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Evaluation and management of intestinal obstruction

Evaluation and management of intestinal obstruction






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    Evaluation and management of intestinal obstruction Evaluation and management of intestinal obstruction Document Transcript

    • January 15, 2011 ◆ Volume 83, Number 2 www.aafp.org/afp American Family Physician 159Evaluation and Managementof Intestinal ObstructionPATRICK G. JACKSON, MD, and MANISH RAIJI, MDGeorgetown University Hospital, Washington, District of ColumbiaIntestinal obstruction accounts forapproximately 15 percent of all emer-gency department visits for acuteabdominal pain.1Complications ofintestinal obstruction include bowel isch-emia and perforation. Morbidity and mor-tality associated with intestinal obstructionhave declined since the advent of moresophisticated diagnostic tests, but the condi-tion remains a challenging surgical diagno-sis. Physicians who are treating patients withintestinal obstruction must weigh the risks ofsurgery with the consequences of inappropri-ate conservative management. A suggestedapproach to the patient with suspected smallbowel obstruction is shown in Figure 1.PathophysiologyThe fundamental concerns about intesti-nal obstruction are its effect on whole bodyfluid/electrolyte balances and the mechani-cal effect that increased pressure has onintestinal perfusion. Proximal to the pointof obstruction, the intestinal tract dilates asit fills with intestinal secretions and swal-lowed air.2Failure of intestinal contents topass through the intestinal tract leads to acessation of flatus and bowel movements.Intestinal obstruction can be broadly dif-ferentiated into small bowel and large bowelobstruction.Fluid loss from emesis, bowel edema, andloss of absorptive capacity leads to dehydra-tion. Emesis leads to loss of gastric potassium,hydrogen, and chloride ions, and signifi-cant dehydration stimulates renal proximaltubule reabsorption of bicarbonate and lossof chloride, perpetuating the metabolic alka-losis.3In addition to derangements in fluidand electrolyte balance, intestinal stasis leadsto overgrowth of intestinal flora, which maylead to the development of feculent emesis.Additionally, overgrowth of intestinal florain the small bowel leads to bacterial translo-cation across the bowel wall.4Ongoing dilation of the intestine increasesluminal pressures. When luminal pressuresexceed venous pressures, loss of venousdrainage causes increasing edema andhyperemia of the bowel. This may eventu-ally lead to compromised arterial flow tothe bowel, causing ischemia, necrosis, andAcute intestinal obstruction occurs when there is an interruption in the forward flow of intes-tinal contents. This interruption can occur at any point along the length of the gastrointestinaltract, and clinical symptoms often vary based on the level of obstruction. Intestinal obstruc-tion is most commonly caused by intra-abdominal adhesions, malignancy, or intestinal hernia-tion. The clinical presentation generally includes nausea and emesis, colicky abdominal pain,and a failure to pass flatus or bowel movements. The classic physical examination findings ofabdominal distension, tympany to percussion, and high-pitched bowel sounds suggest thediagnosis. Radiologic imaging can confirm the diagnosis, and can also serve as useful adjunc-tive investigations when the diagnosis is less certain. Although radiography is often the initialstudy, non-contrast computed tomography is recommended if the index of suspicion is high orif suspicion persists despite negative radiography. Management of uncomplicated obstructionsincludes fluid resuscitation with correction of metabolic derangements, intestinal decompres-sion, and bowel rest. Evidence of vascular compromise or perforation, or failure to resolve withadequate bowel decompression is an indication for surgical intervention. (Am Fam Physician.2011;83(2):159-165. Copyright © 2011 American Academy of Family Physicians.)▲Patient information:A handout on intestinalobstruction, written by theauthors of this article, isprovided on page 166.Downloaded from the American Family Physician Web site at www.aafp.org/afp. Copyright © 2011 American Academy of Family Physicians. For the private, noncommer-cial use of one individual user of the Web site. All other rights reserved. Contact copyrights@aafp.org for copyright questions and/or permission requests.
    • Intestinal Obstruction160 American Family Physician www.aafp.org/afp Volume 83, Number 2 ◆ January 15, 2011perforation. A closed-loop obstruction, inwhich a section of bowel is obstructed proxi-mally and distally, may undergo this pro-cess rapidly, with few presenting symptoms.Intestinal volvulus, the prototypical closed-loop obstruction, causes torsion of arterialinflow and venous drainage, and is a surgicalemergency.Causes and Risk FactorsThe most common causes of intestinalobstruction include adhesions, neoplasms,and herniation (Table 1). Adhesions resultingfrom prior abdominal surgery are the pre-dominant cause of small bowel obstruction,accounting for approximately 60 percentof cases.5Lower abdominal surgeries, includ-ing appendectomies, colorectal surgery,gynecologic procedures, and hernia repairs,confer a greater risk of adhesive smallbowel obstruction. Less common causes ofobstruction include intestinal intussuscep-tion, volvulus, intra-abdominal abscesses,gallstones, and foreign bodies.Management of Small Bowel ObstructionFigure 1. Algorithm for evaluation and treatment of patients with suspected small bowelobstruction.Patient presents with signs andsymptoms of small bowel obstructionClinically stable?No YesRadiography orcomputed tomographyVascular compromiseor perforation?CompleteobstructionPartialobstructionNo oral intake,nasogastric intubation,intravenous rehydrationExploratorylaparotomyNo oral intake,nasogastric intubation,intravenous rehydrationYes NoResolution within 24 to 48 hours? Resolution within 24 to 48 hours?Yes NoNo YesAdvance dietUpper gastrointestinal/small bowel follow-through/enteroclysis?Resolution?NoYesExploratorylaparotomyExploratorylaparotomyExploratorylaparotomy
    • Intestinal ObstructionJanuary 15, 2011 ◆ Volume 83, Number 2 www.aafp.org/afp American Family Physician 161History and Physical ExaminationPatients should be asked about their historyof abdominal neoplasia, hernia or herniarepair, and inflammatory bowel disease,because these conditions increase the riskof obstruction. The hallmarks of intesti-nal obstruction include colicky abdominalpain, nausea and vomiting, abdominal dis-tension, and a cessation of flatus and bowelmovements. It is important to differentiatebetween true mechanical obstruction andother causes of these symptoms (Table 2).Distal obstructions allow for a greater intes-tinal reservoir, with pain and distensionmore marked than emesis, whereas patientswith proximal obstructions may have mini-mal abdominal distension but markedemesis. The presence of hypotension andtachycardia is an indication of severe dehy-dration. Abdominal palpation may reveal adistended, tympanitic abdomen; however,this finding may not be present in patientswith early or proximal obstruction. Aus-cultation in patients with early obstructionreveals high-pitched bowel sounds, whereasthose with late obstruction may present withminimal bowel sounds as the intestinal tractbecomes hypotonic.Diagnostic Testing and ImagingLABORATORY TESTSLaboratory evaluation of patients with sus-pected obstruction should include a com-plete blood count and metabolic panel.Hypokalemic, hypochloremic metabolicalkalosis may be noted in patients withsevere emesis. Elevated blood urea nitrogenlevels are consistent with dehydration, andhemoglobin and hematocrit levels may beincreased. The white blood cell count maybe elevated if intestinal bacteria translocateinto the bloodstream, causing the systemicinflammatory response syndrome or sepsis.The development of metabolic acidosis, espe-cially in a patient with an increasing serumlactate level, may signal bowel ischemia.RADIOGRAPHYThe initial evaluation of patients withclinical signs and symptoms of intestinalobstruction should include plain uprightabdominal radiography. Radiography canquickly determine if intestinal perforationhas occurred; free air can be seen above theliver in upright films or left lateral decubi-tus films. Radiography accurately diagno-ses intestinal obstruction in approximately60 percent of cases,6and its positive predic-tive value approaches 80 percent in patientswith high-grade intestinal obstruction.7However, plain abdominal films can appearnormal in early obstruction and in highjejunal or duodenal obstruction. Therefore,when clinical suspicion for obstruction ishigh or persists despite negative initial radi-ography, non-contrast computed tomogra-phy (CT) should be ordered.8In patients with small bowel obstruc-tion, supine views show dilation of multipleloops of small bowel, with a paucity of air inthe large bowel (Figure 2). Those with largebowel obstruction may have dilation of theTable 1. Causes of IntestinalObstructionAdhesive disease (60 percent)Neoplasm (20 percent)Herniation (10 percent)Inflammatory bowel disease (5 percent)Intussusception (< 5 percent)Volvulus (< 5 percent)Other (< 5 percent)Table 2. Differential Diagnosis of Abdominal Pain,Distension, Nausea, and Cessation of Flatus andBowel MovementsAlternate diagnosis CluesAscites Acute liver failure, history of hepatitis oralcoholismMedications (e.g., tricyclicantidepressants, narcotics)Review of medications; diagnosis ofexclusionMesenteric ischemia History of peripheral vascular disease,hypercoagulable state, or postprandialabdominal angina; recent use ofvasopressorsPerforated viscus/intra-abdominal sepsisFever, leukocytosis, acute abdomen, freeair on imagingPostoperative paralytic ileus Recent abdominal surgery with nopostoperative flatus or bowel movementPseudo-obstruction(Ogilvie syndrome)Acutely dilated large intestine, history ofintestinal dysmotility, diabetes mellitus,scleroderma
    • Intestinal Obstruction162 American Family Physician www.aafp.org/afp Volume 83, Number 2 ◆ January 15, 2011colon, with decompressed small bowel in thesetting of a competent ileocecal valve. Uprightor lateral decubitus films may show ladderingair fluid levels (Figure 3). These findings, inconjunction with a lack of air and stool in thedistal colon and rectum, are highly suggestiveof mechanical intestinal obstruction.COMPUTED TOMOGRAPHYCT is appropriate for further evaluation ofpatients with suspected intestinal obstruc-tion in whom clinical examination and radi-ography do not yield a definitive diagnosis.CT is sensitive for detection of high-gradeobstruction (up to 90 percent in some series),9and has the additional benefit of definingthe cause and level of obstruction in mostpatients.10-12In addition, CT can identifyemergent causes of intestinal obstruction,such as volvulus or intestinal strangulation.CT findings in patients with intestinalobstruction include dilated loops of bowelproximal to the site of obstruction, with dis-tally decompressed bowel. The presence of adiscrete transition point helps guide opera-tive planning (Figure 4). Absence of contrastmaterial in the rectum is also an impor-tant sign of complete obstruction. For thisFigure 3. Lateral decubitus view of the abdomen, showing air-fluidlevels consistent with intestinal obstruction (arrows).Figure 2. Supine view of the abdomen in a patient with intestinalobstruction. Dilated loops of small bowel are visible (arrows).Figure 4. Axial computed tomography scanshowing dilated, contrast-filled loops ofbowel on the patient’s left (yellow arrows),with decompressed distal small bowel onthe patient’s right (red arrows). The cause ofobstruction, an incarcerated umbilical hernia,can also be seen (green arrow), with proxi-mally dilated bowel entering the hernia anddecompressed bowel exiting the hernia.The rights holder did not grant the American Academy of FamilyPhysicians the right to sublicense this material to a third party. Forthe missing item, see the original print version of this publication.The rights holder did not grant the American Academy of FamilyPhysicians the right to sublicense this material to a third party. Forthe missing item, see the original print version of this publication.The rights holder did not grant the Ameri-can Academy of Family Physicians theright to sublicense this material to a thirdparty. For the missing item, see the origi-nal print version of this publication.
    • Intestinal ObstructionJanuary 15, 2011 ◆ Volume 83, Number 2 www.aafp.org/afp American Family Physician 163reason, rectal administration of contrastmaterial should be avoided. A C-loop of dis-tended bowel with radial mesenteric vesselswith medial conversion is highly suspiciousfor intestinal volvulus. Thickened intesti-nal walls and poor flow of contrast materialinto a section of bowel suggests ischemia,whereas pneumatosis intestinalis, free intra-peritoneal air, and mesenteric fat strandingsuggest necrosis and perforation.Although CT is highly sensitive and spe-cific for high-grade obstruction, its valuediminishes in patients with partial obstruc-tion. In these patients, oral contrast mate-rial may be seen traversing the length of theintestine to the rectum, with no discrete areaof transition. Fluoroscopy may be of greatervalue in confirming the diagnosis.The American College of Radiology rec-ommends non-contrast CT as the initialimaging modality of choice.13However,because most causes of small bowel obstruc-tion will have systemic manifestations or failto resolve—necessitating operative interven-tion—the additional diagnostic value of CTcompared with radiography is limited. Radi-ation exposure is also significant. Therefore,in most patients, CT should be ordered whenthe diagnosis is in doubt, when there is nosurgical history or hernias to explain the eti-ology, or when there is a high index of suspi-cion for complete or high-grade obstruction.CONTRAST FLUOROSCOPYContrast studies, such as a small bowelfollow-through, can be helpful in the diag-nosis of a partial intestinal obstruction inpatients with high clinical suspicion and inclinically stable patients in whom initial con-servative management was not effective.14The use of water-soluble contrast material isnot only diagnostic, but may also be thera-peutic in patients with partial small-bowelobstruction. A randomized controlled trialof 124 patients showed a 74 percent reduc-tion in the need for surgical intervention inpatients receiving gastrografin fluoroscopywithin 24 hours of initial presentation.15Contrast fluoroscopy may also be useful indetermining the need for surgery; the pres-ence of contrast material in the rectumwithin 24 hours of administration has a97 percent sensitivity for spontaneous resolu-tion of intestinal obstruction.16,17There are several variations of contrastfluoroscopy. In the small-bowel follow-through study, the patient drinks contrastmaterial, then serial abdominal radiographsare taken to visualize the passage of contrastthrough the intestinal tract. Enteroclysisinvolves naso- or oro-duodenal intubation,followed by the instillation of contrast mate-rial directly into the small bowel. Althoughthis study has superior sensitivity comparedwith small-bowel follow-through,18it is morelabor-intensive and is rarely performed.Rectal fluoroscopy can be helpful in deter-mining the site of a suspected large bowelobstruction.ULTRASONOGRAPHYIn patients with high-grade obstruction,ultrasound evaluation of the abdomen hashigh sensitivity for intestinal obstruction,approaching 85 percent.19However, becauseof the wide availability of CT, it has largelyreplaced ultrasonography as the first-lineinvestigation in stable patients with suspectedintestinal obstruction. Ultrasonographyremains a valuable investigation for unstablepatients with an ambiguous diagnosis and inpatients for whom radiation exposure is con-traindicated, such as pregnant women.MAGNETIC RESONANCE IMAGINGMagnetic resonance imaging (MRI) may bemore sensitive than CT in the evaluation ofintestinal obstruction.20MRI enteroclysis,which involves intubation of the duodenumand infusion of contrast material directlyinto the small bowel, can more reliablydetermine the location and cause of obstruc-tion.21However, because of the ease and cost-effectiveness of abdominal CT, MRI remainsan investigational or adjunctive imagingmodality for intestinal obstruction.TreatmentManagement of intestinal obstruction isdirected at correcting physiologic derange-ments caused by the obstruction, bowel rest,and removing the source of obstruction. The
    • Intestinal Obstruction164 American Family Physician www.aafp.org/afp Volume 83, Number 2 ◆ January 15, 2011former is addressed by intravenous fluidresuscitation with isotonic fluid. The use ofa bladder catheter to closely monitor urineoutput is the minimum requirement forgauging the adequacy of resuscitation; otherinvasive measures, such as arterial canaliza-tion or central venous pressure monitoring,can be used as the clinical situation war-rants. Antibiotics are used to treat intestinalovergrowth of bacteria and translocationacross the bowel wall.22The presence of feverand leukocytosis should prompt inclusion ofantibiotics in the initial treatment regimen.Antibiotics should have coverage againstgram-negative organisms and anaerobes,and the choice of a specific agent should bedetermined by local susceptibility and avail-ability. Aggressive replacement of electro-lytes is recommended after adequate renalfunction is confirmed.The decision to perform surgery for intes-tinal obstruction can be difficult. Perito-nitis, clinical instability, or unexplainedleukocytosis or acidosis are concerning forabdominal sepsis, intestinal ischemia, orperforation; these findings mandate imme-diate surgical exploration. Patients with anobstruction that resolves after reduction ofa hernia should be scheduled for electivehernia repair, whereas immediate surgeryis required in patients with an irreducibleor strangulated hernia. Stable patients witha history of abdominal malignancy or highsuspicion for malignancy should be thor-oughly evaluated for optimal surgical plan-ning. Abdominal malignancy can be treatedwith primary resection and reconstructionor palliative diversion, or placement of vent-ing and feeding tubes.Treatment of stable patients with intesti-nal obstruction and a history of abdominalsurgery presents a challenge. Conservativemanagement of a high-grade obstructionshould be attempted initially, using intesti-nal intubation and decompression, aggres-sive intravenous rehydration, and antibiotics.The inclusion of oral magnesium hydroxide,simethicone, and probiotics decreased thelength of hospitalization in a randomizedcontrolled trial of 144 patients with partialsmall bowel obstructions (number neededto treat = 7).23Caution should be used whenclinical and radiologic evidence suggest com-pleteobstruction,becausetheuseofintestinalstimulation can exacerbate the obstructionand precipitate intestinal ischemia.SORT: KEY RECOMMENDATIONS FOR PRACTICEClinical recommendationEvidencerating References CommentsAbdominal radiography is an effective initialexamination in patients with suspected intestinalobstruction.C 6, 7 Radiography has greater sensitivity inhigh-grade obstruction than in partialobstruction.Computed tomography is warranted whenradiography indicates high-grade intestinalobstruction or is inconclusive.C 8-10 Computed tomography can reliably determinethe cause of obstruction, and whetherserious complications are present, in mostpatients with high-grade obstructions.Upper gastrointestinal fluoroscopy with smallbowel follow-through can determine the needfor surgical intervention in patients with partialobstruction.C 14, 15 Contrast material that passes into the cecumwithin four hours of oral administration ishighly predictive of successful nonoperativemanagement.Antibiotics can protect against bacterialtranslocation and subsequent bacteremia inpatients with intestinal obstruction.C 22 Enteric bacteria have been found in culturesfrom serosal scrapings and mesenteric lymphnode biopsy in patients requiring surgery.Clinically stable patients can be treatedconservatively with bowel rest, intubationand decompression, and intravenous fluidresuscitation.A 22-26 Several randomized controlled trials haveshown that surgery can be avoided withconservative management.Surgery is warranted in patients with intestinalobstruction that does not resolve within 48 hoursafter conservative therapy is initiated.B 25 Study found that conservative managementbeyond 48 hours does not diminish the needfor surgery, but increases surgical morbidity.A = consistent, good-quality patient-oriented evidence; B = inconsistent or limited-quality patient-oriented evidence; C = consensus, disease-oriented evidence, usual practice, expert opinion, or case series. For information about the SORT evidence rating system, go to http://www.aafp.org/afpsort.xml.
    • Intestinal ObstructionJanuary 15, 2011 ◆ Volume 83, Number 2 www.aafp.org/afp American Family Physician 165Conservative management is successful in40 to 70 percent of clinically stable patients,with a higher success rate in those with partialobstruction.24-26Although conservative man-agement is associated with shorter initial hos-pitalization (4.9 versus 12 days), there is also ahigher rate of eventual recurrence (40.5 versus26.8 percent).27With conservative manage-ment, resolution generally occurs within 24to 48 hours. Beyond this time frame, the riskof complications, including vascular compro-mise, increases. If intestinal obstruction is notresolved with conservative management, sur-gical evaluation is required.25Figures 2 through 4 provided by Cirrelda J. Cooper, MD.The AuthorsPATRICK G. JACKSON, MD, is chief of gastrointestinal sur-gery at Georgetown University Hospital, Washington, DC.MANISH RAIJI, MD, is a third year surgical resident atGeorgetown University Hospital.Address correspondence to Patrick G. Jackson, MD, 3800Reservoir Rd., 4th Floor, PHC, Washington, DC 20007.Reprints are not available from the authors.Author disclosure: Nothing to disclose.REFERENCES1. Irvin TT. Abdominal pain: a surgical audit of 1190 emer-gency admissions. Br J Surg. 1989;76(11):1121-1125.2. Wright HK, O’Brien JJ, Tilson MD. Water absorption inexperimental closed segment obstruction of the ileumin man. Am J Surg. 1971;121(1):96-99.3. Wangensteen OH. Understanding the bowel obstruc-tion problem. Am J Surg. 1978;135(2):131-149.4. Rana SV, Bhardwaj SB. Small intestinal bacterial over-growth. Scand J Gastroenterol. 2008;43(9):1030-1037.5. Shelton BK. Intestinal obstruction [published correctionappears in AACN Clin Issues. 2000;11(1):following tableof contents]. AACN Clin Issues. 1999;10(4):478-491.6. Maglinte DD, Heitkamp DE, Howard TJ, Kelvin FM, Lap-pas JC. Current concepts in imaging of small bowelobstruction. Radiol Clin North Am. 2003;41(2):263-283.7. Lappas JC, Reyes BL, Maglinte DD. Abdominal radiog-raphy findings in small-bowel obstruction: relevanceto triage for additional diagnostic imaging. AJR AmJ Roentgenol. 2001;176(1):167-174.8. Stoker J, van Randen A, Laméris W, Boermeester MA.Imaging patients with acute abdominal pain. Radiology.2009;253(1):31-46.9. Suri S, Gupta S, Sudhakar PJ, Venkataramu NK, Sood B,Wig JD. Comparative evaluation of plain films, ultra-sound and CT in the diagnosis of intestinal obstruction.Acta Radiol. 1999;40(4):422-428.10. Furukawa A, Yamasaki M, Furuichi K, et al. Helical CT inthe diagnosis of small bowel obstruction. Radiographics.2001;21(2):341-355.11. Gazelle GS, Goldberg MA, Wittenberg J, Halpern EF,Pinkney L, Mueller PR. Efficacy of CT in distinguishingsmall-bowel obstruction from other causes of small-boweldilatation. AJR Am J Roentgenol. 1994;162(1):43-47.12. Frager DH, Baer JW, Rothpearl A, Bossart PA. Distinc-tion between postoperative ileus and mechanical small-bowel obstruction: value of CT compared with clinicaland other radiographic findings. AJR Am J Roentgenol.1995;164(4):891-894.13. Ros PR, Huprich JE. ACR Appropriateness Criteria onsuspected small-bowel obstruction. J Am Coll Radiol.2006;3(11):838-841.14. Hayanga AJ, Bass-Wilkins K, Bulkley GB. Current man-agement of small-bowel obstruction. Adv Surg. 2005;39:1-33.15. Choi HK, Chu KW, Law WL. Therapeutic value of gas-trografin in adhesive small bowel obstruction afterunsuccessful conservative treatment: a prospective ran-domized trial. Ann Surg. 2002;236(1):1-6.16. Abbas S, Bissett IP, Parry BR. Oral water soluble contrastfor the management of adhesive small bowel obstruc-tion. Cochrane Database Syst Rev. 2007;(3):CD004651.17. Anderson CA, Humphrey WT. Contrast radiographyin small bowel obstruction: a prospective, randomizedtrial. Mil Med. 1997;162(11):749-752.18. Dunn JT, Halls JM, Berne TV. Roentgenographic con-trast studies in acute small-bowel obstruction. ArchSurg. 1984;119(11):1305-1308.19. Lim JH, Ko YT, Lee DH, Lee HW, Lim JW. Determiningthe site and causes of colonic obstruction with sonog-raphy. AJR Am J Roentgenol. 1994;163(5):1113-1117.20. Matsuoka H, Takahara T, Masaki T, Sugiyama M,Hachiya J, Atomi Y. Preoperative evaluation by magneticresonance imaging in patients with bowel obstruction.Am J Surg. 2002;183(6):614-617.21. Wiarda BM, Horsthuis K, Dobben AC, et al. Magneticresonance imaging of the small bowel with the trueFISP sequence: intra- and interobserver agreement ofenteroclysis and imaging without contrast material. ClinImaging. 2009;33(4):267-273.22. Sagar PM, MacFie J, Sedman P, May J, Mancey-Jones B,Johnstone D. Intestinal obstruction promotes gut trans-location of bacteria. Dis Colon Rectum. 1995;38(6):640-644.23. Chen SC, Yen ZS, Lee CC, et al. Nonsurgical manage-ment of partial adhesive small-bowel obstruction withoral therapy: a randomized controlled trial. CMAJ.2005;173(10):1165-1169.24. Mosley JG, Shoaib A. Operative versus conservative man-agement of adhesional intestinal obstruction. Br J Surg.2000;87(3):362-373.25. Fevang BT, Jensen D, Svanes K, Viste A. Early opera-tion or conservative management of patients with smallbowel obstruction? Eur J Surg. 2002;168(8-9):475-481.26. Williams SB, Greenspon J, Young HA, Orkin BA. Smallbowel obstruction: conservative vs. surgical manage-ment. Dis Colon Rectum. 2005;48(6):1140-1146.27. Cox MR, Gunn IF, Eastman MC, Hunt RF, Heinz AW.The safety and duration of non-operative treatmentfor adhesive small bowel obstruction. Aust N Z J Surg.1993;63(5):367-371.