Surfactant treatment in experimental Escherichia coli pneumonia

Ventilator-Associated Pneumonia in the Neonatal Intensive Care Unit

See Bonus NeoBriefs videos and downloadable teaching slides Intubated infants in the NICU are at risk of developing ventilator-associated pneumonia (VAP), a common type of health care-associated infection. The Centers for Disease Control and Prevention developed guidelines for diagnosing VAP in patients younger than 1 year, which include worsening gas exchange, radiographic findings, and at least 3 defined clinical signs of pneumonia. VAP in infants is treated with empiric antibiotics selected based on local resistance patterns and individualized patient data. Many NICUs have implemented prevention bundles in an effort to decrease VAP by ensuring the cleanest environment for intubated neonates (hand hygiene, sterile handling of equipment), positioning of infants to prevent gastric reflux, and constantly reevaluating for extubation readiness. Although these prevention bundle elements are intuitive and generally low risk, none are based on strong research support. This article reviews the epidemiology, pathogenesis, diagnosis, treatment, and prevention of VAP in NICU patients, focusing on recent evidence, highlighting areas of emerging research, and identifying persistent knowledge gaps.

In vivo effect of pneumonia on surfactant disaturated-phosphatidylcholine kinetics in newborn infants

Background

Bacterial pneumonia in newborns often leads to surfactant deficiency or dysfunction, as surfactant is inactivated or its production/turnover impaired. No data are available in vivo in humans on the mechanism of surfactant depletion in neonatal pneumonia. We studied the kinetics of surfactant's major component, disaturated-phosphatidylcholine (DSPC), in neonatal pneumonia, and we compared our findings with those obtained from control newborn lungs.

Methods

We studied thirty-one term or near-term newborns (gestational age 39.7±1.7 weeks, birth weight 3185±529 g) requiring mechanical ventilation. Fifteen newborns had pneumonia, while 16 newborns were on mechanical ventilation but had no lung disease. Infants received an intratracheal dose of ¹³C labeled dipalmitoyl-phosphatidylcholine at the study start. We measured the amount and the isotopic enrichment of DSPC-palmitate from serial tracheal aspirates by gas chromatography and gas chromatography-mass spectrometry, respectively, and we calculated the DSPC half-life (HL) and pool size (PS) from the isotopic enrichment curves of surfactant DSPC-palmitate.

Results

The mean DSPC amount obtained from all tracheal aspirates did not differ between the two groups. DSPC HL was 12.7 (6.5–20.2) h and 25.6 (17.9–60.6) h in infants with pneumonia compared with control infants (p = 0.003). DSPC PS was 14.1 (6.6–30.9) mg/kg in infants with pneumonia and 34.1 (25.6–65.0) mg/kg in controls, p = 0.042. Myeloperoxidase (MPO) activity, as a marker of lung inflammation, was 1322 (531–2821) mU/ml of Epithelial Lining Fluid (ELF) and 371(174–1080) mU/ml ELF in infants with pneumonia and in controls, p = 0.047. In infants with pneumonia, DSPC PS and HL significantly and inversely correlated with mean Oxygenation Index (OI) during the study (DSPC PS vs. OI R = −0.710, p = 0.004 and HL vs. OI R = −0.525, p = 0.044, respectively).

Conclusions

We demonstrated for the first time in vivo in humans that DSPC HL and PS were markedly impaired in neonatal pneumonia and that they inversely correlated with the degree of respiratory failure.

Inhibition of pulmonary nuclear factor kappa-B decreases the severity of acute Escherichia coli pneumonia but worsens prolonged pneumonia

Introduction

Nuclear factor (NF)-κB is central to the pathogenesis of inflammation in acute lung injury, but also to inflammation resolution and repair. We wished to determine whether overexpression of the NF-κB inhibitor IκBα could modulate the severity of acute and prolonged pneumonia-induced lung injury in a series of prospective randomized animal studies.

Methods

Adult male Sprague-Dawley rats were randomized to undergo intratracheal instillation of (a) 5 × 10⁹ adenoassociated virus (AAV) vectors encoding the IκBα transgene (5 × 10⁹ AAV-IκBα); (b) 1 × 10¹⁰ AAV-IκBα; (c) 5 × 10¹⁰ AAV-IκBα; or (d) vehicle alone. After intratracheal inoculation with Escherichia coli, the severity of the lung injury was measured in one series over a 4-hour period (acute pneumonia), and in a second series after 72 hours (prolonged pneumonia). Additional experiments examined the effects of IκBα and null-gene overexpression on E. coli-induced and sham pneumonia.

Results

In acute pneumonia, IκBα dose-dependently decreased lung injury, improving arterial oxygenation and lung static compliance, reducing alveolar protein leak and histologic injury, and decreasing alveolar IL-1β concentrations. Benefit was maximal at the intermediate (1 × 10¹⁰) IκBα vector dose; however, efficacy was diminished at the higher (5 × 10¹⁰) IκBα vector dose. In contrast, IκBα worsened prolonged pneumonia-induced lung injury, increased lung bacterial load, decreased lung compliance, and delayed resolution of the acute inflammatory response.

Conclusions

Inhibition of pulmonary NF-κB activity reduces early pneumonia-induced injury, but worsens injury and bacterial load during prolonged pneumonia.

The protective effects of Ambroxol in Pseudomonas aeruginosa-induced pneumonia in rats

INTRODUCTION

To evaluate the effect of Ambroxol on the pulmonary surfactant (PS) in rat pneumonia induced by Pseudomonas aeruginosa (PA).

MATERIAL AND METHODS

The pneumonic rats were obtained by injecting ATCC27853 intratracheally. One hundred and twenty SD rats were randomized into four groups: normal saline and Ambroxol was injected intraperitoneally following PA challenge in the PA/NS and PA/AM group; the other two groups were NS/AM and NS/NS. The wet/dry weight ratio (W/D), and pathological changes were assayed. Total proteins (TP), total phospholipid (TPL), and dipalmitoylphosphatidylcholine (DPPC) in bronchial alveolar lavage fluid (BALF) were analysed. Some BALF was cultured for colony counts. Ultrastructural change of the lung was observed by electron microscopy.

RESULTS

The W/D ratio in the PA/AM group was lower than that in the PA/NS group; both were higher than that in the NS/NS group (p < 0.05). There were more neutrophils in the PA/NS group than in the PA/AM group (p < 0.05), and more in the PA/AM group than in the NS/NS group (p < 0.05). The ratio of DSPC/TPL and DSPC/TP in the BALF in PA/NS group was lower than that in the PA/AM group; DSPC/TPL and DSPC/TP ratios also increased in the NS/AM group. The PA colony numbers in the PA/AM group were lower than in the PA/NS group (p > 0.05). In the PA/NS group, vacuolation occurred in the lamellar body of alveolar type 2 cells (AT2) and the PS layer was rough and broken in some areas. In the PA/AM group, the degree of vacuolation of the lamellar body was less than in the PA/NS group.

CONCLUSIONS

Ambroxol could protect rats from pneumonia by improving the level of endogenous PS, especially DPPC.

An official American Thoracic Society workshop report: features and measurements of experimental acute lung injury in animals

Acute lung injury (ALI) is well defined in humans, but there is no agreement as to the main features of acute lung injury in animal models. A Committee was organized to determine the main features that characterize ALI in animal models and to identify the most relevant methods to assess these features. We used a Delphi approach in which a series of questionnaires were distributed to a panel of experts in experimental lung injury. The Committee concluded that the main features of experimental ALI include histological evidence of tissue injury, alteration of the alveolar capillary barrier, presence of an inflammatory response, and evidence of physiological dysfunction; they recommended that, to determine if ALI has occurred, at least three of these four main features of ALI should be present. The Committee also identified key "very relevant" and "somewhat relevant" measurements for each of the main features of ALI and recommended the use of least one "very relevant" measurement and preferably one or two additional separate measurements to determine if a main feature of ALI is present. Finally, the Committee emphasized that not all of the measurements listed can or should be performed in every study, and that measurements not included in the list are by no means "irrelevant." Our list of features and measurements of ALI is intended as a guide for investigators, and ultimately investigators should choose the particular measurements that best suit the experimental questions being addressed as well as take into consideration any unique aspects of the experimental design.

Hypercapnic acidosis attenuates severe acute bacterial pneumonia-induced lung injury by a neutrophil-independent mechanism

OBJECTIVE

Deliberate induction of hypercapnic acidosis protects against lung injury after nonseptic lung injury. In contrast, concerns exist regarding the effects of hypercapnic acidosis in the setting of severe pulmonary sepsis. The potential for the effects of hypercapnic acidosis to be neutrophil-mediated remains to be determined. We investigated whether hypercapnic acidosis--induced by adding CO2 to inspired gas--would protect against severe acute lung injury induced by pulmonary Escherichia coli instillation and the role of neutrophils in mediating this effect.

DESIGN

Prospective randomized animal study.

SETTING

University Research Laboratory.

SUBJECTS

Adult male Sprague-Dawley rats.

INTERVENTIONS

In series 1, after induction of anesthesia and tracheostomy placement, animals were randomized to normocapnia (FICO2 0.00, n = 12) or hypercapnic acidosis (FICO2 0.05, n = 12). E. coli (0.5-3.0 x 10(15) colony-forming units) was instilled intratracheally and the animals were ventilated for 6 hrs to allow a severe acute lung injury to evolve. In series 2, animals were randomized to neutrophil depletion or nondepletion before bacterial instillation, in a three-group design: normocapnia alone (Normo + polymorphonuclear neutrophils [PMN], n = 9), normocapnia with neutrophil depletion (Normo - PMN, n = 9), or hypercapnic acidosis with neutrophil depletion (hypercapnic acidosis - PMN, n = 9). After intratracheal E. coli administration these animals were also ventilated for 6 hrs.

RESULTS

Hypercapnic acidosis protected against evolving pneumonia-induced acute lung injury, attenuating the increase in airway pressure, and the decrement in lung compliance and arterial PO2. However, hypercapnic acidosis did not reduce histologic injury. Hypercapnic acidosis also protected against evolving pneumonia-induced acute lung injury in the presence of neutrophil depletion, reducing both physiologic and histologic indices of lung injury.

CONCLUSIONS

Hypercapnic acidosis reduces indices of intratracheal E. coli induced lung injury by a mechanism that seems to be neutrophil-independent.

Expanded use of surfactant therapy in newborns

Although there is no doubt that administration of exogenous surfactant to very preterm babies who have respiratory distress syndrome is safe and efficacious, surfactant inactivation or deficiency plays a role in the pathophysiology of other pulmonary disorders affecting newborn infants. Preliminary data suggest that there may be a role for surfactant administration to babies who have meconium aspiration syndrome, pneumonia, and possibly bronchopulmonary dysplasia. Further investigation is necessary but seems warranted.

Hypercapnic acidosis does not modulate the severity of bacterial pneumonia-induced lung injury

OBJECTIVE

Deliberate induction of hypercapnic acidosis protects against lung injury after ischemia-reperfusion, endotoxin-induced, and ventilation-induced lung injury. The efficacy of hypercapnic acidosis in bacterial lung infection, a common cause of acute respiratory distress syndrome, is not known. Furthermore, its effect may differ depending on the presence or absence of antibiotic therapy. We investigated whether hypercapnic acidosis-induced by adding CO2 to inspired gas-would protect against acute lung injury induced by pulmonary Escherichia coli instillation in an in vivo model in the presence and absence of effective antibiotic therapy.

DESIGN

Prospective randomized animal study.

SETTING

University research laboratory.

SUBJECTS

Adult male Wistar-Kyoto rats.

INTERVENTIONS

The animals were anesthetized and ventilated. In series 1, rats were administered intravenous ceftriaxone (100 mg x kg) and randomized to normocapnia (Normocapnia-ABx; Fico2 0.00, n = 10) or hypercapnia (Hypercapnia-ABx; Fico2 0.05, n = 10) groups. E. coli (8.4 x 10 colony forming units) was instilled intratracheally. Series 2 animals did not receive antibiotics. They were randomized to normocapnia (Normocapnia, n = 10) or hypercapnia (Hypercapnia, n = 10) groups, and intratracheal E. coli was administered. All animals were ventilated for 6 hrs.

MEASUREMENTS AND MAIN RESULTS

In series 1, there were no differences between Hypercapnia-ABx and Normocapnia-ABx groups with regard to: (a-a)o2 gradient (mean +/- sem; 215 +/- 13 vs. 252 +/- 22 mm Hg), Pao2, bronchoalveolar lavage neutrophil count, static lung compliance, or histologic injury. Lung bacterial yield was not different between the groups. In series 2, in the absence of antibiotic therapy, there were no differences between Hypercapnia and Normocapnia groups in: (a-a)o2 gradient (mean +/- sem, 345 +/- 25 vs. 332 +/- 23 mm Hg), systemic Pao2, bronchoalveolar lavage neutrophil count, or static lung compliance. Lung bacterial yield was not altered by hypercapnia in either series 1 or 2.

CONCLUSIONS

We conclude that hypercapnic acidosis did not alter the magnitude of the lung injury induced by intratracheal E. coli instillation in the presence or absence of antibiotics.

Influence of modified natural and synthetic surfactant preparations on bacterial killing by polymorphonuclear leucocytes

In addition to its biophysical functions, surfactant plays an important role in pulmonary host defense. In this investigation we studied the influence of various commercially available surfactants on the phagocytosis of bacteria that are common pathogens in the neonatal period. Group B streptococci (GBS), Escherichia coli and Staphylococcus aureus were cultured with isolated human polymorphonuclear leucocytes (PMN) and non-specific serum in the presence or absence of different modified natural (Curosurf, Alveofact, Survanta) or totally synthetic, protein-free surfactant preparations (Exosurf, Pumactant). Prior to and after 30 and 60 min of incubation with PMN at different surfactant concentrations (1, 10 or 20 mg/ml), the number of viable bacteria was determined by colony counting. Killing of S. aureus by PMN was not influenced by any of the surfactants. Alveofact and Curosurf had no significant negative impact on phagocytosis. At 20 mg/ml, Curosurf even reduced the number of viable E. coli. Survanta at 10 and 20 mg/ml and Exosurf at all concentrations impaired the killing of non-encapsulated GBS and E. coli. Pumactant at 1-20 mg/ml interfered with the phagocytosis of E. coli. In further experiments we demonstrated that Curosurf did not interfere with the phagocytosis of an encapsulated GBS-strain opsonised by a specific antiserum either. In additional experiments we analysed the influence of the different surfactants on the release of reactive oxygen metabolite by PMN and found that the changes in nitroblue tetrazolium reduction did not necessarily correlate with the findings of the studies on killing. In conclusion, we found that killing by PMN was influenced by the bacterial species and the composition and concentration of the different surfactant preparations. The strongest impairment in phagocytic function of PMN was observed with the protein-free synthetic surfactant Exosurf, a phospholipid preparation that contains the alcohols hexadecanol and tyloxapol as spreading agents.

Surfactant use for neonatal lung injury: beyond respiratory distress syndrome

Surfactant has led to a significant reduction in neonatal mortality for premature infants with lung immaturity and respiratory distress. However, surfactant therapy has been shown to be effective in the treatment of a number of other neonatal respiratory disorders and the evidence for surfactant use in such circumstances is presented. Meconium aspiration is characterised by severe atelectasis, the influx of neutrophils, edema, and hyaline membranes, with decreased levels of SP-A and SP-B and the large aggregate fraction of lung surfactant, and altered surfactant surface morphology. Meconium contains cholesterol, free fatty acids and bilirubin all of which can interfere with surfactant function in a dose-dependent fashion. Providing larger amounts of surfactant can overcome some of this inhibition. Animal models of meconium aspiration treated with surfactant have improved histology, lung mechanics and gas exchange. Studies in human infants with meconium aspiration have found elevated concentrations of total protein, albumin, and membrane-derived phospholipid in lung lavage fluid, and haemorrhagic pulmonary edema. Clinical studies in such neonates have reported improved gas exchange and clinical outcomes following surfactant treatment. More recently surfactant lavage has been shown to be a potentially efficacious therapy for such infants. The inflammatory exudate containing plasma proteins and cytokines which accompanies neonatal pneumonia may inactivate surfactant. Surfactant treatment given to animals following the tracheal instillation of group B Streptococcal resulted in significantly less bacterial growth and improved lung function. Small clinical experiences have demonstrated the benefit of surfactant to infants with pneumonia/sepsis. Pulmonary haemorrhage, which some consider a complication of surfactant therapy, has also been effectively managed using surfactant instillation. The hemoglobin and red blood cell lipids may act to inhibit natural surfactant and treatment with surfactant has been shown to improve outcome for infants with pulmonary haemorrhage. Animal models of congenital diaphragmatic hernia (CDH) have hypoplastic lungs with evidence of decreased lamellar bodies in their type II pneumocytes and resultant surfactant deficiency, and respond to surfactant replacement with improved gas exchange and lung mechanics. The lungs of human infants with CDH contain less phospholipids and phosphatidylcholine per milligram of DNA than control infants. Case reports have reported a benefit of surfactant for infants with CDH. In the near-term infants with severe respiratory distress, surfactant is one of the therapies along with inhaled nitric oxide and high frequency ventilations, that have resulted in improved outcomes. Surfactant treatment may be of significant benefit in newborn infants with respiratory compromise secondary to a number of insults, and further prospective evidence of its efficacy in such disorders is needed.

Experimental models of pulmonary infection

Experimental models of pulmonary infection are being discussed, focused on various aspects of good experimental design, such as choice of animal species and infecting strain, and route of infection/inoculation techniques (intranasal inoculation, aerosol inoculation, and direct instillation into the lower respiratory tract). In addition, parameters to monitor pulmonary infection are being reviewed such as general clinical signs, pulmonary-associated signs, complication of the pulmonary infection, mortality rate, and parameters after dissection of animals. Examples of pulmonary infection models caused by bacteria, fungi, viruses or parasites in experimental animals with intact or impaired host defense mechanisms are shortly summarized including key-references.

Total extracellular surfactant is increased but abnormal in a rat model of gram-negative bacterial pneumonia

An in vivo rat model was used to evaluate the effects of Escherichia coli pneumonia on lung function and surfactant in bronchoalveolar lavage (BAL). Total extracellular surfactant was increased in infected rats compared with controls. BAL phospholipid content in infected rats correlated with the severity of alveolar-capillary leak as reflected in lavage protein levels (R(2) = 0.908, P < 0.0001). Western blotting showed that levels of surfactant protein (SP)-A and SP-D in BAL were significantly increased in both large and small aggregate fractions at 2 and 6 h postinstillation of E. coli. SP-B was also increased at these times in the large aggregate fraction of BAL, whereas SP-C levels were increased at 2 h and decreased at 6 h relative to controls. The small-to-large (S/L) aggregate ratio (a marker inversely proportional to surfactant function) was increased in infected rats with >50 mg total BAL protein. There was a significant correlation (R(2) = 0.885, P < 0.0001) between increasing S/L ratio in BAL and pulmonary damage assessed by total protein. Pulmonary volumes, compliance, and oxygen exchange were significantly decreased in infected rats with >50 mg of total BAL protein, consistent with surfactant dysfunction. In vitro surface cycling studies with calf lung surfactant extract suggested that bacterially derived factors may have contributed in part to the surfactant alterations seen in vivo.

Surfactant alteration and replacement in acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a frequent, life-threatening disease in which a marked increase in alveolar surface tension has been repeatedly observed. It is caused by factors including a lack of surface-active compounds, changes in the phospholipid, fatty acid, neutral lipid, and surfactant apoprotein composition, imbalance of the extracellular surfactant subtype distribution, inhibition of surfactant function by plasma protein leakage, incorporation of surfactant phospholipids and apoproteins into polymerizing fibrin, and damage/inhibition of surfactant compounds by inflammatory mediators. There is now good evidence that these surfactant abnormalities promote alveolar instability and collapse and, consequently, loss of compliance and the profound gas exchange abnormalities seen in ARDS. An acute improvement of gas exchange properties together with a far-reaching restoration of surfactant properties was encountered in recently performed pilot studies. Here we summarize what is known about the kind and severity of surfactant changes occurring in ARDS, the contribution of these changes to lung failure, and the role of surfactant administration for therapy of ARDS.

Effect of surfactant and specific antibody on bacterial proliferation and lung function in experimental pneumococcal pneumonia

OBJECTIVE

To investigate the effect of surfactant and specific antibody on bacterial proliferation in experimental pneumococcal pneumonia.

METHODS

Near-term newborn rabbits received a standard dose (10(7)) of type 3 pneumococci via the airways. Control animals were sacrificed 1 minute later. Other animals were ventilated for 5 hours and treated via the tracheal cannula with surfactant (Curosurf 200 mg/kg), a mixture of surfactant and a polyclonal antipneumococcal antibody, the antibody without surfactant, or saline.

RESULTS

There was a significant bacterial proliferation in lung tissue in all animals ventilated for 5 hours. Bacterial growth, expressed as log10 colony forming units (CFU) per gram of lung tissue was less prominent in animals treated with a mixture of surfactant and specific antibody than in animals treated with antibody alone (median, 7.51, range, 6.80--7.70 vs. median, 7.92, range, 7.07--8.50; P < 0.05). Dynamic lung-thorax compliance was improved with surfactant or surfactant plus antibody in comparison with saline or antibody alone.

CONCLUSIONS

The data suggest that the suppressive effect of the antibody on bacterial proliferation becomes evident only when surfactant is administered together with the antibody.

Influence of modified natural or synthetic surfactant preparations on growth of bacteria causing infections in the neonatal period

Connatal bacterial pneumonia is common in neonates. Animal studies and initial clinical reports indicate that surfactant dysfunction is involved in the pathophysiology of severe neonatal pneumonia. Since respiratory distress syndrome and connatal pneumonia may be difficult to differentiate in the first hours of life, neonates with respiratory failure due to bacterial infections might receive surfactant. Under such conditions surfactant components might be catabolized by bacteria and promote bacterial growth. We therefore investigated the influence of three modified natural (Curosurf, Alveofact, and Survanta) and two synthetic (Exosurf and Pumactant) surfactant preparations on the growth of bacteria frequently cultured from blood or tracheal aspirate fluid in the first days of life. Group B streptococci (GBS), Staphyloccocus aureus, and Escherichia coli were incubated in a nutrient-free medium (normal saline) for 5 h at 37 degrees C, together with different surfactants at concentrations of 0, 1, 10, and 20 mg/ml. With the exception of E. coli, incubation in saline alone led to a variable decrease in CFU. In the presence of Alveofact, Exosurf, and Pumactant the decline in bacterial numbers was less marked than in saline alone. Curosurf was bactericidal in a dose-dependent fashion for GBS and had a strong negative impact on the growth of a GBS subtype that lacked the polysaccharide capsule. In contrast, Survanta (10 and 20 mg/ml) significantly promoted the growth of E. coli, indicating that surfactant components may actually serve as nutrients. We conclude that bacterial growth in different surfactant preparations is influenced by microbial species and the composition and dose of the surfactant. Further studies are necessary to elucidate the mechanisms behind our findings and to evaluate the effects of surfactant on bacterial growth in vivo.

Improvement in respiratory compliance after surfactant therapy evaluated by a new method

Descriptions of the effects of intratracheally applied surfactant on respiratory system compliance (C(rs)) have been somewhat controversial because the commonly used methods for assessing pulmonary function were designed for a linear pressure/volume (P/V) relation of the respiratory system. In infants with lung disease a linear P/V relation cannot be expected. Therefore, a new method (APVNL) was employed which enabled us to calculate respiratory system compliance (C(rs)) and resistance (R(rs)) based on changes in volume (V). This method is independent of the P/V relation, and was used to assess the effects of intratracheal instillation of surfactant. Fourteen infants (gestational age, 24 to 30 weeks) with respiratory distress syndrome were treated with bovine surfactant intratracheally while the fractional inspired oxygen concentration (FiO(2)) exceeded 50%. C(rs) was evaluated for the infants using the APVNL method and the method of linear regression (LR) based on the equation of motion designed for linear P/V relationships. Two hours after surfactant treatment, the median reduction of FiO(2) was 33% (95% CI: 20-50%; P < 0.01). There was no correlation between the change in FiO(2) and the change in C(rs), using either the APVNL method or the LR method. Two hours after surfactant treatment, the median improvement in C(rs) was 0.37 mL/cmH(2)O/kg (95% CI: 0.07-1. 16 mL/cmH(2)O) at a change in V of 1 mL/kg (P < 0.02) and 0.23 mL/cmH(2)O/kg (95% CI: 0-0.57 mL/cmH(2)O) at a change in V of 2 mL/kg (P < 0.05) when the APVNL method was used. The LR method could not show a significant change in C(rs) after surfactant treatment. Further, R(rs) did not show significant changes 2 hr after surfactant administration. We conclude that the APVNL method is more appropriate for evaluating changes of C(rs) elicited by surfactant treatment than the LR method. The APVNL method demonstrated significant initial improvements in compliance as lung volumes were increased; there were no significant further decreases in C(rs) as peak inspiratory pressures and the upper limits of tidal volume were approached.

Combined treatment with surfactant and specific immunoglobulin reduces bacterial proliferation in experimental neonatal group B streptococcal pneumonia

Neonates suffering from group B streptococcal (GBS) pneumonia often lack type-specific opsonizing antibodies. We studied the influence of combined intratracheal treatment with surfactant and a specific antibacterial polyclonal antibody (IgG fraction) on bacterial proliferation and lung function in an animal model of GBS pneumonia. Near-term newborn rabbits received an intratracheal injection of either the specific IgG antibody, nonspecific IgG, surfactant, a mixture of surfactant and the antibody, or 0.9% saline. At 30 min the rabbits were infected with a standard dose (10(8)) of the encapsulated GBS strain 090 Ia. After 5 h of mechanical ventilation the mean estimated increase in bacterial number in lung homogenate (log10 colonies/g) was 0.76 in the antibody group, 0.92 in the nonspecific IgG group, 0.55 in the surfactant group, and 1.29 in the saline group. A mean decrease in bacterial number (-0.05) was observed in the group that received combined treatment with surfactant and antibody (p < 0.05 versus all other groups). Lung-thorax compliance was significantly higher in both groups of surfactant-treated animals compared with saline or IgG treatment. We conclude that in experimental neonatal GBS pneumonia combined treatment with surfactant and a specific immunoglobulin against GBS reduced bacterial proliferation more effectively than either treatment alone.

Surfactant replacement therapy. An update on applications

Surfactant replacement therapy has been shown to be an effective and often life-saving treatment for newborn infants with respiratory distress syndrome (RDS). This article provides the clinician with an update regarding the various other applications of surfactant replacement therapy, as well as issues related to surfactant administration for the preparations approved for use in pediatric patients.