Sleep specialists’ knowledge about the benefits of NPPV therapy can benefit patients with COPD, OSA, and neurologic disorders.
The history of noninvasive ventilation has been long-standing. The first functional iron lung (negative pressure) was invented in 1876, and 13 years later, Alexander Graham Bell produced his design as an iron lung prototype for newborns. The field of pulmonary medicine grew out of necessity because of the polio epidemic from the 1920s to the 1950s.1 Eventual developments in positive pressure ventilation enabled life-saving measures by invasive techniques for acute respiratory failure via intubation and continuous mechanical ventilation with bedside monitoring. Today, noninvasive positive pressure ventilation (NPPV) can be delivered by a volume ventilator, a pressure controlled ventilator, a continuous positive airway pressure (CPAP) machine, or a bilevel PAP device.2 With the production of quality masks that provide a reasonably effective seal, the efficacy of noninvasive ventilation progressed to non-critical care environments and even home care situations by eliminating the need for intubation.
CPAP therapy has been around for about 30 years and was initially designed for premature babies whose lungs had not developed the necessary surfactant to maintain patency, thus allowing oxygen to leave the alveoli (terminal air sacs) and cross the alveolar-capillary membrane wall, therein oxygenating tissue cells. It was used to expand the alveoli so that oxygen would have more time to make the transfer before the sacs “collapsed.” This pneumatic splint concept holds true for obstructive sleep apnea (OSA) patients whose primary problem is the “collapse” of the rear segment of the airway proximal to the base of the tongue and above the trachea itself. CPAP is considered 95% successful in the treatment of OSA when compliance has been achieved.
Bilevel PAP is designed for two pressure levels to be delivered; the higher pressure is upon inspiration and the lower pressure upon expiration. The higher pressure works like pressure support on a ventilator and enables the patient to take in a greater tidal volume (inspiration) without using the musculature required to generate a negative pressure of -2 cm H2O, which is necessary for normal inspiration. Patients who are debilitated from any number of diseases cannot “suck in” forcefully enough to generate a viable volume of air to sustain his or her oxygen and ventilatory requirements. This becomes an even greater problem when the patient also has OSA. A patient who is diagnosed with both chronic obstructive pulmonary disease (COPD) and OSA has what is known as “overlap syndrome.”3 Overlap patients are becoming more prevalent in sleep laboratories, and technologists must have the skills and the tools to deal with their specific needs. The expiratory pressure is the equivalent to positive end-expiratory pressure (PEEP), and it is the mechanism that actually holds the airway open by acting as this pneumatic splint. The soft mucosal tissue is held open by applying a “pillow of air” (pressure) that remains constant throughout the exhalation cycle. By maintaining this airway patency, there can be no obstructive apneas once the appropriate pressure has been delivered. This is, of course, only theoretical, since a number of factors can predispose the resurgence of apneic events (alcohol consumption, the addition of sedatives, extreme muscle fatigue, and disease changes).
COPD Patients Benefit
Bilevel PAP is extremely useful for COPD patients because it enables the decreased expiratory pressure, allowing for reduced effort for exhalation. CPAP mode is difficult for many of these patients because it actually increases their work of breathing, causing greater oxygen consumption and resulting in falling Spo2s and increased cardiac output, often evidenced by cardiac arrhythmias. When COPD patients relate that they are “smothering,” this is not an exaggeration. It is not that they are not getting enough air; they are getting too much air and cannot breathe back out against that much pressure.
CPAP is not contraindicated in every COPD patient, but the astute technologist will observe the increased respiratory rate, the drop in oxygen saturation, the increase in heart rate, and the “bucking” against the normal inspiratory/expiratory cycle. The technologist can certainly change the mode to bilevel to make the patient more comfortable, gaining a better outcome for the overall titration. The expiratory pressure is increased until all obstructive apneas are resolved and the inspiratory pressure is increased thereafter to eliminate hypopneas, upper airway resistance syndrome, and snoring. Appropriate documentation for the patient’s intolerance to CPAP must be performed to verify the actual need for the increase in cost to the insurance company for the bilevel PAP system. The patient’s intolerance of one mode does not preclude the treatment of this problem, and the additional cost is a small price to pay in light of the long-term effects of OSA in regard to hypertension, higher risk for cardiac disease, and the potential for cardiovascular accidents.
Backup Respiratory Rate
A third mode of ventilation consists of the addition of a backup respiratory rate. (This involves the application of a ventilatory device.) It can be used at the hospital or at home for patients who have a history of respiratory insufficiency or for OSA. Patients who fit this category can maintain ventilation without mechanical intervention for a period of time, but they have difficulty maintaining this while they are asleep. Persons who would benefit from this mode would include neurologic patients and cardiac patients who demonstrate central sleep apnea. The variable between the regular bilevel systems and those with a set backup rate is the automaticity of the inhalation time. For example, one mode awaits a spontaneous effort at inhalation from the patient and then it delivers the preset pressure as input by the technologist. This mode is designed to automatically begin inhalation if the patient does not inhale spontaneously within a set time. Protocols determined by the medical director and the director of the laboratory should be in place prior to implementing this mode. If there are no protocols, then the physician should be contacted for specific orders.
A normal respiratory rate (RR) for a healthy adult is around 12 breaths per minute (BPM). An abnormal RR would be 6-8 BPM or less, for respiratory insufficiency. Clinical indications for noninvasive positive pressure ventilation would include:
- respiratory insufficiency (RR < 6 BPM);
- Spo2 < 90%;
- cardiac arrhythmias; and
- frequent awakenings “to breathe” following central apneas.
A thorough review of the patient’s history and physical examination is essential for technologists to be prepared for the potential needs of their patients. Information regarding the patient’s cardiac history (congestive heart failure) would be useful, since this diagnosis is predisposed to a central apnea component. Another item of interest in the history and physical examination might involve a neurologic disorder that could impact the quality of a standard titration. Myasthenia gravis, amyotrophic lateral sclerosis, Chiari syndrome, and motor vehicle accidents with head trauma are a few diagnoses that could require a backup respiratory rate intervention throughout the night. From a pulmonary standpoint, those patients who present with “overlap syndrome” are prime candidates who could benefit from the “inquiring mind” of a good technologist. The technologist would designate the room assignment according to specific equipment needs, assuming that not every room has the same capabilities for backup-rate delivery systems. If a room is set up with both an NPPV device with backup-rate capability plus an end-tidal carbon dioxide monitor, all the better.
The evolution of technology continues to be essential for the good of the patient and provides an ongoing opportunity for education on the part of the caregiver. As our patients get sicker and sicker, NPPV will become a front-line therapy for the treatment of OSA patients with COPD or neurologic disorders. Much has happened in the short years of sleep medicine, and as the field continues to grow and develop its own specialty, technologists must step up to the plate and become the medical professionals that society needs. This article provides a very basic introduction to NPPV therapy, but hopefully it will serve to inspire sleep specialists to delve deeper into the potentials of this beneficial treatment.
Kendall R. White, RPSGT, is director; and Paula G. Williams, RPSGT, CRT, MA, is QA coordinator, both at Diagnostic Center for Sleep Disorders, Chattanooga, Tenn.
1. Sharma S. Ventilation, noninvasive. 2003. Available at: http://www.emedicine.com/med/topic3371.htm. Accessed February 18, 2004.
2. Sharma S. Noninvasive positive pressure ventilation. Ventilation, noninvasive. 2003. Available at: http://www.emedicine. com/med/topic3371.htm. Accessed February 18, 2004.
3. Synchrony BiLevel Guidelines. Clinical Information. Murrysville, Pa: Respironics Inc; 2002.