Bench-to-bedside review: Ventilator strategies to reduce lung injury -- lessons from pediatric and neonatal intensive care

Comparison of conventional mechanical ventilation and high-frequency oscillatory ventilation in congenital diaphragmatic hernias: a systematic review and meta-analysis

Outcomes of conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation (HFOV) in patients with congenital diaphragmatic hernia (CDH) were compared through a systematic review and meta-analysis. Outcome measures included mortality and incidence of chronic lung disease (CLD). Odds ratio (OR) and 95% confidence interval (95%CI) were evaluated. Subgroup analyses were performed according to the strategy for applying HFOV in CDH patients. Group A: CMV was initially applied in all CDH patients, and HFOV was applied in unstable patients. Group B: chronologically analyzed. (CMV and HFOV era) Group C: CMV or HFOV was used as the initial MV. Of the 2199 abstracts screened, 15 full-text articles were analyzed. Regarding mortality, 16.7% (365/2180) and 32.8% (456/1389) patients died in CMV and HFOV, respectively (OR, 2.53; 95%CI 2.12-3.01). Subgroup analyses showed significantly worse, better, and equivalent mortality for HFOV than that for CMV in group A, B, and C, respectively. CLD occurred in 32.4% (399/1230) and 49.3% (369/749) patients in CMV and HFOV, respectively (OR, 2.37; 95%CI 1.93-2.90). The evidence from the literature is poor. Mortality and the incidence of CLD appear worse after HFOV in children with CDH. Cautious interpretation is needed due to the heterogeneity of each study.

Surfactant deactivation in a pediatric model induces hypovolemia and fluid shift to the extravascular lung compartment

BACKGROUND

Surfactant deficiency is the pivotal abnormality in Neonatal and Acute Respiratory Distress Syndrome. Surfactant deactivation can produce hypoxemia, loss of lung compliance, and pulmonary edema, but its circulatory consequences are less understood.

OBJECTIVE

To describe the sequential hemodynamic changes and pulmonary edema formation after surfactant deactivation in piglets.

METHODS

Surfactant deactivation was induced by tracheal instillation of polysorbate 20 in 15 anesthetized and mechanically ventilated Large White piglets. The hemodynamic consequences of surfactant deactivation were assessed at 30, 120, and 240 min by transpulmonary thermodilution and traditional methods.

RESULTS

Surfactant deactivation caused hypoxemia, reduced lung compliance, and progressively increased lung water content (P < 0.01). Early hypovolemia was observed, with reductions of the global end-diastolic volume and stroke volume (P < 0.05). Reduced cardiac output was observed at the end of the study (P < 0.05). Standard monitoring was unable to detect these early preload alterations. Surprisingly, the bronchoalveolar protein content was greatly increased at the end of the study compared with baseline levels (P < 0.01). This finding was inconsistent with the notion that the pulmonary edema induced by surfactant deactivation was exclusively caused by high surface tension.

CONCLUSIONS

Hypovolemia develops early after surfactant deactivation, in part due to the resulting fluid shift from the intravascular compartment to the lungs.

Acute Pulmonary Infections

Acute lower respiratory infection is a common cause of morbidity in infants and children, and at times, requires intensive care and mechanical ventilation. Viral bronchiolitis and bacterial pneumonia account for the majority of lower respiratory tract infections that lead to respiratory insufficiency and pediatric intensive care admission. Twenty-seven percent of children who require mechanical ventilation for at least 24 h in pediatric intensive care units are diagnosed with bronchiolitis and 16% have the diagnosis of pneumonia. The median length of time intubated for an acute pulmonary infection leading to respiratory failure is approximately 7 days.

Inhaled nitric oxide improves systemic microcirculation in infants with hypoxemic respiratory failure

OBJECTIVES

To investigate the effect of inhaled nitric oxide on the systemic microcirculation. We hypothesized that inhaled nitric oxide improves the systemic microcirculation. Inhaled nitric oxide improves outcome in infants with persistent pulmonary hypertension of the newborn diagnosed by improving pulmonary blood flow and oxygenation. It reduces pulmonary vascular resistance without decline in systemic blood pressure. Inhaled nitric oxide is also utilized in the treatment of acute hypoxemic respiratory failure in children and adults. It is thought to improve regional ventilation perfusion by regional selective pulmonary vasodilation.

DESIGN

Pilot study.

SETTING

Intensive care unit of a level III university children's hospital.

PATIENTS

Consecutive ventilated patients who were treated with inhaled nitric oxide (20 ppm) were enrolled in this study. Eight patients (five boys, three girls) were included; five had congenital diaphragmatic hernia diagnosed, one had persistent pulmonary hypertension of the newborn diagnosed, one had acute respiratory distress syndrome diagnosed, and one had bronchiolitis diagnosed. The median age was 0 months (range, 0-38 months).

INTERVENTIONS

Inhaled nitric oxide administration.

MEASUREMENTS AND MAIN RESULTS

The microcirculation was assessed in the buccal mucosa within 1 hr before and within 1 hr after the start of inhaled nitric oxide using orthogonal polarization spectral imaging. The median functional capillary density before the inhaled nitric oxide was started was 4.0 cm/cm (range, 1.8-5.6 cm/cm) and improved to 4.9 cm/cm (range, 2.8-6.6 cm/cm; p = .017) after the start of inhaled nitric oxide.

CONCLUSIONS

Inhaled nitric oxide improves the systemic microcirculation in children with hypoxemic respiratory failure.

Lung protective strategy and prone ventilation resulting in successful outcome in a patient with ARDS due to H1N1

Acute respiratory distress syndrome (ARDS) is an acute respiratory condition caused by various pulmonary and extrapulmonary conditions including H1N1 virus infection. ARDS has a high mortality worldwide and in India various studies suggest that mortality in children is as high as 73-75%. Different lung protective ventilation strategies have recently been adopted to reduce mortality. The authors report a successful outcome in a 3.5-year-old child with ARDS secondary to H1N1 infection following use of a very low tidal volume (4-6 ml/kg) along with high positive end-expiratory pressure breathing and prone ventilation. As far as we are aware, this is the first case report of a successful outcome in a child with ARDS secondary to H1N1 in India.

Changing perspectives on the perinatal management of isolated congenital diaphragmatic hernia in Europe

Congenital diaphragmatic hernia (CDH) should be diagnosed in the prenatal period and prompt referral to a tertiary referral center for imaging, genetic testing, and multidisciplinary counseling. Individual prediction of prognosis is based on the absence of additional anomalies, lung size, and liver herniation. In severe cases, a prenatal endotracheal balloon procedure is currently being offered at specialized centers. Fetal intervention is now also offered to milder cases within a trial, hypothesizing that this may reduce the occurrence of bronchopulmonary dysplasia in survivors. Postnatal management has been standardized by European high-volume centers for the purpose of this and other trials.

Pathogenesis and prevention of chronic lung disease in the neonate

Often used interchangeably, chronic lung disease (CLD) or bronchopulmonary dysplasia (BPD) develops primarily in extremely low birth weight infants weighing <1000 g who receive prolonged oxygen therapy and or positive pressure ventilation. CLD, which occurs in as many as 30 percent of infants born weighing <1000 g, contributes significantly to the morbidity and mortality seen in very low birth weight infants. Despite extensive research aimed at identifying risk factors and devising preventative therapies, many questions about the etiology and pathogenesis of BPD remain. This article reviews the embryologic development of the lung and the pathogenesis of CLD or BPD. The authors discuss some of the measures that have been used in an attempt to both prevent and treat BPD.

Prenatal diagnosis, prediction of outcome and in utero therapy of isolated congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) can be associated with genetic or structural anomalies with poor prognosis. In isolated cases, survival is dependent on the degree of lung hypoplasia and liver position. Cases should be referred in utero to tertiary care centers familiar with this condition both for prediction of outcome as well as timed delivery. The best validated prognostic indicator is the lung area to head circumference ratio. Ultrasound is used to measure the lung area of the index case, which is then expressed as a proportion of what is expected normally (observed/expected LHR). When O/E LHR is < 25% survival chances are < 15%. Prenatal intervention, aiming to stimulate lung growth, can be achieved by temporary fetal endoscopic tracheal occlusion (FETO). A balloon is percutaneously inserted into the trachea at 26-28 weeks, and reversal of occlusion is planned at 34 weeks. Growing experience has demonstrated the feasibility and safety of the technique with a survival rate of about 50%. The lung response to, and outcome after FETO, is dependent on pre-existing lung size as well gestational age at birth. Early data show that FETO does not increase morbidity in survivors, when compared to historical controls. Several trials are currently under design.

[Fetoscopic tracheal occlusion for the treatment of severe congenital diaphragmatic hernia: preliminary results]

OBJECTIVES

To evaluate survival and lung growth in fetuses with severe congenital diaphragmatic hernia (CDH) treated with fetoscopic tracheal occlusion (FETO) compared with control fetuses and to analyze possible complications of the anesthetic techniques used.

PATIENTS AND METHODS

This prospective study was performed on fetuses with CDH. FETO was undertaken before the 29th week of gestation on fetuses with a lung-to-head ratio (LHR) less than 1. FETO was not performed on fetuses with an LHR between 1.0 and 1.5 or those with an LHR less than 1 where consent was not given. Lung growth was monitored by means of LHR. FETO was performed under fetal intramuscular anesthesia and maternal epidural anesthesia and sedation with remifentanil.

RESULTS

Seventeen fetuses were included in the study. FETO was performed on 11 fetuses and was effective in 9. The median percentage difference between LHR at diagnosis and prior to FETO was 1.15% (P=.183); between diagnosis and before removing the balloon, the difference was 130.5% (P=.003); and between diagnosis and before delivery, 90.18% (P=.003). In the control group (n=6), the median percentage difference between LHR at diagnosis and before delivery was 49.25% (P=.028). No significant hemodynamic or respiratory changes occurred in either mother or fetus during fetoscopy. All the fetuses in the control group died; 45.5% of those in the FETO group survived.

CONCLUSIONS

The use of FETO in cases of CDH appears to increase survival and lung growth. Fetal anesthesia in association with maternal epidural anesthesia and sedation makes it possible to place and remove the endotracheal balloon via fetoscopy with acceptable maternal comfort and without notable complications.

Persistent pulmonary hypertension of the newborn

In utero, fetal pulmonary vascular resistance (PVR) is high, but rapidly falls after birth. Expansion of the lungs, increase in oxygenation, release of vasoactive mediators, growth factors and remodeling of the vascular wall, all contribute to the reduction in PVR. Persistent pulmonary hypertension of the newborn (PPHN) is defined as a failure of the pulmonary vasculature to relax at birth, resulting in hypoxemia. PPHN is in fact a variety of disorders that have a common presentation. Some of the pathophysiological mechanisms and the therapeutic approaches are discussed below.

Prenatal intervention for isolated congenital diaphragmatic hernia

PURPOSE OF REVIEW

We aim to review the recent literature regarding early prenatal prediction of outcome in babies diagnosed with isolated congenital diaphragmatic hernia, as well as results of fetal therapy for this condition.

RECENT FINDINGS

Current survival rates in population-based studies are around 55-70%. Highly specialized centers report 80% and more, but discount the hidden mortality, mainly in the antenatal period. Fetuses presenting with liver herniation and a lung-to-head ratio of less than 1.0 measured in midgestation have a poor prognosis. Other volumetric techniques are being evaluated for use in midtrimester. Recently, a randomized trial failed to show benefit from prenatal therapy, but lacked power to document the potential advantage of prenatal therapy in severe cases. We proposed percutaneous fetal endoluminal tracheal occlusion with a balloon at 26-28 weeks through a 3.3 mm incision. In severe cases, fetal endoluminal tracheal occlusion increased lung size as well as survival, with an early (7 day) survival, late neonatal (28 day) survival and survival at discharge of 75, 58 and 50%, respectively, comparing favorably with 9% in contemporary controls. Airways can be restored prior to birth improving neonatal survival (83.3% compared with 33.3%). The procedure carries a risk for preterm prelabour rupture of the fetal membranes, although that may decrease with experience.

SUMMARY

Fetuses with severe congenital diaphragmatic hernia can be identified in the second trimester. Fetal endoluminal tracheal occlusion can be considered as a minimally invasive fetal therapy, improving outcome in such highly selected cases.