Anorectal Manometry (ARM) is a diagnostic procedure used to evaluate the strength and coordination of the muscles and nerves within the rectum and anus. This non-invasive test helps medical professionals understand how well these structures work together to control bowel movements. It is frequently employed to investigate various pelvic floor disorders, providing objective measurements of function that are not possible through a physical examination alone. The information gathered from ARM is essential for determining the cause of symptoms and guiding the most effective treatment strategy.
The Purpose of Anorectal Manometry
The primary reason for performing Anorectal Manometry is to investigate the underlying causes of chronic constipation and fecal incontinence. The test directly assesses the function of the anal sphincter muscles, composed of the involuntary internal sphincter and the voluntary external sphincter. Measuring the pressure generated by these muscles helps identify weakness or poor coordination contributing to a patient’s symptoms.
For individuals experiencing fecal incontinence, ARM helps determine if the anal sphincter muscles are too weak to maintain closure, especially during moments of increased abdominal pressure like coughing or sneezing. Low resting pressure, maintained mostly by the internal sphincter, can indicate a deficiency. For chronic constipation, the test identifies dyssynergic defecation (anismus), where the pelvic floor muscles paradoxically tighten instead of relaxing during a bowel movement attempt.
ARM also assesses rectal sensation and the reflexes necessary for normal evacuation. It measures the volume the rectum can hold before the urge to defecate (rectal capacity and compliance). Furthermore, it checks for the rectoanal inhibitory reflex, the involuntary relaxation of the internal sphincter when the rectum is stretched. This procedure is also valuable for pre-operative assessment before colorectal surgeries to predict functional outcomes.
Preparing for the Procedure
Specific preparation is required before Anorectal Manometry to ensure the rectum is clear for accurate measurements. Patients are instructed to use one or two over-the-counter enemas, such as a Fleet saline enema, at home on the day of the procedure. This preparation removes any stool from the lower rectum and anal canal prior to the test.
Patients are advised to refrain from eating solid food for a few hours before the appointment. They can continue to drink clear liquids or water up to two hours prior to the test. Taking regular prescribed medications with small sips of water is permitted, but this must be discussed with the ordering physician.
It is sometimes necessary to temporarily stop certain medications, particularly those that affect muscle function or gut motility, for up to 48 hours before the test. This includes narcotic pain relievers, specific muscle relaxants, or agents that stimulate bowel movements. Adjustments may also be needed for diabetic medications, so reviewing all current prescriptions with the healthcare provider is important.
The appointment usually takes between 30 and 60 minutes. Patients do not require sedation since their active cooperation is necessary for the various maneuvers.
How Anorectal Manometry is Performed
The procedure begins with the patient lying on their left side with knees bent. A thin, flexible catheter, about the size of a thermometer, is gently inserted a few inches into the rectum. This catheter contains multiple pressure sensors and records the pressure data in real-time.
The first measurements taken are the resting pressure and the maximum squeeze pressure. Resting pressure reflects the tone of the internal anal sphincter, the muscle that unconsciously maintains continence. The patient is then asked to squeeze their anal muscles as tightly as possible to measure the strength of the external anal sphincter.
Assessing rectal sensation and reflexes involves using a small balloon attached to the catheter tip. The technician gradually inflates the balloon with air, asking the patient to report the first feeling of sensation and the strong urge to defecate. This evaluates the nerves and the rectum’s ability to expand (compliance).
A crucial part of the test is the balloon expulsion test, which evaluates the patient’s ability to coordinate muscles for defecation. A water-filled balloon is placed in the rectum, and the patient attempts to push it out while sitting on a commode. Expelling the balloon within one minute is normal; a prolonged time suggests a failure of the muscles to relax and coordinate effectively.
Interpreting the Test Results
The data collected provides a detailed pressure profile that translates into a functional assessment of the pelvic floor. Readings are immediately available to the physician, who interprets the numerical values in the context of the patient’s symptoms. A lower than normal maximum resting pressure suggests weakness in the internal anal sphincter, a common finding in fecal incontinence.
If the patient cannot expel the balloon or if pressure sensors show the anal sphincter contracting during pushing, this indicates pelvic floor dyssynergia. This paradoxical muscle action is a frequent cause of chronic constipation and guides treatment. The absence of the rectoanal inhibitory reflex (internal sphincter failing to relax upon rectal distention) can point toward a diagnosis like Hirschsprung’s disease.
The ARM results are instrumental in guiding the selection of appropriate therapies. If muscles are weak, a patient may be directed toward pelvic floor strengthening exercises or biofeedback training. Biofeedback uses the manometry equipment to provide real-time visual feedback, helping patients learn to relax or contract their muscles. In cases of severe sphincter weakness, the results may inform decisions regarding potential surgical intervention.