Syndromes of infection

Syndromes of infection

Syndromes of infection

Septicaemia is uncontrolled bacterial infection in the blood.Unlike septicaemia, transient bacteraemia is fairly common in normal subjects. Septicaemia is a much more seriouscondition which is likely to lead to death if untreated.

Aetiology A wide range of bacteria can cause septicaemia, but theycan be divided into those that do so as part of a primaryinfection by a single organism acquired in the community,and those that cause septicaemia as a complication of another process, such as abdominal sepsis following surgery, when there is often a mixed infection. Community-acquired infections are usually recognized as part of aspecific illness, as when Strep, pneumoniae septicaemiacomplicates pneumonia, meningococcaemia with meningitis,or E. coli septicaemia with pyelonephritis. The otherkind of septicaemia is usually seen in hospitals, often in adebilitated patient, and the likely bacteria can often bepredicted from the clinical situation.

Pathogenesis Whole bacteria and substances released by bacterial lysistrigger a complex series of events. A major component isendotoxin, the lipopolysaccharide component of Gramnegativebacterial cell walls, of which lipid A is thoughtto be responsible for most of the toxic effects. Lipid Acan activate complement and Hageman factor and cancause the release of cytokines, including tumour necrosisfactor. Important pathological consequences ensuing fromactivation of the potent inflammatory pathways arehypotension, increased vascular permeability and consumptivecoagulopathy.Less attention has been paid to the effects of Grampositiveorganisms, but activation of inflammatoryprocesses can certainly be triggered by cell membranecomponents of these organisms. An example is alternatepathway complement activation by teichoicacid found in Staph. aureus membranes.Clinical features and diagnosisThe manifestations depend on the age of the patient, theillness being more featureless and more lethal at extremesof age. Signs are usually non-specific, but there are signsin the skin suggestive of the diagnosis, such as purpuriclesions associated with meningococcaemia and pustularlesions in staphylococcal septicaemia. Usually there is arapid deterioration in the patient's condition, including achange in mental state. Fever is often present, with tachycardiaand a bounding pulse, but as the condition progressesthe patient becomes hypothermic with a rapidthready pulse and peripheral vasoconstriction. The lattersituation is often considered to be typical of Gram- negative septicaemia, but also occurs with Gram-positivesepticaemia. For this reason the general term septicaemicshock is usually used. Prolonged hypotension leads to acuterenal failure, and disseminated intravascular coagulationcauses bleeding. Acute respiratory distress syndrome frequently complicates hospital-acquired septicaemia.The diagnosis is based on clinical assessment, but bloodcultures, urine cultures, wound swab and any aspirate froman infected site should be obtained at the time the patientis seen, so that antibiotic treatment can be started withoutundue delay. The antibiotic regimen can be changed if necessarywhen culture results are available and the responseto treatment has been assessed. Blood cultures should betaken whether the patient is febrile or not.ManagementTreatment is urgent because of the high mortality. Antibioticsand circulatory support are the mainstays of management. AntibioticsThe initial choice of antibiotics is based on a logical guessat the bacteria responsible. As few antibiotics aspossible are given to achieve the necessary cover. Atpresent a common choice is a combination of a broadspectrumpenicillin, such as ampicillin, with an aminoglycosidesuch as gentamicin. One problem is that many patientsare in incipient renal failure, which enhances the toxicityof gentamicin. Newer drugs, such as cefotaxime andpiperacillin, are active against Gram-positive and Gramnegativebacteria and lack the toxicity of gentamicin, butthey are more expensive. If anaerobic septicaemia is suspectedmetronidazole is often used, and for hospitalacquiredstaphylococcal infection a B-lactamase-resistantpenicillin, such as flucloxacillin, is added. Pseudomonasinfections are treated with a combination of drugs, e.g.azlocillin and gentamicin.

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