Infection prevention in intensive care by selective decontamination of the digestive tract

Decreased duration of intravenous cephalosporins in intensive care unit patients with selective digestive decontamination: a retrospective before-and-after study

Selective digestive decontamination (SDD) reduces the rate of infection and improves the outcomes of patients admitted to an intensive care unit (ICU). A risk associated with its use is the development of multi-drug-resistant organisms. We hypothesized that a 1-day reduction in systemic antimicrobial exposure in the SDD regimen would not affect the outcomes of our patients. In this before-and-after study design, 199 patients and 248 patients were included in a 3-day SDD group and a 2-day SDD group, respectively. The rates of hospital-acquired pneumonia and ICU infections were similar in both groups. The rates of bloodstream infection and bacteriuria were significantly lower in the 2-day SDD group than in the 3-day SDD group. Compared with the patients in the 3-day group, the patients in the 2-day SDD group received fewer antibiotics and less exposure to mechanical ventilation, and they used fewer ICU resources. The rates of ICU mortality and 28-day mortality were similar in both groups. The incidence of multi-drug-resistant organisms was similar in both groups. Within the limitations inherent to our study design, reducing the exposure of prophylactic systemic antibiotics in the SDD setting from 3 days to 2 days was not associated with impaired outcomes. Future randomized controlled trials should be conducted to test this hypothesis and investigate the effects on the development of multi-drug resistant organisms.

Reduction of the intestinal endotoxin pool by three different SDD regimens in human volunteers

Aerobic Gram-negative bacilli (AGNB) carried in the gut by healthy individuals generate 1 mg of 'physiological' endotoxin per g of faeces. Successful eradication of AGNB from the gut would be expected to lead to a lowering of the intestinal endotoxin pool. This prompted us to evaluate the reduction of intestinal endotoxin in 6 healthy volunteers who each received 3 different oral antibiotic regimens. Regimen 1 was polymyxin E (600 mg/day), regimen 2 polymyxin E (400 mg/day) combined with tobramycin (320 mg/day) and regimen 3 pefloxacin (800 mg/day). Each regimen was separated by an antibiotic free period of 3 months. A faecal sample (minimally 2 g) was obtained from each volunteer, before treatment began and afterwards 3 times a week on alternating days (Monday, Wednesday, Friday) for 3 weeks. Each volunteer produced 30 samples, 10 each per oral antibiotic. The samples were serially diluted in nutrient broth for the colony count of AGNB, whilst endotoxin was measured using the classical Limulus amoebocyte lysate micro-assay. The base-line value of faecal AGNB was 10 3-4 colony forming units/g of faeces. All samples obtained on day 3 following antibiotic intake were negative for AGNB, and remained negative during antibiotic intake. The AGNB free carrier state was associated with a reduction in gut endotoxin. The reduction was approximately 10 ng (1 log) for polymyxin E and pefloxacin, whilst the combination of polymyxin/tobramycin significantly reduced the intestinal endotoxin concentrations from 1 mg to 100 ng in the gut; a reduction of 104. Although AGNB were killed by the three regimens, the 'free' endotoxin left in the gut was effectively neutralised by the combination polymyxin/tobramycin only. From a clinical point of view, gut-derived endotoxaemia may play a role in the systemic inflammatory response syndrome and hence the outcome, in critically ill intensive care patients. This study supports other work which indicates that mortality is significantly reduced in only those intensive care patients who received oral polymyxin/tobramycin.

Effects of selective decontamination of digestive tract on mortality and antibiotic resistance in the intensive-care unit

PURPOSE OF REVIEW

Since its introduction in 1984 several small trials have studied the infection prevention regimen of selective decontamination of the digestive tract (SDD) in intensive care patients. Although meta-analyses of these studies suggested that SDD could reduce mortality, it continued to be a highly controversial strategy. There were not only serious doubts about the methodological quality of the meta-analyses, fear also existed that SDD would lead to increased antibiotic resistance. Recently, two new large randomized trials have been published that studied the effects of SDD on mortality and resistance. In this article, we will review the concept on which SDD is based and the present knowledge of the effects of SDD on mortality and antibiotic resistance.

RECENT FINDINGS

In accordance with earlier meta-analyses of small studies, two recent randomized trials have confirmed that selective decontamination of the digestive tract significantly lowers mortality and decreases the emergence of antibiotic resistance. Limitation of these studies is the fact that they were conducted in intensive-care units (ICUs) with a low prevalence of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococcus (VRE).

SUMMARY

There is convincing evidence that selective decontamination of the digestive tract (SDD) lowers mortality as well as resistance in circumstances with low prevalence of methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococcus (VRE). SDD should still be considered experimental in area's where MRSA and VRE are endemic. However, given the important potential benefits of SDD, more studies are urgently needed to adapt SDD in a way that proves effective in those settings.

All great truths are iconoclastic: selective decontamination of the digestive tract moves from heresy to level 1 truth

OBJECTIVE

The objective was to compare evidence of the effectiveness, costs and safety of the traditional parenteral antibiotic-only approach against that gathered from 53 randomised trials involving more than 8,500 patients and six meta-analyses on selective decontamination of the digestive tract (SDD) to control infection on the intensive care unit (ICU). PHILOSOPHY: Traditionalists believe that all infections are due to breaches of hygiene except those established in the first 2 days, and that all micro-organisms can cause death. In contrast, newer insights show that transmission via the hands of carers are responsible only for infections occurring after one week, and that only a limited range of 15 potential pathogens contribute to mortality. INTERVENTIONS TO PREVENT ICU INFECTION: The traditional approach is based on hand disinfection aiming at the prevention of transmission of all micro-organisms, to control all infections that occur after 2 days on the ICU. The second feature is the restrictive use of systemic antibiotics, only in cases of microbiologically proven infection. In contrast, SDD aims to control the three types of infection: primary, secondary endogenous and exogenous due to 15 potential pathogens. The classical SDD tetralogy comprises four components: (i) a parenteral antibiotic, cefotaxime, administered for three days to prevent primary endogenous infections typically occurring "early"; (ii) the oropharyngeal and enteral antimicrobials, polymyxin E, tobramycin and amphotericin B administered in throat and gut throughout the treatment on the ICU to prevent secondary endogenous infections tending to develop "late"; (iii) a high standard of hygiene to control transmission of potential pathogens; and (iv) surveillance samples of throat and rectum to monitor the efficacy of the treatment.

ENDPOINTS

(i) Infectious morbidity; (ii) mortality; (iii) antimicrobial resistance; and (iv) costs.

RESULTS

Properly designed trials on hand disinfection have never demonstrated a reduction in either pneumonia and septicaemia, or mortality. Two randomised trials using restrictive antibiotic policies failed to show a survival benefit at 28 days. In both trials the proportion of resistant isolates obtained from the lower ways was >60% despite significantly less use of antibiotics in the test group. A formal cost effectiveness analysis of the traditional antibiotic policies has not been performed. On the other hand, two meta-analyses have shown that SDD reduces the odds ratio for lower airway infections to 0.35 (0.29-0.41) and mortality to 0.80 (0.69-0.93), with a 6% overall mortality reduction from 30% to 24%. No increase in the rate of super infections due to resistant bacteria could be demonstrated over a period of 20 years of clinical research. Four randomised trials found the cost per survivor to be substantially lower in patients receiving SDD than for those traditionally managed.

CONCLUSIONS

The traditionalists still rely on level 5 evidence, i.e. expert opinion, with a grade E recommendation, whilst the proponents of SDD are able to cite level 1 evidence allowing a grade A recommendation in their attempts to control infection on the ICU. The main reason for SDD not being widely used is the primacy of opinion over evidence.

Influence of selective decontamination of the digestive tract on cell-mediated immune function and bacteria/endotoxin translocation in thermally injured rats

OBJECTIVE

To determine the influence of pretreatment with selective decontamination of the digestive tract (SDD) on systemic immunosuppression, and the relationship between bacteria/endotoxin translocation and abnormalities of immune function in thermally injured rats.

DESIGN, MATERIALS, AND METHODS

Animals were subjected to a 40% full-thickness scald injury, and divided into SDD-treated and control groups. The treatment group received SDD (polymyxin E, tobramycin, and 5-flucytosine) by gavage twice daily for 3 days before the experiment and continued for 5 days after thermal injury. The control group was given the same amount of water. The parameters reflecting cell-mediated immunity, including splenocyte proliferation in response to mitogens, interleukin 2 (IL-2) production, and lymphocyte subpopulation, were measured before injury and 1 and 5 days after burn, respectively.

MEASUREMENTS AND MAIN RESULTS

Thermal injury resulted in marked reduction in splenocyte proliferative response to T-cell mitogens, IL-2 production, and T-helper/suppressor cells (CD4/CD8) ratio. Prophylactic treatment with SDD significantly decreased the incidences of bacterial translocation and endotoxemia, prevented suppressive mitogenic response and inadequate IL-2 production (p < 0.05-0.01) but did not affect the abnormal ratio of CD4 to CD8 T lymphocytes in blood (p > 0.05).

CONCLUSIONS

These results suggest that bacteria/endotoxin translocation from the gut appears to be involved in cell-mediated immune dysfunction as a consequence of thermal injury. Pretreatment with SDD might attenuate postburn immunosuppression by preventing translocation events.

The role of selective digestive tract decontamination on mortality and respiratory tract infections. A meta-analysis

PURPOSE

To review available clinical trials of selective digestive decontamination (SDD) in patients requiring intensive care.

DATA SOURCES

All relevant English-language articles from 1982 through 1992 were identified through MEDLINE search and article bibliographies.

STUDY SELECTION

Twenty-one articles were identified; 16 articles were selected for analysis based on inclusion and exclusion criteria.

DATA EXTRACTION

Occurrence rates for mortality, acquired pneumonia, and acquired tracheobronchitis were extracted for patients treated with SDD and for control patients. Cumulative risk differences were calculated for each of these outcomes.

RESULTS

There was no significant difference between cumulative mortality rates for control patients (0.262; n = 1,165) and patients receiving SDD (0.243; n = 1,105) (p = 0.291; beta error rate = 0.16). The acquired pneumonia greater than that in patients receiving SDD (0.074; n = 1,031) (p < 0.0001). The acquired tracheobronchitis rate in control patients (0.117; n = 549) was also significantly greater than that in patients receiving SDD (0.065; n = 494) (p = 0.004). The rate of acquired pneumonia due to Gram-positive bacteria was similar between the control patients (0.033; n = 660) and the SDD-treated patients (0.033; n = 646) (p = 0.933). Colonization with pathogenic Gram-positive bacteria and pneumonia due to antibiotic-resistant Gram-positive bacteria appeared to occur more frequently in SDD-treated patients.

CONCLUSIONS

These results suggest that SDD decreases the overall incidence of acquired pneumonia and tracheobronchitis in patients requiring intensive care. SDD had no apparent effect on the hospital mortality rate. The routine use of SDD cannot be supported by this meta-analysis. SDD may be useful in specific circumstances where a particular ICU or ICU population is found to have an excessive incidence of acquired infections. Any use of SDD should include careful patient surveillance for the emergence of infection due to bacteria not covered by the prophylaxis regimen and due to antibiotic-resistant bacteria.

Problems in assessing the technology of critical care medicine

Technology assessment is becoming increasingly important in the area of critical care due both to the explosion of technology associated with this discipline and to the realization that future demand for these health care resources will undoubtedly exceed the ability to pay. Technology assessment remains both confusing and controversial to many physicians. This review tries to address some of the confusion by reviewing the basic strategies involved in this process. From there, problems and prospects for the evaluation of critical care as a program are presented, followed by the assessment of components within the area of critical care. Finally, recommendations are made on how technology assessment could proceed in the future to best achieve the efficient provision of this service.

Prevention of pneumonia by selective decontamination of the digestive tract (SDD)

Prevention of respiratory tract infections is only possible when the pathogenesis is known. Three types of infection can be distinguished: primary endogenous infections, caused by pathogens carried in the throat at the commencement of mechanical ventilation, generally develop early and can only be prevented by intravenous antibiotics. Secondary endogeneous infections, caused by hospital-acquired pathogens, generally develop later and can be prevented by selective decontamination of the digestive tract (SDD). The GI-tract is decontaminated by oral nonabsorbable antibiotics and for oropharyngeal decontamination a sticky antibiotic ointment is used. To date 16 controlled SDD trials in intensive care have been fully published. In all except one study, the pneumonia rate decreased significantly from 40%-50% in controls to about 10% in SDD-treated patients. All studies showed a consistent reduction of ventilator days, ICU-stay and an improved outcome in SDD-treated patients. However, in only few studies did these differences reach statistical significance. Selection of resistant strains has not been observed during prolonged use of SDD. Sucralfate reduces the pneumonia rate compared to H2-blockers or antacids by not interfering with the gastric barrier. However, gastric colonization is reduced rather than eliminated and sucralfate has almost no effect on oropharyngeal or tracheal colonization. Whether sucralfate is significantly better than a placebo remains to be established. SDD is superior to sucralfate in preventing both colonization and infection.

Bowel microorganisms--a target for selective antimicrobial control

This article reviews the eight factors that determine the outcome of selective antimicrobial control (SAC) a technique aimed at the clearance of intestinal Gram-negative bacillary carriage by means of lethal faecal anti-microbial concentrations. They are as follows: (i) the carrier state; (ii) compliance; (iii) SAC aiming at prophylaxis vs treatment; (iv) minimum bactericidal concentration (MBC) of the antimicrobial; (v) dosage; (vi) pharmacokinetics; (vii) faecal inactivation; and (viii) microorganisms to be controlled. In the second part, non-absorbable SAC regimens are compared with absorbable trimethoprim/sulphamethoxazole (TMP/SMZ) and the fluoroquinolones in different clinical settings including neutropenia, intensive care, hepatic encephalopathy, liver transplantation and the salmonella carrier state. Ablation of gut carriage and superinfections are the main endpoints reviewed in this article. The newer fluoroquinolones are potent SAC agents to deal with enterobacteria. Pseudomonads are the major gap in their SAC spectrum. TMP/SMZ emerges as a SAC agent of limited value, whilst the newer non-absorbable combination of polymyxin/tobramycin seems to be the most potent SAC programme since it has activity against pseudomonads. In a third part, three current issues--the emergence of resistance, the selectivity and the tissue effect are discussed. Finally, a potent fluoroquinolone combined with oral polymyxin/tobramycin seems to be the most effective SAC programme currently available to control enterobacteria and pseudomonads in patients in whom bacterial translocation is a risk with minimal risk of resistance emerging.

Selective decontamination of the digestive tract (SDD) in intensive care patients: a critical evaluation of the clinical, bacteriological and epidemiological benefits

Twenty trials (17 controlled and three observational cohort studies) on selective decontamination of the digestive tract (SDD) have been undertaken to date. SDD is defined as a technique which aims to eradicate carriage of disease-causing microorganisms by means of lethal oropharyngeal and faecal antimicrobial concentrations. The SDD concept and the criteria for the choice of the antimicrobials used in the SDD programme are explained. Abolition of the carrier state is thought to provide clinical, bacteriological and epidemiological benefits. Infection-specific morbidity and mortality, emergence of antibiotic resistance and outbreaks are the main endpoints evaluated in this review. Of the 15 controlled studies that considered carriage, 14 demonstrated a significant reduction of Gram-negative bacillary (GNB) carriage. Severe infections, including pneumonia and septicaemia, caused by enterobacteria and pseudomonads have been virtually eliminated in these trials. Five of the 12 centres that evaluated mortality showed a significant decrease among patients who received SDD. Two recent trials describe the control of an outbreak with a multiresistant Klebsiella by SDD. There are three indications for the use of SDD so far: (i) in trauma patients; (ii) in certain elective surgical procedures including liver transplantation and oesophageal resection; and (iii) in control of outbreaks of ICU infection. Future lines of research may include a properly designed trial with mortality as endpoint and studies on the transfer of SDD from the ICU into the ward as part of prophylaxis in major surgery.

Selective decontamination of the gastrointestinal tract as an infection control measure

An outbreak caused by a Klebsiella aerogenes resistant to ceftazidime, cefuroxime, cefotaxime, ampicillin and piperacillin and sensitive to aminoglycosides, imipenem and temocillin occurred in a teaching hospital's busy multi-disciplinary Intensive Care Unit over a 3-month period. Four patients had bacteraemia and a further four were colonized. Traditional infection control measures failed to eradicate the outbreak. The introduction of a selective gastrointestinal decontamination regimen consisting of tobramycin, amphotericin and colistin as a gel to the oropharynx, nose and rectum and a suspension via a nasogastric tube resulted in rapid disappearance of the outbreak strain with no new isolates being detected clinically or in surveillance specimens over an 8-week period.