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- Materials and methods
Chronic constipation is a common condition with a prevalence of 2–27% in population studies in North America.1, 2 In tertiary care centres, dyssynergic defecation (DD) is seen in up to 50% of patients referred with chronic constipation.3 DD is significantly associated with a poor quality of life, with 74% and 69% of patients reporting an impact on their social life and work respectively.4 Medical management is often ineffective with 47% of patients dissatisfied with laxatives or fibre therapy.5
The efficacy of anorectal biofeedback therapy (BFT) in constipation was first reported in 1987.6 Since then, there has been a number of controlled studies examining the efficacy of BFT with mixed results.7 Recently, three randomised controlled trials have demonstrated a 70–81% success rate of BFT in patients with functional constipation and DD.8–10 In these studies,8–10 BFT was shown to be more effective than laxatives, muscle relaxants and placebo. Its benefit has also been shown to last for at least 12 months.9 Therefore, BFT is now considered one of the safest and effective therapeutic options for patients with chronic constipation and DD.
Given the high prevalence of constipation and DD,2, 3 there is potentially a large pool of patients who could be treated with BFT and there is a need to prioritise patients. A number of previous studies have examined factors, which predict success or failure of BFT in constipation.11–14 Results of these studies, however, have been inconsistent except for willingness to participate which has been shown to correlate with success of BFT.11 The inconsistencies in results may be due to small sample sizes in many of these studies and the differences in techniques used. These conflicting results make it difficult for clinicians to assess which group of patients is likely to have a successful outcome with BFT. Moreover, development of a model to predict success of BFT would be very useful clinically. This is analogous to the Model for End-Stage Liver Disease (MELD) score used to predict mortality risk as well as prioritising organ allocation, in patients with end-stage liver disease.15
The aims of this study were (i) to further explore clinical and physiological factors which predict success or failure of BFT in patients with chronic constipation, using a comprehensive anorectal manometry and biofeedback protocol16–18 and (ii) to derive a statistical model which helps to predict the success of BFT.
- Top of page
- Materials and methods
Using a comprehensive manometric-based anorectal biofeedback protocol, we have determined important factors, which predict outcome of BFT in a large group of patients with chronic constipation and disordered defecation. We have further established a clinically useful model, which helps to predict an individual’s likelihood of success with BFT. This is important as constipation is common, and BFT is a safe and effective, yet labour-intensive treatment for constipation. We believe, this predictive model can assist clinicians in prioritising patients who should undergo BFT.
In this study, a harder stool was predictive of a substantial improvement in bowel satisfaction after BFT. This is the first time stool consistency has been shown to be associated with success of BFT. This finding is not unexpected as hard stool is a common feature of DD4 and BFT improves dyssynergia, which potentially leads to better efficiency in stool evacuation. Our finding of shorter duration of laxative use as a predictor of successful BFT is consistent with Chiarioni et al.12 in their study of 52 patients with chronic constipation. The willingness to participate was associated with improvement in bowel satisfaction, but was not a useful variable for our predictive model, as the data were skewed with most patients having an extremely high score.
The two physiological parameters predictive of a substantial improvement in bowel satisfaction after BFT in our study were high straining rectal pressure and prolonged balloon expulsion time. Again, our findings demonstrate for the first time that high straining rectal pressure is associated with success of BFT. During attempted defecation, contraction of the anterior abdominal wall muscle and diaphragm leads to an increase in intra-abdominal pressure during straining.29 However, an inappropriately high straining rectal pressure may in fact represent a feature of DD, as with the rise in rectal pressure during defecation present in Type I dyssynergia described by Rao et al.30 Prolonged balloon expulsion time was an independent predictor of a successful BFT in this study, again consistent with Chiarioni et al.12 Our results therefore suggest that patients with physiological features of dyssynergia are more likely to respond to BFT. Interestingly, however, paradoxical contraction of the anal sphincter on straining was not predictive of successful BFT in our study.
Our predictive model is a clinically relevant tool, which helps in selecting patients for BFT. This model predicts a ≥5 point increase in 10 cm VAS global bowel satisfaction score after BFT, which equates to a 50% improvement from baseline. Although we chose a 5-point increase in bowel satisfaction, we did not feel that it limits the outcome as in order to determine factors predicting success, having approximately equal numbers across categories maximises statistical power. Furthermore, this is quite a conservative approach in order to not over interpret data. Hence, by simply applying the data regarding laxative use, stool consistency, straining rectal pressure and balloon expulsion time, one can readily calculate an individual patient’s likelihood of a substantial improvement with BFT from the model and graph. For example, if a patient reports hard stool and short duration of laxative use (which equates to a value of 2 and 1, respectively, on the Knowles Constipation Questionnaire21) and has a straining rectal pressure of 60 mmHg and a balloon expulsion time of 70 s at baseline, the predictive score using the model and values of β from Table 3, can be calculated as: Si = [(0.89 × 2) + (−0.72 × 1) + (0.03 × 60) + (0.01 × 70)] which results in Si = 3.56. Using Figure 1, one can determine from the graph the predicted probability of success with BFT. In our hypothetical case, a value of 3.56 corresponds to a predicted probability of success of approximately 0.98 (98%). On the other hand, a patient who reports normal stool consistency, a long duration of laxative use, and has a straining rectal pressure of 30 mmHg, and a balloon expulsion time of 20 s, will have a predictive score of −0.34, which corresponds to a predicted probability of success of only 15%. This model is particularly relevant in a busy tertiary referral centre, which potentially has a large number of patients with DD and constipation that requires treatment with BFT. We propose that those with a higher predicted probability of success with BFT be given priority over those with a lower predicted probability of success.
In conclusion, we have found that important clinical and physiological features are associated with the outcome of BFT in patients with constipation, including stool consistency, laxative use, straining rectal pressure and balloon expulsion time. In addition, we have developed a predictive model to help clinicians prioritise the large number of potential patients referred for BFT, which can be a labour intensive and therefore costly treatment.