The functional outcomes after IPAA surgery are difficult to accurately predict, regardless if performed by the same surgeon utilizing the same technique. Factors which may be predictive of functional outcomes are important for coaching and expectation management, which are particularly important in early pouch life. Unfortunately, there are few reliable predictors of IPAA pouch function. In this study, we examined the role of IPAA contractility and changes over time while also examining the association of contractility with functional outcomes and quality of life metrics for the patient.
In our study, we demonstrated that early post ileostomy takedown pouch contractile waves generate a mean pressure of 26.11 ± 8.1 mmHg. This finding of contractile waves appears to be independent of pouch design. The early work by Taylor et al. investigating J pouch manometry data revealed mean contractile waves of 26–30 + mm Hg (converted from cm H2O). This data is very comparable to our demonstration of mean contractile amplitude at 26.11mm Hg (Study 1) and 27.45mm Hg (Study 2) in S-pouches. Additionally, contractile frequency is also similar across studies, adding further support that contractility is similar between J- and S- pouches.
Following ileal pouch construction, we found that about half of the ileal pouches in our study population had high amplitude contractile waves within the first few months after ileostomy takedown. When analyzing the functional effect of high amplitude contractility, there was a statistically significant association with increased risk of nighttime spotting in early pouch life. Interestingly, it is well recognized that nocturnal fecal incontinence is common in early pouch life, but decreases with pouch maturation [14, 15].
A plausible mechanistic explanation for early pouch nocturnal incontinence is based upon the interplay between anal canal pressure and pouch generated contractile waves. When pouch contractile waves approach and surpass the pressure of the anal sphincter (a low or negative pouch-anal gradient) in a full pouch, a brief period of incontinence may occur as pouch contents may be expelled from a high pressure to low pressure zone. Lending evidence to this mechanistic explanation, is the finding that five of the six patients in our study who reported nighttime spotting ≥ 2 times per week demonstrated high amplitude contractile waves. Those five patients had a mean of 0.3 contractions/minute.
Although we did not measure sleeping sphincter pressures in our patient population, Orkin et al. demonstrated a mean anal pressure of 31mm Hg+/- 8 in IPAA patients who experience nocturnal leakage [16]. This value in comparison to our mean contractile wave pressure of 26.11 +/- 8.1 mm Hg reveals the opportunity for discrete periods of time where pouch generated pressure could exceed resting anal canal pressure, ultimately yielding a brief incontinent episode.
Our data also suggests that as patients are further removed from surgery, nocturnal continence may improve. One potential explanation for this finding is that anal sphincter pressures improve as patients become more remote from surgery. It is well known that anal sphincter function can be altered after IPAA, resulting in decreased resting anal pressure following surgery [17]. Becker et al., displayed that early decreases in resting anal sphincter tone after IPAA did not persist as anal pressures returned to baseline values with time [18]. Sphincter pressure improvement however cannot be the only driving factor of functional improvement as it has been also demonstrated that sphincter impairment is minimized when utilizing a double stapled technique compared to hand sewn pouch construction [19, 20].
Our findings of decreasing contractions in the mature pouch, may suggest another explanation for improvement in nocturnal incontinence over time. We demonstrated that by one-year post ileostomy takedown, only 30% of patients were still noted to have any contractile activity waves. In those in whom contractility persisted, frequency was greatly decreased at two-thirds the observed frequency measured in early pouch life. With contractile waves occurring at such an infrequent rate, there would be few opportunities for an alignment between a nadir anal sphincter pressure and contractile waves with a full pouch. The reasons for decreased contractile frequency observed with pouch maturation are not fully understood.
The primary limitation of this study is that it is a single center, retrospective review with a small sample size. This small sample size leads to relatively large confidence intervals in some of our statistical analysis. While there is some uncertainty regarding the direct correlation of our data analysis of a single pouch configuration (S-pouch) as it compares to the J-pouch, it serves as a strength in its examination of the physiologic as well as functional parameters in a large, homogeneous patient population and fits with similar findings first reported in the ileal J pouch design.
The advantage of this study is that it is the only study to date that has investigated pouch contractility and its impact on function and patient quality of life over the first year of pouch life when profound functional changes are known to occur.