Question 28

College answer

Not available.

Discussion

This question is identical to Question 22 from the second paper of 2017.

Rationale

• Critical illness causes an overgrowth of normal and opportunistic flora.
  • Specifically, the organisms which enjoy a population explosion are exactly those which are known to cause common nosocomial infections: predominantly oropharyngeal and upper GI organisms.
• Increased population of this flora leads to the proliferation of multiple bacterial clones, which is an ideal environment for developing antimicrobial resistance.
• Thus, it stands to reason that if one were to eradicate these organisms, one would reduce the incidence of nosocomial infection in critical illness, and reduce the incidence of antimicrobial resistance.

Protocol

• There is no agreed-upon protocol.
• Usual antibiotics are the "PTA" cocktail:
  • polymyxin E
  • tobramycin
  • amphotericin B
    • The SuDDICU authors have complained that these days its harder and harder to get "good old fashioned amphotericin" and the more recent trials have used nystatin instead, which is a poorly absorbed polyene antifungal (i.e. from the same class), cheap and already enjoying universal popularity as a treatment for oral candidiasis.
• This goop is applied to the oral cavity, and injected down the NG tube.
• Vancomycin can be added if there are high local rates of colonisation
• A controversial step is the addition of a short course of IV antibiotics.
• This is usually a broad spectrum cephalosporin eg. cephotaxime, and it is used for 4 days only. Many study protocols omit this.
• Surveillance cultures of the throat and rectum are recommended

The beneficial effects are expected to manifest in the following ways:

• Decreased incidence of VAP.
• Decreased incidence of pseudocyst infection in acute pancreatitis.
• Decreased systemic infection rate in cases of gastrointestinal haemorrhage.
• Decreased incidence of spontaneous bacterial peritonitis in patients with ascites.
• Protection against early gram-negative sepsis following liver transplantation

Potential drawbacks:

• May result in increased rates of antimicrobial resistance
• Expensive in terms of antibiotic doses, staff workload, and processing of surveillance samples
• Local flora may not respond to standard antibiotic cocktails

Evidence:

• To date, there are numerous RCTs - LITFL counted 60, with over 15,000 patients. A recent (2013) meta-analysis has identified 64 studies.
• The studies have revealed that
  • There is a mortality benefit (OR = 0.73, NNT = 18)
  • Specificaly, the largest trial to date (de Smet, 2009) found an all-cause mortality reduction by 3.5%, from an absolute rate of 27.5% down to 25%.
  • Length of stay is decreased
  • VAP incidence is decreased by 72%
  • The "full-scale" SDD protocol (with a short course of IV antibiotics) is superior to the "limited" SDD where only the oropharynx is decontaminated (and both strategies are superior to oral chlorhexidine)
  • A 2004 Cochrane review found that whereas the "full-scale" SDD decreases the incidence of respiratory tract infections and mortality, the use of oropharyngeal decontamination alone had no effect on mortality- only on incidence of pneumonia.
• Most recently, SuDDICU (2022) did not demonstrate a statistically significant difference in in-hospital mortality (27.0% vs 29.1%); but: there were fewer positive blood cultures, fewer MRO infections and - for some, most importantly - no  increase in the rate of C.difficile infection. 

Critique of the evidence

• The pre-SuDDICU studies all suffer from heterogeneity and poor experimental design.
• Outcome definitions vary considerably, especially as there is no universally accepted definition of VAP.
• Most of the studies were conducted in countries with a lower local MRSA prevalence (Germany and the Netherlands). In these affluent Norther European nations, rates of multiresistant organism colonization would not be representative.
• Placebo solutions may have been microbial vehicles in these studies, increasing the incidence of VAP among the control group.
• There are no good studies of the effect of SDD on the development of multi-resistant organisms (but poor-quality studies suggest that there is no effect).

Local practice

• There is little support for this practice among the Australian intensivist community.
• The practice has been regarded with skepticism in Australian ICUs, and there has been no broad department-level support for it here. Opponents cite paucity of good quality evidence and non-generalisability of European data in local intensive care units.