Ventilation support

In summary, these changes collectively lead to reduced ventilation and secretion clearance, along with an increased work of breathing.

For an acute, motor-complete NLI at T6 or above, but especially at C5 and above, significant respiratory function changes occur due to neuromuscular weakness and paralysis, compounded by the presence of spinal shock, as well as autonomic nervous system (ANS) disruption. Key respiratory muscles affected include the intercostal, abdominal and diaphragm muscles.

At this time, weakened or paralysed respiratory muscles present with flaccidity and increased compliance due to spinal shock. This affects diaphragm positioning and function, as well as breathing mechanics. Ultimately, this results in reduced ventilation and secretion clearance. Paradoxical breathing can also develop, which is very inefficient and increases the work of breathing.

For more information on respiratory function changes following SCI, refer to Respiratory changes.

Without adequate and timely intervention, the combination of hypoxaemia, hypercapnia and respiratory fatigue is a key precursor to the onset of respiratory failure. In addition to this, chronic hypoventilation also contributes to sleep-disordered breathing, compounded by any other obstructive and central factors.

A range of physiological and clinical markers can indicate the need for invasive ventilation to address the onset of respiratory fatigue and/or failure.

Potential physiological markers include:

• impaired alveolar ventilation
  • SpO₂ <90 % on supplemental oxygen
  • PaO₂ <60 mmHg on room air
  • PaCO₂ >45 mmHg and/or pH <7.35 on room air
• declining spirometry and measures of ventilation, including reduced minute ventilation
  • respiratory rate (RR) >30 breaths/min or <8 breaths/min indicating either respiratory stress or disruption to central control
  • maximal inspiratory pressure (MIP) <-40 cmH₂0 indicating significantly reduced inspiratory muscle strength and a high risk of developing respiratory fatigue
  • tidal volume (VT) <5 mL/kg
  • forced vital capacity (FVC) <15-20 mL/kg or <30% of predicted
  • peak cough flow (PCF) <160 L/min and MEP <60 cmH₂0 (spontaneous breathing) indicating a high risk of retained secretions and associated respiratory complications
• radiological evidence of significant hemi-diaphragm dysfunction, atelectasis, aspiration or pneumonia.

Potential clinical indicators include:

• a decreased level of consciousness or capacity to maintain a patent airway, including abnormal bulbar function
• a high NLI such as
  • an SCI at C1–2, with complete diaphragm, intercostal and abdominal muscle paralysis
  • an acute SCI at C3, with significant diaphragm weakness and dysfunction, as well as full intercostal/abdominal paralysis
  • an acute SCI at C4–5, with partial diaphragm weakness and dysfunction, as well as full intercostal/abdominal paralysis
  • any acute SCI at C6-T6, with full diaphragm muscle activity, but ongoing dysfunction due to full or partial intercostal/abdominal muscle impairment
• an ascending neurological level of cervical or thoracic SCI
• traumatic SCI with significant concomitant injuries or complications, impairing respiratory function
• age >50 years and comorbidities, including chronic pulmonary obstructive disease
• a high sputum load and weakened or absent cough, with ineffective secretion clearance
• paradoxical breathing in the presence of spinal shock and significant ANS dysfunction
• signs of increased work of breathing and the onset of respiratory fatigue
• progression towards or onset of respiratory failure, which typically occurs by day 1–5 post-injury—even with non-invasive ventilation use

Potential negative and adverse outcomes include:

• ventilation dependency and slow weaning, including the development of VAP and VIDD
  • prolonging ICU and hospital admission
  • limiting progression to sitting and engagement in rehabilitation
• invasive ventilation restricting laryngeal function and the capacity for speaking: this has been reported to increase patient frustration, fear, powerlessness and anxiety, as well as the incidence of treatment error
• impaired swallowing: this necessitates alternative feeding and hydration management
• endotracheal intubation and tracheostomy complications such as granulation formation, stomal infection, tracheomalacia, tracheal perforation, stenosis and fistula formation
• laryngeal dysfunction post extubation and decannulation
• full-time and life-long invasive ventilation may be required for an SCI at C1-2, and possibly C3, in the absence of neurological recovery.

To be appropriate for NIV, a person with a SCI must be conscious and have capacity to maintain a patent airway, including normal bulbar function.

A range of clinical markers can indicate the need for NIV to manage the onset of respiratory fatigue and/or failure.

Potential clinical indicators include:

• a lower NLI and motor-incomplete injury
• less significant concomitant injuries or complications, impairing respiratory function
• age <50 years and less significant comorbidities
• a low sputum load and some capacity for secretion clearance
• reduced minute ventilation, where only tidal volume needs some improvement
• impaired alveolar ventilation, where only functional residual capacity needs enhancement
• some signs of increased work of breathing over 24-hour period, but no immediate risk of respiratory fatigue
• an appropriate goal to permit independent ventilation and some speech
• a need to avoid long-term complications associated with invasive ventilation e.g. VAP, VIDD, laryngeal dysfunction
• weaning from invasive ventilation, when ongoing ventilatory support is still required
• short and long-term management of sleep-disordered breathing.

NIV requires an expiratory valve/leak port in the interface or circuit to prevent CO₂ rebreathing.

Considerable time is often required to optimise the interface fit. This is to minimise unwanted air leakage for successful ventilation support, while also maximising skin care, comfort and user compliance. Options to trial may include nostril or nasal pillows, along with face masks and mouthpieces.

Non-invasive ventilation is typically prescribed by an intensivist or a sleep/respiratory physician. An experienced physiotherapist or nurse may also lead its implementation, in consultation with the medical team.

Beyond the acute management phase, a person with SCI may be prescribed NIV for use in the community. Ongoing support and review is useful to assist user compliance, by problem-solving technical issues, as well as adjusting titration as respiratory function changes e.g. ageing.

During the acute phase of management, the appropriateness of the selected NIV mode and parameters should be evidenced by improved ventilation measures, preferably within 1-2 hours of commencement.

Potential negative and adverse outcomes include:

• frequent nursing cares and therapy treatments if sputum load increases, because it does not provide direct airway access
• inadequate improvements in ventilation and relief from the work of breathing, with worsening hypercapnia and respiratory acidosis
• complications when using supplemental oxygen, due to inadequate monitoring and titration e.g. may mask worsening respiratory status
• complications such as gastric distension, aspiration
• difficulty achieving user tolerance and compliance with the interface and ventilator settings
• trial process can be time and staff intensive, as well as distressing for the person with an SCI.

Continuous positive airway pressure (CPAP) ventilation provides a low level of continuous positive airway pressure through inspiration and expiration.

Overall, CPAP:

• provides continuous positive pressure during both inspiration and expiration
• effectively supports airway patency by
  • preventing lower airway collapse and promoting smooth muscle airway relaxation via prostaglandin release
  • facilitating collateral ventilation to reduce atelectasis and improve alveolar volume and oxygenation
  • increasing functional residual capacity, lung compliance and gas pressure behind secretions
• reduces the overall work of breathing, provided positive pressure is adequate
• assists in the management of
  • pulmonary oedema
  • weaning process following invasive ventilation
  • obstructive sleep apnoea, associated with sleep-disordered breathing.

Typically, start with a positive-end expiratory pressure (PEEP) at 10% of the person’s body weight e.g. between 5–10 cmH₂O.

Bi-level positive airway pressure (BiPAP) ventilation delivers two levels of positive airway pressure across inspiration and expiration.

Overall, BiPAP:

• establishes a pressure gradient between inspiration and expiration
  • augmenting tidal volumes
    • generating a more effective cough to manage secretion retention
    • reducing associated risks of atelectasis and pneumonia
  • improving minute ventilation
  • delivering pressure support to the lungs
  • improving alveolar volume and oxygenation, while also managing hypercapnia
  • reducing the overall work of breathing, especially inspiratory effort; this reduces the risk of respiratory fatigue and may delay or prevent intubation
• assists in the management of
  • hypoventilation and early progression towards respiratory fatigue and failure
  • secretion clearance when there is high risk of respiratory fatigue using more conventional interventions
  • weaning high-risk users from invasive ventilation and intubation
  • supporting mobilisation and developing exercise tolerance following the acute management phase.

In practice, the inspiratory positive airway pressure (IPAP) is normally set above the expiratory positive airway pressure (EPAP) to increase tidal volume; the greater the difference between IPAP and EPAP, the greater the augmented tidal volume. There may also be other settings to consider such as rise and fall time, as well as sensitivity with respect to triggering a breath or cycle of breaths.

BiPAP devices can offer a range of modes, including:

• Spontaneous (S) mode, the ventilator supports the user’s own breaths
  • For example, start with an IPAP of 10 to 15 cmH₂O, with an EPAP of 4-5 cmH₂O; then increase IPAP in 1cmH₂O increments, until maximum tolerance or target tidal volume of 6-8mL/kg ideal body weight is achieved (an IPAP of 12-16cmH₂O is often sufficient); slightly higher EPAP may be required e.g. obesity to maintain airway patency, although usually a minimal EPAP is needed; minimise FiO₂ to maintain SpO₂ 88-92%
• Spontaneous/Timed (S/T) mode, the ventilator provides the same support but also includes a backup respiratory rate (BRR) set just below the user’s natural respiratory rate, ensuring a minimum number of breaths
  • For example, start with an IPAP of 8cmH₂O and an EPAP of 4cmH₂O, with a rise time 0.3 seconds, BRR of 12-16 breaths per minute, inspiratory time 1.4 seconds; then increase IPAP in 1cmH₂O increments, until maximum tolerance or target tidal volume of 6-8mL/kg ideal body weight is achieved (an IPAP of 12-16cmH₂O is often sufficient); slightly higher EPAP may be required e.g. obesity to maintain airway patency, although usually a minimal EPAP is needed; minimise FiO₂ to maintain SpO₂ 88-92%.

Mouthpiece ventilation (MPV) provides non-invasive ventilation (NIV) on demand, via a mouthpiece. It is typically used in the management of people with degenerative neuromuscular diseases and respiratory dysfunction, who are living in the community. However, it is another ventilation support consideration for a person with SCI, who may require intermittent daytime ventilation support.

MPV is often used during the day to manage the neuromuscular fatigue of inspiration associated with activities of daily living (ADLs), such as sitting, speaking, or coughing. However, when MPV is used during the day, another form of optimised NIV is required for sleeping (providing a degree of neuromuscular rest from the fatigue of spontaneous breathing during the day, while addressing hypoventilation associated with sleep-disordered breathing overnight).

Overall, MPV:

• provides inspiratory ventilation assistance on demand
  • to avoid the need for mechanical ventilation (typically when there is a degree of daytime hypercapnia +/- dyspnoea despite optimised nocturnal NIV)
  • to support the weaning process for extubation/decannulation
• can be easier to trigger as the negative pressure generated by the mouth during the inspiratory “sip” is much higher than that generated by a deep breath alone
• allows the user to detach from the interface when not required
  • minimising claustrophobia
  • improving self-image
  • reducing the risk of facial pressure sores
• supplements tidal volumes and helps maintain minute ventilation
  • supporting the work of breathing when sitting
  • permitting air stacking to achieve maximum insufflation capacity (MIC)
  • improving independent speech and cough
  • reducing care needs associated with frequent need for lung volume and cough augmentation
  • providing an alternative means of breathing in case of other ventilator device failure
• reduces the overall work of breathing associated with ADLs
• improves quality of life.

The MPV setup needs to:

• use a suitable ventilator (volume-cycled, pressure/flow triggered)
• provide a
  • a single limb circuit
  • a filter (to soften the ventilator constant flow at the user)
  • a one-way valve (to prevent alarming if the user exhales into the circuit)
  • an angled mouthpiece (positioned within reach of the user)
• offer settings to accommodate the user’s oromotor control and achieve a voluntary lip seal
• balance device sensitivity to achieve triggering by a “sip” inspiratory action, but avoid auto-triggering.

The user must:

• have adequate oropharyngeal muscle strength (including control to close their soft palate and seal the nasopharynx, as well as open and their glottis/vocal folds to direct the air into their lungs)
• have sufficient head and neck range of motion to access the mouthpiece repeatedly
• be alert and able to co-operate and communicate.

MPV delivers an on-demand inspiratory volume: either via a single “sip” for normal MPV or via multiple “sips” to perform air stacking. The latter aims to specifically achieve lung volume recruitment (LVR) and considerable optimisation of settings will be important to establish with each user. Achieving a tidal volume of 700-1500 mL for adult patients will typically provide a satisfying to deep breath, while achieving MIC will require a pre-set pressure limit of 45-70 cmH₂0. Practising LVR is recommended at least 2-3x each day, for up to 5 breaths each time to maintain maximal insufflation capacity. A manual assisted cough may still be required to assist with secretion clearance. This can be determined by comparing peak cough flow (PCF_unassisted) following MPV+LVR assisted peak cough flow (PCF_assisted) following MPV+LVR+manual cough.

Potential limitations for consideration include:

• a degree of air leak occurs via the nose
• some negative effects can result, such as gastric distension, increased saliva and induced vomiting
• being inappropriate for ventilation support for sleep
• being insufficient ventilation support during periods of acute illness.

A video demonstrating combined use of NIV, including MPV can be found here.

General physiological and clinical indicators/criteria include:

• afebrile
• normal chest x-ray
• 48 hours of nil tidal volume ventilation support (with FiO₂ <25% and PEEP <5 cmH₂O)
• maximal inspiratory pressure (MIP) >24 cmH₂0 and vital capacity (VC) >1500 mL or >10–15 mL/kg of ideal weight, sustained throughout the day and across several days to demonstrate diaphragm strength and endurance
• peak cough flow (PCF) >160 L/min (or >270 L/min using cough augmentation)
• stable vital signs and medical condition, including during cares
  • SpO2 >95% (with FiO₂ <25% and PEEP <5 cmH₂O)
  • blood gases PaO₂ approaching 80+ mmHg and PaCO₂ approaching 35–45 mmHg
  • pH within range of 7.35–7.45
  • normal fluid balances
• manageable secretions
• resolution of other injuries or risk factors impacting respiratory function
• no contraindications for NIV or physiotherapy lung volume augmentation and secretion management techniques
• no required surgical or x-ray diagnostic procedures close to extubation that require sedation
• effective pain management
• sufficient alertness and compliance
• adequate swallow function as per feeding plan.

General clinical approaches include:

• adequate staging
  • allowing weaning and decannulation to occur over sufficient period e.g. 7-14 days
  • aiming to achieve 2 main stages:
    • initially 16 hours ventilator free which represents 1 day period (using NIV as needed)
    • then 24-48 hours ventilator free which represents 1-2 day/night cycles (using NIV as needed)
• adequate preparation
  • establishing baseline physiological and spirometry measures (MIP, VC, maximal expiratory pressure (MEP) and PCF)
  • maximising nutrition and incorporating medications, to increase respiratory muscle mass and build strength/improve diaphragm contractility
  • introducing specific lung volume augmentation, including air/breath stacking and inspiratory muscle training (IMT) techniques to
    • improve chest wall and lung compliance
    • develop respiratory muscle strength
    • establish competence and confidence with techniques
  • introducing non-invasive secretion management strategies, including mechanical insufflation-exsufflation device and manual assisted coughing to
    • clear sputum load
    • develop respiratory endurance
    • establish competence and confidence with techniques
  • introducing early cuff deflations to condition diaphragm and accessory muscles by
    • breathing around the cuff, to build tolerance
    • using speaking valve, to introduce speech and ventilation demand
    • commencing assessment and rehabilitation of swallowing function, to manage any risk of aspiration while improving quality of life
  • introducing periodic ventilator-free breathing (PVFB) to achieve a training effect with respiratory muscles
    • when staffing levels allow for close monitoring and responsive intervention
    • when it is early in the day, following morning cares and a rest period with adequate ventilatory support
    • with short, structured trial periods—increasing in frequency and duration: beginning with short 5 min periods, followed by a minimum 2-hour rest for the diaphragm before next session (rest is with unaltered ventilator parameters)
    • when positioned in supine for quiet breathing, then during respiratory treatments, then inclined sitting, then sitting out of bed (with an abdominal binder to reduce the work of breathing), then incorporated into functional activities (e.g. being hoisting out of bed or speech sessions)
  • once PVFB is well established, gradually
    • reducing ventilation tidal volumes during rest periods
    • transitioning to pressure support ventilation
    • trialling and identifying the most tolerable NIV settings and interfaces
    • weaning to daytime NIV (with or without ventilator-free breathing periods)
    • gradually introducing overnight NIV
  • progressing tracheostomy before full decannulation by
    • introducing cuffless tracheostomy/smaller tracheostomy tubes
    • optimising stomal seal/use of a cap
    • practising secretion clearance to the mouth.