Open lung ventilation preserves the response to delayed surfactant treatment in surfactant-deficient newborn piglets

Quantitative lung ultrasound detects dynamic changes in lung recruitment in the preterm lamb

BACKGROUND

Lung ultrasound (LUS) may not detect small, dynamic changes in lung volume. Mean greyscale measurement using computer-assisted image analysis (Q-LUS_MGV) may improve the precision of these measurements.

METHODS

Preterm lambs (n = 40) underwent LUS of the dependent or non-dependent lung during static pressure-volume curve mapping. Total and regional lung volumes were determined using the super-syringe technique and electrical impedance tomography. Q-LUS_MGV and gold standard measurements of lung volume were compared in 520 images.

RESULTS

Dependent Q-LUS_MGV moderately correlated with total lung volume (rho = 0.60, 95% CI 0.51-0.67) and fairly with right whole (rho = 0.39, 0.27-0.49), central (rho = 0.38, 0.27-0.48), ventral (rho = 0.41, 0.31-0.51) and dorsal regional lung volumes (rho = 0.32, 0.21-0.43). Non-dependent Q-LUS_MGV moderately correlated with total lung volume (rho = 0.57, 0.48-0.65) and fairly with right whole (rho = 0.43, 0.32-0.52), central (rho = 0.46, 0.35-0.55), ventral (rho = 0.36, 0.25-0.47) and dorsal lung volumes (rho = 0.36, 0.25-0.47). All correlation coefficients were statistically significant. Distinct inflation and deflation limbs, and sonographic pulmonary hysteresis occurred in 95% of lambs. The greatest changes in Q-LUS_MGV occurred at the opening and closing pressures.

CONCLUSION

Q-LUS_MGV detected changes in total and regional lung volume and offers objective quantification of LUS images, and may improve bedside discrimination of real-time changes in lung volume.

IMPACT

Lung ultrasound (LUS) offers continuous, radiation-free imaging that may play a role in assessing lung recruitment but may not detect small changes in lung volume. Mean greyscale image analysis using computer-assisted quantitative LUS (Q-LUS_MGV) moderately correlated with changes in total and regional lung volume. Q-LUS_MGV identified opening and closing pressure and pulmonary hysteresis in 95% of lambs. Computer-assisted image analysis may enhance LUS estimation of lung recruitment at the bedside. Future research should focus on improving precision prior to clinical translation.

An Unsettled Promise: The Newborn Piglet Model of Neonatal Acute Respiratory Distress Syndrome (NARDS). Physiologic Data and Systematic Review

Despite great advances in mechanical ventilation and surfactant administration for the newborn infant with life-threatening respiratory failure no specific therapies are currently established to tackle major pro-inflammatory pathways. The susceptibility of the newborn infant with neonatal acute respiratory distress syndrome (NARDS) to exogenous surfactant is linked with a suppression of most of the immunologic responses by the innate immune system, however, additional corticosteroids applied in any severe pediatric lung disease with inflammatory background do not reduce morbidity or mortality and may even cause harm. Thus, the neonatal piglet model of acute lung injury serves as an excellent model to study respiratory failure and is the preferred animal model for reasons of availability, body size, similarities of porcine and human lung, robustness, and costs. In addition, similarities to the human toll-like receptor 4, the existence of intraalveolar macrophages, the sensitivity to lipopolysaccharide, and the production of nitric oxide make the piglet indispensable in anti-inflammatory research. Here we present the physiologic and immunologic data of newborn piglets from three trials involving acute lung injury secondary to repeated airway lavage (and others), mechanical ventilation, and a specific anti-inflammatory intervention via the intratracheal route using surfactant as a carrier substance. The physiologic data from many organ systems of the newborn piglet—but with preference on the lung—are presented here differentiating between baseline data from the uninjured piglet, the impact of acute lung injury on various parameters (24 h), and the follow up data after 72 h of mechanical ventilation. Data from the control group and the intervention groups are listed separately or combined. A systematic review of the newborn piglet meconium aspiration model and the repeated airway lavage model is finally presented. While many studies assessed lung injury scores, leukocyte infiltration, and protein/cytokine concentrations in bronchoalveolar fluid, a systematic approach to tackle major upstream pro-inflammatory pathways of the innate immune system is still in the fledgling stages. For the sake of newborn infants with life-threatening NARDS the newborn piglet model still is an unsettled promise offering many options to conquer neonatal physiology/immunology and to establish potent treatment modalities.

Efficacy of a new technique - INtubate-RECruit-SURfactant-Extubate - "IN-REC-SUR-E" - in preterm neonates with respiratory distress syndrome: study protocol for a randomized controlled trial

Background

Although beneficial in clinical practice, the INtubate-SURfactant-Extubate (IN-SUR-E) method is not successful in all preterm neonates with respiratory distress syndrome, with a reported failure rate ranging from 19 to 69 %. One of the possible mechanisms responsible for the unsuccessful IN-SUR-E method, requiring subsequent re-intubation and mechanical ventilation, is the inability of the preterm lung to achieve and maintain an “optimal” functional residual capacity. The importance of lung recruitment before surfactant administration has been demonstrated in animal studies showing that recruitment leads to a more homogeneous surfactant distribution within the lungs. Therefore, the aim of this study is to compare the application of a recruitment maneuver using the high-frequency oscillatory ventilation (HFOV) modality just before the surfactant administration followed by rapid extubation (INtubate-RECruit-SURfactant-Extubate: IN-REC-SUR-E) with IN-SUR-E alone in spontaneously breathing preterm infants requiring nasal continuous positive airway pressure (nCPAP) as initial respiratory support and reaching pre-defined CPAP failure criteria.

Methods/design

In this study, 206 spontaneously breathing infants born at 24⁺⁰–27⁺⁶ weeks’ gestation and failing nCPAP during the first 24 h of life, will be randomized to receive an HFOV recruitment maneuver (IN-REC-SUR-E) or no recruitment maneuver (IN-SUR-E) just prior to surfactant administration followed by prompt extubation. The primary outcome is the need for mechanical ventilation within the first 3 days of life. Infants in both groups will be considered to have reached the primary outcome when they are not extubated within 30 min after surfactant administration or when they meet the nCPAP failure criteria after extubation.

Discussion

From all available data no definitive evidence exists about a positive effect of recruitment before surfactant instillation, but a rationale exists for testing the following hypothesis: a lung recruitment maneuver performed with a step-by-step Continuous Distending Pressure increase during High-Frequency Oscillatory Ventilation (and not with a sustained inflation) could have a positive effects in terms of improved surfactant distribution and consequent its major efficacy in preterm newborns with respiratory distress syndrome. This represents our challenge.

Trial registration

ClinicalTrials.gov identifier: NCT02482766. Registered on 1 June 2015.

Characterization of inflammation in a rat model of acute lung injury after repeated pulmonary lavage

AIM OF THE STUDY

Repeated pulmonary lavage allows to reliably reproduce failure of gas exchange and major histological findings of acute lung injury (ALI). However, because the capacity of pulmonary lavage to induce pulmonary inflammation is not well established in rodents, this study aims to characterize the induction of pulmonary inflammation in a rat model of ALI.

MATERIALS AND METHODS

Male adult rats were divided into a treatment group (n = 9) that received pulmonary lavage with consecutive mechanical ventilation, and a control group that received mechanical ventilation only (n = 9). Arterial blood gas analyses were performed every 30 min throughout the study. Pressure-volume curves, and lung tissue and plasma samples, were obtained at 240 min after the start of mechanical ventilation. Protein content and surface activity of bronchoalveolar lavage fluid was assessed. Transcriptional and translational regulation of pro- and anti-inflammatory cytokines IL-1β, TNF-α, IL-6, and IL-10 was determined in lungs and plasma. Markers of cellular stress were measured in lung tissue.

RESULTS

Pulmonary lavage significantly decreased lung compliance, induced hypoxia and hypercapnia, and mediated respiratory acidosis. Protein content of lavage fluid was significantly increased and contained washed out surfactant. Expression of IL-1β, TNF-α, and IL-6 mRNA and protein expression of IL-1β and TNF-α was significantly induced in lavaged lungs, without spillover into the systemic circulation. Markers of cellular stress were significantly upregulated in lavaged lungs.

CONCLUSIONS

This model of ALI applied in rats can induce pulmonary inflammation. The model might be used to develop therapeutic strategies that target pulmonary inflammation in ALI.

Titration of mean airway pressure and FiO2 during high frequency oscillatory ventilation in a porcine model of acute lung injury

BACKGROUND

High frequency oscillatory ventilation (HFOV) is frequently utilized for patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, precise criteria to titrate mean airway pressure (mPaw) and FiO(2) as the patient's condition improves are lacking. We hypothesized that reducing mPaw and FiO(2) too quickly after reaching target arterial oxygen saturation levels would promote ventilator induced lung injury (VILI).

MATERIALS AND METHODS

ALI was induced by instilling 3% Tween 20. Pigs were placed supine and received 30 min of nonprotective ventilation. Pigs were separated into two groups: HFOV constant (HFOVC, n = 3) = constant mPaw and FiO(2) for the duration; HFOV titrated (HFOVT, n = 4) = FiO(2) and/or mPaw were reduced every 30 min if the oxygen saturation remained between 88%-95%. Hemodynamic and pulmonary measurements were made at baseline, after lung injury, and every 30 min during the 6-h study. Lung histopathology was determined by quantifying alveolar hyperdistension, fibrin, congestion, atelectasis, and polymorphonuclear leukocyte (PMN) infiltration.

RESULTS

Oxygenation was significantly lower in the HFOVT group compared to the HFOVC group after 6 h. Lung histopathology was significantly increased in the HFOVT group in the following categories: PMN infiltration, alveolar hyperdistension, congestion, and fibrin deposition.

CONCLUSIONS

Rapid reduction of mPaw and FiO(2) in our ALI model significantly reduced oxygenation, but, more importantly, caused VILI as evidenced by increased lung inflammation and alveolar hyperdistension. Specific criteria for titration of mPaw and inspired oxygen are needed to maximize the lung protective effects of HFOV while maintaining adequate gas exchange.

Surfactant replacement and open lung concept--comparison of two treatment strategies in an experimental model of neonatal ARDS

Background

Several concepts of treatment in neonatal ARDS have been proposed in the last years. The present study compared the effects of open lung concept positive pressure ventilation (PPV_OLC) with a conventional ventilation strategy combined with administration of two different surfactant preparations on lung function and surfactant homoeostasis.

Methods

After repeated whole-lung saline lavage, 16 newborn piglets were assigned to either PPV_OLC (n = 5) or surfactant treatment under conventional PPV using a natural bovine (n = 5) or a monomeric protein B based surfactant (n = 6).

Results

Comprehensive monitoring showed each treatment strategy to improve gas exchange and lung function, although the effect on Pa_O2 and pulmonary compliance declined over the study period in the surfactant groups. The overall improvement of the ventilation efficiency index (VEI) was significantly greater in the PPV_OLC group. Phospholipid and protein analyses of the bronchoalveolar lavage fluid showed significant alterations to surfactant homoeostasis in the PPV_OLC group, whereas IL-10 and SP-C mRNA expression was tendentially increased in the surfactant groups.

Conclusion

The different treatment strategies applied could be shown to improve gas exchange and lung function in neonatal ARDS. To which extent differences in maintenance of lung function and surfactant homeostasis may lead to long-term consequences needs to be studied further.