What Is Known/What Is New
What Is Known
- Anorectal disorders are common in the paediatric population.
- Structural and functional abnormalities of the anorectum or pelvic floor have been demonstrated in patients, resulting in a variety of symptoms, most commonly, constipation and faecal incontinence.
- Several underlying aetiologies can have similar clinical presentations but need different treatments, therefore, reliance on symptoms alone is inadequate, underlining the need for a accurate and more definitive diagnosis.
What Is New
- Recent advances in diagnostic techniques, particularly, the advent of high-resolution and high-definition anorectal manometry have provided a better understanding of the pathophysiology of anorectal disorders.
- A great diversity of equipment and protocols are used among centres, which may lead to heterogeneous interpretation of results.
- Standard protocol for anorectal manometry have been provided.
Appropriate anorectal function, such as continence and evacuation of bowel contents, requires adequate function, and coordination of multiple muscles, involving chronological contraction and relaxation of the colon, rectum, anus, and pelvic floor (1). Anorectal disorders, resulting from disturbances of this intricate system, are common in the paediatric population (2–5). Both structural and functional abnormalities of the anorectum or pelvic floor have been demonstrated in patients, resulting in a variety of symptoms, most commonly, constipation, and faecal incontinence. Childhood functional constipation has a prevalence ranging from 0.7% to 29.6%, with organic causes of constipation recognized in less than 5% of cases (6). Faecal incontinence is also common in children with a worldwide reported prevalence of 0.8% to 7.8%; it is related to functional and organic causes, and mostly associated with stool retention. Organic causes account for <5% of cases of faecal incontinence and include conditions that affect the anorectum, anal sphincters, myenteric nerves or the spinal cord (7,8). Several underlying aetiologies including Hirschsprung disease, anorectal malformations, neuromuscular disorders, and dyssynergic defaecation can have similar clinical presentations but need different treatments. Therefore, reliance on symptoms alone is inadequate, underlining the need for an accurate and more definitive diagnosis (9). Recent advances in diagnostic techniques, particularly the advent of high-resolution and high-definition anorectal manometry have provided better delineation of the anatomical changes and phenotypes, as well as a better understanding of the pathophysiology of anorectal disorders. This article aims to provide clinicians an updated review on indications and performance of anorectal manometry in paediatric patients.
EQUIPMENT
Anorectal manometry (ARM) is used to obtain an objective (quantitative and qualitative) assessment of function and can identify disorders that are not always recognised on clinical picture alone. It provides comprehensive information regarding abnormalities in anorectal function by evaluating recto-anal muscles and dynamic characteristics, including coordination, integrity and magnitude of sphincter tonic contractions, baseline reflexes, subjective perineal and internal rectal sensation, and recto-anal coordination (10,11).
The ARM system consists of 2 major components: a pressure-sensing catheter that uses 2 types of incorporated sensors, water-perfused or solid-state micro-transducers, as well as an amplifying and recording system. There are 2 types of equipment: conventional manometry that measures pressure with only few sensors and presents these measurements as line traces (Fig. 1a and b) high-resolution, with many (at least 10) closely spaced sensors presenting a more detailed pressure map of the anorectum (Fig. 1b). Both types of manometry can use water-perfused or solid-state sensors. In clinical practice, conventional water-perfused manometry has gradually being replaced by newer manometric technologies (12), a high-resolution (HR-ARM) (13) and a 3-dimensional high-definition catheter (3D-HR-ARM) (14). High-resolution catheters can record luminal pressures from a high number of data points, which can then be used to generate 2-dimensional topographical colour-contour plots of intraluminal pressure (Fig. 1b). This allows for greater coverage and clearer visualization of the anorectal pressure profile compared with conventional manometry and minimises the loss of potentially important information, for example, resulting from pseudorelaxation of anal sphincters (in case of misplacement of sensors) or visualisation of focal defects of anal pressure (14,15). Additionally, 3D-HR-ARM records point pressures longitudinally and radially using a rigid probe with 256 solid-state microtransducers of pressure, placed circumferentially (3 mm) and longitudinally (4 mm) apart, with recorded pressures presented in a multidimensional fashion in a 16 × 16 matrix (Fig. 1c) (14,15). It provides significantly greater anatomic detail including the possibility of differentiating internal and external sphincters, which was not achieved previously (16). There is not yet enough evidence to suggest using 3D in replacement of 2D HR-ARM; however.
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FIGURE 1: Resting pressure measurement during anorectal manometry: (A) conventional line tracings, (B) high-resolution spatiotemporal plot, (C) 3-dimensional reconstruction of anal canal of a healthy child, (D) 3-dimensional reconstruction of anal canal obtained from patient with faecal incontinence and with the presence of pressure defect in proximal left part of anal canal. Ant = anterior; L = left; post = posterior; R = right.
STUDY INDICATIONS
Irrespective of the aetiopathogenesis, which is often not or incompletely defined, anorectal disorders in children are likely to involve an interplay between organic, functional, and behavioural disturbances. ARM is a technique able to test all these components by recording intraluminal pressures of the rectum and anal canal, triggering sensations and evaluating coordination of bear-down manoeuvres. Therefore, it is indicated in cases of:
- 1. anorectal symptoms, encompassing chronic (severe) constipation, faecal incontinence, faecal urgency, irrespective of their functional or organic origin (11,17),
- 2. disorders of neuromuscular origin (18),
- 3. spinal cord malformations (19),
- 4. rectal trauma (20,21),
- 5. pre- and post-surgery for Hirschsprung disease (21–23), anorectal malformations (24,25), and/or proctocolectomy (26),
- 6. the identification of patients that may benefit from botulinum toxin injection into the anal sphincter complex (27,28),
- 7. biofeedback therapy (29–32),
- 8. in patients with persistent symptoms (eg, faecal incontinence) after surgery for anorectal disorders may benefit from the usage of 3D-HR-ARM because of its ability to detect sphincter defects (26,33).
STUDY PERFORMANCE
Although ARM can be performed in patients of any age, only children from the age of 5 years are able to reliably cooperate with the sensory testing and complete the dynamic components of the test, such as squeeze and bear-down manoeuvers (17). For younger children, the test is usually limited to the analysis of anal sphincter resting pressure and the recto-anal inhibitory reflex (RAIR) (34). Additionally, successful completion of the study is dependant on the patient's development, comorbidities, and cooperation.
NEED FOR SEDATION OR ANAESTHESIA
The ARM study should ideally be performed in an awake patient but this is not always feasible and anaesthesia must be given, particularly in younger children and in children with behavioural disorders, when the primary aim of the test is the evaluation of the RAIR. Muscle relaxants should be avoided. It has been shown that ketamine and midazolam do not affect the sphincter pressure or the reflex response whereas propofol decreases the resting sphincter pressure in a dose-dependent manner (35,36). Sevofluorane and nitrous oxide are additional options that might be used in uncooperative children.
PRE-TEST PREPARATION
Children who are anxious and unfamiliar with the test may benefit from comprehensive explanations, and if it is possible to organise, even pre-test ‘mock’ visits with members of the investigation team to familiarise themselves with the proposed procedure, location, and staff, with the ability to have their queries answered appropriately. There is no need to stop medications before the test. Bowel preparation (enema or suppository) should be given 1 hour before the ARM or on the evening before the investigation to ensure an empty rectum.
PROCEDURE
On the day of the procedure, if sedation is required, the patients should not eat or drink before the anaesthesia. The patients should, ideally, arrive to the hospital 1 to 2 hours before the procedure to allow them to settle, meet, or ask questions to the investigation team. As stress may affect parameters and performance of test, it should be minimized as much as possible and the procedure should start only once the child is comfortable and aware of the process.
Studies are performed in the left lateral decubitus position, with knees drawn to the chest, thus both hips and knees flexed beyond 90°. In children that are anxious, the parent or a play specialist could sit facing the child and aid in distracting the child, for example, with an iPad or a book or a toy, depending on the age of the patient.
A careful and gentle digital rectal examination (DRE) with an appropriate, nonanaesthetising, lubricant applied to the examining finger and the anus is performed before the examination. In the presence of stool, a rectal enema should be administered. DRE is also useful to evaluate the anatomy of abnormalities and gain a baseline assessment of the function of the anal area. It also provides a sense of stool loading and the extent of the patient's ability to follow commands.
The same lubricant should be applied to the ARM probe to aid placement. The probe is then inserted into the anal canal and rectum ensuring that the patient is as relaxed as possible to avoid contracting the anal sphincter, which may cause discomfort. Asking the patient to take slow deep breaths may be helpful in achieving relaxation during placement and ultimately better baseline measurements. The probe tip is advanced into the rectum and positioned ensuring that the sensors span the rectum (proximal sensors near probe tip) to just beyond the anal verge (distal sensors), see Figure 1. The probe should then be held there for at least 90 seconds for the anorectal area to settle after the insertion and to adapt to the presence of the probe before obtaining data. Some authors suggest taping the exteriorized portion probe to the buttocks (11), which may be problematic for children who are anxious or move as it can displace the catheter in less cooperative children, while others suggest to wait for longer times before testing (37).
The ARM manoeuvres are performed in a sequence with a 30 second recovery period between each manoeuvre. The standard sequence includes, as follows.
Resting Pressure
After the patient is relaxed and comfortable with the probe in place, the basal resting sphincter pressure is obtained. At best, it is recommended to record a period of 1 minute to obtain reliable mean values because of possible variations in anal tone (ultraslow waves). A low resting pressure could be indicative of weakness or disruption of the sphincter musculature (38,39).
Squeeze Pressure
This parameter is used to assess the strength of striated muscles of the anal canal, mainly external anal sphincter (EAS) and with less contribution of puborectalis muscle (PRM). Squeeze pressure is recorded after the patient is asked to voluntarily contract the anal muscles for at least 5 seconds. It is recommended to obtain at least 2 measures separated by 30 seconds of rest. The result may be expressed in 2 ways: incremental anal squeeze pressure: the highest pressure increase over the baseline resting pressure (measured 5 seconds before the squeeze), or maximum anal squeeze pressure: the highest pressure recorded over 2 seconds during an episode of contraction. A weak squeeze pressure may indicate myogenic or neurogenic causes. It may also reflect the lack of cooperation during the test (30).
Bear-Down Manoeuvre (Simulated Defaecation)
While still lying in the left lateral position, the child is asked to bear down for 15 to 30 seconds exactly as if trying to defecate. The child should not be distracted at this point to ensure that he/she is focusing on the manoeuvre. Pressures are recorded simultaneously inside the rectum and in the anal canal, usually over 2 to 5 seconds chosen from 15 to 30 seconds of the pushing episode, when the intrarectal pressure reaches its peak value. Several variables are calculated as follows: intrarectal pressure: the mean pressure recorded in the rectum, residual anal pressure: lowest pressure recorded within the anal canal, percent of anal canal relaxation: which is a result of the calculation based on (residual anal pressure − resting pressure before push) × 100%. The defaecation dynamics (anorectal coordination) may be expressed by additional variables such as: recto-anal pressure differential (RAPD): result of equation (residual anal pressure − intrarectal pressure), and/or defaecation index (DI): intrarectal pressure divided by residual anal pressure. With normal defaecation dynamics, there is an expected increase in rectal thrust pressure because of abdominal muscle contraction coordinated with a decrease in anal sphincter pressure. Patients in which these coordinated movements do not occur are thought to have dyssynergic defaecation often resulting in constipation (13).
Ano-Anal and Cough Reflex
The pressure in the anal canal is recorded during intentional axial movement of the catheter (usually as 3 short slides of the catheter inside the anal canal) performed to elicit contraction of anal muscles. Evaluation of the cough reflex is based on recording pressure increase during 1 cough. This reaction is mediated by pudendal nerves and S4 sacral roots. The lack of increase in resting pressure is suggestive of damage to sacral reflex arc (40–42).
Recto-Anal Inhibitory Reflex
The recto-anal inhibitory reflex (RAIR) is evaluated by rapidly inflating (over a period of 1–3 seconds) the rectal balloon with 5 mL increments in infants and by 10 mL increments in older children (17). The volume to elicit a RAIR varies and is dependent on the age of the child and size of the rectum, type of catheter size, and so forth. The results are described as RAIR presence in case of substantial decrease in anal resting pressure and/or the volume of air eliciting reflex. The results of RAIR may be influenced by several factors, such as inflation volume, rectal volume, cooperation of the patient (voluntary contraction can reduce RAIR relaxation), catheter migration (pseudorelaxation), and the choice of inflation pattern (rate of inflation) (40,43–45). The reflex is obtained to assess the presence of the local enteric reflex and is classically absent in Hirschsprung disease (11,17).
Rectal Sensation
Rectal sensation is assessed by inflating the balloon continuously with air in incremental volumes. First sensation is defined as the lowest balloon volume sensed by the patient. The urge of sensation is the lowest balloon volume at which the patients develops the urge to defecate, whereas the maximum tolerable sensation is the inflation size associated with severe urgency or/and pain (11). All thresholds are noted as volume of air triggering sensation. Decreased sensitivity (increased thresholds) may indicate megarectum (46), whereas increased sensitivity may reflect visceral hypersensitivity (47).
The conventional protocol for anorectal manometry consists of consecutively performed elements separated by 30 second recovery periods (Fig. 2). The standard sequence may need to be modified based on patient indications, history, age, and cooperation. There are also additional elements that may be evaluated by manometry, for example, anal canal length (performed in case of incontinence post-surgical procedures), squeeze increment and endurance squeeze (in case of neurological disorders), cough reflex (in case of incontinence and suspicion of damage to sacral reflex arc), presence of ultra-slow waves, and others (11,48) that are beyond the scope of this review.
FIGURE 2: The protocol of anorectal manometry. Modified with permission from
(9,11,17).
NORMAL VALUES
It should be emphasised that in paediatrics, normal values lack validation and reproducibility. Of note, normal values from manometric parameters may differ according to age, with lower values of resting pressure and thresholds for RAIR in neonates compared with older children (Table 1) (49,50). Moreover, recorded pressure values may depend on the specific type of pressure sensor used during the test (water-perfused vs solid-state) (51,52), the diameter of the catheter (greater diameter may produce higher pressure values obtained by solid-state sensors) (53,54), the protocol used by investigator (duration of the recording, eg, resting pressure over 30 or 60 seconds) or even the software used to process the recorded data (maximum, mean, median, or increment) (55). Therefore, it is important to use normal values obtained with the same equipment and adequate protocol. Using water-perfused conventional manometry, Kumar et al recorded resting pressure in 90 otherwise healthy children and subdivided the group to 3 age groups: neonates, children ages 1 to 16 months, and 18 months to 12 years. The ranges of mean resting pressure (upper and lower limits of normal) were: 11 to 50, 23 to 55, and 30 to 60 mmHg, respectively (49). Using a water-perfused high-resolution catheter, Tang et al recorded resting pressures in infants ages 1 to 85 days, the values ranged from 19 to 39 mmHg (50). In older children, normal values of 3D-HR-ARM analysis were published, demonstrating resting pressure of 83 mmHg (±23) (56). In cooperative children (above 4 years old), squeeze pressure was approximatley 2 times higher than resting pressure, and equalled 191 mmHg (±64). Thresholds for first sensation, urge, and discomfort were also established (48, 81, and 142 cm3, respectively) (56). Different criteria for a positive RAIR are reported in literature. Traditionally the RAIR was considered to be present if the balloon inflation elicits a decrease of at least 5 mmHg in anal pressure in conventional manometry (17). Others used different criteria, such as decrease of 20 mmHg in anal pressure (22) or report percentages instead of absolute values, for example, decrease >25% in anal pressure in 3D-HR-ARM (56) or >50% of anal pressure in HR-ARM (57). There are a few studies in small numbers of children reporting normal values but recorded with old types of equipment, that are no longer in use (58–61), therefore, their usefulness may be questionable.
TABLE 1 -
Normal values for manometric measurements in regard to age and equipment
| Manometric equipment |
Age |
N |
Mean resting pressure (mmHg) |
Maximal squeeze pressure (mmHg) |
Anal canal length (cm) |
Threshold of RAIR (mL) |
Fist sensation (mL) |
Urge (mL) |
Discomfort (mL) |
| CM (35)
|
<1 month (GA 34–39 weeks) |
30 |
31 ± 11 |
n/a |
1.7 ± 0.3 |
10 ± 4 |
n/a |
n/a |
n/a |
|
1 to 16 months |
30 |
42 ± 9 |
n/a |
1.9 ± 0.6 |
14 ± 10 |
n/a |
n/a |
n/a |
|
18 months to 12 years |
30 |
43 ± 9 |
n/a |
3.0 ± 0.5 |
25 ± 12 |
n/a |
n/a |
n/a |
| HR-ARM (36)
|
Newborns (GA 28–42 weeks) 1 to 85 days old |
180 |
29.7 ± 9.9 |
n/a |
1.9 ± 0.5 |
n/a |
n/a |
n/a |
n/a |
| 3D-HR-ARM (41)
|
2 to 17 years |
61 |
83 ± 23 |
191 ± 64 |
2.6 ± 0.7 |
15.7 ± 11 |
24 ± 23 |
46 ± 35 |
191 ± 64 |
Data expressed as mean ± SD. 3D-HR-ARM = 3-dimensional high-resolution anorectal manometry; CM = conventional water-perfused manometry; GA = gestational age; HR-ARM = high-resolution anorectal manometry; n/a = nonavailable; RAIR = recto-anal inhibitory reflex.
CONCLUSIONS
During the past decades, the technological advancement in manometric equipment lead to substantial improvement of anorectal function testing. More advanced investigations might, however, lead to difficulties in interpretation. Additionally, a great diversity of equipment and protocols are used among centres, which may lead to heterogeneous interpretation of the results. Our aim was to provide a comprehensive update on the current indications and a unified standard protocol for paediatric anorectal manometry. More studies to standardise methods of testing and validate reference values are strongly recommended in children.
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