Open Access

Systematic review: The relation between nutrition and nosocomial pneumonia: randomized trials in critically ill patients

  • Deborah Cook1,
  • Bernard De Jonghe2 and
  • Daren Heyland3
Critical Care19971:3

DOI: 10.1186/cc1

Received: 27 June 1997

Published: 13 August 1997

Abstract

Objective

To review the effect of enteral nutrition on nosocomial pneumonia in critically ill patients as summarized in randomized clinical trials.

Study identification and selection

Studies were identified through MEDLINE, SCISEARCH, EMBASE, the Cochrane Library, bibliographies of primary and review articles, and personal files. Through duplicate independent review, we selected randomized trials evaluating approaches to nutrition and their relation to nosocomial pneumonia.

Data abstraction

In duplicate, independently, we abstracted key data on the design features, population, intervention and outcomes of the studies.

Results

We identified four trials of enteral vs total parenteral nutrition, one trial of early enteral nutrition vs delayed enteral nutrition, one trial of gastric vs jejunal tube feeding, one trial of intermittent vs continuous enteral feeding, and three trials evaluating different enteral feeding formulae. Sample sizes were small, pneumonia definitions were variable and blinded outcome assessment was infrequent. Randomized trial evidence is insufficient to draw conclusions about the relation between enteral nutrition and nosocomial pneumonia.

Conclusions

Nutritional interventions in critically ill patients appear to have a modest and inconsistent effect on nosocomial pneumonia. This body of evidence neither supports nor refutes the gastropulmonary route of infection.

Keywords

enteral nutrition nosocomial pneumonia parenteral nutrition prevention ventilator-associated pneumonia

Introduction

Nosocomial pneumonia is an important cause of morbidity and mortality in hospitalized patients. Diagnosis and treatment continues to challenge clinicians and stimulate investigators. Prevention of this serious infection has been the focus of numerous studies, conferences and professional documents. Nosocomial pneumonia prevention strategies may be directed at the ventilator circuit (frequency of tubing circuit changes and gas humidification strategies), the endotracheal tube (intubation orifice, secretion drainage and suctioning) or body position (kinetic bed therapy and semirecumbancy). Other nonpulmonary approaches are pharmacologic (selective digestive decontamination and stress ulcer prophylaxis) or nutritional (the type, site and timing of enteral feeds).

The largest number of published randomized trials in intensive care medicine have evaluated selective digestive decontamination and stress ulcer prophylaxis. Five meta-analyses [1,2,3,4,5] suggest that selective digestive decontamination confers a large, clinically important and statistically significant reduction in nosocomial pneumonia rates (common odds ratio approximately 0.30, 95% CI 0.28–0.48). Nevertheless, selective digestive decontamination is not widely used, in part due to concern about long-term microbial resistance patterns and antibiotic costs [6]. Stress ulcer prophylaxis trials have been recently summarized in a meta-analysis suggesting that sucralfate, as compared with histamine-2-receptor antagonists or antacids, is associated with a trend toward a lower rate of nosocomial pneumonia (common odds ratio 0.78, 95% CI 0.60–1.01) [7]. Other experiments show that modifying gastric pH with acidified enteral feeds decreases gastric colonization, thereby supporting this underlying biologic rationale [8]. However, sucralfate is not considered of proven benefit due to the possibility that sucralfate confers a protective effect only when compared with gastric pH-altering drugs (which themselves are associated with a modest increase in nosocomial pneumonia compared to control) [7].

Kinetic bed therapy has been reviewed in a meta-analysis of six trials in seriously and critically ill patients, which indicated a significantly lower rate of pneumonia and atelectasis in patients receiving continuous postural oscillation [9]. A less expensive and adaptable pneumonia prevention strategy focussing on body position has been studied in three randomized trials [10,11,12]. Torres et al [10] found that after instillation of radioactive technetium sulfur colloid into the stomach, radioactive counts in endobronchial secretions were significantly higher in samples obtained while patients were supine than when they were semirecumbent. In another study, scintigraphic evidence of esophageal reflux was found in 81% of patients in the supine position compared to 64% in the semirecumbent position [11]. Orozco-Levi et al administered nasogastric technetium sulfur colloid and found that radioactive counts in endobronchial secretions increased over time, but were higher in the supine than the semirecumbent position [12]. Although a causal relationship between pneumonia and this secondary endpoint of aspiration of gastric contents has not been convincingly demonstrated, these trials are in keeping with the gastropulmonary route of infection.

The gastropulmonary route of infection is a concept at least two decades old [13], support for which is derived from multiple human observational studies and experimental evidence [14, 15]. Enteral nutrition, compared to parenteral nutrition, is associated with decreased translocation in animals and decreased infectious morbidity in critical illness in humans [16]. Accordingly, it holds the promise of affording protection against nosocomial pneumonia. However, enterally feeding critically ill patients is often associated with intolerance, thereby predisposing them to aspiration pneumonia. The goal of this systematic review is to critically appraise and summarize the randomized trials of nutritional strategies and their influence on nosocomial pneumonia in critically ill patients.

Methods

Study identification

To identify randomized trials, we searched two computerized databases from 1980 onwards. For MEDLINE, we used the following text words and keywords: critical care, intensive care units, pneumonia, respiratory tract infection, mechanical ventilation, gastropulmonary, enteral nutrition, randomized controlled trials, prospective studies. For EMBASE, we used: pneumonia, prevention, control. Frequently cited articles were identified and SCISEARCH (Science Citation Index online) was used to locate any additional relevant randomized trials. We also used the Cochrane Library, searching the Clinical Trials Registry for randomized trials, and the Cochrane Database of Systematic Reviews (CDSR) as well as the Database of Abstracts of Reviews (DARE) for systematic reviews containing relevant primary studies. We confined our search to studies enrolling non-neutropenic adult humans without the human immunodeficiency virus. We had no language restrictions.

The titles (and the abstracts, when available) in the MEDLINE and EMBASE printouts, and the reference lists of all primary and review articles were reviewed independently in duplicate. Any additional relevant articles were thereby identified and retrieved.

Study selection

The following selection criteria were applied to the full manuscripts by two reviewers independently:
  1. 1.

    Population: critically ill adults, including trauma and burn patients.

     
  2. 2.

    Interventions: nutritional support.

     
  3. 3.

    Outcomes: nosocomial pneumonia.

     
  4. 4.

    Design: published randomized trials in humans.

     

A priori, we excluded relevant nutritional interventions in seriously but not necessarily critically ill patients, studies examining surrogate endpoints for pneumonia [8], studies which did not report how pneumonia was diagnosed [17,18,19], studies which evaluated or reported composite infectious outcomes [20], and duplicate publications [21].

Study characteristics and data abstraction

Two reviewers abstracted data from the randomized trials to describe the method of treatment allocation, the proportion of patients who were excluded post-randomization, whether cointerventions were described, whether the endpoints were assessed by investigators blinded to the intervention, and the outcome definitions employed. Disagreements between reviewers on design characteristics and raw data abstraction were resolved by discussion and consensus.

Analysis

We measured agreement between reviewers on the selection of articles for inclusion in the review. We standardized presentation of the randomized trial results using relative risk, and calculated 95% confidence intervals using the log transformation method. Since study questions and trial designs differed, we did not statistically pool results of these trials, or subgroups of them, in a meta-analysis.

Results

Study identification and selection

The search yielded four trials of enteral vs total parenteral nutrition [22,23,24,25], one trial of early enteral nutrition vs delayed enteral nutrition [26], one trial of gastric vs jejunal tube feeding [27], one trial of intermittent vs continuous enteral feeding [28], and three trials evaluating different enteral feeding formulae [29,30,31]. Agreement was 100% for selection of these trials and systematic reviews.

Study characteristics

Study characteristics are reported in Table 1. Patients were medical or surgical ICU patients, burn, or trauma victims. Two studies were explicit about concealment of randomization using sealed envelopes [26,28]. The nature of some of these comparisons precluded blinding of patients and caregivers. Patients were unlikely to be aware of the details of their care and were not participating in assessment of the presence of nosocomial pneumonia. However, lack of blinding could have affected the care delivered by bedside nurses, respiratory therapists and intensivists, which could have affected the development of lung infection. In one trial, the neurosurgeon evaluating outcomes was blinded [22]; in another, confirmation of outcome was conducted by a second blinded surgeon [24]. Two of the three studies comparing different feeding products employed blinded outcome assessment [29,31].

Cointerventions are interventions which are unrelated to the study question, yet may impact on the outcome, and could be unequally distributed across groups. These include stress ulcer prophylaxis and selective digestive decontamination (Table 1). Other cointerventions not mentioned, but potentially important to standardize or report, might include chest physiotherapy and position of the patients.

In two trials, the pneumonia definition incorporated but did not require invasive bronchoscopic techniques [24,28]; in a third trial, a positive bronchoalveolar lavage was required for the diagnosis [31].

Study results

The results of these randomized trials are presented in Table 2. The four trials evaluating total parenteral vs enteral nutrition yield inconsistent results. In one, there was a trend toward a lower rate of pneumonia associated with enteral nutrition [23], in another study the pneumonia rate was significantly lower in the enteral nutrition group [24], and in the remaining two studies, the pneumonia rate was slightly higher in patients receiving enteral nutrition [22,25].

One study examined early enteral nasoduodenal nutrition begun within 24 h vs nasoduodenal enteral nutrition delayed for 72 h. In patients receiving early feeds, there was a trend toward increased pneumonia (8/19 vs 4/19, respectively) [26].

Considering the potential for enteral nutrition to cause aspiration pneumonia, one study tested the effect of proximal vs distal delivery sites [27]. Two cases of pneumonia were identified amongst those 19 patients receiving prepyloric gastric feeds and no cases were observed in the 19 patients receiving post-pyloric feeds through a jejunal tube.

To avoid continuous alkalinization and intragastric Gram-negative growth associated with enteral feeding, intermittent enteral nutrition was compared with continuous enteral nutrition in one trial [28]. Five of 30 patients in each group developed nosocomial pneumonia.

Three studies examined different enteral feeding formulae and their relation to lung infection. The first compared modular tube feeds (a high protein, low fat, linoleic acid-restricted formulation enhanced with arginine, cysteine, vitamin A, zinc, omega-3-polyunsaturated fatty acids, and ascorbic acid) against Osmolite and Traumacal and found a trend toward lower pneumonia rates in the modular tube feed patients [29]. There was no difference in pneumonia between trauma patients fed Immun-Aid (containing glutamine, arginine, omega-3-polyunsaturated fatty acids, nucleotides, and branched chain amino-acids) vs Vivonex (standard enteral formulae) [30]. In another study of trauma patients, Immun-Aid was associated with a trend toward a lower pneumonia rate than patients fed with Promote (an isonitrogenous, isocaloric diet) [31].
Table 1

Nutrition and nosocomial pneumonia: study characteristics

Author [reference]

Intervention

Population

Allocation

Cointerventions

Exclusion post-

Blinding of

Definition of

     

randomization

outcome accessor

VAP

Young et al [22]

Nasogastric

Head injury

`Was randomly

All patients received

7 Exclusions:

Neurosurgen

Infiltrate and

 

enteral nutrition

patients

assigned to'

prokinetic

5-early death, 2

evaluating

leukocytosis

 

vs total

   

-withdrew

outcomes was

premature cells,

 

parenteral

    

blinded

fever, positive

 

nutrition

     

sputum culture

Moore et al [23]

Enteral nutrition

Trauma patients

`Randomized by

Broad spectrum

No exclusions:

Outcome

New infiltrate and

 

via needle

requiring

computer

antibiotics to both

4-early death,

assessment not

fever, leukocytosis

 

catheter

emergency

assignment'

groups

3-reoperation,

blinded

and purulent

 

jejunostomy vs

celiotomy

  

3-chronic illness,

 

sputum

 

total parenteral

   

2-ATI> 40,

  
 

nutrition

   

2-head injury,

  
     

1-mechanical

  
     

failure,

  
     

1-transfer

  

Kudsk et al [24]

Enteral nutrition

Patients with blunt

`Computer

NR

2 Exclusions:

Secondary

New infiltrate and

 

via needle

and penetrating

generated

 

death within 4

confirmation of

leukocytosis,

 

jejunostomy vs

abdominal trauma

randomization

 

days

outcome by

positive sputum or

 

total parenteral

 

table'

  

blinded surgeon

BAL, or purulent

 

nutrition

     

sputum

Borzotta et al [25]

Enteral nutrition

Patients with

`Computer

Jejunostomy group

NR

Outcome

Infiltrate and

 

via needle

severe closed head

generated random

had gastrostomy

 

assessment not

fever, leukocytosis,

 

catheter

injury

number

tube drainage

 

blinded

leukorrhea and

 

jejunostomy vs

 

assignment'

   

bacteria on Gram

 

nutrition

      

Eyer et al [26]

Early (<24 h)

Patients with blunt

`Randomization by

All patients received

14 Exclusions:

Outcome

New infiltrate and

 

nasoduodenal

abdominal trauma

card drawn from

either sucralfate or

3-regular diet,

assessment not

significant growth

 

tube feeding vs

 

sealed envelope'

antacids but group not

3-steroids,

blinded

on sputum

 

late (>72 h)

  

specified

2-no NGT,

 

culture with <10

 

nasoduodenal

   

6-miscellaneous

 

epithelial cells,

 

tube feeding

     

>25 wbc/hpf OR

       

secretions, fever

       

and leukocytosis

Montecalvo et al [27]

Gastric vs jejunal

Medical and

`Randomly

25 Patients received

5 Patients crossed

Cultures

New and

 

tube feeding

surgical ICU

assigned

sucralfate; 1 H2RA;

over from jejunal to

reviewed blinded

persistent

  

patients

according to

2 H2RA and antacids;

gastric group and

to group

infiltrate and

   

computer

8 sucralfate and

2 patients crossed

assignment

three of: purulent

   

generated random

either H2RA or

over from gastric

 

sputum with

   

number code'

antacids; 1 no stress

to jejunal group;

 

numerous

    

ulcer prophylaxis, but

these 7 patients

 

bacteria, purulent

    

group not specified

were included until

 

sputum with

     

the day they

 

nosocomial

     

crossed over

 

pathogen, T>386,

       

or wbc >10

Bonten et al [28]

Intermittent

Mixed ICU

`Randomization

Intermittent: 13-

None

Outcome

New and

 

enteral feeding

patients and

was performed

antacids and 17-

 

assessment not

persistent

 

(18 h) vs

cardiac surgery

with sealed

sucralfate;

 

blinded

infiltrate and 3 of:

 

continuous

patients needing

envelopes'

continuous: 7 -

  

T>38 or T<355

 

enteral feeding

ventilation > 3

 

antacids and 23 -

  

OR wbc > 10

 

(24 h)

days

 

sucralfate

  

and/or left shift

       

or wbc < 3 OR 10

       

wbc/hpf on ET

       

Gram strain OR

       

positive ET

       

aspirate and one

       

of these: BAL

       

(positive if > 104

       

CFU/ml) OR

       

PSB (positive if

       

>103 CFU/ml)

       

OR positive

       

blood culture OR

       

positive pleural

       

culture

Gottsschlich et al [29]

Modular tube

Burn patients

`Random number

NR

NR

Physicians,

Infiltrate and

 

feeding vs two

(>10% BSA)

table stratified for

  

nurses,

positive sputum

 

standard enteral

 

age, center and

  

technicians,

culture and

 

feeding

 

burn size'

  

clinical and

systemic

 

(Osmolite vs

    

research

antibotics

 

Traumacal)

    

personnel were

 
      

blinded

 

Moore et al [30]

Early enteral

Trauma patients

`Randomized by a

NR

16 exclusions:

Outcome

New and

 

immune-

 

computer-

 

9-inappropriate

assessment not

progressive

 

enhancing

 

generated

 

randomizations,

blinded

infiltrate, fever,

 

feeding vs

 

schedule'

 

7-drop -outs

 

leukocytosis,

 

standard enteral

   

1-early death

 

positive sputum

 

feeding

     

Gram stain with

 

(Vivonex)

     

many polys

Kudsk et al [31]

Early immune-

Trauma patients

`Computer-

Short-term broad

NR

All caregivers

New or changing

 

enhancing

requiring

generated

spectrum antibiotics

 

blinded except

infiltrate and

 

feeding via

emergency

randomization

to both groups

 

nutritionist

fever,

 

jejunostomy vs

celiotomy

table'

   

leukocytosis,

 

standard enteral

     

purulent sputum

 

feeding

     

underwent BAL

 

(Promote)

     

(positive if > 103

       

CFU/hpf)

Abbreviations: ATI=acute trauma index; BAL=bronchoalveolar lavage; NGT=nasogastric tube; wbc=white blood cells; hpf=high power field; H2RA=histamine-2-receptor antagonists; ET=endotracheal; CFU=colony forming units; BSA=body surface area; NR=not reported; VAP=ventilator-associated pneumonia; PSB=protected specimen brush.

Table 2

Results of randomized trails of nutrition and nosocomial pneumonia

Intervention (author [reference])

Pneumonia rates

Relative risk (95% Cl)

Nasogastric enteral nutrition vs parenteral nutrition (Young [22])

TPN: 6/23 (26%)

1.23 (0.51–2.95)

 

EN: 9/28 (32%)

 

Jejunostomy feeding vs total parenteral nutrition (Moore [23])

TPN: 6/30 (20%)

Undefined

 

EN: 0/29 (0%)

 

Jejunostomy feeding vs total parenteral nutrition (Kudsk [24])

TPN: 14/45 (31%)

0.38 (0.16–0.90)

 

EN: 6/51 (12%)

 

Jejunostomy feeding vs total parenteral nutrition (Borzotta [25])

TPN: 9/23 (39%)

1.06 (0.56–2.02)

 

EN: 15/36 (42%)

 

Early nasoduodenal vs late nasoduodenal feeding (Eyer [26])

Late: 4/19 (21%)

2.00 (0.72–5.54)

 

Early: 8/19 (42%)

 

Jejunal vs gastric feeding (Montecalvo [27])

Gastric: 2/19 (11%)

Undefined

 

Jejunal: 0/19 (0%)

 

Intermittent enteral feeding vs continuous enteral feeding (Bonten [28])

CEF: 5/30 (17%)

1.0 (0.32–3.10)

 

IEF: 5/30 (17%)

 

Modular tube feeding (MTF) vs Osmolite vs Traumacal (Gottschlich [29])

Osmolite: 6/14 (43%)

0.27 (0.07–1.15)*

 

Traumacal: 9/19 (47%)

0.25 (0.06-0.99)

 

MTF: 2/17 (12%)

 

Immun-Aid vs Vivonex (Moore [30])

Vivonex: 4/47 (9%)

0.92 (0.24–3.48)

 

Immun-Aid: 4/51 (8%)

 

Immun-Aid vs Promote (Kudsk [31])

Promote: 3/17 (18%)

Undefined

 

Immun-Aid: 0/16 (0%)

 

Abbreviations: EN = enteral nutrition; TPN = total parenteral nutrition; CEF = continuous enteral feeding; IEF = intermittent enteral feeding. * Osmolite compared to MTF. Traumacal compared to MTF.

Discussion

The results of these 10 trials of feeding strategies, either individually or in aggregate, provide inconclusive evidence about the relation between enteral nutrition and nosocomial pneumonia. These studies enrolled a total of 582 patients and contribute 117 cases of pneumonia. The single trial showing a significantly lower pneumonia rate associated with jejunal enteral nutrition over parenteral nutrition [24] has not been translated into widespread clinical policy, perhaps due to the inconvenience and expertise required for jejunostomy tubes. Aside from concerns about type I and II error when interpreting the trials in this review, there are other relevant outcomes addressed by some, but not all of these studies, including effects on nutritional markers and adverse outcomes such as catheter sepsis and patient comfort. Readers are referred to the original articles for these important details.

Factors such as cost, and ease with which the feeding strategy can be employed, are additional issues that bear on the interpretation and application of these trial results in practice. Intensivists also consider evidence from observational studies when making clinical decisions. Given these provisos, it is not surprising that definitive statements about enteral nutrition and lung infection are not forthcoming. Some guidelines from the Center for Disease Control on the prevention of nosocomial pneumonia [32] focus on gastropulmonary approaches. Stress ulcer prophylaxis with an agent that does not increase gastric pH was `suggested for implementation in many hospitals and supported by suggestive clinical and epidemiologic studies and a strong theoretical rationale'. Other interventions labelled as `unresolved for which no recommendations were made' included jejunal feeding, intermittent enteral feeding and selective digestive decontamination. In the American Thoracic Society statement on prevention of hospital-acquired pneumonia in adults [33], some prophylactic interventions were classified as having `probable effectiveness, used widely in some clinical settings', such as distal enteral nutrition, semi-erect positioning, and sucralfate. Selective digestive decontamination was considered `of unproven value used on a limited investigational or clinical basis'.

Nutrition is integral to the care of an ICU patient. The method, site and timing of enteral nutrition may have a protective or predisposing influence on the risk of nosocomial infection [34], though strong proof from experiments in humans does not currently exist. Although a meta-analysis of published and unpublished trials of general surgical and trauma patients suggested a lower pneumonia rate in patients receiving enteral nutrition vs total parenteral nutrition [35], published data from ventilated medical ICU patients are sparse, and generalizing to other populations may not be reasonable. Interventions requiring further investigation with large rigorous studies of ICU patients include those discussed in this review, as well as the size of feeding tubes [36], their insertion site, where the tubes are located in the gastrointestinal tract [37], feeding advancement schedules, and the effect of prokinetic drugs [38].

Declarations

Acknowledgements

We would like to thank Barbara Hill for her help with the manuscript preparation and Lauren Griffith for her help with the analyses.

Authors’ Affiliations

(1)
Department of Medicine, Division of Critical Care, St Joseph's Hospital, McMaster University
(2)
Service de Réanimation Medicale, Hôpital de Poissy
(3)
Department of Medicine, Division of Critical Care, Queen's University

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