Malignant ascites (MA) is a complication of advanced cancer defined by the pathological accumulation of fluid within the peritoneal cavity. This condition develops when cancer cells spread to the lining of the abdomen (peritoneum) or obstruct the lymphatic drainage system. MA is a grave prognostic sign, signaling late-stage progression. Death results from a cumulative failure of several interconnected physiological systems.
Respiratory and Circulatory System Failure
The sheer volume of fluid creates intra-abdominal hypertension, which directly compromises cardiopulmonary function. This pressure pushes the diaphragm upward, restricting the full downward movement needed for deep inhalation. The resulting reduction in lung volume causes dyspnea (shortness of breath), leading to inadequate oxygen exchange and chronic hypoxia.
High intra-abdominal pressure also affects the circulatory system by compressing the inferior vena cava (IVC), the largest vein returning deoxygenated blood to the heart. This compression severely impedes venous return, reducing the volume of blood the heart can pump (cardiac output). The decrease in effective cardiac output can precipitate low-blood-pressure shock, a fatal consequence of mechanical restriction.
Acute Organ Dysfunction and Systemic Collapse
Malignant ascites disrupts fluid balance through “third spacing,” a major driver of systemic collapse. Fluid accumulating in the peritoneal cavity is drawn from the vascular system, reducing the circulating blood volume despite the patient having excess fluid overall. This severe hypovolemia leads to pre-renal acute kidney injury (AKI) because the kidneys receive insufficient blood flow to filter waste products.
The body attempts to compensate for this low volume by over-activating the renin-angiotensin-aldosterone system (RAAS), which signals the kidneys to retain sodium and water, further exacerbating fluid accumulation. This circulatory dysfunction can progress to Hepatorenal Syndrome (HRS), a severe functional failure of the kidneys. HRS involves renal vasoconstriction that shuts down kidney function due to extreme systemic circulatory changes. The resulting failure to excrete toxins and manage electrolytes leads to uremia and metabolic chaos.
Metabolic Depletion and Cancer Cachexia
The physical presence of the ascites fluid initiates chronic metabolic depletion and muscle wasting. The distended abdomen presses against the stomach and intestines, causing early satiety (a sensation of fullness after consuming little food). This physical restriction, combined with nausea and vomiting, significantly reduces nutrient intake and absorption.
The cancer and the chronic inflammatory state drive cancer cachexia, characterized by involuntary loss of skeletal muscle and fat mass. Inflammatory mediators alter the body’s metabolism, causing muscle protein to break down faster than it can be built. This leads to a profound loss of functional reserve and irreversible exhaustion.
Fatal Infectious Complications
The stagnant pool of ascitic fluid is highly susceptible to severe infection, often becoming the final fatal event. The most common complication is Spontaneous Bacterial Peritonitis (SBP), a bacterial infection of the ascitic fluid without a surgically treatable source. Bacteria, typically originating from the gut, can translocate across the intestinal wall and colonize the fluid.
The fluid’s high protein content and the patient’s compromised immune system make it an ideal medium for bacterial growth. SBP rapidly progresses to sepsis, a life-threatening response that causes widespread inflammation and organ damage. Uncontrolled septic shock leads to a precipitous drop in blood pressure and multi-system organ failure, which can be rapidly fatal.