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[病例讨论] 小肠梗阻

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发表于 2019-9-10 10:33:19 | 显示全部楼层 |阅读模式
从克利夫顿悬索桥跳出比遭受急性肠梗阻和下降手术更不危险。 (Fredrick Treves,1853-1923)

到目前为止,小肠梗阻(SBO)的最常见原因是术后粘连和疝气。其他较不常见的机械病因是推注阻塞(例如牛黄),恶性或炎性(例如克罗恩病)原因或肠套叠。引起SBO的疝气在第22节讨论;术后早期小肠梗阻(EPSBO)和麻痹性肠梗阻在>章节48中讨论。在>第31节讨论了减肥腹部手术后SBO的发展。这里提到了腹部,肠套叠,癌症患者的SBO。 ,放射性肠炎和胆结石肠梗阻。在>章节37.1中提到了腹膜结核作为SBO的原因。然而,本章的大部分内容都专注于粘合剂SBO。

威廉·奥斯勒爵士(Sir William Osler,1849-1919)过去常说“肠粘连是诊断贫困的避难所”,但问题的真相是,医学上由外科医生制造的粘连导致超过三分之二的粘连。阻碍事件,无论确切的机制是什么。请注意,在这个腹腔镜手术的时代,一些患者可能不会自愿参加以前的手术史,并且当先前的手术一直是腹腔镜输卵管结扎术时,腹部瘢痕通常几乎看不见。 Banal-yes,但它可能留下一个“带”粘连导致完整的SBO。还要记住,上腹部,上睑下,手术与小肠粘连相关的可能性要小于粘连。最后,由于您不是内科医生,我们几乎不需要提醒您,粘连几乎从未(从未在手术中说过)导致结肠梗阻。

困境

大多数粘连SBO患者(至少有一半,如果不是更多)对保守(非手术)治疗有反应。但是,坚持SBO的保守治疗可能会延迟对受损(绞窄)肠道的识别,从而导致预后不良。显然,您面临的挑战是解决以下问题:

哪些患者需要进行紧急剖腹手术治疗即将发生或已确定的肠绞窄?什么时候开始,保守治疗适当和安全?

一旦实施,在认为有必要进行手术之前,保守治疗需要持续多长时间?换句话说,如何在不冒肠道妥协的情况下避免手术?

所有外科医生都承认,表明肠道可能受损的症状和体征需要立即手术。然而,世界各地的外科医生倾向于在宣布失败之前提供关于非手术治疗持续时间的广泛意见。有些人仍然传播过时的格言“永远不要让太阳落山或上升过肠道阻塞”,而其他人则坚持避免看似永远的手术。

我们的目标是为您提供回答这些问题的指南,并帮助您开发常识性方法。首先,我们需要澄清一些术语。

定义

“简单”阻塞:肠被阻塞,压缩或扭结,但其血管供应不受威胁。

绞窄阻塞:对受阻肠段的血管供应受到损害。

闭环阻塞:在近端和远端点阻塞一段肠。通常,涉及的肠是绞窄的。

理解术语部分阻塞与完全阻塞对于治疗计划至关重要。一些外科医生提供基于症状的定义,这是众所周知的不准确的。对我们来说,区分局部和完全SBO的最佳方法是放射学,从不起眼的腹部平片X射线开始(参见>章节5)

部分阻塞:除了小肠扩张和液体水平外,结肠中还有气体。

完全阻塞:结肠内未见气体。

部分SBO的大多数发作将在没有手术的情况下解决,而大多数患有完全阻塞的患者将需要一个。


图21.1.“我怀疑这是肠梗阻...”

临床特征(>图21.1)

SBO的三个重要临床表现是绞痛腹痛,呕吐和腹胀。便秘和没有肠胃气胀是SBO相对较晚的症状。这些特征的模式取决于障碍的部位,原因和持续时间。例如,在高阻塞时,呕吐是显着的,而疼痛和扩张是不存在或轻微的;随着阻塞程度的下降,痉挛性疼痛变得更加明显。在远端SBO中,扩张是一种突出的症状,随后出现呕吐。多汁性呕吐是长期,远端,完全SBO的标志,并且是梗阻附近的大量细菌过度生长的特征(记住:粪便的主要部分是由细菌构成)。这是一个不好的预后信号:鼻胃管(NG)吸出越厚,越臭,阻塞物自发消退的可能性就越小。当我们看到对不起,来自NG管的粪便时,我们开始准备患者进行手术!

在仰卧和直立的腹部X射线上看到的基本射线照相特征是在阻塞物附近的肠的气体膨胀,液体水平的存在,并且在完全SBO中,在阻塞物远端没有气体。平行条纹(由valvulae conniventes引起)横向流过管腔,是扩张小肠的特征。结肠气体阴影缺乏这种模式。 (另见>第4章和第5章。)

有绞窄吗?

是否存在绞窄是至关重要的。如果答案是“是”,则不仅是强制操作,而且还需要及时执行。勒死最重要的特征是持续疼痛。可能存在腹膜刺激(保护,反跳痛)的迹象,但请记住:

死肠可以存在于相对“无辜”的腹部。

腹膜刺激的迹象很少用于区分“简单”阻塞和绞窄,因为当扩张严重时,它们也可能在“简单”SBO中发现。肠的扩张环是柔软的;你肯定已经看到内科医生积极地向患有胃肠炎的患者进行扩张性呕吐和诊断“腹膜炎”吗?

Closed-loop obstruction always equals strangulation. Here, a loop of bowel is twisted (volvulus), and its blood supply is compromised. Plain abdominal X-ray is commonly misleading in this situation. The intestine above the twisted loop may be full of fluid and thus appears opaque; all one sees is a single dilated loop of bowel (but CT would be diagnostic; see below). Patients with this type of obstruction tend to cry out in pain—like a siren.

Remember: no isolated clinical feature or laboratory finding can tell you if the intestine is strangulating or dead. Only fools let themselves be guided by isolated lactic acid levels. Do not wait for fever, leukocytosis, or acidosis to diagnose isch-emic bowel because when all these systemic signs are present, the intestine is already dead!

Having diagnosed strangulation, you will be congratulated for having expedi-tiously resuscitated and wheeled your patient to the operating room. Save yourself the embarrassment of explaining, the next day, the presence of the long midline inci-sion to deal with a knuckle of ischemic gut trapped in the groin. Never forget that a common cause of strangulated bowel is an external hernia! The suspicion of strangu-lation must make you examine, or rather re-examine more carefully, the five external hernial orifices: two inguinal, two femoral, and one umbilical (> 章节 22).

By now, you understand that nothing, nothing can accurately distinguish between simple and strangulating SBO. So, how do you play it safe?

Management

Fluid and Electrolytes

There is hardly a need to remind you that SBO results in significant losses, or sequestration, of extracellular fluid and electrolytes (into the lumen of the bowel, within its edematous wall, and as the obstruction progresses, into the peri-toneal cavity), which have to be replaced intravenously. The aggressiveness of fluid management and hemodynamic monitoring depends on the condition of the individual patient. The fluid of choice is Ringer’s lactate. The charting of urine output in a catheterized patient is the minimal monitoring necessary. Even patients scheduled for urgent laparotomy for strangulation require adequate pre-operative resuscitation (> 章节 6). Patients with SBO sometimes have intra-abdominal hypertension (we have seen patients with distal SBO presenting with full-blown abdominal compartment syndrome), which may falsely raise their cardiac filling pressures (central venous pressure [CVP], wedge). These patients require all the more aggressive fluid administration to maintain adequate cardiac output (>章节 40).

Nasogastric Aspiration

“My work essentially has been that of plumber of the alimentary canal. I have worked on both ends, but largely in between,” wrote Owen H. Wangensteen (1898– 1981) of Minneapolis. And indeed, already in the 1930s he had introduced the NG tube as a crucial and indispensable aid in the management of SBO. So, how sad and pathetic it is to find—70 years later—patients admitted from the emergency room with the diagnosis of SBO, with their abdomens distended, their pajamas stained green, and no tube sticking from the nose.

A large NG tube (at least 18F diameter) is needed. The NG tube has both therapeutic and diagnostic functions. It controls vomiting, but its main aim is to decompress the dilated stomach and consequently the gut proximal to the obstruction. In a simple obstruction, decompression of the bowel results in rapid pain relief and alleviates the distension. Essentially, the segment of intestine proximal to the obstruction and distal to the gastroesophageal junction behaves like a closed loop; decompression of the stomach with an NG tube converts it to a simple obstruction. In strangulation or closed-loop obstruction, the pain per-sists despite NG aspiration.

Insertion of an NG tube is extremely unpleasant. Many patients remember it as the most horrendous experience of their hospital stay (and would certainly resist fiercely any attempt at reinsertion). The procedure can, however, be made much “kinder”: soften the rigid tube by immersion for a minute or two in very hot water, spray the nostril of the patient with a local anesthetic, and lubricate the tube. There is no advantage in connecting the NG tube to a suction appara-tus; drainage by gravity is as effective. Long nasointestinal tubes (Cantor, Linton, Moss, whatever some of the names) are a gimmick with unproven benefits— requiring cumbersome manipulations and causing delay when operation is -necessary.

When to Operate?

An hour or two of fluid replenishment is compulsory in the management of every patient. Reassess your resuscitated and NG-decompressed patient. What is the pattern of pain now? Is there improvement on abdominal re-examination?

Immediate operation is required in a minority of patients: those who did not improve, those who experience continuous pain, or those with significant abdominal tenderness combined with the features stated (e.g., fecal NG aspirate, systemic inflammatory response syndrome [SIRS]). Here, abdominal X-rays usually show a complete obstruction. The probability of strangulation is high. Book these patients for an emergency operation.

An initial nonoperative approach is often possible because most patients improve at first on the “drip-and-suck” regimen. It would be safe to bet, at this stage, that patients with radiological partial obstruction will eventually escape surgery, whereas those with complete obstruction will eventually visit the operating room. But, how long is it safe to continue with conservative management? Some surgeons would abort the conservative trial at 24 hrs if the patient fails to “open up” because of the nagging concern about strangulation even in a benign-looking abdomen. Others are prepared to persevere, up to 5 days in a carefully monitored patient—especially in patients who give a history of repeated episodes of adhesive SBO.

In the absence of an immediate indication for operation, we favor the use of an oral water-soluble contrast medium (e.g., Gastrografin) as soon as the diag-nosis of SBO is made. Gastrografin, a hyperosmolar agent that promotes intesti-nal “hurry,” plays two roles: diagnostic-prognostic and therapeutic.

The Gastrografin “Challenge”

After the initial gastric decompression, instill 100 ml Gastrografin via the NG tube, which is then clamped. After 4–6 hrs, a simple plain abdominal X-ray is obtained. This is not a formal radiological study under fluoroscopy. Make sure that your patient does not get barium (> 章节 4).

        Presence of contrast in the large bowel proves that the obstruction is partial. In most of these instances, the Gastrografin is very soon passed per rectum as well. In partial SBO, Gastrografin is often therapeutic as it expedites reso-lution of the obstructing episode. On the other hand, failure of Gastrografin to reach the colon within 6 hrs indicates a complete obstruction. The prob-ability of spontaneous resolution after a failed Gastrografin “challenge” is very low; most of these patients will require surgery anyway, so why not operate on them now!

        Another sign of failed Gastrografin challenge is the failure of Gastrografin to leave the stomach and enter the small bowel. It signifies significant back-pressure in the obstructed bowel and the need for an immediate operation.

So, if we admit a patient during evening hours with suspected adhesive SBO and without features mandating an immediate operation, we perform the Gastrografin challenge, and if by the morning the contrast has not reached the colon, we would operate. Of course, the results of the Gastrografin challenge test should be correlated with the whole clinical picture. Note that Gastrografin may pass across a chronic small bowel narrowing. Thus, for the obstructive episode to be considered “resolved,” the abdominal symptoms and signs should disappear as well.

This approach has led us to modify that old fashioned aphorism (“never let the sun rise over an intestinal obstruction”); the new version should read: “Never let a patient with a complete intestinal obstruction escape an operation for more than 24 hrs.”

Additional Investigations (Computed Tomography)

Clinical examination and plain abdominal radiographs complemented by a Gastrografin challenge are sufficient to allow us to reach the correct decision in the majority of patients. Is additional imaging necessary or useful? Ultrasonography has been reported by enthusiasts to define accurately the site of obstruction and estab-lish whether strangulation is present. It requires access to an expert, which most institutions lack. Oral and intravenous contrast-enhanced computed tomography (CT) has been shown accurately to define the level of obstruction (the “transition point”) and identify a strangulated bowel segment (see > 章节 5). This, however, does not mean that CT is usually necessary and, if obtained, that it has much impact on the decision to wait or to operate in patients with adhesive SBO; you do not need to see the transition point to know that it is there. But, should you find yourself working in one of these places where the abdominal CT has replaced the plain abdominal X-ray, see to it that the “oral” contrast used is water soluble—the result being a more detailed and more expensive Gastrografin challenge.

We would, however, obtain CT, selectively, when suspecting a nonadhesive etiology of obstruction, as in the following scenarios:

        History of abdominal malignancy. A CT finding of diffuse carcinomatosis indicates that symptomatic management is the correct option.

        “Virgin” abdomen (discussed in a separate section).

        Clinical picture not consistent with the usual partial adhesive SBO. Para-lytic ileus may be easily confused with a partial SBO (> 章节 48). There is air in the large bowel, and the Gastrografin may go through, but the patient remains symptomatic; fever or leukocytosis may be present. CT will document the under-lying responsible cause for the paralytic ileus, such as acute appendicitis or acute diverticulitis.

        Suspected Crohn’s Disease (>章节 24).

        Early postoperative SBO (>章节 48).

        Post-laparoscopic SBO (> 章节 48).

But, whether you want it or not, many of your SBO patients would have already passed through the scanner by the time you are summoned to see them. So look for a “transition point” which signifies what the radiologists call “high grade obstruction”—a finding which however does not rule out successful conservative treatment. Search also for the classical CT features of intestinal compromise such as pneumatosis intestinalis and portal venous gas; look for features of “fixed” obstruction (e.g. intussusception, torsion of mesentery); and observe for less spe-cific features associated with intestinal compromise (e.g. free intraperitoneal fluid, mesenteric edema)—which if present make the decision to go to the OR easier. And obviously, a plain abdominal X ray taken a few hours after the CT scanning would show you whether the contrast has progressed into the colon, or whether it has left the stomach at all. Obviously, all these CT features of SBO should be incorporated into the whole clinical picture and decision making.

Antibiotics

In animal models of SBO, systemic antibiotics delay intestinal compromise and decrease mortality. In clinical practice, there is no need for antibiotics in patients treated conservatively, and we operate whenever the suspicion of intesti-nal compromise is entertained. A single preoperative dose of antibiotics is admin-istered prophylactically; no postoperative antibiotics are necessary even if bowel resection has been performed (> Chaps. 7 and 47). The only indication for postop-erative antibiotic administration would be long-standing bowel gangrene with established intra-abdominal infection.

The Conduct of the Operation

        The incision for abdominal re-entry is discussed in > 章节 10, but we need to remind you to carefully avoid iatrogenic enterotomies with their associated postoperative morbidity. Finding your way into the peritoneal cavity may take time but be patient for this is the longest part of the procedure. The rest is usually simpler. In this scenario, the gentle hand of the “slow” surgeon is much preferred over that of the macho cowboy.

        Find a loop of collapsed small bowel and follow it proximally. It will lead you to the point of obstruction just distal to the dilated obstructed intestine. Now, deal with the cause of obstruction, be it a simple band or a bowel kink. Mobilize the involved bowel segment using sharp and blunt dissection with traction applied on the two structures to be separated.

        Resect only nonviable bowel or when the obstructed segment is impossible to be freed. Frequently, an ischemic-looking loop of bowel is dusky after being released.

Do not rush to resect; cover the bowel with a warm, wet laparotomy pad and wait patiently; it will usually pink up within 10 min. If not, it requires resection.

\ Concentrate on the loop that is responsible for the obstruction; there is no need to free the whole intestine by dividing all the remaining innocent adhesions. This maneuver may be cosmetically appealing, but adhesions lysed today will re--form tomorrow. As aptly stated by Timothy Fabian: “Lysis of all small bowel adhesions is not required because I believe that the bowel is ‘locked in the open position’ by these chronic adhesions.”

\ Occasionally, multiple points of obstruction appear to be present with no clear area of demarcation between dilated and collapsed bowel. This is more common in pa-tients after multiple operations for SBO or those with early postoperative SBO. In this situation, the whole length of the “frozen” gut has to be unraveled—again, very care-fully and patiently in order not to damage the bowel. This is tedious surgery indeed.

How Is an Iatrogenic Intestinal Injury Managed During Adhesiolysis?

To manage an iatrogenic intestinal injury during adhesiolysis, transmural enterotomies should be repaired transversely. We recommend a running, one--layered, absorbable, monofilament technique (> 章节 13). Superficial serosal tears should be left alone. Areas where the mucosa pouts through the defect should be repaired with a running monofilament seromuscular suture.

Decompress or Not?

Ah yes. The proverbial double-edged sword! On the one hand, excessive bowel distension impedes abdominal closure and contributes to postoperative intra-abdominal hypertension with its well-known deleterious physiological con-sequences (> 章节 40). On the other hand, bowel decompression may contribute to postoperative ileus and even cause peritoneal contamination. We, like most oth-ers, would decompress the distended bowel if abdominal closure seems to need excessive tension. Gently milk its contents toward the stomach, from where it is sucked, through the NG tube, by the anesthetist. Milk the bowel very gently by suc-cessively squeezing the loops in a sequential manner as the obstructed bowel is thin walled and very easily injured. The practice of “stripping” the gut between your fingers is brutal and potentially damaging. Do not pull too hard on the mes-entery; it may tear as well (remember that injury to the peritoneal surfaces pro-motes formation of adhesions). Palpate the stomach from time to time; if full, gently squeeze and shake it to restore patency of the NG tube. For a distal SBO, you may also milk the small bowel contents toward the collapsed colon. Open decom-pression through an enterotomy is unwise given the risk of gross bacterial con-tamination. Needle decompression is not effective with the thick bowel contents.

Obviously, open decompression should be performed if bowel is being resected; insert a Poole sucker or a large sump drain connected to the suction through the proximal line of bowel transection and gently “accordion” the bowel onto your suction device.

Before closing, run the bowel again for missed enterotomies. Check for hemostasis as extensive adhesiolysis leaves large, oozing, raw areas; intraperito-neal blood promotes ileus, infection, and more adhesion formation. Close the abdomen safely (> 章节 43). SBO is a setup for wound dehiscence and a ticket to the M & M conference (> 章节 59).

Laparoscopic Approach

Wouldn’t it be nice to relieve the SBO laparoscopically? Indeed, laparoscopic lysis of the obstructing adhesions seems attractive because in many cases the cause of SBO is a single fibrous band. This is easier said than done. The collective published experience (and that which is not published, which is more realistic) points to a higher risk of injury to the distended and friable obstructed intestine during the laparoscopic operation. This, of course, translates to a higher rate of septic complications and postoperative morbidity.

Should you wish to attempt laparoscopic approach, do it selectively on the easier cases:

        First episode of SBO

        Abdomen not excessively distended (e.g., more proximal SBO)

        Patient stable and able to endure a prolonged pneumoperitoneum—super-imposed on an already distended abdomen

The first port should be placed through an open approach and away from the old incision. Most important, do not be obstinate; know when to abort— before you create too many holes.

Special Circumstances

The “Virgin” Abdomen

Patients presenting with SBO but without a previous history of abdominal surgery need special attention; it is here that you have to suspect nonadhesive causes of SBO, including rare “zebras” like, for example, the one and only obstruct-ing obturator hernia you are likely to diagnose and treat during your entire glori-ous surgical career.

So, the patient presents with clinical and radiological features of SBO but with no abdominal wall scar of previous surgery. What do you do? (First, ask again about all past procedures, including that laparoscopic ovarian cystectomy and a tiny scar hidden in the umbilicus; while you are at it, why not re-examine the groin for incarcerated hernias.) Evidence of a complete obstruction is of course an indi-cation for a laparotomy, but what about partial SBO? As with the adhesive partial obstruction, we recommend a Gastrografin challenge. In an obstruction caused by an intraluminal bolus, whether from parasites or dry fruits, Gastrografin may dis-impact the bowel. In these cases, we would recommend abdominal imaging to exclude an underlying cause. Non-resolving partial obstruction despite the Gastrografin challenge suggests a mechanical cause, such as a congenital band, an internal hernia, malignancy, inflammation, or even an impacted bezoar. Laparotomy usually uncovers a treatable cause of obstruction. A preoperative CT scan “just to find out what we are dealing with” is not mandatory and may only delay the operation without changing its indication. But when in doubt, if readily available, and in the absence of clinical strangulation, it may be helpful. Cecal car-cinoma is a typical cause of distal “SBO” in the virgin (or non-virgin) abdomen. The clinical presentation is commonly gradual and “smoldering.” Gastrografin may pass through into the cecum. In this case, CT would be diagnostic. SBO due to previously undiagnosed but suspected Crohn’s disease is an exception; here, a CT may be very suggestive, indicating continued conservative therapy (> 章节 24).

Intussusception

Although common in pediatric patients (> 章节 35), intussusception is a very rare cause of SBO in adults. In adults, the “leading point” is usually organic (e.g., neoplasm, inflammatory lesions) and seldom idiopathic as in children. Patients with small bowel or ileocolic intussusception present with nonspecific features of SBO (in a virgin abdomen), necessitating operative treatment. A spe-cific preoperative diagnosis can be obtained with ultrasound or CT, showing the multiple concentric ring sign (bowel within bowel) but will not change what you need to do—operate and resect the involved segment of bowel. Although contro-versial, some would attempt reduction of intussusception when there are no exter-nal signs of ischemia or malignancy, and if after reduction no leading point is found (i.e., idiopathic intussusception), one could leave the bowel alone.

The Known Cancer Patient

A patient is admitted with SBO a year or two following an operation for gas-tric or colonic cancer. You should first attempt to obtain information about the findings of the previous laparotomy. The more advanced the cancer, the higher the probability that the current obstruction is malignant. Clinically, cachexia, ascites, or an abdominal mass suggests diffuse carcinomatosis. These cases present a medical and ethical dilemma. On the one hand, one wishes to relieve the obstruction and offer the patient a further spell of quality life. On the other hand, one tries to spare a terminal patient an unnecessary operation. Each case should be assessed on merit. In the absence of stigmata of advanced disease, surgery for complete obstruction is justifiable. In many instances, adhesions may be found; in others, a bowel segment obstructed by local spread or metastases can be bypassed. When diffuse carcino-matosis is suspected clinically or on CT scan, a reasonable option would be to insert a palliative, venting percutaneous gastrostomy, allowing the patient to drink and to die peacefully at home or in a hospice environment.

Radiation Enteritis

Radiation treatment of abdominal or pelvic malignancies is not an uncom-mon cause of SBO; this usually develops months or even years after irradiation. A relentless course of multiple episodes of partial SBO, initially responding to conservative treatment but eventually culminating in a complete obstruction, is characteristic. There is also the uncertainty about the obstruction being malig-nant or adhesive in nature. One always hopes that it is adhesive because SBO due to radiation injury is “bad news” indeed. When forced to operate for complete obstruction, one finds irradiated loops of bowel glued or welded together and onto adjacent structures. The paper-thin bowel tears easily. Accidental enterotomies are frequent, difficult to repair, and commonly result in postoperative fistulas. Short involved segments of bowel are best resected, but when longer segments are encountered, usually stuck in the pelvis, it is safest to bail out with an enteroenteric or enterocolic bypass, using nonirradiated bowel for this purpose. Postoperative short-bowel syndrome is common whatever the procedure. Long-term prognosis is poor; radiation enteritis is almost as bad as the malignancy the radiation had attempted to control (see also > 章节 48).

Recurrent Multiple Episodes of SBO

In recurrent multiple episodes of SBO, the patient is typically re-admitted every second month for SBO and has undergone, in the past, multiple operations for this condition. How should this patient be managed? We would treat this patient as any other patient presenting with adhesive SBO. Fortunately, most such epi-sodes are “partial” and responsive to conservative treatment. When complete obstruction develops, operative management is obviously necessary. Attempts at preventing subsequent episodes with plication of bowel or mesentery or long-tube stenting are recommended by some. The evidence in favor of such maneuvers is anecdotal at best. We do not practice them. Occasionally, a patient develops obstruction early in the aftermath of an operation for adhesive SBO; this is a case par excellence for prolonged nonoperative management, with the patient main-tained on total parenteral nutrition (TPN) until adhesions mature and the obstruc-tion resolves. (See also > 章节 48.)

A Word About Patience

You will understand by now that in some circumstances a laparotomy for SBO will be a long and difficult operation due to multiple adhesions or radiation enteritis, for example. If you begin an operation expecting a quick-and-easy pro-cedure and are then confronted by a nightmare abdomen, the first thing you must do is reset your mental clock. Failure to do this may mean that you will attempt to rush the procedure, and this inevitably leads to disaster, with multiple inadvertent enterotomies, peritoneal contamination, and ultimately an even longer and more dangerous procedure. Upon entering such a disastrous abdomen unexpectedly, inform everybody immediately that the procedure is now going to take a few hours while you unravel all the loops necessary to get at the problem and fix it. And then, take your time and fix it carefully and slowly.

Gallstone Ileus

Gallstone ileus develops typically in elderly patients with long-standing cholelithiasis. It is caused by a large gallstone eroding into an adjacent segment of bowel—usually the duodenum; then, the gallstone migrates distally until stranded at the narrow ileum. Presentation is usually vague as initially the stone may disimpact spontaneously, causing intermittent episodes of partial obstruc-tion. You will never miss the diagnosis once you habitually and obsessively search for air in the bile ducts on any plain abdominal X-ray you order (> 章节 5). The air enters the bile duct via the enterocholecystic fistula created by the eroding gallstone. Treatment is operative and should be tailored to the condition of the patient. In frail and sick patients, deal only with the SBO: place an enterotomy proximal to the stone and remove it and search for additional stones in the bowel above; you do not want to have to re-operate. In patients who are younger and reasonably fit and well, you may want also to deal with the cause of the prob-lem—the gallbladder. Perform a cholecystectomy and close the duodenal defect; place your suture line transversely to avoid narrowing of the duodenum. But again, not removing the gallbladder after dealing with the obstructing gallstone is a perfectly reasonable option.

Bezoars

Bezoars are tightly packed collections, or “balls,” of partially digested or undigested material forming in the stomach and then migrating distally, where they may obstruct the terminal ileum. You may encounter one of the following types of bezoars:

        Phytobezoars: partially digested agglomerations of vegetables or fruits that form in patients with altered gastric physiology (e.g., following gastric resection, vagotomy, or bariatric operation and even in patients with diabetic gastroparesis) or health food “crazies” and elderly forget-to-chewers. Many sorts of fruits and vegetables are implicated, particularly when consumed in large quantity (I once suffered partial SBO after consuming, within an hour, a whole bag of baby car-rots), but consumption of persimmons is especially notorious in this regard, with patients developing multiple episodes of SBO.

        Trichobezoars: these most commonly occur in younger patients with psy-chiatric disturbances who chew and swallow their own hair. Trichobezoars form in the stomach and often reach a huge size; they break into smaller pieces and migrate into where they can obstruct at several points.

        Parasitic bezoars: consisting of conglomerates of parasites such as Ascaris lumbricoides, these may obstruct the distal ileum. Obviously, these are common in endemic areas.

Patients present usually with features of partial or smoldering SBO and a virgin abdomen. History is suggestive, and CT images—showing the actual intraluminal bezoars—are diagnostic. As mentioned, Gastrografin challenge can dislodge the obstructing parasites, or other types of bezoars, pushing them into the cecum. But when the obstruction is complete, you have to operate and deal with the obstructing bezoar like you did with the gallstone (see the section on gallstone ileus). It is crucial to palpate the entire small bowel, including the duo-denum (and the stomach), for additional bezoars and remove all of them. Preoperative CT may be helpful in mapping such additional bezoars for you. You do not want the patient to develop early postoperative SBO caused by a missed bezoar—needing another laparotomy for removal—do you?

SBO After Gastrectomy

With the disappearance of gastrectomies performed for benign disease and the declining rate of gastric cancer, there are not too many postgastrec-tomy patients to present with SBO, but some do. According to my friends Professor David Dent (Cape Town, South Africa) and Dr. Hernan Diaz (Santiago, Chile)—both of them “old gastrectomists”—the reasons for SBO in these patients are:

        Simple adhesive obstruction—what is common is common

        Recurrent gastric carcinoma, with loops of bowel “frozen” by peritoneal carcinomatosis

        Bolus obstruction by bezoars

        Internal herniation of small bowel through defects of the mesocolon or behind the jejunal loop forming the Billroth II (or Roux-en-Y) gastroen-terosotomy—be it antecolic or retrocolic

        Twisting or volvulus of redundant afferent or efferent jejunal loops

Obviously, the more complex the original postgastrectomy reconstruction, the more potential peritoneal defects created, and the “looser” the various intestinal loops, the higher the risk will be for bowel to kink, rotate, herniate, and obstruct. (Now you understand why we prefer Billroth I reconstruction after gastrectomy; > 章节 17.)

        Another specific type of obstruction is the jejunogastric intussusception. Both the afferent or efferent loops can invaginate into the gastric remnant, but the retrograde efferent loop intussusception is more common. This can occur from a few days up to many years after the gastrectomy. Sudden onset of epigas-tric pain, vomiting, and hematemesis and a palpable epigastric mass in a patient with previous gastric surgery are the classic triad.

        Obstruction of the afferent loop after Billroth II or Roux-en-Y reconstruc-tion—by whichever of the mentioned mechanisms—produces a closed-loop ob-struction (between the obstructing point and the duodenal stump). High intraluminal pressures are commonly associated with elevation of serum pancre-atic enzymes (amylase) and, if the obstruction is not relieved, with necrosis of the involved loop and the attached duodenum. The clinical picture of epigastric pain, upper abdominal mass, and hyperamylasemia may confuse you to think that you are dealing with acute pancreatitis.

The proximal location of the obstruction is suggested by the frequent vom-iting, lack of abdominal distention, and paucity of dilated small bowel on plain abdominal X-ray. CT with oral contrast is a superb diagnostic aid, showing the exact anatomy of obstruction and the ring sign of small bowel within the stom-ach in the case of jejunogastric intussusception. Occasionally, endoscopy is needed to clarify the picture. Do understand that acute afferent loop obstruction is a dire emergency; you have to operate before the closed-loop obstruction results in complete necrosis of the duodenum!

At operation, the anatomy has to be restored, and this entails resection of nonviable loops of bowel and reconstruction of the upper gastrointestinal tract, as you would do after partial or total gastrectomy.

Small Bowel Volvulus

Small bowel volvulus is also called midgut volvulus, distinguishing it from foregut volvulus (> 章节 16) and hindgut volvulus (> 章节 25).

Volvulus, the “twisting strangulation” of an intestinal segment around an axis formed by a band or an adhesion, is a common occurrence in adhesive SBO. A narrow-based loop of small bowel suspended by a Meckel diverticulum can also undergo torsion. But, what about “spontaneous” volvulus, one that involves the entire, or almost entire, small intestine?

Spontaneous volvulus of the small bowel, while very rare in the “developed world,” is not uncommon in rural areas of the Indian subcontinent, central Asia, and Africa. It seems more common in healthy farmers returning home for a large evening meal or, in Moslem countries, during the fast of Ramadan—when large meals are consumed at night after the day of fasting. The common pathway appears to be a huge load of high-fiber, indigestible food, arriving suddenly in an empty small bowel. The sudden distention creates rotational kinking forces. At operation, typically the twisted bowel is loaded with liters of claylike undigested food and is often suspended on an unusually long mesentery. Occasionally, small bowel volvu-lus occurs in combination with that of the sigmoid colon, forming the so-called ileosigmoid knot, in which the ileum and the sigmoid entangle each other to form a knot and become gangrenous. An arrangement of the small bowel and sigmoid colon on long, narrow mesenteries would appear to be a prerequisite.

Like in any other condition resulting in an acute vascular compromise of the bowel, patients present with severe central abdominal pain that is out of pro-portion to the abdominal findings; systemic signs of hypovolemia and toxemia are however dramatic and dominant. An urgent operation is indicated, during which the ischemic intestine is managed as discussed above and in > 章节 23.

Intestinal Malrotation

Most cases of midgut malrotation present within the first weeks or months of life. The rest can present sporadically throughout childhood and even in adults. The anatomy of malrotation is depicted in > Figure 21.2: note how close the D-J flexure (point X) is to the cecum (point Y) and how narrow the base of the -mesentery is and thus prone to torsion. Strangulating midgut volvulus in these patients can present acutely, but more commonly, especially in older children and adults, volvulus is preceded by recurring attacks of upper and central abdominal colicky pain and intermittent vomiting of bile and is often relieved by diarrhea. Once again, patients presenting with acute midgut volvulus are in great pain and appear ill but have minimal abdominal findings on examination.


Fig. 21.2.  Small bowel malrotation and volvulus. (Modified from George G. Youngson, Common Pediatric Disorders.

Classically, the diagnosis was achieved by contrast studies: upper gastrointes-tinal barium examination showing loss of the duodenal C (corkscrew duodenum) and the D-J flexure to the right of the midline. Barium enema would show the cecum riding high under the liver. CT, however, has become the optimal diagnostic modality, showing the small bowel located entirely within the right hemiabdomen and the colon situated on the left. Features of the twisted mesentery and intestinal wall ischemia are seen as well. Midgut volvulus can also be diagnosed on Doppler ultrasound by demonstrating the “whirlpool sign”—-wrapping of the superior mesenteric vein and the mesentery around the superior mesenteric artery.

Emergency laparotomy is mandated. Remember that these patients are grossly hypovolemic and need aggressive fluid resuscitation. At operation, detort the twisted bowel, working in a counterclockwise rotation. dead bowel needs resection, usually massive resection. Regarding whether to anastomose and whether second-look operation is necessary, see > 章节 23.

After resecting the dead bowel or convincing yourself that it is viable, you want to address the anatomical pathology of malrotation by doing what has been described by William E. Ladd (1880–1967):

        Divide the peritoneal folds (Ladd bands) that cross from the cecum to the liver, compressing the duodenum.

        Mobilize the right colon.

        Mobilize the D-J flexure, freeing the ligament of Treitz—straightening the duodenal loop.

        Divide any thick peritoneal folds compressing the SMA.

        Place the bowel in a new pattern as depicted in > Fig. 21.2c; note that now point X is far from point Y.

        Remove the appendix to prevent “atypically situated” appendicitis.

Obviously, after having to resect most of the small bowel you do not worry about recurrence of the volvulus, and there is no impetus to correct the anatomy, except points 1, 4, and 6.

Prognosis

Overall, about half the patients presenting with an adhesive SBO can be man-aged without an operation. About a third of patients operated once for adhesive SBO will have recurrent problems within 30 years. For patients admitted several times for adhesive SBO, the relative risk of recurrence increases with increasing number of prior obstructive episodes; more than two-thirds of patients with four or more SBO admissions will re-obstruct. In addition, the risk of recurrence is a bit lower in patients in whom the last obstructive episode was treated surgically, but this does not mean that those patients who were treated conservatively will have an increased need for operation during their future admissions for SBO. The aim is therefore to operate only when necessary but not to delay a necessary operation.

The only thing predictable about small bowel obstruction is its unpredictability.
参考:Schein's Common Sense Emergency Abdominal Surgery

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