It is difficult to auscultate bowel sounds sometimes as this skill requires patience and mastery. Experienced physicians often make diagnoses based on palpation and auscultation of the abdomen alone. What are the different types of Bowel sounds then?
Few insights before jumping to examination:
What part of Stethoscope is used to auscultate for bowel sounds?
Different sources cite different parts. Both diaphragm and bell can be used to listen to the sounds.
How many quadrants should be auscultated?
All four quadrants should be auscultated. If there are no sounds heard, one should spend 5-7 minutes before rushing to a conclusion.
What is the frequency of bowel sounds?
It can be 2-4 per minute or heard every 5-10 seconds. Different sources cite different frequencies.
Should auscultation be performed even before palpation?
Some sources cite that palpation can stimulate peristalsis. This will cause subsequent bowel sounds that would not be heard otherwise. Light palpation can be used sometimes to stimulate peristalsis and hence, the sounds.
How to hold the stethoscope?
There should be minimal pressure on the diaphragm. This is to prevent stimulation of peristalsis which will mask the true auscultation findings.
You have to start from scratch for this and ask- “What is a Normal Bowel Sound?”. In this post, we will explore all the types, causes, and mechanisms behind them.
What are Normal Bowel Sounds?
These are believed to occur during the passage of food or fluid through the intestines. Because the intestines are hollow, the sounds they make reverberate throughout the abdomen and are frequently described as sounding like water running through pipes.
In a healthy person, bowel sounds can be heard 5–35 times per minute. It should be noted that to properly listen for them, the clinician would need to auscultate the abdomen for some time, as sounds can be absent for up to 4 minutes in healthy people.
Features
The features include:
- Intermittent
- 5-35 in frequency
- Gurgling/ Clicking/ Rumbling in quality
- Low or moderate pitch
- Irregular pattern
Absent Bowel Sounds
The complete absence of these on auscultation, as the name implies. It is unclear how long one must listen before they are considered absent, with times ranging from 1 to 5 minutes.
Causes
The list has been divided as follows:
Common
Common causes of absent bowel sounds include:
- Intestinal obstruction (Late)
- Paralytic ileus of any cause, e.g.:
- Infection
- Trauma
- Bowel obstruction
- Hypokalaemia
- Vascular ischemia
- Side effects of drugs
- Peritonitis
- Pancreatitis
Less Common
The two less common causes of absent bowel sounds are:
- Mesenteric ischaemia
- Pseudo-obstruction (Ogilvie syndrome)
Mechanism
Generally, the absence of bowel movements may be brought on by an inactive bowel that is not undergoing peristalsis or by an obstruction in an active intestine that prevents the passage of food or liquid.
The specific mechanisms are as follows:
Bowel Obstruction
The intestines are pressing up against a fixed object in a mechanical obstruction caused by any factor (hernia, volvulus, adhesion). Since food and water are not moving in their typical oscillatory fashion (as in a blocked pipe), no sound is made.
Inflammation develops if the obstruction persists, and if the vascular supply is impaired, normal peristalsis could also stop. This leads to absent bowel sounds on auscultation.
Infection
There is evidence that the lipopolysaccharides (LPS) found in Gram-negative bacteria start an inflammatory response in the intestinal smooth muscle layer, which then reduces smooth muscle contractility, leading to an ileus, even though this is not fully understood.
Postoperative Ileus
A reduction in intestinal smooth muscle activity is thought to be the result of the smooth muscle layer becoming inflamed as a result of manipulation of the small intestine.
Additionally, there is evidence to support the notion that after surgery, the gut experiences bacterial overgrowth, which, along with an increase in lipopolysaccharides, may be a factor in the inflammation brought on by manipulation.
The inhibition of enteric plexus synaptic circuits, which control the normal propulsion of the intestines, is most likely the mechanism by which inflammation results in ileus.
Pre-synaptic inhibition of enteric motor neurons and/or persistent discharge of inhibitory neurons are the causes of this suppression.
Hypokalaemia
Muscle cells require potassium for normal polarization and repolarization. Hyperpolarization of muscle cells brought on by hypokalemia reduces the excitability of the neurons and consequently the activity of the smooth muscles, which results in ileus.
Pseudo-Obstruction
It is unclear what causes or how Ogilvie syndrome, also known as pseudo-obstruction, develops. It is believed that a functional bowel obstruction results from an imbalance of autonomic innervation.
An adynamic distal colon results from a disruption of the normal sacral parasympathetic tone.
According to other studies, the cause is elevated sympathetic tone, which reduces gut motility and causes sphincters to close. Peristalsis may not occur or may occur improperly.
Hyperactive Bowel Sounds (borborygmus)
These are defined as frequent, obnoxious, gurgling, or “rushing” bowel sounds that can occasionally be heard even without a stethoscope.
Features
- Peristalsis- Increased
- Frequency- More than 5 per minute
- Pitch- Initially high-frequency, low-pitched gurgling/rumbling sounds
- Quality- Tinkling (read further)
- Intensity/ Loudness- Increased (exaggerated)
- Pattern- Rhythmic with peristaltic activity
Causes
The list has again been divided as follows:
Common
Common causes of hyperactive bowel sounds include:
- Bowel obstruction
- Crohn’s disease/ulcerative colitis
- Food hypersensitivity
- Gastroenteritis
- Diarrhoea
- Laxative use
- Normal
Less Common
The less common causes of absent bowel sounds are:
- Gastrointestinal haemorrhage
- Carcinoid syndrome
- Small bowel malabsorption
- Early small bowel obstruction
Mechanism
The bowel increases peristalsis when an obstruction is present to move the blockage.
High-pitched Bowel Sounds (tinkling)
An abdominal auscultation may produce a high-pitched “tinkling” sound that is sometimes compared to pouring water into an empty glass.
Causes
Bowel obstruction is the only cause one should look for when tinkling is heard.
Mechanism
There is not much evidence for the mechanism. It is believed to represent air or fluid building up and pressing against the intestine, much like rain hitting a tin roof.
Hope you liked our post on Types of Bowel Sounds- Absent, Hyperactive and High-pitched. If you have any comments or feedback, please leave them below.