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Published ahead of print on February 20, 2004, doi:10.1164/rccm.200312-1779OC
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American Journal of Respiratory and Critical Care Medicine Vol 169. pp. 1046-1053, (2004)
© 2004 American Thoracic Society

Reducing Atelectasis Attenuates Bacterial Growth and Translocation in Experimental Pneumonia

Anton H. van Kaam, Robert A. Lachmann, Egbert Herting, Anne De Jaegere, Freek van Iwaarden, L. Arnold Noorduyn, Joke H. Kok, Jack J. Haitsma and Burkhard Lachmann

Department of Anesthesiology and Laboratory of Pediatrics, Erasmus-MC Faculty, Rotterdam; Department of Neonatology, Emma Children's Hospital AMC; Department of Pathology Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; and Department of Pediatrics, University of Göttingen, Göttingen, Germany

Correspondence and requests for reprints should be addressed to Anton H. van Kaam, M.D., Department of Neonatology (Room H3-150), Emma Children's Hospital AMC, University of Amsterdam, P.O. Box 22700, 1100 DD, Amsterdam, The Netherlands. E-mail: a.h.vankaam{at}amc.uva.nl


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Besides being one of the mechanisms responsible for ventilator-induced lung injury, atelectasis also seems to aggravate the course of experimental pneumonia. In this study, we examined the effect of reducing the degree of atelectasis by natural modified surfactant and/or open lung ventilation on bacterial growth and translocation in a piglet model of Group B streptococcal pneumonia. After creating surfactant deficiency by whole lung lavage, intratracheal instillation of bacteria induced severe pneumonia with bacterial translocation into the blood stream, resulting in a mortality rate of almost 80%. Treatment with 300 mg/kg of exogenous surfactant before instillation of streptococci attenuated both bacterial growth and translocation and prevented clinical deterioration. This goal was also achieved by reversing atelectasis in lavaged animals via open lung ventilation. Combining both exogenous surfactant and open lung ventilation prevented bacterial translocation completely, comparable to Group B streptococci instillation into healthy animals. We conclude that exogenous surfactant and open lung ventilation attenuate bacterial growth and translocation in experimental pneumonia and that this attenuation is at least in part mediated by a reduction in atelectasis. These findings suggest that minimizing alveolar collapse by exogenous surfactant and open lung ventilation may reduce the risk of pneumonia and subsequent sepsis in ventilated patients.

Key Words: open lung ventilation • surfactant • sepsis

Pneumonia is a common finding in adult, pediatric, and newborn patients who are admitted to the intensive care unit (1–3). Its occurrence leads to an increased mortality rate, especially when complicated by severe sepsis or septic shock (4–6). Both mechanical ventilation and preceding colonization of the upper respiratory tract are considered important risk factors in the development of pneumonia (1–3, 7). The precise mechanisms responsible for the progression from colonization to pneumonia and more importantly to sepsis remain unclear. Animal studies have shown that alveolar macrophages (AMs), which are considered the first line of host defense against organisms entering the lower respiratory tract (8), play an essential role in bacterial clearance and survival in experimental pneumonia (9, 10). In contrast to AMs, the role of pulmonary surfactant in the development of pneumonia is much less clear. Besides several nonspecific defense mechanisms, the main effect of pulmonary surfactant on host defense is attributed to surfactant protein (SP)-A and SP-D (11).

The contribution of the biophysical properties of pulmonary surfactant, that is, lowering the alveolar surface tension and thus preventing alveolar collapse and edema, to the host defense of the lung has not been extensively explored. The degree of atelectasis might prove important, as atelectrauma is considered one of the important mechanisms responsible for the development of ventilator-induced lung injury, and previous animal studies showed that reducing atelectasis by positive end-expiratory pressure (PEEP) mitigates both bacterial growth in the lung and translocation from the lung into the blood stream (12–14).

We therefore hypothesized that exogenous surfactant would enhance bacterial clearance from the lung and attenuate systemic bacterial dissemination in experimental pneumonia and that this effect is at least in part mediated by a reduction in the degree of atelectasis.

To test this hypothesis, we induced experimental pneumonia in newborn piglets by intratracheal injection of Group B streptococci (GBS), which are the leading cause of serious infections in human newborns and are of growing importance in invasive infections in adults (15, 16). Using whole lung lavage and exogenous surfactant, we created different conditions of the pulmonary surfactant system. We used natural modified surfactant containing only phospholipids and hydrophobic SPs (SP-B and SP-C) because this type of surfactant is frequently used in daily clinical practice and proved to be superior to synthetic preparations not containing SP-B and SP-C (17). Furthermore, natural modified surfactant does not contain SP-A and SP-D, which enabled us to make a more valid assessment of the effect of reducing atelectasis on bacterial growth and translocation in experimental pneumonia.

To elucidate the role of atelectasis further, additional groups of both surfactant-sufficient and surfactant-deficient animals were subjected to open lung ventilation aiming to recruit collapsed alveoli and prevent subsequent atelectasis by applying sufficient PEEP (open lung concept [OLC]) (18).

Besides assessing the effects of these different interventions on bacterial growth in the lung and bacterial translocation to the bloodstream, we also measured the effects on survival and severity of lung injury. Some of the results of these studies have been previously reported in the form of an abstract (19, 20).


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Animals
Newborn piglets were anesthetized, tracheotomized, supplied with central lines, and ventilated for 5 hours. The study was approved by the institutional Animal Investigation Committee.

Animals were subjected to one or more of the following interventions: (1) lung lavage: respiratory failure was induced by saline lavage (18); (2) surfactant treatment: animals received an intratracheal bolus of 300 mg/kg of natural modified surfactant (HL 10; Leo Pharmaceutical Products, Ballerup, Denmark) or an equal volume of air; (3) bacteria: thirty minutes after surfactant/air bolus, 2 aliquots of 5 ml/kg (108 cfu/ml) of an encapsulated GBS Ia 90 low-density serologic subtype were injected intratracheally in the right and left lateral position to ensure equal distribution; (4) conventional positive pressure ventilation (PPVCON): PEEP was set at 4–5 cm H2O, and peak inspiratory pressure was adjusted to maintain a tidal volume at approximately 7 ml/kg; (5) OLC–positive pressure ventilation (PPVOLC): during this ventilation strategy, collapsed alveoli are recruited by applying high levels of peak inspiratory pressure for a short period of time using oxygenation as an indirect tool to assess the degree of atelectasis. Recruited alveoli are thereafter stabilized by applying sufficient levels of PEEP, and the pressure amplitude (peak inspiratory pressure minus PEEP) is reduced as much as possible to minimize alveolar overdistension (18).

Experimental Groups
Animals were randomly assigned to different intervention groups (n = 13 per group): (1) healthy: healthy animals receiving GBS and PPVCON; (2) lavaged: lavaged animals receiving GBS and PPVCON; (3) surfactant: lavaged animals receiving surfactant, GBS, and PPVCON; (4) OLC: lavaged animals receiving GBS and PPVOLC; (5) surfactant-OLC: lavaged animals receiving surfactant, GBS, and PPVOLC; and (6) saline: lavaged animals (n = 8) receiving 10 ml/kg of saline instead of GBS, followed by PPVCON.

To check bacterial viability and distribution, eight animals (four lavaged and four healthy) were killed 5 minutes after GBS instillation (growth control subjects). Total, left, and right lung weights were recorded, and the cfu per lung were determined.

Data Acquisition and Outcome Variables
Ventilation and hemodynamics.
Ventilatory and hemodynamic variables were recorded throughout the experiments. Volume expansion and/or dopamine infusion were started when appropriate. Blood gas analysis was performed after each intervention and hourly after GBS instillation.

Cfu in blood.
Blood cultures were drawn before GBS instillation and hourly thereafter. The cfu per milliliter were calculated by spreading 1 ml of whole blood on blood agar plates.

Survival.
The survival time after GBS instillation was recorded for all animals.

Lung function.
Lung compliance and volumes at transpulmonary pressures of 35 (total lung capacity) and 5 cm H2O were recorded postmortem (18).

Bronchoalveolar lavage.
The lungs were removed and weighed, and bronchoalveolar lavage (BAL) of the right lung was performed (18). Protein concentration was measured using the Bradford method (21), and SP-A was measured by ELISA using porcine SP-A–specific rabbit and chicken antibodies.

Cfu in lung homogenate.
The left lung was homogenized (13), and a 1-ml aliquot was serially diluted and spread on blood agar plates for calculation of viable cfu. The number of cfu per lung was expressed as log10 and was calculated from homogenate volume, left and total lung weight.

Histology.
The lungs of three animals per group were fixated (18), and blocks of tissue taken from the three lobes of the right lung were stained with hematoxylin/eosin. The presence of bacteria, inflammatory cells, edema, and hyaline membranes were semiquantatively scored as described in the online supplement.

Statistical Analysis
Data (mean ± SD) were analyzed using SPSS version 11 (SPSS, Chicago, IL). Intergroup differences were analyzed by analysis of variance and the Bonferroni post hoc test. Pearson's correlation and {chi}2 test were used when appropriate. Kaplan Meier curves and log rank test were used for survival and bacterial translocation; p <= 0.05 was considered statistically significant.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Animals
A total of 81 animals were included, with a mean age of 74 ± 16 (SD) hours and weighing 2.0 ± 0.4 kg. There were no intergroup differences in age, weight, or number of lavages needed to induce lung injury. No air leaks were observed during the study period.

Growth Control Subjects
Figure 1 shows that the viability of the GBS bacteria in the lung 5 minutes after intratracheal injection was similar to that of the GBS solution. Furthermore, there was an excellent correlation (r = 0.97, p < 0.001) between the number of cfu per lung calculated on the basis of the left lung and both the left and the right lung, indicating an even distribution of the GBS solution between the right and left lungs after intratracheal injection.



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  		Figure 1. Correlation between the number of cfu injected intratracheally and the number of cfu isolated from the lung. Calculation of the total number of cfu in the lung was based on the left lung (open symbols; r = 0.79, p < 0.05) and the left and right lung (closed symbols; r = 0.76, p < 0.05). Animals were either healthy (circles) or lavaged (triangles).

 
Survival
Eleven of the 13 animals in the lavaged group died during the ventilation period, with a mean survival time of 211 ± 49 minutes (Figure 2) . This was significantly different from the other groups, in which all animals survived the 5-hour ventilation period.



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  		Figure 2. Survival plots for the different groups (lavaged, triangles; all other groups, squares) after Group B streptococci (GBS) instillation into the airways. Lavaged = lavaged + GBS + conventional positive pressure ventilation (PPVCON).

 
Cfu in Lung Homogenate
The number of cfu per lung instilled intratracheally was similar in all intervention groups (Figure 3) . The number of cfu per lung decreased after 5 hours of ventilation in the healthy group (p < 0.001) and remained stable in the OLC and surfactant-OLC groups. In the lavaged and the surfactant group, the number of cfu per lung increased over time (p < 0.001 and p < 0.01, respectively), but this growth was significantly less in the surfactant group.



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  		Figure 3. The initial number of cfu (mean ± SD) expressed as log10 cfu per lung, injected in the lung and the subsequent proliferation during the ventilation period. Healthy = GBS + PPVCON; lavaged = lavaged + GBS + PPVCON; surfactant = lavaged + GBS + surfactant + PPVCON; open lung concept (OLC) = lavaged + GBS + OLC-positive pressure ventilation (PPVOLC); surfactant-OLC = lavaged + GBS + surfactant + PPVOLC. ap < 0.001; bp < 0.005 vs. healthy; cp < 0.05 vs. lavaged, OLC, and surfactant-OLC; dp < 0.001 vs. OLC and surfactant-OLC.

 
The total lung weight corrected for body weight at the end of the experiments was significantly higher in the lavaged group compared with all other groups (Table 1) . The lung weight in the surfactant group was significantly higher compared with the healthy, OLC, and surfactant-OLC groups. There were no differences between these latter three groups.


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  		TABLE 1. Data on lung weight, lung mechanics, and alveolar protein influx||

 
Cfu in Blood
None of the animals had positive blood cultures before GBS instillation. As shown in Figure 4 , blood cultures remained negative throughout the ventilation period for all animals in the healthy and the surfactant-OLC groups.



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  		Figure 4. Kaplan-Meier curves displaying the percentage of animals in each group with negative blood cultures during the ventilation period. Healthy = GBS + PPVCON (squares); lavaged = lavaged + GBS + PPVCON (triangles); surfactant = lavaged + GBS + surfactant + PPVCON (diamonds); OLC = lavaged + GBS + PPVOLC (circles); surfactant-OLC = lavaged + GBS + surfactant + PPVOLC (squares). ap < 0.001 vs. all other groups; bp < 0.01 vs. healthy and surfactant-OLC.

 
In the lavaged group, all except one animal had GBS-positive blood cultures, with a mean time to bacteremia of 97 ± 18 minutes. The use of surfactant or OLC ventilation resulted in a comparable reduction in the number of animals with GBS-positive blood cultures (7 of 13 and 6 of 13, respectively) and the time to bacteremia (291 ± 6 and 245 ± 23 minutes, respectively). The maximum number of cfu per milliliter of blood was also significantly higher in the lavaged group (265 ± 165) compared with the surfactant group (6 ± 5; p < 0.001) and the OLC group (33 ± 53; p < 0.005).

Gas Exchange
PaO2 or PaCO2 levels after the instrumentation period and after lung lavage were comparable in the different groups (Figure 5) . In the lavaged group, oxygenation deteriorated over time as animals developed severe pneumonia (Figure 5A). Adding surfactant significantly improved oxygenation. In both groups ventilated with PPVOLC, PaO2 levels returned to prelavage values, and this was maintained throughout the ventilation period, indicating successful application of the open lung approach. Except for higher PaCO2 levels in the lavaged group, the PaCO2 levels were comparable between the different groups after GBS or saline instillation (Figure 5B).



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  		Figure 5. Changes (mean ± SD) in PaO2 (A) and PaCO2 (B) levels in the six treatment groups. Healthy = GBS + PPVCON (closed squares); lavaged = lavaged + GBS + PPVCON (open triangles); surfactant = lavaged + GBS + surfactant + PPVCON (closed triangles); OLC = lavaged + GBS + PPVOLC (closed circles); surfactant-OLC = lavaged + GBS + surfactant + PPVOLC (open circles); saline = lavaged + saline + PPVCON (open squares). Values represent changes before (H) and after (L) lavage, after surfactant or air bolus (S/A), and during the 5-hour ventilation period after GBS instillation. The number of animals still alive in the lavaged group at the time points of 4 and 5 hours are indicated. ap < 0.001 vs. all other groups; bp < 0.001 surfactant and surfactant-OLC vs. lavaged, OLC, and saline; cp < 0.001 OLC and surfactant-OLC vs. all other groups; dp < 0.001 OLC and surfactant-OLC vs. lavaged, surfactant, and saline, and p < 0.05 vs. healthy; ep < 0.001 vs. lavaged, surfactant, and saline; fp < 0.001 surfactant and saline vs. lavaged; gp < 0.001 healthy, surfactant, and surfactant-OLC vs. lavaged, OLC, and saline; hp < 0.005 lavaged vs. healthy, surfactant, surfactant-OLC, and saline; ip < 0.001 vs. all other groups; jp < 0.01 lavaged vs. healthy, surfactant, and saline.

 
Ventilatory and Circulatory Parameters
There were no differences in ventilatory and circulatory parameters between the different groups before and immediately after lung lavage. As expected, the mean airway pressure and PEEP were higher in the groups ventilated with PPVOLC compared with the PPVCON groups (Table 2) . The mean expiratory tidal volume during PPVCON was within the target range and was slightly below this range during PPVOLC (Table 2).


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  		TABLE 2. Ventilatory parameters over time in the groups||||||

 
In contrast to the other groups, the mean arterial blood pressure from animals in the lavaged group deteriorated over time, which was accompanied by an increase in heart rate (Table 3) . In accordance with these findings, 12 animals in the lavaged group compared with less than two animals in the other groups required intravascular volume support (p < 0.001) and dopamine infusion (p < 0.001).


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  		TABLE 3. Circulatory parameters over time in the groups||

 
Lung Function
Pressure–volume curves constructed postmortem showed a severe deterioration of lung function in the lavaged group (Table 1). Surfactant therapy attenuated this deterioration, but not completely. There were no differences between the other groups.

Proteins in BAL
Alveolar protein influx was the most severe in the lavaged group, and although surfactant therapy reduced protein influx to some extent, this difference was not statistically significant (Table 1). The recovery of BAL fluids was not different among the groups (data not shown).

SP-A in BAL
SP-A levels measured in BAL obtained at the end of the ventilation period in the healthy, lavaged, surfactant, OLC, surfactant-OLC, and saline groups were detectable in 50%, 30%, 50%, 40%, 40%, and 40%, respectively, of the animals. As shown by Table 1, the mean SP-A content was not significantly different between the groups.

Histology
The histology findings were consistent with the other outcome parameters showing relatively mild abnormalities in the healthy animals after 5 hours of ventilation compared with signs of severe pneumonia in the lavaged group (Table 4) . Treatment with either exogenous surfactant or OLC ventilation significantly mitigated histologic severity of pneumonia.


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  		TABLE 4. Data on semiquantitative histologic lung injury scores||

 

   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
This study demonstrated that a surfactant preparation, consisting mainly of phospholipids, SP-B and SP-C, is able to attenuate bacterial proliferation in the lung and more importantly bacterial translocation to the blood stream. Furthermore, this study suggests that this attenuation is at least in part mediated by a reduction in the degree of atelectasis.

The fact that only the healthy, nonlavaged animals in this study were able to clear GBS bacteria from the lung seems to confirm the importance of local pulmonary host defense factors such as endogenous surfactant and AMs (8, 11). Whole lung lavage, which induces surfactant deficiency and removes part of the local host defense factors such as AMs (22, 23), resulted in GBS proliferation in the lung and bacterial translocation into the blood stream in nearly all animals. These changes also had a severe clinical impact with deteriorating lung mechanics and hemodynamics, resulting in an almost 80% mortality despite the use of intravascular volume expansion and inotropic support. Restoring the surfactant system with exogenous surfactant reduced both GBS proliferation and translocation and also prevented septic shock and subsequent death in all animals.

To test the hypothesis that this effect of exogenous surfactant was mediated by a reduction in atelectasis, animals were ventilated after lung lavage using an open lung approach, which aims to recruit collapsed alveoli and maintain alveolar patency by applying sufficient PEEP (18, 24). In this study, we assessed the degree of atelectasis indirectly by measuring arterial oxygenation. Both experimental and human studies have shown an excellent correlation between oxygenation and lung volume (25, 26). OLC ventilation reduced bacterial translocation comparable to the surfactant-treated animals, whereas GBS proliferation in the lung was even more attenuated.

These results suggest that the attenuation of bacterial growth and translocation by exogenous surfactant is indeed in part mediated by a reduction in atelectasis. The increased reduction in GBS proliferation in the OLC group seems to be consistent with this assumption because, based on oxygenation, the high mean airway pressures during OLC ventilation are more effective in reversing atelectasis than exogenous surfactant.

We can only speculate on the reasons why a reduction in atelectasis mitigated bacterial growth in the lung. First, Shennib and colleagues showed that the in vitro function of AMs can be impaired if the lung is subjected to several hours of atelectasis (27).

Second, both the wet-lung weight and the histologic evaluation showed that animals subjected to lung lavage had a higher degree of interstitial and alveolar edema compared with animals treated with exogenous surfactant or OLC ventilation, which might also have impaired antibacterial activity of the AMs (28).

Besides atelectasis, other factors might also have played a role in the reduction of bacterial growth after surfactant treatment. First, surfactant treatment has been shown to induce endogenous SP-A production, which might result in increased bacterial clearance (29, 30). However, we found no differences in SP-A content of the alveolar wash at the end of the ventilation period. Second, in vitro experiments have shown that some surfactant preparations are able to mitigate growth of GBS directly (31). This study suggests that this direct inhibitory effect of surfactant on bacteria is of limited importance in vivo because adding surfactant to the OLC group did not further reduce bacterial growth. Third, recent studies have shown that overexpression of SP-B inhibits endotoxin-induced lung inflammation and that SP-C interacts with bacterial lipopolysaccharide, indicating a possible role for these hydrophobic SPs in pulmonary host defense (32, 33). However, to date, it is unknown whether these effects are also present in vivo when administering these SPs as part of natural modified surfactant in experimental pneumonia. Future studies need to address these unresolved issues. Finally, in vitro experiments have shown that surfactant can suppress the release of different cytokines such as tumor necrosis factor-{alpha} from human AMs or monocytes, and it has been suggested that this suppression might be beneficial in nonbacterial pulmonary inflammation (34, 35). However, recent studies in bacterial inflammation using both Gram-positive and Gram-negative bacteria to induce experimental pneumonia have reported that proinflammatory cytokines, such as tumor necrosis factor-{alpha}, are essential for bacterial clearance from the lung, making this explanation for the reduction in bacterial growth due to surfactant unlikely (36–38).

Besides mitigating bacterial growth in the lung, reducing atelectasis by either surfactant treatment or OLC ventilation also resulted in a lower rate of bacterial translocation from the lung into the blood stream. Although the reduced bacterial burden could explain this reduction in bacterial translocation, other mechanisms should be considered. It has been suggested that bacteria present in the lung may enter the blood stream directly through the alveolar epithelial barrier (39).

High tidal volumes (volutrauma) and repeated opening and collapse of atelectatic lung units (atelectrauma) during mechanical ventilation can increase the permeability of the alveolar epithelium (12, 40) and can lead to decompartmentalization of a nonbacterial inflammatory response in the lung (41). Reducing atelectasis by either surfactant therapy or high levels of PEEP attenuates these permeability changes (41–43). This might in part explain the reduced bacterial translocation in both the surfactant and the OLC group. Our findings are consistent with previous reports showing that high levels of PEEP mitigate bacterial translocation in experimental pneumonia (13, 44); however, in contrast to these studies, in this study we ventilated the animals with a low tidal volume. This seems to indicate that even during a low-stretch ventilation strategy, insufficient PEEP resulting in alveolar collapse can lead to increased bacterial translocation.

The most striking finding in this study was the complete reversal of bacterial translocation after adding surfactant to OLC ventilation. This finding suggests an additional effect of surfactant on translocation, not mediated through a reduction in atelectasis. Indeed, animal experiments have shown that surfactant preserves alveolar epithelial permeability independent of the degree of atelectasis or changes in mechanical ventilation (45). Furthermore, in vitro experiments showed that dipalmitoyl phosphatidylcholine, the major component of human surfactant, attenuates alveolar epithelial injury by GBS hemolysin (46).

This study has several limitations that need to be addressed. First, we cannot exclude that the lavage procedure itself enhanced bacterial translocation, although previous studies have shown that the histologic alterations in the lung after a lavage procedure are mild (18, 22), as substantiated by the low lung injury score in the saline group after 5 hours of ventilation. Second, because of different degrees of atelectasis, oxygenation also varied between the groups, ranging from normoxia in lavaged animals to hyperoxia in animals treated with exogenous surfactant and/or OLC ventilation.

However, recent data showing that hyperoxia increases rather than decreases bacterial growth and translocation during experimental pneumonia strengthen rather than weakens the results of this study (47).

Although extrapolation of animal data to humans should be done with caution, we feel that this study might have important implications for the pathogenesis of ventilator-associated pneumonia. In many patients with acute respiratory failure, there is evidence for surfactant abnormalities leading to increased alveolar surface tension and subsequent atelectasis (48–50). Based on this study, these changes can lead to increased bacterial growth in the lung and, more importantly, increased bacterial translocation into the blood stream leading to severe septic shock. Indeed, patients suffering from acute respiratory distress syndrome have an increased risk of pulmonary infection and often succumb to dissemination of the pulmonary infection with overwhelming sepsis and multiple organ failure (51, 52). Our findings also seem to indicate that early surfactant treatment and application of a lung-protective ventilation strategy aiming at minimizing both alveolar stretch and collapse might prove beneficial in reducing the risk for pneumonia in ventilated patients and reduce the incidence of sepsis and mortality often seen in these patients. A recent report in preterm infants with GBS pneumonia showed that exogenous surfactant was well tolerated and improved short-term outcome parameters (53).

In conclusion, this study shows that natural surfactant mitigates bacterial growth and attenuates bacterial translocation in experimental GBS pneumonia. A reduction in the degree of atelectasis is one of the mechanisms responsible for these beneficial effects. This goal can also be achieved by an open lung ventilation strategy. Our findings offer new insights into the pathogenesis of ventilator-associated pneumonia and subsequent sepsis in patients with acute respiratory failure. In addition, our results emphasize the importance of lung-protective ventilation and surfactant therapy in respiratory failure.


   Acknowledgments
 
The authors thank the Melssen family for their generous support. From the Department of Anesthesiology, Erasmus-MC Faculty, the authors also thank S. Krabbendam for expert technical assistance and Laraine Visser-Isles for English editing. Surfactant was a gift from Leo Pharmaceutical Products, Ballerup, Denmark.


   FOOTNOTES
 
Supported by Christiaens BV and the Melssen family.

This article has an online supplement, which is accessible from this issue's table of contents online at www.atsjournals.org

Conflict of Interest Statement: A.H.V. has participated as a speaker in scientific meetings or courses organized and financed by various pharmaceutical companies (Boehringer Ingelheim, Nycomed) and received financial support from Christiaens for the present research project; R.A.L. has no declared conflict of interest; E.H. has participated as a speaker in scientific meetings or courses organized and financed by various pharmaceutical companies (Chiese, Abbott, Boehringer, Altana, Draeger) and has two industry-sponsored grants pending (AltanaPharma, Chiesi); A.D. has no declared conflict of interest; F.V. has no declared conflict of interest; L.A.N. has no declared conflict of interest; J.H.K. has no declared conflict of interest; J.J.H. has no declared conflict of interest; B.L. is a member of the Advisory Board of Halas Pharma GmbH and has shares in that same company and received a research grant from Leo Pharma for surfactant research.

Received in original form December 30, 2003; accepted in final form February 20, 2004


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
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