Spontaneous Bacterial Peritonitis
(SBP)
Of patients hospitalized with ascites,
between 10 percent and 30 percent will
develop SBP. This infection is thought
to occur either by spontaneous passage
of normal bacteria that reside in the
gut into the ascitic fluid, or by seeding
of bacteria into the blood from a distant
source (e.g., a urinary infection or lung
infection), leading to growth of this
bacteria in the ascitic fluid (O’Grady
et al. 2000).
Patients who have low protein concentrations
in the ascites (less than 1.5
g/dl) are at higher risk of developing
SBP. Once a patient has had an episode
of SBP, there is a 7 in 10 chance that a
new episode will occur within the next
year. With every episode, 2 to 3 of every
10 patients will die from complications
of the infection, and only 3 of every
10 are expected to survive for 2 years
(Garcia-Tsao 2001).
The diagnosis of SBP is made when
high numbers of a type of white blood
cell that is especially protective against
bacterial infections (i.e., polymorphonuclear
cells [PMN]) are found in the
ascitic fluid (i.e., in excess of 250 per
ml). Patients are diagnosed as having
SBP if bacteria are found in the ascitic
fluid, but the concentration of bacteria
in the fluid is extremely low—an estimated
1 bacterium per milliliter of
fluid—so that the bacteria cannot be
seen by examining the fluid under the
microscope. In order to have a reasonable
chance of getting a positive culture, the
fluid should be injected at the bedside
into blood culture bottles specially
designed to recover small amounts of
bacteria. This technique will detect the
vast majority of infections. If improper
techniques are used (e.g., sending the
fluid to the laboratory to be placed on
a culture plate), chances of proper diagnosis
decrease to 4 out of 10.
Patients with SBP may not have
symptoms, or manifestations of the
infection may appear to be unrelated to the abdominal cavity. For example, SBP
patients may have confusion, changes
in kidney function, poorly controlled
ascites, or overall progressively deteriorating
health. Despite the fact that more
than half of the patients with SBP complain
of some degree of abdominal pain
or discomfort, the physical exam of the
abdomen usually is completely benign.
Usually only one type of bacteria
appears in the culture of patients who
have SBP. Clinicians should suspect the
possibility of a secondary peritonitis
(e.g., some intra-abdominal perforation
or abscess formation in the abdomen)
if (1) multiple kinds of bacteria are
recovered from the culture, or (2) the
patient develops an infection consistent
with SBP but in the presence of total
protein concentration in the ascitic fluid
of more than 1.5 g/dl, or (3) the
patient fails to respond promptly to
proper antibiotic therapy. A secondary
infection also should be suspected if
direct examination of fluid under the
microscope shows bacteria because, as
mentioned, the concentration of bacteria
in SBP is so low that bacteria should
not be detectable by microscopic examination
(Andy and Ke-Qin 2001;
Garcia-Tsao 1992).
Patients who develop SBP are at
extremely high risk of developing kidney
dysfunction and hepatorenal syndrome.
Expansion of the volume within the
blood vessels (i.e., the intravascular volume)
using intravenous albumin infusions
has been shown to decrease the
frequency of hepatorenal syndrome
and, for that reason, improves survival
rates in patients who develop SBP (Sort
et al. 1999). Because of concerns about
kidney toxicity, it is important to avoid
antibiotics or other medications that may
exacerbate kidney damage. Current
therapy for SBP includes use of the
antibacterial drug cefotaxime.
Patients at special risk for SBP are
those who are hospitalized and have a
total protein concentration in the ascitic
fluid that is less than 1.5 g/dl, those who
have gastrointestinal bleeding from any
source, and those who have had previous
episodes of SBP (Andy and Ke-Qin
2001). Prophylactic therapy (i.e., antibiotic
treatment) is indicated for all
these groups of patients.