Anorectal Manometry: concepts, indications, and technique

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Anorectal manometry is an examination used to evaluate the function of the rectum and sphincter apparatus. Its utility is mainly valued in patients who present functional disorders, such as intestinal constipation and fecal incontinence, assisting in the management of these patients. In this article we will learn about the concepts, the main indications and the technique of execution.

Introduction

The pelvic floor is a peculiar muscular structure, with an important function in maintaining anal continence and influence on defecation, and its dysfunction, whether for functional, anatomical and/or neurological reasons, results in morbidities with significant social, emotional, psychological and economic impact. Urinary incontinence, prolapse of pelvic organs, anal incontinence, evacuatory dysfunction and sexual disorders, among others, are considered abnormalities of the pelvic floor.

The evacuation disorders, whether fecal incontinence (FI) or chronic intestinal constipation (CIC), represent alterations of the pelvic floor quite frequent in the general population more commonly in those with risk factors, that is, elderly, women with obstetric past, comorbidities (such as scleroderma, hypothyroidism, diabetes mellitus), history of pelvic radiotherapy, bedridden patients or with locomotion deficits, history of orificial surgeries, chronic use of analgesics, opioids and psychiatric medications, among others.

Fecal incontinence has a very variable incidence and fundamentally dependent on the age of the study population, so that the incidence oscillates between 1.4 to 18%, with an average of 2 to 8.4%. On the other hand, chronic intestinal constipation (CIC) is one of the most common functional gastrointestinal disorders with high prevalence in the population, affecting 16% of adults and up to 33% of those over 60 years of age, more specifically females with a prevalence of 2 to 3:1 when compared to males.

Anorectal manometry can assist the attending physician, whether he is a gastroenterologist, digestive tract surgeon, coloproctologist or other medical specialty to better understand the disorder being evaluated and assist in its management. We will discuss the indications, concepts and techniques of anorectal manometry below.

Indications

Anorectal manometry (MNAR) can be indicated mainly for cases of:

• fecal incontinence (FI);
• intestinal constipation;
• dysinergia of the pelvic floor;
• prolapse of pelvic organs: rectocele, enterocele, mucosal prolapse, rectal procidence and cystocele;
• chronic pelvic pain: endometriosis, proctalgia fugax;
• pre-operative of orificial surgeries and reconstruction of intestinal transit;
• post-operative of colorectal surgery, notably in patient with the syndrome of anterior resection of the rectum.

Technique for execution

About 2-3 hours before the exam, retrograde intestinal preparation is indicated with a bottle of phosphoenema® or two of Minilax® (evacuatory enemas). No dietary restriction is necessary. At the time of the exam, the patient is positioned in left lateral decubitus with the lower limbs semi-flexed (Simms position) and then anal inspection is performed followed by rectal touch with the aim of:

• assessing whether there is an excess of feces in the rectal ampulla;
• measuring subjectively the tone of the internal and external sphincters of the anus, respectively during rest and anal contraction;
• assessing the relaxation of the puborectal muscle and the force of rectal propulsion;

In addition, the rectal touch has the final purpose of guiding the adequate and careful insertion of the anorectal manometry catheter.

Parameters evaluated

The following data are evaluated during the MNAR:

• Resting pressure: provided fundamentally by the action of the internal anal sphincter muscle (EAI – values in mmHg);
• Functional anal canal length: normally between 2-3 cm in females and a little longer in males;
• Contraction pressure: action performed by the anorectal striated musculature, that is, by the external anal sphincter (EAE) and puborectal muscle (PR – values in mmHg);
• Action of the sphincter musculature during the Valsalva maneuver or evacuatory effort in order to observe adequate relaxation of the same or signs suggestive of paradoxical contraction of the PR muscle, also described as pelvic floor dysinergia;
• Ability to sustain contraction: corresponds to the fatigue index during 30 seconds of the anorectal striated musculature with measurement in percentage and in duration time;
• Rectoanal inhibitory reflex: demonstrates the relaxation of the EAI to the stimulation of the nerve receptors in the anorectal ring from the stepped insufflation of air in the balloon, positioned at the distal end of the manometry catheter (it can be positive, negative or indeterminate);
• Sensitivity and capacity of the rectum: measurement made with the instillation of water inside this same balloon (values measured in ml);
• Sphincter asymmetry index at rest and during contraction: measures the symmetry of the anorectal sphincter complex in its circumference, in percentage.

After obtaining these data, it is recommended to perform the rectal balloon expulsion test, primarily in patients with clinical symptoms of intestinal constipation and those with manometric signs suggestive of paradoxical contraction of the puborectal muscle to MNAR.

For this, about 50 to 60 ml of water is left inside the rectal balloon with the probe positioned just above the anorectal ring and the patient is asked, mainly in the sitting position on a toilet, to eliminate the balloon, simulating an evacuation. The test is considered negative if there is elimination in up to three attempts with a maximum time of 60 seconds each. If the balloon containing water is not eliminated after 3 attempts, the test is positive, and may corroborate with pelvic floor dysinergia.

Conventional x High resolution

The conventional MNAR had, in our environment, its dissemination and execution methodology from 1993. For this, a probe with eight radial holes located at its end is used and through which the sphincter pressures are measured through the resistance offered to the flow of water at 0.3-0.5 ml/minute/channel. For its execution, the probe is inserted up to 6 cm from the anal edge and the catheter is pulled at each centimeter in a stationary manner.

On the other hand, the most recent MNAR devices, known as high resolution, have 24 or 36 channels, distributed radially and staggered from 1 to 6 cm from the end of the catheter. For its execution, the probe is inserted 6 cm from the anal edge, leaving it static with successive measurements of the above mentioned data, following a specific protocol known as the London Protocol, which better standardized the high resolution MNAR in relation to the conventional one.

This new MNAR execution technology has as main advantages:

• graphs with better spatial visualization;
• less discomfort to the patient, notably those with anal pain, such as chronic fissure;
• better technical standardization;
• less need for the participation of the nursing technician who assists the exam;

However, despite these advantages and a greater performance of the technological system in the preparation of reports, any of the available techniques does not replace the importance of the correct execution and interpretation of the data by the doctor who performs the exam.

Conclusion

The anorectal manometry exam, whether conventional or high resolution, is an important propaedeutic resource in the approach of patients with pelvic floor disorders, especially in anal incontinence and refractory intestinal constipation, and can also be used as a method in the pre-operative of colorectal and/or orificial surgeries in specific situations.

Also read: Screening for anal intraepithelial neoplasia and prevention of anal cancer

How to cite this article

Pinto RA, Neto IJFC, Marques CFS. Anorectal Manometry: concepts, indications and technique Gastropedia 2023, vol. 2. Available at: https://gastropedia.com.br/cirurgia/manometria-anorretal-conceitos-indicacoes-e-tecnica