Biology Reference
In-Depth Information
reliability, especially if single, small-volume samples are submitted,
as is often the practice with critically ill newborns. For example,
Schelonka et al. (1996) estimated that as many as 60% of culture results
may be falsely negative if only 0.5 ml of blood is obtained from
infants with low-colony-count sepsis. And drawing more blood from an
infant who weighs less than 1500 g may be quite tricky—after all, her
entire blood volume is less than 100 ml.
The situation is further complicated because not all infants with clinical
signs of sepsis have positive blood cultures. In general, the AAP, the
American Academy of Obstetrics and Gynecology (AAOG), and the
Centers for Disease Control and Prevention (CDC) all recommend sepsis
screening and/or treatment for various risk factors related to GBS
diseases. The diagnostic challenge is manifested even more clearly by
the fact the CDC allows for a diagnosis of neonatal ''clinical sepsis'' with
either a negative blood culture or no blood culture at all (see Cabal et al.
[1980] for more details). Following these recommendations, many
neonates now are subjected to routine treatment, even when blood
culture results are negative. Because the mortality rate for untreated
sepsis can be as high as 50%, the hazard of untreated sepsis is too great
to wait for confirmation by positive cultures. Clinical neonatologists
caring for VLBW infants recognize sepsis and NEC as potentially
catastrophic illnesses and do not hesitate to begin antibiotic treatment
empirically at the first appearance of symptoms. In general, most
clinicians initiate treatment while awaiting culture results from the
laboratory. Gerdes and Polin (1987) estimated that 10 to 20 infants are
treated for sepsis for every infant with a positive blood culture.
In summary, the high risk of sepsis or NEC in VLBW infants, the high
mortality rate, and the lack of reliable clinical means for early diagnosis
of these diseases all underscore the need for new diagnostic tools that
would provide sufficient warning to ensure successful treatment.
Identifying one or more biomedical variables that would provide
comparatively early danger signals for these babies is therefore of
utmost importance.
An optimal surveillance strategy should: (1) Be based on non-invasive
monitoring methods; (2) utilize continuous monitoring of the newborns;
and (3) provide dynamic estimates of the infant's risk for developing
sepsis or SIRS. Because as a rule all infants in the NICU have certain vital
characteristics that are continuously monitored, such as temperature,
HR, and blood pressure, a method for assessing the risk of sepsis and
SIRS based on these characteristics would be highly desirable and easy
to use.
We now focus on a proposed solution using HR characteristics. This
novel method, proposed by University of Virginia researchers,
can successfully predict sepsis and SIRS 12 to 24 hours before the clinical
diagnosis is made (Griffin et al. [2003]). Our next section serves as an
