Health resource utilization of labor induction versus expectant management

BACKGROUND

Although induction of labor of low-risk nulliparous women at 39 weeks reduces the risk of cesarean delivery compared with expectant management, concern regarding more frequent use of labor induction remains, given that this intervention historically has been thought to incur greater resource utilization.

OBJECTIVE

The objective of the study was to determine whether planned elective labor induction at 39 weeks among low-risk nulliparous women, compared with expectant management, was associated with differences in health care resource utilization from the time of randomization through 8 weeks postpartum.

STUDY DESIGN

This is a planned secondary analysis of a multicenter randomized trial in which low-risk nulliparous women were assigned to induction of labor at 39 weeks or expectant management. We assessed resource utilization after randomization in 3 time periods: antepartum, delivery admission, and discharge through 8 weeks postpartum.

RESULTS

Of 6096 women with data available, those in the induction of labor group (n = 3059) were significantly less likely in the antepartum period after randomization to have at least 1 ambulatory visit for routine prenatal care (32.4% vs 68.4%), unanticipated care (0.5% vs 2.6%), or urgent care (16.2% vs 44.3%), or at least 1 antepartum hospitalization (0.8% vs 2.2%, P < .001 for all). They also had fewer tests (eg, sonograms, blood tests) and treatments (eg, antibiotics, intravenous hydration) prior to delivery. During the delivery admission, women in the induction of labor group spent a longer time in labor and delivery (median, 0.83 vs 0.57 days), but both women (P = .002) and their neonates (P < .001) had shorter postpartum stays. Women and neonates in both groups had similar frequencies of postpartum urgent care and hospital readmissions (P > .05 for all).

CONCLUSION

Women randomized to induction of labor had longer durations in labor and delivery but significantly fewer antepartum visits, tests, and treatments and shorter maternal and neonatal hospital durations after delivery. These results demonstrate that the health outcome advantages associated with induction of labor are gained without incurring uniformly greater health care resource use.

Comparison of adaptive radiotherapy techniques for the treatment of bladder cancer

OBJECTIVE

Day-to-day anatomical variations complicate bladder cancer radiotherapy treatment. This work quantifies the impact on target coverage and irradiated normal tissue volume for different adaptive strategies.

METHODS

20 patients were retrospectively planned using different three-dimensional conformal radiotherapy treatment strategies for whole-bladder carcinoma: (i) "conventional" treatment used isotropic expansion of the clinical target volume (CTV) by 15 mm to the planning target volume (PTV) for daily treatment; (ii) "plan of the day" used daily volumetric on-treatment imaging [cone beam CT (CBCT)] to select from four available plans with varying superior PTV margins; (iii) "composite" strategies used on-treatment CBCTs from Fractions 1-3 to inform a composite CTV and adapted PTV (5- and 10-mm margins for composite 1 and composite 2, respectively) for subsequent treatment. Target coverage was evaluated from available CBCTs (the first three fractions then the minimum weekly thereafter), and the reduction in the irradiated volume (i.e. within the 95% isodose) was quantified.

RESULTS

Plan of the day improved target coverage (i.e. all of the bladder within the 95% isodose throughout the treatment) relative to conventional treatment (p=0.10), while no such benefit was observed with composite 2. Target coverage was reduced with composite 1 relative to conventional treatment. The mean irradiated volume was reduced by 17.2%, 35.0% and 14.6% relative to conventional treatment, for plan of the day, composite 1 and composite 2, respectively (p<0.01 in all cases). No parameters predictive of large changes in bladder volume later in the treatment were identified.

CONCLUSIONS

Adaptive techniques can maintain or improve target coverage while allowing for reduced irradiated volume and possibly reduced toxicity. The plan-of-the-day technique appeared to provide the optimal balance between target coverage and normal tissue sparing.

ADVANCES IN KNOWLEDGE

This study suggests that plan-of-the-day techniques will provide optimal outcomes for adaptive bladder radiotherapy.

A megavoltage scatter correction technique for cone-beam CT images acquired during VMAT delivery

Kilovoltage cone-beam CT (kV CBCT) can be acquired during the delivery of volumetric modulated arc therapy (VMAT), in order to obtain an image of the patient during treatment. However, the quality of such CBCTs is degraded by megavoltage (MV) scatter from the treatment beam onto the imaging panel. The objective of this paper is to introduce a novel MV scatter correction method for simultaneous CBCT during VMAT, and to investigate its effectiveness when compared to other techniques. The correction requires the acquisition of a separate set of images taken during VMAT delivery, while the kV beam is off. These images--which contain only the MV scatter contribution on the imaging panel--are then used to correct the corresponding kV/MV projections. To test this method, CBCTs were taken of an image quality phantom during VMAT delivery and measurements of contrast to noise ratio were made. Additionally, the correction was applied to the datasets of three VMAT prostate patients, who also received simultaneous CBCTs. The clinical image quality was assessed using a validated scoring system, comparing standard CBCTs to the uncorrected simultaneous CBCTs and a variety of correction methods. Results show that the correction is able to recover some of the low and high-contrast signal to noise ratio lost due to MV scatter. From the patient study, the corrected CBCT scored significantly higher than the uncorrected images in terms of the ability to identify the boundary between the prostate and surrounding soft tissue. In summary, a simple MV scatter correction method has been developed and, using both phantom and patient data, is shown to improve the image quality of simultaneous CBCTs taken during VMAT delivery.

Anatomical failure following laparoscopic antireflux surgery (LARS): does it really matter?

INTRODUCTION

Failure rates of laparoscopic antireflux surgery (LARS) vary from 2-30%. A degree of anatomical failure is common, and the most common failure is intrathoracic wrap herniation. We have assessed anatomical integrity of the crural repair and wrap using marking Liga clips placed at the time of surgery and compared this with symptomatic outcome.

PATIENTS AND METHODS

A prospective study was undertaken on 50 patients who underwent LARS in a single centre over a 3-year period. Each had an X-ray on the first postoperative day and a barium swallow at 6 months at which the distance was measured between the marking Liga clips. An increase in interclip distance of > 25-49% was deemed 'mild separation', and an increase of > 50% 'moderate separation'. Patients completed a standardised symptom questionnaire at 6 months.

RESULTS

At 6 months' postoperatively, 22% had mild separation of the crural repair with a mean Visick score of 1.18, and 54% had moderate separation with a mean Visick score of 1.26. Mild separation of the wrap occurred in 28% with a mean Visick score of 1.21 and 22% moderate separation with a mean Visick score of 1.18. Three percent had mild separation of both the crural repair and wrap with a mean Visick score of 1.0, and 16% moderate separation with a mean Visick score of 1.13. Of patients, 14% had evidence of some degree of failure on barium swallow but only one of these was significant intrathoracic migration of the wrap which was symptomatic and required re-do surgery.

CONCLUSIONS

The prevalence of some form of anatomical failure, as determined by an increase in the interclip distance, is high at 6 months' postoperatively following LARS. However, this does not seem to correlate with a subjective recurrence of symptoms.

Randomized clinical trial of laparoscopic total (Nissen) versus posterior partial (Toupet) fundoplication for gastro-oesophageal reflux disease based on preoperative oesophageal manometry

Background

Laparoscopic fundoplication is an accepted treatment for symptomatic gastro-oesophageal reflux disease. The aim of this study was to clarify whether total (Nissen) or partial (Toupet) fundoplication is preferable, and whether preoperative oesophageal manometry should be used to determine the degree of fundoplication performed.

Methods

Preoperative oesophageal manometry was used to stratify 127 patients with established gastro-oesophageal reflux disease into effective (75) and ineffective (52) oesophageal motility groups. Patients in each group were randomized to Nissen (64) or Toupet (63) fundoplication.

Results

No significant differences between the operative groups were seen in heartburn, regurgitation or other reflux-related symptoms up to 1 year after surgery. Dysphagia of any degree (27 versus 9 per cent; P = 0·018) and chest pain on eating (22 versus 5 per cent; P = 0·018) were more prevalent at 1 year in the Nissen group. There were no differences in postoperative symptoms between the effective and ineffective motility groups. Surgery failed in eight patients on postoperative pH criteria, three in the Nissen group and five in the Toupet group.

Conclusion

Any differences in the symptomatic outcome of laparoscopic Nissen and Toupet fundoplication appear minimal. There is no reason to tailor the degree of fundoplication to preoperative oesophageal manometry.

The extended learning curve for laparoscopic fundoplication: a cohort analysis of 400 consecutive cases

Many studies have looked at the learning curve associated with laparoscopic Nissen fundoplication (LNF) in a given institution. This study looks at the learning curve of a single surgeon with a large cohort of patients over a 10-year period. Prospective data were collected on 400 patients undergoing laparoscopic fundoplication for over 10 years. The patients were grouped consecutively into cohorts of 50 patients. The operating time, the length of postoperative hospital stay, the conversion rate to open operation, the postoperative dilatation rate, and the reoperation rate were analyzed. Results showed that the mean length of operative time decreased from 143 min in the first 50 patients to 86 min in the last 50 patients. The mean postoperative length of hospital stay decreased from 3.7 days initially to 1.2 days latterly. There was a 14% conversion to open operation rate in the first cohort compared with a 2% rate in the last cohort. Fourteen percent of patients required reoperation in the first cohort and 6% in the last cohort. Sixteen percent required postoperative dilatation in the first cohort. None of the last 150 patients required dilatation. In conclusion, laparoscopic fundoplication is a safe and effective operation for patients with gastroesophageal reflux disease. New techniques and better instrumentation were introduced in the early era of LNF. The learning curve, however, continues well beyond the first 20 patients.

Developments in and experience of kilovoltage X-ray cone beam image-guided radiotherapy

This paper offers a realistic review of kilovoltage X-ray cone beam tomography integrated with the treatment machine for image-guided radiotherapy in the light of experience taking a commercial system from prototype development into clinical use. It shows that key practicalities cannot be ignored, in particular the regular characterization of mechanical flex during gantry rotation, the mapping of defects in flat panel image transducers and their response to X-ray exposure. The number of X-ray projections and the doses required for clinically useful cone beam reconstruction at different therapy sites are considered in the context of imaging that is fit for purpose. Three roles for cone beam tomography in radiotherapy are identified: patient setup in three dimensions (3D), where even low dose cone beam tissue detail is superior to megavoltage imaging; disease targeting where, despite wide field scatter and slow scanning, it is possible to generate images that are suitable for tumour delineation even at challenging sites; adaptive treatment planning, where calibrated cone beam images have been shown to provide sufficient target detail to support "plan of the day" selection and have the potential for planning with bulk corrections. With frequent use in mind, the need to limit patient dose during setup, yet maximize much needed image quality in the target zone, is considered. Finally, it is noted that the development of cone beam tomography for radiotherapy is far from complete, with X-ray source, image transducer, reconstruction algorithms and techniques for image profile collection still being researched.

Radiotherapy Treatment Verification in the UK: An Audit of Practice in 2004

AIMS

To audit current practice related to treatment verification undertaken in radiotherapy departments throughout the UK.

MATERIALS AND METHODS

A questionnaire was circulated to the radiotherapy service managers of 62 radiotherapy centres in the UK. This looked in detail at the department demographics, imaging equipment, site-specific verification protocols, and training and competency assessment of staff responsible for verification.

RESULTS

The response rate was 48% (30/62). All departments were using megavoltage imaging equipment in routine clinical practice. Twenty-four out of 29 (83%) departments that had electronic portal imaging capability were using image analysis software for verification. Twenty-nine out of 30 (97%) departments had site-specific written verification protocols. Twenty out of 30 (67%) treatment centres audited set-up errors within their department. Forty-three per cent of centres were using simulator image as the reference image of choice across all sites. Electronic portal imaging, alone or in combination with portal film, was being used for verification in 75% of the centres. Fifty-three per cent of centres used off-line correction strategies for measuring set-up errors across all sites. Radiographer-led interventions were primarily in the pelvis.

CONCLUSION

Presently in the UK, verification strategies vary widely at individual treatment sites and between departments. Dedicated departmental verification teams, with input from radiographers, physicists and clinicians, may assist in the effective implementation of evidence-based verification. The inclusion of comprehensive verification protocols within multicentre radiotherapy trials encourages standardisation across treatment centres.

An assessment of clinically optimal gold marker length and diameter for pelvic radiotherapy verification using an amorphous silicon flat panel electronic portal imaging device

Verification of target organ position is essential for the accurate delivery of conformal radiotherapy. Megavoltage electronic portal imaging with flat panel amorphous silicon detectors delivers high quality images that can be used for verification of bony landmark position. Gold markers implanted into the target organ can be visualized and used as a surrogate of actual organ position. On-line compensation for marker displacement, by adjusting patient position, can reduce geometric errors associated with radiation delivery. This study assesses the optimal marker length and diameter to be used with an amorphous silicon (a-Si) flat panel detector and electronic portal images (EPIs), prior to implementation of a clinical programme of gold marker insertion in prostate cancer patients. Seven marker sizes varying from 3 mm to 8 mm in length and 0.8 mm to 1.1 mm in diameter were investigated in a group of patients undergoing pelvic radiotherapy using an 8 MV Elekta SL20 linear accelerator. Markers were placed on the skin entry and exit sites of the treatment beam and EPIs in both lateral and anterior pelvic views were acquired. Three observers independently assessed visibility success and failure using a subjective scoring system. Markers less than 5 mm in length or 0.9 mm in diameter were poorly visualized (<70% visualization success in lateral EPIs). The marker measuring 0.9 mm x 5 mm appears to be clinically optimal in pelvic radiotherapy patients (80% visualization success in lateral EPIs) and will be used for actual organ implantation.

A poor response to proton pump inhibition is not a contraindication for laparoscopic antireflux surgery for gastro esophageal reflux disease

BACKGROUND

We aimed to determine if a poor response to proton pump inhibitors (PPIs) can predict a poor outcome following laparoscopic antireflux surgery (LARS) in our surgically treated population.

METHODS

A total of 324 patients undergoing LARS were included in this study. Following standardized assessment, patients recorded the efficacy of their medication on visual analogue scales. Pre- and postoperative symptom scores were recorded, with outcomes measured by modified Visick scores.

RESULTS

There were 233 good responders (>50% relief) and 91 poor responders (<49% relief). Both groups demonstrated a significant decline in postoperative symptom scores. Ninety-four percent of good responders had an excellent or good outcome, compared to 87% of poor responders. Twenty-seven patients reported a fair or poor outcome, despite improved postoperative symptom scores. Fifteen of these patients reported continuing heartburn; five had positive pH tests.

CONCLUSION

Our results do not support the assumption that a poor response to PPIs equates to a poor outcome after LARS.

Laparoscopic fundoplication in mentally normal children with gastroesophageal reflux disease

Laparoscopic antireflux surgery has been performed in neurologically impaired and scoliotic children. We aimed to assess the effectiveness of laparoscopic fundoplication in mentally normal children with gastroesophageal reflux disease that failed to respond to medical therapy. Data were prospectively collected (symptoms, medical therapy, endoscopies' findings) on 12 children (nine boys, three girls) aged 9-15 years with gastroesophageal reflux disease. Pre- and postoperative ambulatory 24-h pH and DeMeester and Johnson scores were also recorded. Effectiveness of surgery was assessed by comparison of pre- and postoperative total acid exposure time, Visick grade, need for antireflux medication and symptom scores. In total, 11 children underwent a laparoscopic Nissen fundoplication and one underwent a Toupet procedure. Median length of stay was 2 (2-3) nights. The median preoperative pH acid exposure time (AET) was 4.7 (0.8-16.4) percent compared with postoperative AET of 0.4 (0-3) percent. Early postoperative dysphagia occurred in four out of 12 patients, requiring a total of six dilatations. Postoperative Visick scores were: grade I=7 and grade II=5. Laparoscopic fundoplication can be safely performed and is effective in children with GERD who have failed to respond to medical therapy.

Preoperative esophageal body motility does not influence the outcome of laparoscopic Nissen fundoplication for gastroesophageal reflux disease

We evaluated a policy of performing laparoscopic antireflux surgery without tailoring the procedure to the results of preoperative esophageal motility tests. A total of 117 patients (82 with normal esophageal motility; 35 with ineffective motility, IEM) underwent laparoscopic Nissen fundoplication for symptomatic gastroesophageal reflux. There were no significant differences in preoperative symptom length, dysphagia, DeMeester symptom scores, acid exposure times or lower esophageal sphincter pressures between the two groups. Both groups showed postoperative improvements in DeMeester symptom scores, dysphagia and acid exposure, with no differences between groups. At 1 year after surgery, 95% of the normal motility group and 91% of the IEM group had a good/excellent outcome from surgery. None of the IEM group required postoperative dilatation or reoperation. Patients with IEM fare equally well from laparoscopic Nissen fundoplication as those with normal esophageal motility. There is no merit in tailoring antireflux surgery to the results of preoperative motility tests.

Changes to the TEF schemes can have significant impacts on regulation and management of PCDD/F and PCB

The changes recommended by the World Health Organisation (WHO) to the toxic equivalency factors (TEFs) for polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/F) and the recommendation to extend both the TEF scheme and the tolerable daily intake (TDI) to include "dioxin-like" PCB congeners have significant implications for regulators who have relied heavily on the International TEF (I-TEF) scheme in setting and monitoring limits and exposure to these compounds. This paper examines example data sets of sources, environmental concentrations, food and exposure to indicate likely changes in calculated toxic equivalent (TEQ) due to the recommended changes to TEFs. Many published data sets available do not provide congener specific data for PCDD/F which limits the ability to recalculate TEQs. There are even fewer congener specific data published to enable calculation of TEQs for the dioxin-like PCBs. In general TEQs calculated using the WHO scheme for emissions to air were found to show small increases (in the order of 1-10%) in comparison to the I-TEQ (for PCDD/F), some sludge samples showed substantial decreases (up to 70%). Levels in food and calculations of exposure showed that the change to TEFs for PCDD/F increased calculated exposure by 10-20% while the change to PCB TEFs decreased calculated TEQ attributable to PCB by 0-10%. The effects of including PCB in the overall TEQ and the changes to TEFs for PCDD/F substantially increase calculated TEQ exposure. Congener specific data should be presented to allow calculation of desired TEQ and the impact of the changes on emission limits, regulations on sludge use and environmental quality standards should all be carefully considered. The absence of data on emissions of dioxin-like PCB means that it is not possible to estimate with any certainty the impact on overall TEQ emissions of including the nominated PCB. Given the potential for confusion with the proliferation of TEFs and the extension to include both PCDD/F and PCB in the calculation of TEQs it is important that great care is taken to clearly express which compounds are included and which TEF scheme has been applied in each case.

Results of laparoscopic Nissen fundoplication at 2-8 years after surgery

BACKGROUND

Although the long-term results of open fundoplication for gastro-oesophageal reflux disease are well documented, there have been few reports of the long-term results of laparoscopic fundoplication.

METHODS

Between January 1993 and July 1999, 179 consecutive patients underwent laparoscopic floppy Nissen fundoplication. Of these, 175 were available for long-term follow-up. Structured symptom questionnaires were completed by 140 patients (80 per cent) at 2-5 years (n = 92) or 5-8 years (n = 48) after operation.

RESULTS

Patient satisfaction with surgery was 91 per cent at a median follow-up of 48 (range 24-99) months. Visick scores of I or II were recorded by 84 per cent. Ninety per cent of patients remained free from significant reflux symptoms. Side-effects were common (22 per cent) but rarely affected patient satisfaction. Of the 19 patients (14 per cent) taking regular antireflux medication, eight used it for non-reflux symptoms and 12 had normal postoperative pH tests.

CONCLUSION

Laparoscopic floppy Nissen fundoplication is an effective and durable treatment for gastro-oesophageal reflux disease. Longer-term follow-up of patients operated on beyond the learning curve can be expected to show further improvements in surgical outcome.

Patient self-assessment of test-day symptoms in 24-h pH-metry for suspected gastroesophageal reflux disease

BACKGROUND

Marked daily fluctuations may occur in the pattern and degree of gastroesophageal reflux (GOR) and in patients' symptoms. The aim of this study was to observe how patients' self-assessment of their symptoms on the day of a 24-h pH test correlates with the likely outcome of the test and the potential value in repeating it.

METHODS

367 patients with symptoms suggestive of GOR underwent 24-h pH tests. Fifty-eight patients had repeat studies. Patients assessed the severity of their test-day symptoms as 'better than typical', 'typical' or 'worse than typical'.

RESULTS

A 'typical' or 'worse than typical' day was more likely to produce an abnormal test result (P < 0.0001). A normal first test on a 'better than typical' day was more likely to be followed by an abnormal second test than a normal first test on a 'typical' or 'worse than typical' day (55% versus 22%; P = 0.025). The symptom index score, the total acid exposure time on the first test and the presence of oesophagitis were not associated with an abnormal second test (P not significant).

CONCLUSIONS

Patients' self-assessment of the severity of their test-day symptoms should be included in the interpretation of 24-h pH tests for suspected GOR. Patients with a normal pH test on a 'better than typical day warrant a repeat test.

Laparoscopic antireflux surgery in the treatment of the acid-sensitive oesophagus

BACKGROUND

Approximately 10 per cent of patients referred for 24-h oesophageal pH tests with symptoms suggestive of gastro-oesophageal reflux disease will have a normal endoscopic examination and normal distal oesophageal acid exposure times, but a clear temporal correlation between their symptoms and episodes of acid reflux. These patients have an 'acid-sensitive oesophagus', which forms part of the spectrum of reflux-related conditions. Their response to antireflux surgery has not been reported previously. This study represents a prospective cohort analysis of a clearly defined group of patients with acid-sensitive oesophagus who have undergone laparoscopic antireflux surgery.

METHODS

Nineteen patients (nine male and ten female; median age 32 years) underwent laparoscopic antireflux surgery for acid-sensitive oesophagus. All had had an incomplete response to medical therapy.

RESULTS

Eighteen of 19 patients were graded Visick I or II at 6 months after operation; all 16 patients followed for 1 year were graded Visick I or II. There were significant falls in DeMeester symptom score (4.0 versus 0.5; P < 0.001), symptom events (20 versus none; P < 0.001), number of reflux episodes (17 versus two; P < 0.001) and overall acid exposure times (1.2 versus 0.3 per cent; P < 0.001) after operation.

CONCLUSION

Laparoscopic antireflux surgery is a valid and effective treatment for patients with an acid-sensitive oesophagus. Presented in poster form to the British Society of Gastroenterology, Birmingham, March 2000 and the American Gastroenterological Association, San Diego, May 2000

Arthur Roland Elvidge (1899-1985): contributions to the diagnosis of brain tumors and cerebrovascular disease

The contributions of Arthur Elvidge (1899-1985), Wilder Penfield's first neurosurgical recruit, to the development of neurosurgery have been relatively neglected, although his work in brain tumors extended the previous work of Percival Bailey and Harvey Cushing. He published rigorous correlations of clinical and histological information and formulated a revised, modern nosology for neuroepithelial tumors, including a modern histological definition of glioblastoma multiforme. Well ahead of his time, he believed that glioblastoma was not strictly localized and was the first to comment that the tumor frequently showed "satellitosis." He was the first neurosurgeon in North America to use angiography as a radiographic aid in the diagnosis of cerebrovascular disease. Having studied with Egas Moniz, he was the first to detail the use of angiographic examinations specifically for demonstrating cerebrovascular disorders, believing that it would make possible routine surgery of the intracranial blood vessels. Seeking to visualize all phases of angiography, he was the impetus behind the design of one of the first semi-automatic film changers. Elvidge and Egas Moniz made the first observations on thrombosis of the carotid vessels independently of each other. Elvidge elucidated the significance of embolic stroke and commented on the ischemic sequelae of subarachnoid hemorrhage. Besides his contributions to neurosurgery, he codiscovered the mode of transmission of poliomyelitis. Elvidge's soft-spoken manner, his dry wit and candor, mastery of the understatement, love of exotic travel, and consummate dedication to neurosurgery made him a favorite of patients, neurosurgery residents, nurses, and other hospital staff. His accomplishments and example as teacher and physician have become part of neurosurgery's growing legacy.

Bilateral hypoglossal nerve injury with occipital condylar fracture

BACKGROUND

A 20-year-old woman with a right occipital condylar fracture and bilateral hypoglossal nerve injury is presented. Only 17 cases of condylar fracture have been reported in the literature.

METHODS

The patient was evaluated with plain films, coronal and axial cut CT, and MRI.

RESULTS

MRI showed a severely distorted but otherwise normal medulla and a displaced condylar bone fragment.

CONCLUSION

Condylar fracture may cause twelfth nerve palsy by injuring the central or peripheral nerve.

Influence of chlorobenzoates on the utilisation of chlorobiphenyls and chlorobenzoate mixtures by chlorobiphenyl/chlorobenzoate-mineralising hybrid bacterial strains

Chlorobenzoates (CBA) arise as intermediates during the degradation of polychlorinated biphenyls (PCBs) and some chlorinated herbicides. Since PCBs were produced as complex mixtures, a range of mono-, di-, and possibly trichloro-substituted benzoates would be formed. Chlorobenzoate degradation has been proposed to be one of the rate-limiting steps in the overall PCB-degradation process. Three hybrid bacteria constructed to have the ability to completely mineralise 2-, 3-, or 4-monochlorobiphenyl respectively, have been studied to establish the range of mono- and diCBAs that can be utilised. The three strains were able to mineralise one or more of the following CBAs: 2-, 3-, and 4-monochlorobenzoate and 3,5-dichlorobenzoate. No utilisation of 2,3-, 2,5-, 2,6-, or 3,4-diCBA was observed, and only a low concentration (0.11 mM) of 2,4-diCBA was mineralised. When the strain with the widest substrate range (Burkholderia cepacia JHR22) was simultaneously supplied with two CBAs, one that it could utilise plus one that it was unable to utilise, inhibitory effects were observed. The utilisation of 2-CBA (2.5 mM) by this strain was inhibited by 2,3-CBA (200 microM) and 3,4-CBA (50 microM). Although 2,5-cba and 2,6-cba were not utilised as carbon sources by strain jhr22, they did not inhibit 2-cba utilisation at the concentrations studied, whereas 2,4-cba was co-metabolised with 2-cba. The utilisation of 2-, 3-, and 4-chlorobiphenyl by strain JHR22 was also inhibited by the presence of 2,3- or 3,4-diCBA. We conclude that the effect of the formation of toxic intermediates is an important consideration when designing remediation strategies.