Positive end-expiratory pressure for preterm infants requiring conventional mechanical ventilation for respiratory distress syndrome or bronchopulmonary dysplasia

Preterm lung and brain responses to mechanical ventilation and corticosteroids

Mechanical ventilation is necessary to maintain oxygenation and ventilation in many preterm infants. Unfortunately, even short periods of mechanical ventilation can cause lung and airway injury, and initiate the lung inflammation that contributes to the development of bronchopulmonary dysplasia (BPD). The mechanical stretch leads to airway cell differentiation and simplification of the alveoli, and releases cytokines that cause systemic response in other organs. Mechanical ventilation also leads to brain injury (IVH, white and gray matter) and neuronal inflammation that can affect the neurodevelopment of preterm infants. In efforts to decrease BPD, corticosteroids have been used for both prevention and treatment of lung inflammation. Corticosteroids have also been demonstrated to cause neuronal injury, so the clinician must balance the negative effects of both mechanical ventilation and steroids on the brain and lungs. Predictive models for BPD can help assess the infants who will benefit most from corticosteroid exposure. This review describes the lung and brain injury from mechanical ventilation in the delivery room and chronic mechanical ventilation in animal models. It provides updates on the current guidelines for use of postnatal corticosteroids (dexamethasone, hydrocortisone, budesonide, budesonide with surfactant) for the prevention and treatment of BPD, and the effects the timing of each steroid regimen has on neurodevelopment.

Outcomes of and factors associated with the development of bronchopulmonary dysplasia with pulmonary hypertension in very low birth weight infants: A retrospective study in a medical center

Introduction

Bronchopulmonary dysplasia (BPD) with pulmonary hypertension (PH) leads to increased morbidity and mortality in extremely preterm infants. Recent studies have analyzed factors associated with development of PH in BPD; however, this research remains inconclusive, and controversy exists regarding the correlation between BPD and PH. This study aimed to investigate potential associated factors, clinical characteristics, and outcomes of BPD with pulmonary hypertension in very low birth weight (VLBW) preterm infants.

Methods

We conducted a retrospective study, reviewing the records of infants with gestational age (GA) <32 weeks and birth weight <1,500 g admitted to a tertiary neonatal intensive care unit between January 2020 and October 2021 who were diagnosed with moderate to severe BPD. Echocardiogram was performed at the postmenstrual age of 36 weeks or before discharge. The diagnosis of PH was based on the findings of echocardiogram. Prenatal and postnatal characteristics, demographic data, treatment details, and outcomes were collected and analyzed.

Results

A total of 139 VLBW infants with BPD were enrolled and divided into a PH group (n = 25) and a non-PH group (n = 114). The mean GA was 27.3 ± 2.3 weeks and the mean birth weight of infants with BPD was 927.3 ± 293.3 g. A multivariate logistic regression model revealed that a high positive end-expiratory pressure (PEEP) setting (OR: 2.105; 95% CI: 1.472-3.011; p < 0.001) in established BPD and surgical closure of patent ductus arteriosus (PDA; OR: 6.273; 95% CI: 1.574-24.977; p = 0.009) were associated with BPD-PH. Neonates with BPD who developed pulmonary hypertension remained hospitalized for longer (p < 0.001), received invasive mechanical ventilation support for longer (p < 0.001), had a higher incidence of retinopathy of prematurity (ROP; OR: 4.201; 95% CI: 1.561-11.304; p = 0.003), were more likely to require oxygen support at discharge (OR: 5.600; 95% CI: 2.175-14.416; p < 0.001), and were more likely to undergo tracheostomy (OR: 35.368; 95% CI: 4.03-310.43; p < 0.001).

Conclusion

PDA ligation and a higher PEEP setting were associated with BPD-PH in our cohort study. Compared with VLBW infants with BPD but without PH, infants with BPD and PH were hospitalized for longer, and also had a higher incidence of oxygen support after discharge, ROP, and tracheostomy.

Pediatric Simulation of Intrinsic PEEP and Patient-Ventilator Trigger Asynchrony During Mechanical Ventilation

BACKGROUND

Intrinsic PEEP during mechanical ventilation occurs when there is insufficient time for expiration to functional residual capacity before the next inspiration, resulting in air trapping. Increased expiratory resistance (R_E), too rapid of a patient or ventilator breathing rate, or a longer inspiratory to expiratory time ratio (T_I/T_E) can all be causes of intrinsic PEEP. Intrinsic PEEP can result in increased work of breathing and patient-ventilator asynchrony (PVA) during patient-triggered breaths. We hypothesized that the difference between intrinsic PEEP and ventilator PEEP acts as an inspiratory load resulting in trigger asynchrony that needs to be overcome by increased respiratory muscle pressure (P_mus).

METHODS

Using a Servo lung model (ASL 5000) and LTV 1200 ventilator in pressure control mode, we developed a passive model demonstrating how elevated R_E increases intrinsic PEEP above ventilator PEEP. We also developed an active model investigating the effects of R_E and intrinsic PEEP on trigger asynchrony (expressed as percentage of patient-initiated breaths that failed to trigger). We then studied if trigger asynchrony could be reduced by increased P_mus.

RESULTS

Intrinsic PEEP increased significantly with increasing R_E (r = 0.97, P = .006). Multivariate logistic regression analysis showed that both R_E and negative P_mus levels affect trigger asynchrony (P < .001).

CONCLUSIONS

A passive lung model describes the development of increasing intrinsic PEEP with increasing R_E at a given ventilator breathing rate. An active lung model shows how this can lead to trigger asynchrony since the P_mus needed to trigger a breath is greater with increased R_E, as the inspiratory muscles must overcome intrinsic PEEP. This model will lend itself to the study of intrinsic PEEP engendered by a higher ventilator breathing rate, as well as higher T_I/T_E, and will be useful in ventilator simulation scenarios of PVA. The model also suggests that increasing ventilator PEEP to match intrinsic PEEP can improve trigger asynchrony through a reduction in R_E.

Evidence for the Management of Bronchopulmonary Dysplasia in Very Preterm Infants

Background: Very preterm birth often results in the development of bronchopulmonary dysplasia (BPD) with an inverse correlation of gestational age and birthweight. This very preterm population is especially exposed to interventions, which affect the development of BPD. Objective: The goal of our review is to summarize the evidence on these daily procedures and provide evidence-based recommendations for the management of BPD. Methods: We conducted a systematic literature research using MEDLINE/PubMed on antenatal corticosteroids, surfactant-replacement therapy, caffeine, ventilation strategies, postnatal corticosteroids, inhaled nitric oxide, inhaled bronchodilators, macrolides, patent ductus arteriosus, fluid management, vitamin A, treatment of pulmonary hypertension and stem cell therapy. Results: Evidence provided by meta-analyses, systematic reviews, randomized controlled trials (RCTs) and large observational studies are summarized as a narrative review. Discussion: There is strong evidence for the use of antenatal corticosteroids, surfactant-replacement therapy, especially in combination with noninvasive ventilation strategies, caffeine and lung-protective ventilation strategies. A more differentiated approach has to be applied to corticosteroid treatment, the management of patent ductus arteriosus (PDA), fluid-intake and vitamin A supplementation, as well as the treatment of BPD-associated pulmonary hypertension. There is no evidence for the routine use of inhaled bronchodilators and prophylactic inhaled nitric oxide. Stem cell therapy is promising, but should be used in RCTs only.

BPD treatments: The never-ending smorgasbord

Despite important advances in neonatal care, rates of bronchopulmonary dysplasia (BPD) have remained persistently high. Numerous drugs and ventilator strategies are used for the prevention and treatment of BPD. Some, such as exogenous surfactant, volume targeted ventilation, caffeine, and non-invasive respiratory support, are associated with modest but important reductions in rates of BPD and long-term respiratory morbidities. Many other therapies, such as corticosteroids, diuretics, nitric oxide, bronchodilators and anti-reflux medications, are widely used despite conflicting, limited or no evidence of efficacy and safety. This paper examines the range of therapies used for the prevention or treatment of BPD. They are classified into those supported by evidence of effectiveness, and those which are widely used despite limited evidence or unclear risk to benefit ratios. Finally, the paper explores emerging therapies and approaches which aim to prevent or reduce BPD and long-term respiratory morbidity.

Lung recruitment manoeuvres for reducing mortality and respiratory morbidity in mechanically ventilated neonates

BACKGROUND

Preterm infants and neonates with respiratory conditions commonly require intubation and conventional mechanical ventilation (CMV) to maintain airway patency and support their respiration. Whilst this therapy is often lifesaving, it simultaneously carries the risk of lung injury. The use of lung recruitment manoeuvres (LRMs) has been found to reduce the incidence of lung injury, and improve oxygenation and lung compliance in ventilated adults. However, evidence pertaining to their use in neonates is limited, and there is no consensus of opinion as to whether LRMs are appropriate or effective in this population.

OBJECTIVES

To determine the effects of LRMs on mortality and respiratory outcomes in mechanically ventilated neonates, when compared to no recruitment (routine care).  SEARCH METHODS: We used the standard search strategy of Cochrane Neonatal to search the Cochrane Central Register of Controlled Trials (CENTRAL 2020, Issue 4) in the Cochrane Library, MEDLINE via Ovid (1946 to 13 April 2020), and CINAHL via EBSCOhost (1989 to 13 April 2020). We also handsearched the reference lists of retrieved studies to source additional articles.  SELECTION CRITERIA: We included randomised controlled trials (RCTs), quasi-RCTs and randomised cross-over studies that compared the effect of LRMs to no recruitment (routine care) in mechanically ventilated neonates.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility, extracted data and evaluated risk of bias in the included studies. When studies were sufficiently similar, we performed a meta-analysis using mean difference (MD) for continuous data and risk ratio (RR) for dichotomous data, with their respective 95% confidence intervals (CIs). We used the GRADE approach to assess the certainty of the evidence for key (clinically important) outcomes.

MAIN RESULTS

We included four studies (152 participants in total) in this review. Three of these studies, enrolling 56 participants, contributed data to our prespecified outcomes. Two studies enrolling 44 participants on CMV for respiratory distress syndrome compared a stepwise LRM with positive end-expiratory pressure (PEEP) to routine care. Meta-analysis demonstrated no evidence of a difference between the LRM and routine care on mortality by hospital discharge (RR 1.00, 95% CI 0.17 to 5.77; low-certainty evidence), incidence of bronchopulmonary dysplasia (RR 0.25, 95% CI 0.03 to 2.07; low-certainty evidence), duration of supplemental oxygen (MD -7.52 days, 95% CI -20.83 to 5.78; very low-certainty evidence), and duration of ventilatory support (MD -3.59 days, 95% CI -12.97 to 5.79; very low-certainty evidence). The certainty of the evidence for these outcomes was downgraded due to risk of bias, imprecision, and inconsistency. Whilst these studies contributed data to four of our primary outcomes, we were unable to identify any studies that reported our other primary outcomes: duration of continuous positive airway pressure therapy, duration of neonatal intensive care unit stay, and duration of hospital stay.  The third study that contributed data to the review enrolled 12 participants on CMV for respiratory and non-respiratory causes, and compared two different LRMs applied after endotracheal tube suctioning to routine care. It was determined that both LRMs may slightly improve end-expiratory lung volume at 120 minutes' post-suctioning, when compared to routine care (incremental PEEP LRM versus routine care: MD -0.21, 95% CI -0.37 to -0.06; double PEEP LRM versus routine care: MD -0.18, 95% CI -0.35 to -0.02). It was also demonstrated that a double PEEP LRM may slightly reduce mean arterial pressure at 30 minutes' post-suctioning, when compared with routine care (MD -16.00, 95% CI -29.35 to -2.65).  AUTHORS' CONCLUSIONS: There is insufficient evidence to guide the use of LRMs in mechanically ventilated neonates. Well-designed randomised trials with larger sample sizes are needed to further evaluate the potential benefits and risks of LRM application in this population.

Increased peak end-expiratory pressure in ventilated preterm lambs changes cerebral microvascular perfusion: direct synchrotron microangiography assessment

Positive end-expiratory pressure (PEEP) improves oxygenation in mechanically ventilated preterm neonates by preventing lung collapse. However, high PEEP may alter cerebral blood flow secondarily to the increased intrathoracic pressure, predisposing to brain injury. The precise effects of high PEEP on cerebral hemodynamics in the preterm brain are unknown. We aimed to assess the effect of PEEP on microvessels in the preterm brain by using synchrotron radiation (SR) microangiography, which enables in vivo real-time high-resolution imaging of the cerebral vasculature. Preterm lambs (0.8 gestation, n = 4) were delivered via caesarean section, anesthetized, and ventilated. SR microangiography of the right cerebral hemisphere was performed with iodine contrast administered into the right carotid artery during PEEP ventilation of 5 and 10 cmH₂O. Carotid blood flow was measured using an ultrasonic flow probe placed around the left carotid artery. An increase of PEEP from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm) in all four lambs. Additionally, the higher PEEP increased the cerebral contrast transit time in three of the four lambs. Carotid blood flow increased in two lambs, which also had increased carbon dioxide levels during PEEP 10. Our results suggest that PEEP of 10 cmH₂O alters the preterm cerebral hemodynamics, with prolonged cerebral blood flow transit and engorgement of small cerebral microvessels likely due to the increased intrathoracic pressure. These microvascular changes are generally not reflected in global assessment of cerebral blood flow or oxygenation.NEW & NOTEWORTHY An increase of positive end-expiratory pressure (PEEP) from 5 to 10 cmH₂O increased the diameter of small cerebral vessels (<150 µm) but decreased the diameter of larger cerebral vessels (>500 µm). This suggests increased intrathoracic pressure due to high PEEP can drive microvessel engorgement in the preterm brain, which may play a role in cerebrovascular injury.