Can mechanical ventilation strategies reduce chronic lung disease?

Trends in the Incidence of Bronchopulmonary Dysplasia after the Introduction of Neurally Adjusted Ventilatory Assist (NAVA)

OBJECTIVE

This study investigates the difference in the rates of bronchopulmonary dysplasia in very low birth weight infants before and after the introduction of neurally adjusted ventilatory assist (NAVA).

STUDY DESIGN

A retrospective cohort study comparing rates of Bronchopulmonary dysplasia (BPD) before and after implementation of NAVA. Eligibility criteria included all very low birth weight VLBW neonates needing ventilation. For analysis, each cohort was divided into three subgroups based on gestational age. Changes in the rate of BPD, length of stay, tracheostomy rates, invasive ventilator days, and home oxygen therapy were compared.

RESULTS

There were no differences in the incidence of BPD in neonates at 23-25 6/7 weeks' and 29-32 weeks' gestation between the two cohorts. A higher incidence of BPD was seen in the 26-28 5/7 weeks' gestation NAVA subgroup compared to controls (86% vs. 68%, p = 0.05). No significant difference was found for ventilator days, but infants in the 26-28 6/7 subgroup in the NAVA cohort had a longer length of stay (98 ± 34 days vs. 82 ± 24 days, p = 0.02), a higher percentage discharged on home oxygen therapy (45% vs. 18%, respectively, p = 0.006), and higher tracheostomy rates (3/36 vs. 0/60, p = 0.02), compared to the control group.

CONCLUSIONS

The NAVA mode was not associated with a reduction in BPD when compared to other modes of ventilation. Unexpected increases were seen in BPD rates, home oxygen therapy rates, tracheostomy rates, and the length of stay in the NAVA subgroup born at 26-28 6/7 weeks' gestation.

Protective technologies of modern methods of respiratory support in neonatal practice

The article  presents  an analysis of literature data  on modern  protective regimens  for invasive respiratory support  in premature newborns  with respiratory distress  syndrome. We have considered positive and negative  aspects of the used methods  of invasive ventilation of the lungs, which are currently widely used as a method  of respiratory therapy  in obstetric hospitals  at any level, even in the category  of children  with extremely and very low birth weight. Modern  protective mechanical ventilation provides for 2 main directions for reducing ventilator-induced lung damage: a decrease in tidal volume (Vt) and the principle  of tolerable  (permissive) hypercapnia. The use of the technique of permissive hypercapnia and regimens with a target volume can reduce the likelihood of ventilator-induced lung injury in newborns. Despite the limited indications for mechanical ventilation in modern neonatology and the widespread use of non-invasive ventilation, for patients who really need mechanical ventilation, the use of volume-targeted regimens offers the best chance of reducing  ventilation complications.

Adjusting ventilator settings to avoid air trapping in extremely premature infants reduces the need for tracheostomy and length of stay

Despite the improving understanding of how lung mechanics and tidal volume requirements evolve during the evolution of bronchopulmonary dysplasia (BPD), clinical management continues to be heterogeneous and inconsistent at many institutions. Recent reports have examined the use of high tidal-volume low respiratory rate strategies in these patients once disease has been well established to help facilitate their eventual extubation and improve their long-term neurodevelopmental outcomes. In this retrospective observational research study, we describe how intentional adjustment of ventilator settings based on patient lung mechanics by an interdisciplinary BPD team improved the care of the at-risk population of infants, reduced the need for tracheostomies, as well as length of stay over a period of over 3 years. The team aimed to establish consistency in the management of these children using a high tidal volume, low-rate approach, and titrating PEEP to address the autoPEEP and bronchomalacia that is frequently observed in this patient population.

Improving Newborn Respiratory Outcomes With a Sustained Inflation: A Systematic Narrative Review of Factors Regulating Outcome in Animal and Clinical Studies

Respiratory support is critically important for survival of newborns who fail to breathe spontaneously at birth. Although there is no internationally accepted definition of a sustained inflation (SI), it has commonly been defined as a positive pressure inflation designed to establish functional residual capacity and applied over a longer time period than normally used in standard respiratory support (SRS). Outcomes vary distinctly between studies and to date there has been no comprehensive investigation of differences in SI approach and study outcome in both pre-clinical and clinical studies. A systematic literature search was performed and, after screening, identified 17 animal studies and 17 clinical studies evaluating use of a SI in newborns compared to SRS during neonatal resuscitation. Study demographics including gestational age, SI parameters (length, repetitions, pressure, method of delivery) and study outcomes were compared. Animal studies provide mechanistic understanding of a SI on the physiology underpinning the cardiorespiratory transition at birth. In clinical studies, there is considerable difference in study quality, delivery of SIs (number, pressure, length) and timing of primary outcome evaluation which limits direct comparison between studies. The largest difference is method of delivery, where the role of a SI has been observed in intubated animals, as the inflation pressure is directly applied to the lung, bypassing the obstructed upper airway in an apnoeic state. This highlights a potential limitation in clinical use of a SI applied non-invasively. Further research is required to identify if a SI may have greater benefits in subpopulations of newborns.

Comparison of extubation success using noninvasive positive pressure ventilation (NIPPV) versus noninvasive neurally adjusted ventilatory assist (NI-NAVA)

OBJECTIVE

Compare rates of initial extubation success in preterm infants extubated to NIPPV or NI-NAVA.

STUDY DESIGN

In this pilot study, we randomized 30 mechanically ventilated preterm infants at the time of initial elective extubation to NI-NAVA or NIPPV in a 1:1 assignment. Primary study outcome was initial extubation success.

RESULTS

Rates of continuous extubation for 120 h were 92% in the NI-NAVA group and 69% in the NIPPV group (12/13 vs. 9/13, respectively, p = 0.14). Infants extubated to NI-NAVA remained extubated longer (median 18 vs. 4 days, p = 0.02) and experienced lower peak inspiratory pressures (PIP) than infants managed with NIPPV throughout the first 3 days after extubation. Survival analysis through 14 days post extubation showed a sustained difference in the primary study outcome until 12 days post extubation.

CONCLUSIONS

Our study is the first to suggest that a strategy of extubating preterm infants to NI-NAVA may be more successful.

Neurally adjusted ventilatory assist compared to other forms of triggered ventilation for neonatal respiratory support

BACKGROUND

Effective synchronisation of infant respiratory effort with mechanical ventilation may allow adequate gas exchange to occur at lower peak airway pressures, potentially reducing barotrauma and volutrauma and development of air leaks and bronchopulmonary dysplasia. During neurally adjusted ventilatory assist ventilation (NAVA), respiratory support is initiated upon detection of an electrical signal from the diaphragm muscle, and pressure is provided in proportion to and synchronous with electrical activity of the diaphragm (EADi). Compared to other modes of triggered ventilation, this may provide advantages in improving synchrony.

OBJECTIVES

Primary• To determine whether NAVA, when used as a primary or rescue mode of ventilation, results in reduced rates of bronchopulmonary dysplasia (BPD) or death among term and preterm newborn infants compared to other forms of triggered ventilation• To assess the safety of NAVA by determining whether it leads to greater risk of intraventricular haemorrhage (IVH), periventricular leukomalacia, or air leaks when compared to other forms of triggered ventilation Secondary• To determine whether benefits of NAVA differ by gestational age (term or preterm)• To determine whether outcomes of cross-over trials performed during the first two weeks of life include peak pressure requirements, episodes of hypocarbia or hypercarbia, oxygenation index, and the work of breathing SEARCH METHODS: We performed searches of the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cohrane Library; MEDLINE via Ovid SP (January 1966 to March 2017); Embase via Ovid SP (January 1980 to March 2017); the Cumulative Index to Nursing and Allied Health Literature (CINAHL) via EBSCO host (1982 to March 2017); and the Web of Science (1985 to 2017). We searched abstracts from annual meetings of the Pediatric Academic Societies (PAS) (2000 to 2016); meetings of the European Society of Pediatric Research (published in Pediatric Research); and meetings of the Perinatal Society of Australia and New Zealand (PSANZ) (2005 to 2016). We also searched clinical trials databases to March 2017.

SELECTION CRITERIA

We included randomised and quasi-randomised clinical trials including cross-over trials comparing NAVA with other modes of triggered ventilation (assist control ventilation (ACV),synchronous intermittent mandatory ventilation plus pressure support (SIMV ± PS), pressure support ventilation (PSV), or proportional assist ventilation (PAV)) used in neonates.

DATA COLLECTION AND ANALYSIS

Primary outcomes of interest from randomised controlled trials were all-cause mortality, bronchopulmonary dysplasia (BPD; defined as oxygen requirement at 28 days), and a combined outcome of all-cause mortality or BPD. Secondary outcomes were duration of mechanical ventilation, incidence of air leak, incidence of IVH or periventricular leukomalacia, and survival with an oxygen requirement at 36 weeks' postmenstrual age.Outcomes of interest from cross-over trials were maximum fraction of inspired oxygen, mean peak inspiratory pressure, episodes of hypocarbia, and episodes of hypercarbia measured across the time period of each arm of the cross-over. We planned to assess work of breathing; oxygenation index, and thoraco-abdominal asynchrony at the end of the time period of each arm of the cross-over study.

MAIN RESULTS

We included one randomised controlled study comparing NAVA versus patient-triggered time-cycled pressure-limited ventilation. This study found no significant difference in duration of mechanical ventilation, nor in rates of BPD, pneumothorax, or IVH.

AUTHORS' CONCLUSIONS

Risks and benefits of NAVA compared to other forms of ventilation for neonates are uncertain. Well-designed trials are required to evaluate this new form of triggered ventilation.

Ventilation strategies for preventing oxidative stress-induced injury in preterm infants with respiratory disease: an update

Reactive oxygen and nitrogen species are produced by several inflammatory and structural cells of the airways. The lungs of preterm newborns are susceptible to oxidative injury induced by both reactive oxygen and nitrogen species. Increased oxidative stress and imbalance in antioxidant enzymes may play a role in the pathogenesis of inflammatory pulmonary diseases. Preterm infants are frequently exposed to high oxygen concentrations, infections or inflammation; they have reduced antioxidant defense and high free iron levels which enhance toxic radical generation. Multiple ventilation strategies have been studied to reduce injury and improve outcomes in preterm infants. Using lung protective strategies, there is the need to reach a compromise between satisfaction of gas exchange and potential toxicities related to over-distension, derecruitment of lung units and high oxygen concentrations. In this review, the authors summarize scientific evidence concerning oxidative stress as it relates to resuscitation in the delivery room and to the strategies of ventilation.

Comparison of Two Levels of Pressure Support Ventilation on Success of Extubation in Preterm Neonates: A Randomized Clinical Trial

Background:

Pressure Support Ventilation (PSV) is one of the modes of mechanical ventilation that can be used alone as a weaning strategy in neonates. However, studies on the appropriate pressure level for this mode in neonates are limited.

Objectives:

Because the use of adequate pressure support in this mode, keeping the appropriate neonate’s tidal volume, and preventing the respiratory complications, this study was aimed to compare extubation failure in the two levels of pressure support ventilation of 10 and 14 cmH2O when removing the neonates from the ventilator.

Materials & Methods:

In this randomized clinical trial 50 premature infants of 27-37 weeks with respiratory distress syndrome (RDS) were under mechanical ventilation for at least 48 hours, were randomly assigned to two groups. One group was extubated in PSV mode with pressure of 14 cmH₂O and the other with 10 cmH₂O. Extubation failure rate and complications such as pneumothorax, death and respiratory parameters were compared in the two groups.

Results:

Twenty five neonates in each group were assessed. Weaning time, extubation failure rate, and mean airway pressure was lesser in PSV of 10 cmH20 group than Level of 14 cmH2O and those differences were statistically significant (P<0.05). Difference between work of breathing, ventilation time, pneumothorax and mortality rate between two groups were not statistically significant (P>0.05).

Conclusion:

The results of our study show that extubation of the neonates using 10 CmH₂O in PSV mode increases the success rate of extubation. Although when Volume- assured PSV can be used, it is more logical to use it for guaranteeing tidal volume, but using the appropriate level of pressure support when the PSV mode is used alone is inevitable and further studies are necessary to demonstrate the level of pressure in this mode.

Systemic hydrogen sulfide administration partially restores normal alveolarization in an experimental animal model of bronchopulmonary dysplasia

Arrested alveolarization is the pathological hallmark of bronchopulmonary dysplasia (BPD), a complication of premature birth. Here, the impact of systemic application of hydrogen sulfide (H2S) on postnatal alveolarization was assessed in a mouse BPD model. Exposure of newborn mice to 85% O2 for 10 days reduced the total lung alveoli number by 56% and increased alveolar septal wall thickness by 29%, as assessed by state-of-the-art stereological analysis. Systemic application of H2S via the slow-release H2S donor GYY4137 for 10 days resulted in pronounced improvement in lung alveolarization in pups breathing 85% O2, compared with vehicle-treated littermates. Although without impact on lung oxidative status, systemic H2S blunted leukocyte infiltration into alveolar air spaces provoked by hyperoxia, and restored normal lung interleukin 10 levels that were otherwise depressed by 85% O2. Treatment of primary mouse alveolar type II (ATII) cells with the rapid-release H2S donor NaHS had no impact on cell viability; however, NaHS promoted ATII cell migration. Although exposure of ATII cells to 85% O2 caused dramatic changes in mRNA expression, exposure to either GYY4137 or NaHS had no impact on ATII cell mRNA expression, as assessed by microarray, suggesting that the effects observed were independent of changes in gene expression. The impact of NaHS on ATII cell migration was attenuated by glibenclamide, implicating ion channels, and was accompanied by activation of Akt, hinting at two possible mechanisms of H2S action. These data support further investigation of H2S as a candidate interventional strategy to limit the arrested alveolarization associated with BPD.

Increased volume of tracheal aspirate fluid predicts the development of bronchopulmonary dysplasia

BACKGROUND

Elevated cytokine concentrations were observed in tracheal aspirate fluid (TAF) of infants on mechanical ventilation who subsequently developed bronchopulmonary dysplasia (BPD). However, there are few reports that systematically evaluate the amount of TAF as an indicator of BPD development.

AIM

To clarify whether TAF volume during the first week of life predicts BPD development in extremely low gestational age newborns (ELGANs).

STUDY DESIGN

We analyzed 51 infants, born at gestational age of <28 weeks and ventilated for more than 7 days after birth, among whom, 26 were diagnosed with BPD based on the clinical definition of oxygen dependence at 36 weeks postmenstrual age (BPD group) and 25 were included in the non-BPD group. Sum of TAF scores (STS) was calculated by semi-quantification of TAF volume at each suctioning and the suctioning frequency during the first week of life.

RESULTS

STS was significantly higher in the BPD group than in the non-BPD group (median (interquartile range): 77 (29-126) vs. 28 (22-59), p<0.001). STS (cut-off, 60) with area under the curve in receiver operating analysis of 0.75 was significantly predictive of BPD development. Multivariate logistic regression analysis adjusted for perinatal characteristics showed that STS≥60 was a significant risk factor for BPD development (odds ratio, 7.50; confidence interval, 1.16-48.40, p=0.034).

CONCLUSION

Increased TAF volume during the first week of life was an independent predictor for BPD development in ventilated ELGANs, indicating that increased pulmonary capillary permeability may influence the pathogenesis of BPD.

Nasal high-frequency oscillation for lung carbon dioxide clearance in the newborn

BACKGROUND

Noninvasive ventilation has been used increasingly in recent years to minimize the duration of endotracheal mechanical ventilation in neonates due to its association with lung injury. Nasal high-frequency oscillation (nHFO) is a relatively new noninvasive modality but evidence for its use is limited.

OBJECTIVE

The goal of this study was to compare the CO2 clearance efficacy of nHFO and noninvasive positive pressure ventilation (NIPPV) in a neonatal lung model.

DESIGN/METHODS

A newborn mannequin with dimensions and anatomy similar to a term infant was utilized. It was connected to a commercially available neonatal mechanical ventilator using a manufacturer-provided nasal adaptor. Various modes of noninvasive ventilation were compared as CO2 clearance was measured at the oropharynx by an end-tidal CO2 analyzer following the addition of a known amount of CO2 into the lung. Measurements were obtained at two different lung compliances using nHFO and compared with nCMV and nasal continuous positive airway pressure (nCPAP) as a control. Pressures near the nasal adaptor and the larynx were simultaneously measured with in-line pressure transducers.

RESULTS

Whereas no CO2 elimination was observed under nCPAP, its clearance with nHFO was 3-fold greater as compared to NIPPV. On nHFO, CO2 clearance was inversely proportional to frequency and maximal at 6 and 8 Hz. At a lower lung compliance, CO2 clearance was significantly higher at 6 Hz as compared to 10 Hz. During nHFO set to deliver a MAP of 10.0, we documented pressures of 7.2 ± 0.3 at the nasal adaptor and only 2.3 ± 0.3 cm H2O at the larynx.

CONCLUSIONS

Nasal HFO is effective and superior to NIPPV at lung CO2 elimination in a newborn mannequin model. The use of nHFO as the preferred mode of noninvasive ventilation warrants further clinical studies.

Permissive hypercapnia in the management of congenital diaphragmatic hernia: our institutional experience

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a potentially lethal anomaly associated with pulmonary hypoplasia and persistent pulmonary hypertension. Permissive hypercapnia is a strategy designed to reduce lung injury from mechanical ventilation in infants. It has been shown to be a potentially superior method of ventilator management for patients with CDH. In 2001, the Divisions of Neonatology and Pediatric Surgery at the University of Virginia Children's Hospital established permissive hypercapnia as the management strategy for treatment of CDH. We hypothesized that permissive hypercapnia would be associated with improved outcomes in this patient population.

STUDY DESIGN

This retrospective review compares outcomes of infants treated for CDH in the extracorporeal membrane oxygenation (ECMO) era before and after initiation of permissive hypercapnia at a single institution. Outcomes were compared using univariate statistical analysis.

RESULTS

Ninety-one patients were available for analysis and were divided into 2 groups: 42 (Group 1) treated before and 49 (Group 2) treated after implementation of permissive hypercapnia. Survival was higher in Group 2 (85.8% vs 54.8%; p = 0.001; relative risk [RR] 3.17). Morbidity was lower in Group 2 and approached statistical significance (65.3% vs 83.3%; p = 0.052). Patients in Group 2 were repaired later, had a lower rate of ECMO use, and were extubated earlier. There was no difference in hospital stay.

CONCLUSIONS

The use of permissive hypercapnia for infants with CDH was associated with decreased mortality, a longer period of ventilation before repair with a shorter period of ventilation after repair, a lower rate of ECMO use, and no lengthening of hospital stay. Permissive hypercapnia remains the standard of care for ventilation of infants with CDH at our institution.

Changes in respiratory support of preterm infants in the last decade: are we improving?

BACKGROUND

Ventilator-induced lung injury has been recognized as a major contributing factor for bronchopulmonary dysplasia (BPD) in preterm infants. In the last decade, focus has shifted towards a more gentle respiratory approach.

AIM

To evaluate whether guideline changes in respiratory management in the delivery room and the unit improved the incidence of BPD in very preterm infants.

METHODS

Three cohorts of infants <30 weeks of gestation, born at the Leiden University Medical Center in the Netherlands in 1996-1997 (cohort '96), 2003-2004 (cohort '03) and 2008-2009 (cohort '08), were compared retrospectively. The major change was increasing use of continuous positive airway pressure in time, and monitoring the tidal volume during mechanical ventilation in cohort '08. The primary outcome was BPD at 36 weeks.

RESULTS

The incidence of BPD did not change from 47% in cohort '96 to 55% in cohort '03 (n.s.), but decreased significantly to 37% in cohort '08 (cohort '96 vs. '08 and cohort '03 vs. '08: p < 0.01). We observed the same effect when only moderate and severe BPD were counted with 27% in cohort '96, 31% in cohort '03 and 14% in '08 (cohort '96 vs. '03: p = n.s., cohort '96 vs. '08: p < 0.01, cohort '03 vs. '08: p < 0.05). The mortality rate was not significantly different between the three cohorts.

CONCLUSION

The incidence of BPD in our cohort of preterm infants has decreased during the last decade and could be due to the changes in respiratory management.

Ventilatory management and bronchopulmonary dysplasia in preterm infants

Improvements in antenatal and neonatal care have resulted in increased survival of very preterm infants. However, the incidence of bronchopulmonary dysplasia (BPD) has not changed, probably as a consequence of a demographic shift. The underlying pathophysiology of BPD appears to differ for the current population of preterm infants compared to that described by Northway et al., and management strategies should be targeted to limit ventilator-induced lung injury. Non-invasive respiratory support techniques are currently under evaluation, but results of the trials have thus far failed to show a reduction in BPD. This review will focus upon various ventilation modalities for preventing and managing bronchopulmonary dysplasia.

Newer forms of conventional ventilation for preterm newborns

Although life saving, mechanical ventilation can cause complications such as ventilator-induced lung injury and bronchopulmonary dysplasia in very preterm babies. The ventilator-induced lung injury is multi-factorial. There has been an introduction of a number of newer forms of mechanical ventilation, which are aimed to reduce such complications. These are based on sound physiologic principles and clinicians should familiarize themselves with these advances.

High tidal volume ventilation activates Smad2 and upregulates expression of connective tissue growth factor in newborn rat lung

High tidal volume (V(T)) ventilation plays a key role in ventilator induced lung injury and bronchopulmonary dysplasia. However, little is known about the effect of high V(T) on expression of growth factors that are critical to lung development. In a previous study, we demonstrated that connective tissue growth factor (CTGF) inhibits branching morphogenesis. In this study, we investigated the effect of high V(T) on CTGF expression in newborn rat lungs. Newborn rats were ventilated with normal V(T) (10 mL/kg) or high V(T) (25 mL/kg) for 6 h. Nonventilated animals served as controls. We found that high V(T) upregulated CTGF expression. To identify the potential signaling pathways mediating high V(T) induction of CTGF, newborn rats were ventilated with high V(T) for 1 or 3 h. Temporal expression of TGF-betas, p-Smad2, Smad7, and CTGF was analyzed. High V(T) ventilation did not change gene expression of TGF-betas and Smad7 but induced rapid and sustained expression of p-Smad2 that precedes increased CTGF expression. CTGF and p-Smad2 were localized in bronchiolar epithelial cells, alveolar walls and septa. These data suggest that high V(t) ventilation activates the Smad2 pathway, which may be responsible for downstream induction of CTGF expression in newborn rat lungs.

[Factors related to respiratory complications in very low birth weight infants with respiratory distress syndrome]

INTRODUCTION

Very low birth weight (VLBW) infants, with a birth weight below 1500 g and a structurally immature lung, are at high risk for developing bronchopulmonary dysplasia. This risk is even higher if respiratory distress syndrome is present. Other acute lung diseases, such as air leak and pulmonary hemorrhage, can also be present. The aim of this study was to analyze the statistical relevance of several neonatal factors in the development of pulmonary complications in a sample of VLBW infants with respiratory distress syndrome.

PATIENTS AND METHODS

A total of 209 VLBW infants with respiratory distress syndrome were studied. The variables analyzed were delivery date, respiratory distress syndrome grade, sex, birth weight, gestational age, referral (from within the hospital or elsewhere), prenatal corticosteroid administration, type of gestation, type of delivery, amniorrhexis time, Apgar test at 1 and 5 minutes, surfactant administration, hours of life at which the first dose of surfactant was administered, and early sepsis. A multiple logistic regression analysis was developed using Hosmer-Lemeshow methodology.

RESULTS

In the multivariate analysis, air leak was related to respiratory distress syndrome grade and surfactant administration. Pulmonary hemorrhage was related to lower birth weight and absence of prenatal corticosteroid administration. Bronchopulmonary dysplasia was related to single pregnancies, absence of prenatal corticosteroid administration, lower birth weight, lower Apgar score at 1 minute, and higher respiratory distress syndrome grade.

CONCLUSIONS

Respiratory morbidity in VLBW infants with respiratory distress syndrome could be influenced by several interrelated intrinsic and extrinsic variables.

Hypercapnia shortens emergence time from inhaled anesthesia in pigs

BACKGROUND

Anesthetic clearance from the lungs and the circle rebreathing system can be maximized using hyperventilation and high fresh gas flows. However, the concomitant clearance of CO2 decreases PAco2, thereby decreasing cerebral blood flow and slowing the clearance of anesthetic from the brain. This study shows that in addition to hyperventilation, hypercapnia (CO2 infusion or rebreathing) is a significant factor in decreasing emergence time from inhaled anesthesia.

METHODS

We anesthetized seven pigs with 2 MACPIG of isoflurane and four with 2 MACPIG of sevoflurane. After 2 h, anesthesia was discontinued, and the animals were hyperventilated. The time to movement of multiple limbs was measured under hypocapnic (end-tidal CO2 = 22 mm Hg) and hypercapnic (end-tidal CO2 = 55 mm Hg) conditions.

RESULTS

The time between turning off the vaporizer and to movement of multiple limbs was faster with hypercapnia during hyperventilation. Emergence time from isoflurane and sevoflurane anesthesia was shortened by an average of 65% with rebreathing or with the use of a CO2 controller (P < 0.05).

CONCLUSIONS

Hypercapnia, along with hyperventilation, may be used clinically to decrease emergence time from inhaled anesthesia. These time savings might reduce drug costs. In addition, higher PAco2 during emergence may enhance respiratory drive and airway protection after tracheal extubation.

Hypercapnic Hyperventilation Shortens Emergence Time from Isoflurane Anesthesia

BACKGROUND

To shorten emergence time after a procedure using volatile anesthesia, 78% of anesthesiologists recently surveyed used hyperventilation to rapidly clear the anesthetic from the lungs. Hyperventilation has not been universally adapted into clinical practice because it also decreases the Paco2, which decreases cerebral bloodflow and depresses respiratory drive. Adding deadspace to the patient's airway may be a simple and safe method of maintaining a normal or slightly increased Paco2 during hyperventilation.

METHODS

We evaluated the differences in emergence time in 20 surgical patients undergoing 1 MAC of isoflurane under mild hypocapnia (ETco2 approximately 28 mmHg) and mild hypercapnia (ETco2 approximately 55 mmHg). The minute ventilation in half the patients was doubled during emergence, and hypercapnia was maintained by insertion of additional airway deadspace to keep the ETco2 close to 55 mmHg during hyperventilation. A charcoal canister adsorbed the volatile anesthetic from the deadspace. Fresh gas flows were increased to 10 L/min during emergence in all patients.

RESULTS

The time between turning off the vaporizer and the time when the patients opened their eyes and mouths, the time of tracheal extubation, and the time for normalized bispectral index to increase to 0.95 were faster whenever hypercapnic hyperventilation was maintained using rebreathing and anesthetic adsorption (P < 0.001). The time to tracheal extubation was shortened by an average of 59%.

CONCLUSIONS

The emergence time after isoflurane anesthesia can be shortened significantly by using hyperventilation to rapidly clear the anesthetic from the lungs and CO2 rebreathing to induce hypercapnia during hyperventilation. The device should be considered when it is important to provide a rapid emergence, especially after surgical procedures where a high concentration of the volatile anesthetic was maintained right up to the end of the procedure, or where surgery ends abruptly and without warning.

Early respiratory management of respiratory distress syndrome in very preterm infants and bronchopulmonary dysplasia: a case-control study

BACKGROUND

In the period immediately after birth, preterm infants are highly susceptible to lung injury. Early nasal continuous positive airway pressure (ENCPAP) is an attempt to avoid intubation and may minimize lung injury. In contrast, ENCPAP can fail, and at that time surfactant rescue can be less effective.

OBJECTIVE

To compare the pulmonary clinical course and outcome of very preterm infants (gestational age 25-32 weeks) with respiratory distress syndrome (RDS) who started with ENCPAP and failed (ECF group), with a control group of infants matched for gestational age, who were directly intubated in the delivery room (DRI group). Primary outcome consisted of death during admission or bronchopulmonary dysplasia (BPD).

RESULTS

25 infants were included in the ECF group and 50 control infants matched for gestational age were included in the DRI group. Mean gestational age and birth weight in the ECF group were 29.7 weeks and 1,393 g and in the DRI group 29.1 weeks and 1,261 g (p = NS). The incidence of BPD was significantly lower in the ECF group than in the DRI group (4% vs. 35%; P<0.004; OR 12.6 (95% CI 1.6-101)). Neonatal mortality was similar in both groups (4%). The incidence of neonatal morbidities such as severe cerebral injury, patent ductus arteriosus, necrotizing enterocolitis and retinopathy of prematurity, was not significantly different between the two groups.

CONCLUSION

A trial of ENCPAP at birth may reduce the incidence of BPD and does not seem to be detrimental in very preterm infants. Randomized controlled trials are needed to test whether early respiratory management of preterm infants with RDS plays an important role in the development of BPD.

Resuscitation and ventilation strategies for extremely preterm infants: a comparison study between two neonatal centers in Boston and Stockholm

AIM

To evaluate if different resuscitation and ventilatory styles exist between two neonatal units, and if the less aggressive approach has a beneficiary effect on BPD outcome.

METHOD

Inborn infants delivered at a gestational age <28 weeks were retrospectively studied (Boston = 70 and Stockholm = 102). Data were collected from birth to discharge or to 40 weeks.

RESULTS

The study groups were similar with regard to gestational age, birth weight, gender and CRIB score, whereas SNAPPE-II score was greater in Stockholm and prenatal steroids were given less frequently in Boston. In Stockholm, continuous positive airway pressure (CPAP) was applied in the delivery room for 56% of the infants and the prevalence of infants not requiring intubation or mechanical ventilation (MV) during the first week of life was 22%. In Boston all infants were initially intubated. Subsequently, CPAP was used less often, and higher mean airway pressures (MAWPs) were applied during the first 4 weeks of life. Mortality and moderate/severe BPD at 36 weeks were similar; however, at 40 weeks oxygen supplementation was more frequent in Boston. Site was a predictor for moderate/severe BPD or death at 40 weeks.

CONCLUSION

Practice style differences exist and the less aggressive approach with more CPAP administration was successful. It did not decrease the risk for BPD at 36 weeks; however, at 40 weeks, fewer infants were on oxygen support, and a strong association was found between site, MAWP or MV with pulmonary morbidity indicating that CPAP could have a beneficiary role in outcome.

Pathogenesis of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD), initially described 40 years ago, is a dynamic clinical entity that continues to affect tens of thousands of premature infants each year. BPD was first characterized as a fibrotic pulmonary endpoint following severe Respiratory Distress Syndrome (RDS). It was the result of pulmonary healing after RDS, high oxygen exposure, positive pressure ventilation, and poor bronchial drainage secondary to endotracheal intubation in premature infants. With improved treatment for RDS, including surfactant replacement, oxygen saturation monitoring, improved modes of mechanical ventilation, antibiotic therapies, nutritional support, and infants surviving at younger gestations, the clinical picture of BPD has changed. In the following pages, we will summarize the multifaceted pathophysiologic factors leading to the pulmonary changes in "new" BPD, which is primarily characterized by disordered or delayed development. The contribution of hyperoxia and hypoxia, mechanical forces, vascular maldevelopment, inflammation, fluid management, patent ductus arteriosus (PDA), nutrition, and genetics will be discussed.

Lower parathyroid hormone-related protein content of tracheal aspirates in very low birth weight infants who develop bronchopulmonary dysplasia

Since parathyroid hormone-related protein (PTHrP) secreted by pulmonary alveolar type II cells is a key physiologic paracrine factor in maintaining alveolar homeostasis, we hypothesized that its levels in the tracheal aspirates (TA) of ventilated very low birth weight infants (VLBWI) would correlate with the development of bronchopulmonary dysplasia (BPD). Therefore, we examined whether TA PTHrP content during the first week of life correlates with the later development of BPD. Forty VLBWI [birth weight, 943 +/- 302 g (mean +/- SD); gestational age, 27 +/- 2 wk; 21 males and 19 females], who were ventilated for respiratory distress syndrome, were studied. The TA were collected once daily until the infants were extubated and immediately frozen at -70 degrees C for subsequent assays for PTHrP and matrix metalloproteinase-8 (MMP-8), a previously described, nonspecific TA biomarker for BPD. The levels of these proteins were correlated with the later development of BPD. PTHrP in the TA during the first week of life was significantly lower in those infants who developed BPD (12/40) than among those who did not (28/40). The PTHrP levels also correlated with the duration of mechanical ventilation needed in these infants. In contrast, MMP-8 levels did not correlate with BPD. We conclude that lower TA PTHrP content during the first week of life in ventilated VLBWI inversely correlates with prolonged ventilation and the later development of BPD.

Progress in Discovery and Evaluation of Treatments to Prevent Bronchopulmonary Dysplasia

BACKGROUND

Recent improvements in the survival of extremely preterm infants have been accompanied by evolution in the pathogenesis and histopathology of bronchopulmonary dysplasia (BPD). Although oxygen and barotrauma-induced injury remain important contributing factors, pulmonary developmental arrest appears to play an equally important causal role in prolonged respiratory illness, especially among the most immature surviving preterm newborns. To date, clinical trials have failed to demonstrate a substantial benefit of a single treatment or preventive strategy for BPD.

OBJECTIVES

To evaluate the current evidence in favor of treatments that might prevent BPD.

METHODS

Review of clinical studies of preventive treatment strategies for BPD.

RESULTS

High frequency oscillatory ventilation, permissive hypercapnea, and inhaled nitric oxide might offer benefit to infants at risk of BPD. These and other potential preventive therapies for BPD, such as superoxide dismutase, inositol, and alpha(1)-proteinase inhibitor, deserve further study.

CONCLUSIONS

Although some current treatments offer promise, no preventive therapy for BPD has proven safe and effective, except for intramuscular vitamin A. Additional studies of respiratory technologies, management strategies, and protective molecules are needed.

Effects of pressure support ventilation plus volume guarantee vs. high-frequency oscillatory ventilation on lung inflammation in preterm infants

The aim of the present study was to evaluate if high-frequency oscillatory ventilation (HFOV) might reduce lung inflammation in preterm infants with infant respiratory distress syndrome (RDS) in comparison with the early application of another potentially lung-protective ventilation strategy, such as pressure support ventilation plus volume guarantee (PSV + VG). Infants at less than 30 weeks of gestation with RDS were enrolled consecutively in the study if they required mechanical ventilation, and were randomly allocated to receive HFOV or PSV + VG. Bronchial aspirate samples for the measurement of interleukin (IL)-1beta, IL-8, and IL-10 were obtained before surfactant treatment (T1), after 6-18 hr of ventilation (T2), after 24-48 hr of ventilation (T3), and before extubation (T4). Thirteen patients were enrolled in the HFOV group, and 12 in the PSV + VG group. The mean values of IL-1beta, IL-8, and IL-10 at T4 were lower in the HFOV group than in the PSV + VG group. The present study demonstrates that early treatment with HFOV is associated with a reduction of lung inflammation in comparison with PSV + VG in preterm infants with RDS.

Volutrauma activates the clotting cascade in the newborn but not adult rat

Coagulopathy and alveolar fibrin deposition are common in sick neonates and attributed to the primary disease, as opposed to their ventilatory support. Hypothesizing that high tidal volume ventilation activates the extrinsic coagulation pathway, we air ventilated newborn and adult rats at low (10 ml/kg) or high (30 ml/kg) tidal volume and compared them with age-matched nonventilated controls. Blood was collected at the end of the experiment for measurement of clot time, tissue factor, and other coagulation factor content. Similar measurements were obtained from lung lavage material. The newborn clot time (44+/-1) was lower and plasma tissue factor content higher (103.4+/-0.4) than adults (88+/-4 s and 26.6+/-1.4 units; P<0.01). High, but not low, tidal volume ventilation of newborns for as little as 15 min significantly reduced clot time and increased plasma tissue factor content (P<0.01). High volume ventilation increased plasma factor Xa (0.1+/-0.1 to 1.6+/-0.4 nM; P<0.01) and thrombin (1.3+/-0.2 to 2.2+/-0.4 nM; P<0.05) and decreased antithrombin (0.12+/-0.01 to 0.05+/-0.01; P<0.01) in the newborn. Lung lavage material of high volume-ventilated newborns showed increased (P<0.01) factor Xa and thrombin. No changes in these parameters were observed in adult rats that were high volume ventilated for up to 90 min. Compared with adults, newborn rats have a greater propensity for volutrauma-activated intravascular coagulation. These data suggest that mechanical ventilation promotes neonatal thrombosis via lung tissue factor release.

Strategies for preventing bronchopulmonary dysplasia

PURPOSE OF REVIEW

Neonatologists and pulmonary biologists have long sought preventive treatments for bronchopulmonary dysplasia (BPD). The purpose of this review is to highlight recent reports of a number of potential treatments intended to prevent BPD and to discuss the controversies surrounding preventive strategies.

RECENT FINDINGS

The evolution of BPD from a disorder of pulmonary injury affecting moderately preterm infants, to one characterized by a developmental pulmonary arrest among survivors of extreme prematurity has important implications for BPD prevention. Recent recognition that the pathogenesis of BPD might have prenatal origins raises new challenges and opportunities for studies of BPD prevention; however, most current preventive strategies for BPD focus on respiratory management. Neither past nor current clinical trials have shown a conclusive benefit of a single preventive treatment strategy. Promising but still largely unproven preventive respiratory treatments include: high frequency oscillatory ventilation, permissive hypercapnea, and inhaled nitric oxide. Observational and recent laboratory data support the need for randomized clinical trials of continuous positive airway pressure versus mechanical ventilation. Additionally, clinical trials are needed to address the deficit in our knowledge of the potential benefits and risks of postnatal low dose corticosteroid treatment. Further study of superoxide dismutase, inositol, and alpha-1 proteinase inhibitor also are warranted on the basis of recent clinical trials or meta-analyses.

SUMMARY

Only Vitamin A has proven a safe and effective preventive treatment for BPD. Additional studies of respiratory technologies, management strategies, and protective molecules are needed. Directed cytokine and genetic therapies are on the horizon.