Celso Moura Rebello

Lung morphometry, collagen and elastin content: changes after hyperoxic exposure in preterm rabbits

INTRODUCTION Elastic and collagen fiber deposition increases throughout normal lung development, and this fiber network significantly changes when development of the lung is disturbed. In preterm rats and lambs, prolonged hyperoxic exposure is associated with impaired alveolization and causes significant changes in the deposition and structure of elastic fibers. OBJECTIVES To evaluate the effects of hyperoxic exposure on elastic and collagen fiber deposition in the lung interstitial matrix and in alveolarization in preterm rabbits. METHODS After c-section, 28-day preterm New-Zealand-White rabbits were randomized into 2 study groups, according to the oxygen exposure, namely: Room air (oxygen = 21%) or Oxygen (oxygen ≥ 95%). The animals were killed on day 11 and their lungs were analyzed for the alveolar size (Lm), the internal surface area (ISA), the alveoli number, and the density and distribution of collagen and elastic fibers. RESULTS An increase in the Lm and a decrease in the alveoli number were observed among rabbits that were exposed to hyperoxia with no differences regarding the ISA. No difference in the density of elastic fibers was observed after oxygen exposure, however there were fewer collagen fibers and an evident disorganization of fiber deposition. DISCUSSION This model reproduces anatomo-pathological injuries representing the arrest of normal alveolar development and lung architecture disorganization by just a prolonged exposition to oxygen. CONCLUSIONS In the preterm rabbit, prolonged oxygen exposure impaired alveolization and also lowered the proportion of collagen fibers, with an evident fiber network disorganization.

Evaluation of peak inspiratory pressure, tidal volume and respiratory rate during ventilation of premature lambs using a self-inflating bag

OBJECTIVEnTo evaluate the peak inspiratory pressure, tidal volume and respiratory rate achieved during manual ventilation of premature lambs, using a self-inflating bag.nnnMETHODSnIn this descriptive, experimental study, five pairs of physicians, selected at random among 35 neonatologists working at a neonatal intensive care unit and with experience in the resuscitation of newborn infants, ventilated five intubated premature lambs using a self-inflating bag. Pressure and flow monitor signals were passed through a transducer and digitized for recording and analysis. Tidal volume and pressure curves were obtained from the integral of flow rate, at peak, during the last 50 seconds of every fifth minute, and analyzed.nnnRESULTSnMedian pressure was 39.8 (IQ(25-75%) 30.2-47.2) cmH(2)O; being below 20 in 1.1% of cases and above 40 in 49.1%. Seven out of 10 physicians produced more than six pressure peaks of over 40 cmH(2)O. Median tidal volume/kg was 17.8 (IQ(25-75%) 14.1-22.4) mL, being below 5 mL in 0.1% of cases and greater than or equal to 20 mL in 37.7%. All of the physicians propelled five or more ventilation cycles with tidal volume/kg of 20 mL or more. Respiratory rate was between 30 and 60 cycles/minute in 65.9% of cases, being below 30 in 6.8% of cases and over 60 in 27.3% of cases.nnnCONCLUSIONSnThere was major variation in peak inspiratory pressure and tidal volume/kg values, which were in many cases elevated, attaining levels that habitually cause biotrauma, while respiratory rates were adequate in the majority of cases.

Pulmonary responses to nutritional restriction and hyperoxia in premature rabbits.

OBJECTIVESnTo analyze the effects of nutritional restriction and hyperoxia on lung weight and pulmonary morphometry in premature rabbits during the first 11 days of life.nnnMETHODSnNew Zealand White rabbits were delivered by C-section at 28 days gestational age and randomized into four groups: control diet and room air, control diet and hyperoxia (> or = 95% O2), nutritional restriction and room air and nutritional restriction and hyperoxia (> or = 95% O2). Nutritional restriction was achieved by reducing all nutrients by 30% in comparison with the control diet. Lung tissue slides were stained with hematoxylin-eosin, modified resorcin-orcein and picrosirius, before morphometric analysis was performed.nnnRESULTSnFrom the fourth day onwards, less weight was gained by the nutritional restriction and hyperoxia group (p < 0.001), and from the sixth day on, by the nutritional restriction and room air group (p < 0.001), in comparison with their respective control groups. Nutritional restriction decreased alveoli number (p < 0.001) and collagen deposition (p < 0.001). Hyperoxia was responsible for reductions in number of alveoli (p < 0.001) and collagen deposition (p < 0.001), in addition to higher mean linear intercept values (p < 0.05) and thickening of alveolar septa (p < 0.001). When nutritional restriction was associated with hyperoxia, the reductions in number of alveoli (p < 0.001) and of collagen deposition (p < 0.001) intensified.nnnCONCLUSIONSnNutritional restriction intensified the changes of pulmonary architecture findings caused by hyperoxia, in particular through alterations to alveolarization and collagen deposition.

Prediction of Length of Hospital Stay in Neonatal Units for Very Low Birth Weight Infants

OBJECTIVE:To develop models for estimating the length of hospital stay (LOS) of very low birth weight infants (VLBW), based on perinatal risk factors present during the first week of life and during the entire hospitalization period.STUDY DESIGN:The files of 155 VLBW were analyzed, and the influence of individual risk factors were initially evaluated by univariate analysis, using multiple-regression. Two mathematical models were built to estimate the LOS.RESULTS:The first model, using risk factors present during the first 3 days of life, is as follows: LOS = −0.074A + 22.06B + 22.85C − 16.78D − 2.07E + 10.51F + 203.12 (R2 = 0.63). (The letters are added to show what each number represents: A: birth weight; B: occurrence of respiratory distress syndrome; C: endotracheal intubation during resuscitation; D: 1-minute Apgar score; E: gestational age; F: presence of complications during delivery.) The second model, using factors present during the entire hospitalization period, is: LOS = 0.61G + 29.19H + 24.68I + 14.21J + 23.56K + 9.54L + 7.41M + 20.43 (R2 = 0.82). (G: age receiving nutritional support of ≥120 kcal/kg per day; H: occurrence of systemic candidiasis; I: birth weight < 1000 gm; J: presence of delivery complication; K: occurrence of bronchopulmonary dysplasia; L: birth weight ≥ 1000 gm and ≤ 1249 gm; M: occurrence of anemia).CONCLUSION: Both models are applicable for estimating the hospitalization period, and the addition of variables present during the entire hospitalization period improved the accuracy of the model.

Effect of postnatal malnutrition on hyperoxia-induced newborn lung development

Several factors are associated with bronchopulmonary dysplasia. Among them, hyperoxia and lung immaturity are considered to be fundamental; however, the effect of malnutrition is unknown. Our objective was to evaluate the effects of 7 days of postnatal malnutrition and hyperoxia on lung weight, volume, water content, and pulmonary morphometry of premature rabbits. After c-section, 28-day-old New Zealand white rabbits were randomized into four groups: control diet and room air (CA, N = 17), control diet and > or = 95% O2 (CH, N = 17), malnutrition and room air (MA, N = 18), and malnutrition and > or = 95% O2 (MH, N = 18). Malnutrition was defined as a 30% reduction of all the nutrients provided in the control diet. Treatments were maintained for 7 days, after which histological and morphometric analyses were conducted. Lung slices were stained with hematoxylin-eosin, modified orcein-resorcin or picrosirius. The results of morphometric analysis indicated that postnatal malnutrition decreased lung weight (CA: 0.83 +/- 0.19; CH: 0.96 +/- 0.28; MA: 0.65 +/- 0.17; MH: 0.79 +/- 0.22 g) and water content, as well as the number of alveoli (CA: 12.43 +/- 3.07; CH: 8.85 +/- 1.46; MA: 7.33 +/- 0.88; MH: 6.36 +/- 1.53 x 10-3/mm) and elastic and collagen fibers. Hyperoxia reduced the number of alveoli and increased septal thickening and the mean linear intercept. The reduction of alveolar number, collagen and elastic fibers was intensified when malnutrition and hyperoxia were associated. These data suggest that dietary restriction enhances the magnitude of hyperoxia-induced alveolar growth arrest and lung parenchymal remodeling. It is interesting to consider the important influence of postnatal nutrition upon lung development and bronchopulmonary dysplasia.

Respostas pulmonares à restrição nutricional e à hiperoxia em coelhos prematuros

OBJETIVOS: Este modelo experimental foi desenvolvido para analisar os efeitos da restricao nutricional e da hiperoxia, durante 11 dias, sobre o peso e a morfometria pulmonares, em coelhos prematuros. METODOS: Apos cesarea, coelhos New Zealand White com idade gestacional de 28 dias foram randomizados nos seguintes grupos: dieta controle e ar ambiente, dieta controle e hiperoxia (> 95% O2), restricao nutricional e ar ambiente e restricao nutricional e hiperoxia (>95% O2). A restricao nutricional foi obtida com uma reducao em 30% de todos os nutrientes da dieta controle. As lâminas de pulmao foram coradas com hematoxilina-eosina, resorcina-orceina modificada e picrosirius, sendo posteriormente realizada a analise morfometrica RESULTADOS: Observou-se um menor ganho de peso no grupo restricao nutricional e hiperoxia (p < 0,001) a partir do quarto dia e, no grupo restricao nutricional e ar ambiente (p < 0,001), a partir do sexto dia de vida, em relacao aos respectivos grupos controles. A restricao nutricional reduziu o numero de alveolos (p < 0,001) e o deposito de colageno (p < 0,001). A hiperoxia produziu uma reducao do numero de alveolos (p < 0,001) e do deposito de colageno (p < 0,001), alem de maiores intercepto linear medio (p < 0,05) e espessamento de septos inter-alveolares (p < 0,001). A restricao nutricional associada a hiperoxia intensificou a reducao do numero de alveolos (p < 0,001) e do deposito de colageno (p < 0,001). CONCLUSOES: A restricao nutricional intensificou as alteracoes morfometricas pulmonares produzidas pela hiperoxia, especialmente em relacao a alveolizacao e deposito de colageno.

Ventilação oscilatória de alta freqüência em pediatria e neonatologia

This article intends to review literature on high frequency oscillatory ventilation and describe its main clinical applications for children and neonates. Articles from the last 15 years were selected using MedLine and SciElo databases. The following key words were used: high frequency oscillatory ventilation, mechanical ventilation, acute respiratory distress syndrome, children, and new-born. The review describes high frequency oscillatory ventilation in children with acute respiratory distress syndrome, air leak syndrome, and obstructive lung disease. Respiratory distress syndrome, bronchopulmonary dysplasia, intracranial hemorrhage, periventricular leukomalacia, and air leak syndrome were reviewed in neonates. Transition from conventional mechanical ventilation to high frequency ventilation and its adjustments relating to oxygenation, CO2 elimination, chest radiography, suctioning, sedatives and use of neuromuscular blocking agents were described. Weaning and complications were also reported. For children, high frequency oscillatory ventilation is a therapeutic option, particularly in acute respiratory distress syndrome, and should be used as early as possible. It may be also useful in the air leak syndrome and obstructive pulmonary disease. Evidence that, in neonates, high frequency oscillatory ventilation is superior to conventional mechanical ventilation is lacking. However there is evidence that better results are only achieved with this ventilatory mode to manage the air leak syndrome.

A Hyperoxic Lung Injury Model in Premature Rabbits: The Influence of Different Gestational Ages and Oxygen Concentrations

Background Many animal models have been developed to study bronchopulmonary dysplasia (BPD). The preterm rabbit is a low-cost, easy-to-handle model, but it has a high mortality rate in response to the high oxygen concentrations used to induce lung injury. The aim of this study was to compare the mortality rates of two models of hyperoxia-induced lung injury in preterm rabbits. Methods Pregnant New Zealand white rabbits were subjected to caesarean section on gestational day 28 or 29 (full term u200a=u200a31 days). The premature rabbits in the 28-day gestation group were exposed to room air or FiO2 ≥95%, and the rabbits in the 29-day gestation group were exposed to room air or FiO2 u200a=u200a80% for 11 days. The mean linear intercept (Lm), internal surface area (ISA), number of alveoli, septal thickness and proportion of elastic and collagen fibers were quantified. Results The survival rates in the 29-day groups were improved compared with the 28-day groups. Hyperoxia impaired the normal development of the lung, as demonstrated by an increase in the Lm, the septal thickness and the proportion of elastic fibers. Hyperoxia also decreased the ISA, the number of alveoli and the proportion of collagen fibers in the 28-day oxygen-exposed group compared with the control 28-day group. A reduced number of alveoli was found in the 29-day oxygen exposed animals compared with the control 29-day group. Conclusions The 29-day preterm rabbits had a reduced mortality rate compared with the 28-day preterm rabbits and maintained a reduction in the alveoli number, which is comparable to BPD in humans.

Utilization of the lower inflection point of the pressure-volume curve results in protective conventional ventilation comparable to high frequency oscillatory ventilation in an animal model of acute respiratory distress syndrome.

INTRODUCTION Studies comparing high frequency oscillatory and conventional ventilation in acute respiratory distress syndrome have used low values of positive end-expiratory pressure and identified a need for better recruitment and pulmonary stability with high frequency. OBJECTIVE To compare conventional and high frequency ventilation using the lower inflection point of the pressure-volume curve as the determinant of positive end-expiratory pressure to obtain similar levels of recruitment and alveolar stability. METHODS After lung lavage of adult rabbits and lower inflection point determination, two groups were randomized: conventional (positive end-expiratory pressure = lower inflection point; tidal volume=6 ml/kg) and high frequency ventilation (mean airway pressures= lower inflection point +4 cmH2O). Blood gas and hemodynamic data were recorded over 4 h. After sacrifice, protein analysis from lung lavage and histologic evaluation were performed. RESULTS The oxygenation parameters, protein and histological data were similar, except for the fact that significantly more normal alveoli were observed upon protective ventilation. High frequency ventilation led to lower PaCO2 levels. DISCUSSION Determination of the lower inflection point of the pressure-volume curve is important for setting the minimum end expiratory pressure needed to keep the airways opened. This is useful when comparing different strategies to treat severe respiratory insufficiency, optimizing conventional ventilation, improving oxygenation and reducing lung injury. CONCLUSIONS Utilization of the lower inflection point of the pressure-volume curve in the ventilation strategies considered in this study resulted in comparable efficacy with regards to oxygenation and hemodynamics, a high PaCO2 level and a lower pH. In addition, a greater number of normal alveoli were found after protective conventional ventilation in an animal model of acute respiratory distress syndrome.

Different doses of exogenous surfactant for treatment of meconium aspiration syndrome in newborn rabbits

OBJECTIVEnTo evaluate the effects of 2 different doses of exogenous surfactant on pulmonary mechanics and on the regularity of pulmonary parenchyma inflation in newborn rabbits.nnnMETHODnNewborn rabbits were submitted to tracheostomy and randomized into 4 study groups: the Control group did not receive any material inside the trachea; the MEC group was instilled with meconium, without surfactant treatment; the S100 and S200 groups were instilled with meconium and were treated with 100 and 200 mg/kg of exogenous surfactant (produced by Instituto Butantan) respectively. Animals from the 4 groups were mechanically ventilated during a 25-minute period. Dynamic compliance, ventilatory pressure, tidal volume, and maximum lung volume (P-V curve) were evaluated. Histological analysis was conducted using the mean linear intercept (Lm), and the lung tissue distortion index (SDI) was derived from the standard deviation of the means of the Lm. One-way analysis of variance was used with a = 0.05.nnnRESULTSnAfter 25 minutes of ventilation, dynamic compliance (mL/cm H2O.kg) was 0.87 +/- 0.07 (Control); 0.49 +/- 0.04 (MEC*); 0.67 +/- 0.06 (S100); and 0.67 +/- 0.08 (S200), and ventilatory pressure (cm H2O) was 9.0 +/- 0.9 (Control); 16.5 +/- 1.7 (MEC*); 12.4 +/- 1.1 (S100); and 12.1 +/- 1.5 (S200). Both treated groups had lower Lm values and more homogeneity in the lung parenchyma compared to the MEC group: SDI = 7.5 +/- 1.9 (Control); 11.3 +/- 2.5 (MEC*), 5.8 +/- 1.9 (S100); and 6.7 +/- 1.7 (S200) (*P < 0.05 versus all the other groups).nnnCONCLUSIONSnAnimals treated with surfactant showed significant improvement in pulmonary mechanics and more regularity of the lung parenchyma in comparison to untreated animals. There was no difference in results after treatment with either of the doses used.