The incidence of sepsis in cats is unknown, partly because sepsis can be challenging to diagnose in cats. Sepsis should be
considered as a potential cause of illness in critically ill cats, whether they present in an emergency situation or are receiving
medical care. Diagnosing sepsis in cats depends on maintaining a high index of suspicion and recognizing the risk factors
and unique features of the feline response to sepsis. This article applies the recent sepsis classification scheme, PIRO,1 to diagnosing sepsis in cats.
Illustration by Melissa Galitz
DEFINING SEPSIS AND SIRS
At the 1991 American College of Chest Physicians/Society of Critical Care Medicine consensus conference,2 sepsis was defined as evidence of infection plus a clinical picture of systemic inflammatory response syndrome (SIRS)—SIRS
being defined as the presence of two of the following clinical criteria: tachycardia, tachypnea, a fever or hypothermia, and
leukocytosis or leucopenia.
Severe sepsis is sepsis with evidence of organ dysfunction and hypotension or hypoperfusion. Septic shock is severe sepsis
with refractory hypotension.
Almost any patient that comes into the emergency room will fulfill at least two of the SIRS criteria. Because of its lack
of specificity, the definition of SIRS leaves much to be desired in both human and veterinary medical applications (Table 1). In published SIRS criteria recommended for dogs, the sensitivity ranges from 77% to 97% while the specificity is between
64% and 77%.3 No such study has been performed in cats.
Table 1: SIRS Criteria for Cats, Dogs, and People
In 2001, there was a second physicians' consensus conference,1 that expanded the criteria for SIRS by recommending the inclusion of physical parameters and biomarkers (measurable factors
in blood or biological samples that can be used to identify or stage disease). Many of the parameters and some of the biomarkers
may also prove useful in veterinary species. This newer approach, designated as PIRO, incorporates four factors in the stratification.
Predisposition. Although many factors can influence susceptibility to disease, predisposing genetic factors are an area of active research
in people. While it has long been recognized that certain dog or cat breeds or human families may be more susceptible to diseases
than are other breeds or families, individual genetic variations or polymorphisms appear to further contribute to disease
susceptibility. Other predisposing factors may be age, concurrent conditions, and sex.
Infection. Clinically, we recognize that certain bacteria, location of infection, or extent of infection contribute to the risk of developing
sepsis or septic shock.
Response of the host. Our inability to readily identify and monitor biomarkers is the biggest limitation for this component of the stratification
scheme. However, if we can determine whether a cat is in an excessively proinflammatory state vs. exhibiting immune paralysis
or whether it has evidence of adrenal or coagulation dysfunction, we will be better able to choose appropriate and directed
Organ dysfunction. The extent of organ dysfunction will negatively influence the outcome, even more so in cats than in people.
There does not seem to be a breed or sex predilection for sepsis in cats. Cats with pyothorax are more likely to come from
multicat households and have a higher incidence of outdoor access.4 In one study of septic peritonitis, male cats outnumbered female cats.5
Diabetes mellitus is reported as a predisposing factor for hepatic abscesses in dogs and people, but no such predisposition
has been reported in cats.6 Although there are no epidemiologic reports of the incidence of sepsis associated with immune suppression in cats, it is
likely that immunosuppressive diseases, such as feline leukemia virus or feline immunodeficiency virus infection, and immune
suppression associated with chemotherapy increase the predisposition for sepsis.