Improving ventilation in children using bilevel positive airway pressure.
Until recently, options for mechanical ventilation for children with chronic respiratory problems included negative pressure ventilation or positive pressure ventilation through an artificial airway (Padman, Lawless, & Von Nesson, 1994) (see Figure 1). The first method, negative pressure ventilation, was a commonly utilized, noninvasive technique, dating back to the 1830s (Hill, 1997). An example of this is the iron lung, which was common during polio epidemics (Hill, 1993; Pierson, 1997). The use of noninvasive ventilation sharply declined, and in the 1950s it was replaced by positive pressure ventilation using an endotracheal tube (Hill, 1997). This mode provided more effective ventilation of acutely ill patients, as evidenced by lower mortality rates (Hill, 1993; Pierson, 1997). Presently, the trend is again reversing; noninvasive positive pressure ventilation is becoming a more widely used procedure to support patients with respiratory failure both in the chronic and the acute settings (Hill, 1997; Pierson, 1997; Teague, 1997). In the past decade, this method of ventilation has been extended to the pediatric population.
[Figure 1 ILLUSTRATION OMITTED]
Defining Noninvasive Positive Pressure Ventilation
The term "noninvasive ventilation" refers to a method of achieving alveolar ventilation without endotracheal intubation or other invasive respiratory techniques, such as tracheotomy (Hill, 1993). The term "noninvasive positive pressure ventilation" (NPPV) was defined as the "application of positive pressure via the upper respiratory tract for the purpose of augmenting alveolar ventilation" (American Respiratory Care Foundation [ARCF], 1997, p. 364). There are different modalities of NPPV. These include: (a) CPAP - continuous positive airway pressure, (b) IPPB - intermittent positive pressure breathing, and (c) BiPAP - bilevel positive airway pressure.
CPAP provides a constant flow of positive pressure to prevent collapse of alveoli. IPPB is a type of CPAP that is used for an intermittent purpose to deliver aerosol medications. BiPAP differs from the previous two in that it provides constant positive pressure at two different pressure settings: one for inspiration and one for expiration.
How BiPAP Works
In the healthy child, normal spontaneous breaths inflate alveoli in the lungs to maintain adequate gas exchange. In the patient with a compromised respiratory system, alveoli may not be adequately inflated due to weakened respiratory muscles, weakened respiratory drive, airway obstruction, injury to lung tissue, or underdeveloped lungs. Alveolar hypoventilation leads to hypoxia and hypercarbia (Teague & Fortenberry, 1995).
There are various approaches to help improve one's respiratory status. Positive end expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) are both used in children with poor ventilation and oxygenation (Bolton & Kline, 1994). In the patient with altered respiratory status, alveoli may close at the end of expiration and may not reopen with the next inspiration (Bolton & Kline, 1994). Both PEEP and CPAP provide pressure to keep alveoli open; PEEP is pressure at the end of expiration and CPAP is pressure applied continuously. Both work by increasing one's functional residual capacity, which is the volume of air in the lungs at the end of expiration. A larger number of open alveoli increases the surface area available for gas exchange. Work of breathing is decreased because less work is necessary to reinflate the collapsed alveoli. PEEP is administered by a ventilator, while CPAP can be used in the spontaneously breathing patient (see Figure 2).
[Figure 2 ILLUSTRATION OMITTED]
Likewise, the addition of pressure at the beginning of inspiration provides additional pressure support ventilation. Pressure support ventilation (PSV) is a way of assisting the work of inspiration. Inspiration is supported by positive pressure, which increases tidal volume and minute ventilation (Padman, Nadkarni, Von Nesson & Goodill, 1994). More areas of alveoli are prevented from collapsing (Joris, Sottiaux, Chiche, Desaive, & Lamy, 1997). Additionally, pressure support is thought to decrease the work of breathing by resting accessory muscle use (Akingbola, Servant, Custer, & Palmisano 1993) (see Table 1).
Table 1. Results of Pressure Support * Increase tidal volume * Increase minute ventilation * Decreases accesory muscle use * Decreases work of breathing
BiPAP works by combining the benefits of PSV and CPAP, and keeps the lungs open during the entire respiratory cycle (Joris et al., 1997). Inspiratory pressure causes lung inflation and may be adjusted by way of the IPAP (inspiratory positive airway pressure) controls on the BiPAP. Expiratory pressure prevents alveolar collapse and is delivered by the EPAP (expiratory positive airway pressure) controls on the BiPAP (see Figure 3). Rate or frequency of cycling between IPAP and EPAP may also be controlled with a range from 6 to 30 cycles per minute (Strumpf, Carlisle, Millman, Smith, & Hill, 1990). The amount of time spent in IPAP (10%- 90%) may also be regulated (Akingbola et al., 1993). BiPAP is available in two modes. In the spontaneous mode, the IPAP and the EPAP are set, and the patient triggers inspiration and expiration. In the spontaneous timed mode, back-up breaths are delivered when the patient's rate of breathing falls below a preset level (Strumpf et al., 1990). There is also the less used timed mode in which inspiratory time and rate are completely controlled by the machine.
[Figure 3 ILLUSTRATION OMITTED]
Basically, as the patient initiates a breath, the machine imposes a preset inspiratory pressure or IPAP. Pressure in the ventilator then drops to a preset expiratory pressure or EPAP. This is done in synchrony with the patient's breathing pattern (Akingbola et al., 1993).
Typically the respiratory therapist begins by selecting the appropriate expiratory pressure for the child, for example, an EPAP of 5-6 cm [H.SUB.2]0. Inspiratory pressure is then added at 10-12 cm [H.SUB.2]0 and titrated upward accordingly. Pressures of 12 of IPAP and 6 of EPAP indicate that a pressure support of about 6 cm is being delivered. A rate of 6 to 30 cycles may be delivered according to the child's status.
Reduced dyspnea, decreased respiratory rate, decreased use of accessory muscles, improved blood gas values, and synchronization with the BiPAP ventilator would indicate effective ventilation. Naturally, agitation, increased confusion, hemodynamic instability, worsened oxygenation, or difficulty clearing secretions would serve as indicators that BiPAP is not effective. Alternative treatment should be sought (ARCF, 1997).
The type of ventilator designed exclusively for delivery of NPPV is called the pressure target ventilator. Although several devices are available for NPPV (including volume targeted ventilators), the majority of published research regarding pediatrics describe experiences with the BiPAP system (Teague & Fortenberry, 1995). BiPAP systems are mainly available as contoured nasal or oral masks attached to a ventilation system. The masks are secured to the patient using a headband or similar attachment device (see Figures 4, 5, and 6). Humidified oxygen may be added into a mask side port (Teague, 1997). Although alarms are not built into every ventilator, they may easily be added.
[Figures 4-6 ILLUSTRATION OMITTED]
Factors in the Decision to Choose NPPV
Several factors contribute to the clinician's decision to choose NPPV over traditional ventilation methods. The first factor stems from the recognition that chronic respiratory conditions are becoming more prevalent in the pediatric population. There is a growing population of children surviving lung injury induced by extracorporeal membrane oxygenation and high frequency ventilation who require long periods of ventilatory support by way of tracheotomy or intubation (Teague & Fortenberry, 1995). While ventilation of these patients has been successful, there are medical and psychological problems that may develop with prolonged tracheotomy (Waldhorn, 1992). NPPV use during the recovery phase of lung injury may serve to avoid the complications of tracheotomy (Teague & Fortenberry, 1995). Since BiPAP is usually used nocturnally, the functions of speaking and eating are preserved (Padman, Nadkarni, et al., 1994).
Likewise, although endotracheal intubation extends life by improving respiratory status, several complications are associated with it. These include aspiration and laryngeal or tracheal injury. In addition, pneumonia and sinusitis contribute to increased hospital stays and increased mortality (Brochard, 1996; Padman, Lawless, et al., 1994). Heavy sedation and restraint to prevent accidental extubation may be required (Brochard, 1996; Fortenberry, Del Toro, Jefferson, Evey, & Haase, 1995). The presence of the endotracheal tube itself may contribute to post-extubation respiratory distress (Brochard, 1996).
These factors contribute to a longer and more complicated hospital course. The high cost associated with prolonged stay for assisted ventilation in intensive care may be spared by use of BiPAP, since it can be used at home or outside of the ICU. Padman, Lawless, and colleagues (1994) and Padman, Nadkarni, and associates (1994) have shown successful use of BiPAP outside of the hospital intensive care unit.
BiPAP may be a more appropriate choice of ventilatory support for children with conditions, if they were intubated, where extubation may prove to be unlikely (Brochard, 1996). An example is the child with cystic fibrosis or severe muscular dystrophy (Padman, Nadkarni, et al., 1994). Additionally, consideration should be given to the use of BiPAP rather than intubation and invasive ventilation in patients with severe chronic neurological dysfunction and terminal disease processes such as HIV and cancer (Brochard, 1996). Additional issues exist in that these latter children have increased vulnerability to infection due to their immunocompromised state (Akingbola et al., 1993).
Potential alternatives to lessen these issues may be the use of negative pressure ventilation; however this method poses many limitations, including the large size of the tank and altered patient mobility. Additionally, it may contribute to apnea and upper airway obstruction (Padman, Lawless, et al., 1994).
Potential Uses for BiPAP
There are several pediatric conditions in which BiPAP has potential use as a method of ventilation. The following section analyzes current literature and past practice to form conclusions regarding usage of BiPAP in pediatric patients. Respiratory problems will be divided into chronic and acute disorders.
Chronic respiratory distress. NPPV is usually applied nocturnally for 6 to 10 hours to patients with chronic respiratory problems. There are three theories regarding how improvement in daytime gas exchange occurs: (a) tired respiratory muscles are rested and restored; (b) there is improvement of lung compliance; and (c) there is reversal of the diminished respiratory center's sensitivity to carbon dioxide, thought to cause gradual hypoventilation (Hill, 1993).
BiPAP has possible use in the child with central hypoventilation syndrome (CHS). Children with this syndrome demonstrate abnormal breathing patterns with symptoms of cyanosis, apnea, and hypopnea. Etiology is linked to a lack of sensitivity of central chemoreceptors to carbon dioxide, resulting in abnormal responses to hypercapnia and hypoxia (Pia Villa et al., 1997; Teague, 1997). A recent study demonstrated successful use of NPPV in a 4-month-old child with CHS. In this child's case, nocturnal use of BiPAP improved all of her symptoms, including hypercapnia and hypoxia and tracheotomy was avoided (Pia Villa et al., 1997). This report on the use of BiPAP in infants with central hypoventilation syndrome is an isolated one; more controlled studies are necessary before recommendations can be made (Teague, 1997).
In adults, BiPAP has improved symptoms of hypoventilation and hypercarbia experienced in those with progressive neuromuscular and restrictive wall disorders, such as muscular dystrophy, post polio syndrome, multiple sclerosis, tuberculosis, and kyphoscoliosis (Hill, 1993; Teague, 1997; Waldhorn, 1992). Use of BiPAP may enhance ventilation by resting chronically fatigued muscles (Waldhorn, 1992). Padman, Lawless, and colleagues (1994) were able to demonstrate decreases in hospital days, respiratory rate, heart rate, and serum bicarbonates and improved arterial blood gases in patients with varied restrictive disorders, including spinal muscle atrophy, cystic fibrosis, spinal cord injury, and muscular dystrophy. Currently, patients with spinal muscle atrophy and similar degenerative muscle disorders are using BiPAP as part of their pulmonary management upon discharge from the hospital.
Use in chronic obstructive airway disease (COAD), such as cystic fibrosis, has also been demonstrated. Muscle fatigue associated with inadequate nutrition is thought to contribute to failure in children with COAD (Teague, 1997). "BiPAP could be used to 'unload' the inspiratory muscles, and thereby, raise minute ventilation in those patients whose respiratory effort is limited by muscle fatigue" (Teague, 1997, p. 417). Muscle energy expenditure and work of breathing would, in theory, be decreased. This effect was evidenced in 1994, when Padman, Nadkarni, and associates (1994) studied the effects of BiPAP on seven children with cystic fibrosis. Blood gas values improved and in five patients, BiPAP maintained their stability until transplantation.
Use of NPPV in children with bronchopulmonary dysplasia may be limited in view of the fact that high peak inspiratory pressures are required in this type of disease. Most of the ventilators currently available would not have the ability to meet the high inspiratory pressure demand of this population (Teague, 1997).
Nocturnal obstructive hypoventilation (NOH) is seen in children with morbid obesity, Down syndrome, craniofaciai anomalies, and congenital abnormality of the larynx and trachea, all which contribute to upper airway obstruction. NOH may result in severe hypoventilation due to partial upper airway narrowing. Treatment includes several stages of surgery to improve the upper airway. NPPV has potential use to reduce airway occlusions and improve gas exchange in the phase before surgical correction is complete. However, only preliminary studies exist and more controlled study is needed (Teague, 1997).
Obstructive sleep apnea (OSA) is characterized by "symptoms ranging from obstructive apnea with mild hypoxemia to prolonged episodes of obstructive hypopnea with hypercarbia" (Teague, 1997, p. 415). Adenotonsillectomy often cures OSA in children. Due to its potential to assist inspiratory effort and relieve inspiratory muscle fatigue thought to cause OSA, BiPAP may also be beneficial in these children (Teague, 1997). It was successfully utilized in children with respiratory compromise post adenotonsillectomy (Rosen, Muckle, Mahowald, Goding, & Ullevig, 1994). BiPAP can be used for these children both in the hospital and at home.
Children with chronic respiratory failure using nocturnal NPPV should be seen by their caregiver every 2-4 months (Teague, 1997). Rationale for this is based on the fact that children with progressive neuromuscular diseases may have gradually increasing Pa[CO.sub.2] values, which may be treated with adjustments in IPAP (Hill, 1997). Follow-up visits should include monitoring of growth, swallowing, muscle strength, pulmonary function, and arterial blood gas values (Teague, 1997).
Acute respiratory distress. NPPV could potentially be used in the relief of acute respiratory distress in children. While several reports of the success of NPPV in preventing intubation in adults exist, fewer are available in regards to children (Teague, 1997). In 1993, Akingbola and associates reported the successful use of NPPV in two children with atelectasis and pulmonary edema. Fortenberry and colleagues (1995) demonstrated decreased respiratory rates and improved gas exchange in children with mild to modest hypoxemic respiratory distress following treatment with nasal BiPAP.
In acute respiratory distress, there is a reduction in a person's functional residual capacity, which causes a ventilation-perfusion mismatch resulting in hypoxemia. Control of this type of distress is managed with interventions that increase lung volume (Akingbola et al., 1993). Additionally, some of the improvement seen in BiPAP may be attributed to "support for respiratory muscles or (due to) the stenting of upper airways or large bronchi" (Fortenberry et al., 1995, p. 1061).
There is potential for BiPAP to be used in facilitating the weaning process from mechanical ventilation (Sassoon, 1995). Nasal masks could be considered for use in patients immediately post-extubation, especially if there is residual muscle weakness (Fortenberry et al., 1995). Currently, at A.I. DuPont Hospital for Children, NPPV is used in these situations in eligible patients, along with close monitoring in the intensive care unit.
Status asthmaticus may be characterized by severe hypoxemia and respiratory muscle fatigue (Teague, 1997). BiPAP has been successfully used for treatment of adults with exacerbation of asthma (Meduri, Cook, Turner, Cohen, & Leeper, 1996). At this time, routine use of NPPV in children with acute asthma is not recommended until further studies are available (Teague, 1997).
Although studies exist confirming the successful use of NPPV in the acutely ill population, "most studies of NPPV have actually excluded patients who need immediate intubation" (Wunderink & Hill, 1997, p. 395). This is obviously due to lack of time in an emergency situation to consider a less utilized, less validated technique.
Contraindications to BiPAP
McGarry (1992) argues against the use of BiPAP in cases in which the patient is on the verge of being intubated or recently extubated. He believes that patients enduring acute distress on BiPAP will be unable to protect their airway and are, therefore, more prone to gastric insufflation, vomiting, and aspiration, leading to respiratory arrest. Hill (1997) contends that aspiration, although possible, is an infrequent complication seen more often in patients with previously impaired airway protection ability.
Severe hypoxemia is most likely not amenable to treatment with BiPAP. Reasons for failure to control hypoventilation may be attributed to conditions requiring a higher peak pressure (greater than 25 cm [H.SUB.2]0) than the BiPAP is able to deliver (McGarry, 1992; Padman, Lawless, et al., 1994).
Exclusion criteria for use of BiPAP in children in acute distress include excessive airway secretions, inability to protect one's airway, and inability to cooperate (Teague, 1997; Turner, 1997). Choanal stenosis with nasopharyngeal airway occlusion and severe laryngomalacia are examples of conditions that would absolutely preclude NPPV use (Teague, 1997).
As with any therapy, nurses must be aware of potential complications and side effects (see Tables 2 and 3). Common complications regarding use of the mask include excoriation at the points of skin contact and acneiform rashes (Hill, 1997). Application of protective barriers such as duoderm and use of antibiotic creams may solve these issues (Hill, 1997; Turner, 1997). Alternating between different types of masks may also ameliorate skin problems. Eye irritation related to the mask or air is comforted with lubricating drops, and nasal burning or dryness is eased with increased humidification (Hill, 1997).
Table 2. Pros and Cons of BiPAP Positive Negative Speech function preserved Pressure sores, discomfort Increased mobility Rashes Swallowing function preserved Nasal dryness, irritation Fosters independence Eye irritation Portability of ventilator Air leaks Decreased costs Possible aspiration Table 3. Strategies for Successful Use of BiPAP in Children * Explain the therapy to the family and child * Select proper mask size * Avoid very tight mask fit * Monitor and make appropriate adjustments in fit and ventilator settings * Use protective barriers for skin * Use humidification, nasal decongestants * Allow breaks in wearing time if possible
Poor mask fit contributes to skin and eye irritation. It also may be responsible for leaks around the mask. A leak is acceptable as long as it does not alter the ventilator's capability to cycle from expiration to inspiration and back again (Turner, 1997). Caution is advised in adjusting the mask too tightly to avoid leaks (Hill, 1997). A better approach is to apply various size masks on the child to find the best fit (Hill, 1997). Following application of the mask, careful adjustment of alarms for sensitivity in changes facilitates monitoring for leaks (Turner, 1997).
Nasal masks are the more usual mode of use, but oronasal masks are also available. Use of oronasal masks increases the chance of aspiration; masks should be made of a see-through plastic and used with much caution (Fortenberry et al., 1995).
Special preparation of the child and family combined with a clinician experienced in the use of BiPAP ensures a greater chance of success. The mask is more easily tolerated if it is placed on the child at low pressure settings (5-6 cm [H.SUB.2]0 inspiratory pressure and 6-10 cm [H.sub.2]0 expiratory pressure). Once synchronization with ventilation is achieved, pressures may be titrated to higher levels (Teague, 1997).
Gastric distension is a rare complication. None of the 28 children using BiPAP experienced gastric distension and a nasogastric tube was unnecessary (Fortenberry et al., 1995). Although flatulence has been reported, it has not been described as intolerable (Hill, 1997).
Another potential complication is the rebreathing of carbon dioxide, which could potentially result in increased work of breathing (Lofaso et al., 1995). There is a nonrebreathing valve available to prevent this. Lofaso and associates (1995) compared the BiPAP ventilator with its normal exhalation valve to a BiPAP with a nonrebreathing isolation valve. Results revealed that use of BiPAP without the nonrebreathing valve increases work of breathing and minute ventilation (Lofaso et al., 1995).
Although use of BiPAP in the pediatric population continues to grow, there is a need for more prospective controlled trials to confirm the capabilities of the technique (Fortenberry et al., 1995). Research must focus on data to compare success rates, costs, and outcomes of BiPAP to standard therapies (Hill, 1997). Additionally, more reports of the types and acuity of conditions, and location of use would enhance knowledge regarding BiPAP. There is a need for more controlled randomized studies to determine the ability of BiPAP to slow worsening lung function and manage acute exacerbations (Padman, Lawless, et al., 1994). Indeed, a most challenging task is to distinguish those situations in which BiPAP may be superior to traditional therapy (Teague, 1997).
Acknowledgment: The author special thanks Brenda Lennon, RRT. for her assistance with this article.
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Nadine O'Neill, BSN, RN, CCRN, is a Staff Nurse, A.I. duPont Hospital for Children, Wilmington, DE, and a Graduate Student, University of Delaware, Newark, DE.
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