²Children’s Community Matron, Nottingham Children’s Hospital

Introduction

Long-term ventilation (LTV) of children demands harmonious and well-orchestrated co-ordination of care between various health professionals and their families. Health professionals must lead, utilising the other agencies commonly involved, aiming to optimise care for children at home (Noyes 2006). One of the roles of the medical team is to identify situations when LTV may be indicated; nursing staff commonly lead on establishing care routines and become key workers in the journey home. Physiotherapists take the lead in optimising lung clearance. Carers, individuals without professional training who develop specific caring skills for LTV children, may be part of the team supporting transition home.

Normal respiration

Respiration in humans evolved to meet the continuous but variable demands of metabolism for gas exchange. Cyclical processes, breathing and heart contractions, lead to intimate and precise matching of two transport systems (blood and respired gases) in the respiratory zone of the lungs as discussed in Chapter 1. The muscular pumps responsible for gas and blood flow share a common compartment, the chest. This has a symmetrical skeleton upon which the respiratory muscles act and within which the elastic properties of the lung exert an important influence. The circulation of blood is cyclical yet continuous within systemic and pulmonary circulations, there is marked elasticity on the arterial ‘delivery’ side and capacitance on the venous ‘recovery’ side. The timing of gas flow down the airways (conducting zone) into the airspaces (respiratory zone) is controlled by cyclical central nervous system pacemaker-like activity, itself influenced by chemoreceptors.

Chemoreceptor organs have generous blood flows that sense carbon dioxide and oxygen levels within the brain and the carotid body. Optimal airway calibre is ensured by phasic airway wall stiffening while inspiratory muscles draw gas into the respiratory zone. In health, at rest expiration then occurs passively as elastic recoil acts to expel gases back to air.

These processes are highly integrated and interdependent; they also lie at the centre of healthy metabolism. In the absence of disease there is considerable performance reserve to meet peaks in demand and allow recuperation during quieter periods.

The respiratory zone is free from contamination due to the combined effects of local immunity, the mucociliary escalator and cough. The normal cough reflex involves three well-co-ordinated phases: initial inspiration to 60–70% of total inspiratory capacity, then a brief but vital compressive period when forceful expiratory efforts are held by a closed glottis and finally the explosive expiratory period generating a plume of cleared respiratory secretions. Enhanced clearance aims to recreate the effects of coughing.

Pathophysiological aspects

Hypoxaemia, hypercarbia and lack of sleep are the three cardinal adverse effects that occur when the system fails. They may be ameliorated or reversed by breathing support as part of a package of care. A window of opportunity for intervention often presents, before and after which it may cause harm.

Inadequate gas exchange may be improved by LTV, particularly when there is relatively little parenchymal lung disease. The controlled gas flows of ventilation may straightforwardly overcome the ventilatory failure associated with disordered muscle function (low, high or variable tone) and the consequent restrictive pattern of lung function or moderate tracheobronchial or supraglottic obstruction.

This support is often effective in the long term. Children with advanced parenchymal disease may benefit temporarily during a period when time is precious. Sleep has a generally depressant effect on breathing and inadequate breathing commonly disturbs sleep. This vicious cycle may be interrupted by nocturnal LTV, enabling healthy daytime activities.

The restrictive pattern of lung disease commonly results from the compounded effects of muscular disease, skeletal deformity and paucity of lung growth and may be accompanied by cardiac elements. The metabolic consequences of sleep-disordered breathing (SDB), for example type 2 diabetes and ischaemic heart disease, emerge over a longer timescale. Intervention to support healthy gas exchange and avoid the increased work of breathing associated with most of these conditions may prevent or ameliorate these effects.

Lung development, growth and in particular healthy postnatal acquisition of increased numbers of alveoli are dependent upon chest movements. The normal excursions of tidal breathing and deeper breaths during increased demand (e.g. exercise) each play their part (Davies and Reid 1970). Without these growth-stimulating trophic effects, lung capacity is stunted and respiratory failure a natural consequence. Providing non-invasive ventilation (NIV) can promote healthier lung growth (Bach and Bianchi 2003).

Indications for long-term ventilation

Broadly, long-term ventilation may be of benefit in the circumstances listed in Box 7.1.

Predicting long-term ventilation

Ventilatory failure is the most common cause of death for all the patient groups in Box 7.1. Mechanical breathing support as part of a package of care can improve survival, quality of life or both. The timing and sequence of interventions require judgement, based upon measurements and intelligence about the individual patient in the context of knowledge about particular diseases and general principles.

Neuromuscular diseases

Our understanding of neuromuscular disorders has recently included descriptions of their molecular basis and improved characterization of the varied phenotypes.

Duchenne muscular dystrophy

Some diseases are relentlessly and predictably progressive; Duchenne muscular dystrophy is arguably the best described. It is rare in girls and mainly affects boys. Independent ambulation generally ceases around entry to secondary school and respiratory failure is highly probable by late adolescence. These boys are capable of performing pulmonary function tests; longitudinal values reveal individual variation in decline that for forced vital capacity (FVC) averages 8% per annum (Phillips et al. 2001). A decline in FVC below 1 litre suggests survival of about 3 years (median value) without breathing support.

Short-term reversible decline in breathing performance occurs; for example, viral illnesses in this population cause a prolonged and disproportionate impairment in breathing (Noyes 2006; Poponick et al. 1997). An important predictive measurement is hypercarbia with the onset of sleep, REM related, after which a requirement for breathing support is expected within 2 years (Phillips et al. 1999; Ward et al. 2005). Peak cough flows (PCF) are measured when individuals cough, after a maximal inspiration, either through a peak flow meter or more sophisticated flow-sensitive device; normal values have been established from 5 years (Bianchi, Baiardi 2008). Their use for triggering interventions has not been established; in adult practice a value of less than 160 L/s often triggers action (Weese-Mayer and Berry-Kravis 2004). When used to demonstrate the effectiveness of chest clearance techniques, the measurements provide encouragement.

Hypercarbia that persists around the clock – diurnal ventilatory failure – is, by consensus, an indication for offering non-invasive ventilation in Duchenne muscular dystrophy (Weese-Mayer and Berry-Kravis 2004) as it has been shown to prolong survival and improve quality of life (Simonds and Elliott 1995). Populations with Duchenne muscular dystrophy in which NIV is commonplace have witnessed increased survival (Jeppesen et al. 2003). Clear advantages of NIV described in this group include improved gas exchange (both CO₂ and O₂) (Simonds et al. 1998, 2000) and better sleep (Mellies et al. 2003). Similar benefits are observed in those presenting with acute decompensation with respiratory infection.

Spinal muscular atrophy

Children with spinal muscular atrophy (SMA) share a common genotype that varies greatly in expression – their phenotype. Natural outcomes range from death in the early years to survival into adulthood. By consensus, three types are recognised by their course: type 1 presenting in the first 6 months; type 2 between 6 and 18 months and others named type 3. Muscles particularly affected by the condition are the intercostal and bulbar groups. Breathing support for infants with type 1 SMA remains the exception and for those with type 2 the rule (Schroth 2009).

Other neuromuscular diseases

Disease progression cannot always be predicted with confidence. Neuromuscular disorders with a more variable overall course include myasthenia, spinal muscular atrophy with respiratory ­disease (SMARD) and other muscular dystrophies. Individuals with these conditions may ­experience a phase of weakness severe enough to require temporary breathing support, bridging to a healthier future and helping with lung growth or during a period of intense investigation for precise diagnosis.

Non-invasive ventilation: part of a package of care

Preparation for the possibility of NIV may occur in the phase before the onset of diurnal ventilatory failure. For the patient and their family, this is a further period of change during which much has to be accommodated. Patient surveys reveal that professionals and families usually underestimate their quality of life (Bach et al. 1991). Options for treatment should be presented in a clear-cut, non-directive fashion.

As the likelihood of respiratory infection is increased, protection should be implemented via immunization, having broad-spectrum antibiotics readily available and the learning of techniques enhancing lung clearance (Weese-Mayer and Berry-Kravis 2004). Lung clearance techniques should be tailored to the individual and their family. Mucociliary mechanisms are intact in neuromuscular disease while factors that can affect function include infection, mucous viscosity and exposure to cigarette smoke (Houtmeyers et al. 1999). Coughing is poor, leading to retained secretions. With effective glottic control, the inspiratory phase can be mimicked using breath-stacking techniques; air is delivered sequentially in supratidal volumes and held by glottal closure until a comfortable inspiratory capacity has been achieved. The final breath in the stack is followed by prompt external compression timed to coincide with release of the vocal cords.

When glottic control is poor chest clearance may be enhanced by mechanical insufflation-exsufflation (MIE). Active inspiratory and expiratory flows are switched rapidly in a time ratio of 2/1. The technique is well tolerated and maximal inspiratory and expiratory flows increase in proportion to the pressure utilised (Fauroux et al. 2008) with the effect of enhancing chest clearance; consensus agreement exists about its use (McCool and Rosen 2006; Miske et al. 2004).

Sleep-related hypercarbia would be expected during this phase, that varies in duration. As disease progression is generally slow patients may not describe symptoms, as the effects of respiratory failure may be tolerated. Specific symptom enquiry, with SDB in mind, may identify symptoms. In general, symptoms will prompt the introduction of NIV.

Many conditions requiring LTV allow that need to be anticipated. Skilful enquiry and the monitoring of breathing in children and young people with neuromuscular disease at outpatient clinics may allow the stepwise provision of support. As gas exchange and lung clearance deteriorate, support to optimise both may be required.

When coughing becomes inadequate, instructions in the techniques that enhance lung clearance generally precede the need for ventilation. The first experience of the child or young person with a ventilator may be when learning the techniques used to improve lung clearance.

Acute presentations

Alternatively, LTV requirements may be identified relatively acutely due to unpredictable events. These infants, children and young people will usually be resident on intensive care units. Failure to extubate and/or sustain breathing independently will prompt consideration of LTV, whether in the context of palliative or long-term support (Bach et al. 1991).

Neonatal care

In the neonatal intensive care unit, decisions regarding the aims of care may be particularly finely balanced and will require accurate diagnosis, allowing a discussion based on as high a degree of certainty as can be achieved at the beginning of independent life.

Infants with profound respiratory failure due to myopathy or congenital central alveolar hypoventilation require prompt diagnostic work-up but may not be easy to identify initially. Congenital central alveolar hypoventilation is diagnosed by identifying abnormalities in the gene (PHOX2B), that provides instructions for the production of protein in the early stages of development, with evidence of abnormal breathing responses to chemoreceptor stimulation. Autonomic nervous system instability, endocrine and other central nervous system-driven physiological anomalies may complicate management. Breathing support is generally required during sleep and may be required continuously, particularly during infective or other exacerbations (Maitra et al. 2004; Trang et al. 2005; Weese-Mayer et al. 1992).

Home ventilation for neonatal chronic lung disease may become more commonplace but currently this is unusual.

Upper airway obstruction

Some populations with a high prevalence of SDB are listed in Box 7.2. In Down’s syndrome up to two-thirds may have multichannel physiological recordings that define SDB (Dyken et al. 2003; Marcus et al. 1991) and the complexity of anatomical and functional factors contributing has been systematically described (Uong et al. 2001). Tonsillectomy may be effective in alleviating SDB (Bower 1995).

Outcomes of long-term ventilation

Long-term ventilation most commonly aims to enable children with ventilatory failure to live with their family at home, go to school and enjoy the best quality of life possible. LTV may be used as an aid for palliative care; respiratory failure is a common mode of death. As breathing becomes less effective and the effort required increases, the degree of comfort or distress and its timescale vary. Hypoxia and hypercarbia have sedative effects whereas dyspnoea, cough and secretions are unpleasant. Admission to hospital for nursing intervention may entrap the child and their family. LTV may enable comfort and care at home given appropriate support.

Long-term ventilation as a bridge to transplantation

Successful transplantation of lungs or heart and lungs may transform the lives of patients and their families with end-stage lung disease. LTV in combination with other intensive interventions increases the likelihood of successful transplantation for individuals. In advanced cystic fibrosis, advancing respiratory failure occurs with chronically infected bronchiectatic airways, impeding expiratory flow and causing airspace hyperinflation; consequently hypoxemia and hypoxic respiratory drive with nocturnal hypercarbia arise. Benefits from NIV might accrue from the resting of respiratory muscles, improved sleep and enhanced chest clearance, improving quality of life or allowing transplantation.

The optimal timing and regimen for patients with cystic fibrosis (CF) patients are unclear. Although benefits of NIV have been reported and gas exchange and dyspnoea improve in the short term, the acceptability of and adherence to positive pressure support strategies are poor and a substantial minority of potential users do not persist with the technique (Bower 1995; Fauroux et al. 1999; Gozal 1997; Moran et al. 2009).

Long-term ventilation considered and not commenced

Evidence that LTV prolongs life and improves the quality of life of some patient groups means that decisions to commence support may be straightforward on an outcomes basis, but this is not always the case.

From a day-to-day perspective, we consider the views of the individual and their family; potential benefit is balanced with possible harm in a rounded manner. Views vary amongst families according to their values, beliefs and other circumstances. The clinical team’s job is to present a clear-cut description for the family to consider. Anticipation of future needs and exploration of what is acceptable at the outset help to negotiate the approach adopted. Views will often alter with circumstantial changes. The key outcome is that a personal resuscitation plan and escalation plan are agreed and disseminated between family and professionals (Wolff et al. 2011).

Where life is judged, either by the family or their child, as unbearable or of no purpose, if the child is in a permanent vegetative state or there is no chance of recovery and suffering is ­prolonged, life-sustaining treatment may be withheld or withdrawn (Royal College of Paediatrics 2004).

When disagreement between parties arises, the legal process may be involved. Often, in the background individuals or groups are advocating different plans of action, having considered the ethical and moral issues affecting the individual, their family and community. Where disagreement arises, the best framework for decision making is arguably one that involves experts in arbitration. More broadly, society’s views must be considered and accounted for. Distributive justice requires that decisions made do not come into conflict with the needs of the many. When conflict exists or is foreseen, a second opinion and the views of the local clinical ethics committee may help (Larcher et al. 2010).

Technical aspects of long-term ventilation: equipment

Ventilation requires that gases for breathing are delivered down a circuit and via an interface to the patient’s airway. Recent technical developments have improved the patient’s experience and refinements to the options available are ongoing.

Ventilators (Figure 7.1)

Machines designed to support breathing entrain and accelerate gas flows to achieve targets set by the supervising medical team according to individual requirements. Components have improved in their performance, particularly size, quietness and responsiveness. Improvements are still required, particularly for our smallest and most profoundly affected patient groups.

As most breathing assistance is provided in the setting of considerable leakage of the gas flow produced, most ventilation is targeted to achieve a given pressure to the airway. (Ventilation to a given volume when measurement of that volume is inexact is difficult and may be dangerous.) The flow required to do this is preferably triggered by the earliest patient effort to optimise synchronised support. Flows to achieve the required pressure(s) are generated rapidly and are then sustained to maintain that pressure. Top pressures reached assist inspiration and give way to a lower setting, often still positive, that assists in sustaining airway calibre and thereby lung inflation.

Figure 7.1 Ventilator.

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