Selective Digestive Decontamination,Selective Oropharyngeal Decontamination,and Oropharyngeal Chlorhexidine: Three Different Maneuvers

To the Editor:

We read Reed's review of selective digestive decontamination (SDD) [1]. He acknowledges that decontamination protocols save lives. However, his conclusion that “the recent inclusion of chlorhexidine oral rinses in the ventilator bundle by the Institute for Healthcare Improvement (IHI) may mean that effective SDD will become standard” does not make sense. We believe that the author's failure to distinguish SDD and selective oropharyngeal decontamination (SOD) clearly from oropharyngeal chlorhexidine rinses may explain his unjustified conclusion.

Selective digestive decontamination is an antimicrobial prophylaxis against severe infections of the lower airways and the blood stream. SOD and oropharyngeal chlorhexidine are modified SDD maneuvers aimed at the prevention of lower-airway infections using antimicrobials and antiseptics, respectively. The former technique employs parenteral and enteral antimicrobial agents. Parenteral cefotaxime is intended to control oropharyngeal overgrowth of normal bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus. Enteral antimicrobials amphotericin B or nystatin, polymyxin, and tobramycin are applied into the oropharynx using a sticky gel and into the gut using a suspension to control oropharyngeal and gut overgrowth of Candida species and “abnormal” aerobic gram-negative bacilli (AGNB). The parenteral antibiotic and the gut component of the enteral antimicrobials are omitted in SOD and oropharyngeal chlorhexidine rinsing. Meticulous hygiene and regular surveillance cultures of the throat are mandatory with all three prophylactic maneuvers. An extra surveillance culture of the rectum is part of the full SDD protocol.

The author discusses a recent Dutch SDD/SOD trial [2] extensively, the trial demonstrating a significant reduction in the odds of death with SDD (16%) and SOD (14%) compared with standard care (odds ratio [OR] 0.835; 95% confidence interval [CI] 0.72, 0.968; p=0.016 and OR 0.858; 95% CI 0.739, 0.996; p=0.045, respectively). The reduction in the mortality rate was higher in the SDD than in the SOD group, albeit not significantly. A recent meta-analysis of nine randomized controlled trials showed that SOD significantly reduces lower-airway infections but not death [3]. In contrast, there is robust evidence that the full SDD protocol significantly reduces morbidity, that is, fewer lower-airway [4] and blood stream [5] infections, and mortality rate [4, 6].

The most recent large meta-analysis on the prevention of ventilator-associated pneumonia (VAP) with oral antiseptics showed a significant reduction in such infections [7]. However, subgroup analysis revealed that the reduction in VAP was significant only in cardiac surgery patients, which hampers comparison with critically ill patients in general. In mixed and surgical or trauma intensive care unit populations, the reduction in VAP was not significant. Most importantly, oropharyngeal chlorhexidine has never been shown to provide a survival benefit [8].

Finally, Doctor Reed cites high cost, emerging resistance, and labor intensity as major impediments to the adoption of SDD. Although the cost-effectiveness of SDD has not yet been calculated formally, the daily costs of SDD, about $12, can hardly be an issue for a maneuver that significantly reduces severe infections and provides a survival benefit. Patients with rectal-swab AGNB who were resistant to the marker antibiotics numbered less with SDD than with SOD [2]. In the same study, bacteremia attributable to highly resistant pathogens was significantly reduced by SDD compared with SOD (OR 0.37; 95% CI 0.16, 0.85) and standard care (OR 0.41; 95% CI 0.18, 0.94), whereas SOD failed to have an impact compared with standard care (OR 1.10; 95% CI 0.59, 2.07) [9]. In addition, lower respiratory-tract colonization by highly resistant pathogens was less with SDD (OR 0.58; 95% CI 0.43, 0.78) than with SOD (OR 0.65; 95% CI 0.49, 0.87) compared with standard care [9]. SDD involves regular surveillance cultures (i.e., throat and rectal swabs on admission and twice weekly) followed by daily application of SDD medication in the throat and gut. Although the labor intensity of SDD has not been assessed formally, our experience with SDD over more than 25 years reveals that caring for patients who suffer from pneumonia and blood stream infections is more labor intensive than the SDD routine [10].

In conclusion, there is a vast body of evidence showing that, compared with SOD or oral chlorhexidine, only the full protocol of SDD, including parenteral and enteral antimicrobials, results in a significant reduction of both severe infections and death. We believe that the three maneuvers should be distinguished clearly.