College Answer

Introductory statement:

SDD is a prophylactic strategy to prevent or minimise the incidence of nosocomial infection from endogenous organisms and to prevent or minimise cross-infection by the application of non-absorbable oral and enteric antibiotics and parenteral antibiotics.

Classically SDD has four components:

• Administration of orobase and enteral antibiotics (eg polymixin B, tobramycin and amphotericin)
• Parenteral antibiotic eg cefotaxime
• Good hygiene to prevent cross-contamination
• Microbiological surveillance of throat swabs and faecal samples

Variations exist.

• Oropharyngeal eradication only (SOD). 
• Enteral only. 
• Oral and enteral only. 
• Different antibiotics.

OR any reasonable and adequate introduction.

Rationale:

Nosocomial infections cause significant morbidity and mortality in the ICU. These infections arise from a limited number of potentially pathogenic micro-organisms (PPM) carried by healthy individuals (eg Staph aureus, E coli and C albicans) and opportunistic, aerobic Gram-negative bacilli (eg Klebsiella, Pseudomonas Acinetobacter) that colonise individuals when critically ill.

The goal of SDD is to prevent or eradicate, if already present, at the start of ICU admission, the carriage of PPMs from the oropharynx and GI tract, leaving the indigenous flora, which protect against overgrowth with resistant bacteria, largely undisturbed.

Arguments against;

• SDD might lead to increased antibiotic resistance of colonising bacteria
• There is already a significant overuse of antimicrobial therapy

Evidence:

Over 60 RCTs with >15,000 patients (mostly in Europe) show benefits in terms of:

• mortality (NNT ~18)
• overall infection
• lower airway infections
• blood stream infections
• oropharyngeal carriage
• rectal carriage
• MODS
• ICU length of stay

Patient groups studied include general ICU, burns, gastrointestinal surgery and transplant patients.

• The evidence does not suggest an increase in MROs
• However the number of trials with good scientific methods are few
• In the trials that suggested benefit, there was baseline variance in patient demographics and overall care
• The trials that suggest benefit have been conducted in areas with a low prevalence of multi-resistant organisms (northern Europe).
• There is a suggestion that selective oral decontamination is equally as effective as SDD, so the iv cephalopsporins are not required

Await the results of the international multi-centre RCT SuDDICU.

Summary statement and Personal approach:

Any reasonable statement of candidate’s own approach, for example

• Risk benefits
• Adoption by communities vs. units
• Protocols driven by local flora and practice vs. world evidence
• Not widely used in intensive care practice in ANZ
• The need for a definitive trial, especially in the ANZ community

Discussion

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.

Critique of the evidence

• The 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 scepticism 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.