Septic cats are not small septic dogs

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1 Vet Times The website for the veterinary profession Septic cats are not small septic dogs Author : ROGER WILKINSON Categories : Vets Date : September 29, 2008 ROGER WILKINSON reminds practitioners to sometimes expect the unexpected when approaching the septic feline, and offers an overview of recent research, bacteriology and antimicrobial management IN the past, we seemed to have coped without the term systemic inflammatory response syndrome (SIRS). However, it does usefully group together conditions of differing aetiology such as bacterial sepsis, pancreatitis, severe trauma, extensive neoplasia, burns, heat stroke or ischaemia that result in a common syndrome of disturbed haemodynamics, vascular permeability, coagulation and, sometimes, impaired organ function. The terms SIRS, sepsis, septic shock and severe sepsis have not always been well-defined entities. However, some consensus has been achieved over the years (Table 1). Physical signs According to traditional descriptions, the vasodilation accompanying SIRS in its initial hyperdynamic phase is characterised by red mucous membranes, rapid capillary refill time (CRT), tachycardia and normal or increased rectal temperature or, at least, this is the case in dogs. In a seminal paper in August 2000, Brady et al described the actual clinical signs observed in a series of cats with severe sepsis confirmed at necropsy (Tables 2 and 3). Cats included in this series were shown to have been suffering from conditions including pyothorax, septic peritonitis, 1 / 16

2 endocarditis, salmonellosis, pyometra and pneumonia. Common findings in these cats were hypothermia, bradycardia, lethargy, icterus (63 per cent were hyperbilirubinaemic), tachypnoea, diffuse abdominal pain and weak pulses. They were frequently anaemic and hypoalbuminaemic. The fact that cats were only included if full postmortem findings were available may have skewed findings towards individuals with deteriorating condition. However, many clinicians believe such findings are also common in cats with severe sepsis that go on to survive, and that convincing hyperdynamic signs are not commonly seen in septic cats. This type of presentation in cats is consistent with the hypodynamic phase of SIRS described in other species, in which with the progression to severe sepsis vasoconstriction, weak pulses and slow CRT are frequently seen. The bradycardia noted in septic cats is unusual and unexplained, although similar findings have been noted in some septic, hypothermic children. Diffuse abdominal pain has also been reported in septic dogs. This is an interesting finding and is worth bearing in mind, since it may mislead the clinician when the focus of infection is nonabdominal (for example, endocarditis or pyothorax). The frequency of observations of tachypnoea in these septic cats may reflect the susceptibility of feline lungs to endotoxaemia. In the study by Brady et al, the lungs of many cats showed histological evidence of thrombi, pneumonia, oedema and haemorrhage, regardless of the site of primary infection. Pulmonary effusion has also been reported as a surprisingly c ommon sign associated with acute pancreatitis in cats although many of these animals would have received intravenous fluid therapy and might, perhaps, have suffered iatrogenic fluid overload. Anaemia appears to be another somewhat unexpected sign in many septic cats, and may well be multifactorial. Feline haemoglobin is especially susceptible to oxidative damage and Heinz bodies are often seen in blood smears of septic cats. It is likely that the high incidence of icterus in septic cats is due to haemolysis. Histopathological evidence of hepatobiliary pathology has generally been lacking, and serum alkaline phosphatase was not raised in the cats in Brady s series. Diagnosis Using the findings of this series, Brady et al suggested a set of diagnostic criteria for diagnosing severe sepsis in cats (Table 4). To be fair to the authors, these criteria were suggested as a hypothesis to be tested with prospective studies. To what extent these findings are specific to sepsis as opposed to severe trauma, for example remains to be rigorously tested. The sensitivity of these criteria is also open to debate. For example, it has recently been shown that in a 2 / 16

3 population of bacteraemic (blood culture positive) cats, only 60 per cent fulfilled two or more criteria (Greiner et al, 2008). Blood culture itself may also be a relatively insensitive tool for the diagnosis of sepsis, although this depends on how many cultures are taken and the incubation conditions. In one series, only 23 per cent of cats with a clinical diagnosis of likely sepsis had positive cultures. Bacteriology of feline sepsis There are surprisingly few series of septic cats published with detailed bacteriology. In a survey of bacteria isolated from blood cultures of 66 Bavarian client-owned cats with signs of sepsis (either clinical evidence of sepsis or two SIRS criteria fulfilled) presented to a university small animal clinic, a single species was isolated in 88 per cent of cases (Table 5). Of these, 45 per cent were Gram positive, 43 per cent were Gram negative and 12 per cent were obligate anaerobes. The most common species were Enterobacteriaceae, anaerobes, Staphylococci and Streptococci. This is broadly similar to the findings of the few previous reports in cats. Gram-negative bacteria appear to afflict a greater proportion of septic cats than dogs. In their 2008 paper, Greiner et al found no clinical or clinico-pathological parameters capable of distinguishing between Grampositive and Gram-negative infections without bacteriology. Interestingly, no single antibiotic agent was effective against more than 77 per cent of these isolates (Table 6). Given that the routine use of enrofloxacin is perhaps unwise, in view of potential adverse effects on the feline retina, the most effective readily available antibiotics are effective against fewer than two out of three isolates. Even the efficacy of amoxicillin-clavulanate against E coli the most common agent in feline bacteraemia has been shown to have suffered a statistically significant fall in veterinary patients in the UK (Normand et al, 2000). Empirical treatment would appear to be more of a hit-andmiss affair than would perhaps have been generally assumed. In severe sepsis and in immunocompromised patients, the routine use of antibiotic combinations may well be warranted. References American College of Chest Physicians/ Society of Critical Care Medicine Consensus Conference (1992). Definitions for sepsis and organ failure and guidelines for the use of innovative therapies in sepsis, Critical Care Medicine 20: Brady C A, Otto C M et al (2000). Severe sepsis in cats: 29 cases ( ), JAVMA 217: / 16

4 Greiner M, Wolf G and Hartmann K (2007). Bacteraemia in 66 cats a nd antimicrobial susceptibility of the isolates ( ), Journal of Feline Medicine and Surgery 9: Greiner M, Wolf G and Hartmann K (2008). A retrospective study of the clinical presentation of 140 dogs and 39 cats with bacteraemia, JSAP April 14 (epub ahead of print). Normand E H et al (2000). Trends of antimicrobial resistance in bacterial isolates from a small animal referral hospital, The Veterinary Record 146: / 16

5 This cat had severe trauma following a dog bite. It developed septic shock with low blood pressure that was unresponsive to intravenous fluid therapy. Note that the animal s mucous membranes are distinctly jaundiced this is a relatively common finding in severely septic cats. 5 / 16

6 This cat had severe trauma following a dog bite. It developed septic shock with low blood pressure that was unresponsive to intravenous fluid therapy. Note that the animal s mucous membranes are distinctly jaundiced this is a relatively common finding in severely septic cats. 6 / 16

7 A blood smear from the cat pictured in the previous two images (Rapi-Diff, x1000). This immature granulocyte with ring nucleus is especially indicative of a severely toxic state 7 / 16

8 a cat with pyothorax. A Rapi-diff stained cytology preparation (x1000) of the pleural effusion demonstrates large numbers of degenerate neutrophils and bacteria. This patient was markedly hypothermic another, and perhaps unexpected, sign associated with feline severe sepsis. 8 / 16

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11 a cat with pyothorax. A Rapi-diff stained cytology preparation (x1000) of the pleural effusion demonstrates large numbers of degenerate neutrophils and bacteria. This patient was markedly hypothermic another, and perhaps unexpected, sign associated with feline severe sepsis. TABLE 1. Definitions relating to sepsis 11 / 16

12 TABLE 2. Physical signs in cats with severe sepsis 12 / 16

13 Table 3. Clinico-pathological findings in cats with severe sepsis 13 / 16

14 Table 4. Suggested diagnostic criteria for severe sepsis in cats (to fulfil three of four criteria) 14 / 16

15 Table 5. Species of bacteria isolated from the blood of septic cats 15 / 16

16 Table 6. Efficacy of antibiotics against bacteria isolated from the blood of septic cats 16 / 16 Powered by TCPDF (