The respiratory system is a delicate balance between the central respiratory control and ventilator muscle function in overcoming the respiratory load of breathing (Figure 1). The common causes of an imbalance in this system include severe chronic lung disease, ventilatory muscle weakness and a central hypoventilation disorder.
In addition, more and more patients are surviving critical and catastrophic illnesses in the pediatric intensive care unit,1 but go on to develop long term severe chronic lung disease or chronic respiratory failure. In these children, chronic respiratory failure (CRF) is the inability to wean off ventilator support in the pediatric intensive care after a month of medical stability despite multiple attempts. Patients with CRF need to be on long term assisted mechanical ventilation.
Some children may have an underlying neuromuscular weakness or severe lung disease, such as an interstitial process that predisposes them to a higher risk of CRF following an acute illness.2Patients requiring such long term supportive ventilation are often referred to as "medically fragile" or "technologically dependent" and comprise a unique population with complex medical needs.3
Currently several modalities are used for chronic assisted ventilation including non-invasive positive pressure ventilation and invasive positive pressure ventilation via tracheostomy tube.
Home Mechanical Ventilation in Pediatrics
The decision to initiate chronic ventilatory support is increasingly being made electively where the families are given opportunities to make an informed choice about the management of CRF. In the absence of acute respiratory failure, non-invasive ventilator support may be initiated first for nocturnal hypoventilation thus helping in preventing pulmonary hypertension and other complications of CRF.4-6 Nocturnal ventilation allows ventilatory muscle rest and improves endurance for spontaneous breathing while awake and is thereby associated with an improved quality of life.5,6
Alternatively, chronic ventilatory support may be provided by positive pressure ventilation and home mechanical ventilation via tracheostomy placement at the outset. This is the most common method of providing infants and children with assisted ventilation at home.5-12 Ideally children with relatively stable ventilator settings are candidates for home mechanical ventilation.12 This generally means a FIo2 less than 40% and a peak inspiratory pressure (PIP) less than 40 cm H2O.
Portable ventilators provide various modes of ventilator support, have continuous flow, can provide positive end-expiratory pressure (PEEP) and pressure support. In case of a superimposed respiratory infection, portable ventilators may not be capable of adequately ventilating the child and hospitalization may be required. Higher settings of assisted ventilation may be required during these episodes and patients are often briefly transitioned to a hospital ventilator. A tracheostomy offers the advantage of providing ready access to the airway for hospital ventilators without the need for endotracheal intubation.
|FIGURE 1 LEGEND: In order to sustain adequate ventilation, ventilatory muscle power and central respiratory drive must be sufficient to overcome the respiratory load. In normal individuals, this balance is tipped to the right, as they have more than enough ventilatory muscle power and central drive to overcome the respiratory load. However, sufficient decreases in ventilatory muscle power and/or central drive, sufficient increases in the respiratory load, or some combination of the above, may tip the balance toward respiratory failure.
Lessons Learned at Children's Hospital Los Angeles
Children's Hospital Los Angeles has been discharging children on home mechanical ventilation since 1977, and we would like to pass on some lessons we have learned over the years.
1. Small uncuffed tracheostomy tubes: In children, small uncuffed tracheostomy tubes are preferred. These tubes are associated with a leak around them which provides a margin of safety as the child can ventilate around the tube, prevents the development of tracheomalacia from compression of the vascular supply of tracheal mucosa, and also allows phonation.
Since contemporary ventilators use continuous flow and generation of PEEP, this also facilitates ability to phonate, often with the help of a one-way positive pressure speaking valve.12 As the child grows, the tracheostomy tube needs to be upsized to achieve adequate ventilation.
2. Pressure control ventilation: Pressure control ventilation is preferred in children. If the same PIP is achieved at each breath, the same tidal volume will be achieved for each breath so long as pulmonary mechanics remain constant. The tidal volume can be achieved regardless of the large and variable leak around the tracheostomy tube.
A significant portion of the ventilator-delivered breath may escape in a leak around the uncuffed tracheostomy. Thus using the ventilator in a volume-cycled mode is inadequate, because it is impossible to predict the amount of ventilator-delivered breath escaping through the tracheostomy leak. Since this leak is large and variable in infants and younger children, a single tidal volume setting cannot compensate for this. Thus using a pressure-control modality of ventilation becomes paramount in these younger children.
Of note, the ventilator's high-pressure alarm, useful in detecting an occluded tracheostomy tube, will not function when pressure control, pressure ventilation is used. Thus, a back-up alarm on the patient, such as a pulse oximeter is always prescribed. The pulse oximeter alarm should be used at all times during sleep and when a ventilator-dependent patient is not being observed.
3. Ventilator settings: In children without significant lung disease, ventilators are often adjusted to achieve goal PETco2 of 30-35 torr and a Spo2 of >95%. In our experience, children on chronic ventilator support have fewer complications and do better clinically if they are hyperventilated to a certain degree.5,12-14 This allows a margin of safety in case of emergencies and eliminates a subjective feeling of dyspnea.
The ideal ventilator settings for a patient on home mechanical ventilation should involve a physiological respiratory rate for age. Even if adequate gas exchange is achieved (Pco2 <40 torr and Spo2 >95%), home mechanical ventilation is rarely successful when lower ventilator rates are used than a healthy child of the same age would adopt naturally. In the home, ventilator settings can not be frequently changed to maintain perfect blood gas values.
Therefore, ventilator setting changes should be made only to correct persistent trends or major abnormalities of blood gas values.9,12,15-17,22
4. Auto-cycling: Auto-cycling is an asynchrony between patient and ventilator breaths, setting off the ventilator generated breaths in a rapid and repeated fashion. The two most common scenarios for this are: (1) the sensitivity is set too low, and trivial movements by the patient can trigger ventilator breaths; or (2) a large leak from the ventilator circuit where adequate pressures, particularly PEEP, cannot be easily delivered. This is most commonly seen with continuous flow ventilators. Auto-cycling may be addressed by increasing bias flow on the ventilator to stabilize PEEP, increasing sensitivity settings to raise the trigger threshold, and/ or checking circuit connections for large leaks as well as ensuring adequate tracheostomy tube size.
5. Sprinting: We practice sprint weaning rather than gradual lowering of ventilator settings. Sprinting is similar in philosophy to athletic training whereby muscle endurance is improved by short bursts of increased activity. In a similar fashion, by disconnecting the patient from the ventilator for short periods, ventilator muscle strength is enhanced and sprinting time can then be gradually increased. It may be possible to eventually wean patients off ventilator support completely or at least for short periods of time.
In fact, nearly 50% of our patients on home mechanical ventilation due to chronic lung disease were completely weaned from ventilatory support within 5 years.20 This enhances mobility and can improve quality of life. Sprinting can be attempted when a patient maintains adequate gas exchange (Spo2 ³95% and PETco2 30-40 torr) on stable ventilator settings. Even if a child cannot be completely weaned, nocturnal ventilation can provide ventilator muscle rest and recovery and thus permit daytime sprinting. Often, patients need to be maintained on supplemental oxygen during sprints.
Continuous non-invasive monitoring of gas exchange is performed during sprints. Patients need to be connected back to the ventilator for signs of respiratory distress or abnormal gas exchange. Patients weaned off the ventilator are generally patients with bronchopulmonary dysplasia from prematurity, patients following acute respiratory distress syndrome following chemotherapy or other toxic agents, and patients with transient central hypoventilation from CNS processes.
6. Unplanned hospital readmissions: It is important to educate families that opting for home mechanical ventilation does not resolve all the problems. We have noted a high rate (40%) of unplanned hospital readmissions in the first year.19 The most common causes of readmission were pneumonia, tracheitis and tracheostomy related complications. The single most important predictor of unplanned hospital readmission within 3 months was changes made in the medical regiment within one week of original discharge on home mechanical ventilation.19 This underscores the fact that these patients must be medically stable prior to hospital discharge.
7. Mortality: Overall, our children discharged on home mechanical ventilation had a 20% 5-year mortality rate, and a 35% 10-year mortality rate.20 Nearly half of the deaths (49%) were unexpected, and progression of underlying disease accounted for only 34% of deaths. In a separate analysis of patients with congenital heart disease,21 a higher mortality was noted (89%) in patients with more advanced disease and a Risk Adjusted classification for Congenital Heart Surgery (RACHS-1) score >4. Six patients in this series had single ventricle anatomy with palliative procedures.
The incidence of mortality for single ventricle patients was 50% with only one of the surviving patients having reached final palliation and successful weaning off the ventilator. Knowledge of poor outcomes in the cardiac patients is important when counseling families about initiation of home mechanical ventilation.
8. Tracheostomy accidents: Some inadvertent risks of home mechanical ventilation in children include tracheostomy obstruction from mucus plugging, tracheal bleeding, and tracheostomy decannulation. Mucus can obstruct and plug the airways within minutes.
There is no standardized schedule for suctioning and requirements vary depending on individual patient needs. Ventilator alarms and backup monitoring devices may not be sufficiently sensitive to detect a mucus plug, and hence additional training needs to be provided to caregivers to assess for signs of airway obstruction. Tracheal bleeding may be a result of granulation tissue formation along tracheal mucosa, as a result of trauma from aggressive suctioning, or from tracheitis. Bleeding is potentially life threatening. Significant granulation tissue needs evaluation by bronchoscopy and possibly laser removal. Oral or inhaled antibiotics can help with infections.
Accidental decannulation of the tracheostomy is a life threatening emergency and requires immediate replacement as tracheostomy stomas can constrict and close very quickly. The back-up low pressure alarm may fail to go off if a small tracheostomy tube is decannulated while maintaining connection with the ventilator because of the sufficient resistance inside a small tracheostomy tube that can falsely simulate an intact circuit.22 A high minute volume alarm may go off quickly due to the large air leak, but this does not always occur.
Therefore, a direct monitor on the patient (pulse oximeter) is always advised as additional protection.
9. Importance of trained caregivers in the home: Care of the ventilator-dependent child at home is an arduous process. It involves commitment and dedication of the caregivers in the home, as well as support from physicians and medical personnel. A primary and secondary caregiver is identified prior to discharge. A back up ventilator is provided to all patients who are ventilator-dependent ³20 hrs/day or when they live long distances from medical or technical assistance.12,16,22
training focused more on technical aspects of ventilator alarms and emergency responses. In addition there is a tremendous need for home care companies to facilitate this process of training by mutually working towards education of families and caregivers; providing back-up support for equipment check, troubleshooting and preventive maintenance; and providing 24-hour emergency availability in the event of equipment malfunction.
Nurses with pediatric critical care expertise are helpful in assisting families for 8-24 hrs/day in the home care of their child, especially for infants and young children who may be particularly unstable. We recently surveyed knowledge of home care givers for mechanically ventilated patients.23
In general, both parents and in-home nurses missed questions about the significance of ventilator alarms. There were no differences in knowledge between nurses and parents based on language spoken, whether the child was part-time vs. full-time ventilator dependent, or those who had responded to an emergency at home vs. those who had not. The length of time the child had been on home mechanical ventilation did not correlate with knowledge. This study demonstrated that caregivers of children on home mechanical ventilation should receive
Physicians, respiratory therapists, nurses, other medical personnel, caregivers and home care companies can cohesively contribute to the complex and challenging needs of these medically fragile children.
10. Education and preparation for home care: Children on home mechanical ventilation are a complex population, and they require an inter-disciplinary approach to care; multidisciplinary action plans including both inpatient and outpatient settings, ensuring adequate preparation and education for discharge with hands-on and independent practice. In spite of the currently available educational materials, DVDs and booklets, simulation educational models on emergency care could better train caregivers in unexpected situations.
The practical lessons we have learned over the years have helped to better predict which diagnoses yield better outcomes and recognize candidates for weaning. We have been able to improve our readmission outcomes by focusing on the management of pneumonia and tracheostomy-related complications. Our future is dependent on active participation and collaboration from our home health providers and caregivers.
Aliva De, Sheila S. Kun, and Thomas G. Keens are a part of the Division of Pediatric Pulmonology at the Children's Hospital Los Angeles, and the Department of Pediatrics at Keck School of Medicine, University of Southern California, Los Angeles.