Reviews

Update And Perspective on Noninvasive Respiratory Muscle Aids: Part 2: The Expiratory Aids

Why are Expiratory Muscle Aids Needed?

Adequate expiratory muscle function is critical for clearing airway secretions and bronchial mucus plugs. This may be a continual problem for patients with airway or pulmonary disease or with inability to swallow saliva without aspiration. For patients with global alveolar hypoventilation and functional bulbar musculature, it becomes a problem during respiratory tract infections (RTIs), following general anesthesia, and during other periods of bronchial hypersecretion.

A normal cough requires a

Manually Assisted Coughing

Techniques of manually assisted coughing involve different hand and arm placements for expiratory cycle thrusts (Fig 1). For patients with less than 1.5 L of VC, efficacy is enhanced by preceding the assisted exsufflation with a deep insufflation. A positive pressure blower (Zephyr, Lifecare, Lafayette, Colo), intermittent positive-pressure breathing (IPPB) machine, or portable ventilator is useful for delivering the deep insufflation. Manually assisted coughing requires a cooperative patient,

Mechanical Insufflation-Exsufflation

The life-saving value of exsufflation with negative pressure was made clear through the relief of obstructive dyspnea as a result of immediate elimination of large amounts of purulent sputum, and, in a second episode, by the substantial clearing of pulmonary atelectasis after 12 hours' treatment.⁷

In the late-1940s, Henry Seeler, working for the US Air Force, developed a mechanical insufflator-exsufflator designed to deliver alternating positive and negative pressures to ventilate and exsufflate

Mechanical Oscillation Techniques

Beck first described the use of high frequency chest wall oscillation to facilitate bronchial secretion clearance in patients with chronic bronchial asthma and emphysema in 1966. Oscillation can be applied externally to the chest wall or abdomen or directly to the airway as high frequency positive-pressure ventilation, jet ventilation, or oscillation in which there are rapid small amplitude pressure swings above and below atmospheric pressure.³⁷ All of these techniques have been noted to have

Other Techniques which Assist Respiratory Muscle Effort

For patients with paralyzed abdominal musculature from spinal cord injury, use of a thoracoabdominal corset restricts the descent of the diaphragm and limits the increase in FRC which otherwise usually increases significantly when the patient assumes the upright position. Although it does not assist respiratory muscles for the patient when supine, when sitting, it assists diaphragm activity by permitting increased excursion. It has no significant effect on PCEF in the supine position; however,

Difficulties in Initiating the Use of Noninvasive Aids and Conclusion

Despite patient and care-giver preferences for noninvasive approaches, the ability of these methods to lower the cost of home mechanical ventilation, to eliminate the need for hospitalization, intubation, and bronchoscopy particularly for neuromuscular/restrictive patients who develop global alveolar hypoventilation, and their safety and efficacy for long-term ventilatory support and secretion management, it has been problematic for physicians and medical centers in the United States to

ACKNOWLEDGMENT

Dr. Phillip Soudon provided Figure 3.