592
U N I T 6
Respiratory Function
pathogenesis of primary pulmonary arterial hyperten-
sion. Oral endothelin antagonists (e.g., ambristan,
bosentran) have proved to be effective in treating mod-
erate to severe primary pulmonary hypertension and
may become the treatment of choice for all stages of
the disease.
66
Sildenafil (e.g., Revatio), a highly selective
phosphodiesterase-5 inhibitor that acts in a manner sim-
ilar to nitric oxide to produce vasodilation, is approved
for use in pulmonary hypertension. Lung transplan-
tation may be an alternative for persons who do not
respond to other forms of treatment.
Cor Pulmonale
The term
cor pulmonale
refers to right heart failure
resulting from primary lung disease or pulmonary
hypertension. The increased pressures and work result
in hypertrophy and eventual failure of the right ven-
tricle. The manifestations of cor pulmonale include the
signs and symptoms of the primary lung disease and the
signs of right-sided heart failure (see Chapter 20). Signs
of right-sided heart failure include venous congestion,
peripheral edema, shortness of breath, and a productive
cough, which becomes worse during periods of heart
failure. Plethora (i.e., redness), cyanosis, and warm,
moist skin may result from the compensatory polycythe-
mia and desaturation of arterial blood that accompany
chronic lung disease. Drowsiness and altered conscious-
ness may occur as the result of carbon dioxide retention.
Management of cor pulmonale focuses on the treatment
of the lung disease and heart failure. Low-flow oxygen
therapy may be used to reduce the pulmonary hyper-
tension and polycythemia associated with severe hypox-
emia caused by chronic lung disease.
Acute Respiratory Disorders
The function of the respiratory system is to add oxygen
to the blood and remove carbon dioxide. Disruptions in
gas exchange occur with acute lung injury respiratory
distress syndrome, and respiratory failure. Although the
mechanisms prompting these conditions may vary, both
are life-threatening situations with a high risk of mor-
bidity and mortality.
Acute Lung Injury/Acute Respiratory
Distress Syndrome
Acute respiratory distress syndrome (ARDS) is a clini-
cal syndrome that is characterized by severe dyspnea
of rapid onset, hypoxemia, and pulmonary infiltrates.
Acute lung injury (ALI) is a less-severe form of the dis-
order, but has the potential for evolving into ARDS. The
two conditions are differentiated by the extent of hypox-
emia as determined by the ratio of the partial pressure of
oxygen in the arterial blood (PO
2
) to fraction of inspired
oxygen (FIO
2
).
67–70
The incidence of ALI/ARDS is not
consistently reported, although it is estimated to occur
in approximately 150,000 to 200,000 persons each year
in North America. Despite the most sophisticated inter-
ventions, the mortality rate varies from 35% to 60%
and morbidity is extensive, including physical, cogni-
tive, and emotional sequelae.
15,71
Both ARDS and ALI can result from a number of con-
ditions, including aspiration of gastric contents, major
trauma (with or without fat emboli), sepsis secondary
to pulmonary or nonpulmonary infections, acute pan-
creatitis, hematologic disorders, metabolic events, and
reactions to drugs and toxins (Chart 23-2).
Etiology and Pathogenesis
Although a number of conditions may lead to ALI/ARDS,
they all produce similar pathologic lung changes that
include diffuse epithelial cell injury with increased perme-
ability of the alveolar–capillary membrane (Fig. 23-15).
The increased permeability permits fluid, plasma pro-
teins, and blood cells to move out of the vascular com-
partment into the interstitium and alveoli of the lung.
15,69
Diffuse alveolar cell damage leads to accumulation of
fluid, surfactant inactivation, and formation of a hyaline
membrane that is fibrous and impervious to gas exchange.
abnormal proliferation and contraction
of vascular smooth muscle, coagulation
abnormalities, and marked intimal fibrosis
leading to obliteration or obstruction of the
pulmonary arteries and arterioles.
■■
Cor pulmonale describes right heart failure
caused by pulmonary disease and long-standing
pulmonary hypertension.
SUMMARY CONCEPTS
■■
The pulmonary circulation is a low-pressure
system that links the right heart and systemic
venous system with the left heart and the
systemic arterial system and functions as a
conduit for exchange of the dissolved gases in the
blood with the ventilated air in the alveoli.
■■
Pulmonary embolism develops when a blood-
borne substance lodges in a branch of the
pulmonary artery and obstructs blood flow.
The embolus can consist of a thrombus, air, fat,
or amniotic fluid.The most common form is
thromboemboli arising from the deep venous
channels of the lower extremities.
■■
Pulmonary hypertension represents an elevation
in the pulmonary arterial pressure. It may arise
as a secondary disorder associated with other
disease conditions, usually cardiac or pulmonary,
or as a primary disorder, characterized by
