Positive end-expiratory pressure preserves surfactant function in preterm lambs

Providing Positive End-Expiratory Pressure during Neonatal Resuscitation: A Meta-analysis

Our objective was to conduct a systematic review and meta-analysis evaluating the effects of administering positive end-expiratory pressure (PEEP) during neonatal resuscitation at birth. Medline, Web of Science, Scopus, Cochrane Central Register of Controlled Trials, and Clinicaltrials.gov databases were systematically searched from inception to 15 December 2020. Randomized controlled trials and cohort studies were held eligible. Studies were included if they compared the administration of PEEP using either a T-piece resuscitator or a self-inflating bag with a PEEP valve versus resuscitation via a self-inflating bag without a PEEP valve. Data were extracted by two reviewers independently. The credibility of evidence was appraised with the Grading of Recommendations, Assessment, Development, and Evaluations approach. Random-effects models were fitted to provide pooled estimates of risk ratio (RR) and 95% confidence intervals (CIs). Overall, 10 studies were included, comprising 4,268 neonates. This included five randomized controlled trials, one quasi-randomized trial, and four cohort studies. The administration of PEEP was associated with significantly lower rates of mortality till discharge (odds ratio [OR]: 0.60, 95% CI: 0.49-0.74, moderate quality of evidence). The association was significant in preterm (OR: 0.57, 95% CI: 0.46-0.69) but not in term (OR: 1.03, 95% CI: 0.52-2.02) neonates. Low-to-moderate quality evidence suggests that providing PEEP during neonatal resuscitation is associated with lower rates of mortality in preterm neonates. Evidence regarding term neonates is limited and inconclusive. Future research is needed to determine the optimal device and shed more light on the long-term effects of PEEP administration during neonatal resuscitation. This study is registered with PROSPERO with registration number: CRD42020219956. KEY POINTS: · PEEP administration during neonatal resuscitation in the delivery room reduces mortality in preterm.. · Evidence regarding term neonates is limited and inconclusive.. · Future research is needed to determine the optimal device..

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.

Positive end-expiratory pressure during resuscitation at birth in very-low birth weight infants: A randomized-controlled pilot trial

BACKGROUND

There is limited evidence of the effect of positive end-expiratory pressure (PEEP) during resuscitation soon after birth. Premature neonates may experience respiratory distress from surfactant insufficiency and providing PEEP after the very first breath, may improve outcomes following appropriate resuscitation. The objective of this study was to evaluate the short term respiratory outcomes after positive pressure ventilation (PPV) with PEEP in preterm infants at birth.

METHODS

A prospective randomized-controlled, pilot trial was conducted. Premature neonates ≤ 32 weeks gestational age or birth weight < 1500 g were recruited. Subjects were allocated to either PEEP of 5 cm H₂O (PEEP-5) or no PEEP (PEEP-0) if PPV was administered. Pre-ductal, peripheral capillary oxygen saturation (SpO₂) and fraction of inspired oxygen concentration (FiO₂) were monitored at 1, 3, 5, 10, 15, and 20 min after birth. FiO₂ was adjusted to achieve targeted SpO₂ using the 2010 neonatal resuscitation protocol guidelines.

RESULTS

56% (14/25; PEEP-0) and 50% (13/26; PEEP-5) infants received PPV. Mean gestational age was 30 (PEEP-0) vs 31 (PEEP-5) weeks. The mean [SD] birthweight (g) of PEEP-0 was significantly lower than PEEP-5 (1050.4 [262.7] vs 1218.8 [236.8], p = 0.02). Pre-ductal SpO_2, FiO₂ delivered at each time point, and rates of pneumothorax, surfactant administration and oxygen dependency at 36 weeks postmenstrual age or death was similar.

CONCLUSION

Due to the small sample size and potential bias accrued through random allocation of higher birthweight infants to the PEEP-5 group, the results did not confirm differences in outcomes between the groups, despite evidence favoring postnatal ventilation with PEEP. A further randomized, controlled clinical trial with a larger sample size is warranted to determine the utility and safety of PEEP during the resuscitation of premature infants immediately after birth.

Variation in Positive End-Expiratory Pressure Levels for Mechanically Ventilated Extremely Low Birth Weight Infants

OBJECTIVE

To test the hypothesis that significant positive end-expiratory pressure (PEEP) level variation exists between neonatal centers.

STUDY DESIGN

We performed a secondary analysis cohort study of the Nasal Intermittent Positive-Pressure Ventilation trial. Our study population was extremely low birth weight infants requiring mechanical ventilation within 28 days of life. The exposure was neonatal center; 34 international centers participated in the trial. Subjects from centers with fewer than 5 eligible cases were excluded. The main outcome was the maximal PEEP level used during the first course of mechanical ventilation. Infant characteristics judged a priori to directly influence clinical PEEP level selection and all characteristics associated with PEEP at P <.05 in bivariable analyses were included with and without center in multivariable linear regression models. Variation in PEEP level use between centers following adjustment for infant characteristics was assessed.

RESULTS

A total of 278 extremely low birth weight infants from 17 centers were included. Maximal PEEP ranged from 3 to 9 cm H₂O, mean = 5.7 (SD = 0.9). Significant variation between centers remained despite adjustment for infant characteristics (P < .0001). Further, center alone explained a greater proportion of the PEEP level variation than all infant characteristics combined.

CONCLUSIONS

Marked variation in PEEP levels for extremely low birth weight infants exists between neonatal centers. Research providing evidence-based guidance for this important aspect of respiratory care in preterm infants at high risk of lung injury is needed.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00433212.

Surfactant for Respiratory Distress Syndrome: New Ideas on a Familiar Drug with Innovative Applications

In the last 4 decades, advances in neonatology have led to a significant increase in the survival of preterm infants. One of the biggest advances was the introduction of surfactant replacement therapy for the treatment of respiratory distress syndrome. This is the main cause of respiratory insufficiency in preterm infants and is one of the major causes of perinatal morbidity and mortality. Surfactant replacement therapy is already a well-investigated and established therapy in neonatology. However, surfactant replacement therapy has progressed and been refined over recent decades, especially with the increasing care for preterm infants born before 26 weeks' gestational age and the recent clinical focus on avoiding mechanical ventilation. Clinical evidence is evolving on new types of surfactant, surfactant dosages, co-medication given before, with, or after surfactant replacement, and new technical advances regarding the mode of administration.

Physiology of non-invasive respiratory support

Non-invasive ventilation (NIV) is used in neonates to treat extrathoracic and intrathoracic airway obstruction, parenchymal lung disease and disorders of control of breathing. Avoidance of airway intubation is associated with a reduction in the incidence of chronic lung disease among preterm infants with respiratory distress syndrome. Use of nasal continuous positive airway pressure (nCPAP) may help establish and maintain functional residual capacity (FRC), decrease respiratory work, and improve gas exchange. Other modes of non-invasive ventilation, which include heated humidified high-flow nasal cannula therapy (HHHFNC), nasal intermittent mandatory ventilation (NIMV), non-invasive pressure support ventilation (NI-PSV), and bi-level CPAP (SiPAP™), have also been shown to provide additional benefit in improving breathing patterns, reducing work of breathing, and increasing gas exchange when compared with nCPAP. Newer modes, such as neurally adjusted ventilatory assist (NAVA), hold the promise of improving patient-ventilator synchrony and so might ultimately improve outcomes for preterm infants with respiratory distress.

Reliability of Single-Use PEEP-Valves Attached to Self-Inflating Bags during Manual Ventilation of Neonates--An In Vitro Study

Introduction

International resuscitation guidelines suggest to use positive end-expiratory pressure (PEEP) during manual ventilation of neonates. Aim of our study was to test the reliability of self-inflating bags (SIB) with single-use PEEP valves regarding PEEP delivery and the effect of different peak inflation pressures (PIP) and ventilation rates (VR) on the delivered PEEP.

Methods

Ten new single-use PEEP valves from 5 manufacturers were tested by ventilating an intubated 1kg neonatal manikin containing a lung model with a SIB that was actuated by an electromechanical plunger device. Standard settings: PIP 20cmH₂O, VR 60/min, flow 8L/min. PEEP settings of 5 and 10cmH₂O were studied. A second test was conducted with settings of PIP 40cmH₂O and VR 40/min. The delivered PEEP was measured by a respiratory function monitor (CO₂SMO⁺).

Results

Valves from one manufacturer delivered no relevant PEEP and were excluded. The remaining valves showed a continuous decay of the delivered pressure during expiration. The median (25^th and 75^th percentile) delivered PEEP with standard settings was 3.4(2.7–3.8)cmH₂O when set to 5cmH₂O and 6.1(4.9–7.1)cmH₂O when set to 10cmH₂O. Increasing the PIP from 20 to 40 cmH₂O led to a median (25^th and 75^th percentile) decrease in PEEP to 2.3(1.8–2.7)cmH₂O and 4.3(3.2–4.8)cmH₂O; changing VR from 60 to 40/min led to a PEEP decrease to 2.8(2.1–3.3)cmH₂O and 5.0(3.5–6.2)cmH₂O for both PEEP settings.

Conclusion

Single-use PEEP valves do not reliably deliver the set PEEP. PIP and VR have an effect on the delivered PEEP. Operators should be aware of these limitations when manually ventilating neonates.

Acute Neonatal Respiratory Failure

Acute respiratory failure requiring assisted ventilation is one of the most common reasons for admission to the neonatal intensive care unit. Respiratory failure is the inability to maintain either normal delivery of oxygen to the tissues or normal removal of carbon dioxide from the tissues. It occurs when there is an imbalance between the respiratory workload and ventilatory strength and endurance. Definitions are somewhat arbitrary but suggested laboratory criteria for respiratory failure include two or more of the following: PaCO₂ > 60 mmHg, PaO₂ < 50 mmHg or O₂ saturation <80 % with an FiO₂ of 1.0 and pH < 7.25 (Wen et al. 2004).

The role of surfactant and non-invasive mechanical ventilation in early management of respiratory distress syndrome in premature infants

BACKGROUND

Surfactant replacement therapy has been used for few decades for the treatment of respiratory distress syndrome (RDS) and has significantly improved morbidity and mortality in premature infants. Non-invasive respiratory support has recently emerged as a strategy in the early management of RDS. In this review, we discuss the different strategies of early management of RDS.

DATA SOURCES

A literature search of PubMed database was conducted to review the subject. The quality of evidence of key clinical studies was graded according to a modified grading system of the international GRADE group.

RESULTS

Continuous positive airway pressure (CPAP) with selective surfactant is a safe alternative to routine intubation, surfactant and mechanical ventilation in preterm infants with spontaneous breathing, and such an approach has been associated with decreased risk of death and bronchopulmonary dysplasia. There is a risk of pneumothorax when using a high pressure of CPAP (≥8 cm of H2O), a high partial pressure of carbon dioxide (PCO2 >75 mm of Hg), and a high fraction of inspired oxygen (FiO2 >0.6) as a threshold for intubation while on CPAP.

CONCLUSION

Not all preterm infants need surfactant treatment, and non-invasive respiratory support is a safe and effective approach.

Minimally invasive surfactant therapy with a gastric tube is as effective as the intubation, surfactant, and extubation technique in preterm babies

AIM

Preterm infants requiring surfactant replacement have been treated using the INSURE technique, which requires sedation and comprises tracheal intubation, surfactant instillation and extubation. However, minimally invasive surfactant therapy (MIST) does not require sedation, minimises airway injury and avoids placing positive pressure ventilation on an immature lung. This study compared the feasibility of the two techniques and the outcomes in preterm babies with respiratory distress syndrome (RDS).

METHODS

Preterm infants with RDS prospectively received surfactant via a gastric tube placed in the trachea by direct laryngoscopy with no sedation. Technique-related complications and respiratory outcomes were analysed.

RESULTS

We compared 44 patients who received MIST with a historic cohort of 31 patients who received INSURE. This showed no differences in the rate of intubation and mechanical ventilation in the first 72 h, or secondary respiratory outcomes and relevant morbidities, between the babies who received INSURE and those who received MIST. More babies in the MIST group (35%) needed a second dose of surfactant than the INSURE group (6.5%) (p < 0.0001).

CONCLUSION

Surfactant administration using MIST, with no sedation, is feasible in preterm infants with RDS. No significant differences in secondary respiratory outcomes were found between the MIST and INSURE techniques.

SP-B and SP-C containing new synthetic surfactant for treatment of extremely immature lamb lung

Although superiority of synthetic surfactant over animal-driven surfactant has been known, there is no synthetic surfactant commercially available at present. Many trials have been made to develop synthetic surfactant comparable in function to animal-driven surfactant. The efficacy of treatment with a new synthetic surfactant (CHF5633) containing dipalmitoylphosphatidylcholine, phosphatidylglycerol, SP-B analog, and SP-C analog was evaluated using immature newborn lamb model and compared with animal lung tissue-based surfactant Survanta. Lambs were treated with a clinical dose of 200 mg/kg CHF5633, 100 mg/kg Survanta, or air after 15 min initial ventilation. All the lambs treated with air died of respiratory distress within 90 min of age. During a 5 h study period, Pco(2) was maintained at 55 mmHg with 24 cmH(2)O peak inspiratory pressure for both groups. The preterm newborn lamb lung functions were dramatically improved by CHF5633 treatment. Slight, but significant superiority of CHF5633 over Survanta was demonstrated in tidal volume at 20 min and dynamic lung compliance at 20 and 300 min. The ultrastructure of CHF5633 was large with uniquely aggregated lipid particles. Increased uptake of CHF5633 by alveolar monocytes for catabolism was demonstrated by microphotograph, which might be associated with the higher treatment dose of CHF5633. The higher catabolism of CHF5633 was also suggested by the similar amount of surfactant lipid in bronchoalveolar lavage fluid (BALF) between CHF5633 and Survanta groups, despite the 2-fold higher treatment dose of CHF5633. Under the present ventilation protocol, lung inflammation was minimal for both groups, evaluated by inflammatory cell numbers in BALF and expression of IL-1β, IL-6, IL-8, and TNFα mRNA in the lung tissue. In conclusion, the new synthetic surfactant CHF5633 was effective in treating extremely immature newborn lambs with surfactant deficiency during the 5 h study period.

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

BACKGROUND

Conventional mechanical ventilation (CMV) of neonates has been used as a treatment of respiratory failure for over 30 years. While CMV facilitates gas exchange, it may simultaneously damage the lung. Positive end expiratory pressure (PEEP) has received less attention than other ventilation parameters when considering this balance of benefit and possible harm. While an appropriate level of PEEP may exert substantial benefits in ventilation, both inappropriately low or high levels may lead to harm. An appropriate level of PEEP for neonates may also be best achieved by an individualized approach.

OBJECTIVES

1. To compare the effects of different levels of PEEP in preterm newborn infants requiring CMV for respiratory distress syndrome (RDS).2. To compare the effects of different levels of PEEP in preterm infants requiring CMV for bronchopulmonary dysplasia (BPD).3. To compare the effects of different methods for individualizing PEEP to an optimal level in preterm newborn infants requiring CMV for RDS.

SEARCH METHODS

The search was performed in accordance with the standard search strategy for the Cochrane Neonatal Review Group. The Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), Ovid MEDLINE, EMBASE, study references and experts were utilized for study identification.

SELECTION CRITERIA

All randomized and quasi-randomized controlled trials studying preterm infants (less than 37 weeks gestational age) requiring CMV with endotracheal intubation and undergoing randomization to either different PEEP levels (RDS or BPD) or two or more alternative methods for individualizing PEEP levels (RDS only) were included. Cross-over trials were included but we limited the findings to those in the first cross-over period.

DATA COLLECTION AND ANALYSIS

Data collection and analysis were performed in accordance with the recommendations of the Cochrane Neonatal Review Group.

MAIN RESULTS

An initial evaluation identified 10 eligible articles. Ultimately, a single study met our inclusion criteria. The study addressed the effects of different levels of PEEP in preterm newborn infants requiring CMV for RDS. Only short term physiologic measures were reported. All results were limited to a small sample size without statistically significant results. No trials addressing the effect of PEEP in infants with BPD or strategies to individualize the management of PEEP were identified.

AUTHORS' CONCLUSIONS

There is insufficient evidence to guide selection of appropriate PEEP levels for RDS or CMV. There is a need for well designed clinical trials evaluating the optimal application of this important and frequently applied intervention.

Positive end-expiratory pressure and surfactant decrease lung injury during initiation of ventilation in fetal sheep

The initiation of ventilation in preterm, surfactant-deficient sheep without positive end-expiratory pressure (PEEP) causes airway injury and lung inflammation. We hypothesized that PEEP and surfactant treatment would decrease the lung injury from initiation of ventilation with high tidal volumes. Fetal sheep at 128-day gestational age were randomized to ventilation with: 1) no PEEP, no surfactant; 2) 8-cmH(2)O PEEP, no surfactant; 3) no PEEP + surfactant; 4) 8-cmH(2)O PEEP + surfactant; or 5) control (2-cmH(2)O continuous positive airway pressure) (n = 6-7/group). After maternal anesthesia and hysterotomy, the head and chest were exteriorized, and the fetus was intubated. While maintaining placental circulation, the fetus was ventilated for 15 min with a tidal volume escalating to 15 ml/kg using heated, humidified, 100% nitrogen. The fetus then was returned to the uterus, and tissue was collected after 30 min for evaluation of early markers of lung injury. Lambs receiving both surfactant and PEEP had increased dynamic compliance, increased static lung volumes, and decreased total protein and heat shock proteins 70 and 60 in bronchoalveolar lavage fluid compared with other groups. Ventilation, independent of PEEP or surfactant, increased mRNA expression of acute phase response genes and proinflammatory cytokine mRNA in the lung tissue compared with controls. PEEP decreased mRNA for cytokines (2-fold) compared with groups receiving no PEEP. Surfactant administration further decreased some cytokine mRNAs and changed the distribution of early growth response protein-1 expression. The use of PEEP during initiation of ventilation at birth decreased early mediators of lung injury. Surfactant administration changed the distribution of injury and had a moderate additive protective effect.

The Neopuff's PEEP valve is flow sensitive

AIM

The current recommendation in setting up the Neopuff is to use a gas flow of 5-15 L/min. We investigated if the sensitivity of the positive end expiratory pressure (PEEP) valve varies at different flow rates within this range.

METHODS

Five Neopuffs were set up to provide a PEEP of 5 cm H(2) O. The number of clockwise revolutions to complete occlusion of the PEEP valve and the mean and range of pressures at each quarter clockwise revolution were recorded at gas flow rates between 5 and 15 L/min.

RESULTS

  At 5, 10 and 15 L/min, 0.5, 1.7 and 3.4 full clockwise rotations were required to completely occlude the PEEP valve, and pressures rose from 5 to 11.4, 18.4 and 21.5 cm H(2) O, respectively. At a flow rate of 5 L/min, half a rotation of the PEEP dial resulted in a rise in PEEP from 5 to 11.4cm H(2) O. At 10 L/min, half a rotation resulted in a rise from 5 to 7.7cm H(2) O, and at 15 L/min PEEP rose from 5 to 6.8cm H(2) O.

CONCLUSION

Users of the Neopuff should be aware that the PEEP valve is more sensitive at lower flow rates and that half a rotation of the dial at 5 L/min gas flow can more than double the PEEP.

Inhibitors of inflammation and endogenous surfactant pool size as modulators of lung injury with initiation of ventilation in preterm sheep

BACKGROUND

Increased pro-inflammatory cytokines in tracheal aspirates correlate with the development of BPD in preterm infants. Ventilation of preterm lambs increases pro-inflammatory cytokines and causes lung inflammation.

OBJECTIVE

We tested the hypothesis that selective inhibitors of pro-inflammatory signaling would decrease lung inflammation induced by ventilation in preterm newborn lambs. We also examined if the variability in injury response was explained by variations in the endogenous surfactant pool size.

METHODS

Date-mated preterm lambs (n = 28) were operatively delivered and mechanically ventilated to cause lung injury (tidal volume escalation to 15 mL/kg by 15 min at age). The lambs then were ventilated with 8 mL/kg tidal volume for 1 h 45 min. Groups of animals randomly received specific inhibitors for IL-8, IL-1, or NF-κB. Unventilated lambs (n = 7) were the controls. Bronchoalveolar lavage fluid (BALF) and lung samples were used to quantify inflammation. Saturated phosphatidylcholine (Sat PC) was measured in BALF fluid and the data were stratified based on a level of 5 μmol/kg (~8 mg/kg surfactant).

RESULTS

The inhibitors did not decrease the cytokine levels or inflammatory response. The inflammation increased as Sat PC pool size in BALF decreased. Ventilated lambs with a Sat PC level > 5 μmol/kg had significantly decreased markers of injury and lung inflammation compared with those lambs with < 5 μmol/kg.

CONCLUSION

Lung injury caused by high tidal volumes at birth were decreased when endogenous surfactant pool sizes were larger. Attempts to decrease inflammation by blocking IL-8, IL-1 or NF-κB were unsuccessful.

Synthetic surfactant based on analogues of SP-B and SP-C is superior to single-peptide surfactants in ventilated premature rabbits

BACKGROUND

Respiratory distress syndrome (RDS) is currently treated with surfactant preparations obtained from natural sources and attempts to develop equally active synthetic surfactants have been unsuccessful. One difference in composition is that naturally derived surfactants contain the two hydrophobic proteins SP-B and SP-C while synthetic preparations contain analogues of either SP-B or SP-C. It was recently shown that both SP-B and SP-C (or SP-C33, an SP-C analogue) are necessary to establish alveolar stability at end-expiration in a rabbit RDS model, as reflected by high lung gas volumes without application of positive end-expiratory pressure.

OBJECTIVES

To study the efficacy of fully synthetic surfactants containing analogues of both SP-B and SP-C compared to surfactants with only one protein analogue.

METHODS

Premature newborn rabbits, treated with synthetic surfactants, were ventilated for 30 min without positive end-expiratory pressure. Tidal volumes as well as lung gas volumes at end-expiration were determined.

RESULTS

Treatment with 2% Mini-B (a short-cut version of SP-B) and 2% SP-C33, or its C-terminally truncated form SP-C30, in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol, 68:31 (w/w) resulted in median lung gas volumes of 8-9 ml/kg body weight, while animals treated with 2% Mini-B surfactant or 2% SP-C33/SP-C30 surfactant had lung gas volumes of 3-4 ml/kg, and those treated with Curosurf, a porcine surfactant, 15-17 ml/kg. In contrast, mixing SP-C33 with peptides with different distributions of positively charged and hydrophobic residues did not improve lung gas volumes.

CONCLUSIONS

The data indicate that synthetic surfactants containing analogues of both SP-B and SP-C might be superior to single-peptide surfactants in the treatment of RDS.

The effect of a PEEP valve on a Laerdal neonatal self-inflating resuscitation bag

BACKGROUND

Self-inflating bags are used to provide ventilation during neonatal resuscitation. However, they cannot provide positive end expiratory pressure (PEEP) unless a PEEP valve is attached. The ability of Laerdal neonatal self-inflating bags fitted with PEEP valves to reliably deliver PEEP is unclear. The aim of this study was to measure the delivered PEEP at different set PEEP levels and inflation rates.

METHODS

We connected disposable and non-disposable 240 mL Laerdal self-inflating resuscitation bags fitted with PEEP valves to a leak-free test lung. We measured PEEP delivered with the valve set at 5, 7 and 10 cm H(2)O whilst inflating the test lung at rates of 20, 40 and 60 min. Studies were done with 8 L/min of gas flow and with no gas flow.

RESULTS

The PEEP delivered was close to the set level immediately after inflation but declined rapidly between inflations. The mean PEEP was higher with faster ventilation rates. When PEEP was set at 7 cm H(2)O, using a non-disposable bag, and an inflation rate of 60/min the mean (SD) PEEP was 5.4 (0.19) cm H(2)O. The PEEP delivered was unrelated to the gas flow into the device.

CONCLUSION

The 240 mL Laerdal self-inflating bag with a PEEP valve delivers PEEP that loses pressure quickly. The level of PEEP delivered is less than that set, particularly at rates below 40/min.

Feasibility and short-term effects of biphasic positive airway pressure versus assist-control ventilation in preterm lambs

Biphasic positive airway pressure (BiLevel) ventilation allows utilization of two alternating positive end-expiratory pressures (PEEP) while permitting unrestricted spontaneous breathing with superimposed synchronized pressure support. We aimed to compare whether BiLevel versus assist-control (A-C) ventilation provides effective gas exchange and reduces severity of early lung injury in preterm lambs. Preterm lambs delivered at 134 d (term = 150 d) were quasirandomized to BiLevel (PEEP low/high 5/20 cm H2O) or A-C5 (PEEP 5 cm H2O) ventilation. Ventilation parameters and arterial blood gases were recorded at regular intervals. Postmortem measurements included pressure-volume relationship, lung inflammatory score, wet/dry body weight ratio, and messenger RNA (mRNA) expression of early markers of lung injury. There were no significant differences between groups in baseline characteristics, oxygenation index (p = 0.49), or partial pressure of carbon dioxide (Paco2) (p = 0.08). BiLevel group lambs showed improved pressure-volume relationship (p = 0.006), lower lung inflammatory score (p = 0.013), and trend toward lower messenger RNA expression of markers of lung injury compared with A-C5 group lambs. In unsedated preterm lambs, BiLevel ventilation provides gas exchange equivalent to A-C ventilation and potentially results in reduced lung injury.

Positive end-expiratory pressure enhances development of a functional residual capacity in preterm rabbits ventilated from birth

The factors regulating lung aeration and the initiation of pulmonary gas exchange at birth are largely unknown, particularly in infants born very preterm. As hydrostatic pressure gradients may play a role, we have examined the effect of a positive end-expiratory pressure (PEEP) on the spatial and temporal pattern of lung aeration in preterm rabbit pups mechanically ventilated from birth using simultaneous phase-contrast X-ray imaging and plethysmography. Preterm rabbit pups were delivered by caesarean section at 28 days of gestational age, anesthetized, intubated, and placed within a water-filled plethysmograph (head out). Pups were imaged as they were mechanically ventilated from birth with a PEEP of either 0 cmH2O or 5 cmH2O. The peak inflation pressure was held constant at 35 cmH2O. Without PEEP, gas only entered into the distal airways during inflation. The distal airways collapsed during expiration, and, as a result, the functional residual capacity (FRC) did not increase above the lung's anatomic dead space volume (2.5 ± 0.8 ml/kg). In contrast, ventilation with 5-cmH2O PEEP gradually increased aeration of the distal airways, which did not collapse at end expiration. The FRC achieved in pups ventilated with PEEP (19.9 ± 3.2 ml/kg) was significantly greater than in pups ventilated without PEEP (−2.3 ± 3.5 ml/kg). PEEP greatly facilitates aeration of the distal airways and the accumulation of FRC and prevents distal airway collapse at end expiration in very preterm rabbit pups mechanically ventilated from birth.

Imaging lung aeration and lung liquid clearance at birth using phase contrast X-ray imaging

The transition to extra-uterine life at birth is critically dependent on airway liquid clearance to allow the entry of air and the onset of gaseous ventilation. We have used phase contrast X-ray imaging to identify factors that regulate lung aeration at birth in spontaneously breathing term and mechanically ventilated preterm rabbit pups. Phase contrast X-ray imaging exploits the difference in refractive index between air and water to enhance image contrast, enabling the smallest air-filled structures of the lung (alveoli; < 100 microm) to be resolved. Using this technique, the lungs become visible as they aerate, allowing the air-liquid interface to be observed as it moves distally during lung aeration. Spontaneously breathing term rabbit pups rapidly aerate their lungs, with most fully recruiting their functional residual capacity (FRC) within the first few breaths. The increase in FRC occurs mainly during individual breaths, demonstrating that airway liquid clearance and lung aeration is closely associated with inspiration. We suggest that transpulmonary pressures generated by inspiration provide a hydrostatic pressure gradient for the movement of water out of the airways and into the surrounding lung tissue after birth. In mechanically ventilated preterm pups, lung aeration is closely associated with lung inflation and a positive end-expiratory pressure is required to generate and maintain FRC after birth. In summary, phase contrast X-ray imaging can image the air-filled lung with high temporal and spatial resolution and is ideal for identifying factors that regulate lung aeration at birth in both spontaneously breathing term and mechanically ventilated preterm neonates.

Relationship between oxygen saturation and the mode of oxygen delivery used in newborn resuscitation

OBJECTIVE

To compare the rate of increase in oxygen saturation in babies receiving supplemental oxygen during resuscitation with those transitioning in room air.

STUDY DESIGN

Prospective observational study. Infants were resuscitated with supplemental oxygen and continuous recording of preductal oxygen saturation was started immediately after birth. Oxygen saturation measurements from healthy newborns transitioned in room air were used for comparison.

RESULT

A total of 186 infants were included--70 received supplemental oxygen and 116 were transitioned in room air. Compared with healthy infants transitioned in room air, infants receiving 100% oxygen by positive-pressure ventilation (PPV) did not differ significantly in the rate of increase in oxygen saturation (1.5% per minute, P=0.26), whereas infants receiving 100% free-flow oxygen had a significantly slower rate of increase in oxygen saturation (1.2% per minute, P=0.04).

CONCLUSION

Babies receiving 100% oxygen by free flow had a slower increase in oxygen saturation compared with healthy infants transitioned in room air, whereas those receiving 100% oxygen by PPV had a similar increase in oxygen saturation compared with healthy infants transitioned in room air.

Effects of positive end-expiratory pressure, inhaled nitric oxide and surfactant on expression of proinflammatory cytokines and growth factors in preterm piglet lungs

We hypothesized that imbalance of proinflammatory cytokines and growth factors (GFs) in immature lungs of early postnatal life may be affected by protective ventilation strategy, and evaluated correlations of these aspects. Preterm neonate piglets were mechanically ventilated with low tidal volume and 5-6 or 10-12 cm H2O positive end-expiratory pressure (PEEP) with or without surfactant and inhaled nitric oxide (iNO) for 6 h, followed by biochemical, biophysical, and histopathological assessment of lung injury severity. Compared with surfactant and the control, iNO combined with lower PEEP exerted better oxygenation, lower activity of myeloperoxidase, lower expression of mRNA of interleukin (IL)-1beta, IL-6, IL-8, and platelet derived growth factor-B (PDGF-B), but higher expression of insulin-like growth factor-I (IGF-I), whereas that of tumor necrosis factor-alpha, keratinocyte GF, hepatocyte GF, vascular endothelial growth factor, and TGF-beta1 had no or modest changes. IL-1beta, IL-6 mRNA were closely correlated to PDGF-B mRNA and myeloperoxidase, but inversely to IGF-I mRNA, Pao2/FiO2 and dynamic lung compliance at 6 h. These results indicate that the association of lower PEEP and iNO may be more protective than surfactant on preventing lung injury and facilitating reparation by affecting the expression of proinflammatory cytokines and GFs.

Surfactant proteins B and C are both necessary for alveolar stability at end expiration in premature rabbits with respiratory distress syndrome

Modified natural surfactant preparations, used for treatment of respiratory distress syndrome in premature infants, contain phospholipids and the hydrophobic surfactant protein (SP)-B and SP-C. Herein, the individual and combined effects of SP-B and SP-C were evaluated in premature rabbit fetuses treated with airway instillation of surfactant and ventilated without positive end-expiratory pressure. Artificial surfactant preparations composed of synthetic phospholipids mixed with either 2% (wt/wt) of porcine SP-B, SP-C, or a synthetic poly-Leu analog of SP-C (SP-C33) did not stabilize the alveoli at the end of expiration, as measured by low lung gas volumes of ∼5 ml/kg after 30 min of ventilation. However, treatment with phospholipids containing both SP-B and SP-C/SP-C33 approximately doubled lung gas volumes. Doubling the SP-C33 content did not affect lung gas volumes. The tidal volumes were similar in all groups receiving surfactant. This shows that SP-B and SP-C exert different physiological effects, since both proteins are needed to establish alveolar stability at end expiration in this animal model of respiratory distress syndrome, and that an optimal synthetic surfactant probably requires the presence of mimics of both SP-B and SP-C.

Immediate respiratory management of the preterm infant

Infants born prematurely have underdeveloped lungs characterised by both morphological and biochemical abnormalities. Respiratory distress syndrome (RDS) is the leading cause of morbidity and mortality in this population. Both surfactant replacement therapy with mechanical ventilation and continuous positive airway pressure (CPAP) have been shown to be of benefit. However, considerable controversy exists about how best to use these therapies. This paper will review the pathophysiology of RDS and the evidence supporting each of these treatments.

Cardiorespiratory effects of changes in end expiratory pressure in ventilated newborns

BACKGROUND

Positive pressure ventilation in premature infants can improve oxygenation but may diminish cerebral blood flow and cardiac output. Low superior vena cava (SVC) flow increases risk of intraventricular haemorrhage, and higher mean airway pressure is associated with low SVC flow. Whether this is a direct effect of positive pressure ventilation or a reflection of severity of lung disease is not known. This study aimed to determine if positive end expiratory pressure (PEEP) in ventilated newborns could be increased without clinically relevant cardiorespiratory changes.

METHOD

Ventilated newborns were studied before and 10 min after increasing PEEP (5 cm H(2)O to 8 cmH(2)O) and again when PEEP returned to baseline. Echocardiographic and respiratory function measurements were collected during the intervention.

RESULTS

In 50 infants, increased PEEP was associated with a non-significant difference in mean SVC flow of -5 ml/kg/min (95% CI -12 to 3 ml/kg/min) but a significant reduction in right ventricular output of 17 ml/kg/min (95% CI 5 to 28 ml/kg/min). The increase in lung compliance was non-significant (median difference 0.02 ml/cmH(2)O/kg) and the decrease in lung resistance (18 cmH(2)O/l/s; 95% CI 10 to 26 cm H(2)O/l/s) was significant. Changes (%) in lung compliance and SVC flow, when corrected for Paco(2), were positively associated (regression coefficient 0.4%; 95% CI 0.2% to 0.6%).

CONCLUSION

A short-term increase in PEEP does not lead to significant changes in systemic blood flow, although 36% of infants in the present study had clinically important changes in flow (+/-25%). The intervention can improve dynamic lung function, especially airway resistance. Improvements in compliance tend to be associated with improvements in blood flow.

Brief, large tidal volume ventilation initiates lung injury and a systemic response in fetal sheep

RATIONALE

Premature infants are exposed to potentially injurious ventilation in the delivery room. Assessments of lung injury are confounded by effects of subsequent ventilatory support.

OBJECTIVES

To evaluate the injury response to a brief period of large tidal volume (Vt) ventilation, simulating neonatal resuscitation in preterm neonates.

METHODS

Preterm lambs (129 d gestation; term is150 d) were ventilated (Vt = 15 ml/kg, no positive end-expiratory pressure) for 15 minutes to simulate delivery room resuscitation, either with the placental circulation intact (fetal resuscitation [ FR]) or after delivery (neonatal resuscitation [NR]). After the initial 15 minutes, lambs received surfactant and were maintained with either ventilatory support (FR-VS and NR-VS) or placental support (FR-PS) for 2 hours, 45 minutes. A control group received no resuscitation and was maintained with placental support. Samples of bronchoalveolar lavage fluid, lung, and liver were analyzed.

MEASUREMENTS AND MAIN RESULTS

Inflammatory cells and protein in bronchoalveolar lavage fluid, heat shock protein-70 immunostaining, IL-1beta, IL-6, IL-8, monocyte chemotactic protein-1, serum amyloid A (SAA)-3, Toll-like receptor (TLR)-2, and TLR4 mRNA in the lungs were increased in the FR-PS group compared with control animals. There were further elevations in neutrophils, IL-6, and IL-8 mRNA in the FR-VS and NR-VS groups compared with FR-PS. SAA3, TLR2, and TLR4 mRNA increased in the liver in all resuscitation groups relative to control animals.

CONCLUSIONS

Ventilation for 15 minutes with a Vt of 15 ml/kg initiates an injurious process in the preterm lung and a hepatic acute-phase response. Subsequent ventilatory support causes further increases in some injury indicators.

Positive End-Expiratory Pressure Modifies Response to Recombinant and Natural Exogenous Surfactant in Ventilated Immature Newborn Rabbits

BACKGROUND AND OBJECTIVES

Different types of surfactant preparations were shown not to exert uniform response in preterm infants suffering from respiratory distress syndrome (RDS). Therefore, the effects of a recombinant surfactant protein C (rSP-C) based preparation and a natural surfactant were compared applying different levels of positive end-expiratory pressure (PEEP) in experimental RDS.

METHODS

Preterm rabbits (n = 7-14 per group; 27 days gestation; term 30 days) were randomized for receiving either 100 mg/kg rSP-C or natural bovine surfactant and were compared with saline treated controls. Animals were ventilated for 30 min with either 0.3 or 0 kPa PEEP at standardized tidal volumes and lung mechanics were measured as well as lung histology and mRNA expression of surfactant associated proteins B and C by real-time PCR.

RESULTS

The PEEP level applied (0.3 vs. 0 kPa) largely influenced dynamic compliance after administration of rSP-C surfactant (4.45 vs. 2.58 ml/kg), whereas natural surfactant improved compliance regardless of the PEEP applied (4.86 vs. 4.24 ml/kg) compared to controls (2.41 vs. 1.55 ml/kg). Accordingly, administration of PEEP significantly increased alveolar count in all groups as well as SP-C mRNA expression, whereas SP-B expression and protein content both remained unchanged.

CONCLUSION

Response to rSP-C surfactant depends on the PEEP level applied in our model of neonatal RDS. These findings should be considered for the conception of clinical trials regarding treatment strategies in neonatal RDS.

New Synthetic Surfactant – How and When?

Animal-derived surfactant preparations are very effective in the treatment of premature infants with respiratory distress syndrome but they are expensive to produce and supplies are limited. In order to widen the indications for surfactant treatment there is a need for synthetic preparations, which can be produced in large quantities and at a reasonable cost. However, development of clinically active synthetic surfactants has turned out to be more complicated than initially anticipated. The hydrophobic surfactant proteins, SP-B and SP-C, which are involved in the adsorption of surface-active lipids to the air-liquid interface of the alveoli and increase alveolar stability, are either too big to synthesize, structurally complex or unstable in pure form. A new generation of synthetic surfactants containing simplified phospholipid mixtures and small amounts of peptides replacing the hydrophobic proteins is currently under development and will in the near future be introduced into the market. However, more trials need to be performed before any conclusions can be drawn about the effectiveness of these synthetic surfactants in relation to natural animal-derived preparations.

Continuous positive airway pressure during neonatal resuscitation

Despite the large body of information regarding the beneficial effects of continuous positive airway pressure (CPAP) in infants with respiratory distress syndrome (RDS) data are insufficient at this time to support or refute its use during neonatal resuscitation. An individualized approach to infants with respiratory distress is recommended.

A survey of delivery room resuscitation practices in the United States

OBJECTIVE

To determine current resuscitation practices of neonatologists in the United States.

METHODS

A 15-question survey was developed and mailed to neonatal directors in May 2004.

RESULTS

Of the total of 797 surveys mailed, 84 were returned undeliverable or unanswered and 450 were returned completed (63% response rate). Respondents were mainly (70%) from level III NICUs. Most programs resuscitate newborns in the delivery room (83%), rather than in a separate room. The number and background of individuals attending deliveries vary greatly, with 31% of programs having <3 individuals attending deliveries. Flow-inflating bags are most commonly used (51%), followed by self-inflating bags (40%) and T-piece resuscitators (14%). Pulse oximeters are used during resuscitation by 52% of programs, and 23% of respondents indicated that there was a useful signal within 1 minute after application. Blenders are available for 42% of programs, of which 77% use pure oxygen for the initial resuscitation and 68% use oximeters to alter the fraction of inspired oxygen. Thirty-two percent of programs use carbon dioxide detectors to confirm intubation, 48% routinely and 43% when there is difficulty confirming intubation. Preterm infants are wrapped with plastic wrap to prevent heat loss in 29% of programs, of which 77% dry the infant before wrap application. A majority of programs (76%) attempt to provide continuous positive airway pressure or positive end expiratory pressure (PEEP) during resuscitation, most commonly with a flow-inflating bag (58%), followed by a self-inflating bag with PEEP valve (19%) and T-piece resuscitator (16%). A level of 5 cm H2O is used by 55% of programs.

CONCLUSIONS

Substantial variations exist in neonatal resuscitation practices, some of which are not addressed in standard guidelines. Future guidelines should include recommendations regarding the use of blenders, oximeters, continuous positive airway pressure/PEEP, and plastic wrap during resuscitation.

Effects of tidal volume and positive end-expiratory pressure during resuscitation of very premature lambs

BACKGROUND

Guidelines recommend neonatal resuscitation without controlling tidal volume or positive end-expiratory pressure (PEEP). However, these may improve gas exchange, lung volume and outcome.

AIM

To investigate resuscitation of very premature lambs with a Laerdal bag without PEEP versus volume guarantee ventilation with PEEP.

METHODS

Anaesthetized lambs (n=20) delivered at 125 d gestation were randomized to three groups receiving 15 min resuscitation: (1) Laerdal bag and no PEEP; (2) ventilation with a tidal volume of 5 ml/kg and 8 cm H(2)O PEEP; (3) ventilation with 10 ml/kg and 8 cm H(2)O PEEP. They were then all ventilated for 2 h with tidal volumes of 5 or 10 ml/kg, and 8 cm H(2)O PEEP. Ventilation parameters and blood gases were recorded.

RESULTS

Different tidal volumes affected PaCO(2) within minutes, with 10 ml/kg causing severe hypocarbia. PEEP had little effect on PaCO(2). Oxygenation improved significantly with PEEP of 8 cm H(2)O, irrespective of tidal volume.

CONCLUSION

Very premature lambs can be resuscitated effectively using volume-guarantee ventilation and PEEP. Tidal volumes affected PaCO(2) within minutes but had little effect on oxygenation. PEEP halved the oxygen requirement compared with no PEEP. Resuscitating premature babies with controlled tidal volumes and PEEP might improve their outcome.

A comparison of three neonatal resuscitation devices

BACKGROUND

Ventilation during neonatal resuscitation involves the use of self-inflating bags, flow-inflating bags, and T-piece resuscitators. The ability of operators to deliver desired peak inspiratory pressures (PIP), positive end expiratory pressures (PEEP), prolonged inflations and the length of time to transition between different pressures has not been compared for all three of these devices.

OBJECTIVE

To compare the ability of neonatal resuscitation personnel to deliver predetermined ventilation interventions using these devices in advance of a clinical trial of neonatal resuscitation.

DESIGN/METHODS

We studied 31 operators (neomatologists, neonatal respiratory therapists, neonatal fellows, a pediatrician, pediatric residents, neonatal nurse practitioners, and neonatal nurses) using a T-piece resuscitator (Neopuff), Fisher and Paykel Healthcare, Auckland, New Zealand), a self-inflating bag (Baby Blue II, Vital Signs, Totowa, NJ), and a flow-inflating bag (Model E191 Anesthesia Associates, San Marcos, CA). The self-inflating bag was tested with and without the manufacturer's PEEP valve. Using a continuous pressure recording system and a neonatal manikin, we evaluated the ability to deliver a consistent PIP of 20 or 40 cmH2O and a PEEP of 5 cmH2O during 30 s of ventilation, the ability to maintain a 5 s inflation at a PIP of 20 cmH2O and the time to transition from a PIP of 20 to 40 cmH2O. Each device was evaluated with and without a qualitative CO2 detector (Pedicap) Nellcor Pleasanton, CA).

RESULTS

The T-piece resuscitator delivered the desired PIP more precisely and consistently compared with the self-inflating bag at a target of 20 cmH2O (maximum PIP 20.7 cmH2O, S.D.=0.8 versus 24.7 cmH2O, S.D.=2.8; p<0.001). At a target of 40 cmH2O, the maximum pressure delivered with the T-piece resuscitator was significantly less than both the flow-inflating bag and the self-inflating bag (39.7 cmH2O, S.D.=2.1 versus 44 cmH2O, S.D.=3.3 versus 45.3 cmH2O, S.D.=4.7; p<0.001). It took significantly longer to increase the PIP from 20 to 40 cmH2O using the T-piece resuscitator compared to the self-inflating bag or the flow-inflating bag (5.7 s versus 2.2 s versus 1.8 s; p<0.001), and three operators could not make the transition in the allotted 15 s time limit. During the 5 s prolonged inflation, the T-piece resuscitator and the flow-inflating bag maintained a pressure greater than 18 cmH2O for a longer time than the self-inflating bag (4 s versus 3.7 s versus 2.2 s; p<0.001). The self-inflating bag with the PEEP valve in place provided significantly less PEEP than both the T-piece resuscitator and the flow-inflating bag (3.6 cmH2O versus 4.4 cmH2O versus 4.4 cmH2O; p<0.005). The Pedicap did not significantly affect any of the observed results, and there were no consistent operator differences between different disciplines or years of experience.

CONCLUSIONS

The T-piece resuscitator delivered the desired pressures more accurately, but required greater time to increase the PIP from 20 to 40 cmH2O. It was difficult to maintain a prolonged inflation and deliver the desired PEEP with the self-inflating bag even with the PEEP valve in place. There is a need for improvement in the design and function of current manual resuscitation devices and for prospective trials to evaluate the optimal method of bag and mask ventilation during resuscitation of the newborn infant.

Continuous positive airway pressure causes lung injury in a model of sepsis

Continuous positive airway pressure, aimed at preventing pulmonary atelectasis, has been used for decades to reduce lung injury in critically ill patients. In neonatal practice, it is increasingly used worldwide as a primary form of respiratory support due to its low cost and because it reduces the need for endotracheal intubation and conventional mechanical ventilation. We studied the anesthetized in vivo rat and determined the optimal circuit design for delivery of continuous positive airway pressure. We investigated the effects of continuous positive airway pressure following lipopolysaccharide administration in the anesthetized rat. Whereas neither continuous positive airway pressure nor lipopolysaccharide alone caused lung injury, continuous positive airway pressure applied following intravenous lipopolysaccharide resulted in increased microvascular permeability, elevated cytokine protein and mRNA production, and impaired static compliance. A dose-response relationship was demonstrated whereby higher levels of continuous positive airway pressure (up to 6 cmH2O) caused greater lung injury. Lung injury was attenuated by pretreatment with dexamethasone. These data demonstrate that despite optimal circuit design, continuous positive airway pressure causes significant lung injury (proportional to the airway pressure) in the setting of circulating lipopolysaccharide. Although we would currently avoid direct extrapolation of these findings to clinical practice, we believe that in the context of increasing clinical use, these data are grounds for concern and warrant further investigation.

Spontaneous breathing or mechanical ventilation alters lung compliance and tissue association of exogenous surfactant in preterm newborn rabbits

In preterm infants with respiratory distress syndrome, surfactant administration followed by immediate extubation to spontaneous breathing with nasal continuous positive airway pressure reduces the need for mechanical ventilation. With this treatment approach, repeated doses of surfactant are rarely indicated. We used a rabbit model to test the hypothesis that exogenous surfactant therapy followed by spontaneous breathing results in a more sustained initial treatment response compared with treatment followed by mechanical ventilation. Preterm rabbits (gestational age 28.5 d) were treated with pharyngeal deposition of 200 mg/kg radiolabeled surfactant (14C-Curosurf) and randomized to 4 h of spontaneous breathing or mechanical ventilation or to a control group, killed immediately after surfactant administration. With pharyngeal deposition, 46 +/- 10% (mean +/- SEM) of the administered surfactant reached the lungs. The dynamic lung-thorax compliance was higher in spontaneously breathing compared with mechanically ventilated animals (median, 9.9 and 0.75 ml x cm H2O(-1) x kg(-1), respectively; p < 0.05). The relative distribution of 14C-Curosurf in bronchoalveolar lavage fluid and homogenized lung tissue showed a higher degree of tissue association in the spontaneously breathing animals [53 +/- 4 versus 26 +/- 3% (mean +/- SEM)] than in mechanically ventilated animals (p < 0.01), the latter figure being very similar to that of the control group (25 +/- 5%). There was a higher degree of lipid peroxidation and fewer microbubbles in bronchoalveolar lavage fluid from mechanically ventilated animals. We conclude that the initial lung tissue association of exogenous surfactant is impaired by mechanical ventilation. This is associated with a reduction of dynamic compliance and evidence of increased surfactant inactivation.

Surfactant and Physiologic Responses of Preterm Lambs to Continuous Positive Airway Pressure

Although continuous positive airway pressure (CPAP) is used frequently for preterm infants, the relationships between the amount of surfactant and lung physiologic and injury responses to CPAP are unknown. Therefore, saturated phosphatidylcholine (Sat PC) was measured to quantify the surfactant necessary for preterm lambs to breathe successfully on a CPAP of 5 cm H(2)O (CPAP 5). Five of 21 lambs delivered at 130-136 days gestation failed to keep PCO(2) below 100 mm Hg by 2 hours. The lambs that failed had less than 1.9 micromol/kg Sat PC in bronchoalveolar fluid (approximately 3% the pool size at term), less surfactant secretion, and less large aggregate surfactant. Physiologic responses of other 132-day preterm lambs after 2 or 6 hours of CPAP 5, 8 cm H(2)O CPAP (CPAP 8), or mechanical ventilation were then characterized. At 6 hours, oxygenation and lung gas volumes were higher with CPAP 8 relative to the other groups and VE was decreased with CPAP 8 relative to CPAP 5. Lung dry/wet ratios were greater for the CPAP groups than for the mechanical ventilation group. A small amount of endogenous Sat PC is required for preterm lambs to breathe successfully with CPAP. CPAP 8 improves early newborn respiratory transition relative to CPAP 5.

Bronchopulmonary dysplasia in preterm infants: pathophysiology and management strategies

Bronchopulmonary dysplasia (BPD) has classically been described as including inflammation, architectural disruption, fibrosis, and disordered/delayed development of the infant lung. As infants born at progressively earlier gestations have begun to survive the neonatal period, a 'new' BPD, consisting primarily of disordered/delayed development, has emerged. BPD causes not only significant complications in the newborn period, but is associated with continuing mortality, cardiopulmonary dysfunction, re-hospitalization, growth failure, and poor neurodevelopmental outcome after hospital discharge. Four major risk factors for BPD include premature birth, respiratory failure, oxygen supplementation, and mechanical ventilation, although it is unclear whether any of these factors is absolutely necessary for development of the condition. Genetic susceptibility, infection, and patent ductus arteriosus have also been implicated in the pathogenesis of the disease. The strategies with the strongest evidence for effectiveness in preventing or lessening the severity of BPD include prevention of prematurity and closure of a clinically significant patent ductus arteriosus. Some evidence of effectiveness also exists for single-course therapy with antenatal glucocorticoids in women at risk for delivering premature infants, surfactant replacement therapy in intubated infants with respiratory distress syndrome, retinol (vitamin A) therapy, and modes of respiratory support designed to minimize 'volutrauma' and oxygen toxicity. The most effective treatments for ameliorating symptoms or preventing exacerbation in established BPD include oxygen therapy, inhaled glucocorticoid therapy, and vaccination against respiratory pathogens.Many other strategies for the prevention or treatment of BPD have been proposed, but have weaker or conflicting evidence of effectiveness. In addition, many therapies have significant side effects, including the possibility of worsening the disease despite symptom improvement. For instance, supraphysiologic systemic doses of glucocorticoids lessen the incidence of BPD in infants at risk for the disease, and promote weaning of oxygen and mechanical ventilation in infants with established BPD. However, the side effects of systemic glucocorticoid therapy, most notably the recently recognized adverse effects on neurodevelopment, preclude their routine use for the prevention or treatment of BPD. Future research in BPD will most probably focus on continued incremental improvements in outcome, which are likely to be achieved through the combined effects of many therapeutic modalities.

Positive end-expiratory pressure above lower inflection point minimizes influx of activated neutrophils into lung*

OBJECTIVES

To compare the effects of low vs. high tidal volume (Vt) with three positive end-expiratory pressure (PEEP) strategies on activated neutrophil influx into the lung.

DESIGN

Prospective, randomized controlled animal study.

SETTING

Animal laboratory in a university hospital.

SUBJECTS

Newborn piglets.

INTERVENTIONS

Surfactant-depleted piglets were randomized in littermate pairs; to PEEP of either 0 (zero end-expiratory pressure [ZEEP]; n = 6), 8 cm H2O (PEEP 8; n = 5), or 1 cm H2O above the lower inflection point (LIP) (PEEP>LIP; n = 6). Within each pair piglets were randomized to a low VT (5-7 mL/kg) or high VT strategy (17-19 mL/kg). After 4 hrs of mechanical ventilation, 18-fluorodeoxyglucose (18FDG) was injected and positron emission tomography scanning was performed.

MEASUREMENTS AND MAIN RESULTS

VT and PEEP changes on influx constants of 18FDG were assessed by analysis of variance. A within-litter comparison of Vt was nonsignificant (p = .50). A between-litter comparison, ordered in linear trend rank, from ZEEP, to PEEP 8, to PEEP>LIP, showed a strong effect of PEEP on influx constant (p = .019).

CONCLUSIONS

PEEP set above the LIP on the inspiratory limb of the pressure-volume curve affords a stronger lung protection than VT strategy.

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

As in the adult with acute lung injury and acute respiratory distress syndrome, the use of lung-protective ventilation has improved outcomes for neonatal lung diseases. Animal models of neonatal respiratory distress syndrome and congenital diaphragmatic hernia have provided evidence that 'gentle ventilation' with low tidal volumes and 'open-lung' strategies of using positive end-expiratory pressure or high-frequency oscillatory ventilation result in less lung injury than do the traditional modes of mechanical ventilation with high inflating pressures and volumes. Although findings of retrospective studies in infants with respiratory distress syndrome, congenital diaphragmatic hernia, and persistent pulmonary hypertension of the newborn have been similar to those of the animal studies, prospective, randomized, controlled trials have yielded conflicting results. Successful clinical trial design in these infants and in children with acute lung injury/acute respiratory distress syndrome will require an appreciation of the data supporting the modern ventilator management strategies for infants with lung disease.

Positive end-expiratory pressure for resuscitation of newborn infants at birth

BACKGROUND

Effective ventilation is the key to successful neonatal resuscitation. Positive pressure ventilation is initiated with manual ventilation devices which may or not deliver positive end-expiratory pressure (PEEP). PEEP is known to have beneficial effects in preterm animal models and its use is ubiquitous in mechanical ventilation in neonatal intensive care.

OBJECTIVES

To determine whether the use of PEEP during positive pressure ventilation at neonatal resuscitation reduces mortality or morbidity.

SEARCH STRATEGY

The standard search strategy of the Cochrane Neonatal Review Group was used. Pub Med (1966 to May 2004) was searched using the MeSH headings Infant, Newborn, Resuscitation, Positive Pressure Respiration and the text words Positive End-Expiratory Pressure or PEEP. The Cochrane Central Register of Controlled Trials (The Cochrane Library, Issue 1, 2004) was searched using text words Newborn and Resuscitation. No language restrictions were applied. The abstracts of the Society for Pediatric Research and the European Society for Pediatric Research, were searched from 1995-May 2004. Abstracts were also searched in Anaesthesiology, Canadian Journal of Anaesthesia, British Journal of Anaesthesia, Anaesthesia and Intensive Care and Anaesthesia and Analgesia.

SELECTION CRITERIA

Randomised and quasi-randomised controlled trials comparing ventilation devices providing PEEP with those not providing PEEP in the resuscitation of infants at birth.

DATA COLLECTION AND ANALYSIS

Assessment of methodology regarding blinding of randomisation, intervention and outcome measurements as well as completeness of follow-up was planned. We planned to evaluate the treatment effect using a fixed effects model using relative risk (RR), relative risk reduction, risk difference (RD) and number needed to treat (NNT) for categorical data and using mean, standard deviation and weighted mean difference (WMD) for continuous data. We planned an evaluation of heterogeneity to help determine the suitability of pooling results.

MAIN RESULTS

No studies were found meeting the criteria for inclusion in this review.

REVIEWERS' CONCLUSIONS

There is insufficient evidence to determine the efficacy and safety of PEEP during positive pressure ventilation at neonatal resuscitation. Randomised clinical trials comparing positive pressure ventilation with and without PEEP at neonatal resuscitation are warranted.

Positive end expiratory pressure during resuscitation of premature lambs rapidly improves blood gases without adversely affecting arterial pressure

Positive end expiratory pressure (PEEP) is important for neonatal ventilation but is not considered in guidelines for resuscitation. Our aim was to investigate the effects of PEEP on cardiorespiratory parameters during resuscitation of very premature lambs delivered by hysterotomy at approximately 125 d gestation (term approximately 147 d). Before delivery, they were intubated and lung fluid was drained. Immediately after delivery, they were ventilated with a Dräger Babylog plus ventilator in volume guarantee mode with a tidal volume of 5 mL/kg. Lambs were randomized to receive 0, 4, 8, or 12 cm H(2)O of PEEP. They were ventilated for a 15-min resuscitation period followed by 2 h of stabilization at the same PEEP. Tidal volume, peak inspiratory pressure, PEEP, arterial pressure, oxygen saturation, and blood gases were measured regularly, and respiratory system compliance and alveolar/arterial oxygen differences were calculated. Lambs that received 12 cm H(2)O of PEEP died from pneumothoraces; all others survived without pneumothoraces. Oxygenation was significantly improved by 8 and 12 cm H(2)O of PEEP compared with 0 and 4 cm H(2)O of PEEP. Lambs with 0 PEEP did not oxygenate adequately. The compliance of the respiratory system was significantly higher at 4 and 8 cm H(2)O of PEEP than at 0 PEEP. There were no significant differences in partial pressure of carbon dioxide in arterial blood between groups. Arterial pressure was highest with 8 cm H(2)O of PEEP, and there was no cardiorespiratory compromise at any level of PEEP. Applying PEEP during resuscitation of very premature infants might be advantageous and merits further investigation.

Technique for intrapartum administration of surfactant without requirement for an endotracheal tube

OBJECTIVE

To evaluate the feasibility and safety of administering surfactant into the nasopharynx during delivery, thus permitting the baby to aspirate the solution into the fluid-filled airway as an air-fluid interface is established. This process avoids the endotracheal intubation (ETI) and positive pressure ventilation (PPV) usually associated with prophylaxis, thus avoiding the pulmonary barotrauma associated with the conventional method of surfactant administration.

STUDY DESIGN

In all, 23 neonates weighing 560 to 1804 g and born at 27 to 30 weeks had their nasopharyngeal airways suctioned and then 3.0-4.5 ml Infasurf instilled into the nasopharynx before delivery of the shoulders. Continuous positive airway pressure (CPAP) of 10 cmH(2)O was administered by mask as the babies initiated breathing. Nasal CPAP at 6 cmH(2)O was then continued for a minimum of 48 hours.

RESULTS

In all, 13 of 15 babies delivered vaginally were weaned quickly to room air and required no further surfactant or endotracheal intubation for RDS. Five of eight babies delivered by C-section required subsequent endotracheal intubation soon after birth and two received subsequent endotracheal tube surfactant.

CONCLUSION

Nasopharyngeal surfactant instillation at birth appears to be relatively safe and simple to accomplish, especially for vaginal births. A large randomized clinical trial will be required to determine the efficacy of this technique when compared to prophylaxis by endotracheal intubation and to nCPAP alone.

Positive pressure ventilation at neonatal resuscitation: review of equipment and international survey of practice

BACKGROUND

The equipment used to provide positive pressure ventilation to newborns needing resuscitation at delivery varies between institutions. Devices were reviewed and their use surveyed in a sample of neonatal centres worldwide.

AIM

To determine which equipment is used to resuscitate newborns at delivery in a sample of teaching hospitals around the world.

METHODS

A questionnaire was sent via e-mail to a neonatologist at each of 46 NICUs in 23 countries on five continents, asking which resuscitation equipment they used. If it was not returned, follow-up was by e-mail.

RESULTS

Data were obtained from 40 (87%) centres representing 19 countries. Round face masks are used at 34 (85%) centres, anatomically shaped masks are used exclusively at six (15%) and a mixture of types are used at 11 (28%). Straight endotracheal tubes are used exclusively at 36 (90%) centres: shouldered tubes are used infrequently at three of the four centres that have them. The self-inflating bag is the most commonly used manual ventilation device (used at 33 (83%) centres), the Laerdal Infant Resuscitator the most popular model. Flow-inflating bags are used at 10 (25%) centres. The Neopuff Infant Resuscitator is used at 12 (30%) centres. Varying oxygen concentrations are provided during neonatal resuscitation at half of the centres, while 100% oxygen is routinely used at the other half.

CONCLUSIONS

This survey shows considerable variation in practice, reflecting this lack of evidence and consequent uncertainty among clinicians. Comparison of the two most popular manual ventilation devices, the Laerdal Infant Resuscitator and the Neopuff Infant Resuscitator, is urgently required.