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 fibrin.