Page 124 - Medicine and Surgery

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120 Chapter 3: Respiratory system

(non-cardiogenic) and exudation of a protein-rich pulmonary arterial pressure is raised) unlike in car-
fluid into alveolar spaces. diogenic pulmonary oedema.
Type I pneumocytes, which make up 90% of the Other investigations to look for an underlying cause

alveolar epithelium mostly die, and Type II pneu- (e.g. blood cultures coagulation screen and d-dimers
mocytes, which produce surfactant are disrupted in for DIC, amylase for pancreatitis).
function.
During this phase, there is alveolar collapse, lung Management
compliance falls (i.e. the lungs become stiff) and gas 1 Identification and eradication of any underlying cause
exchange is impaired, and there may also be evi- such as sepsis.
dence of airflow obstruction. Increased shunting and 2 Supportive treatment with following:
deadspace occurs (ventilation–perfusion mismatch) Ventilatory support – low volume, pressure-limited
and hypoxaemia results. cycles reduce further damage.
2 In some cases the acute phase resolves with complete Fluid restriction and removal if necessary to min-
recovery within a week. In other cases, where damage imise pulmonary oedema.
to lung tissue has been severe the disease progresses to To attempt to improve ventilation/perfusion mis-
afibrosing alveolitis phase: match the patient can be alternately nursed prone
The mechanism is unclear, but interstitial fibrosis
and supine, or treated with nebulised prostacyclin
develops with loss of the normal architecture of or nitric oxide.
the lung, obliterating the vasculature and leading High dose steroids are no longer recommended in
to pulmonary hypertension, worsening lung com- ARDS for treatment or prophylaxis.
pliance and in the long-term emphysema and hon-
Prognosis
eycomb lung.
Dependant on the underlying cause, mortality can be
very high in patients with septic shock who develop
Clinical features
multi-organ failure. Increasing age and pre-existing dis-
The first sign is tachypnoea, followed by hypoxia, wors-
ease worsen the outcome.
ening dyspnoea and fine bi-basal crackles that become
widespread.ARDSisoftenthefirstmanifestationofmul-
tiple organ failure, so the features of other organ failure
Suppurative lung disorders
may develop such as renal and liver failure.
Cystic fibrosis
Complications
Often complicated by secondary infection (nosocomial Definition
pneumonia). Autosomal recessive disorder with multisystem involve-
ment including chronic suppurative lung disease, pan-
creatic insufficiency and liver cirrhosis.
Investigations
Chest X-ray and CT scan show bilateral diffuse shad-

owing with an alveolar pattern. Later the picture may Incidence
progress to a complete whiteout. With the fibrotic 1in 2500 births are homozygous, 1 in 25 carriers (het-
phase, linear opacities become visible. erozygous) in Caucasians.
Blood gases are used to detect and monitor respira-

tory failure, other investigations such as U&E and liver Age
function tests may be required, as multiorgan failure 90% diagnosed in childhood, and 10% in adolescents
is common. and adults.
The pulmonary wedge pressure should be measured

by insertion of a Swan–Ganz catheter. In ARDS Sex
the pulmonary wedge pressure is normal (although M = F