Anorectal manometry (ARM) is a medical test used to measure pressures in the anus and rectum and to assess their function. The test is performed by inserting a catheter, that contains a probe embedded with pressure sensors, through the anus and into the rectum. Patients may be asked to perform certain maneuvers, such as coughing or attempting to defecate, to assess for pressure changes. Anorectal manometry is a safe and low risk procedure.
From 2014 to 2018, the international anorectal physiology working group (IAPWG) meet several times to develop consensus on indications for anorectal manometry. Their assessment concluded that anorectal manometry was indicated when used in assessment of fecal incontinence, constipation, evacuation disorders (including Hirschsprung's disease), functional anorectal pain and in the assessment of anorectal function preoperatively or after a traumatic obstetric injury. In addition to the indications outlined by the IAPWG, anorectal manometry has been used as a component of anorectal biofeedback.
Since its introduction in 2007, high resolution anorectal manometry (HR-ARM) has increasingly replaced conventional anorectal manometry as the standard. There has been increasing usage of high-definition (3D) anorectal manometry (HD-ARM) as well. Current advances in anorectal manometry include the development of bedside portable technology.
Medical uses
Fecal incontinence After eliminating structural causes of fecal incontinence from the differential diagnosis, anorectal manometry may be used to evaluate deficiencies in sphincter function or anorectal sensation. An abnormal resting pressure or squeeze pressure may indicate problems with either the internal anal sphincter or the external anal sphincter respectively. Both increased and decreased anorectal sensation has also been detected in individuals with fecal incontinence. The use of HD-ARM can allow recognition of pressure asymmetry within the anorectum. Some patients with fecal incontinence benefit from muscle strength training which may make use of anorectal biofeedback.
Constipation Anorectal manometry can be used in the diagnostic workup of individuals with chronic constipation without a known cause or with chronic constipation that has not improved on a trial of laxatives and/or fiber. For example, on a digital rectal exam, a physician may notice specific findings that point to dyssynergic defecation, a cause of chronic constipation. In such instances, the physician may order an anorectal manometry study to verify their findings. Abnormal results, such as the presence of a paradoxical contraction of the anal sphincter muscles during defecation (i.e. the muscles are squeezing instead of relaxing), can also be used to guide treatment (e.g. anorectal biofeedback). Other abnormal findings on manometry consistent with chronic constipation include an unsatisfactory generation of the propulsive force needed to defecate and a decreased movement of pelvic floor muscles.
Anorectal manometry, especially HR-ARM and HD-ARM, has also been used to evaluate constipation due to structural causes such as a rectocele, an enterocele, or an intra-anal intussusception.
Hirschsprung's disease In infants and children, anorectal manometry may be used to assist in the diagnosis of Hirschsprung's disease. The absence of the rectoanal inhibitory reflex (RAIR) is almost always pathognomonic for Hirschsprung's disease in this population. Anorectal manometry is not significantly less sensitive and specific when compared to the gold standard method of diagnosis, rectal suction biopsy. In adults, the absence of the RAIR is less likely due to Hirschsprung's disease and may indicate the presence of megarectum.
Functional anorectal pain Functional anorectal pain includes disorders such as levator ani syndrome, proctalgia fugax and unspecified functional anorectal syndrome. Although diagnosis of these disorders is largely clinical, anorectal manometry may be used for further diagnostic assessment. For example, the degree of anal sphincter hypertension may be determined which may be useful information when treating functional anorectal pain with biofeedback therapy.
Biofeedback The goal of anorectal biofeedback is to help patients improve defecating behaviors by providing patients with visual and verbal feedback. Visual feedback tools, such as anorectal manometry, are often used to aid patients in learning how to modify their behaviors. Patients may work on improving muscle strength, muscle relaxation or sensation during defecation.
The effectiveness of anorectal biofeedback as a treatment remains an ongoing source of debate and research. A systemic review article concluded that although better than placebo, there remained limited evidence demonstrating the effectiveness of anorectal biofeedback for chronic idiopathic constipation. In patients with defecatory disorders, including dyssynergic defecation, pelvic floor biofeedback therapy had been shown to be more effective than laxatives. An American-European Neurogastroenterology & Motility task force (ANMS-ESNM) recommended the use of biofeedback in the short and long treatment of constipation with dyssynergic defecation and fecal incontinence. They did not recommend biofeedback treatment for constipation without dyssynergic defecation, nor in children with constipation.
Types Types of anorectal manometry include: Non-high resolution (conventional) manometry (non-HRM) High resolution anorectal manometry (HR-ARM) High-definition anorectal manometry (HD-ARM or 3D-ARM)
HR-ARM and HD-ARM are newer methods that use multiple closely spaced sensors in the anus and rectum, compared to 3-6 widely spaced sensors used by non-HRM, to generate a more refined view. An additional benefit to HR-ARM and HD-ARM is the increased ease in analyzing the results as pressure readings are displayed in both color and as a line plot. Accompanying the benefits shared by both high-resolution and high-definition methods, the HD-ARM method employs additional sensors placed circumferentially around the catheter allowing for closer interpretation of individual sensor pressure readings. In comparison to non-HRM, however, both of the newer methods utilize equipment that is more expensive and has a shorter design life.
Procedure
Equipment The specifics of the equipment used for the procedure will ultimately depend on the type of manometry and the manufacturer of the device. Nonetheless, most share some common features: Catheter - used to insert the probe and balloon into the anorectum. The catheter may be water-perfused, solid-state or air-charged. Probe - contains sensors whose number and arrangement depend on the manufacturer and type of manometry Sensors - records pressures and transmits them back to the controller software Balloon - used to assess sensation when inflated with air. Most balloons used are non-latex and are manufactured to expand to 400 ml. A separate catheter with a water-inflatable balloon may be used to conduct a balloon expulsion test. Software - receives data from sensors. Data is then used to calculate values to be used for analysis and to provide visual feedback.
Technique In 2019, the International Anorectal Physiology Working Group (IAPWG) released a standardized testing protocol for the use of anorectal manometry. One of the goals of this protocol was to standardize procedural techniques to better facilitate meaningful data sharing. This protocol is the most recent published guideline for anorectal manometry since the one published in 2002 which was not widely adopted.
Preparation Fasting is not a requirement for this procedure. Patients are informed as to how the procedure is performed, its benefits and risks. Risks include the possibility of developing discomfort, pain, minor bleeding, dizziness or a rare perforation. In the testing room, the patient is placed on their left side with their knees bent. A digital rectal exam is then performed prior to the procedure to evaluate initial anatomy and function, check for stool, and to assess patient's understanding of the verbal instructions employed during the procedure.
Tests Anorectal manometry is often performed alongside a rectal sensory test (RST) and a balloon expulsion test (BET). The RST is performed after the manometry while the BET may be performed immediately prior to the manometry or subsequent to the RST. The total time to conduct all three tests is 15 to 20 minutes.
Manometry This test takes approximately 10 minutes. With the use of a lubricant, an anorectal manometry catheter is introduced into the anus. The catheter is advanced until the base of the balloon is above the anal canal by and the most distal sensor is below the anal verge. In order, the following maneuvers are then performed: +Descriptions and purpose of maneuvers performed during manometry testManeuverDescriptionPurposeLength of TimeStabilizationNo instructionAllow return to baseline3 minutesRestPatient asked to restMeasure resting pressure, detect presence of ultraslow waves60 secondsShort squeezeSqueeze as if preventing expulsion of feces or flatusMeasure squeeze pressure3 five second squeezes each separated by 30 seconds of recoveryLong squeezeSqueeze as if preventing expulsion of feces or flatusMeasure squeeze pressure30 seconds followed by a 60-second interval of recoveryCoughCough onceMeasure changes in pressure during cough1 cough followed by a 30-second interval of recovery followed by another 1 coughPushPush as if defecatingMeasure changes in pressure during defecation, detect presence of RAIR3 fifteen second pushes separated by 30 seconds of recovery
RST During the rectal sensory test, air is placed into the catheter balloon and slowly inflated either continuously or step-wise. The patient is asked to verbalize when they first sense the balloon, when the urge to defecate is first present and when they can no longer tolerate the balloon.
BET To perform the balloon expulsion test, a catheter with a balloon on its tip is introduced into the patient's anorectum. The balloon is then distended to 50ml with water. Patients are then instructed to transfer from lying on their side to sitting on a toilet. Next, patients are asked to push out the balloon as if they are defecating. The time it takes for the expulsion of the balloon is then recorded.
Analysis
Resting pressure The anal resting pressure is the recorded pressure within the anus during muscle relaxation. After insertion of the catheter, a short amount of time is allowed for the muscles to relax. Afterwards, pressures are recorded over 60 seconds. The maximum resting pressure is the highest pressure reached during this time period, while the mean resting pressure is the average pressure during this time period. In healthy individuals, women, especially older women, have an average lower anal resting pressures than men.
Squeeze pressure The anal squeeze pressure is the recorded pressure within the anus during a voluntary contraction of the external anal sphincter. Similar to resting pressures, squeeze pressures in healthy women are lower than healthy men. If using high-definition anorectal manometry, asymmetry in squeeze pressures can also be measured.
Change of pressure during defecation