IAPWG Recommendations for Testing and Classification of Anorectal Function

Based on emerging new evidence and expert consensus, the International Anorectal Physiology Working Group (IAPWG) released recommendations for the standardization of anorectal function testing protocols and introduced the London Classification system for disorders of anorectal function. This report was published in Neurogastroenterology & Motility.

Symptoms of anorecetal dysfunction affects the quality of life of between 1-5% of the population. The investigators performed a review of literature on the performance, terminology used, and interpretation of anorectal function testing, comprising of high-resolution anorectal manometry (HR-ARM), the rectal sensory test (RST), and the balloon expulsion test (BET). Although these are commonly used to evaluate patients with symptoms of anorectal dysfunction, practice varies significantly. Following the Delphi method, the IAPWG reached a consensus on anorectal testing protocols for each technique and proposed the London Classification of anorectal dysfunction based on objective physiological measurements.

Recommendations for Study Indications

The IAPWG recommends that anorectal function testing be performed following a referral from a specialist and after organic pathology has been excluded. Indications for anorectal function testing are to assess symptoms of a constipation/evacuation disorder, fecal incontinence, functional anorectal pain, preoperative anorectal function, and anorectal function in obstetric patients following obstetric injury or traumatic birth.

Recommendations for Patient Preparation

Patients preparing for anorectal function testing should undergo a clinical interview, in which presenting symptoms, medications and allergies, and history of medical, surgical, and obstetric events are documented. Patients may eat and drink up to the time of the test and may continue all existing medications. Using a water or phosphate enema prior to testing is optional but should be documented to elucidate the impact of bowel preparation on anorectal function. Patient consent must be obtained, and clinicians should explain the procedure and answer any questions before commencing testing.

Recommendations for Digital Rectal Examination

Although not expected to be fully diagnostic, a digital rectal examination is recommended prior to intubation in order to provide an initial assessment of pelvic floor structure, function, and sensitivity; to exclude local pathology and fecal loading; and to test patient understanding of instructions such as “push” and “squeeze.”

Recommendations for Test Specifications

High-Resolution Anorectal Manometry

The IAPWG does not recommend a single HR-ARM system configuration over another, but based recommendations on the use of solid-state systems: manometric sensors should record circumferential pressure, not unidirectional pressure; the longitudinal recording length should be a minimum 6 inches; and thin, flexible catheters are recommended over rigid, “high-definition” catheters.

Probe placement in HR-ARM studies should be performed in the left lateral position with the patient’s hips and knees flexed, and a non-anesthetizing lubricant is recommended. Prior to inflation, the base of the rectal balloon (attached to the catheter) should be placed 3 to 5 cm above the upper border of the anal canal in order to prevent impingement. The distal sensor should sit external to the anal verge.

The probe should be immediately withdrawn if any pain or discomfort is reported by the patient; if further pain or discomfort is felt upon second insertion, a medical assessment is recommended.

Rectal Sensory Test

In RST studies, probe placement should also be performed in the left lateral position with the patient’s hips and knees flexed. An integrated balloon should be used with either a manometric probe or with a separate system; all components should be latex-free and balloon capacity should be no less than 400 mL. A continuous (ramp) or phasic distension method may be used, but notably, results from the 2 different methods are not interchangeable. Insufflation should be performed with air using an inflation rate of 1 to 5 mL per second for ramp distention or 10 mL per second for phasic distention.

Balloon Expulsion Test

The IAPWG recommends the use of a flexible catheter in BET studies, up to 16 Fr in diameter, with a non-latex, compliant balloon attached to the tip. The introduction of a fixed volume of 50 mL of tepid water, recommended for balloon distention, should be performed with the patient lying in the left lateral position. The BET is performed as the patient is transferred into a sitting position, ideally on a toilet. To assess parameters of evacuation, methods such as barium or ME defecography tests may be used as an alternative to BET; however, agreement between tests is only fair.

Recommendations for Study Sequence

The IAPWG recommends a standardized protocol for anorectal function testing that includes a stabilization period, a period of rest, and a sequence of maneuvers (squeeze, cough, and push) with appropriate recovery intervals in between. RST testing follows the HR-ARM maneuvers, and the BET should be performed immediately before or after HR-ARM and RST testing.

Recommendations for Maneuver Descriptions

High-Resolution Anorectal Manometry

Following catheter insertion and prior to test maneuvers, a 3-minute stabilization period should be observed, allowing anal tone to return to baseline after intubation. Basal anal tone is then measured at rest over a 60-second period in which the patient should be reminded to relax and avoid movement. Ultraslow waves at a frequency of 0.5 to 2 cycles per minute may be observed during the stabilization period and rest maneuver.

A short squeeze maneuver measures anal pressure during a patient’s voluntary effort to contract the pelvic floor. The IAPWG recommends 3 squeezes lasting 5 seconds each separated by a 30-second recovery interval, using the best of 3 attempts for analysis. A long (endurance) squeeze measures anal pressure during a sustained effort to contract the pelvic floor and is performed over a 30-second period, followed by a 60-second recovery interval.

A cough maneuver measures rectoanal pressure changes during cough, assessing the anal sphincter reflex during abrupt changes in intra-abdominal or intrapelvic pressure. The clinician should direct the patient to perform a single cough with adequate effort to ensure the greatest increase in pressure. A total of 2 coughs should be performed separated by a 30-second recovery interval, using the best attempt for analysis.

A push maneuver is used to measure rectoanal pressure changes during simulated defecation; rectal balloon insufflation is not required during a push maneuver. The IAPWG recommends 3 pushes lasting 15 seconds each separated by 30-second recovery intervals. Clinicians should use the best of 3 attempts for analysis due to high false-positive rates associated with the maneuver.

Finally, a single rectoanal inhibitory reflex (RAIR) maneuver should be performed, measuring the anal response reflex to rapid rectal distension. The normal response to RAIR testing is characterized by a decrease of anal pressure during balloon distension, in which a starting volume of at least 30 mL is recommended. However, a large capacity rectum may fail to respond to low distending volumes in RAIR testing and increasing balloon volumes may be required if megarectum is suspected.

Rectal Sensory Test

RST testing measures rectal sensitivity to distension using a rectal balloon that is positioned at least 3 to 5 cm beyond the upper border of the anal canal; balloon volume is then recorded for 3 sensory thresholds: first constant sensation volume, desire to defecate volume, and maximum tolerated volume. In addition, sustained urgency volume is recommended as an optional threshold in RST testing.

Balloon Expulsion Test

BET testing assesses the ability of a patient to expel a balloon from their rectum, measuring the time it takes to complete balloon expulsion.

Recommendations for Standard Instructions

The IAPWG strongly recommends the standardized and consistent application of verbal commands. Clinicians should assess the patient’s understanding of commands during clinical assessment, and during the study, instruction should be given before performing each maneuver.

High-Resolution Anorectal Manometry

For short squeeze maneuvers, commands are as follows: “Squeeze as hard as you can for 5 seconds as though you are stopping yourself passing wind or stopping yourself opening your bowels.”

For long squeeze maneuvers, commands are as follows: “Squeeze as hard as you can for as long as you can.” Every 5 seconds, the clinician should provide cues by saying “keep squeezing, keep squeezing.”

For cough maneuvers, commands are as follows: “Please give a single cough.” The IAPWG recommends the clinician demonstrate a cough and emphasize that a single — not a double — cough is required.

For push maneuvers, commands are as follows: “Push down as though you are sitting on the toilet opening your bowels/passing a bowel movement/trying to defecate.”

Rectal Sensory Test

For the first constant sensation volume, commands are as follows: “I am going to put some air into the balloon. Tell me when you first feel a sensation inside your bottom that doesn’t go away.”

For the desire to defecate volume, commands are as follows: “Tell me when you feel a constant urge to defecate/open your bowels.”

For maximum tolerated volume, commands are as follows: “Tell me when it becomes too uncomfortable and you need me to stop.”

Balloon Expulsion Test

For BET testing, commands are as follows: “Try to push the balloon out into the toilet like you’re opening your bowels/trying to defecate.”

Recommendations for Measurements

The IAPWG recommends that anorectal function outcomes are described using a combination of qualitative and quantitative measurements. The rest maneuver measures anal resting pressure (mmHg) and the presence or absence of ultraslow waves. The squeeze maneuver measures anal squeeze pressure (mmHg) while endurance squeeze pressure is measured in seconds. The push maneuver measures rectal and anal pressure changes during push (mmHg), and the cough maneuver measures rectal and anal pressure during cough (mmHg). RAIR is measured by the presence or absence of the rectoanal inhibitory reflex. All RST thresholds are measured by balloon insufflation volumes (mL), and the BET measures the time it takes to expel a rectal balloon in seconds.

Recommendations for Description of Normality

When normal values are based on published data, the IAPWG recommends that the equipment setup and procedure are identical to the protocols described in the referenced manuscript. When normal values are based on a study of local volunteers, variability regarding gender, parity, and age should be taken into consideration.

Recommendations for the London Classification of Anorectal Physiological Dysfunction

To describe findings from the combined results of HR-ARM, BET and RST, the IAPWG developed the following classification system divided into 4 parts: disorder of the rectoanal inhibitory reflex, disorders of anal tone and contractility, disorders of anorectal coordination, and disorders of rectal sensation.

Diagnoses may be categorized per the Chicago Classification system: a major finding (a pattern not seen in controls that likely represents a physiological alteration associated with symptom generation), a minor finding (a pattern seen in patients with anorectal symptoms but that may also be seen in controls), and an inconclusive finding (a pattern seen in both the controls and patients with anorectal symptoms).

Diagnostic classification should further introduce uniform terms to describe physiological features of interest: “(hypo/hyper)tension” to describe anal resting tone, “(hypo)contractility” to describe anal squeeze, “expulsion” to describe ability to expel a rectal balloon, “propulsion” to describe an increase in rectal pressure during push, “dyssynergia” to describe the failure of coordinated anal relaxation during push, and “(hypo/hyper)sensitivity” to describe rectal sensation.

Limitations of the study included that the vast majority of recommendations reflect coalescence of expert opinion, rather than systematic review of clinical evidence; the consensus describes only 3 simple office-based tests of function and due to the heterogeneity of current data and equipment available, the recommendations were specific, quantitative ‘reference limits’ for diagnosis of anorectal disorders.

The authors concluded that these recommendations “provides a much‐needed framework for clinicians performing and interpreting tests of anorectal function. It is expected that these recommendations will evolve as experience with this technology increases and data from physiological and clinical studies emerge.”

Disclosure: Multiple authors declare affiliations with the pharmaceutical industry. Please refer to reference for a complete list of authors’ disclosures.

Reference

Carrington EV, Heinrich H, Knowles CH, et al. The international anorectal physiology working group (IAPWG) recommendations: standardized testing protocol and the London classification for disorders of anorectal function [published online August 12, 2019]. Neurogastroenterol Motil. doi: 10.1111/nmo.13679