Encyclopedia of Health and Medicine

214 The Pulmonary System
against these infections among their criteria for
accepting recipients. Long-term immunosuppression
carries numerous risks, including a significantly
increased likelihood for developing
LYMPHOMA, a cancer of the LYMPH structures.
A major complication that affects up to 50 percent
of lung transplant recipients is bronchiolitis
obliterans, a condition in which the bronchioles
(the smallest airways in the lungs) become
inflamed and then fibrotic. The fibrotic (SCAR) tissue
blocks the narrow openings of the bronchioles,
preventing air from reaching the alveoli. As
greater numbers of bronchioles become involved,
pulmonary function deteriorates. Bronchiolitis is
itself an indication for lung transplantation. CORTI-
COSTEROID MEDICATIONS can help limit the INFLAMMA-
TION though cannot prevent the condition from
developing or progressing.
Outlook and Lifestyle Modifications
Most people who receive transplanted lungs can
return to many of their regular activities, including
physical exercise, with few restrictions unless
complications develop. It is important to avoid cigarette
smoke and other substances that may irritate
or inflame the lungs, and to minimize
exposure to other people who have viral or bacterial
infections such as sore throats and other common
illnesses. Lung transplantation requires
regular medical care for follow-up and evaluation
of pulmonary function and lung health, with
immediate treatment for potential problems and
complications. About 45 percent of people who
undergo lung transplantation live five years or
longer with their donor lungs.
See also HEART TRANSPLANTATION; ORGAN TRANS-
PLANTATION; SURGERY BENEFIT AND RISK ASSESSMENT.
mechanical ventilation A method for providing
assisted respiration to an individual whose LUNGS
cannot maintain respiratory support on their own
(RESPIRATORY FAILURE). During mechanical ventilation,
a machine (the ventilator) rhythmically
pushes air into the lungs through an endotracheal
tube or TRACHEOSTOMY tube. An endotracheal tube
is a flexible plastic tube inserted through the NOSE
or MOUTH into the TRACHEA, with an inflatable cuff
that holds it in place. A tracheostomy tube enters
the trachea through an incision in the neck,
bypassing the upper airways (including the mouth
and throat). The lungs continue to do the work of
OXYGEN–CARBON DIOXIDE EXCHANGE.
Mechanical ventilation may provide full respiratory
support, in which BREATHING occurs only
with the ventilator’s function, or partial respiratory
support, in which the ventilator functions
only when the person’s natural breathing is insufficient.
As with normal respiration the inhalation
phase of the RESPIRATORY CYCLE is active, with the
ventilator sending air under pressure into the
lungs, and the exhalation phase is passive, with
the ventilator allowing the thoracic cavity’s relaxation
to expel air. The ventilator typically utilizes
continuous POSITIVE AIRWAY PRESSURE (CPAP), which
keeps the trachea, bronchi, and bronchioles from
collapsing.
There are numerous applications for, and varying
levels of, mechanical ventilation. Temporary
mechanical ventilation is customary after major
cardiovascular or pulmonary operations and during
recovery from major trauma. Other circumstances
in which mechanical ventilation is a
therapeutic option include
• high-level (cervical and upper thoracic) SPINAL
CORD INJURY that affects the nerves regulating
contraction of the DIAPHRAGM and intercostal
muscles (the muscles of breathing)
• injury to the respiratory centers of the BRAIN
and brainstem
• degenerative neurologic conditions that affect
respiratory function
• increased respiratory demands that exceed the
lungs’ ability to deliver, such as in severe infections
The ventilator is primarily a mechanized bellows
that fills with air (and supplemental oxygen if necessary)
that inflates the lungs using positive pressure.
The doctor determines the RESPIRATORY RATE,
air volume (amount of air the ventilator delivers),
and flow pressure (pressure under which the ventilator
delivers air to the person). In some situations
the person does not need help with breathing but
just needs an endotracheal tube or tracheostomy to
protect the airway and minimize the risk of aspirating
foreign matter into the lungs. In such a situa-