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18
K. B. Wilkins and J. R. Notaro
rior sphincter defects from obstetric injury,
sphincteroplasty is an option. Patients need to
be informed that while good results are usual
in the short-term, after 5years, a signicant
proportion of patients are back to their baseline function. Repeat sphincteroplasty after a
failed repair is typically not recommended
unless other options are not feasible. Because
of this observed deterioration with time,
sacral nerve stimulation has become a rstline surgical alternative in those with a
sphincter defect <180°. Colostomy is again
an alternative for those without improvement
following other interventions or in those who
do not want to pursue other options.
Refer to Algorithm in Fig. 3.3
A. Normal bowel habit can range from three
formed stools per day to one stool every 3days.
Denitions of constipation vary but usually
include infrequent hard stools that require signicant straining to pass. The Rome IV criteria
dene constipation in a patient with 2 or more
of the following: less than three bowel movements a week, straining with more than 25% of
bowel movements, sensation of incomplete
evacuation or blockage more than 25% of bowel
movements, manual maneuvers to facilitate
more than 25% of bowel movements, and
lumpy or hard stools in more than 25% of bowel
movements. Also, loose stools are rarely present
without laxatives and the patient must not meet
criteria for IBS. Chronic constipation aficts
roughly 15% (range: 2–30%) of the U.S. population. In 2006, the number of constipationrelated medical visits was nearly $6 million
USD. Constipation—related health costs are
nearly $7 billion a year in the U.S., of which
$725,000 USD per year is spent on laxatives.
It is crucial to remember that constipation is a
symptom with many causes. It is not an independent disease entity. Effective treatment can
only be initiated after determining the specic
cause. The etiology of constipation can be
multifactorial thus posing a diagnostic and
therapeutic challenge.
B. and C. After establishing that the patient
meets criteria for constipation by determining
the frequency and consistency of the stool, a
careful history is obtained. The rst step is to
perform a dietary review of ber/roughage/
water intake including a thorough medication
review to eliminate antidepressants, anticholinergics, opiates, antacids (aluminum/calcium), calcium channel blockers,
sympathomimetics, psychotropic drugs and
cholestyramine, as the etiology of constipation. The presence or absence of an urge to
defecate can be an invaluable clue to the
underlying process. The patient is asked if
they frequently delay the call to stool. The
patient is queried about the use of enemas in
the past and the response to such treatment.
No response to enemas may indicate colonic
inertia whereas a normal response to an enema
may indicate rectal outlet obstruction.
Coexisting medical conditions such as
Parkinson’s, multiple sclerosis, diabetic autonomic neuropathy, spinal cord lesions, cerebral vascular accidents (CVA)/strokes,
scleroderma, and amyloidosis can cause debilitating constipation. Hypothyroidism and
hyperparathyroidism are two common endocrine abnormalities that cause constipation.
Therefore a metabolic workup including thyroid function tests and parathyroid hormone
levels, calcium, magnesium, and phosphorus
values, should establish or refute the diagnosis
indicated in this scenario.
A focused anorectal exam may provide impor-
tant clues. Rectal exam can assess for
impaction, rectocele, rectal prolapse, and
baseline subjective function of the pelvic
oor (asking the patient to squeeze and push
on the examining nger). Anoscopy and
rigid sigmoidoscopy will exclude obstructing distal masses and solitary rectal ulcer
syndrome. A physical exam can also exclude
other causes of irregular bowel function as
caused by benign or malignant conditions.
Abdominal pain, weight loss, and anemia
raise suspicion of a mechanical obstruction
and should generally prompt colonoscopy
and X-ray/CT scan.
3 Physiologic Testing
19
Fig. 3.3 Algorithm for the initial evaluation and physiologic testing for constipation
D.–H. When constipation is present without
any urge to defecate with poor response to
enemas, colonic inertia is suspected. Transit
studies are used to provide a measurement of
the colonic motor function. Radiographic
markers studies including the Sitz marker test,
is simple, noninvasive and relatively inexpensive. The two most common protocols involve
the ingestion of a single gelatinous capsule
containing 24 radiopaque rings. One option is
to have a single plain lm X-ray on day 5.
Alternatively, one may obtain a plain X-ray on
days 1, 3, and 5 (possibly 7) if there are still
retained markers seen.
The latter method also gives indirect information
regarding gastric emptying and small-bowel
motility as well. Additionally, if the majority
of markers accumulate in the rectosigmoid by
day 3, obstructed defecation is suggested. A
disadvantage however is multiple visits to the
X-ray department and increased ionizing radiation exposure. Regardless of method, the
location and number of markers is recorded.
Elimination of greater than 80% of markers is
a normal study. If less than 80% of the markers are eliminated and diffusely located
throughout the colon, colonic inertia is
suspected.
Scintigraphy, following the ingestion of a radio-
labeled meal or charcoal, is performed using a
gamma camera imager. This represents a time
efcient and accurate means of measuring
gastric, small bowel, and colonic transit. It is
expensive, and radiation exposure along with
limited expertise, pose signicant disadvantages. Wireless motility capsule utilizes pH,
pressure, and temperature to measure motility.
After orally ingesting the capsule, information
is transmitted to a portable data receiver worn
by the patient. There is nearly a 90%
20
K. B. Wilkins and J. R. Notaro
correlation with radio-opaque marker tests. It
is easy to perform, lacks radiation exposure,
and provides information on whole gut transit.
It is expensive due to a non-reusable capsule.
Newer techniques such as high-resolution
colonic manometry, and colonic barostat, have
been used to directly characterize colonic contraction patterns and categorize colonic dysmotility. These tend to be available only in
specialized digestive disease centers, are
expensive and technically very challenging.
Even after colonic inertia is evident on colonic
transit study, certain patients require additional testing including the hydrogen breath
test, gastric emptying study/nuclear scintigraphy, or wireless motility capsule to eliminate
dysmotility proximal to the colon. Obviously
performing a subtotal colectomy on these
patients will not necessarily improve their
symptoms. They instead would benet from
prokinetic and intestinal pacemaker in select
cases. In those patients with isolated colonic
inertia, a trial of colonic prokinetic agents is
warranted, after maximizing ber and water.
Osmotic agents such as lubiprostone and linaclotide, stimulate intestinal uid secretion by
acting on the intestinal chloride channel and
guanylate cyclase receptor, respectively. After
initial success, then withdrawal from U.S.
market, tegaserod, is again available (since
2014) via an emergency treatment investigational new drug protocol through the
FDA. Newer agents, such as renzapride, a
mixed 5-HT4 receptor agonist and 5-HT3
receptor antagonist, holds promise. If the
colonic transit studies are normal and inertia is
excluded, continue with ber, water, laxatives,
and treatment for IBS-C.
I. Surgical options may be discussed in patients
who are refractory to all dietary and medical
management. After exclusion of distal outlet
obstruction, subtotal colectomy with ileorectal anastomosis can be offered in select
patients. Segmental resections are fraught
with prohibitive recurrences and subsequent
patient dissatisfaction.
J. The act of defecation is a multi-step process
involving many components—ranging from
rectal compliance and anal sampling to
abdominal Valsalva and sphincter relaxation.
The pelvic oor comprised of the levator ani
muscles and the endopelvic fascia, plays a
crucial role in defecation. Pelvic oor disorders and dysfunction can result in various
organ prolapses and functional disturbances
of the evacuation process; rectal outlet
obstruction is one such pelvic oor
dysfunction.
Rectal outlet obstruction, also referred to as
obstructed defecation syndrome, is suspected
when a constipated patient gets the urge to
defecate, but evacuates only partially or not at
all. Response to laxatives is a watery loose
stool (+/− over ow incontinence) without
relief of the rectal pressure. Using an enema
can have a successful response but does vary
among patients and their specic pathology.
The causes of obstructive defecation syndrome are multiple and varied (Fig.3.4).
Physical exam alone has signicant limitations in
establishing the diagnosis. It may only be
helpful with an obvious abnormality such as
procidentia or rectoceles. Otherwise the
colorectal surgeon must rely on anorectal
physiology laboratory testing and imaging to
conrm both the diagnosis and the pathology
involved.
K. Once clinical suspicion of rectal outlet
obstruction is established, extensive investigation is warranted (Fig.3.2). In order to establish effective medical or surgical treatment,
specic anorectal pathology must be identied. The assessment of obstructive defecation
syndrome includes both anorectal physiology
laboratory testing and X-rays. Anal manometry will assess resting pressures and rule out
hypertonia. The strain maneuver measures the
pressure in the high pressure zone while bearing down. It should reduce for a few seconds
while attempting to defecate. Failure to relax
the sphincters is termed anismus or nonrelaxing puborectalis. Although the presence
3 Physiologic Testing
Fig. 3.4 Pathology
associated with outlet
obstruction. Pathologic
ndings are separated
into those conditions for
which surgery may be
considered versus those
conditions for which
biofeedback is indicated
21
of a recto anal inhibitory reex (RAIR) eliminates Hirschsprung’s disease, its absence does
not necessarily conrm it. However, failure to
elicit the RAIR should prompt transanal full
thickness rectal biopsies for conrmation. The
balloon expulsion test is performed during
manometry. The balloon is placed in the rectum and inated with 50ml of air or water (or
alternatively until the patient has a sensation
to defecate). Failure to evacuate the balloon
within 1 min suggests outlet obstruction. In
normal sized rectums, 200–250cc of balloon
ination will elicit an uncomfortably strong
urge to defecate is termed the maximum tolerated volume. Greater volume than this suggests mega rectum—a cause or consequence
of outlet obstruction. EMG can complement
or conrm anal manometric ndings of anismus, non-relaxing puborectalis, or paradoxical contraction of the puborectalis.
Once the anorectal physiology laboratory ndings
suggest outlet obstruction, radiographic testing
can not only verify the diagnosis but provide
specic etiologies and guide treatment plans.
Imaging techniques such as ultrasound (endovaginal and transperineal), MRI (dynamic pelvic oor MRI or MR defecography), and
cinedefecography (dynamic defecating proctography or cystocolpodefecography) have
successfully diagnosed pelvic oor disorders.
Cinedefecography, traditionally performed as
dynamic defecating proctography, has long
being considered the gold standard for evaluating the posterior pelvic compartment. It
documents the defecatory process in realtime. By opacifying the bladder, vagina and
small-bowel, cystocolpodefecography also
detects abnormalities of the anterior and middle pelvic compartments. Distinct advantages
are its anatomical position (patient is in a
seated position), quick performance timing,
and relatively low cost; a considerable dose of
ionizing radiation is a distinct disadvantage.
Recently MR defecography or dynamic pelvic
oor MR, has challenged cinedefecography as
the new standard. It has multiplanar capability, excellent soft tissue contrast and ability to
evaluate anterior, middle and posterior pelvic
compartments. It offers information on both
morphology and physiology with this test.
Although traditionally the colorectal surgeon
concentrates on the posterior pelvic compartment for analyzing disorders of defecation,
the simultaneous assessment of the anterior
and middle compartments may become
increasingly benecial to recognize coexisting
conditions and reduce recurrences. The lack
of ionizing radiation is also an advantage.
Proponents, however point out that the obligatory supine position does not parallel the usual
22
K. B. Wilkins and J. R. Notaro
physiological position of defecation. An open
magnet would address this concern, however,
their availability is relatively limited.
Various ultrasound techniques are another
class of emerging technology in the diagnosis and management of outlet obstruction. Transperineal ultrasound is performed
with the patient in dorsal lithotomy position
after voiding. Using the ultrasound gel, the
probe is placed rmly on the perineum.
Both sagittal and coronal views are obtained
by rotating the probe. Two-dimensional
and 3-dimensional imaging is possible.
Additional information is obtained by endoluminal placement of the probe into the
vagina (endovaginal ultrasound). Unlike the
transperineal technique, this one requires
a full bladder. These ultrasounds are performed at rest, on Valsalva and during pelvic
oor contraction. Although both can detect
a myriad of pathology causing rectal outlet
obstruction, a rectocele is best evaluated
with a transperineal approach. The placement of the probe into the vagina (endovaginal ultrasound) may reduce/camouage a
rectocele. Ultrasound is the least expensive
of all the aforementioned techniques. It is
often better tolerated than cinedefecography
or MRI.Disadvantages include the possible
shifting of organ position just by the operator’s placement and compression of the
transducer, and the overall limited eld of
view compared to the other two techniques.
L. and M. The aforementioned evaluation
should help categorize the patient’s rectal outlet obstruction into mechanical causes (rectocele, rectal intussusception, procidentia,
perineal descent, sigmoidocele and enterocele) or functional disorders (anismus, nonrelaxing or paradoxical puborectalis
syndrome). This distinction is crucial since
the latter generally is treated conservatively
while the former are candidates for surgical
intervention if conservative treatment has
failed to improve symptoms (Fig.3.4).
The following is a brief summary of the vast
pathological causes of obstructive defecation
syndrome and the recommended treatments.
A rectocele is dened as a herniation of the
rectal wall into the posterior vagina, due to
an abnormally thin, weak rectovaginal septum. It can be seen in more than 75% of parous women and rarely in men. In extreme
cases, the posterior vaginal wall may protrude beyond the vaginal orice. Symptoms
do not necessarily parallel the size of a rectocele. Treatment starts with optimizing
stool consistency and a trial of biofeedback
to maximize pelvic oor relaxation. Surgical
repair is reserved if conservative treatment
failures. Although rectocele repair can be
approached both transvaginally and transrectally, the former has shown superiority
in select studies.
Rectal intussusception (internal or incomplete
rectal prolapse) has been described in
approximately 65% of patients with pelvic
oor disorders. It consists of an invagination
of the rectal wall that can be located in the
anterior or posterior location or circumferentially. Procidentia occurs when the intussusception protrudes distal to the anal verge.
Although early, minor rectal intussusception
may not actually obstruct defecation, it may
still lead to the debilitating sensation of
incomplete evacuation. Solitary rectal ulcer
syndrome may be associated with prolapse of
all degrees and in extreme cases, rectal prolapse can lead to incarceration and
strangulation.
Surgical repair of rectal prolapse depends on the
severity of the symptoms. Any review of the
literature reveals an exuberant number of surgical techniques—mainly because no single
procedure addresses all issues. The higher
morbidity of abdominal approaches are generally offset/rewarded with lower recurrence
rates. Conversely the perineal approaches are
fraught with higher recurrences yet reportedly
less morbidity and mortality.
3 Physiologic Testing
23
When the small bowel, or sigmoid colon herni-
ates into the Douglas pouch, an enterocele or
sigmoidocele, respectively, is formed. They
are not always symptomatic, but when
indicated, surgical repair is accomplished by
obliterating the cul-de-sac.
A generalized weakness of the pelvic oor is
referred to as descending perineal syndrome.
It is diagnosed when the anorectal junction
descends more than 3 cm below the pubococcygeal line. It is caused by the incessant
straining associated with obstructive defecation. Pelvic oor weakness and pudendal neuropathy from childbirth trauma also
contributes. Treatment generally involves biofeedback for pelvic oor strengthening while
also maximizing relaxation during the strain
maneuver.
Anismus, non-relaxing puborectalis (NRPR),
and paradoxical puborectalis, comprise a
spectrum of pelvic oor dyssynergy.
Insufcient, or absence of, puborectalis muscle relaxation is the underlying pathology. It
has been reported in almost half of constipated
patients with outlet obstruction. Treatment,
once again is conservative, with biofeedback
to maximize pelvic oor relaxation. If a coexisting mechanical cause of outlet obstruction
is present, conservative measures take priority
over surgical ones.
If none of the pathology in Fig.3.4 are diagnosed,
continued conservative management is indicated. Along with dietary manipulation, optimization of stool consistency, empiric trial of
prokinetic and biofeedback, psychosocial support can also be helpful.
Suggested Reading
Abdool Z, Sultan AH, Thakar R.Ultrasound imaging of
the anal sphincter complex: a review. Br J Radiol.
2012;85:865–75.
Ahmad AN, Hainsworth A, Williams AB, Schizas
AMP. A review of functional pelvic oor imaging
modalities and their effectiveness. Clin Imaging.
2015;39:559–65.
Alavi K, Chan S, Wise P, Kaiser AM, Sudan R, Bordeianou
L.Fecal incontinence: etiology, diagnosis, and management. J Gastrointest Surg. 2015;19:1910–21.
Bordeianou LG, Carmichael JC, Paquette IM, et al.
Consensus statement of denitions for anorectal physiology testing and pelvic oor terminology (Revised).
Dis Colon Rectum. 2018;61:421–7.
Dietz HP, Beer-Gabel M. Ultrasound in the investiga-
tion of posterior compartment vaginal prolapse and
obstructed defecation. Ultrasound Obstet Gynecol.
2012;40:14–27.
Jorge JM, Wexner SD.Etiology and management of fecal
incontinence. Dis Colon Rectum. 1993;36(1):77–97.
Khatri G.Magnetic resonance imaging of pelvic oor dis-
orders. Top Magn Reson Imaging. 2014;23:259–73.
Lalwani N, Moshiri M, Lee JH, Bhargava P, Dighe
M.Magnetic resonance imaging of pelvic oor dysfunction. Radiol Clin N Am. 2013;51:1127–39.
Olson CH.Diagnostic testing for fecal incontinence. Clin
Colon Rectal Surg. 2014;27:85–90.
Paquette I, Varma M, Kaiser A, Steele S, Rafferty J.The
American society of colon and rectal surgeons’ clinical practice guideline for the treatment of fecal incontinence. Dis Colon Rectum. 2015;58:623–36.
Paquette IM, Varma M, Ternent C, et al. The American
Society of Colon and Rectal Surgeons’ Clinical
Practice Guideline for the Evaluation and Management
of Constipation. Dis Colon Rectum. 2016;59:479–92.
Rezvan A, Jakus-Waldman S, Abbas MA, Yazdany T,
Nguyen J.Review of the diagnosis, management and
treatment of fecal incontinence. Female Pelvic Med
Reconstr Surg. 2015;21:8–17.
Zbar AP.Posterior pelvic oor disorders and obstructed
defecation syndrome: clinical and therapeutic
approach. Abdom Imaging. 2013;38:894–902.
Mechanical Bowel Preparation
forElective Colon andRectal
Surgery
ChayaShwaartz andOdedZmora
4
Refer to Algorithm in Fig. 4.1
A. The use of mechanical bowel preparation
(MBP) prior to an elective colorectal surgery
was the standard of care for many years aiming to clear the bowel of fecal matter and to
lower the risk of postoperative infectious
complications. The initial evidence questioning the usefulness of mechanical bowel preparation has been derived from studies on the
management of colorectal trauma. Multiple
studies have shown that despite the fact that
the colon is unprepared, the mechanism of
injury is not as controlled as in elective surgery, and there is often a delay between the
injury and the repair, primary repair of the
colon is safe in the setting of trauma.
B. Postoperative complications such as surgical
site infection (SSI) and anastomotic leak are of
major concern both in emergent and elective
colorectal surgery. Despite the improvement in
surgical techniques, and powerful antibiotics for
the control of sepsis, the rate of these complica-
C. Shwaartz
Department of Surgery, Sheba Medical Center,
Tel Aviv, Israel
O. Zmora (*)
Department of Surgery, Shamir Medical Center
(Assaf Harofe), Tel Aviv, Israel
Department of Surgery, Sackler School of Medicine,
Tel-Aviv University, Tel Aviv, Israel
e-mail: ozmora@post.tau.ac.il
tions is still high, leading to morbidity and mortality, prolonged length of stay, and higher cost.
SSIs occur in about 15% of colorectal cases.
Additionally, the risk for anastomotic leak is
reported as between 3% to 20% following
colorectal surgery, leading to a signicantly
higher mortality rate in these patients.
C. The use of MBP in elective colon and rectal
surgery has been assessed in several single
and multicenter randomized controlled trials,
which showed that MBP did not decrease the
risk for postoperative complications. These
results led to decreasing use of MBP.
D. It seems that there is a trend towards decreased
use of bowel preparation (see Algorithm in
Fig.4.1). In 2003, a survey including more than
500 surgeons (American Society of Colon and
Rectal Surgeons members) showed that 98% of
the surgeons participating in the survey used
MBP and 75% were using oral antibiotics. A
few years later (2006), a multinational survey
in Europe and the US showed that 86–97% of
patients received bowel preparation. In a recent
large multicenter national cohort, about 50% of
the patients undergoing elective colectomy
received bowel preparation.
E. Recent data generated from several indepen-
dent analysis of large databases show that MBP
in combination with oral antibiotics is associated with reduced risk of postoperative SSI and
anastomotic leak in patients undergoing elective colorectal surgery.This reduction has not
been shown in randomized controlled trials.
© Springer Nature Switzerland AG 2020
S. R. Steele et al. (eds.), Clinical Decision Making in Colorectal Surgery,
https://doi.org/10.1007/978-3-319-65942-8_4
25
26
C. Shwaartz and O. Zmora
Fig. 4.1 Algorithm for mechanical bowel preparation for elective colon and rectal surgery
Single Center Studies
G. Between 2000 and 2007, several larger well
designed single center studies were performed.
F. Brownson etal.were the rst to publish on this
topic in 1992, with their randomized trial of
179 patients to either preparation with polyethylene glycol or no mechanical preparation.
This pioneer study was published as a meeting
abstract, which was not followed by a full
manuscript. Surprisingly, patients who had
received preparation experienced a signicantly increased rate of anastomotic leak and
intra-abdominal infection, compared to
patients without preparation. However, there
was no signicant difference in the rate of
wound infection. This nding was followed by
two studies, which were published in the 1990s
by Burke etal. and Santos etal.both of which
failed to show any signicant difference in the
intra-abdominal infection rate. However,
wound infection, was more common in
patients who had received mechanical preparation in the latter study.
In 2003, the senior author published the largest
non-multicenter study published, which
included 380 patients undergoing elective
colon and rectal surgery with primary anastomosis, of whom 193 were randomized to colon
and rectal surgery without preoperative
mechanical bowel preparation. Importantly, all
patients from both groups received oral antibiotics prior to surgery. Patients undergoing rectal surgery were given one phosphate enema
on the day of surgery, to avoid extrusion of
stool when using a trans- anally inserted stapling device. Importantly, patients with tumors
smaller than 2cm in diameter were excluded
from the study, as palpation of small tumors
may be difcult in an unprepared bowel, and
these patients may require intra-operative
colonoscopy to identify these smaller lesions.
Patients who required a diverting stoma proximal to the anastomosis were excluded from the
4 Mechanical Bowel Preparation forElective Colon andRectal Surgery
27
data analysis, thereby reducing the number of
low rectal or coloanal anastomoses in this
study. The two groups were well matched in
parameters of demographic characteristics,
indications for surgery and type of surgical
procedure. There was no difference in the rate
of surgical infectious complications between
the two groups. Overall, infectious complication rate was 10.2% in the preparation group,
and 8.8% in the non-preparation group. Wound
infection, anastomotic leak, and intraabdominal abscess occurred in 6.4%, 3.7%,
and 1.1% in the bowel preparation group versus 5.7%, 2.1%, and 1%, in the no bowel preparation group.
H. Ram etal. used the exact same protocol to ran-
domize 329 patients, and found no signicant
difference in infectious and overall complication rate between patients who underwent preoperative mechanical bowel preparation and
those who had not, and Miettinen et al. randomized 267 patients, in a similar fashion, and
found slight and non- signicant increase in
anastomotic leak and wound infection rates in
patients who had preoperative mechanical
bowel preparation. Pena-Soria etal. also presented similar results from a randomized trial
including 129 patients that underwent an elective colon or proximal rectal resection with a
primary anastomosis by a single surgeon.
I. Several studies suggested that when an ileo-
colonic anastomosis is planned, for instance,
in a right, subtotal or total abdominal colectomy, surgery can be safely performed without mechanical bowel preparation. Advocates
of this approach suggest that since the column of stool proximal to the anastomosis,
which may mechanically disrupt the anastomosis, is avoided in these cases, mechanical
cleansing may not be required. We have performed a subgroup analysis of our data,
including only patients with left- sided anastomoses, in order to assess whether this type
of anastomosis may be safely performed in
the elective setting without mechanical bowel
preparation. We included 249 patients with
colo-colonic and colo-rectal anastomosis,
and showed that the overall infectious com-
plication rate was 12.5% in the preparation
group, and 13.2% in the non-preparation
group. Wound infection, anastomotic leak,
and intra-abdominal abscess were not signicantly different among the groups, occurring
in 6.6%, 4.2%, and 1.6% in the preparation
group, versus 10%, 2.3%, and 0.7% in the
non-preparation group. Bucher etal. prospectively randomized 153 patients undergoing
colon and rectal surgery with left-sided anastomosis, and found a signicantly increased
complication rate in patients who received
mechanical bowel preparation. The overall
rate of abdominal infectious complications
was 22% in the preparation group and 8% in
the non- preparation group, and this difference was statistically signicant. Anastomotic
leak occurred in 6% of the preparation group
and 1% in the non-preparation group (nonsignicant), and mean length of hospital stay
was longer for patients who had mechanical
bowel preparation (14.9days versus 9.9days).
J. The only single center randomizedstudy sug-
gesting that mechanical bowel preparation
given prior to colon and rectal surgery may
actually lead to improved outcomes was published by Platell etal. in 2006. In this study,
335 patients were randomized to receive
either oral mechanical bowel preparation
using polyethylene glycol, or trans-anal preparation using phosphate enema. Patients
undergoing any type of elective resection of
colon or rectum with anastomosis were eligible for this study, with or without defunctioning stoma. Although there was no signicant
difference in overall anastomotic leak rate
between the two groups, there was a signicant difference in the severity of the leaks.
Six out of seven patients, who developed
anastomotic leak following preparation with
enema only, required re-operation, as compared to none of the three patients who
received oral mechanical preparation and
leaked. Owing to this difference in reoperation rates, the study was prematurely
terminated, before reaching its accrual goal.
Three of the patients who required reoperation for anastomotic leak underwent
28
C. Shwaartz and O. Zmora
ultra-low anterior resection, a procedure
which was not within the inclusion criteria of
most other randomized trials.
K. Single center studies have the advantage of
relative homogeneity of the operative and
perioperative techniques, which is an important factor inuencing the surgical outcome.
However, assuming an infectious complication rate of 10%, designing a prospective
study which will be able to detect a difference
of 5% in the infection rate, in a one tailed statistical test (which only examines if the treatment is better than the control, and not the
possibility that treatment is actually worse),
assuming an alpha level of 0.05, with a statistical power of 90%, approximately 770
patients are required to be randomized into
each group, for a total of 1540 patients. It is
virtually impossible for one institution to
acquire such a large number of patients in a
reasonable timeframe. Thus, single center
studies have the advantage of homogeneity in
techniques, but usually lack sufcient power
leading to type II error.
Special Considerations
Localization ofSmall Lesions
L. Mechanical bowel preparation may have sev-
eral advantages unrelated to the risk of infection. It facilitates palpation of the entire colon
during surgery, and enables the surgeon to
perform intra-operative colonoscopy, if
required. The intraoperative localization of
small tumors may require careful palpation of
the colon, which may be more difcult if the
colon is loaded with fecal material. Large
tumors would usually be easily distinguished
from solid feces, but the identication of
small tumors may be difcult. In our randomized controlled trial, we have excluded all
patients with tumors smaller than 2 cm in
diameter and reported no difculties in tumor
localization. Platell et al. did not exclude
small tumors leading to difculty inlocaliza-
tion of the tumor in six patients. Thus, we
strongly advise selective mechanical bowel
preparation in patients with small tumors that
have not been marked preoperatively with
endoscopic tattoo, to allow for adequate palpation and possibly intraoperative endoscopy
for tumor localization, if required.
M. In addition, the unprepared bowel does not
allow palpation of the rest of the bowel to
exclude synchronous lesions. In the era of
modern endoscopy and other imaging techniques, the vast majority of patients have
high-quality colonic workup prior to surgery,
and the necessity of intraoperative palpation
is thus limited. In cases where adequate preoperative full endoscopic colonoscopy or
high quality virtual colonoscopy is not possible, mechanical bowel preparation should be
considered.
Low Rectal or Coloanal Anastomosis
N. Most randomized controlled trials assessing
the utility of mechanical bowel preparation
did not include patients with low rectal or
coloanal anastomosis. In our daily practice,
most of the patients undergoing coloanal
anastomosis concomitantly underwent temporary proximal diversion and were thereby
excluded from our study. Interestingly, in the
study by Platell and his colleagues, half of the
patients who required re-operation for anastomotic leak underwent ultra-low rectal anastomosis with enema preparation only.
Additionally, in a propensity score matching
analysis by Kim etal., the authors compared
the outcomes between patients receiving MBP
vs. patients who did not receive bowel preparation. However, patients who underwent leftsided or rectal resection who did not receive
MBP had received rectal enemas. In this
study, there were signicantly higher rates of
severe post-operative complications in these
patients compared to patients that received
MBP (14% vs. 2%, p=0.03). In a randomized
trial, the French GRECCAR III study, it was