Feasibility study of analgesia via epidural versus continuous wound infusion after laparoscopic colorectal resection

Background

With the adoption of enhanced recovery and emerging new modalities of analgesia after laparoscopic colorectal resection (LCR), the role of epidural analgesia has been questioned. This pilot trial assessed the feasibility of a randomized controlled trial (RCT) comparing epidural analgesia and use of a local anaesthetic wound infusion catheter (WIC) following LCR.

Methods

Between April 2010 and May 2011, patients undergoing elective LCR in two centres were randomized to analgesia via epidural or WIC. Sham procedures were used to blind surgeons, patients and outcome assessors. The primary outcome was the feasibility of a large RCT, and all outcomes for a definitive trial were tested. The success of blinding was assessed using a mixed-methods approach.

Results

Forty-five patients were eligible, of whom 34 were randomized (mean(s.d.) age 70(11·8) years). Patients were followed up per-protocol; there were no deaths, and five patients had a total of six complications. Challenges with capturing pain data were identified and resolved. Mean(s.d.) pain scores on the day of discharge were 1·9(3·1) in the epidural group and 0·7(0·7) in the WIC group. Median length of stay was 4 (range 2–35, interquartile range 3–5) days. Mean use of additional analgesia (intravenous morphine equivalents) was 12 mg in the WIC arm and 9 mg in the epidural arm. Patient blinding was successful in both arms. Qualitative interviews suggested that patients found participation in the trial acceptable and that they would consider participating in a future trial.

Conclusion

A blinded RCT investigating the role of epidural and WIC administration for postoperative analgesia following LCR is feasible. Rigorous standard operating procedures for data collection are required.

Patient optimization for gastrointestinal cancer surgery

BACKGROUND

Although surgical resection remains the central element in curative treatment of gastrointestinal cancer, increasing emphasis and resource has been focused on neoadjuvant or adjuvant therapy. Developments in these modalities have improved outcomes, but far less attention has been paid to improving oncological outcomes through optimization of perioperative care.

METHODS

A narrative review is presented based on available and updated literature in English and the authors' experience with enhanced recovery research.

RESULTS

A range of perioperative factors (such as lifestyle, co-morbidity, anaemia, sarcopenia, medications, regional analgesia and minimal access surgery) are modifiable, and can be optimized to reduce short- and long-term morbidity and mortality, improve functional capacity and quality of life, and possibly improve oncological outcome. The effect on cancer-free and overall survival may be of equal magnitude to that achieved by many adjuvant oncological regimens. Modulation of core factors, such as nutritional status, systemic inflammation, and surgical and disease-mediated stress, probably influences the host's immune surveillance and defence status both directly and through reduced postoperative morbidity.

CONCLUSION

A wider view on long-term effects of expanded or targeted enhanced recovery protocols is warranted.

Laparoscopic repair of primary perineal hernias: the approach of choice in the 21st century

Perineal hernias are rare and result from the herniation of a viscus through the pelvic floor. Symptomatic perineal hernias are repaired surgically, historically via an open perineal, abdominal or abdominoperineal approach. We describe laparoscopic repair of a primary perineal hernia with mesh using the transabdominal approach. We believe that for uncomplicated primary perineal hernias laparoscopic repair is technically feasible, and associated with rapid recovery and minimal complications.

Continuum model for steady, fully developed saltation above a horizontal particle bed

We propose a continuum model for steady, fully developed saltation above a horizontal particle bed that provides local, analytical expressions for the particle pressure and shear stress. This analytical approach contrasts with discrete numerical simulations in which the trajectories of individual particles are computed as they interact with gravity, the wind, and the bed. The continuum model has the advantage that it can easily be extended to nonuniform and unsteady situations. We employ it to predict the fields of concentration, particle velocity, and wind velocity in steady, fully developed saltation above a particle bed over a range of wind speeds. The predicted profiles are in good agreement with those measured in wind tunnel experiments.

Perineum compression during EAUS enhances visualization of anterior anal sphincter defects

OBJECTIVE

Endo-anal ultrasound (EAUS) can detect anal sphincter injuries. However, anterior external anal sphincter (EAS) defects can be difficult to define. We assessed different EAUS techniques to determine if any particular method improved defect identification.

METHOD

Ninety females with faecal incontinence were prospectively studied. Wexner faecal incontinence scores were obtained. All patients underwent anorectal manometry and EAUS using three different techniques: standard, digit-assisted (gloved finger pressing on posterior vaginal wall) and balloon-assisted (standard balloon inflated into the vagina). The three techniques were assessed by comparing defect characteristics (detection, angle, edges and scar tissue), and perineal body thickness. All measurements were performed at the mid anal canal level.

RESULTS

are expressed as medians (IQR). Results Standard EAUS (S-EAUS) identified a sphincter defect in 54 patients. Digit assisted EAUS (D-EAUS) and balloon-assisted EAUS (B-EAUS) ultrasound revealed a sphincter defect in additional 11 and 9 patients respectively compared to S-EAUS. Correlation of maximum squeeze pressure with EAUS findings improved on D-EAUS and B-EAUS. The defect angle was significantly wider with D-EAUS and B-EAUS [S-EAUS 90 degrees (63-97), D-EAUS 100 degrees (81-101.5), B-EAUS 100 degrees (80-105), P = 0.0005]. The perineal body was significantly thicker when measured with B-EAUS [D-EAUS 9 mm (7-10) vs B-EAUS 10 mm (8-11), P = 0.0005]. Inter-observer agreement was comparable [S-EAUS (K) = 0.677, D-EAUS (K) = 0.658, B-EAUS (K) = 0.601].

CONCLUSION

EAS anterior defect detection and definition on EAUS may be improved by the demarcation and gentle pressure on the posterior vaginal wall.

Defunctioning stomas in patients with locally advanced rectal cancer prior to preoperative chemoradiotherapy

OBJECTIVE

A literature search did not produce any evidence-based objective criteria to determine which patients with locally advanced rectal cancer would benefit from a defunctioning stoma prior to neoadjuvant chemoradiotherapy. Our criteria for formation of a defunctioning stoma are: faecal incontinence and inability to cannulate the tumour at colonoscopy. The aim of this study was to examine whether these current criteria are appropriate.

METHOD

Forty-nine consecutive locally advanced rectal cancer patients treated from February 2003 to November 2006 were identified from our colorectal database. All received long-course chemoradiotherapy (Bossett regimen) and definitive surgery was performed 6-8 weeks later.

RESULTS

Of the 49 patients, 31 presented with diarrhoea and two with faecal incontinence; nine patients were defunctioned by trephine stoma prior to treatment [cannulation impossible at colonoscopy (n = 8); faecal incontinence (n = 1)]. One patient with faecal incontinence refused early defunctioning stoma. Median hospital stay was 12 days (interquartile range: 7-30), and complications included pneumonia (n = 1) and peristomal cellulitis (n = 2). Of the 40 patients who went directly to neoadjuvant chemoradiotherapy, two subsequently required a defunctioning stoma for severe diarrhoeal symptoms during therapy. Eight patients had worsening diarrhoeal symptoms but tolerated treatment. Three patients, who had stoma formation, did not proceed to definitive surgery following neoadjuvant therapy: poor operative fitness (n = 2) and disease progression (n = 1).

CONCLUSION

Stenosis causing inability to cannulate the tumour at colonoscopy and faecal incontinence were the only objective indications for an early defunctioning stoma. Worsening diarrhoea during therapy (unless severe) did not appear to be a good indication for a defunctioning stoma.

Anterior anal fissures are associated with occult sphincter injury and abnormal sphincter function

OBJECTIVE

The pathogenesis of chronic anal fissure (CAF) remains incompletely understood but most are associated with a high resting anal pressure and reduced perfusion at the fissure site. To date, no major distinction has been made between anterior and posterior anal fissures and their aetiology and treatment. We compared anterior and posterior fissures in patients who have failed to respond to medical treatment with respect to their underlying aetiology, anal canal pressures and sphincter muscle integrity.

METHOD

Seventy consecutive patients (54 female:16 male) with a symptomatic CAF and 39 normal controls (19 female:20 male) without evidence of significant ano-rectal pathology were prospectively assessed by manometry and anal endosonography.

RESULTS

Anterior anal fissures were identified in a younger age group [33 years (IQR 26-37) vs 41 years (IQR 36-52)] and predominantly in women. Anterior fissure patients were significantly more likely to have underlying external anal sphincter defects compared with posterior fissures [OR 10.9 (95% CI 3.4-35.4)]. Maximum resting pressure was not significantly elevated for anterior fissures compared with controls (P = 0.316) but was significantly elevated in posterior fissures (P = 0.005). The maximum squeeze pressure was significantly lower in the anterior fissure group [167 cmH2O (IQR 126-196) vs 205 cmH2O (IQR 174-262), P = 0.004]. A history of obstetric trauma was significantly associated with anterior fissure location [OR 13.9 (95% CI 3.4-55.7)].

CONCLUSIONS

Anterior anal fissures are associated with occult external anal sphincter injury and impaired external anal sphincter function compared with posterior fissures. These findings have implications for treatment, especially if a definitive procedure, such as lateral internal sphincterotomy, is considered.

Prospective validation study of an algorithm for triage to MRCP or ERCP for investigation of suspected pancreatico-biliary disease

BACKGROUND

In patients with suspected pancreatico-biliary disease, endoscopic retrograde cholangiopancreatography (ERCP) should be reserved for those requiring therapeutic intervention. However, difficulty arises in identifying patients likely to require therapy in the early phase of diagnostic work-up. An algorithm has been developed by the authors based upon prospective assessment of ERCP patients for triage of patients to magnetic resonance cholangiopancreatography (MRCP) or ERCP with suspected pancreatico-biliary disease. We aimed to validate this algorithm in an independent group of patients using a different group of endoscopists blinded to the algorithm.

METHODS

Patients were stratified into different categories by clinical, ultrasound and liver function test findings. The algorithm stratified patients by the likelihood of therapeutic intervention. The accuracy of the algorithm for a therapeutic outcome was assessed by receiver operator characteristics (ROC) curve analysis.

RESULTS

Hundred and twenty-five consecutive patients (Oct 2005 to July 2006) were prospectively assessed by MRCP or ERCP according to the algorithm, and the outcomes recorded. Fifty-seven patients were triaged to MRCP and 63 patients were triaged to ERCP. A category was not assessable in five patients. Three patients from the MRCP group required subsequent therapeutic ERCP. Diagnostic ERCP was performed in three patients in the ERCP group. ERCP-related complications occurred in four patients. The algorithm performed well in predicting the requirement for intervention as determined by the area under the ROC curve [0.84 (95%CI 0.76-0.92)].

CONCLUSIONS

Our study confirms that an algorithm-based approach can reproducibly predict those patients requiring therapeutic biliary intervention.

Correlation between anal manometry and endosonography in females with faecal incontinence

OBJECTIVE

Female faecal incontinence (FI) is largely because of sphincter injury at childbirth. Sphincter assessment aims to identify surgically correctable defects. We aimed to identify endoanal ultrasonography (EAUS) parameters that correlate with sphincter function.

METHOD

One hundred females with FI and 28 healthy asymptomatic females were prospectively assessed. Wexner FI score was recorded and all subjects underwent anorectal manometry and EAUS. Multiple EAUS parameters were assessed and correlated with external (EAS) and internal (IAS) anal sphincter function, determined by maximum squeeze pressure (MSP) and maximum resting pressure (MRP) respectively. Parameters included sphincter quality (echogenicity), thickness, perineal body thickness (PBT) and defect characteristics (angle, length). Results are expressed as medians and interquartile range (IQR).

RESULTS

Median Wexner score was 14 (12-17). Maximum EAS thickness significantly correlated with MSP (P = 0.019). EAS defects were detected in 84 patients and seven controls (P < 0.0001). Full-length EAS defects were only detected in FI group and had significantly lower MSP [MSP mmHg: full length 85 (65-103) vs partial length 119 (75-155), P = 0.006]. FI patients were more likely to have a mixed echogenicity of EAS compared with controls. EAS ring quality, PBT and defect angle were not significant. IAS quality was significantly associated with MRP [MRP mmHg: uniform 62 (43-82) vs mixed 47 (30.5-57.5), P = 0.002].

CONCLUSION

Certain EAUS parameters can be predictive of anal sphincter function. These include the presence of an EAS defect and its length, EAS maximum thickness, IAS ring quality. Integration of these parameters can give better EAUS correlation with manometry for FI evaluation.

Prospective study of laparoscopic adjustable gastric banding in the west of Scotland

Obesity is an increasing problem in Scotland and Laparoscopic Adjustable Gastric Bands (LAGB) are an effective method of weight reduction. Most outcome data are reported from high volume units with extensive experience or dedicated bariatric practice. We aimed to assess an experienced laparoscopic surgeon's outcome working outwith a dedicated bariatric practice in the west of Scotland.

METHODS

All LAGB procedures performed by a single surgeon were prospectively assessed from 1997 to 2004. LAGB were inserted using pars flaccida approach. Patient selection was based on BMI >35 or significant obesity related co-morbidities. Outcomes included percentage excess weight loss (%EWL) and excess BMI loss (EBL). We assessed total operating time to assess the learning curve for LAGB placement.

RESULTS

125 patients were assessed (107 F:18 M). 123 patients were in regular follow-up (98%). Median age was 44 years (range 25-63). Mean follow-up was 34 months (range 11-91). Median initial BMI was 49 (range 37-73). 31% were BMI 35-45, 36% were BMI 45-50 and 33% were BMI>50. %EWL at 1,3 and 5 years was 45, 58 and 74, respectively. EBL at 1, 3 and 5 years was 11.7, 16.1, and 21.7, respectively. Complications included 4 converted procedures, 1 failed band insertion after conversion and re-operation for removal in five. Eight patients had tubing access port problems requiring intervention. The median overall total operation time was 80 minutes (range 50 - 160).

CONCLUSIONS

In this cohort LAGB insertion by an experienced laparoscopic surgeon is safe with few re-operations. Satisfactory weight loss is obtained and patient compliance with follow-up is high.

The impact of poor bowel preparation on colonoscopy: a prospective single centre study of 10,571 colonoscopies

OBJECTIVE

Colonoscopy is regarded as the most sensitive method of evaluating the colon. Inadequate preparation reduces sensitivity and has adverse implications for individual patients and the Heath Service.

METHOD

Data concerning the adequacy of bowel preparation and colonoscopy completion rates were prospectively collected on all colonoscopies performed in a single centre between January 1996 and January 2005. In addition, the strategy of further investigation in the event of incomplete examination was assessed.

RESULTS

A total of 10 571 colonoscopies were assessed and poor bowel preparation was identified in 1788 of these cases (16.9%). The completion rate was 67.5% in those with satisfactory preparation. In patients with poor preparation, 36% of colonoscopies were complete. Incomplete examination was more likely with poor preparation [OR = 3.76 (95% CI, 3.38-4.18), P = 0.0005]. Poor preparation was more likely for inpatients [OR = 3.54 (95% CI 3.14-3.96), P = 0.0005]. Even with satisfactory preparation, inpatient completion rates were significantly less [OR = 1.78 (95% CI, 3.14-3.96), P = 0.0005). A further 542 diagnostic procedures were undertaken in the poor preparation group, an additional pound101 950 (euro149 459) in expenditure.

CONCLUSION

This study supports the view that inpatients fare badly. This is partly explained by higher rates of poor preparation; however, completion rates were reduced even with adequate preparation. Failed investigation and prolonged hospital stay increase cost. Colonoscopy completion rates need to be improved with particular attention to inpatients.

Prospective study of the diagnostic evaluation of faecal incontinence and leakage in male patients

OBJECTIVE

Male faecal incontinence (FI) has received little attention. No consistent pathophysiological abnormality has been identified in those studies that have specifically assessed male patients with FI or faecal leakage (FL). This study was designed to re-examine the different theories relating to the pathophysiology of male incontinence and to assess if manometric and ultrasound assessment yields clinically relevant information that directs patient care.

METHOD

This was a prospective study of all men referred to a Coloproctology clinic with incontinence. The Wexner Incontinence score was used to assess severity of symptoms. Specific investigations included anal manometry, rectal sensation and endo-anal ultrasound (EAUS). Results were compared with a group of 20 normal male controls.

RESULTS

A total of 59 symptomatic male patients were investigated (36 FI, 23 FL). FL and control groups had similar maximum resting (MRP) and maximum squeeze pressure (MSP). The incontinence group had a significantly lower MRP & MSP compared with controls [MRP: FI 58 (42-75.5) vs control 85 (72-104)] (P < 0.0001), [MSP: FI 167 (125-215) vs control 248 (192-302)] (P < 0.0001). There was no significant difference in rectal sensation between the groups and the defecation index was also similar. EAUS detected only one external anal sphincter defect amongst the 23 male patients with FL. One external sphincter defect and three internal sphincter defects were identified amongst the 36 patients with incontinence. Of these five patients with sphincter defects, four had previously undergone anorectal surgery. [Results expressed as median (interquartile range): manometry expressed as mmHg].

CONCLUSION

Male patients presenting with faecal incontinence frequently show impaired sphincter function which may be associated with sphincter defects. In contrast, those presenting predominantly with FL have no morphological or physiological changes that might account for their symptoms. Investigating such patients with anorectal physiology and EAUS is usually unhelpful and can be omitted.

Malignant disease in peptic ulcer surgery patients after long term follow-up: A cohort study of 1992 patients

AIMS

To assess the effect of previous peptic ulcer surgery on subsequent malignant events, in particular in relation to previous vagotomy, a historical cohort study was conducted.

METHODS

All patients undergoing surgery for peptic ulcer disease with accurate follow-up data at a large peptic ulcer clinic in the Western Infirmary, Glasgow, from 1965 to 1983 were assessed. All cancer events and specific cancer events (gastric, bronchial, laryngeal, colorectal, bladder, breast, prostate, pancreas, kidney, oesophageal cancers) were determined as outcome measures and expressed as standardised incidence ratio (SIR).

RESULTS

Vagotomy and drainage accounted for 67% of all procedures for peptic ulcer disease. Eighty-three percent were habitual smokers. For all peptic ulcer surgery patients, the SIR for all cancer events was 0.86. For specific cancers, the SIRs were bronchial cancer (SIR 1.13); laryngeal cancer (SIR 2.17), colorectal cancer (SIR 0.67). For vagotomised patients the risk of gastric cancer was significantly elevated (SIR 1.50).

CONCLUSIONS

An excess of cancers attributable to smoking have been found in peptic ulcer surgery patients. Vagotomised patients have a higher risk of gastric cancer after long term follow-up. This finding may have implications for screening and the safety of long term acid suppression with agents such as proton pump inhibitors.

Quality of life and alteration in comorbidity following laparoscopic adjustable gastric banding

OBJECTIVES

Obesity is an increasing problem in the UK and bariatric surgery is likely to increase in volume in the future. While substantial weight loss is the primary outcome following bariatric surgery, the effect on obesity-related morbidity, mortality and quality of life (QOL) is equally important. This study reports on weight loss, QOL, and health outcomes following laparoscopic adjustable gastric banding (LAGB) in a low volume bariatric centre (<20 cases/year) and presents the first assessment of factors relating to the QOL which has been produced from a UK based surgical practice.

STUDY DESIGN

Questionnaire based study of patients who had LAGB. Each patients' initial body mass index (BMI), QOL, and comorbidities were recorded. Change in these parameters was measured including excess weight loss, and output from both the Moorehead-Ardelt QOL questionnaire, and the Bariatric Analysis and Reporting Outcome System (BAROS).

RESULTS

Eighty-one patients (14 males, 67 females) answered the questionnaire. More than 50% excess weight loss was recorded in 52/81 patients (64%). Sixty-four patients (79%) reported improvement in their QOL including self-esteem, physical activity, social involvement, and ability to work. Seventy-one patients had initial obesity related comorbidity. In 61 of these patients (86%) their comorbidities resolved or improved. Minor port site related complications were recorded in nine patients while two patients had removal of the band because of infection.

CONCLUSION

LAGB is a safe method of bariatric surgery. It can achieve satisfactory weight loss with significant improvement in QOL and comorbidity.

The relationship between patient physiology and cancer-specific survival following curative resection of colorectal cancer

The impact of patient physiology on cancer-specific survival is poorly documented. Patient physiology predicted overall, cancer-specific (Physiology Score>30; HR 8.64 (95% CI 3.00-24.92); P=0.0005) and recurrence-free survival (Physiology Score >30; HR 7.44 (95% CI 1.99-27.73); P=0.003) independent of Dukes stage following potentially curative surgery for colorectal cancer. This independent negative association with survival is a novel observation.

Density inversion in rapid granular flows: the supported regime

This paper presents numerical findings on rapid 2D and 3D granular flows on a bumpy base. In the supported regime studied here, a strongly sheared, dilute and agitated layer spontaneously appears at the base of the flow and supports a compact packing of grains moving as a whole. In this regime, the flow behaves like a sliding block on the bumpy base. In particular, for flows on a horizontal base, the average velocity decreases linearly in time and the average kinetic energy decreases linearly with the travelled distance, those features being characteristic of solid-like friction. This allows us to define and measure an effective friction coefficient, which is independent of the mass and velocity of the flow. This coefficient only loosely depends on the value of the micromechanical friction coefficient whereas the infuence of the bumpiness of the base is strong. We give evidence that this dilute and agitated layer does not result in significantly less friction. Finally, we show that a steady regime of supported flows can exist on inclines whose angle is carefully chosen.

A technically difficult endorectal ultrasound is more likely to be inaccurate

OBJECTIVE

Endorectal ultrasound (ERUS) is well established as an accurate modality for local staging of rectal tumours. The aim of this study was to identify reasons for inaccurate staging of tumours, and to assess whether difficulties encountered during scanning are likely to influence accuracy.

PATIENTS AND METHODS

ERUS was performed by a single operator using a 10 MHz rigid instrument. One hundred and seventeen patients that had both ERUS and surgery are included in this study (patients that had pre-operative radiotherapy were excluded). During ERUS, procedural conditions and limiting factors were recorded. Data was collected prospectively.

RESULTS

In 78 (66.7%) patients no technical difficulty was encountered during ERUS. In this group accuracy was 80% for T-stage and 77% for N-stage. Specific reasons for inaccuracy identified in this group were: inflammatory lymph nodes (from a tumour associated abscess and a colovesical fistula) and deep biopsy causing a submucosal defect with intramural haemorrhage in benign lesions (2 cases). In the remaining 39 (33.3%), the following problems were encountered: stenotic lesions (23), patient discomfort (8), poor bowel preparation (6), and scarring from previous surgery (2). In 11 patients from this group, the scan was considered inconclusive and no stage could be determined. For the other 28, the accuracy for T-stage was 68% and for N-stage 67%.

CONCLUSION

A technically difficult ERUS is likely to give an inconclusive or inaccurate result for both T-stage (P = 0.001) and N-stage (P = 0.003). In this situation a repeat scan may be considered (where appropriate). Alternatively, further assessment by MRI or flexible endoscopic ultrasound may be considered.

Membrane elasticity in giant vesicles with fluid phase coexistence

Biological membranes are known to contain compositional heterogeneities, often termed rafts, with distinguishable composition and function, and these heterogeneities participate in vigorous transport processes. Membrane lipid phase coexistence is expected to modulate these processes through the differing mechanical properties of the bulk domains and line tension at phase boundaries. In this contribution, we compare the predictions from a shape theory derived for vesicles with fluid phase coexistence to the geometry of giant unilamellar vesicles with coexisting liquid-disordered (L(d)) and liquid-ordered (L(o)) phases. We find a bending modulus for the L(o) phase higher than that of the L(d) phase and a saddle-splay (Gauss) modulus difference with the Gauss modulus of the L(o) phase being more negative than the L(d) phase. The Gauss modulus critically influences membrane processes that change topology, such as vesicle fission or fusion, and could therefore be of significant biological relevance in heterogeneous membranes. Our observations of experimental vesicle geometries being modulated by Gaussian curvature moduli differences confirm the prediction by the theory of Juelicher and Lipowsky.

The incremental response of random aggregates of identical round particles

This paper is concerned with a dense, randomly packed, granular material that consists of identical spheres or disks with elastic, frictional interactions, that is first isotropically compressed and subsequently loaded along an arbitrary stress path. An analytical relationship between the overall stress and strain increments is determined for the pre-failure regime. The purpose of the modelling is to understand how this relation depends upon the features of the packing and the particle interactions. From the outset it is recognised that the packing and interactive properties for these materials may vary substantially from grain to grain and the heterogeneity introduced in this manner is fully accounted for. Moment equilibrium equations are solved for each particle and force equilibrium equations are solved for each neighbourhood. Then, the heterogeneity of the aggregate is taken into account by introducing means and fluctuations in the description of the local deformations and the measures of the particles and interactions. The general development is illustrated with an example in two dimensions in which the packing and contact interactions are approximated by angular distributions and the heterogeneity is introduced by variations in these. For an isotropic medium with constant contact stiffnesses the theory provides predictions that compare well with results obtained from numerical simulations.

Segregation in binary mixtures under gravity

We employ kinetic theory for a binary mixture to study segregation by size and/or mass in a gravitational field. Simple segregation criteria are obtained for spheres and disks that are supported by numerical simulations.

Secondary causes of intestinal obstruction: rigorous preoperative evaluation is required

The clinical presentation, management and outcome of patients with small intestinal and large bowel obstruction unrelated to adhesive or primary colonic neoplastic disease is not well described. The aim of this study was to determine the clinical presentation, evaluation, operative management, and outcome in patients with secondary causes of intestinal obstruction. The medical records of 200 patients who underwent an operation for intestinal obstruction from January 1995 through December 1997 were reviewed. Seventy-three patients (37%) had secondary causes of intestinal obstruction, and these records were reviewed in detail. The cohort included 37 men and 36 women with a mean age of 52 +/- 2 years. The etiology of intestinal obstruction was metastatic neoplastic obstruction (19%), colonic volvulus (18%), Crohn's disease (14%), herniae (11%), diverticular disease (7%), and miscellaneous causes (31%). Six patients (8%) had intestinal motor disorders and a misdiagnosis of intestinal obstruction. The clinical presentation of patients with secondary causes of obstruction was similar to typical patients with adhesive small bowel obstruction. Preoperative evaluation included frequent use of CT (42%), but intestinal contrast studies were used in 13 (18%) patients only. Two-thirds of the patients required an intestinal resection, and 50 per cent of the patients with a misdiagnosis had a nontherapeutic celiotomy. Operative mortality and morbidity were 3 per cent and 48 per cent, respectively, and 15 per cent of patients required reoperation. Suspected intestinal obstruction from secondary causes requires rigorous preoperative evaluation with liberal use of intestinal contrast examinations to avoid misdiagnosis, operative complications, and reoperations.

Hydraulic theory for a debris flow supported on a collisional shear layer

We consider a heap of grains driven by gravity down an incline. We assume that the heap is supported at its base on a relatively thin carpet of intensely sheared, highly agitated grains that interact through collisions. We adopt the balance laws, constitutive relations, and boundary conditions of a kinetic theory for dense granular flows and determine the relationship between the shear stress, normal stress, and relative velocity of the boundaries in the shear layer in an analysis of a steady shearing flow between identical bumpy boundaries. This relationship permits us to close the hydraulic equations governing the evolution of the shape of the heap and the velocity distribution at its base. We integrate the resulting equations numerically for typical values of the parameters for glass spheres. (c) 1999 American Institute of Physics.