For patients who are able to receive them, NPPV techniques offer the potential to minimize many of the complications associated with long-term mechanical ventilation.

 Alternatives to invasive mechanical ventilation provide a means of reducing pulmonary complications in patients who require long-term ventilatory support. Noninvasive ventilation is commonly thought of as the provision of ventilatory support using techniques that do not require an endotracheal airway. Historically, these methods were developed to provide ventilatory support to patients with respiratory paralysis due to poliomyelitis; even today, they are often used by patients with respiratory failure due to neuromuscular diseases. Perhaps the earliest noninvasive ventilatory device was the iron lung, a huge metal tank that filled the lungs by exerting negative pressure on the body. Disadvantages associated with the bulky device included lack of portability, positioning restrictions, fitting problems, and a tendency to potentiate obstructive sleep apnea.1 Other negative-pressure devices followed the iron lung into the marketplace, but by the 1960s, negative-pressure devices were largely replaced by invasive positive-pressure ventilation, and the movement to develop noninvasive positive-pressure techniques was born.

Therapeutic Rationale
The driving force behind the development of noninvasive positive-pressure ventilation (NPPV) techniques was the need to reduce the complications associated with long-term invasive ventilation. Complications directly related to the processes of intubation and mechanical ventilation may include aspiration of gastric contents; trauma to the teeth, hypopharynx, esophagus, larynx, and trachea; cardiac arrhythmias; hypotension; bleeding; and mediastinitis.2,3 Long-term intubation can result in the loss of airway defense mechanisms, which may lead, in turn, to chronic bacterial colonization, inflammation, and the impairment of airway ciliary function.4 These factors are believed to facilitate the development of bacterial pneumonia, which is seen in roughly 21% of mechanically ventilated patients in intensive care units.4 From the point of view of the patient, long-term endotracheal intubation may cause discomfort and inconveniences (such as inability to eat or speak).5

Continuous Positive Airway Pressure Treatment
Supplied via nasal mask, continuous positive airway pressure (CPAP) has been shown to augment cardiac output, reduce myocardial oxygen consumption, and unload inspiratory muscles by reducing pleural pressure swings.6,7 It is often used to treat patients with long-standing congestive heart failure (CHF), who may suffer from respiratory muscle weakness.8-11 Nightly use of nasal CPAP by patients with CHF and obstructive sleep apnea may lead to an increased left ventricular ejection fraction and reduced dyspnea.12,13 CPAP also reduces the left ventricular preload and afterload by decreasing left ventricular transmural pressures during systole and diastole,14,15 thereby improving the mechanical efficiency of the failing heart.

CPAP can have beneficial hemodynamic effects in patients with CHF. In the normal heart, cardiac output depends largely on preload, and CPAP decreases cardiac output by reducing left ventricular preload without affecting afterload. In patients with CHF, however, because cardiac output is relatively insensitive to changes in preload (but very sensitive to changes in afterload), CPAP-induced reductions in left ventricular transmural pressure can augment cardiac output.16,17 In the early 1980s, Pinsky et al18 showed that, in patients with CHF, intermittent elevations in intrathoracic pressure can improve cardiac output. Subsequent investigations6,19 confirmed these findings and showed that CPAP causes a dose-dependent augmentation in cardiac output when applied acutely to patients with stable CHF and elevated pulmonary capillary wedge pressure,6 and that CPAP may improve the cardiac index when used by patients with acute cardiogenic pulmonary edema.19

Patients with heart failure and systolic dysfunction may develop disordered breathing during sleep. Repeated episodes of apnea and hypopnea may result in oxygen desaturations and arousals, which could adversely affect left ventricular function. Javaheri19 performed a study to determine the short-term effects of CPAP on sleep-disordered breathing and its consequences in heart-failure patients. He prospectively studied 29 male patients whose initial polysomnograms showed an apnea-hypopnea index (AHI) of 15 or more episodes per hour. Twenty-one patients had predominantly central apnea and eight patients had obstructive sleep apnea. All were treated using CPAP during the subsequent night. In 16 patients, CPAP use resulted in the virtual elimination of disordered breathing. In these patients, the mean AHI, arousal index due to disordered breathing, and percent of total sleep time spent at an oxygen-saturation level of less than 90% decreased significantly, and the lowest oxygen-saturation levels also increased significantly with CPAP use. In 13 patients who did not respond to CPAP, these values did not change significantly. In patients whose sleep apnea responded to CPAP, the number of hourly episodes of nocturnal premature ventricular contractions and couplets decreased. In contrast, in patients whose sleep apnea did not respond to CPAP, ventricular arrhythmias did not change significantly. Overall, first-night nasal CPAP eliminated disordered breathing and reduced ventricular irritability in 55% of patients with heart failure and sleep apnea.

CPAP can cause nasal congestion, claustrophobic sensations, and other side effects. Sin et al20 studied patients with sleep apnea to determine short-term and long-term compliance, baseline predictors for long-term CPAP compliance, and whether CPAP use provided sustained improvement in daytime sleepiness. The design chosen was a prospective, longitudinal study of patients referred to a university sleep disorders center. The enrolled subjects were 296 patients with moderate-to-severe obstructive sleep apnea, as defined by an AHI of 20 or more events per hour. Participants were provided with a CPAP device that contained a computer chip for monitoring compliance. They were informed that noncompliance would result in the loss of the machine. Within the first week of the study, patients began making daily telephone contact with a CPAP clinic nurse; follow-up office visits took place after 2 weeks, 4 weeks, 3 months, and 6 months. During each follow-up visit, patients were asked to complete questionnaires concerning their degree of daytime sleepiness. Compliance rates (defined as use of the CPAP machine for 3.5 hours or longer per night) were at or above the 80% mark at each of the follow-up visits. The daytime sleepiness score improved over the entire follow-up period, with the lowest score occurring 6 months after the initiation of treatment. Three variables were found to correlate with increased CPAP use: female gender, increased age, and reduction of daytime sleepiness scores. The investigators concluded that a population-based CPAP program consisting of consistent follow-up, troubleshooting, and regular feedback to both patients and physicians could achieve CPAP compliance rates of more than 85% over a 6-month period.

Abdominal Displacement Ventilators
The rocking bed and the intermittent abdominal pressure ventilator are devices that rely on displacement of the abdominal viscera to assist diaphragm motion and, therefore, ventilation.21,22 They were first developed in the 1950s, and remain in use at some respiratory care centers today.

The rocking bed consists of a mattress on a motorized platform that rocks back and forth. The patient lies supine, with the head and knees raised to prevent sliding. When the head rocks down, the abdominal viscera and diaphragm slide upward, assisting exhalation. As the head rocks up, the viscera and diaphragm slide downward, assisting inhalation. The main advantages of the rocking bed are ease of operation and patient comfort. Disadvantages include bulk, motor noise, and lack of portability.

The intermittent abdominal pressure ventilator wraps around the patient’s midsection and holds an inflatable rubber bladder firmly against the abdomen.22 A positive-pressure ventilator intermittently inflates the bladder. When the patient is sitting, bladder inflation compresses the abdominal contents, forcing the diaphragm upward and actively assisting exhalation. With bladder deflation, gravity returns the diaphragm to its original position, assisting inhalation. The intermittent abdominal pressure ventilator is portable, and it leaves the hands and face unencumbered. Because it requires gravity to pull the diaphragm down during bladder deflation, however, it is ineffective unless patients sit at angles of at least 30°.23 Hence, its nocturnal use is limited to patients who can learn to sleep while sitting.23 It may be valuable as a daytime adjunct for appropriate patients who are using other forms of NPPV at night.24

Intermittent Positive-Pressure Ventilation
Intermittent positive-pressure ventilation (IPPV) therapy provides a means of receiving air under pressure during inhalation. IPPV can be delivered noninvasively through a wide variety of mouthpieces, nasal masks, and oral-nasal masks for nighttime ventilatory support. To use mouthpiece IPPV effectively and conveniently, adequate neck rotation and oral motor function are needed (so that the patient can grab the mouthpiece and receive IPPV without air leakage). A lip seal may be used to minimize loss of air from the mouth. Because many patients prefer to use mouthpiece IPPV or the intermittent abdominal pressure ventilator for daytime use, nasal IPPV (or the noninvasive delivery of IPPV via nasal CPAP mask) is usually practical only for nighttime use.25,26

Glossopharyngeal Breathing
Both inspiratory and, indirectly, expiratory muscle function can be assisted by glossopharyngeal breathing (GPB)—commonly referred to as air stacking. For patients with weak inspiratory muscles and no ability to breathe on their own, GPB may provide normal lung ventilation throughout the day without the need for a ventilator. It may also be useful in the event of sudden ventilator failure.

GPB involves the use of the throat to add to an inspiratory effort by gulping boluses of air into the lungs. The glottis closes with each gulp. GPB is rarely useful in the presence of an indwelling tracheostomy tube. It cannot be used when the tube is uncapped, as it is during tracheostomy IPPV, and even when the tube is capped, the gulped air tends to leak around the outer walls of the tube and out the stoma as airway volumes and pressures increase during the GPB air-stacking process.

For patients who are able to receive them, NPPV techniques offer the potential to eliminate the need for tracheostomy and invasive ventilation, and thereby minimize many of the complications associated with long-term mechanical ventilation.

John D. Zoidis, MD, is a contributing writer for RT.

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