Watching the detectives

Etiology of illness in patients with severe sepsis admitted to the hospital from the Emergency Department. Heffner AC, Horton JM, Marchick MR, Jones AE. Clinical Infectious Diseases 2010; 50: 814-820.

Heffner and colleagues took a look at how the ‘sepsis detectives’ perform in the challenging setting of a busy Emergency Department.

“Clinicians understand that sepsis is often a challenging diagnosis to establish at the bedside. Our report provides data supporting this assertion -namely, that in clinical practice ˜1 in 5 patients with suspected sepsis at admission may actually have a noninfectious disease that mimics the presentation of sepsis.”

This observational study of 211 patients admitted to an Emergency Department for severe sepsis, included 95 (45%) with positive blood cultures. Those with positive cultures were more likely to have vascular lines, and to have been in residential nursing homes. They also had a shorter time to antibiotic therapy in the ED. 44% patients with negative cultures had a clinical infection and 32% has a non-infectious disease that mimicked infection.

When the μGnome’s colleagues chewed the cud over this paper they highlighted a series of points:

  • “sepsis” was categorised according to predefined criteria
  • the study was in a single hospital centre between 2005 and 2007
  • surgical patients were excluded from the study
  • the focus was on very sick patients, possibly reflected in the relatively high mortality rate
  • the timing of blood culture in relation to ED admission was unclear
  • blood culture inoculation volumes and preliminary result turnaround was not reported

The μGnome agrees with the study’s authors. Working out who has an infective cause of severe sepsis syndrome is difficult in the ED.

  • While early clinical intervention offers the best chance of preventing further deterioration, it is more difficult to identify a specific disease process.
  • It is even more difficult to identify the causal infective agent with any degree of certainty.
  • Pressure on ED staff to move patients on before an arbitrary deadline places the front-line clinician in an invidious position. A
  • follow-up, prospective study including rapid molecular methods would be interesting.

One of the recurring problems in this area of clinical practice is the circular arguments that stem from the lack of a true reference standard for systemic infection. Blood culture is not, despite assertions in its favour, a ‘gold standard’:

  • Many positive blood cultures from EDs contain possible skin bacteria that could easily have contaminated the culture during collection from a severely ill patient.
  • False negative results may also occur as a result of prior antibiotic therapy, intermittent showering of bacteria into the peripheral circulation, or from inoculation of too small a quantity of blood.

These issues are likely to provoke further debate when we try to understand what a positive peripheral blood PCR assay means in the absence of a positive blood culture. The concept of a micrognosis was mentioned previously – this concept may help us find a way out of this circular diagnostic dilemma.

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  1. Watching the detectives (micrognome) http://bit.ly/bk1Z7a 1/5 pts in ED with ?sepsis – have noninfectious cause

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