Dear editor: We read with interest the editorial by Segers and de Mol on the prevention of ventilator-associated pneumonia (VAP) after cardiac surgery [1]. We would like to comment on the authors’ statements on the use of selective digestive decontamination (SDD), selective oropharyngeal decontamination (SOD), and oropharyngeal chlorhexidine, as they are based on inaccurate interpretation of the evidence.

The authors refer to a large SDD/SOD study [2] which showed a significant reduction in the odds for mortality of SDD and SOD compared to standard care of 16% (odds ratio [OR] 0.835, 95% confidence interval [CI] 0.72–0.968, P = 0.016) and 14% (OR 0.858, 95% CI 0.739–0.996, P = 0.045), respectively. The reduction in mortality was higher in the SDD group than in the SOD group, albeit not significantly. There are nine randomized controlled trials (RCTs) evaluating the impact of SOD on lower respiratory tract infection and mortality. We performed a meta-analysis of those RCTs showing that SOD significantly reduces lower respiratory tract infections, but not mortality (Table 1). Contrastingly, there is robust evidence from the literature which indicates that the full SDD regimen of parenteral and enteral antimicrobials significantly reduces morbidity, i.e. pneumonia [3] and bloodstream infection [4], and mortality [3, 5].

Table 1 Meta-analysis of randomized controlled trials evaluating the impact of selective oropharyngeal decontamination (SOD) and topical oropharyngeal chlorhexidine in cardiac patients on lower respiratory tract infection and mortality
Full size table

The authors advocate the use of SOD instead of SDD “because it does not include widespread systemic prophylaxis with cephalosporins and involves a lower volume of topical antibiotics, thus minimizing the risk of development of antibiotic resistance”. However, the Dutch study [2] clearly shows that patients with Gram-negative bacteria in rectal swabs resistant to the marker antibiotics are lower with SDD than with SOD. These results confirm that the resistance problem is not a function of intestinally applied volume of antimicrobials, but of systemically administered antibiotics. Remarkably, the use of all systemic antibiotics was higher in the SOD group than in the SDD group. Finally, the Dutch study confirms the findings that SDD does not increase the resistance problem, but actually reduces it [3].

The authors recommend the use of oropharyngeal chlorhexidine in cardiac surgery. Of the five meta-analyses of oropharyngeal chlorhexidine, three demonstrated a significant reduction in pneumonia, but none showed a significant reduction in mortality (see S1 in the Electronic Supplementary Material). The meta-analysis of the only three RCTs of chlorhexidine in cardiac surgery shows that chlorhexidine significantly reduces lower respiratory tract infections (Table 1). However, this result should be cautiously interpreted, as the duration of mechanical ventilation was short, and those studies reported the incidence of nosocomial pneumonia, not that of VAP, e.g. most patients received only few doses of the oral rinsing agent because extubation occurred within 4–12 h after surgery. Again, mortality is not significantly reduced by chlorhexidine.

Therefore, although we welcome the authors’ claim of “prepare and defend”, we advocate prevention of pneumonia using evidence based medicine (EBM) manoeuvres. SDD is the only EBM manoeuvre which has been shown to significantly reduce severe infections, i.e. pneumonia and bloodstream infection, and mortality, whilst SOD and oropharyngeal chlorhexidine still require further investigation.