Patterns and Norms in Anorectal Pressures

Published on Mar 21, 2022

Knowing there is a problem is only half the battle. Before knowing how to fix a problem, you first have to be able to correctly identify it.

Watch this short video from industry-leading expert, Dr. Abhitabh Patil as he shares his knowledge and discusses case studies. In the video you will learn:

  • Differences between normal and abnormal patterns of rectal anal pressure profiles

  • How to use an anorectal manometer to measure resting and squeeze pressures

  • How to decode what the rectal pressure profile may indicate

  • Other special tests to consider for more in-depth investigation

  • Possible treatment strategies

Anorectal Patterns, Norms and Case Studies

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Full transcript:

Dr. Abhitabh Patil: “Let's review some patterns of Anorectal Manometry on the left column, you can see a healthy patient. When there is distension of the rectum, you see a relaxation of the internal anal sphincter. You see a contraction of the external anal sphincter. This is an appropriate response for the recto anal inhibitory reflex. In patients who have Hirschsprung's all the way on the right column. When there's distinction of the rectum, there's minimal to no change in the internal anal sphincter. The external anal sphincter also stays similarly at baseline, or maybe even slightly increased. In the middle you can see how a spinal cord injury patient would respond. With rectal distension they do have relaxation of the internal anal sphincter and some relaxation of the external anal sphincter. This is because the recto anal inhibitory reflex is intact.

Another type of rectal anal pressure profile is exhibited here. This is for the patient who has dyssynergia. On the left you see when there's rectal distension, you have relaxation of the anal canal. This allows expulsion from the rectum out of the anus. This is what we call the rectal gradient. In the first type of patient with dyssynergia type one, you can see when the rectum is distended, there is inappropriate contraction of the anal muscle. This does not provide a gradient and therefore the patient complains of straining or difficulty with defecation. On the next column, you can see a with dyssynergia type two, they have inappropriate anal contraction. And on the final slide, you can see patients with inadequate expulsion who despite having rectal distension have no change in their anal tone. There is no relaxation. Again, these are three profiles of patients with anal rectal dysmotility or pelvic floor dyssynergia. This section we'll describe anorectal manometry, below our listed normal values.

You can see that a normal resting pressure for the internal sphincter muscle is around 60 to 70 millimeters mercury. An appropriate squeeze should rise by one and a half times to roughly 120 to 170 millimeters mercury. Expel empty, where the patient has no bowel bear down maneuver with no air added in the rectal balloon should usually give an increase in the rectal pressures and a decrease in the anal pressures. Again, providing a gradient. Expel full is when there's a full bear down maneuver with 50 CCs of air added into the rectal balloon. You should see an increase from the rectal baseline pressure and a decrease from the anal baseline pressure, again providing a gradient. In the volume sensations we usually measure the first sensation, which is, "I can feel it." This should be around 30 to 50 CCs. Next, we increase the rectal sensation until they reach a desire point.

This is the urge to defecate. “I can hold it for a few minutes.” This is usually 60 to 80 CCs. Next there's the urgency sensation, which is, "I need to go defecate. I can't hold it anymore." This is 100 to 120 minutes. And finally, we do an exhale maneuver. This is a cough maneuver to look for the reflex arc in the rectum sphincters. What you should see is an increase from the rectal baseline pressures and an increase from the anal baseline pressures. Again, when a coughing maneuver is elicited, you should see strengthening of the rectal and anal muscles together. This prevents incontinence. Let's take each of these one by one. So when we look at resting pressure and squeeze pressure, resting pressure can be low in patients with fecal incontinence symptoms, or if there's weakness of the muscle due to myopathy, neuropathy, or atrophy resting pressure can be seen as high in patients with constipation or defecation disorders.

A high tone can also be indicative of anal spasm, which can result in anal fissure and hemorrhoidal symptoms. Finally, the squeeze pressure is sometimes low in patients with fecal incontinence symptoms. Weakness of the muscle can be due to either trauma, pudendal nerve injury or myopathies and neuropathies. Next we evaluate the expel gradient. This is calculated using the expel pressures mentioned before. A positive gradient is normal, and this implies normal expulsion from the rectum through the anus. Again, the rectal pressure goes up and the anal pressure goes down. This should give you a positive gradient. A negative gradient implies that there's abnormal pressure direction. This is indicative of dyssynergia. Finally, we look at the sensations, which is sensation, desire, urgency, and exhale. An abnormally high pressure indicates the presence of megarectum. That is the rectum is floppy and distended and indicates chronic obstruction and abnormally low pressure may indicate visceral hypersensitivity.

That is the patients sense things at a very low volume. Patients with megarectum may have an absent RAIR. This is one of the more common causes of absent RAIR in adults, as opposed to Hirschsprung's which is more common in children. Based on the results of anorectal manometry some treatments to consider include Kegel exercises with strengthen the internal anal sphincter and external anal sphincter, fibers, such as bulking agents, biofeedback therapy and training, which is probably the most effective stimulators such as InterStim. Other tests to consider based on abnormal results may include anorectal ultrasound, pudendal nerve injury with EMG, or work-up for myopathies and neuropathies.

So let's go through case studies. Case study one: the way I like to evaluate these manometry readings is by first starting out with looking at the resting pressure. Here on the left, you see that the anal mean pressure is 78. Next, I like to see the anal mean during a squeeze. We should see at least a one and a half time rise. And this here is appropriate. It goes from 78 to 107. Next, we look at the gradients. Looking over to the right column you see the expel empty has a negative anorectal gradient of negative 18. Whereas, the expel full has a positive gradient of about two. So this is roughly normal. If you look at exhale, anal mean and anal max, this should be roughly about one and a half times the resting pressure. And again, this is a 133, so this is normal. And finally, we look at the recto anal inhibitory reflex, and in this case it's present, and this is also normal.

Next, let's turn our attention to the last sheet of the report. Here, I'd like to draw your attention to the rectal volumes, which is in the center of the page. If you see roughly the sensation is at about 85 to 90, the desire is still around 85 to 90, and urgency can also be seen roughly around 70 to a 100. So this is all normal. So the patient senses, desires and has urgency at normal volumes. The report here would be a normal anorectal manometry.

Case study number two: this is a patient who presented with constipation. So let's evaluate, the anal mean is 78 with the max of 87. If you look at the squeeze pressure, the squeeze pressure is one 17 or 187. So that's normal. That goes up appropriately. If you look at the exhale, the exhale is 144 and the mean is 81. Again, this is a little bit higher than the resting. And again, this is normal as well. If you look at the anal pressures again, the anal pressures are slightly elevated. This is a patient who might have anal spasm. If you look at the gradient, however, the gradient is negative 61. This is grossly abnormal. This implies that the direction of expulsion is upward from the anus up to the rectum. So this is anorectal dismotility or pelvic floor dyssynergia.

Let's turn our attention to the last page, which talks about the rectal volumes. Again here, you see the rectal volumes are 60, 90, and 130. This is roughly normal, but on the higher end of normal. So again, there may be early megarectum.

So in conclusion, this is a patient who has slightly elevated resting anal pressures and has a negative anorectal gradient, which suggests anorectal dysmotility. So this is a patient who probably has pelvic floor dyssynergia and would benefit from fiber and biofeedback therapy.

Case study three. So this is a patient who is referred for fecal incontinence. When we look at the anal mean, it's 46, that's relatively low. When you look at the anal mean, and the anal max, it's very slightly elevated. Again, this is not very normal. It should be higher than this. Finally, when you look at the exhale anal mean and anal max, you can see, again, it's not very high. This means that when the patient coughs or sneezes, that they're going to leak feces. Finally, when you look at the anorectal gradient, these are normal with anorectal gradient of 34. So this patient has weakened anal sphincter muscles. And this is probably the reason why the patient has fecal incontinence.

Let's turn our attention to this last page of the report, where we look at the rectal volumes. Here, you see 40, 60, and 80. These are roughly normal for sensation, desire and urgency. So in conclusion, this patient has weak resting pressures, which is the likely the cause of the patient's fecal incontinence. This patient would benefit from fiber, biofeedback therapy and possibly even Kegel exercises.”

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