The diagnosis of intestinal obstruction

You will see several patterns of intestinal obstruction. They are determined by how a patient's gut is obstructed, and where it obstructs. Firstly, the obstruction can be simple or strangulated.

(1) Simple obstruction is caused by a mechanical block or ileus, without impairment of the blood supply of the gut. The causes include obstruction by a ball of Ascaris worms, or adhesions. Simple obstruction may resolve spontaneously. Operation is usually not urgent, and may be unnecessary.

An obstructed gut dilates above the obstruction, so that it fills with several litres of fluid and gas. Bacteria grow in this pool of fluid, which becomes faeculent and highly infectious for the peritoneal cavity, should it get there. The patient's dilated gut makes his abdomen swell. Initially, the peristaltic activity of his dilating gut increases to overcome the obstruction. This causes rushes of hyperperistaltic bowel sounds, or high-pitched tinkling sounds, or both, which you can hear if you listen to his abdomen. Later, as ileus develops, his gut becomes silent. Inadequate fluid intake combined with the loss of fluid, by repeated vomiting, and into the lumen of his gut, depletes his extracellular fluid, so that he becomes dehydrated, hypovolaemic, shocked, and acidotic. An adult secretes 7 litres of gastrointestinal juice in 24 hours, so his fluid loss can be considerable.

(2) Strangulation obstruction occurs when there is is a mechanical block and the blood supply to the gut is impaired. Strangulated hernias and sigmoid volvulus are common causes. About 6 hours after the interruption of its blood supply the gut becomes gangrenous and may perforate. If it perforates into his peritoneal cavity it causes generalized peritonitis which may end in septic shock; if it perforates into a hernial sac the infection may be more localized. He is very ill and will probably die if you don't operate immediately. If you think that peritoneal irritiation might be due to strangulation obstruction operate soon!

Now for the levels at which gut obstructs:

Small gut obstruction produces effects which differ according to the level at which it occurs. The higher the obstruction the earlier and the worse the patient's vomiting, and the greater the threat to his life from electrolyte imbalance[md]but the less his distension. Conversely, the lower the obstruction the greater his distension, the greater his pain, and the later he starts to vomit.

Large gut obstruction follows a slower course. Because there is more gut to dilate, there is more abdominal distension, which may be so severe as to interfere with his breathing by pushing up his diaphragm. To begin with, only his colon dilates, but his ileocaecal valve usually becomes incompetent (two-thirds of patients), and allows the dilatation to progress proximally into his small gut. The symptoms of dehydration are less severe, because his colon can still absorb fluid above the obstruction.

''Closed-loop obstruction' (unusual) is the result of his ileocaecal valve remaining competent. It is a double obstruction which shuts off a loop (D, 10-5). It can occur in volvulus, and in neglected obstruction of the large gut. Dilatation of the closed loop may obstruct its blood supply and cause gangrene and peritonitis.

The common mistakes are: (1) Not spending enough time, both taking his history and sitting beside him watching, palpating, and listening to his abdomen. (2) Forgetting the possibility that obstructed gut may strangulate, even when the signs of peritoneal irritation are minimal, for example when the strangulated gut of an intussusception is inside viable gut. (3) Not making proper use of X-rays. (4) Operating too early, before you have rehydrated him, or too late, after you have allowed his gut to strangulate. (5) Not emptying his stomach and giving magnesium trisilicate before you operate. (7) Doing a complicated operation when a simpler one would have saved his life. (8) Poor surgical technique[md]open his abdomen with care, dissect dense adhesions gently, make anastomoses carefully, and don't soil his peritoneum with the contents of his obstructed gut[md]the organisms inside it are particularly virulent. (9) Not washing out his peritoneal cavity and instilling tetracycline, when you have spilt the contents of his gut into his peritoneal cavity, or he has peritonitis. Not closing his abdomen sufficiently securely to prevent it bursting (9.9, 9.13). (10) Not replacing fluid and electrolytes before he is able to take fluids by mouth.

SITA (8 years) presented with vague abdominal tenderness and few other signs. She was not well, and the only striking sign was a a pulse of 148 per minute. 12 hours were wasted while she was observed, before a laparotomy was done and a metre of gangrenous gut was resected.]] Mrs PATEL presented with abdominal distension, colicky pain, and vomiting. She was examined by a medical assistant who noted pain in her right lower quadrant and a ''lymph node' in her right groin, and diagnosed appendicitis. He rang up the doctor, who came in, made a cursory examination, and proceeded with an appendicectomy, using a ''gridiron' incision. Her appendix was normal. Later, she had to have an emergency operation for a strangulated femoral hernia. LESSONS (1) Strangulation can be difficult to diagnose. Tachycardia is a useful sign. (2) ''When acute abdominal pain presents, one maxim I enjoin, pray do not miss that tiny lump, in one or other groin.'' (Zachary Cope) Fig. 10-6 OBSTRUCTED GUT[md]ONE. A, an erect film showing the multiple fluid levels of small gut obstruction. B, a supine film showing small and large gut shadows, and gas under the diaphragm.

THE DIAGNOSIS [s8]OF INTESTINAL OBSTRUCTION Here are the typical features of a patient with intestinal obstruction[md]they are often atypical. Follow the steps of inspection, palpation, percussion, and auscultation.

HISTORY PAIN differs in large and small gut obstruction.

If his pain is periumbilical and colicky, comes in spasms, builds up to a crescendo, and then tapers off, his small gut is obstructed. Vomiting may relieve it temporarily. Sometimes he has regular pain[md]free periods at intervals of 2 to 5 minutes. This is the classical pain of small gut obstruction. If peristalsis stops, colic stops[md]so its disappearance may be a bad sign.

If his pain is below his umbilicus and comes at intervals of 6 to 10 minutes, his large gut is likely to be obstructed.

If he has no pain, but only ''gurgling and bloating' his obstruction is subacute in his large gut or his distal small gut.

If his pain is severe and continuous, this suggests strangulation obstruction. He may have continuous and colicky pain. For example, he may have continuous pain from a strangulated hernia at a hernial site, and colicky central abdominal pain.

If pain and fever preceded his symptoms of obstruction, suspect that it may be secondary to abdominal sepsis.

VOMITING. The higher his obstruction, the worse this is. If it is high in his small gut, he vomits profusely and frequently; if it is low in his large gut, he may not vomit at all. After about 3 days of complete obstruction, his vomit becomes faeculent. If paralytic ileus develops, it becomes ''effortless'.

CAUTION ! Look at his vomit. If it is faeculent, his large gut or lower small gut are almost certainly obstructed. Vomiting never becomes faeculent if his upper small gut is obstructed.

ABDOMINAL FULLNESS. The more distal his obstruction, the more he swells. If large gut obstruction has come on slowly, he may say that his ''clothes fit tightly'' or that he ''feels filled up with gas''.

CONSTIPATION. If his small gut is obstructed, his colon may take a day or two to empty, after which ''nothing comes''. The absence of flatus confirms the diagnosis. Constipation may be his major concern in a culture where regular bowel movements occur two or three tims a day. Pain may be tolerable, but the absence of a decent bowel movement may not.

PREVIOUS OPERATIONS OR PERITONEAL SEPSIS. Adhesions and bands can follow any operation or septic process in the abdomen. In a woman enquire especially for symptoms suggesting PID (6.6).

THE EXAMINATION [s7]FOR INTESTINAL OBSTRUCTION DISTENSION AND HYPER-RESONANCE. If he has colic and is vomiting, his gut is obstructed until you have proved otherwise. Distension is not an essential part of the clinical picture. The earliest signs of it are a little fullness in his flanks, or an increased resonance to percussion.

If the percussion note over his abdomen is ''tympanitic', he has distended gas-filled loops of gut, and is obstructed.

If distension is conspicuous and other signs are minimal, suspect large gut obstruction. If it is extreme, suspect sigmoid volvulus.

If you are not sure if his distension is caused by gut obstruction or ascites, examine him for shifting dullness. Remember that fluid and gas in a distended gut can cause shifting dullness, but that it is less obvious than with ascites.

If you are not sure if he is distended or not, measure his girth at some fixed place, and see if it increases.

OBSTRUCTIVE GUT SOUNDS. Listen for these at any time he appears to be in pain, while you are taking his history. This is essential if you are going to pick up the critical sign of intestinal obstruction[md]the half minute during which peristaltic waves make a ladder pattern on his abdominal wall, accompanied by a rush of high pitched tinkles and splashes. If you miss this opportunity it may not return for 15 minutes. So, if he loses interest in the conversation, and grimaces with pain[md]listen quickly. If you hear: (1) runs of borborygmi, or (2) a chorus of tinkling high-pitched musical sounds at the same time that he grimaces with colic, he is almost certainly obstructed. These are very useful early signs. Don't mistake them for: (1) the peristaltic rushes of gastroenteritis, or (2) normal hyperactive bowel sounds.

VISIBLE PERISTALSIS. If he is thin, look for waves of peristalsis passing across his abdomen. If he is very thin this may be normal, especially in a young child.

A TENDER MASS AT ONE OF HIS HERNIAL ORIFICES. Examine his inguinal and femoral canals. If you find a painful tender mass, he has an incarcerated or strangulated hernia.

CAUTION ! (1) You can easily miss a strangulated femoral hernia[md]it may not be tender or painful[md]see the story of Mrs Patel, above. (2) Rarely, a hernia becomes reduced ''en masse' (14.1), so that there is no mass, tender or otherwise.

ABDOMINAL TENDERNESS is not a prominent feature of uncomplicated obstruction. Obvious tenderness over part of the abdomen suggests strangulation.

AN OLD LAPAROTOMY SCAR suggests that the cause of an obstruction may well be a band, an adhesion, or an area of stenosis.

A PALPABLE ABDOMINAL MASS is unusual, apart from a mass at a hernial orifice. Feel carefully, here are some of the masses you might find.

If, in a child, you feel an ill-defined mobile mass (or masses), usually in his umbilical region, sometimes in his iliac fossae, it is probably a mass of Ascaris worms.

If you feel an ill defined lump or lumps in a patient's right lower quadrant, he may have ileocaecal tuberculosis. You may also feel more central lumps caused by caseating tuberculous lymph nodes.

If he has a large, slightly tender, mobile abdominal mass, some of his gut may have infarcted due to torsion or intussusception.

If his mass changes its position from one day to another, and is accompanied by colicky pain, he probably has recurrent intussusception or a mass of Ascaris worms.

If he has a tender indurated mass, suspect that his obstruction is due to an intraperitoneal abscess (6.3).

If you feel hard impacted masses in his colon and rectally, they are masses of faeces, and may be causing his obstruction (not uncommon in the old and debilitated).

If he has one or more masses and also ascites, and is thin and debilitated, he probably has disseminated carcinoma.

RECTAL EXAMINATION must not be forgotten!

If you find fresh blood and mucus on your finger, or he passes these, he probably has a strangulating lesion higher up, or carcinoma of his large gut, or an intussusception. Occasionally, you may feel its tip.

If you feel a hard mass of faeces, suspect that constipation may be causing his obstruction.

If his rectum is empty and even ''ballooned', this is an additional sign of intestinal obstruction, but the reason for it is not clear.

If there is a tense, feeling in his pelvis, as you feel through his rectal wall, it may be caused by tense loops of obstructed gut.

If you feel a tense tender, possibly fluctuant mass bulging into the pouch of Douglas, it is probably a pelvic abscess. You may feel it more easily bimanually, with your other hand exerting pressure suprapubically (6.5).

If you find a hard mass in the rectovesical pouch (a ''rectal shelf'), it is probably malignant. Tumour deposits here may be well-defined hard lumps, or a ''shelf' caused by tumour growing into the surrounding tissue.

HAS HIS GUT STRANGULATED? You may not be certain about this until you do a laparotomy. Strangulation is easy to diagnose when it is advanced, unless it is so advanced that he is in septic shock. Try to diagnose it early. Individually, the features below are not diagnostic, but his gut has probably strangulated if he shows several of them.

(1) The sudden onset of symptoms.

(2) Severe continuous pain. This is the result of irritation of his parietal peritoneum. If he is fairly comfortable and pain- free between waves of hyperperistalsis, his gut is probably not strangulated, but only obstructed (unless it is sealed off in a hernial sac or is an intussusception).

(3) A fast pulse. This is perhaps the most reliable sign; if his pulse is only 88, he is unlikely to have strangulated his gut.

(4) Fever. Simple obstruction does not cause fever. If he is febrile, suspect strangulation, or sepsis.

(5) A low or falling blood pressure.

(6) Localized tenderness, or rebound tenderness. This is a sign of peritoneal irritation, and can be caused by inflammation, blood in the peritoneal cavity, or strangulation. Tenderness may be masked by loops of normal gut over the strangulated area, so its absence is not significant.

(7) The passage of blood or blood and mucus rectally. This is typical of intussusception, but you may see it whenever the blood supply of the gut is impaired.

(8) Signs of peritonitis, (tenderness, guarding, and absent bowel sounds), prostration, and shock are late signs.

Fig. 10-7 OBSTRUCTED GUT[md]TW0. Patient A has distended loops of small gut. Note the different patterns of his jejunum and ileum, The jejunum has ''valvulae conniventes' (transverse bands across it), whereas the ileum is more featureless. His caecum and ascending colon are distended, but there are no signs of his transverse colon or rectum. A barium enema showed a carcinoma just beyond his splenic flexure.

Patient B's large gut is distended down to his sigmoid colon, but he has no rectal bubble. This is typical of distal large gut obstruction; he had a carcinoma of his sigmoid colon. These are supine films, so there are no fluid levels, but the valvulae and haustra are shown well.

X-RAYS [s7]IN INTESTINAL OBSTRUCTION Take films while he is erect and supine. They can usually tell you: (1) That he is obstructed. (2) The site of the obstruction. (3) Its severity. (4) Sometimes its cause, for example, intussusception. See also 10.1.

While he is lying down, take a supine AP film. If he is not well enough to sit up by himself, support him in the sitting position while you take an erect film. This will be more useful than the alternative, which is a lateral decubitus film, taken from the side while he is lying down. Its purpose is to show fluid levels, and gas under his diaphragm.

CAUTION ! Never give contrast media by mouth in intestinal obstruction. A barium enema is occasionally useful in communities where carcinoma of the colon is common, but is seldom needed in the developing world.

When you examine the films, first see if the patient has a distended large gut shadow, and especially a caecal shadow. If he has, his large gut is obstructed. To distinguish large and small gut shadows, remember that: (1) Fine folds or partitions, (valvulae conniventes) extend right across a distended jejunum which is more central in the abdomen. (2) The ileum has no folds distally, and few proximally. (3) His caecum is a rounded mass of gas. (4) The haustral markings of obstructed large gut are rounded and much further apart than the valvulae conniventes of the jejunum, and do not cross its full diameter. The large gut is more peripheral in the abdomen, whereas the small gut is more central.

Gas in his peritoneum, is the only certain sign of gangrene and perforation. You may see it under his diaphragm in an erect chest film, and under his abdominal wall in a lateral supine one.

Gas in the small gut is always abnormal, except: (1) in the duodenal cap, (2) in the terminal ileum (rare), (3) in children under 2 years.

Fluid levels in the small gut, are always abnormal except where gas is normal (see just above). Elsewhere, fluid levels in the small gut indicate: (1) mechanical obstruction, (2) ileus, or (3) gastroenteritis. Look for them in erect films. The larger and more numerous they are, the lower and the more advanced the obstruction.

Gas in the large gut is normal.

Fluid levels in the large gut: (1) may be normal (if there are only a few), or (2) may be caused by gastroenteritis. If the large gut is also distended there is: (1) a mechanical obstruction, (2) ileus, or (3) some other cause for the dilatation, such as amoebic colitis.

CAUTION ! The gas shadows may be far away from the site of the obstruction.

If the films show distended loops of large and small gut irregularly distributed with gas in his rectum, suspect ileus.

If he has no gas shadow in his caecum (which normally contains some gas), suspect that his small gut is obstructed.

If he has a large caecal shadow (which may be huge), his large gut is obstructed. As the pressure builds up, his small gut often starts to distend, because his ileocaecal valve is incompetent (2/3rds of patients).

If you see a really massive gas shadow, his stomach may be dilated, or he may have volvulus of his sigmoid (common, 10.10) or of his caecum and ascending colon (rare, 10.11).

If there is a gas shadow in his rectum and rectal examination is normal clinically, he is unlikely to be obstructed.

If his large gut is relatively empty, and the fluid levels in his erect film pass obliquely upwards from his right iliac fossa to his left hypochondrium, like a stepladder, they suggest volvulus of his small gut (rare but characteristic).

If signs are uncertain, take more films a few hours later.

OTHER INVESTIGATIONS A high haemoglobin or haematocrit are some indication of the severity of his dehydration.

DIFFICULTIES [s7]IN DIAGNOSING INTESTINAL OBSTRUCTION If he has EXCRUCIATING ABDOMINAL PAIN, MASSIVE ABDOMINAL DISTENSION, and CIRCULATORY COLLAPSE, the possibilities include: (1) Volvulus of his sigmoid with gangrene. (2) Volvulus of his sigmoid with secondary volvulus of his small gut (compound volvulus 10-17). (3) Volvulus of his small gut. (4) Perforation of a peptic ulcer presenting late. (5) Generalized peritonitis leading to ileus. (6) Typhoid fever with perforation. (7) Acute pancreatitis. You may not be able to diagnose which of these he has until you operate. He needs rapid resuscitation and urgent surgery, but try to exclude pancreatitis first.

If he has OBVIOUS ABDOMINAL SIGNS, BUT LOOKS COMPARATIVELY WELL, (because he has not been vomiting), suspect large gut or incomplete small gut obstruction.

If he presents with a HISTORY OF SEVERAL DAYS OF FEVER, anorexia and localized abdominal pain, followed by colicky pain and the other symptoms of obstruction, suspect that obstruction has followed intraperitoneal sepsis. Distension may mask the abdominal findings, but you may be able to elicit deep tenderness and induration in his right lower quadrant, suprapubically, rectally, or, in a woman, vaginally.

If he is DISTENDED AND VOMITS but does NOT HAVE THE TYPICAL COLICKY PAIN of obstruction, suspect ileus rather than obstruction, especially if he is toxic and dehydrated. Obstruction appears spontaneously, whereas ileus usually follows some good reason for it, such as local or general peritonitis, a previous operation, or an intraperitoneal injury or haemorrhage.

If he has the other SIGNS OF OBSTRUCTION, but PASSES LOOSE STOOLS with or without flatus, he may have: (1) An incomplete large gut obstruction. (2) A pelvic abscess. (3) A Richter's hernia[md]part of the circumference of his gut may be trapped in a tight inguinal ring, leaving enough lumen for its contents to pass through and cause diarrhoea (14.1).

If SIGNS OF OBSTRUCTION DEVELOP AFTER SURGERY, you will find it difficult to know if his obstruction is mechanical or due to the paralysis caused by ileus[md]see Section 10.13.

The general method is continued in the next section.