Anal endosonographic assessment of the accuracy of clinical diagnosis of obstetric anal sphincter injury

Introduction and hypothesis Obstetric anal sphincter injuries (OASIS) are a common cause of maternal morbidity with an overall incidence in the UK of 2.9% (range 0–8%). They can cause a range of physical symptoms and psychological distress. This study aims to assess the accuracy of clinical diagnosis of OASIS using endoanal ultrasound (EAUS) and the correlation between confirmed injury and change to anorectal physiology squeeze pressure and the incidence of bowel symptoms. Methods and materials Retrospective study of prospectively collected data from 1135 women who attended the Third- and Fourth-Degree Tears Clinic at our institution, 12 weeks post-delivery, between June 2008 and October 2019. Results OASIS was confirmed in 876 (78.8%) women and 236 (21.3%) had no injury. Of the women who underwent anorectal physiology, 45.6% had a mean maximal resting pressure below the normal range and 68.8% had a mean incremental squeeze pressure below normal. Women with confirmed OASIS had significantly lower pressures (p < 0.001) than those without a confirmed sphincter injury. Three hundred ninety-three (34.8%) women reported bowel symptoms, with those with endosonographic evidence of injury more likely to develop flatus incontinence. Conclusion Of the women in this study with a suspected OASIS, 21.2% could be reassured that they did not have an injury. This information is useful for women considering future mode of delivery. Those with confirmed injury are more likely to complain of flatus incontinence and have reduced anal sphincter pressures.

O27 The diameter of an anorectal physiology catheter in the anal canal influences the results

Introduction Conventional “catheter-based” anorectal physiology systems may influence anal canal pressures by stretching the sphincters thereby increasing tension. Anal acoustic reflectometry (AAR) is a “catheter-less” technique as the flexible thin catheter does not distort the anal canal. The aim of this study was to explore whether the size of rigid tube in the anal canal had any effect on tension. Method Participants with no anorectal dysfunction were included. Baseline resting/squeeze AAR measurements were recorded, then repeated with a 6 mm and 10 mm rigid tube placed along-side the AAR catheter. This process was repeated for anorectal manometry (ARM) and Opening pressure (AAR) and mean resting pressure (MRP) were used to calculate tension (pressure (mmHg) x radius (mm)). Result 9 participants were included (7 female/2male) with median age 22 years (21–31 years). Tension at rest (no additional tube) for AAR and ARM was 14 and 135 N/m respectively and 33 and 238 N/m during squeeze. Tension increased in a linear fashion, for both resting and squeeze, as the size of additional rigid tube increased. The largest increase in tension from baseline AAR and ARM measurements was recorded with the 10 mm additional tube (1,807% and 102% respectively). Conclusion The thin AAR catheter exerted the lowest tension at baseline. A large increase in tension was observed as the size of tube increased and therefore the diameter of catheter used in the assessment of anal physiology will affect the results. ARM measurements carried out by devices of different diameter will not be comparable. Take-home Message The diameter of the anorectal physiology catheter in the anal canal influences the results.