Adjuncts in Respiratory Care

Marjorie J Arca, MD, Sarah K Walker, MD

Introduction

Patients with respiratory compromise often require adjunctive therapies to improve lung function and perhaps avoid mechanical ventilation. This section discusses the devices used to deliver supplemental oxygen and air flow, the humidification of inhaled gases, methods to mitigate airway edema, techniques by which chest physiotherapy is performed and noninvasive ventilation.

see also Respiratory Care and Respiratory Care in the Neonate

Medical Treatment

What are the methods of delivering oxygen in a nonventilated patient?

There are several devices that deliver supplemental oxygen and increased airflow whose selection depends upon the patient’s oxygen requirements and their ability to reliably tolerate the devices. These devices are classified as either high flow or low flow systems and can be for hospital or home use. High flow systems do not utilize room air because the flow rate is able to meet the inspiratory flow requirements of the patient while the low flow systems include room air because their rate of oxygen flow is insufficent to fulfill the patient’s inspiratory requirements.

An oxygen tent consists of a clear plastic enclosure that contains the child’s upper or entire body. Tents require inspiratory flow rates of 10 to 20 Lpm and deliver an FiO2 of 0.4 to 0.5. A tent is recommended for FiO2 requirements less than 30 %. Use of the tent limits patient movement and caretaker access and is rarely used in modern management of mild increased oxygen requirements.

An oxygen hood is a clear plastic shell that surrounds the patient’s head. Gas flow rates of 10 to 15 Lpm allow an FiO2 of 0.8 to 0.9 to be achieved.

The traditional nasal cannula is a low flow device that can deliver 1 to 6 Lpm and 22 to 42% FiO2. The approximate FiO2 delivered is calculated by the formula FiO2 = 20% + (4 x O2 flow in Lpm). The actual FiO2 delivered is influenced by the patient’s respiratory rate, tidal volume and inspiratory flow. Clinical practice guidelines recommend maximum nasal cannula flow of 2 Lpm in infants as higher rates can cause an inadvertent continuous positive airway pressure effect. Nasal cannulas have the advantage of being easily used in acute situations and while feeding.

Face masks are classified as simple, partial rebreathing, nonrebreathing and air entrainment (Venturi). Simple face masks consist of a clear plastic mask designed to fit over the nose and mouth and have a valveless oxygen inlet. There are holes on the sides of the masks to entrain room air. This system generates an FiO2 of 0.35 to 0.65 at about 6 to 10 Lpm. Partial rebreathing masks incorporate a mask, a valveless oxygen inlet and an oxygen reservoir bag. A portion of the patient’s exhaled gas enters the reservoir bag and room air can be entrained during inhalation. As a result, the partial rebreathing mask only allows generation of an FiO2 of 0.5 to 0.6 with inspiratory flow rates of 10 Lpm or greater.

A nonrebreathing face mask consists of a face mask connected to a unidirectional valve and oxygen reservoir bag. The valve is within the exhalation port of the mask, thus allowing exhaled gas to exit the mask but preventing room air from being entrained during inhalation. Inhaled gas only comes from the oxygen reservoir and an FiO2 close to 1.0 can be achieved. A disadvantage of a nonrebreathing mask is that oxygen must be flowing to the mask in order for the patients to ventilate without difficulty. Air entrainment or Venturi masks have a dial that mixes oxygen and entrained room air thereby allowing delivery of a predetermined oxygen gas concentration of 24, 28, 31, 35 or 40%. FiO2 delivered through the mask is independent of the patient’s minute ventilation.

What is the role of humidification?

The humidification of inhaled gases is essential in patients requiring supplemental oxygen. Numerous studies have described thick secretions, airway inflammation and mucosal necrosis in ventilated adult patients who had dry inhaled gases. Humidification prevents the inspissation of sputum and secretions within the endotracheal tube and airway as well as preventing heat loss [1]. Because of their increased metabolic rate relative to their size infants are at greater risk for heat loss than adults unless gases are heated and humidified. Infants have higher minute ventilation compared with adults and subsequently expend more energy converting water to vapor resulting in greater heat loss especially with dry gases [1][2].

The humidification of gas can be accomplished by two methods: active humidification using a heated humidifier and passive humidification using a heat and moisture exchanger (HME). The heated humidifier is a wire within the inspiratory limb of the ventilator which heats air and prevents moisture from condensing by keeping it warm. The HME is placed in line between the endotracheal tube and ventilator circuit and traps the heat and humidity of the expired air of a patient and returns it with the next inspiration [3][4]. A Cochrane review demonstrated no major difference between the two methods in preventing pneumonia, indwelling airway occlusion or mortality [5]. Cost differences were difficult to assess, however HME may be associated with higher risk of artificial airway occlusion in the neonatal population.

heat and moisture exchanger
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What methods are used to mitigate the effects of airway edema?

The Reynold’s number determines the likelihood of developing of turbulent rather than laminar flow in the airways. Helium is a noble, low density gas discovered in the 1800s that has a low Reynold’s number. In the setting of narrowed airways, helium is associated with greater total gas flow with lower resistance which translates into decreased work of breathing [6][7]. It was initially proposed as a treatment for pulmonary edema induced at altitude [8]. Heliox is a helium and oxygen gas mixture that allows for better flow through narrowed airways. It is utilized in disease states such as upper airway obstruction, croup, bronchiolitis and asthma. Heliox also has beneficial effects on postextubation stridor and work of breathing in pediatric trauma patients [9]. Heliox does not directly treat any disease but instead decreases the work of breathing and temporizes the immediate issue of oxygen delivery and ventilation allowing upper airway compromise to resolve [10].

Racemic epinephrine 2.25% or L-epinephrine (1:1,000), an aerosolized vasoconstrictor, is administered via an inhaler to treat respiratory illness and has been utilized since the 1970s. There is no difference in action or cardiovascular effects of L-epinephrine which is pharmacologically active versus racemic which is a mixture of L and R isomers [11]. When given as an inhalant, epinephrine affects alpha and beta adrenergic receptors with inotropic and chronotropic effects on the heart, vasoconstriction of the mucosal blood vessels and relaxation of smooth muscle lining the airway leading to bronchodilation and a decrease in pulmonary edema. Its primary use is for patients with croup and bronchiolitis whcih are both associated with acute onset inflammation of the lower and upper airways. In croup racemic epinephrine administration is associated with an improvement in croup score when compared to a placebo [12].

Systemic corticosteroids are utilized to decrease airway inflammation and have been shown to have a definitive benefit in the management of asthma and croup. The benefits of steroid use in acute pharyngitis, bronchiolitis and wheezing are less clear. Practitioners have been concerned with the negative side effects of steroids such as growth disturbance, bone disease, a higher risk of infections and adrenal suppression [13] A Cochrane review of more than 44 clinical studies concluded that the short term use of steroids (one to five day bursts) was safe when used in acutely ill, otherwise healthy children [14]. Shorter courses of intravenous corticosteroids are utilized to prevent and treat postextubation stridor especially in the pediatric population. Five randomized trials yielded inconsistent results with regard to the benefit of steroid administration for stridulous patients after extubation [15]. The most recent adult studies demonstrate a benefit of steroids on postextubation stridor and reintubation when multiple doses are given prior to extubation [16][17][18].

Nebulized hypertonic saline (3%) is utilized in patients with cystic fibrosis to promote mucociliary clearance, decreasing mucous plugging and overall airway edema [19]. Its uses have further expanded to the treatment of bronchiolitis in which it was found to decrease bronchiolitis scores and length of stays compared with normal saline [20]. No formal studies of this aerosol is available in other diseases but it may be a useful adjunctive in the treatment of respiratory illness in the pediatric patient.

What are methods of chest physiotherapy?

Chest physiotherapy refers to a group of treatments that help to improve breathing by dislodging mucus, increasing lung expansion, strengthening respiratory muscles and improving respiratory efficiency.

Percussion is the clapping of the chest wall with the goal of dislodging mucus to facilitate expectoration. Percussion of the chest can be done with a cupped hand, soft rubber percussor or an electric percussor.

soft rubber percussor
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Postural drainage refers to changing the child’s position to help drain mucus. Typically the affected lobe is placed at a higher level (the opposite side in decubitus, head down) to promote drainage. Often percussion is performed while the patient is in the optimal drainage position.

A Cochrane Database review noted that there is no conclusive evidence to justify the use of chest physiotherapy in children with pneumonia [21]. Similarly there is insufficient evidence to determine if chest physiotherapy is beneficial or harmful for ventilated neonatal patients [22].

While effective, percussion and postural drainage are time-consuming for care providers and impede the independence of the patient. As a result several devices have been created to augment mucus mobilization and/or lung expansion.

High-frequency chest wall oscillation (HFCWO) or vest therapy.

The vest is made up of two parts, an air pulse generator and an inflatable vest that wraps around the chest. The air pulse generator makes the vest inflate and deflate against the chest wall with a pressure of 50 cm H2O at a rate of about 25 times per second. The air pulse oscillates the chest mimicking the coughing mechanism and loosening mucus. There are no pediatric studies that show that vest therapy is superior to other methods of airway clearance. A study that compared HFCWO to postural drainage and a flutter device (see below) in pediatric patients with cystic fibrosis showed better treatment satisfaction using the HFCWO and flutter device compared to postural drainage. The study was truncated due to early dropout but did show that forced expiratory flow (FEF 25 to 75%) improved more rapidly with vest therapy [23]. The vests demonstrated more effective clearance and decreased hospitalization compared with manual chest percussion therapy likely owing to ease of use and greater compliance [24].

vest therapy
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Positive expiratory pressure (PEP) device.

This device consists of a face mask or a mouth piece (Therapep®) with a one way valve to which different respiratory resistances can be attached. A manometer is attached between the valve and the resistance to monitor the actual value of the airway pressure (ideally between 10 and 20 cm H2O) during midexpiration. The goal of PEP therapy is to prevent airway collapse by stenting the airways and increasing intrathoracic pressure in order to augment functional residual capacity. Hypothetically the alveoli will be expanded which should reduce atelectasis and enhance the clearance of secretions [25].

positive expiratory pressure
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Intrapulmonary percussive ventilation (IPV) device.

The IPV approach combines aerosol inhalation and internal thoracic percussion applied via a mouthpiece or a mask. The flow of gas released with each pulse can be preset and the pulsation frequency adjusted to the needs of each individual. It is used to open atelectatic lung regions. A few reports have shown promise in the use of this therapy for children [26][27].

intrapulmonary percussive ventilation
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Flutter device.

This is a handheld oscillatory PEP device shaped like a pipe that contains a high density stainless steel ball that sits in a circular cone inside the bowl of the pipe. The ball rises and flows within a cone during expiratory flow through the mouthpiece which creates a PEP between 5 and 35 cm H2O with oscillations or vibrations between 8 and 26 Hz. The frequency of oscillations can be modulated by changing the inclination of the flutter. The combination of the PEP and the oscillations reduces airway collapsibility and results in vibration of the airway walls thus enhancing secretion mobilization and lung function and oxygenation.

flutter
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Acapella device.

This is an oscillatory PEP device similar to the flutter apparatus. It uses a counterweighted plug and magnet to achieve valve closure instead of a steel ball to create oscillations during exhalation. Unlike the flutter it is not gravity dependent. There are three models depending on the patient’s expiratory flow - high flow (greater than 15 Lpm), low flow (less than 15 Lpm) and the AcapellaChoice® that has a numeric dial to adjust the frequency of oscillation.

acapella
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Incentive spirometry.

This device is designed to mimic natural sighing or yawning by encouraging the patient to take long, slow deep breaths. The incentive spirometer provides patients with visual or other positive feedback when they inhale at a predetermined flow rate or volume and sustain the inflation for a minimum of three seconds. The goal of incentive spirometry is to increase transpulmonary pressure and inspiratory volume, improve inspiratory muscle performance and re-establish or simulate the normal pattern of pulmonary hyperinflation. It is used in postoperative patients to open atelectatic segments and prevent postoperative pulmonary complications. Recent data question the utility of incentive spirometry in postoperative pediatric and adult patients and maintain that early ambulation is a better method of preventing pulmonary complications [28]. Blowing bubbles or blowing on pinwheels are effective options for toddlers who have the cognitive capacity and the ability to blow air when instructed to do so.

incentive spirometer
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Noninvasive Ventilation

What is noninvasive ventilation?

Noninvasive ventilation (NIV) is a method by which respiratory support is provided without endotracheal intubation. This can be accomplished by the Neotech RAM nasal cannula® for neonates, standard nasal prongs for older children, nasal masks and face masks. NIV can provide stabilization of the airway and chest wall, alveolar recruitment and reduction of intrapulmonary shunting. The use of noninvasive ventilation has increased in infants, children and adults in the last two decades paralleling the recognition of ventilator associated complications such as pneumonia and ventilator induced lung injury[29]. Relative contraindications to NIV include rapidly progressive respiratory failure, hemodynamic instability, an inability to protect the airway from aspiration and a lack of a properly fitting delivery interface such as a mask. Facial trauma, burns, recent upper airway or upper gastrointestinal tract surgery, presence of a fixed obstruction in the upper airway, impaired consciousness, vomiting, bowel obstruction and undrained pneumothoraces also generally preclude the use of NIV.

What are the methods of noninvasive ventilation?

NIV requires a heated 100% humidified blended gas source, a patient interface, a patient circuit and a pressure generating apparatus [30]. In general NIV is performed by one of two approaches:

High flow nasal cannula (HFNC). Two to 8 liters per minute of oxygen is infused through a narrow diameter interface delivering a high rate of gas into the patient’s nares. The gas is heated and humidified to decrease injury to the mucus membranes [31]. The high flow allows for dead space washout. In infants the pressure generated can mimic the effects of positive end expiratory pressure (PEEP) and may help stent the trachea and bronchus. One disadvantage of HFNC is that there is no method of measuring how much pressure actually reaches the airways [32].

Continuous positive airway pressure (CPAP). Increased pulmonary pressure is provided during the expiratory phase of a spontaneously breathing patient. This appears to increase functional residual capacity, reduce airway resistance, augment diaphragmatic function and decrease the work of breathing. CPAP initially was based on support delivered via an endotracheal tube. It has now been adapted for use with nasal prongs and masks. Nasal access with binasal prongs is especially appropriate for newborns since they are obligatory nasal breathers with an effective seal between the tongue and soft palate [30].

Nasal continuous positive airway pressure (NCPAP) support is essentially constant PEEP and can be delivered using a ventilator or through a specialized CPAP system using either continuous flow or variable flow techniques.With continuous flow NCPAP the PEEP valve on a ventilator or CPAP machine determines the amount of pressure delivered which is independent of gas flow rate. The expiratory resistance can be rapidly adjusted based on data from a sensor in the circuit. The exact pressure delivered to the airway is not known since the pressure sensing device is remotely located from the airway. Bubble CPAP is a form of constant flow NCPAP with the expiratory limb of the circuit immersed under water. The bubbling of the water generates oscillations in CPAP up to 4 cm H2O within the circuit. There are data which suggest that duration of CPAP may be reduced and success of extubation increased with use of bubble CPAP when compared to NCPAP in preterm infants with the respiratory distress syndrome [33].

Variable flow NCPAP generates CPAP just proximal to the nares. Dual injector jets direct flow towards each nostril. Aerodynamic principles (including the Bernoulli and Coanda effects), combine to create fairly constant airway pressure while directing flow toward the patient during inhalation and away from the patient during exhalation [30]. This approach results in a decrease in the work of breathing to a fraction of that observed with continuous flow CPAP against which the patient has to exhale. Interestingly the variable flow approach generates more uniform continuous pressure than is associate with continuous flow.

bubble CPAP
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Components of simple bubble CPAP

Bilevel positive airway pressure (BiPAP) is another modaility of noninvasive ventilation and delivers both inspiratory and expiratory positive airway pressure. Tidal volume is determined by the difference between inspired and expired positive airway pressures. Breaths can be triggered by the patient or the ventilator. There is limited availability of FDA-approved interfaces for the infant and pediatric population.

Nasal intermittent positive pressure ventilation (NIPPV) is an alternative strategy for those neonates and others requiring more support than provided by CPAP. The most common mode used is similar to BiPAP where there are preset peak inspiratory and end-expiratory pressures. Breaths are triggered by the patient or by the ventilator (time-cycled). Patient ventilator synchrony in NIPPV is historically difficult to coordinate and asynchronous breaths can result in high pressure during expiration which may be deleterious. NAVA can potentially be utilized to achieve synchrony.

What are the challenges of noninvasive ventilation?

The main challenge of noninvasive ventilation is the limited interfaces for infants and children. Development of devices to deliver non-invasive ventilation in infants and children have enabled the more widespread use of this modality in pediatrics. Currently available interfaces include face masks, short prong nasal cannulas and intermediate size high flow nasal cannulas (Fisher Paykel, Auckland, New Zealand). The RAM nasal cannula (NeoTech, Valencia, California) has tubing with a larger bore than a standard oxygen or high-flow nasal cannula. This type of tubing reduces resistance and imposed work of breathing during spontaneous breathing.

types of nasal cannulas
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(right to left). Regular nasal cannula, High Flow Nasal Cannula, RAM nasal cannula. The difference between regular and high flow nasal cannulas is the length of intervening tubing.

Complications

In children nasal cannula flow rates greater than 3 liters per minute are associated with dry mucus membranes and nasal cannulas can injure the skin if they are ill fitting with damage at the nares, intranasal septum, columella or philtrum. Traction along the tubing can also cause pressure injury to the patient.

Nasal continuous positive airway pressure (CPAP) devices can be obstructed via thick secretions. The pressure delivered using nasal cannulae or nasal masks is decreased if the patient’s mouth is open. Nonininvasive ventilation (NIV) techniques should only be used in alert patients who can handle their secretions since the stomach can be distended by the positive pressure and may induce nausea and vomiting [32]. Care should be taken in using this approach in patients following operations on the gastrointestinal tract.

Outcomes

Much of the data on nonininvasive ventilation (NIV) comes from the neonatal population. NIV has been shown to decrease need for intubation, decrease the incidence of nosocomial pneumonia, shorten intensive care unit and hospital stays, decrease mortality, preserve airway defenses, improve comfort and decrease the need for sedation. In the child with chronic respiratory compromise noninvasive ventilation alleviates symptoms from chronic hypoventilation, increases sleep duration and quality, improves functional residual capacity and prolongs survival. Predictors of successful outcomes for noninvasive ventilation in the acute setting include a high PaCO2 with low A-a gradient, pH between 7.25 and 7.35, a good level of consciousness and an improvement in ventilation and respiratory rate within one hour of instituting NIV. Predictors of failure using NIV methods include high APACHE scores or very ill children, pneumonia present radiographically, copious secretions, being edentulous, malnutrition and confusion or impaired consciousness [34].

Perspectives and Commentary

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Additional Resources

APSA Handbook of Pediatric Surgical Critical Care

Discussion Questions and Cases

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Last updated: November 2, 2020