Page 139 - Textbook of Pathology, 6th Edition

iv) General condition of the patient e.g. in severely ill patients, pressure to normal levels. This results in similar effects as in 123
as little as 40 ml of air may have serious results. divers and workers in caissons.
The mechanism of death is by entrapment of air emboli
in the pulmonary arterial trunk in the right heart. If bubbles EFFECTS. The effects of decompression sickness depend
upon the following:
of air in the form of froth pass further out into pulmonary Depth or altitude reached
arterioles, they cause widespread vascular occlusions. If Duration of exposure to altered pressure CHAPTER 5
death from pulmonary air embolism is suspected, the heart Rate of ascent or descent
and pulmonary artery should be opened in situ under water General condition of the individual
so that escaping froth or foam formed by mixture of air and Pathologic changes are more pronounced in sudden
blood can be detected.
decompression from high pressure to normal levels than in
ARTERIAL AIR EMBOLISM. Entry of air into pulmonary those who decompress from low pressure to normal levels.
vein or its tributaries may occur in the following conditions: The changes are more serious in obese persons as nitrogen
i) Cardiothoracic surgery and trauma. Arterial air gas is more soluble in fat than in body fluids.
embolism may occur following thoracic operations, Clinical effects of decompression sickness are of 2 types—
thoracocentesis, rupture of the lung, penetrating wounds of acute and chronic.
the lung, artificial pneumothorax etc. Acute form occurs due to acute obstruction of small blood
ii) Paradoxical air embolism. This may occur due to passage vessels in the vicinity of joints and skeletal muscles. The
of venous air emboli to the arterial side of circulation through condition is clinically characterised by the following:
a patent foramen ovale or via pulmonary arteriovenous i) ‘The bends’, as the patient doubles up in bed due to acute
shunts. pain in joints, ligaments and tendons.
iii) Arteriography. During arteriographic procedures, air ii) ‘The chokes’ occur due to accumulation of bubbles in the
embolism may occur. lungs, resulting in acute respiratory distress. Derangements of Homeostasis and Haemodynamics
The effects of arterial air embolism are in the form of iii) Cerebral effects may manifest in the form of vertigo, coma,
certain characteristic features: and sometimes death.
i) Marble skin due to blockage of cutaneous vessels. Chronic form is due to foci of ischaemic necrosis
ii) Air bubbles in the retinal vessels seen ophthalmos- throughout body, especially the skeletal system. Ischaemic
copically. necrosis may be due to embolism per se, but other factors
iii) Pallor of the tongue due to occlusion of a branch of lingual such as platelet activation, intravascular coagulation and
artery. hypoxia might contribute. The features of chronic form are
iv) Coronary or cerebral arterial air embolism may cause as under:
sudden death by much smaller amounts of air than in the i) Avascular necrosis of bones e.g. head of femur, tibia,
venous air embolism.
humerus.
ii) Neurological symptoms may occur due to ischaemic
Decompression Sickness
necrosis in the central nervous system. These include
This is a specialised form of gas embolism known by various paraesthesias and paraplegia.
names such as caisson’s disease, divers’ palsy or iii) Lung involvement in the form of haemorrhage, oedema,
aeroembolism. emphysema and atelactasis may be seen. These result in
dyspnoea, nonproductive cough and chest pain.
PATHOGENESIS. Decompression sickness is produced
when the individual decompresses suddenly, either from iv) Skin manifestations include itching, patchy erythema,
high atmospheric pressure to normal level, or from normal cyanosis and oedema.
v) Other organs like parenchymal cells of the liver and
pressure to low atmospheric pressure. pancreas may show lipid vacuoles.
In divers, workers in caissons (diving-bells), offshore
drilling and tunnels, who descend to high atmospheric
pressure, increased amount of atmospheric gases (mainly Amniotic Fluid Embolism
nitrogen; others are O , CO ) are dissolved in blood and tissue This is the most serious, unpredictable and unpreventible
2
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fluids. When such an individual ascends too rapidly i.e. cause of maternal mortality. During labour and in the
comes to normal level suddenly from high atmospheric immediate postpartum period, the contents of amniotic fluid
pressure, the gases come out of the solution as minute may enter the uterine veins and reach right side of the heart
bubbles, particularly in fatty tissues which have affinity for resulting in fatal complications. The amniotic fluid
nitrogen. These bubbles may coalesce together to form large components which may be found in uterine veins, pulmonary
emboli. artery and vessels of other organs are: epithelial squames,
In aeroembolism, seen in those who ascend to high vernix caseosa, lanugo hair, bile from meconium, and mucus.
altitudes or air flight in unpressurised cabins, the individuals The mechanism by which these amniotic fluid contents enter
are exposed to sudden decompression from low atmospheric the maternal circulation is not clear. Possibly, they gain entry