Laplace's law and the risks and prevention of bladder rupture after enterocystoplasty and bladder autoaugmentation

Relevance of intravesical pressures during transurethral procedures

PURPOSE

Endourology has undergone fundamental changes over the last 2 decades. Maintaining low intrarenal pressure (IRP) during upper urinary tract procedures is an established concept. However, researchers have not yet studied the concept of reduced intravesical pressures (IVPs) during transurethral (TUR) surgery as thoroughly. Low IVP is supposed to decrease complications as fluid retention, TUR syndrome, and incidence of fever. The study aims to give an overview of the contemporarily existing concepts and specify the term of low IVP to avoid TUR-related complications and optimize TUR-related results.

METHODS

A literature search was performed using PubMed, restricted to original English-written articles, including animal, artificial model, and human studies. Different keywords were transurethral resection, transurethral enucleation, transurethral vaporization, pressure, fluid absorption, and TUR syndrome.

RESULTS

Analyzed mean IVPs during TUR vary between 11 and 35 cmH₂O but are mostly kept below 30 cmH₂O. Mean maximum IVPs during TUR range from 20 to 55 cmH₂O. Maximum IVPs seem to be lower when surgeons utilize continuous flow resection, and irrigation pressures are kept low. The results demonstrate a strong correlation between IVP levels and fluid absorption.

CONCLUSIONS

IVP increase remains a neglected predictor of transurethral procedure complications, and endourologists should consider its intraoperative monitoring. Further research is necessary to quantify generated pressures and introduce means of controlling them.

Current pharmacological and surgical treatment of underactive bladder

Generally accepted guidelines are not yet available on the management of underactive bladder (UAB). Although the natural history of UAB is still not fully understood, observation may be an acceptable management option in patients with tolerable lower urinary tract symptoms and little risk of upper urinary tract damage. If needed, scheduled and double voiding may be recommended as an effective and safe add-on therapy. Parasympathomimetics have been widely used for the management of UAB, but the evidence does not support clinical benefit. The efficacy of alpha-blockers has also not yet been clearly demonstrated. However, selective alpha-blockers may help to enhance voiding efficiency and to decrease possible upper tract damage. Sacral neuromodulation is a surgical option for nonobstructive UAB approved by the Food and Drug Administration. However, the response rate of test stimulation is not high and the efficacy of permanent implants does not always coincide with that of test stimulation. Although surgery to reduce outlet resistance may be a viable option in UAB with presumed obstruction, surgery seems to have little role in those without obstruction. Latissimus dorsi detrusor myoplasty has shown promising results in restoring voluntary voiding in selected patients. The procedure requires a multidisciplinary team approach of urologists and plastic reconstructive experts. In summary, current treatments of UAB remain unsatisfactory. The multifactorial nature of UAB pathogenesis complicates the appropriate management for each patient. Future research to establish a more clinically relevant definition of UAB will be required to open new era of UAB management.

Voiding prior to parachuting

OBJECTIVE

Multiple incidents of isolated bladder ruptures have occurred in the military parachuting community after jumps. The aim of this article is to demonstrate the amount of energy it takes to rupture a distended bladder and encourage prejump voiding.

DESIGN

Euthanized pig abdomens were opened immediately postmortem, and the urethra and bladder were isolated. The urethras were attached to a water column, which was gradually increased in height until bladder rupture. During the course of expansion, the differences in water level height, bladder dimensions, and total volume were measured. An acceleration model was constructed by placing a bladder in a rigid cylinder with a soft top to replicate a pelvis. The bladder was then dropped from a standardized height after filling the bladder with gradually increasing volumes.

SETTING

81st Medical Group Clinical Research Laboratory at Keesler AFB, Mississippi.

PARTICIPANTS

Pigs (Sus scrofa domestica) postuse in an Institutional Animal Care and Use Committee (IACUC)-approved protocol.

RESULTS

Mean pressure at rupture = 116 mm Hg (standard deviation [SD] ± 7), mean height = 193 mm (SD ± 42), mean width = 122 mm (SD ± 9), and mean volume = 963 (SD ± 124). Rupture occurred after deceleration at only maximum elasticity.

CONCLUSIONS

The pressure and amount of energy required to rupture a distended bladder is remarkably low, confirming the general application of Laplace's law to a bladder. It is our recommendation that parachutists be urged or required to void, when possible, before parachuting.

Regional biomechanical and histological characterisation of the passive porcine urinary bladder: Implications for augmentation and tissue engineering strategies

The aim of this study was to identify and quantify potential regional and directional variations in the quasistatic uniaxial mechanical properties of the passive urinary bladder wall. Overall, the lower body and trigone regions demonstrated the highest degree of directional anisotropy, whereas the ventral region demonstrated the least directional anisotropy. Significant regional anisotropy was found only along the apex-to-base direction. The dorsal and ventral regions demonstrated a significantly increased distensibility along the apex-to-base direction compared to the other bladder regions, whereas the trigone and lower body regions demonstrated the least distensibility. The trigone, lower body and lateral regions also demonstrated the highest tensile strength both at regional and directional levels. The study detected significant regional and directional anisotropy in the mechanical properties of the bladder and correlated this anisotropy to the distended and non-distended tissue histioarchitecture and whole organ mechanics. By elucidating the inhomogeneous nature of the bladder, the results from this study will aid the regional differentiation of bladder treatments in terms of partial bladder replacement with suitable natural or synthetic biomaterials, as well as the development of more realistic constitutive models of bladder wall biomechanics and improved computational simulations to predict deformations in the natural and augmented bladder.

Rupture and perforation of urinary reservoirs made from bowel

A review of the literature involving the rupture or perforation of urinary reservoirs made from the bowel indicates that this complication is perhaps not as rare as commonly perceived. It is a severe complication for which a high index of suspicion needs to be maintained. Physicians attending to patients with such urinary reconstructions should be aware that the diagnosis is often difficult to confirm without resorting to exploratory laparotomy and in particular that a negative cystogram can be misleading. A practical suggestion to help alert these physicians to the possibility of a ruptured urinary reconstruction is that such patients should carry a medical card stating the type of reservoir they have along with their special circumstances. From the reported experiences, it is, however, clear that in carefully selected cases and with vigilant monitoring, some patients may be managed non-operatively.

An original technique for bladder autoaugmentation with protective abdominal rectus muscle flaps: an experimental study in rats

BACKGROUND

Bladder autoaugmentation uses partial detrusorectomy to create a diverticular bulge in the bladder mucosa. This technique has eliminated certain serious complications of cystoplasty with gastrointestinal tissues (e.g., fluid/electrolyte/acid-base imbalances, mucous hypersecretion), but the exposed mucosa is subject to fibrosis and, sometimes, to perforation, which can annul the benefits of surgery.

METHODS

We have developed an original technique based on traditional autoaugmentation with protection of the herniated mucosa by split-thickness pedunculated rectus abdominis muscle flaps that are sutured to the incised margins of the detrusor. Preliminary testing was done on 30 adult Wistar rats. A control group of 15 rats underwent laparotomy alone. Bladder capacity was measured via suprapubic cystography before and after (4 weeks, 8 weeks, 1 year) surgery, just before sacrifice. Sections of the reconstructed bladder were examined histologically.

RESULTS

Twenty-three bladder-augmented rats and 13 controls survived. In the experimental group, bladder capacity increased by 38% (mean). None of the rats experienced urinary retention, although one developed bladder stones. Histology revealed no pathologic changes (other than chronic inflammatory infiltrates at suture sites) in the mucosa, detrusor, or muscle flaps, which were all viable and well integrated by the fourth postoperative week. There were no signs of mucosal or muscle fibrosis.

CONCLUSIONS

Preliminary results in a rat model suggest that this new technique can produce an enlarged bladder that is fully functional and less vulnerable to fibrotic retraction and rupture. Residual contractility in the muscle flaps might theoretically be exploited to facilitate paraphysiologic micturition.