Positive-Pressure Techniques
A variety of positive airway pressure techniques have been used
to treat or prevent atelectasis. These are often employed as an adjunct to other
components of bronchial hygiene therapy or in patients who have difficulty with the
effort-dependent components (such as incentive spirometry) because of physical weakness
or poor mental status. Positive pressure can be applied noninvasively through a
tight-fitting mask or mouthpiece. IPV and flutter devices (discussed previously)
combine positive pressure with airway vibration.
Intermittent Positive-Pressure Breathing
Intermittent positive-pressure breathing (IPPB) is a technique
that applies short-duration, noninvasive positive-pressure breaths to the lungs during
the inspiratory phase of spontaneously breathing patients. The patient-triggered
breaths deliver a pressure specified by the respiratory therapist or physician.
The primary goal of IPPB is to expand the lungs by increasing inspiratory volume,
thereby treating and preventing atelectasis in patients who are at risk. IPPB may
also have other beneficial effects including decreased work of breathing, treatment
of pulmonary edema, improved cough, improved distribution of aerosolized medications,
and reduction in PaCO2
. This form of
prophylaxis was commonly used in the past; however, recent clinical trials in postoperative
patients have shown an increase in gastric distention and no difference in respiratory
complication compared to patients using incentive spirometry.[31]
[45]
Potential complications of IPPB include aspiration,
pneumothorax, and impaired cardiac output. Some have suggested that patients who
have a small vital capacity (<15 mL/kg) may benefit the most from IPPB, because
the patient can achieve larger tidal volumes with positive-pressure augmented breaths,
although this has not been established in clinical trials.
Positive Expiratory Pressure
Positive expiratory pressure (PEP) can be achieved with a simple
oral device with a fixed-orifice resistor. PEP is generated as the patient exhales
through the device, generating a pressure of 10 to 20 cm H2
O. Pressure
applied during expiration may splint open airways prone to closure, preventing air
trapping and impaction of bronchial secretions. Pursed-lip breathing by patients
with COPD is one adaptive form of applying positive expiratory pressure. PEP has
been shown to be beneficial for postoperative patients,[46]
patients with COPD,[47]
and pediatric patients with
CF.[48]
Continuous Positive Airway Pressure
CPAP delivers constant pressure throughout the respiratory cycle
and can be delivered through a tight-fitting mask. CPAP can be used for several
hours at a time as a mode of noninvasive ventilation and has many potential applications,
including treatment of sleep apnea and cardiogenic pulmonary edema (these are discussed
in a later section). CPAP may be used intermittently for brief periods of time as
an adjunctive therapy for bronchial hygiene. Positive pressure delivered throughout
the respiratory cycle may augment lung expansion and maintain open airways. These
effects may increase clearance of bronchial secretions and prevent atelectasis.
Several small studies have shown CPAP to be at least as effective as incentive spirometry
and routine chest physiotherapy in preventing atelectasis in postoperative patients.
[49]
[50]
Its effort-independent
nature makes CPAP an attractive treatment for atelectasis; however, benefits of this
therapy must be weighed against the cost, potential adverse effects, and requirement
for close observation compared to other types of bronchial hygiene therapy.
Newer Positive-Pressure Devices
Several newer positive-pressure devices are being used in the
ICU. Among these are Ez-PAP (DHD Healthcare, Wampsville, NY), a disposable device
that delivers positive pressure during inspiration and expiration. The Ez-Pap combines
the potential benefits of IPPB and PEP. Positive pressure during inspiration may
increase inspiratory volume and enhance delivery of aerosolized medications, whereas
positive pressure during exhalation may prevent airway collapse. Together, these
effects may aid in treating/preventing atelectasis and may augment mucociliary clearance
of airway secretions. Data on the efficacy of the Ez-PAP in clinical trials are
currently lacking.
Another newer positive-pressure device, CoughAssist (JH Emerson
Co, Cambridge, MA), provides cough augmentation with mechanical insufflation and
exsufflation. This device uses positive pressure during inspiration to increase
inspiratory lung volume followed by a rapid switch to negative pressure, simulating
the flow changes that occur during a cough and thereby facilitating sputum clearance.
One study demonstrated an increase in peak cough flow in patients with neuromuscular
disease,[51]
but there have not yet been any published
trials evaluating clinically relevant outcomes.
