Positive end-expiratory pressure preserves surfactant function in preterm lambs

Neonatal resuscitation: raising the bar

PURPOSE OF REVIEW

To provide an overview of neonatal resuscitation practices with an emphasis on interventions that are not currently accepted or adapted into existing resuscitation guidelines.

RECENT FINDINGS

Current resuscitation guidelines do not contain specific guidelines for the approach to the extremely low birth weight infant. The differences in environment and management between the neonatal ICU and delivery room are striking and are magnified in the resuscitation of extremely low birth weight infants for whom maintenance of a neutral thermal environment is essential. The use of a polyethylene wrap applied at delivery has been shown to reduce the occurrence of hypothermia and decrease mortality. There is substantial evidence that term and near-term newborn infants can be effectively resuscitated with room air, and recent follow-up studies have demonstrated that this approach is not associated with increased significant differences in neurologic handicap, somatic growth, or developmental milestones when compared with the use of 100% oxygen. The safety and potential benefits of this approach require prospective evaluation in the premature and especially extremely low birth weight infant. There is preexisting evidence that demonstrates that the use of prolonged inflations and t-piece resuscitators may be advantageous during resuscitation, but not all guidelines support these interventions. Although regulated continuous positive airway pressure, pulse oximeters, and blenders are routinely used once an infant is admitted to the neonatal ICU, none of these interventions is recommended in the delivery area. Although prospective studies have demonstrated that the use of colorimetric CO2 detectors significantly decreases the time to recognize misplaced endotracheal tubes placed during resuscitation, their use is not required by current guidelines. The duration of an intubation attempt during resuscitation had never been prospectively evaluated, and our recent findings suggest that a limit of 30 seconds is well tolerated and provides adequate time for a successful attempt.

SUMMARY

There is significant potential for improvement in current resuscitation environments and interventions that will only be realized through further prospective research.

Neonatal resuscitation: review of ventilation equipment and survey of practice in Australia and New Zealand

OBJECTIVE

The equipment used to provide positive pressure ventilation at neonatal resuscitation varies between institutions. Available devices were reviewed and their use surveyed in a geographically defined region. The aim of this study was to establish which resuscitation equipment is used at neonatal intensive care units in Australia and New Zealand.

METHODS

A questionnaire was sent to a neonatologist at each of the 29 neonatal intensive care units in Australia and New Zealand, asking which resuscitation equipment they used. If it was not returned, follow up was by email and telephone.

RESULTS

Data was obtained from all units. Round face masks are used at all centres. Anatomically shaped masks are infrequently used at two of the three centres (10%) that have them. Straight endotracheal tubes are used exclusively at 23 (79%) centres. Shouldered tubes are used infrequently at three of the six centres that have them. The Laerdal Infant Resuscitator self-inflating bag is used at 22 (76%) centres. Flow-inflating bags are used at 12 (41%) centres. The Neopuff Infant Resuscitator is used at 14 (48%) centres. Varying oxygen concentrations are provided at delivery at 6/25 (24%) centres.

CONCLUSIONS

There is a paucity of evidence for the efficacy of the equipment used currently to resuscitate newborn infants. This complete survey of the tertiary centres in a geographical region shows considerable variation in practice, reflecting this lack of evidence and consequent uncertainty among clinicians. Further research is necessary to determine which devices are preferable for this most important and common intervention.

Lung inflammatory responses to intratracheal interleukin-1alpha in ventilated preterm lambs

Interleukin-1alpha is an early response proinflammatory cytokine that has been associated with chorioamnionitis and preterm labor, brain injury, and bronchopulmonary dysplasia. However, IL-1alpha also can increase expression of surfactant proteins and induce lung maturation in the preterm fetus. We measured the effects of IL-1alpha given by intratracheal instillation (IT) and compared the responses with injection of i.v. IL-1alpha in surfactant-treated and ventilated premature lambs. IT recombinant ovine IL-1alpha at doses of 5 and 50 microg/kg caused a similar large recruitment of neutrophils into the bronchoalveolar lavage fluid. The neutrophils expressed CD11b, CD14, and CD44, but did not produce increased amounts of H(2)O(2). Cells from the bronchoalveolar lavage fluid had increased expression of proinflammatory cytokines, which also were increased in mRNA from lung tissue. The IT IL-1alpha also suppressed the expression of surfactant protein-C mRNA. Systemic effects were decreased neutrophils in blood, decreased lung function, increased heart rate, and hypotension or death in the 50 microg/kg IL-1alpha IT group and only decreased neutrophils in the blood in the 5 microg/kg IL-1alpha IT group. The i.v. IL-1alpha caused no lung inflammation or injury but did result in severe neutropenia and hypotension leading to early death. IT IL-1alpha can cause intense lung inflammation and systemic shock in ventilated preterm lungs.

Initial responses to ventilation of premature lambs exposed to intra-amniotic endotoxin 4 days before delivery

Preterm delivery is frequently preceded by chorioamnionitis, resulting in exposure of the fetal lung to inflammation. We hypothesized that ventilation of the antenatally inflamed lung would result in amplification of the lung injury. Therefore, we induced fetal lung inflammation with intra-amniotic endotoxin (10 mg of Escherichia coli 055:B5) 4 days before premature delivery at 130 days of gestation. Lung function and lung inflammation after surfactant treatment and 4 h of mechanical ventilation were evaluated. Inflammatory cell numbers in amniotic fluid were increased >10-fold by antenatal endotoxin exposure. Antenatal endotoxin exposure had minimal effects on blood pressure, heart rate, lung compliance, and blood gas values. The endotoxin-exposed lungs required higher ventilation pressures. Ventilation did not increase the number of inflammatory cells or the protein in bronchoalveolar lavage fluid of the endotoxin-exposed animals above that measured in endotoxin-exposed fetuses that were not ventilated. IL-1β, IL-6, and IL-8 mRNA in cells from bronchoalveolar lavage fluid were increased by antenatal endotoxin exposure but not changed by ventilation. IL-1β and IL-8 protein was increased in lung tissue by 4 h of ventilation. Very little inflammation was induced by ventilation in this premature lamb model of surfactant treatment and gentle ventilation. After lung inflammation was induced by intra-amniotic endotoxin injection, ventilation did not increase lung injury.

Rapid compressions in a captive bubble apparatus are isothermal

Captive bubbles are commonly used to determine how interfacial films of pulmonary surfactant respond to changes in surface area, achieved by varying hydrostatic pressure. Although assumed to be isothermal, the gas phase temperature (Tg) would increase by >100 degrees C during compression from 1 to 3 atm if the process were adiabatic. To determine the actual change in temperature, we monitored pressure (P) and volume (V) during compressions lasting <1 s for bubbles with and without interfacial films and used P x V to evaluate Tg. P x V fell during and after the rapid compressions, consistent with reductions in n, the moles of gas phase molecules, because of increasing solubility in the subphase at higher P. As expected for a process with first-order kinetics, during 1 h after the rapid compression P x V decreased along a simple exponential curve. The temporal variation of n moles of gas was determined from P x V >10 min after the compression when the two phases should be isothermal. Back extrapolation of n then allowed calculation of Tg from P x V immediately after the compression. Our results indicate that for bubbles with or without interfacial films compressed to >3 atm within 1 s, the change in Tg is <2 degrees C.

PEEP--a "cheap" and effective lung protection

Mechanical ventilation is a complex therapy with several different parameters which can be altered. In preterm and term infants, more attention has been paid to the levels of peak inspiratory pressure than to the positive end-expiratory pressure (PEEP). An awareness that lung protection can be conferred by an appropriate level of PEEP has increasingly stimulated a renewed interest in achieving the "best PEEP" strategy. We review the history of the introduction of PEEP therapy, some of the early demonstrations of its potential for mischief, the evidence on what levels of PEEP are appropriate in infants, some data concerning the lung-protective value of PEEP and finally some recent efforts at defining measures to determine the so-called "best PEEP". Some of this work has been performed in adults with the acute respiratory distress syndrome. In newborns, we are regrettably forced to conclude that there is, for the immediate present, no easy substitute for sensible clinical observations coupled with a judicious and cautious adjustment of PEEP. We anticipate that a more logical application of PEEP with individualisation of therapy, based on a pressure-volume relationship, will in future enable targeted tests of PEEP as a lung-protection strategy.

Effects of high PCO2 on ventilated preterm lamb lungs

High PCO(2) levels attenuate reperfusion injury and ventilation-induced injury in isolated and perfused lungs. We asked whether premature lambs could tolerate 6 h of ventilation with a PCO(2) >80 mm Hg and whether the high PCO(2) modulated the ventilator-induced injury. Preterm surfactant-treated lambs were ventilated for 30 min with a high tidal volume (V(T)) to induce lung injury. The lambs then were ventilated for 5.5 h with a V(T) of 6-9 mL/kg to achieve a PCO(2) of 40-50 mm Hg in the control group. CO(2) was added to the ventilator circuit of a high PCO(2) group to maintain an average PCO(2) of 95 +/- 5 mm Hg. The high PCO(2) lambs had heart rates, blood pressures, plasma cortisol values, and oxygenation equivalent to the control lambs. The lungs of the high PCO(2) group had significantly higher gas volumes and had less lung injury by histopathology. Indicators of inflammation (white blood cells, hydrogen peroxide production, and IL-1beta and IL-8 cytokine mRNA expression in cells from the alveolar wash) qualitatively indicated less injury in the high PCO(2) group, although the differences were not significant. Preterm lambs tolerated a very high PCO(2) without physiologic compromise for 6 h. The high PCO(2) may attenuate ventilator-induced lung injury in the preterm.

Surfactant phosphatidylcholine half-life and pool size measurements in premature baboons developing bronchopulmonary dysplasia

Because minimal information is available about surfactant metabolism in bronchopulmonary dysplasia, we measured half-lives and pool sizes of surfactant phosphatidylcholine in very preterm baboons recovering from respiratory distress syndrome and developing bronchopulmonary dysplasia, using stable isotopes, radioactive isotopes, and direct pool size measurements. Eight ventilated premature baboons received (2)H-DPPC (dipalmitoyl phosphatidylcholine) on d 5 of life, and radioactive (14)C-DPPC with a treatment dose of surfactant on d 8. After 14 d, lung pool sizes of saturated phosphatidylcholine were measured. Half-life of (2)H-DPPC (d 5) in tracheal aspirates was 28 +/- 4 h (mean +/- SEM). Half-life of radioactive DPPC (d 8) was 35 +/- 4 h. Saturated phosphatidylcholine pool size measured with stable isotopes on d 5 was 129 +/- 14 micro mol/kg, and 123 +/- 11 micro mol/kg on d 14 at autopsy. Half-lives were comparable to those obtained at d 0 and d 6 in our previous baboon studies. We conclude that surfactant metabolism does not change during the early development of bronchopulmonary dysplasia, more specifically, the metabolism of exogenous surfactant on d 8 is similar to that on the day of birth. Surfactant pool size is low at birth, increases after surfactant therapy, and is kept constant during the first 2 wk of life by endogenous surfactant synthesis. Measurements with stable isotopes are comparable to measurements with radioactive tracers and measurements at autopsy.

Decreased indicators of lung injury with continuous positive expiratory pressure in preterm lambs

Continuous positive airway pressure (CPAP) is being used clinically to avoid mechanical ventilation of preterm infants as a strategy to minimize lung injury. There is little experimental information about how CPAP might minimize lung injury after preterm birth. We induced preterm labor in antenatal glucocorticoid-treated sheep carrying twins at 133 d gestation with an inhibitor of progesterone synthesis. The lambs delivered spontaneously approximately 2 d later and were randomized to three groups: no ventilation (n = 4), conventional mechanical ventilation to a target PCO(2) of 40 mm Hg (n = 5), or CPAP using a bubble CPAP device set to deliver 5 cm H(2)O pressure (n = 6). The CPAP lambs breathed without distress and maintained PCO(2) values of approximately 60 mm Hg. At 2 h of age, the lungs of the CPAP lambs held 74 +/- 4 mL/kg air at 40 cm H(2)O pressure, which was more than the 60 +/- 3 mL/kg for the ventilated lambs (p < 0.05). Lymphocyte and monocyte numbers in alveolar washes were equivalent in the unventilated, ventilated, and CPAP lambs. However, no neutrophils were found in the unventilated lambs, and the ventilated lambs had 6.6 times more neutrophils in alveolar washes than did the CPAP lambs (p < 0.05). The cells in alveolar wash from CPAP lambs contained less hydrogen peroxide than did the cells from ventilated lambs (p < 0.05). In this model in preterm lambs CPAP results in lower indicators of acute lung injury than does mechanical ventilation during the first 2 h of life.

Postnatal lung inflammation increased by ventilation of preterm lambs exposed antenatally to Escherichia coli endotoxin

Chorioamnionitis resulting in exposure of the fetal lung to inflammation is frequent before preterm delivery. The initiation of mechanical ventilation in the preterm recruits granulocytes to the lungs and increases proinflammatory cytokine expression in the lungs. We hypothesized that when the prematurely born newborn with chorioamnionitis was ventilated, inflammation would increase. Therefore, we asked whether inflammatory exposure to the fetal lung caused by intra-amniotic endotoxin (10 mg, Escherichia coli 055:beta 5) given at 100 d gestation would alter the inflammatory responses to the mechanical ventilation in surfactant-treated preterm lambs delivered at 130 d gestation. Cells in alveolar washes, proinflammatory cytokine expression, and surfactant protein mRNA expression were not different for saline and endotoxin exposed lambs that were not ventilated. The endotoxin- and saline-exposed control animals had similar lung function for 6 h of ventilation. Bronchoalveolar lavage fluid from the ventilated and antenatal endotoxin-exposed animals contained 5.7 times more monocytes, 12 times more lymphocytes, and a nonsignificant increase in neutrophils. Cells from the bronchoalveolar lavage fluid expressed 3-fold more IL-6 and IL-8 mRNA than did cells from the saline exposed comparison animals. An antenatal exposure of the fetal lung to endotoxin enhanced the subsequent inflammatory response of the ventilated preterm lung.

Multicenter, randomized, controlled study of porcine surfactant in severe respiratory syncytial virus-induced respiratory failure

OBJECTIVE: Recently, natural exogenous surfactant replacement has been used in experimental models and clinical trials for the treatment of severe respiratory syncytial virus (RSV) disease. The present study was aimed at verifying this hypothesis and confirming the results of our previous pilot study by assessing the effect of surfactant treatment in mechanically ventilated infants with severe RSV-induced respiratory failure. DESIGN: Multicenter, randomized, controlled study. SETTING: Six pediatric intensive care units staffed by full-time intensive care physicians. PATIENTS: A total of 40 infants (20 treated and 20 controls) with RSV-induced respiratory failure requiring conventional mechanical ventilation (CMV) were randomly assigned to either exogenous surfactant (treated group) or conventional treatment (control group) over a 1-yr period. INTERVENTIONS: Fifty milligrams per kilogram of body weight of porcine-derived natural surfactant (Curosurf) was administered. The drug was instilled by means of a syringe attached to a small suction catheter inserted into the endotracheal tube down to its tip, momentarily disconnecting the patient from CMV. Main Outcome Measures: The assessment consisted of the following outcome variables: duration of CMV, length of intensive care unit stay, gas exchange, respiratory mechanics, re-treatment need, complications, and mortality. RESULTS: The two groups were similar with regard to demographics, Pediatric Risk of Mortality scores, and baseline Pao(2)/Fio(2), Paco(2), and ventilator settings. A marked increase in Pao(2)/Fio(2) and decrease in Paco(2) were observed in the treated group after surfactant administration. Hemodynamic parameters remained unchanged throughout the study period. Peak inspiratory pressure and static compliance were similar at baseline in the two groups. A decrease in peak inspiratory pressure and increase in static compliance were observed in the treated group after surfactant administration. Among surfactant-treated patients, 15 received the treatment within 24 hrs of admission, whereas the remainder (five patients) were treated later. Among children who were treated later, three needed an additional dose of surfactant. None of the children treated within 24 hrs needed an additional dose. Duration of CMV and length of stay in the intensive care unit were significantly shorter in the treated group (4.6 +/- 0.8 and 6.4 +/- 0.9 days, respectively) compared with the control group (5.8 +/- 0.7 and 8.2 +/- 1.1 days, respectively) (p <.0001). No relevant complications were observed, and all the infants survived. CONCLUSIONS: Consistent with our previous study and others, this study shows that surfactant therapy improves gas exchange and respiratory mechanics and shortens CMV and intensive care unit stay in infants with severe RSV-induced respiratory failure.

Injury responses to different surfactants in ventilated premature lamb lungs

The lung of the preterm infant is easily injured and an initial indication of the injury is an inflammatory response. Surfactant treatment and gentle ventilation will minimize the initiation and progression of injury. We asked if the initial lung injury response differed when preterm ventilated lambs were treated with complete natural sheep surfactant, a lipid extract of sheep surfactant, a surfactant used to treat RDS (Survanta), or a synthetic surfactant containing recombinant SP-C (Venticute). We used a gentle style of ventilation and a positive end expiratory pressure of 4 cmH(2)0 to minimize injury. The surfactants were not distinguishable based on gas exchange, compliance or lung gas volumes over the 6h ventilation period. When compared with unventilated controls the ventilated lambs had increased protein and inflammatory cells in alveolar lavages. The cells from the alveolar lavages produced more H(2)0(2), expressed more surface adhesion antigens and CD-14 receptors, and expressed more mRNA for the pro-inflammatory cytokines IL-1 beta and IL-8 than did cells from unventilated lungs. Lung tissue expressed primarily increased IL-6 mRNA relative to unventilated controls. However, there were no consistent differences in any of the inflammatory indicators between the different surfactant treated groups. Because endotoxin free natural surfactant containing SP-A was not superior to three other surfactants containing differing amounts of the surfactant proteins, additions of these proteins to clinical surfactants may not decrease the indicators of lung inflammation that accompany the initiation of ventilation of the preterm lung.

Neonatal respiratory failure

The classic entity of neonatal distress syndrome, as a lung disease expressing predominant surfactant deficiency, is currently changing to a more complex disease of the developing lung as a result of the number of extremely immature preterm infants. Prenatal factors, such as the fetal inflammatory response syndrome influence short- and long-term outcome in these premature infants presenting with respiratory distress syndrome at birth. Therefore, various previously dismissed treatment strategies, such as surfactant prophylaxis or newer anti-inflammatory approaches have to be reinvestigated in this emerging population. Despite the resurrection of a new picture of bronchopulmonary dysplasia, lung injury induced by mechanical ventilation remains a major issue in neonatal intensive care. With the advance in understanding of mechanical ventilation, it is becoming evident, that improvement in outcome can not be achieved by restoring normal lung physiology in the diseased lung using sophisticated ventilators and ventilation modes. A more disease specific ventilator strategy that will target as early as possible homogenous lung opening while at the same time avoiding overdistention of the lung, has the potential to affect outcome. The possible antiinflammatory properties of surfactant-proteins, nitric oxide and corticosteroids, despite some drawbacks, may show to have a synergistic effect. However, this needs further exploration.

Intratracheal endotoxin causes systemic inflammation in ventilated preterm lambs

Intratracheal endotoxin causes acute inflammation in the adult lung, and injurious styles of mechanical ventilation can result in systemic inflammation derived from the lungs. We asked how ventilated premature and near-term lungs responded to intratracheal endotoxin and if systemic inflammation occurred. Lambs delivered at 130 d gestational age (GA) were treated with surfactant or surfactant plus endotoxin (0.1 mg/kg or 10 mg/kg) (Escherichia coli, serotype O55:B5) and were ventilated for 6 h. Both endotoxin doses resulted in impaired gas exchange and systemic inflammation in the preterm lambs. Lambs at 141 d GA (term 146 d) were given either 10 mg/kg intratracheal endotoxin, 10 mg/kg endotoxin plus high tidal volume ventilation for the first 30 min of life, or 5 microg/kg endotoxin given intravenously. Endotoxin alone (10 mg/kg) caused lung inflammation but no systemic effects after 6 h of ventilation. Lambs given 10 mg/kg endotoxin plus high tidal volume ventilation or 5 microg/kg endotoxin intravenously had decreased gas exchange and systemic inflammation. Endotoxin was detected in the plasma of lambs at 130 d GA but not at 141 d GA. Inflammation in the lungs was more severe in preterm animals. Mechanical ventilation of the endotoxin-exposed preterm lung resulted in systemic effects at a low endotoxin dose and without high tidal volume ventilation.

Deficiency of SP-B reveals protective role of SP-C during oxygen lung injury

Although the surface properties of surfactant protein (SP)-B and SP-C are similar, the contributions that either protein may make to lung function have not been identified in vivo. Mutations in SP-B cause lethal respiratory failure at birth; however, SP-B null mice are deficient in both SP-B and SP-C. To identify potential contributions of SP-C to lung function in vivo, the following transgenic mice were generated and exposed to 95% O(2) for 3 days: (SP-B(+/+),SP-C(+/+)), (SP-B(+/+), SP-C(-/-)), (SP-B(+/-),SP-C(+/+)), (SP-B(+/-),SP-C(+/-)), and (SP-B(+/-),SP-C(-/-)). Hyperoxia altered pressure-volume curves in mice that were heterozygous for SP-B, and these values were further decreased in (SP-B(+/-),SP-C(-/-)) mice. Likewise, alveolar interleukin (IL)-6 and IL-1 beta were maximally increased by O(2) exposure of (SP-B(+/-),SP-C(-/-)) mice compared with the other genotypes. Lung hysteresivity was lower in the (SP-B(+/-),SP-C(-/-)) mice. Surfactant isolated from (SP-B(+/+),SP-C(-/-)) and (SP-B(+/-),SP-C(-/-)) mice failed to stabilize the surface tension of microbubbles, showing that SP-C plays a role in stabilization or recruitment of phospholipid films at low bubble radius. Genetically decreased levels of SP-B combined with superimposed O(2)-induced injury reveals the distinct contribution of SP-C to pulmonary function in vivo.

Volutrauma. What is it, and how do we avoid it?

Lung injury can be initiated at birth with the delivery room resuscitation. Adequate tidal volume must be achieved gradually and adjusted with each subsequent breath to achieve adequate, but not excessive, tidal volume delivery. Time constants vary greatly within the lung because some alveoli are collapsed, and some are inflated. Excessive pressure or volume may lead to high stretch injury when already open alveoli are overdistended. Sufficient alveoli must be recruited to establish the optimal functional residual capacity. This establishes an inflation history of the lung that tends to resist alveolar collapse at the end of expiration, provided that adequate mean airway pressure is provided throughout the ventilatory cycle. The best volume of inflation is achieved at the lowest pressure cost. Maintaining alveolar recruitment with the use of exogenous surfactant and positive end-expiratory pressure avoids alveolar collapse and injury with succeeding distending breaths. Although there have been significant advances in neonatal respiratory care, further improvement in outcomes may be expected by successfully avoiding ventilator-induced lung injury.

Biology of surfactant

Surfactant is a metabolically active assembly of phospholipids and surfactant-specific proteins that is essential for normal lung mechanics. The surfactant proteins SP-A and SP-D also have important innate host defense functions. Surfactant metabolism in the developing lung differs from the adult lung by having slower kinetics of secretion with a longer half-life and more efficient recycling. Ventilation styles that injure the lung also result in altered surfactant function.

Effects of ventilation with different positive end-expiratory pressures on cytokine expression in the preterm lamb lung

Ventilator-induced lung injury increases proinflammatory cytokines in the adult lung. We asked if positive end-expiratory pressure (PEEP) affects proinflammatory cytokine mRNA expression in the preterm lung. Preterm lambs at 129 +/- 3 d gestation were treated with 100 mg/kg recombinant human surfactant protein-C surfactant and ventilated for 2 or 7 h with 0, 4, or 7 cm H(2)O of PEEP. Unventilated fetal lambs were used as controls. Within 2 h of ventilation, alveolar total protein and activated neutrophils were increased and expression of mRNAs for the proinflammatory cytokines interleukin (IL)-1beta, IL-6, IL-8, and tumor necrosis factor-alpha (TNF-alpha) was increased in lung tissue of all ventilated animals relative to unventilated controls. Alveolar protein and neutrophils were higher for 0 and 7 PEEP animals than 4 PEEP animals. IL-1beta, IL-6, and IL-8 mRNAs were significantly elevated in animals ventilated with 0 PEEP compared with 4 PEEP. The percentage fractional area of collapsed alveoli was significantly higher for 0 PEEP compared with 4 and 7 PEEP groups. Mechanical ventilation increased the expression of proinflammatory mediators in surfactant-treated preterm lungs and the use of 4 PEEP minimized this response.

Prevention of bronchopulmonary dysplasia

The clinical syndrome of bronchopulmonary dysplasia (BPD) in preterm infants results primarily from an arrest of lung vascular and alveolar development. The most likely mediators are proinflammatory cytokines that are induced by antenatal exposure to infection, postnatal ventilation, and oxygen exposure. New epidemiologic data suggest that attempts to avoid intubation and ventilation are the best ways to avoid severe BPD. The claim that one ventilation technique is better than another remains unconvincing, and any strategy that maintains the lung open and minimizes tidal volumes probably will be helpful. More adverse effects of postnatal steroids are being recognized. New insights into the pathophysiology of BPD and a new emphasis on minimizing ventilation and ventilator-mediated injury should improve outcomes for very preterm infants.

Animal-derived or synthetic surfactant for the treatment of neonatal respiratory distress syndrome: a review

Animal-derived surfactants containing SP-B and SP-C are more effective in vitro and in animal models than their synthetic counterparts, but are not as effective as unmodified, naturally occurring surfactant. In clinical trials involving newborn babies with respiratory distress syndrome (RDS) these short-term differences are reflected as improvements in gas exchange and lung function. Treatment with animal-derived surfactants results in fewer air leaks and lower neonatal mortality. The evidence is now strong enough to recommend routine use of animal-derived surfactants in very preterm infants with RDS. The newer generation of synthetic surfactants may be important in the future as they have the advantages of currently available animal products with the addition of better resistance to inactivation.

Surfactant protein A recruits neutrophils into the lungs of ventilated preterm lambs

We tested the effects of surfactant protein A (SP-A) on inflammation and surfactant function in ventilated preterm lungs. Preterm lambs of 131 d gestation were ventilated for 15 min to initiate a mild inflammatory response, and were then treated with 100 mg/ kg recombinant human SP-C surfactant or with the same surfactant supplemented with 3 mg/kg ovine SP-A. Addition of SP-A to the SP-C surfactant did not change lung function. After 6 h of ventilation, cell numbers in the alveolar wash were 4.9 times higher in SP-A + SP-C-surfactant-treated animals. Cellular infiltrates consisted of neutrophils that produced less hydrogen peroxide than did cells from SP-C-surfactant-treated animals. Expression of adhesion molecules CD11b and CD44 was significantly greater after SP-A treatment, whereas the expression of CD14 was unchanged. Messenger RNAs (mRNAs) for the proinflammatory cytokines interleukin (IL)-1beta, IL-6, and IL-8, but not tumor necrosis factor-alpha, were increased in SP-A-treated lungs. Surfactant protein mRNAs and protein leakage into alveolar washes were not altered by SP-A, indicating that SP-A treatment produces no evidence of lung injury. The present study identifies an unanticipated role of SP-A in neutrophil recruitment in the lungs of preterm lambs.

Pulmonary aspiration and lung injury

Lung injury after aspiration, although very rare, is a feared and potentially devastating sequela after anaesthesia. This paper summarizes the most recent studies in aspiration lung injury focusing on its clinical epidemiology, new insights in its pathophysiology and innovative concepts in its prevention and therapy.

Lung injury and surfactant metabolism after hyperventilation of premature lambs

We asked whether lung injury and surfactant metabolism differed in preterm lambs after a 1-h period of hyperventilation to P(CO2) values of 25-30 mm Hg. The lambs then were surfactant treated and conventionally ventilated (CV) or high-frequency oscillatory ventilated (HFOV) for an additional 1 or 8 h. The results were compared with lambs that were not hyperventilated or surfactant treated but were ventilated with CV or HFOV. The 1-h hyperventilation resulted in increased alveolar protein, increased recovery of intravascular [131I]albumin in the lungs, and an increase in tumor necrosis factor-alpha mRNA. There were no differences between CV or HFOV in alveolar or total lung recoveries of saturated phosphatidylcholine (Sat PC), tracer doses of [14C]Sat PC and [125I]surfactant protein-B, or in percent Sat PC in large aggregate surfactant in surfactant-treated lambs. The lambs not hyperventilated or treated with surfactant had lower large aggregate pools and lower recoveries of [14C]Sat PC and [125I]surfactant protein-B in total lungs than for the surfactant-treated lungs, but there were no differences between the CV and HFOV groups. Hyperventilation followed by surfactant treatment resulted in a mild injury, but the subsequent use of CV or HFOV did not result in differences in surfactant metabolism.

Effects of ventilation on the surfactant system in sepsis-induced lung injury

The present study examined the effects of mechanical ventilation, with or without positive end-expiratory pressure (PEEP), on the alveolar surfactant system in an animal model of sepsis-induced lung injury. Septic animals ventilated without PEEP had a significant deterioration in oxygenation compared with preventilated values (arterial PO(2)/inspired O(2) fraction 316 +/- 16 vs. 151 +/- 14 Torr; P < 0.05). This was associated with a significantly lower percentage of the functional large aggregates (59 +/- 3 vs. 72 +/- 4%) along with a significantly reduced function (minimum surface tension 17.7 +/- 1.8 vs. 11.8 +/- 3.8 mN/m) compared with nonventilated septic animals (P < 0.05). Sham animals similarly ventilated without PEEP maintained oxygenation, percent large aggregates and surfactant function. With the addition of PEEP, the deterioration in oxygenation was not observed in the septic animals and was associated with no alterations in the surfactant system. We conclude that animals with sepsis-induced lung injury are more susceptible to the harmful effects of mechanical ventilation, specifically lung collapse and reopening, and that alterations in alveolar surfactant may contribute to the development of lung dysfunction.