Lung Expansion Therapy

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Lung Expansion Therapy

Daniel F. Fisher

Chapter Objectives

After reading this chapter you will be able to:

image Describe the various causes of atelectasis.

image Identify which patients need lung expansion therapy.

image Define the clinical findings seen in atelectasis.

image Describe how lung expansion therapy works.

image List the indications, hazards, and complications associated with the various modes of lung expansion therapy.

image Describe the primary responsibilities of the respiratory therapist in planning, implementing, and evaluating lung expansion therapy.

Key Terms

Pulmonary complications are common serious problems seen in patients who have undergone thoracic or abdominal surgery.1,2 Such complications include atelectasis (alveolar collapse), pneumonia, and acute respiratory failure. These respiratory problems can be minimized or avoided if proper respiratory care is implemented during the perioperative period. The most common form of therapy used in high-risk patients is lung expansion therapy.

Lung expansion therapy encompasses a variety of respiratory care modalities designed to prevent or correct atelectasis. The most common modalities include deep breathing/directed cough, incentive spirometry (IS), continuous positive airway pressure (CPAP), positive expiratory pressure (PEP), and intermittent positive airway pressure breathing (IPPB). The common purpose that all of these techniques share is to guide the patient into improving pulmonary function by maximizing alveolar recruitment and optimizing airway clearance.

Various lung expansion therapies can be effective in preventing or correcting atelectasis in selected patients.1 However, the precise method to apply in a given situation is not always clear because no advantage of any one method has been established. The most efficient use of resources is a primary concern with any plan to apply lung expansion therapy.

If all of the following therapies were to be compared, the common factor they share is that they all are designed to increase functional residual capacity (FRC). In other words, these all are supplemental techniques to simulate a deep breath or sigh. In an uncompromised patient, this mechanism is working effectively. In this context, the respiratory therapist (RT) plays a vital role. In consultation with the prescribing physician, the RT should assist in identifying patients most likely to benefit from lung expansion therapy, recommend and initiate the appropriate and most efficient therapeutic approach, monitor the patient’s response, and alter the treatment regimen as needed.

Causes and Types of Atelectasis

Although atelectasis can occur from a large variety of problems, this chapter focuses on the two primary types associated with postoperative or bedridden patients who are breathing spontaneously without mechanical assistance: (1) gas absorption atelectasis and (2) compression atelectasis. Gas absorption atelectasis can occur either when there is a complete interruption of ventilation to a section of the lung or when there is a significant shift in ventilation/perfusion (image). Gas distal to the obstruction is absorbed by the passing blood in the pulmonary capillaries, which causes partial collapse of the nonventilated alveoli. When ventilation is compromised to a larger airway or bronchus, lobar atelectasis can develop.

Compression atelectasis results when the forces within the chest wall and lung—specifically, the pleural pressure—are exceeded by the transmural pressure, which is what distends and maintains the alveoli in an open state.2–4 Compression atelectasis is primarily caused by persistent use of small tidal volumes by the patient. This situation is common when general anesthesia is given, with the use of sedatives and bed rest, and when deep breathing is painful, as when broken ribs are present or surgery has been performed on the upper abdominal region. Weakening or impairment of the diaphragm can also contribute to compression atelectasis. Compression atelectasis results when the patient does not periodically take a deep breath and expand the lungs fully. It is a common cause of atelectasis in hospitalized patients. It may occur in combination with gas absorption atelectasis in a patient with excessive airway secretions who breathes with small tidal volumes for a prolonged period.

Factors Associated With Causing Atelectasis

Atelectasis can occur in any patient who cannot or does not take deep breaths periodically and in patients who are restricted to bed rest for any reason.5 Patients who have difficulty taking deep breaths without assistance include patients with significant obesity, patients with neuromuscular disorders or who are under heavy sedation, and patients who have undergone upper abdominal or thoracic surgery. Diaphragmatic position and function is the major contributor to the onset of atelectasis. In an anesthetized patient, there is a cephalad (toward the head) shift of the diaphragm. For patients who are supine, the lower, dependent portion of the diaphragm performs the most movement. The opposite occurs in patients who are paralyzed—the upper portion of the diaphragm is involved in movement.3,4 Patients undergoing lower abdominal surgery are at less risk for atelectasis than patients undergoing upper abdominal or thoracic surgery, but they still may be at significant risk. Patients with spinal cord injury are prone to respiratory complications, the most common of which is atelectasis. Bedridden patients, such as patients recovering from major trauma, are particularly predisposed to developing atelectasis secondary to lack of mobility. Atelectasis is one of the most important determinants of hypoxemia after abdominal surgery and may account for 24% of deaths within 6 days of surgery.6 It is clinically prudent to consider atelectasis in every assessment of postoperative patients.

Impairment of the function of pulmonary surfactant can also have an impact on the development of atelectasis. Surfactants decrease the surface tension of the walls of the alveoli. When there is deterioration of the function of this vital protein, the relative increase in surface tension can cause the walls of the alveoli to collapse.4

Most postoperative patients also have problems coughing effectively because of their reduced ability to take deep breaths. An ineffective cough impairs normal clearance mechanisms and increases the likelihood of retained secretions, which could lead to the development of gas absorption atelectasis in a patient with excessive mucus production. Patients with a history of lung disease that causes increased mucus production (e.g., chronic bronchitis) are most prone to develop complications in the postoperative period. Similarly, a significant history of cigarette smoking should alert the RT to the high risk for respiratory complications with surgery. Such patients must be identified in the preoperative period and considered strong candidates for airway clearance and lung expansion therapy. Elective surgery for these patients may need to be postponed in some cases until such therapies can be included in the treatment plan. Lung expansion therapy and chest physical therapy in the postoperative period may help improve clearance of secretions by improving the effectiveness of coughing and secretion removal.

image Rule of Thumb

The closer the incision is to the diaphragm, the greater the risk for postoperative atelectasis. Patients with a history of inadequate nutritional intake, as shown by an albumin level less than 3.2 mg/dl, have an increased risk for pulmonary complications in the postoperative period. This increased risk is most likely due to inadequate strength of the inspiratory muscles to maintain a normal FRC and VC.

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Risk Factors for Atelectasis

Clinical Signs of Atelectasis

RTs must be able to recognize the clinical signs of atelectasis in patients so that appropriate therapy can be implemented in a timely fashion. The patient’s medical history often provides the first clue in identifying atelectasis. Recent upper abdominal or thoracic surgery in any patient should suggest possible atelectasis. A history of chronic lung disease or cigarette smoking or both provides additional evidence that the patient is prone to respiratory complications after major surgery or prolonged bed rest.

The physical signs of atelectasis may be absent or very subtle if the patient has minimal atelectasis. When the atelectasis involves a more significant portion of the lungs, the patient’s respiratory rate increases proportionally. Fine, late-inspiratory crackles may be heard over the affected lung region. These crackles are produced by the sudden opening of distal airways with deep breathing. Bronchial-type breath sounds may be present as the lung becomes more consolidated with atelectasis. Diminished breath sounds are common when excessive secretions block the airways and prevent transmission of breath sounds. Tachycardia may be present if atelectasis leads to significant hypoxemia. Patients with preexisting lung disease often present with significant abnormalities in respiratory and heart rates, even when atelectasis is not severe.

image Rule of Thumb

There is a direct relationship between the spontaneous respiratory rate and the degree of atelectasis present. Typically, as atelectasis progresses, respiratory rate increases proportionally.

The chest radiograph is often used to confirm the presence of atelectasis. The atelectatic region of the lung has increased opacity. Evidence of volume loss is present in patients with significant atelectasis. Direct signs of volume loss on the chest film include displacement of the interlobar fissures, crowding of the pulmonary vessels, and air bronchograms. Indirect signs include elevation of the diaphragm; shift of the trachea, heart, or mediastinum; pulmonary opacification; narrowing of the space between the ribs; and compensatory hyperexpansion of the surrounding lung.

Lung Expansion Therapy

All modes of lung expansion therapy increase lung volume by increasing the transpulmonary pressure (Pl) gradient. As detailed elsewhere in this text, PL gradient represents the difference between the alveolar pressure (Palv) and the pleural pressure (Ppl):

< ?xml:namespace prefix = "mml" />PL=Palv−Ppl

image

With all else being constant, the greater the Pl gradient, the more that the alveoli expand.

As depicted in Figure 39-1, the Pl gradient can be increased by either (1) decreasing the surrounding Ppl (see Figure 39-1, A) or (2) increasing the Palv (see Figure 39-1, B). A spontaneous deep inspiration increases the Pl gradient by decreasing the Ppl. The application of positive pressure to the lungs increases the Pl gradient by increasing the pressure inside the lung.

image
FIGURE 39-1 Transpulmonary pressure gradients with spontaneous inspiration (A) and positive pressure inspiration (B).

All lung expansion therapies use one of these two approaches. IS enhances lung expansion via a spontaneous and sustained decrease in Ppl. Positive airway pressure techniques increase Palv in an effort to expand the lung. Positive pressure lung expansion therapies may apply pressure during inspiration only (as in IPPB), during expiration only (as in PEP and expiratory positive airway pressure [EPAP]), or during both inspiration and expiration (CPAP). Although all of these approaches are used in lung expansion therapy, the methods that decrease Ppl (e.g., IS) have more of a physiologic effect than the methods that increase Palv and often are most effective. However, they require an alert, cooperative patient who is capable of taking a deep breath.

The goal of any lung expansion therapy should be to implement a plan that provides an effective strategy in the most efficient manner. Staff time and equipment are the two major issues related to efficiency. For a patient with minimal risk of postoperative atelectasis, deep breathing exercises, frequent repositioning, and early ambulation are usually effective and can be done with minimal coaching and time from clinicians and without equipment.4 For a patient at high risk for atelectasis (e.g., a patient undergoing upper abdominal surgery), IS is usually instituted. The additional staff time and equipment are justified in this high-risk group. Positive pressure therapy requires significantly more staff time and equipment and is reserved for high-risk patients who cannot perform IS techniques. The remainder of this chapter describes the use of IS and positive pressure therapy for the prevention or correction of atelectasis.

Incentive Spirometry

The purpose of IS is to guide the patient to take a sustained maximal inspiratory effort resulting in a decrease in Ppl and maintain the patency of airways at risk for closure. Because of its simplicity, IS has been the mainstay of lung expansion therapy for many years. IS devices are designed to mimic natural sighing by encouraging patients to take slow, deep breaths. IS can be performed using devices that provide visual cues to patients when the desired inspiratory flow or volume has been achieved. IS has been shown to be an efficient and effective prophylaxis against postoperative atelectasis in high-risk patients.5 The first documented use of incentive spirometry as a therapy was in 1972, and this led to the development of a visual feedback device in 1973.7

The desired volume and number of repetitions to be performed are initially set by the RT or other qualified caregiver. The inspired volume goal is set on the basis of predicted values or observation of initial performance. The true benefit from IS is best achieved by repeated use and proper technique.8 The American Association for Respiratory Care (AARC) has developed and published a clinical practice guideline on IS; excerpts from this guideline appear in Clinical Practice Guideline 39-1.

39-1   Incentive Spirometry

AARC Clinical Practice Guideline (Excerpts)*

*For complete guidelines, see American Association for Respiratory Care: Clinical practice guidelines: incentive spirometry. Respir Care 36:1402, 1991.

Physiologic Basis

The basic maneuver of IS is a sustained maximal inspiration (SMI). An SMI is a slow, deep inhalation from the functional residual capacity (FRC) up to (ideally) the total lung capacity, followed by a 5- to 10-second breath hold. An SMI is functionally equivalent to performing an inspiratory capacity (IC) maneuver, followed by a breath hold. Figure 39-2 compares the alveolar and Ppl changes occurring during a normal spontaneous breath and an SMI during IS.

image
FIGURE 39-2 Alveolar (solid lines) and pleural (dotted lines) pressure changes during spontaneous breathing (A) and SMI (B). Note the difference in Pl gradients (double arrows).

During the inspiratory phase of spontaneous breathing, the decrease in Ppl caused by expansion of the thorax is transmitted to the alveoli. With Palv now negative, a pressure gradient is created between the airway opening and the alveoli. This transrespiratory pressure gradient causes gas to flow from the airway into the alveoli. Within certain limits, the greater the transrespiratory pressure gradient, the more that lung expansion occurs.

Hazards and Complications

Given its normal physiologic basis, IS presents few major hazards and complications; those that can occur are listed in Box 39-3. Acute respiratory alkalosis is the most common problem and occurs when the patient performs IS too rapidly. Dizziness and numbness around the mouth are the most frequently reported symptoms associated with respiratory alkalosis. This problem is easily corrected with careful instruction and monitoring of the patient. Discomfort with deep inspiratory efforts secondary to pain is usually the result of inadequate pain control in a postoperative patient. This problem can be rectified by ensuring appropriate analgesia. In addition, pain medication should be coordinated with IS activity.

Box 39-3   Hazards and Complications of Incentive Spirometry

Equipment

The equipment needed for IS is typically simple, portable, and inexpensive. Although advances in technology have produced more complex devices, there is no evidence that these devices produce any better outcomes than their lower cost, disposable counterparts.

IS devices can generally be categorized as volume-oriented or flow-oriented. True volume-oriented devices measure and visually indicate the volume achieved during an SMI. The most popular true volume-oriented IS devices employ a bellows that rises according to the inhaled volume. When the patient reaches a target inspiratory volume, a controlled leak in the device allows the patient to sustain the inspiratory effort for a short period (usually 5 to 10 seconds). Because the bellows types of IS devices are bulky and large, smaller devices that indirectly indicate volume based on flow through a fixed orifice have been developed. These devices sacrifice accurate measurement of the inhaled volume to achieve portability and smaller size (Figure 39-3).

image
FIGURE 39-3 Volumetric incentive spirometer. (Courtesy DHE Healthcare, Canastota, NY.)

Flow-oriented devices measure and visually indicate the degree of inspiratory flow (Figure 39-4). This flow can be equated with volume by assessing the duration of inspiration or time (flow × time = volume). Both flow-oriented and volume-oriented devices attempt to encourage the same goal for the patient: a sustained maximal inspiratory effort to prevent or correct atelectasis. No evidence to date indicates that one type is more beneficial than the other.

image
FIGURE 39-4 Flow-oriented incentive spirometer. (From DeWit, S: Fundamental concepts and skills for nursing, ed 2, St Louis, 2004, Saunders.)

Administration

The successful application of IS involves three phases: planning, implementation, and follow-up. Because many of the components of this process are similar to those previously described, we highlight only the key points and differences in approach.

Preliminary Planning

During preliminary planning, the need for IS should be determined by careful patient assessment. Once the need is established, planning for IS should focus on selecting explicit therapeutic outcomes. Box 39-4 lists potential outcomes that can be considered for patients receiving IS.

Box 39-4   Potential Outcomes of Incentive Spirometry

The outcomes applicable to a specific patient depend on the diagnostic information that supports the need for IS. In this regard, the baseline patient assessment is critical. Patients scheduled for upper abdominal or thoracic surgery should be screened before undergoing the surgical procedure. Assessment conducted at this point helps identify patients at high risk for postoperative complications and allows determination of their baseline lung volumes and capacities. Also, this approach provides an opportunity to orient high-risk patients to the procedure before undergoing surgery, increasing the likelihood of success when IS is provided after surgery.

Implementation

Successful IS requires effective patient teaching. The RT should set an initial goal that is attainable to the patient yet requires a moderate effort. Setting an initial goal that is too low for the patient results in little incentive and an ineffective maneuver, at least initially. The patient should be instructed to inspire slowly and deeply to maximize the distribution of ventilation.

The RT should observe the patient perform the initial inspiratory maneuvers and ensure the patient uses correct technique. Correct technique calls for diaphragmatic breathing at slow to moderate inspiratory flows. Demonstration is probably the most effective way to assist patient understanding and cooperation. Both the operation of the device and the proper breathing technique can be explained easily when the RT uses himself or herself as an example, and much trial and error can be avoided.

The RT instructs the patient to sustain his or her maximal inspiratory effort for 5 to 10 seconds. Many patients have difficulty with this aspect of the maneuver. Nonetheless, patients should be encouraged to try not to breathe in too fast or slowly and to attempt a brief breath hold.

A normal exhalation should follow the breath hold, and the patient should be given the opportunity to rest as long as needed before the next SMI maneuver. Some patients in the early postoperative stage may need to rest for 30 seconds to 1 minute between maneuvers. This rest period helps avoid a common tendency by some patients to repeat the maneuver at rapid rates, causing respiratory alkalosis. The goal is not rapid, partial lung inflation but intermittent, maximal inspiration.

The exact number of sustained maximal inspirations needed to reverse or prevent atelectasis is not known and probably varies according to the patient’s clinical status. However, because healthy individuals average about 6 sighs per hour, an IS regimen should probably aim to ensure a minimum of 5 to 10 SMI maneuvers each hour.9

Follow-up

Assessing the patient’s performance is vital to ensuring achievement of goals. To do so, the RT should make return visits to monitor treatment sessions until the correct technique and appropriate effort are achieved. Suggested monitoring activities for IS are outlined in Box 39-5.

Box 39-5   Monitoring Patients Receiving Incentive Spirometry

Observe patient performance and use:

After the patient has demonstrated mastery of technique, IS may be performed with minimal supervision. Even when IS is self-administered, records of progress pertaining to the patient’s clinical status must be maintained throughout the course of treatment. The result of this assessment can guide the physician and RT in revising the respiratory care plan or terminating treatment after the goals are achieved. For patients with a neuromuscular disease or spinal injury, the use of a mechanical cough device (in-exsufflator) may provide a similar therapeutic objective. However, further study is needed to evaluate this approach.

Intermittent Positive Airway Pressure Breathing

Physiologic Basis

IPPB is a specialized form of NIV used for relatively short treatment periods (approximately 15 minutes per treatment). The intent of IPPB is not to provide full ventilatory support as with some other forms of NIV but to provide some machine-assisted deep breaths assisting the patient to deep breathe and stimulate cough. This section emphasizes the intermittent use of IPPB as a modality for the treatment of atelectasis.

Positive pressure is transmitted from the alveoli to the pleural space during the inspiratory phase of an IPPB treatment, causing Ppl to increase during inspiration. Depending on the mechanical properties of the lung, Ppl may exceed atmospheric pressure during a portion of inspiration. As with spontaneous breathing, the recoil force of the lung, stored as potential energy during the positive pressure breath, causes a passive exhalation. As gas flows from the alveoli out to the airway opening, Palv decreases to atmospheric level, while Ppl is restored to its normal subatmospheric range (Figure 39-5). The AARC has developed and published a clinical practice guideline for IPPB; excerpts from this guideline appear in Clinical Practice Guideline 39-2.

39-2   Intermittent Positive Pressure Breathing

AARC Clinical Practice Guideline (Excerpts)*

Indications

• Need to improve lung expansion

• Presence of clinically significant pulmonary atelectasis when other forms of therapy (e.g., IS) have been unsuccessful or the patient cannot cooperate

• Inability to clear secretions adequately because of pathology that severely limits the ability to ventilate or cough effectively and failure to respond to other modes of treatment

• Need for short-term noninvasive ventilatory support for hypercapnic patients (as an alternative to intubation and continuous ventilatory support)

• Need to deliver aerosol medication

• Although some authors oppose the use of IPPB in the treatment of severe bronchospasm (e.g., acute asthma), we recommend a careful, closely supervised trial of IPPB when treatment using other techniques (metered dose inhaler [MDI] or nebulizer) has been unsuccessful

• IPPB may be used to deliver aerosol medications to patients with ventilatory muscle weakness or fatigue or chronic conditions in which intermittent noninvasive ventilatory support is indicated.

*For complete guidelines, see American Association for Respiratory Care: Intermittent positive pressure breathing—2003 revision and update. Respir Care 48:540, 2003.

image
FIGURE 39-5 Alveolar (solid lines) and pleural (dotted lines) pressure changes during spontaneous breathing (A) and IPPB (B). Note the difference in Pl gradients (double arrows).

Indications

There is little research supporting the use of IPPB as an aerosol delivery system. However, there is supporting evidence that periodic sessions of positive pressure ventilation provided noninvasively can be useful in the treatment of pulmonary complications or exacerbations of lung disease.10–12 NIV, or, more specifically, IPPB, may be useful for patients with clinically diagnosed atelectasis unresponsive to other therapies, such as IS and chest physiotherapy. In addition, short-term use of NIV in the form of IPPB may be useful for patients who are at high risk for atelectasis and unable to participate in more patient-directed techniques such as IS or even deep breathing. IPPB should not be used as a single treatment modality for a patient with gas absorption atelectasis because of excessive airway secretions. In addition, the RT should be aware of potential complications, such as mucous plugging, which can be worsened owing to a humidity deficit that can occur with IPPB therapy. Because of the need for specialized machinery and training, IPPB itself should not be thought of as the first line of therapy. Applying positive pressure to the lung in such cases can cause overinflation of the lung regions not affected by secretions and minimal or no expansion of the affected lung segments. Airways clearance with humidity therapy should be considered in conjunction with IPPB for optimizing results in patients with retained secretions.

In concept, a correctly administered IPPB treatment should provide the patient with augmented tidal volumes, achieved with minimal effort. The optimal breathing pattern to reinflate collapsed lung units with IPPB consists of slow, deep breaths that are sustained or held at end-inspiration. This type of inspiratory maneuver increases the distribution of inspired gas to areas of the lung with low compliance—specifically, the atelectatic areas.

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Importance of Air Bronchograms on the Chest Film

Contraindications

There are several clinical situations in which IPPB should not be used (Box 39-6). With the exception of untreated tension pneumothorax, most of these contraindications are relative. As with all procedures, a sound knowledge of the patient’s condition tempered with good clinical insight should guide the RT in the decision-making process. A patient with any of the conditions listed in Box 39-6 should be carefully evaluated before a decision is made to begin IPPB therapy.

Box 39-6   Clinical Situations Contraindicating Intermittent Positive Airway Pressure Breathing Therapy

Hazards and Complications

As with any clinical intervention, certain hazards and complications are associated with IPPB. These potential problems should be addressed in the initial stages of planning for IPPB. In addition, hazards and complications must be considered throughout the course of therapy as part of the process of assessing the patient for unwanted side effects. The most common complication associated with IPPB is the inducement of respiratory alkalosis. Respiratory alkalosis is induced when the patient hyperventilates during the treatment. Deep, fast breathing leads to a sharp decrease in PCO2 and an equally marked increase in arterial pH. The patient usually feels light-headed and numb around the mouth. Arrhythmias are also possible if the alkalosis is severe or if the patient’s heart is unstable. This problem is easily avoided through proper coaching of the patient before and during treatment.

Another potential complication of IPPB is gastric distention; this occurs when gas from the IPPB device passes directly into the esophagus. Gastric distention is uncommon in an alert patient but is a significant risk for a neurologically obtunded patient. Normally, the esophagus does not open until a pressure of about 20 to 25 cm H2O has been reached. Gastric distention represents the greatest risk in patients receiving IPPB at high pressures. The major hazards and complications of IPPB are listed in Box 39-7.

Box 39-7   Hazards and Complications of Intermittent Positive Airway Pressure Breathing

Administration

Effective IPPB requires careful preliminary planning, individualized patient assessment and implementation, and thoughtful follow-up. In all three phases of the process, the RT should work closely with the prescribing physician to determine patient need, select the appropriate therapeutic approach, and assess patient progress toward predefined clinical outcomes. Only by ensuring that these elements are combined as part of the overall respiratory care plan can the RT expect to achieve the desired results.

Preliminary Planning

During preliminary planning, the need for IPPB is determined, and desired therapeutic outcomes are established. The outcomes chosen for a patient are based on diagnostic information that supports the need for IPPB therapy. In addition, therapeutic outcomes should be as explicit and measurable as possible. Outcomes must also be consistent with the therapeutic indications previously described. Outcomes that are inconsistent with these indications are generally inappropriate. Box 39-8 lists potential accepted and desired outcomes of IPPB therapy. Not all the outcomes listed in Box 39-8 apply to every patient. For example, for a patient exhibiting clinical signs and symptoms of postoperative atelectasis, the following outcomes might be set: improved patient comfort, increased aeration on auscultation, decreased respiratory rate and work of breathing, and improvement in the chest radiograph.

Box 39-8   Potential Outcomes of Intermittent Positive Airway Pressure Breathing Therapy

Baseline Assessment

Before beginning therapy, a baseline patient assessment should be conducted. This information helps individualize the treatment and allows objective evaluation of the patient’s subsequent response to therapy. Together with the patient’s medical history, this baseline assessment also alerts the RT to possible problems or hazards associated with administering IPPB to the patient. The baseline assessment includes a general evaluation of the patient’s clinical status and a specific assessment related to the chosen therapeutic goals. The general assessment, common to all patients for whom IPPB is ordered, includes (1) measurement of vital signs, (2) observational assessment of the patient’s appearance and sensorium, and (3) breathing pattern and chest auscultation.

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Evaluating the Effectiveness of Lung Expansion Therapy

Discussion

The RT should suggest numerous parameters that are useful. One of the best is observation of the patient’s spontaneous respiratory rate at rest. There is a strong correlation between respiratory rate and degree of atelectasis. The more atelectasis present, the higher the spontaneous respiratory rate. If lung expansion therapy is preventing or correcting atelectasis, the respiratory rate would be at or near normal. Auscultation can also be useful and should document the presence of abnormal breath sounds and adventitious lung sounds. A reduction in late-inspiratory crackles and improvement in breath sounds suggest the treatment is effective. Findings on the most recent chest film can be very useful to document the presence or lack of atelectasis. The signs of volume loss disappear with effective lung expansion therapy. In addition, the patient may complain less of dyspnea when the lung is expanded to its healthy position.

Implementation

Implementation of IPPB involves equipment preparation, patient orientation, and careful adjustment of the treatment parameters according to the patient’s response.

Patient Orientation

Successful IPPB therapy depends mainly on the effectiveness of initial patient orientation. Before the first treatment, the RT must carefully explain to the patient the purpose of the therapy. This explanation should be tailored to the patient’s level of understanding and address, at a minimum, the following points: (1) why the physician ordered the treatment, (2) what the treatment does, (3) how it will feel, and (4) what are the expected results.

The IPPB device should not be brought to the bedside until the RT believes that the patient adequately understands the procedure and the importance of cooperation. When the RT decides to bring the equipment to the bedside, a simple functional description may allay any fear or anxiety associated with the use of such an unfamiliar device. A simulated demonstration of the procedure can be particularly useful in this regard. This demonstration can be done effectively with a test lung or, if deemed necessary, by self-application using a separate breathing circuit kept for this purpose. For some patients, an effective demonstration can make the difference between success and failure in implementing the treatment regimen.

Initial Application

To eliminate airway leaks in an alert patient, an initial trial of nose clips may be needed until the technique is understood and the treatment can be performed without them. The mouthpiece must be inserted well past the lips, and a tight seal must be encouraged to prevent gas leakage from the site. The use of a mask as an interface with IPPB is generally not recommended. To provide adequate therapy, the mask often needs to be held tightly to the patient’s face and tends to be quite uncomfortable. If a mask is needed to provide lung expansion therapy, it is generally suggested to find another method such as CPAP or NIV.

The machine should be set so that a breath can be initiated with minimal patient effort. A sensitivity or trigger level of −1 to −2 cm H2O is adequate for most patients. Initially, system pressure is set low enough for the patient to be able to trigger the IPPB machine for both inspiration and expiration. Resulting volumes should be measured, and the pressure or flow should be adjusted accordingly after the treatment has begun. If the device has a flow control, the RT should begin the treatment with a low-to-moderate flow and adjust it according to the patient’s breathing pattern. Generally, the goal is to establish a breathing pattern consisting of about 6 breaths per minute, with an expiratory time of at least three to four times longer than inspiration (inspiratory-to-expiratory [I : E] ratio of ≤1 : 3 to 1 : 4). These settings may need to be adjusted according to individual needs and patient response. Careful monitoring of the breathing pattern and coaching to maintain it must be conducted throughout the treatment.

Adjusting Parameters

After the treatment begins and the patient’s basic ventilatory pattern is established, the pressure and flow should be individually adjusted and monitored according to the goals of the therapy. IPPB therapy should be volume-oriented when used to treat atelectasis. In these situations, arbitrary pressure settings are unacceptable, and tidal volumes must be monitored. A tidal volume goal must be set for each individual patient, and the therapy must be delivered on the basis of these goals.

There are various ways of determining these volume goals. Most clinical centers strive to achieve an IPPB tidal volume of 10 to 15 ml/kg of body weight or at least 30% of the patient’s predicted IC. If the initial volumes fall short of this goal and the patient can tolerate it, the pressure is gradually increased until the goal is achieved. Pressures of 30 to 35 cm H2O may be needed to achieve this end when lung compliance is reduced. If high pressures are required, care needs to be taken to minimize the risk of gastric insufflation.

To achieve the largest inspiratory volumes during IPPB, the RT should encourage the patient to breathe actively during the positive pressure breath. However, no definitive studies exist that show the need to have the patient actively participate in inspiration. Regardless of the approach, IPPB is useful in the treatment of atelectasis only if the volumes delivered exceed the volumes achieved by the patient’s spontaneous efforts.

Discontinuation and Follow-up

Depending on the goals of therapy and condition of the patient, IPPB treatments typically last 15 to 20 minutes. Follow-up activities include posttreatment assessment of the patient, recordkeeping, and equipment maintenance.

Monitoring and Troubleshooting

As indicated in Box 39-9, monitoring of IPPB therapy involves both patient response and machine performance. Information derived from monitoring allows for titration of therapy and can aid in the early identification of common problems.

Box 39-9   Monitoring Intermittent Positive Airway Pressure Breathing Therapy

*Items should be chosen as appropriate for the specific patient.

Machine Performance

In terms of machine performance, large negative pressure swings early in inspiration indicate an incorrect sensitivity or trigger setting. In this case, the RT should increase the sensitivity or alter the trigger level until only 1 to 2 cm H2O is needed to trigger the device into inspiration. If system pressure decreases after inspiration begins or fails to increase steadily until the very end of the machine breath, the problem is too low a flow. In this situation, the flow should be increased (as tolerated) until system pressure increases steadily and holds near the preset value.

Knowing proper IPPB machine operation is vital to being able to troubleshoot the most commonplace issues experienced. Some of these issues include premature transition into exhalation, inability to trigger the machine, or improper flow delivery. Checking the circuit and properly instructing the patient are the best ways to prevent or correct these problems.

Leaks pose a different problem. In the presence of leaks, a pressure-cycled IPPB device does not reach its preset cycling pressure and does not cycle off. This problem is evident when inspiration continues well beyond the expected time. To troubleshoot leaks, the RT needs to differentiate between the machine and patient interface. Machine leaks most commonly occur at connection points, such as the nebulizer or exhalation valve. In addition, a torn or improperly seated exhalation valve diaphragm causes a large system leak. Leaks at the patient interface usually occur at the mouth (loose seal around mouthpiece) or through the nose. If the problem is mouth leaks, additional instruction may help. If not, a flanged mouthpiece may be needed. Leaks through the nose are easily corrected with nose clips.

The last consideration regarding machine performance involves selecting an IPPB machine capable of providing the appropriate FiO2. Some electrically powered IPPB machines are capable of providing only room air or slightly enriched oxygen (O2) concentrations (<40%) and may cause or worsen hypoxemia in some patients needing supplemental O2. To avoid this problem in such patients, an IPPB machine capable of providing a high FiO2, such as the Bird Mark 7 (Care Fusion, Corp, San Diego), should be selected.

Positive Airway Pressure Therapy

Similar to IPPB, positive airway pressure (PAP) adjuncts use positive pressure to increase the Pl gradient and enhance lung expansion. In contrast to IPPB, PAP therapy requires no complex machinery. Some methods do not even need a source of pressurized gas.

Physiologic Basis

There are three current approaches to PAP therapy: PEP, EPAP, and CPAP. All three techniques are effective in treating atelectasis in most postsurgical patients.13,14 Because PEP and EPAP are used most often as part of airway clearance, they are described in Chapter 40. This chapter describes the intermittent use of CPAP for the treatment of atelectasis. Continuous use of CPAP is discussed elsewhere in this text.

PEP and EPAP create expiratory positive pressure only, whereas CPAP maintains a positive airway pressure throughout both inspiration and expiration. Figure 39-6 compares the alveolar and Ppl changes occurring during a normal spontaneous breath (Figure 39-6, A) and CPAP (see Figure 39-6, B). As can be seen, CPAP elevates and maintains high alveolar and airway pressures throughout the full breathing cycle; this increases Pl gradient throughout both inspiration and expiration. Typically, a patient on CPAP breathes through a pressurized circuit against a threshold resistor, with pressures maintained between 5 cm H2O and 20 cm H2O. To maintain system pressure throughout the breathing cycle, CPAP requires a source of pressurized gas.

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FIGURE 39-6 Alveolar (solid lines) and pleural (dotted lines) pressures during spontaneous breathing (A) and CPAP (B). Note the difference in Pl gradients (double arrows).

The following factors involving PAP, EPAP, and CPAP therapy contribute to the beneficial effects: (1) recruitment of collapsed alveoli via an increase in FRC, (2) decreased work of breathing secondary to increased compliance or elimination of intrinsic positive end expiratory pressure (PEEP), (3) improved distribution of ventilation through collateral channels (e.g., Kohn pores), and (4) increase in the efficiency of secretion removal.

Equipment

Equipment used to deliver CPAP varies substantially in design and complexity. For purposes of illustration, the key elements of a simple continuous-flow CPAP circuit are shown in Figure 39-7. A breathing gas mixture from an O2 blender (A) flows continuously through a humidifier (B) into the inspiratory limb of a breathing circuit (C). A reservoir bag (D) provides reserve volume if the patient’s inspiratory flow exceeds that of the system. The patient breathes in and out through a simple valveless T-piece connector (E). A pressure alarm system with manometer (F) monitors the CPAP at the patient’s airway. The alarm system can warn of either low (usually caused by a disconnection) or high system pressure. The expiratory limb of the circuit (G) is connected to a threshold resistor, in this case, a water column (H).

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FIGURE 39-7 Continuous-flow CPAP system. See text for description. (Modified from Branson RD, Hurst JM, Dellayen CB: Mask CPAP: state of the art. Respir Care 30:846, 1985.)

As can be seen, the CPAP circuit is essentially the same as the EPAP circuit, with the exception of the closed reservoir and monitoring system. Because it is a closed system, the CPAP circuit should also have an emergency inlet valve (not shown). This emergency inlet valve ensures that atmospheric air is available to the patient should the primary gas source fail.

Administering Intermittent Continuous Positive Airway Pressure

As with all respiratory care, effective CPAP therapy requires careful planning, individualized patient assessment and implementation and thoughtful follow-up.

Monitoring and Troubleshooting

CPAP poses a danger of hypoventilation. Experience with long-term CPAP shows that patients must be able to maintain adequate excretion of carbon dioxide on their own if the therapy is to be successful. For these reasons, patients receiving CPAP must be closely and continuously monitored for untoward effects. In addition, it is vital that the CPAP device be equipped with a means to monitor the pressure delivered to the airways and alarms to indicate the loss of pressure owing to system disconnect or mechanical failure. There should also be a device allowing for excessive pressure to be released (pop-off). These are essential components of any CPAP device.

The most common problem with PAP therapies is system leaks. When using a mask, a tight seal must be maintained to keep pressure levels above atmospheric levels. Any significant leaks in the system result in the loss of PAP. Because a tight seal requires a tight-fitting mask, pain and irritation may occur in some patients, especially if the therapy is prolonged.

The development of new nasal CPAP units and improvement on the interface itself have addressed some of the comfort issues and correction of leakage associated with CPAP. A more serious problem associated with CPAP is the possibility of gastric insufflation and aspiration of stomach contents. As with IPPB by mask, this potential hazard can be eliminated by use of a nasogastric tube at higher pressure requirements, although this increases the risk of a leak.

The RT must also ensure that the flow is adequate to meet the patient’s needs with the use of CPAP systems. Flow adjustments are made by carefully observing the airway pressure. Flow generally can be considered adequate when the system pressure decreases no more than 1 to 2 cm H2O during inspiration.

Selecting an Approach

The best approach for achieving a given clinical goal is always the safest, simplest, and most effective method for an individual patient. Selecting an approach for lung expansion therapy requires in-depth knowledge of both the methods available and the specific condition and needs of the patient being considered for therapy.

Figure 39-8 presents a sample protocol for selecting an approach to lung expansion therapy. As indicated in the algorithm, the patient first must meet the criteria for therapy by having one or more of the indications previously specified. For patients meeting the inclusion criteria, the RT first determines the degree of alertness. Because an obtunded patient cannot be expected to cooperate with IS or PEP or EPAP therapy, IPPB or NIV is initiated with appropriate monitoring. If the patient is alert, a bedside assessment is conducted. This assessment should include measurement of either the IC or vital capacity (VC) and evaluation of the volume and consistency of the patient’s secretions.

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FIGURE 39-8 Example protocol for selecting an approach for lung expansion therapy. See text for details.

For a patient having no difficulty with secretions, if the VC exceeds 15 ml/kg of lean body weight or the IC is greater than 33% of predicted, IS is given. If either the VC or the IC is less than these threshold levels, IPPB is initiated, with the pressure gradually manipulated from the initial setting to deliver at least 15 ml/kg.

If excessive sputum production is a compounding factor, a trial of PEP therapy is substituted for IS. Based on patient response, bronchodilator therapy and bronchial hygiene measures may be added to this regimen. If monitoring fails to reveal improvement and atelectasis persists, a trial of CPAP should be considered. Because evidence of the effectiveness of CPAP is still contradictory, its use should be limited to treating atelectasis after alternative approaches have been tried without success.

Summary Checklist

• Atelectasis is caused by persistent ventilation with small tidal volumes or by resorption of gas distal to obstructed airways.

• Patients who have undergone upper abdominal or thoracic surgery are at greatest risk for atelectasis. A history of lung disease or significant cigarette smoking increases the risk.

• Patients with atelectasis usually have rapid, shallow breathing; fine, late-inspiratory crackles; and abnormalities on chest radiograph.

• Lung expansion therapy corrects atelectasis by increasing the PL gradient; this can be accomplished by deep spontaneous breaths or by the application of positive pressure.

• The most common problem associated with lung expansion therapy is the onset of respiratory alkalosis, which occurs when the patient breathes too fast.

• RTs are responsible for implementing, monitoring, and documenting results of lung expansion therapy.

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