Intestinal obstruction refers to any condition that causes a blockage in the passage of intestinal contents. It is one of the common surgical acute abdominal emergencies. Intestinal obstruction not only causes morphological and functional changes in the intestines but can also lead to a series of systemic pathophysiological alterations, which can become life-threatening in severe cases.

Etiology and Classification

Classification by Cause of Obstruction

Mechanical Intestinal Obstruction

This is the most common type in clinical settings, caused by various factors leading to narrowing or blockage of the intestinal lumen, which prevents the passage of intestinal contents. Common causes include:

Extramural factors, such as adhesions compressing the intestine, incarcerated hernias, or tumors exerting pressure.
Intramural factors, such as intussusception, inflammatory strictures, tumors, or congenital anomalies.
Intraluminal factors, such as obstruction caused by roundworms, foreign bodies, or fecal impaction.

Functional Intestinal Obstruction

Subdivided into paralytic and spastic types, this results from neuromuscular inhibition or toxic stimulation that disrupts intestinal motility, causing either loss of peristalsis or intestinal spasm without organic narrowing of the lumen. Paralytic obstruction is more common and often occurs after abdominal surgery, abdominal trauma, or diffuse peritonitis. Spastic obstruction is less frequent and may be observed in conditions such as acute enteritis, intestinal dysfunction, or chronic lead poisoning.

Vascular Intestinal Obstruction

This arises from compromised intestinal blood flow due to embolism or thrombosis of the mesenteric vessels, resulting in loss of intestinal motility. Although the intestinal lumen itself remains patent, contents cease to move, and thus, it is categorized as a form of functional obstruction. However, vascular obstruction can rapidly lead to intestinal necrosis, making its management distinctly different.

Classification Based on Impairment of Blood Supply in the Intestinal Wall

Simple Obstruction

This type involves blockage of intestinal contents without impairment of intestinal blood supply.

Strangulated Obstruction

This is caused by compression, embolism, or thrombosis of mesenteric or small intestinal blood vessels, leading to impaired blood supply to the affected segment. Complications can include intestinal necrosis and perforation.

Classification by Location of Obstruction

Obstruction can be categorized as high (jejunal), low small intestinal (ileal), or colonic. When obstruction occurs in the colon, the ileocecal valve prevents reflux from the colon back into the small intestine, creating a "closed-loop obstruction." Any situation where both ends of an intestinal loop are completely blocked, such as volvulus, constitutes a closed-loop obstruction.

Classification by Degree of Obstruction

Obstructions can be classified as complete or incomplete. Based on the speed of disease progression, they can further be divided into acute and chronic intestinal obstruction. Chronic incomplete obstruction typically represents simple obstruction, while acute complete obstruction often corresponds to strangulated obstruction.

The above categories may transform into one another during the disease course. Simple obstruction, if untreated, can evolve into strangulated obstruction. Prolonged mechanical obstruction can cause overdistension of the intestine proximal to the obstruction, which may present clinically as paralytic obstruction. Chronic incomplete obstruction can transition to acute complete obstruction due to inflammatory edema.

Pathology and Pathophysiology

Local Changes

Once mechanical intestinal obstruction occurs, peristalsis increases proximal to the obstruction, with gas and fluid accumulating in the intestinal lumen, leading to distension. Lower obstructions and prolonged duration result in more significant intestinal distension. Distal to the obstruction, the intestinal segment appears collapsed, empty, or contains only small amounts of feces. The junction between the dilated and collapsed intestinal loops represents the obstruction site, which is critical for identifying the obstruction during surgery. Increased intraluminal pressure may disrupt venous return in the intestinal wall, causing congestion, edema, and fluid leakage. Additionally, intestinal wall and capillary permeability increase, leading to petechial hemorrhages on the intestinal wall and blood-stained exudate in the intestinal lumen and the peritoneal cavity. In cases of closed-loop obstruction, intraluminal pressure may rise to even higher levels. Translocation of intestinal contents and bacteria into the peritoneal cavity may induce peritonitis. Eventually, intestinal segments may undergo ischemia, necrosis, and perforation.

Systemic Changes

Water, Electrolyte, and Acid-Base Imbalances

During intestinal obstruction, fluids secreted by the gastrointestinal tract are not reabsorbed into systemic circulation and instead accumulate in the intestinal lumen. The intestinal wall also continues to exude fluid into the lumen, leading to fluid loss into the third space. High-level intestinal obstruction often results in dehydration because of the inability to eat combined with frequent vomiting. Significant losses of gastric acid and chloride ions can result in metabolic alkalosis. Low-level intestinal obstruction often involves loss of alkaline digestive fluids, reduced tissue perfusion, and increased production of acidic metabolic byproducts, leading to severe metabolic acidosis.

Decreased Blood Volume

Intestinal distension may affect venous return from the intestinal wall, while significant plasma exudate leaks into the intestinal lumen and peritoneal cavity. In cases of intestinal strangulation, additional losses of plasma and blood are more likely. Protein breakdown is heightened during intestinal obstruction as hepatic protein synthesis capacity declines, exacerbating decreases in plasma protein levels and blood volume.

Shock

Severe dehydration, reduced blood volume, electrolyte imbalances, acid-base disturbances, bacterial infections, and toxicity may lead to shock. When intestinal necrosis, perforation, and peritonitis occur, systemic toxicity tends to become even more severe. Such conditions can ultimately result in severe hypovolemic and toxic shock.

Respiratory and Cardiovascular Dysfunction

Intestinal distension can raise intra-abdominal pressure, causing the diaphragm to elevate and impair pulmonary gas exchange. Abdominal distension and pain may weaken diaphragmatic breathing. Elevated abdominal pressure and reduced blood volume may also hinder venous return to the inferior vena cava, reducing cardiac output and contributing to respiratory and circulatory dysfunction.

Clinical Presentation

Although the clinical manifestations of intestinal obstruction vary depending on the underlying cause, the common feature remains the inability of intestinal contents to pass smoothly through the lumen. Shared symptoms include abdominal pain, vomiting, abdominal distension, and cessation of flatus or bowel movements.

Symptoms

Abdominal Pain

In mechanical intestinal obstruction, the vigorous peristalsis of intestinal segments above the obstruction may trigger abdominal pain. This pain typically manifests as colicky and intermittent in nature. As the intestinal muscles become fatigued, a temporary state of muscle relaxation may occur, during which the pain subsides. Mechanically induced abdominal pain is therefore characterized as paroxysmal colicky pain. During episodes of pain, hyperactive bowel sounds also appear. When gas and fluid accumulate, bowel sounds may resemble gurgling water or high-pitched metallic tones. Patients often report a sensation of gas moving within the intestines but becoming blocked at a specific site, and visible intestinal loops or peristaltic waves may sometimes be observed. If intervals between episodes shorten and pain becomes persistent and severe, strangulated obstruction should be considered. Paralytic intestinal obstruction, in contrast, involves a lack of peristaltic contractions as the intestinal wall becomes paralyzed. As a result, colicky pain is absent, being replaced instead by continuous distension or discomfort. On auscultation, bowel sounds are diminished or absent.

Vomiting

Vomiting is an early symptom of high-level intestinal obstruction and occurs frequently. The vomitus primarily contains gastric and duodenal contents. In low-level small intestinal obstruction, vomiting occurs later. Initially, the vomitus consists of gastric contents, but in later stages, it contains intestinal contents that have undergone fermentation and putrefaction, taking on a feculent odor. Vomitus may appear brownish or blood-tinged, which can suggest impaired intestinal blood circulation. Vomiting tends to be regurgitative in paralytic intestinal obstruction.

Abdominal Distension

Abdominal distension typically follows pain, and its severity depends on the location of the obstruction. In high-level obstruction, distension may be mild but may sometimes reveal a visible gastric outline. In low-level small intestinal obstruction and paralytic obstruction, distension is more pronounced and generalized. In patients with thinner abdominal walls, distended intestinal loops may be visible as intestinal patterns. In cases of colonic obstruction with a competent ileocecal valve, the intestinal loops above the obstruction may form a closed loop, leading to particularly pronounced abdominal distension. Asymmetrical and uneven abdominal swelling may occur in cases of volvulus or other closed-loop obstructions.

Cessation of Flatus and Bowel Movements

Complete obstruction prevents the passage of intestinal contents beyond the obstruction site, leaving the distal bowel empty. Clinically, this presents as cessation of flatus and bowel movements. However, in the early stages, particularly in high-level obstruction, gas and fecal matter that have accumulated distal to the obstruction may still be expelled. This transient evacuation should not result in misdiagnosis as a non-obstructive or incomplete obstruction. Certain forms of strangulated obstruction, such as intussusception or mesenteric vascular thrombosis, may lead to the passage of bloody, mucus-like stools.

Physical Signs

Systemic conditions in the early stages of simple intestinal obstruction usually show no significant changes. In later stages, due to vomiting, dehydration, and electrolyte imbalances, symptoms such as dry lips, parched tongue, sunken eyes, reduced skin elasticity, and weak pulse may occur. Patients with strangulated intestinal obstruction may present with systemic toxic symptoms and signs of shock.

Abdominal Inspection

Mechanical intestinal obstruction often reveals visible intestinal loops and peristaltic waves. In cases of volvulus, abdominal distention may appear asymmetrical, whereas in paralytic intestinal obstruction, the abdominal distention is generally uniform.

Palpation

In simple intestinal obstruction, mild tenderness may occur due to intestinal distension but without signs of peritoneal irritation. In strangulated intestinal obstruction, fixed tenderness and peritoneal irritation may be present, with palpable tender masses often indicating strangulated intestinal loops.

Percussion

Strangulated intestinal obstruction with intra-abdominal fluid accumulation may show positive shifting dullness.

Auscultation

Bowel sounds are hyperactive, with water splashing or metallic sounds, in cases of mechanical intestinal obstruction. In paralytic intestinal obstruction, bowel sounds are reduced or absent.

Auxiliary Examinations

Laboratory Tests

Early changes in simple intestinal obstruction are often not evident. With disease progression, dehydration and blood concentration may lead to increased white blood cell count, hemoglobin, and hematocrit levels, as well as elevated urine specific gravity. Blood gas analysis and measurement of serum Na+, K+, Cl-, blood urea nitrogen, and creatinine levels may provide insights into acid-base imbalances, electrolyte disturbances, and renal function. The presence of numerous red blood cells or a positive fecal occult blood test in vomitus or stool suggests potential compromise of intestinal blood supply.

X-ray Examination

Within 4–6 hours after the onset of intestinal obstruction, X-rays typically reveal gas accumulation in the intestinal lumen. Imaging may show distended bowel loops and air-fluid levels. The characteristics of the X-ray findings vary with the location of the obstruction. Jejunal mucosal circular folds may appear as "fishbone-like" structures when the loops are filled with gas. Dilated ileal loops often display step-like air-fluid levels. Colonic distension is typically peripheral, showing haustral patterns. For suspected cases of intussusception, volvulus, or colonic tumors, barium enema X-rays or CT scans can aid in diagnosis.

Diagnosis

Diagnosis involves determining whether intestinal obstruction is present, identifying the type and nature of the obstruction, and clarifying the location and cause. These steps are essential for the accurate diagnosis of intestinal obstruction.

Presence of Intestinal Obstruction

Abdominal pain, vomiting, abdominal distension, cessation of flatus and bowel movements, visible intestinal loops or peristaltic waves, and hyperactive bowel sounds usually provide sufficient evidence for diagnosis. Nonetheless, some patients may not fully exhibit these typical signs, especially during the early stages of certain strangulated intestinal obstructions, which can be confused with conditions such as acute gastroenteritis, acute pancreatitis, or ureteral stones. Medical history, a detailed abdominal examination, laboratory tests, and X-rays play an important role in such cases.

Mechanical versus Functional Obstruction

Mechanical intestinal obstruction is characterized by the typical clinical manifestations mentioned earlier, with abdominal distension being initially mild. Paralytic intestinal obstruction, on the other hand, lacks symptoms such as paroxysmal colicky pain associated with heightened peristalsis. Instead, it is marked by weakened or absent intestinal activity, significant abdominal distension, and diminished or absent bowel sounds. Abdominal X-rays and CT scans are particularly useful for differentiation. Paralytic intestinal obstruction shows gaseous distension across both the small and large intestines, while in mechanical obstruction, distension is confined to the bowel loops proximal to the obstruction.

Simple or Strangulated Obstruction

This distinction is critical for determining treatment methods and predicting patient outcomes. The following findings suggest the possibility of strangulated intestinal obstruction, warranting timely surgical intervention:

Abrupt onset of abdominal pain that is severe and persistent from the beginning, or continuous pain during the intervals between exacerbations of colicky pain. In some cases, back and flank pain may occur.
Rapid progression of symptoms, with early signs of shock that do not improve significantly with anti-shock therapy.
Signs of peritonitis, including fever, increased heart rate, and elevated white blood cell count.
Asymmetrical abdominal distension, localized swelling, or the presence of a tender mass (isolated dilated intestinal loops).
Early and frequent vomiting with blood-stained gastric contents, blood-stained evacuated liquid from gastrointestinal decompression, or blood-stained rectal discharge.
X-rays revealing isolated, dilated intestinal loops.
Lack of improvement in symptoms and signs after aggressive non-surgical treatment.

High or Low Obstruction

High-level small intestinal obstruction causes early and frequent vomiting with mild abdominal distension. Low-level small intestinal obstruction is associated with significant abdominal distension, delayed and less frequent vomiting, and possible fecal-like vomitus. Colonic obstruction presents similar clinical manifestations to low-level small intestinal obstruction. X-rays assist in differentiation: Low-level small intestinal obstruction shows dilated loops in the central abdomen arranged in a "step-ladder" pattern, while colonic obstruction reveals dilated loops distributed peripherally with visible haustrations. In colonic obstruction, gas shadows in the colon end abruptly at the site of the obstruction, with cecal distension being most pronounced.

Complete or Incomplete Obstruction

Complete obstruction features frequent vomiting, pronounced abdominal distension, and cessation of fecal and gas passage. X-rays show marked gaseous distension in the bowel proximal to the obstruction, with no air in the colon distal to the obstruction. Incomplete obstruction has less severe vomiting and abdominal distension, with milder gaseous distension visible on X-rays and the possible presence of gas in the colon.

Etiology of the Obstruction

Clinical presentation, patient age, history, physical signs, and imaging results guide the identification of the obstruction's cause. Adhesive intestinal obstruction is the most common type, frequently occurring in patients with prior abdominal surgery, trauma, or inflammatory conditions. Incarcerated or strangulated external hernias are also common causes. Congenital intestinal anomalies are predominant in newborns, while intussusception is more frequent in children under two years old. Ascaris-related obstruction commonly affects children, whereas tumors and fecal impaction are more frequent causes in elderly individuals.

Treatment

The principles of treatment for intestinal obstruction involve addressing the systemic physiological disturbances caused by the obstruction and resolving the obstruction itself. The choice of treatment methods depends on the cause, nature, location of the obstruction, as well as the patient's general condition and the severity of the disease.

Non-Surgical Treatment

Gastrointestinal Decompression

This is one of the primary measures for treating intestinal obstruction. It aims to reduce the accumulation of gas and fluid in the gastrointestinal tract, alleviate intestinal distension, promote the recovery of intestinal blood circulation, and reduce intestinal wall edema. This may help relieve complete obstructions caused by localized edema of the intestinal wall or facilitate the reduction of some mildly twisted intestinal loops. It can also help lower intra-abdominal pressure, improving respiratory and circulatory function impacted by elevated diaphragmatic positioning. For low-level intestinal obstruction, longer small bowel decompression tubes may be utilized.

Correction of Water, Electrolyte, and Acid-Base Imbalances

These represent the most significant physiological disturbances in intestinal obstruction and should be corrected as soon as possible. Before biochemical test results are available, balanced saline solutions should be administered initially. Once laboratory results are available, electrolytes can be adjusted, and acid-base imbalances corrected accordingly. During fluid resuscitation, urine output should be monitored, and central venous pressure may be measured if necessary. In the late stages of simple intestinal obstruction or in strangulated obstruction, significant plasma and blood may leak into the intestinal and peritoneal cavities, necessitating the replacement of plasma and whole blood.

Infection Prevention and Management

Intestinal obstruction may lead to impaired intestinal blood circulation and compromised intestinal mucosal barrier function, resulting in bacterial translocation or direct bacterial penetration through the intestinal wall into the peritoneal cavity, causing infection. Furthermore, elevated diaphragmatic positioning may impair pulmonary gas exchange and secretion clearance, increasing the risk of pulmonary infection.

Other Treatments

Severe abdominal distension may compromise pulmonary function, making oxygen supplementation beneficial for such patients. To reduce gastrointestinal distension, somatostatin may be administered to decrease the secretion of gastrointestinal fluids. The use of analgesics should follow the principles of acute abdominal pain management.

Surgical Treatment

Surgery plays a critical role in the management of intestinal obstruction. The goal of surgical treatment is to resolve the obstruction and address the underlying cause. The surgical approach should be tailored to the patient’s general condition, as well as the cause, nature, and location of the obstruction.

Surgical Procedures to Relieve the Obstruction Alone

These include adhesiolysis, enterotomy to remove intestinal stones or ascaris, reduction of intussusception or volvulus, and similar procedures.

Enterectomy and Anastomosis

When the intestinal segment is affected by tumors, inflammatory strictures, or ischemic necrosis of localized bowel loops, resection of the affected intestine followed by anastomosis is necessary.

For strangulated intestinal obstruction, efforts should be made to relieve the obstruction and restore blood circulation to the intestines before intestinal necrosis occurs. Indicators of non-viable intestines include:

A purple-black and collapsed intestinal wall.
Loss of tension and peristaltic ability, with no contraction in response to stimulation.
Absence of pulsation in terminal branches of the corresponding mesenteric arteries.

Intraoperative determination of intestinal viability can be challenging. When it is uncertain whether small segments of bowel loops have compromised blood flow, resection may be a safer option. However, indiscriminate resection of longer bowel segments, particularly in cases such as total small bowel volvulus, would severely affect the patient's future survival. In such situations, rehydration and oxygen replenishment should be prioritized, and warm saline compresses or the injection of 1% procaine or phentolamine into the root of the mesenteric vessels may be employed to relieve vascular spasms. Viability should be reassessed after 15–30 minutes of observation. If there remains uncertainty, the intestines may be temporarily returned to the abdominal cavity with the abdomen partially closed, and close monitoring should continue. A second-look procedure within 24 hours can be performed to definitively determine viability and, if necessary, proceed with resection.

Intestinal Bypass Anastomosis

When resection of the obstructed segment is deemed difficult, intestinal bypass may be performed to relieve the obstruction. This involves connecting the intestinal segments proximal and distal to the obstruction while bypassing the affected region. Care should be taken not to leave excessively long bypassed segments, particularly the proximal segment, to avoid complications such as blind loop syndrome.

Enterostomy or Exteriorization

For patients with complex lesions at the site of obstruction or severely compromised general conditions that preclude complex surgical procedures, enterostomy or exteriorization of the intestine may be performed to relieve the obstruction. This involves creating a stoma in the proximal intestinal segment to decompress the bowel and resolve the physiological disturbances caused by profound intestinal distension. This approach is particularly suitable for low-level obstructions, such as acute colonic obstruction. In cases where intestinal necrosis or tumors are present, the necrotic or tumor-bearing segments can be resected, and the two bowel ends can be exteriorized through stomas. A subsequent staged procedure can be performed to restore bowel continuity at a later time.