The Management of Chronic Hypoventilation: Mechanical Ventilation (2)
Recently, the development of obstructive apneas and oxygen desaturations during nocturnal use of negative pressure ventilators by normal subjects and by patients with neuromuscular disease has been reported. The prevalence of this problem and how much it interferes with efficacy of the ventilators is unknown, but patients with known obstructive apnea should use alternative forms of ventilatory assistance.
Ventilators that assist the diaphragm by displacing abdominal contents include the abdominal insufflation belt or “pneumobelt” and the rapid rocking bed. The pneumobelt consists of an inflatable rubber balloon held firmly against the abdomen by a corset. When inflated, the balloon compresses the abdominal contents and forces the diaphragm upward, assisting exhalation. Because it relies on gravity to pull the diaphragm downward during inhalation, the pneumobelt becomes ineffective unless the patient sits at an angle of at least 45°, limiting nocturnal use. The rapid rocking bed works by tilting the patient through an arc of about 40° at rates ranging from 13 to 19 per minute. Buy Asthma Inhalers Online
The abdominal contents and diaphragm slide back and forth as the body tilts, assisting ventilation. Both the rocking bed and the pneumobelt function poorly in excessively obese, thin, or scoliotic individuals and both should be used with caution in patients with minimal pulmonary reserve. Despite this caveat, the rocking bed was used to support severely compromised polio patients for up to several decades following the epidemics of the 1950s.