. the thorax is pulled in on inspiration, while the hypercompliant abdomen moves out; with additional loss of diaphragmatic excursion through the zone of apposition (Figure 1).¹⁸

Thus, the upright sitting posture results in lower lung volumes than supine lying since the diaphragm loses its ability to generate the same force of contraction.^14–19 Whilst somewhat counterintuitive to the respiratory clinician, the supine position should be adopted in times of respiratory compromise and throughout the process of weaning from mechanical ventilation in complete cord lesions. The use of abdominal binders applied over the lower ribs and abdomen (Figure 2) is common practise in the specialist centres for use in the upright position,²⁰ improving the VC by as much as 0.32 L.²¹ This application may, in borderline cases, offset the need for mechanical respiratory support.

Assessment and management strategies

The clinical assessment of pulmonary function in acute SCI begins with a careful history regarding respiratory symptoms and a review of underlying cardiopulmonary co-morbidity such as chronic obstructive pulmonary disease or heart failure. Evaluation also includes respiratory rate (RR), chest wall expansion, abdominal wall movement, force of cough, chest, limbs and other associated injuries according to a detailed secondary survey. Arterial blood gas (ABG) analysis and pulse oximetry are especially useful because the bedside diagnosis of carbon dioxide (CO₂) retention or hypoxia may be difficult.

Atelectasis and pneumonia pose significant morbidity and are reported in 40%–70% of cases. Respiratory assessment should be vigilant, simple and repeated frequently at the bedside to warn of impending or frank respiratory failure. Aggressive respiratory management has been advocated for the prevention and treatment of pulmonary complications and has been associated with improved outcomes.^3,22,23

As a minimum, the VC, RR and SaO₂ should all be monitored regularly, and their trends considered, preferably with ABGs performed at frequent intervals during the first few weeks post injury. The initial reduction of VC in the acute phase will increase steadily within the first five weeks post injury.⁸ While a reduction in VC to 10 mL/kg body weight is accepted, further reductions due to loss of compliance or increased resistance (e.g. atelectasis and/or infection), will cause rapid deterioration while a peak cough flow rate (which reduces with lower VCs) of at least 160 L/s is essential to shear mucus along the airway walls, for airway clearance.²⁴ The provision of assisted cough to increase the mucus clearance ability,²⁵ either manually or mechanically²⁷ is vital in reducing the risk of pulmonary complications and subsequent respiratory failure.

A VC < 700 mls may be inadequate to sustain spontaneous breathing and is a major indicator to provide ventilatory support. Prompt support with non-invasive ventilation (NIV) may enable the avoidance of invasive tracheal intubation in acute SCI.²⁶ However, halo fixation may pose particular difficulties with mask fitting for NIV therapy while other risks associated with NIV in a non-specialised spinal centre include the ASCI patient’s susceptibility to profound and rapid desaturation, silent fall into respiratory failure, paralytic ileus and risk of air swallowing posing an increased risk of acute vomiting and aspiration. The loss of arm and hand function must not be forgotten when selecting and managing the NIV interface and airway.

Neurological deficits may be asymmetrical so the all-important diaphragm should be considered as two separate halves. Paralysis of a single hemi-diaphragm in a complete cervical spine injury, which may go unnoticed by the untrained eye, may require longer term or at least part-time respiratory support, since all intercostal and abdominal muscle activity will be lost. There has been identified more recently a crossed phrenic nerve pathway thought able to support the contralateral diaphragm, though the clinical implications of this have not yet been fully explored.²⁷ Where diaphragm function is uncertain, more detailed assessment in the form of fluoroscopic screening,²⁸ M mode ultrasound²⁹ and surface EMG are all useful assessment tools.

Aspiration poses a significant risk in the tetraplegic patient. Kirshblum et al.³⁰ studied 187 acute SCIs. Forty-two patients had signs of aspiration with video fluoroscopic confirmation in 31 of these. Kirshblum’s independent predictors of dysphagia by Videofluoroscopic Swallow Study (VFSS) were tracheostomy tube at the time of admission, recent cervical spine surgery particularly with an anterior approach and age. Clinically, aspiration often goes unnoticed but may present as repeated respiratory infections or repeated/persistent lobar collapses. Assessment of swallowing with speech and language therapist input is vital, as salivary and/or food aspiration can have a major detrimental impact upon respiratory health and complicate the ongoing management. Medications should be reviewed due to the effects of some on muscle fibres, such as corticosteroids and lipid lowering agents. The profound psychological impact of denying oral intake in the medium and/or longer term, in a high SCI individual should not be overlooked.

Respiratory care in the acute stage – An Oswestry experience of respiratory management in self-ventilating tetraplegia patients

The Midland Centre for Spinal Injuries set up in 1965, is one of 12 tertiary specialised spinal injury centres within the United Kingdom. This 44 bedded centre is dedicated to the specialist care for patients with SCI and provides holistic acute management, comprehensive rehabilitation and lifelong care for those living with SCI. The centre caters to a wide geographic area including the West Midlands, north and mid-Wales and the south of the North West region (Cheshire) – a population of the order of approximately 10 million people. Approximately 120 ‘new’ SCI patients are admitted each year.

Over the years, the centre has developed an intensive management programme of respiratory care, as a preventative measure especially, for tetraplegic patients at risk of developing respiratory complications. This includes three hourly high side turns on a mechanical bed with turning system or manual side turns; regular deep breathing exercises; assisted coughing for secretion clearance; use of incentive spirometry to optimise lung capacity,³¹ use of non-invasive biphasic positive airway pressure,³² as a routine prophylactic treatment for improving lung capacity and preventing atelectasis rather than as a mechanism for assisted ventilation. A ‘Cough Assist’ machine is also used in selected patients.³³ In later stages, inspiratory training is used with the Train Air³⁴ which is a computer programme linked to an inspiratory mouthpiece.

Tetraplegic patients use this as part of their gymnasium routine like a paraplegic would use the weight machines. The biggest result is increased voice projection. Close monitoring of respiratory function is also carried out relying on RR, pulse oximetry, regular use of microspirometer to record VC, monitoring peak flow where relevant and ABG analysis. Care is also taken to ensure adequate hydration, and all oxygen delivered is humidified. The management programme has been developed out of practice and expert view of the treating clinicians within the department.

Although widely practiced throughout the world, some of the practices mentioned lack clear scientific evidence. It was therefore felt that an audit of such practice would be useful within the department. An internal audit in 2007 had looked into the respiratory complications in acute tetraplegic patients before and after transfer (between 2003 and 2004) to this centre. This showed that such measures were successful in preventing ‘new’ onset respiratory complications (5 out of 67 patients; 7.5%) but identified certain areas to improve (mainly relating to documentation of respiratory function monitoring).

The re-audit was a retrospective study looking into the respiratory complications amongst all acute tetraplegic patients admitted over a three-year period between 2007 and 2009. The same parameters as in the 2007 audit were considered. These were patient and injury demographics; respiratory complications (i.e. pneumonic consolidation, collapse or atelectasis, pulmonary embolism, pulmonary effusion) before and after admission to the centre, method of management of the spinal column injury, the respiratory management and changes in VC were reviewed.

One hundred and five patients with a Frankel et al.³⁵ Grade A to D, tetraplegia were included (Table 1); 73 were males, and 32 were females. The mean age was 51 years (at the previous audit, this was 44 years) with 31% over 65 years of age. Almost all patients with a SCI are offered an Active Physiological Conservative Management for their SCI with a period of recumbence for about six weeks. This is irrespective of the method of management of their spinal column injury. Mean delay in transfer from the referring hospitals to the centre was 24 days (although almost 25% were admitted within one week of injury and approximately 48% within two weeks); 28% (29/105) had a respiratory complication prior to transfer to the centre, majority of which was pneumonia/consolidation (90%); 48% of those with a respiratory complication (14/29) had required a period of invasive ventilation prior to transfer.

Table 1.

Showing the neurological density (Frankel Grade) of SCI in the two audit periods.

Frankel grades	2007 (n = 20)	2009 (n = 50)	2007 (n = 47)	2009 (n = 55)
A	8; 40%	3; 6%	8; 17%	10; 18%
B	1; 5%	8; 16%	10; 21%	8; 15%
C	8; 40%	30; 60%	24; 51%	20; 36%
D	3; 15%	9; 18%	5; 11%	17; 31%

All patients had undergone the same preventative management programme of respiratory care; of the 20 patients who did develop a respiratory complication after transfer to the centre, 11 had already had respiratory complication prior to their transfer. Only nine out of 105 patients (8.5%) had a ‘new’ onset respiratory problem (five infections, four of whom required antibiotic therapy; whilst pulmonary embolus, postoperative period of ventilation following a gastro-intestinal surgery, pulmonary effusion and a pneumothorax accounted for the remaining cases). The incidence was similar to the 2007 audit (Table 2).

Table 2.

Showing the distribution of pre-admission and post-admission respiratory complications during the two audit periods.

	2007	2009
Total patients included	67	105
Pre-admission respiratory complication	27 (40%)	29 (28%)
Post-admission respiratory complication	5 (20.9%)	20 (19%)
‘New’ respiratory complication post admission	5 (7.5%)	9 (8.5%)

This study had shown that respiratory complications are potentially preventable in self-ventilating tetraplegic patients with a comprehensive management programme.

Invasive mechanical ventilation, weaning and life expectency

The likelihood of tracheostomy requirement for ventilation post-surgical fixation³⁶ is increasingly common outside the specialist centres. When diaphragm function is lost, invasive mechanical ventilatory support is essential, though recovery has been seen to occur as late as 24 months post-injury.³⁷ In the presence of ALI, it is likely that protective ventilation strategies will be adopted in the host intensive care units. Regardless of the timing of ventilation, and in the absence of Acute Lung Injury (ALI), the method of ventilation for SCI patients requires larger tidal volumes¹⁰ (at least 10–15 mL/kg), to ensure effective aeration of the lung bases and avoidance of atelectasis and infection. This is well tolerated by SCI patients, with no known evidence to demonstrate pulmonary damage in the absence of acute lung injury. The effect of large volume ventilation is that of respiratory alkalosis, with no long-term detrimental effect from this.³⁸ Electrolyte monitoring in the acute stabilisation phase is required to reduce the risk of adverse effects occurring.

The discontinuation of mechanical ventilatory support is likely to take some weeks to achieve. Consistent factors underpinning successful weaning after spinal cord damage have been attributed to accurate neurological assessment; prevention of pulmonary atelectasis by regular and frequent respiratory physiotherapy, ventilator free breathing graduated according to VC, rest periods with controlled ventilation, cuff deflation allowing translaryngeal air flow and regular tracheostomy tube changes.³⁹ It may be useful to highlight the significant incidence of sleep apnoea (both central and obstructive in nature – Figure 3) in tetraplegia immediately post injury^9,40 which increases over time,⁴¹ as this is likely to complicate the respiratory picture and even delay weaning if unrecognised.

Watt et al.⁴² compared the long-term survival of 262 patients who were having mechanical ventilation on discharge from a single Spinal Injury Centre with the cohort who had been weaned from mechanical ventilatory support prior to discharge and examined the causes of death and contributory factors. Mean survival was better amongst weaned compared to ventilated patients. The survival from initial ventilation was poor for the older age group, and for the middle age group who remained on ventilation. Patients with any co-morbidity had substantially poorer survival. Groups defined by the AIS scale did not differ strongly, and survival did not differ significantly by neurological level. Pre-existing co-morbidities increased the mortality rate by 3.3.⁴³

While positive pressure mechanical ventilatory support has been the mainstay for supporting ventilator-dependant SCI individuals, this presents its own problems, e.g. difficulties with speech, swallow, impaired cough, respiratory infection and long-term tracheostomy issues. This may result in reduced independence and greater mortality when compared to non-ventilator-dependant individuals with similar injuries.⁴⁴

A small cohort of tetraplegic patients may benefit from the alternative method of ventilatory support in the form of phrenic nerve pacing. Electrodes are surgically implanted around the phrenic nerve, with a radio-frequency receiver implanted in the chest wall and an external transmitter. Regular electrical impulses are applied via the stimulator direct to the phrenic nerve causing the diaphragm to contract, and air to flow into the lungs-akin to more normal physiological breathing. It is essential that the phrenic nerves are intact and the diaphragm muscle is functional for this procedure to be successful. Phrenic pacing is highly specialised and requires extensive testing and investigation but is usually the patient’s own favoured method of ventilation in those patients suitable to undergo implantation.

Conclusions

In summary, acute SCI may be one of the most devastating acute conditions with respiratory dysfunction providing a major cause of mortality and morbidity; the level and completeness of injury being major determinants of the extent of respiratory dysfunction. Other concomitant injuries and co-morbidities not incorporated here will have further detrimental impacts. SCIs are often admitted to a local hospital or trauma centre, so early referral and consultation to a specialist centre when available, where improved health outcomes are achieved, is of paramount importance. Good respiratory health is more likely by ensuring full aeration of the lungs, with proactive chest clearance regimens and monitoring in the acute stage (though vulnerabilities are lifelong). This will also reduce the likelihood of secondary hypoxic cord damage. The minimum basic strategies with complete lesions should include the adoption of large volume ventilation while ventilator dependant; the supine lying position for maximal spontaneous tidal volume exchange and throughout the weaning process; the monitoring of the VC and use of an abdominal binder when upright. Advice, guidance and support from the local tertiary spinal centre should be sought as soon as cord damage is suspected/realised, to ensure the best management strategies are utilised from the outset for all systems and aspects of care.

Footnotes

Acknowledgement

The authors acknowledge Mrs Rebecca Dytor, Advanced Physiotherapist at the Midland Centre for Spinal Injuries, Oswestry, for her contribution to the respiratory audit cycle.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

Provenance and peer review

Commissioned, externally reviewed.

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