Ascites
Ascites, an excess of serous fluid within the
penitoneal cavity, can be recognised clinically only when the amount of fluid
present exceeds 1500 ml; in the obese a greater quantity than this is necessary
before there is clear evidence of the presence of intrapenitoneal fluid.
Ultrasound and CT scanning can detect much smaller volumes of ascitic fluid.
Mechanism
of ascites
The balanced effects of
plasma and
peritoneal colloid osmotic and
hydrostatic pressures determine the exchange of
fluid between the
capillaries and
the peritoneal fluid.
Normal intrapenitoneal
pressure and normal peritoneal fluid colloid osmotic pressure cannot be
measured. Protein rich fluid
enters the
peritoneal cavity
when capillary
permeability to protein is increased,
as in peritonitis
and carcinomatosis peritonei. Capillary pressure may be increased because
of generalised water
retention, cardiac failure, constrictive pericarditis or vena cava obstruction. Capillary pressure is raised selectively
in the portal venous system in the Budd—Chiari syndrome, cirrhosis of the
liver or extra-hepatic portal venous obstruction (see Chapter 52). Plasma
colloid osmotic pressure may be lowered in patients with reduced nutritional
intake, diminished intestinal absorption, abnormal protein losses, or defective
protein synthesis as occurs in cirrhosis. Peritoneal lymphatic drainage may be
impaired resulting in the accumulation of protein-rich fluid.
Clinical
features
The abdomen is distended evenly, with fullness
of the flanks, which are dull to percussion. Usually shifting dullness is
present, but when there is a very large accumulation of fluid this sign is
absent. In such cases, on flicking the abdominal wall, a characteristic fluid
thrill is transmitted from one side to the other. In women, ascites must be
differentiated from an enormous ovarian cyst. The causes of ascites are listed
in Table 56.7.
Congestive
heart failure, the commonest cause of ascites, causes increased venous pressure
in the vena cava and consequent obstruction to the venous outflow from the
liver. This increased pressure can be seen as engorgement of the veins of the
neck — a
striking sign in this condition. The ascitic fluid is light yellow and of low
specific gravity, about 1.010, with a low protein concentration (<25 g/litre).
Patients with constrictive pericarditis (syn. Pick’s disease) have both
penitoneal and pleural effusions due to engorgement of the venae cavae
consequent upon the diminished capacity of the right side of the heart.
In
cirrhosis there is obstruction to the portal venous system which is caused by
obliterative fibrosis of the intrahepatic venous bed. Lymph flow may be
increased. In the Budd—Chiari syndrome (Chapter 52), thrombosis or obstruction of the hepatic veins is
responsible for obstruction to venous outflow from the liver.
The
ascites seen in patients with peritoneal metastases is due to excessive
exudation of fluid and lymphatic blockage. The fluid is dark yellow and
frequently blood stained. The specific gravity, 1.020 or over, and the protein
content (>25
g/litre) are
high. Microscopical examination often reveals cancer cells especially if large
quantities of fluid are ‘spun-down’ to produce a concentrated deposit for
sampling.
Ascites
occurs with low plasma albumin concentrations; for example in patients with
albuminunia or starvation. The ascites in this instance is due to alterations in
the osmotic pressure of the capillary blood, and has a low specific gravity.
Rarely
ascites and pleural effusion are associated with solid fibroma of the ovary (Meigs’
syndrome). The effusions disappear when the tumour is excised.
Treatment
Ascites may be tapped (paracentesis abdominis)
but unless other measures are taken, the fluid soon reaccumulates and repeated
tappings remove valuable protein. Treatment of the specific cause is undertaken
whenever possible, for example if portal venous pressure is raised, it may be
possible to lower it by treatment of the primary condition (Chapter 52). Dietary
sodium restriction to 200 mg per day may be helpful but diuretics are usually
required.
Paracentesis
abdominis
The bladder having been emptied by a catheter,
under local anaesthesia puncture of the peritoneum is carried out with a moderate sized trocar and
cannula at one of
the points
shown in Fig.
56.12. Alternatively a peritoneal drain may be inserted under ultrasound guidance to minimise the risk of visceral injury. In
cases where the effusion is due to cardiac failure the fluid must be evacuated
slowly. In other circumstances this precaution is unnecessary. If the cannula
becomes blocked with fibrin it is
cleared with a stylet or the drain is flushed. After the fluid has been
evacuated the puncture is sealed and a tight hinder is applied to the abdomen.
Some surgeons prefer to perform the ‘tap’ over the liver beneath
the costal margin or in the
midline beneath the xiphisternum.
Permanent
drainage of ascitic fluid
In rare cases where ascites accumulates rapidly after paracentesis and the
patient is otherwise fit, permanent drainage of the ascitic fluid via
a peritoneovenous shunt (e.g. LeVeen) may
render the patient more comfortable. Similar in concept to shunts for
hydrocephalus (Chapter 35), a catheter (e.g. of silicone) is constructed with a
valve so as to allow one-way flow from the peritoneum to a central vein (e.g.
internal jugular). A chamber placed subcutaneously over the chest wall may be
included for manual compression. Insertion is relatively simple. The
complications include overloading the venous system, cardiac failure and
disseminated intravascular coagulopathy. The frequency of these complications
may he reduced by evacuating ascitic fluid and partially replacing it
with normal
saline at the time of shunt insertion. The procedure may also be used for
patients with
terminal malignant ascites giving improved quality of life, despite the risk of
further dissemination of
malignant cells.
Chylous
ascites
In some patients the ascitic fluid appears
milky due to an
excess of chylomicrons
(triglycerides). Most cases are associated
with malignancy, usually lymphomas; other causes are cirrhosis, tuberculosis, filariasis,
nephrotic syndrome, abdominal trauma (including surgery), constrictive
pericarditis, sarcoidosis and congenital lymphatic abnormality. The condition is
rare. The
prognosis is poor
unless the underlying condition can be cured. In addition
to other measures
used to treat ascites, patients should be placed
on a fat-free
diet with medium-chain triglyceride supplements.
Peritoneal
loose bodies (peritoneal mice)
Peritoneal loose bodies almost never cause
symptoms. One or more may be found in a hernial sac or in the pouch of Douglas. The
loose body may
come from an appendix epiploica that has undergone axial rotation followed by
necrosis of its pedicle and detachment, but they are also found in those who
suffer from subacute attacks of pancreatitis. These hyaline bodies attain the
size of a pea or bean,
and contain saponified fat surrounded by