Oscillating Positive Expiratory Pressure, (OPEP) Therapy
David M. Wheeler M. Ed., RRT-NPS
“To know even one life has breathed easier because you have lived. This is to have succeeded.”
– Ralph Waldo Emerson
Oscillating positive expiratory pressure, (OPEP) is a therapeutic method which facilitates airway clearance through the combination of positive expiratory pressure and airflow oscillations during an active exhalation. OPEP devices have been described in the literature since the late 1990s as cost- effective secretion-clearance alternatives to the labor and time consuming interventions such as: postural drainage, percussion, and vibration.3
There are several types of OPEP devices on the market. The quality of the airflow oscillations and pressure thresholds are dependent on the device design and the ability of the patient to generate flow during an active exhaled maneuver, or maneuver that engages the muscles to assist with the flow of gas from the lungs. Thus, the device and the patient work together to produce the therapeutic effect of airway clearance.3
The Mechanisms of Mucociliary Clearance.
Prior to our discussion of the theory and clinical application of OPEP therapy, it is essential that we briefly review the normal mechanisms of mucociliary clearance. This brief review will focus on the endogenous mechanisms of secretion clearance beginning with an examination of airway architecture, mucous composition, ciliary function and finally, the role of the cough.
The conducting airways have been described as a “tree of irregular dichotomies,” fashioned in a pattern of morphogenic dichotomous branching. The conducting airway architecture is fractal, or has the same airway distribution pattern up to the 24th generation. This airway geometry not only supports ventilation, or the movement of gases in and out of the lungs, but assists with the transport of airways secretions, to minimize the propensity for bronchial obstruction.
Airway surface liquid is an essential component of native lung defense and is approximately 10 m deep with two distinct layers; the periciliary sol, (thin layer), beneath the upper layer of mucus gel, (thick, sticky). The sol layer has a low-viscosity, watery, property and surrounds the cilia, while the gel layer is glutinous, dense, sticky, and rides the tips of the cilia.
The “sea grass” of cilia is so very thick that the gel layer cannot penetrate it. The gel layer rides along the top of the beating cilia, which move in a rhythmic wavelike manner at a rate of 3 to 4 mm/min. This metachronal movement propels airway debris cephalad toward the large airways. The centripetal movement of the mucociliary escalator clears secretions to minimize or alleviate airway obstruction.
Airways secretions are produced daily, which range from 1 to 100 mL in healthy individuals. However, there are many factors which make it difficult for individuals to mobilize and evacuate secretions. Aging, tobacco use, environmental exposures, and pulmonary disorders such as bronchiectasis, COPD and cystic fibrosis impair the efficiency of the mucociliary escalator. Neurodegenerative conditions weaken muscles which reduce the ability to actively exhale and cough effectively.
The Function of the Cough
The cough is a fundamental biological defense mechanism and a significant protective mechanism of the respiratory system. The cough’s primary function is ejecting secretions, foreign bodies, and vaporous vexations from the respiratory tract. This complex maneuver is predominantly involuntarily. A cough begins with the irritation or stimulation of airway mechanoreceptors disseminated throughout conducting airways. These receptors are abundant at the carina with specialized irritant chemoreceptors scattered in the distal airway bifurcations where deleterious vapor particles will have a greater probability of depositing.
There are three phases of a cough. Initially, there is an amplified inspiration through an abducted glottis where inhaled volume is transiently larger than tidal volume. Next, the compressive phase occurs, which is initiated by the rapid adduction of the glottis and expiratory muscle contraction. Although the compression phase lasts only hundredths of a second, it may increase intrathoracic pressure to approximately 300 cm H2O.18.
The final phase, of the normal cough, is the expiration phase. The glottic release of amplified intrathoracic pressure produces a subatmospheric drop in central airway pressures and creates a striking pressure gradient and a rapid and dynamic compression of the airways. The combined muscle pressure, intrathoracic pressure, and glottic release intensify an already substantial airflow velocity, creating a shearing force across the surface of the mucociliary stairway, discharging a massive expulsion of mucous and airway debris.18,19 There are conditions in which the intrathoracic pressure, and glottic release causes small airway collapse, trapping secretions and contributing to bronchial obstruction. A huff cough technique, or forced expiratory technique is an alternative method for expelling secretions and airway debris. Rather than exhaling forcefully against a closed glottis, the huff cough, also known as forced expiratory technique, is a forced exhalation with an open glottis. The word “huff” was coined from the sound the individual makes during the expiration with an open glottis.
It is important for the clinician to understand the mechanisms that can impair mucus clearance and evaluate the patient to determine what factors or clinical conditions exist which can impede the acceleration of mucous out of the airway or prevent the patient from using the OPEP device as intended.
Oscillating Positive Expiratory Pressure (OPEP) Therapy
Oscillating positive expiratory pressure, (OPEP) therapy is a mechanical means to manipulate air flow, to mobilize secretions cephalad, and to facilitate evacuation. The clinical intentions of this therapy are the augmentation and/or intensification of native airway defense mechanisms, mobilize mucous and airway debris, present or relieve airways obstruction, and re-establish a normal FRC.1-4,
The OPEP devices interrupt expiratory flow through a resistive apparatus which generates flow oscillations and positive pressure during an active exhalation of exaggerated slightly larger than tidal volume breath. The airflow oscillation has four components; (1) a peak pressure (Ppeak), (2) baseline positive expiratory pressure (PEP), (3) pressure amplitude (AMP) or the difference between Ppeak and PEP, which is a measure of the burst of flow the device creates, and (4) frequency or the number of airflow oscillations occurring in a one-minute time period. There are several different types of commercially available OPEP devices on the market. Virtually every device uses unique mechanisms to produce the oscillations in airflow and attendant positive pressure, Table 1.
The current evidence maintains that the physical mechanisms for providing the expiratory pressure and oscillations are device-dependent but share a common character in that the airflow oscillations have a peak pressure and baseline positive expiratory pressure. The pressure amplitude (AMP) is the gradient between Ppeak and PEP and is reflective of flow velocity, sustained pressure, and airway mechanics while frequency is the number of oscillations occurring in a minute.3,4,
Clinically, the differences in expiratory pressure, oscillation depth, amplitude and flow velocity are a real challenge for the clinician and underline the inherent operational differences of the devices under similar patient conditions. This calls both for greater investigation into the individual devices and greater clinician familiarity with individual device parameters.
The device should match patient need, ability, and therapeutic intention.3,4,23, The mindful clinician will understand that functional capabilities may vary significantly across the range of resistance settings and there may be a significant interaction effect with maneuver time as has been reported by Volsko, et al.3,4,24
The use of these devices with the huff cough can generate a synergy that enhances the efficacy of both device and maneuver. The huff cough is typically performed between a set of exhalations through the OPEP device. The huff cough evacuates airway secretions that are mobilized toward the central- airways, through a series of slow mindful inspirations, and is followed by a three second breath hold and mindful forced exhalations with mini-coughs through an open glottis, where they can be expelled. The combined effect of the huff maneuver with OPEP expiratory flow, pressure, oscillation and amplitude gives one greater flexibility in the clinical toolbox. The OPEP devices have been demonstrated effective in patient scenarios as diverse as cystic fibrosis, neurogenic compromise, bronchiectasis, and the post-operative retention of secretions.25,26,
The OPEP device is an effective appliance in the context of pulmonary rehabilitation and disease management for the patient with COPD. The most commonly used OPEP devices are Flutter®, RC‑Cornet®, and Acapella®. In the greater context of pulmonary rehab and disease management OPEP devices may have a role in the prevention of hospital readmission for the patient with COPD. However, further investigation into outpatient outcomes of the OPEP devices is necessary.
The N-of-1 Trial
Unquestionably, the OPEP device is an essential component of the clinician’s armamentarium yet the device must be used by the patient. Patient compliance is one of the essential factors in the therapeutic relevance of any device but more decidedly so with OPEP therapy. Indeed, these devices can have a significant therapeutic impact when used often and in an appropriate fashion.
The clinical application and subsequent patient compliance with OPEP therapy is a definitive illustration of the concept of the patient-specific “n-of-1” trial. The prudent clinician will work with the patient in the context of their disease to achieve an assessment-driven examination of any and all therapeutic options and their clinical effect.
The n-of-1 trial is a means of structuring treatment decisions with and for the patient, in a highly individualized fashion, and monitoring the patient’s responses to each treatment.29
Regardless of our current practice, we must explore with intellectual rigor innovations in thought, technology, and clinical practice. We must meet the patient in the context of their illness and therapeutic goals while considering their learning and physical abilities. The education of the patient and their caregiver may be the greatest single aspect necessary for the success of this therapy.
What we do at the bedside matters, consequently we must remain fully engaged and intellectual curios in order to have the greatest impact in the lives of our patients. Therefore, it is essential that we as a profession expand and cultivate the utilization of an assessment-based, evidence-grounded practice model in every clinical setting and patient contact. We have both a moral imperative and an ethical duty to treat every patient in an assessment driven, evidence based fashion. OPEP therapy serves as a therapeutic option best employed in this fashion and the mindful clinician will match the best device to individual patient contextual needs.
The essential message for the bedside caregiver is that these devices work and they require an informed clinical guide for the patient to use them in a way that is therapeutically beneficial. I trust the discussion that follows will feed your intellectual curiosity and support your bedside practice.
David Wheeler, MEd, RRT-NPS
Education Coordinator Cardiothoracic Anesthesia Respiratory Therapy
Mr. Wheeler is responsible for creating the evidence-based clinical compass for the respiratory therapy arm of cardiothoracic anesthesia critical care at the Cleveland Clinic, a group that cares for over 6,000 heart and lung cases annually. He is a tireless educator having created over 35 continuing education activities for both RTs and nurses in his facility. David has also developed lung transplant mechanical ventilation protocols that have been used with 300 patients per year. A highly regarded speaker, His extensive writing background includes advanced orientation manuals, numerous pages of content for respiratory critical care issues for the facility's website, and peer-reviewed papers. David has lectured at international, state, and local meetings.
A huff cough technique, or forced expiratory technique is an alternative method for expelling secretions and airway debris.
The OPEP device is an effective appliance in the context of pulmonary rehabilitation and disease management for the patient with COPD.
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