Relationship between respiratory impedance and positive end-expiratory pressure in mechanically ventilated neonates.

PURPOSE: To evaluate the feasibility of forced oscillation technique (FOT) measurements at the bedside and to describe the relationship between positive end-expiration pressure (PEEP) and lung mechanics in different groups of ventilated infants. METHODS: Twenty-eight infants were studied: 5 controls, 16 newborns with respiratory distress syndrome (RDS) and 7 chronically ventilated newborns that developed bronchopulmonary dysplasia. An incremental/decremental PEEP trial was performed by changing PEEP in 1-min steps of 1 cmH(2)O between 2 and 10 cmH(2)O. Forced oscillations at 5 Hz were superimposed on the ventilator waveform. Pressure and flow, measured at the inlet of the ETT, were used to compute resistance (Rrs) and reactance (Xrs). RESULTS: In controls Rrs and Xrs were on average 41 ± 21 and -22 ± 6 cmH(2)O s/l respectively and were almost unaffected by PEEP. RDS infants presented similar Rrs (48 ± 25 cmH(2)O s/l) and reduced Xrs (-71 ± 19 cmH(2)O s/l) at the beginning of the trial. Two behaviours were observed as PEEP was increased: in extremely low birth weight infants Xrs decreased with PEEP with marked hysteresis; in very low and low birth weight infants Xrs and Rrs were less PEEP dependent. Chronically ventilated infants had very high Rrs and very negative Xrs values at very low PEEPs (121 ± 41 and -95 ± 13 cmH(2)O s/l at PEEP = 2 cmH(2)O) that markedly changed as PEEP exceeded 3-4 cmH(2)O. CONCLUSIONS: Rrs and Xrs measurement in preterm newborns is feasible, and data are representative of the lung mechanics and very sensitive to its changes with PEEP, making FOT a promising technique for the non-invasive bedside titration of mechanical ventilation in preterm newborns.

Pharyngeal pressure value using two continuous positive airway pressure devices.

The aim of the study was to measure the difference between the set continuous positive airway pressure (CPAP) value and the pharyngeal pressure reading during CPAP in premature infants with mild respiratory distress syndrome, using two different devices: hood CPAP and the conventional nasal system. The preliminary results suggest that hood CPAP may produce more stable pharyngeal pressure than the conventional nasal device.

Increased levels of IGF-1 and beta2-microglobulin in epithelial lining fluid of preterm newborns developing chronic lung disease. effects of rhG-CSF.

UNLABELLED: Insulin-like growth factor-1 (IGF-1) is involved in regulating the Th-1/Th-2 balance, favoring the development of the Th-2 compartment which enhances fibrosis, one of the main characteristics of Chronic Lung Disease (CLD) in premature newborns. Limited data is available concerning a possible association between early epithelial lining fluid (ELF) concentrations of IGF-1 (total and free forms), IGF-binding protein-3 (IGFBP-3), beta2-microglobulin and subsequent development of CLD in preterm neonates. If neutropenic, preterm neonates are frequently treated with recombinant human granulocyte colony stimulating factor (rhG-CSF). The objective of the study was to correlate ELF concentrations of IGF-1 and beta2 microglobulin during the first week of life both in non-neutropenic and in rhGCSF-treated neutropenic preterm neonates, with subsequent development in CLD. Thirty preterm neonates with Respiratory Distress Syndrome (6 with neutropenia) were studied. Eleven out of 24 non-neutropenic preterm infants (46%) and all of the six neutropenic subjects (100%) developed CLD. With the exception of first day values, there was a clear similarity in the behaviors of assayed molecules between non-neutropenic and neutropenic patients developing CLD. Non-neutropenic patients without CLD showed significantly lower values of free IGF-1 and beta2M both on days 1 and 3. Total IGF-I and cell counts were different only on the 3rd day. CONCLUSIONS: 1) the mechanisms leading to CLD might be mediated by high levels of IGF-family molecules soon after birth 2) beta2M could be a marker of increased bronchoalveolar lavage fluid cellularity with potential inflammatory properties 3) G-CSF treatment induces an increased synthesis of IGF-1 molecules by cells recruited in the lung, with possible enhancement of the fibrogenic mechanisms.

Spontaneous minute ventilation is a predictor of extubation failure in extremely-low-birth-weight infants.

OBJECTIVE: To validate the percentage of time spent below a target value of spontaneous expiratory minute ventilation (< 125 ml/min per kg) during a 2-h period of continuous positive airway pressure (CPAP) via an endotracheal tube (ETT) as a predictor of failed extubation in preterm infants. METHODS: Forty-one infants intubated for at least 24 h, with birth weight between 500 and 1000 g, who were clinically stable and at ventilator setting compatible with an extubation attempt, were studied during a 2-h period of ETT CPAP. Dynamic lung compliance and total lung resistance were measured during a period of quiet breathing, while tidal volume (Vt), respiratory rate and the corresponding spontaneous expiratory minute ventilation values were calculated for the complete recording period of 2 h using a customized computer program. The time each patient spent below the target spontaneous expiratory minute ventilation value was reported as a percentage of the total recorded time (% spontaneous expiratory minute ventilation < 125 ml/min per kg). Extubation failure was defined as the need for reintubation within 72 h. RESULTS: Eleven out of 41 babies (26.8%) experienced failure of extubation (failure group) while 30 infants (73.2%) were successfully extubated (success group). There were no significant differences in dynamic lung compliance and lung resistance between the two groups, but the mean values of respiratory rate and spontaneous expiratory minute ventilation were significantly lower in the failure group than in the success group: 43 (37-56) breaths/min and 240 (160-353) ml/min per kg vs. 53 (28-67) breaths/min and 309 (223-434) ml/min per kg, respectively (p = 0.0129 and p = 0.0039). Moreover, the babies in whom extubation failed spent a longer time below the target value of spontaneous expiratory minute ventilation when compared with successfully extubated babies (p < 0.0001). Percentage of time spent with spontaneous expiratory minute ventilation < 125 ml/min per kg had a larger area than transcutaneous (Tc)PCO2, TcPO2 and pulse oxymetry saturation (SpO2) under the receiver operator characteristic curves. CONCLUSION: The measurement of spontaneous expiratory minute ventilation prior to extubation could be useful in identifying those babies who are not ready for spontaneous ventilation.

Effect of dexamethasone on tracheobronchial aspirate fluid cytology and pulmonary mechanics in preterm infants.

The changes induced on respiratory mechanics and on tracheobronchial aspirate fluid (TAF) cytology by dexamethasone courses started at two different postnatal ages in preterm infants at risk of chronic lung disease (CLD) were reported in this clinical trial designed in two phases. The first phase of the study included 20 neonates with birth weight < or = 1,250 g and gestational age < or = 32 weeks, who were oxygen and ventilator dependent on the 10th day of life. They were randomly assigned to the moderately early dexamethasone (MED) group or to the control group. The second phase of the study included 20 neonates with the same characteristics, oxygen and ventilator dependent on the 4th day of life, randomly assigned to the early dexamethasone (ED) group or to the control group. Both treated groups received dexamethasone intravenously for 7 days (0.5 mg/kg/day for the first 3 days, 0.25 mg/kg/day for the next 3 days, and 0.125 mg/kg/day for the last day of treatment). The control groups received no steroid treatment. A significantly lower absolute cell count and percentage of neutrophils (PMN) in the TAF and significantly higher dynamic lung compliance (Cdyn) values were observed in both the MED treated compared to the untreated infants and the ED treated infants compared to the control group. Moreover these changes were more precocious in the ED Group compared to the MED Group. Our study suggests that dexamethasone could be more efficacious in reducing effects of ventilator-induced lung injury in preterm infants at high risk of CLD when started earlier.

Early changes of pulmonary mechanics to predict the severity of bronchopulmonary dysplasia in ventilated preterm infants.

OBJECTIVES: To verify whether early pulmonary mechanics measurements are useful to predict subsequent bronchopulmonary dysplasia (BPD) and its severity. METHODS: Pulmonary mechanics were studied at 3, 5, 7 and 10 days of age in 52 preterm infants with birth weight < 1250 g, affected by respiratory distress syndrome and ventilated for more than 72 h. Pulmonary function was assessed using a previously standardized method based on the measurement of airflow with a Fleisch OO pneumotachograph and airway pressure with a model P7D differential pressure transducer. At 28 days pulmonary outcome was classified into three groups: no BPD, mild BPD (oxygen dependency and hazy lung on X-ray) and severe BPD (oxygen dependency and Northway stage 3/4). RESULTS: Of the 52 infants, 39 survived to 28 days: no BPD (11 infants), mild BPD (16 infants) and severe BPD (12 infants). The no-BPD group had significantly higher gestational age and birth weight, fewer males and a lower incidence of patent ductus arteriosus than both BPD groups, while no differences were detected between the BPD groups. Lung compliance was significantly higher in the mild-BPD group than in the severe-BPD group at 7 and 10 days of life (p < 0.01 and p < 0.001, respectively). The corresponding odds ratio confirmed that ventilated infants with lower lung compliance values had a significantly higher probability of developing severe BPD. Respiratory system resistance did not show any predictive value. CONCLUSIONS: Our findings indicate that low lung compliance values determined on the 7th and 10th days of life are a reliable predictive tool of the severity of later BPD.

High total antioxidant activity and uric acid in tracheobronchial aspirate fluid of preterm infants during oxidative stress: an adaptive response to hyperoxia?

The effect of O2 exposure, expressed by mean daily fractional inspired oxygen concentration (FiO2), was evaluated during the first 6 d of life in the tracheobronchial aspirate fluid of 16 mechanically ventilated preterm infants in terms of both antioxidant response and oxidative damage, by measuring total antioxidant activity, uric acid concentrations and protein carbonyl content. Each day linear regression analysis was performed and a positive correlation was found between total antioxidant activity and FiO2 during the study period, especially on day 2 of life (r = 0.91, p < 0.0001), but uric acid correlated only in the first 3 d, especially on the 2nd day (r = 0.83, p < 0.0001). No correlation was found between carbonyl content and FiO2. The highest values of total antioxidant activity (416 and 790 micromol l(-1)) were found in 2 babies ventilated with highest FiO2: 1 and 0.80, respectively. Total antioxidant activity was not detectable or was very low in the babies not requiring O2 therapy. The highest value of uric acid (270 micromol l(-1)) was found in the baby ventilated with 100% oxygen. Uric acid concentrations obtained in these babies were much higher then those reported in the bronchoalveolar lavage fluid of adults. Preterm babies seem to have an antioxidant response in the tracheobronchial aspirate fluid following an oxidative stress and uric acid may be physiologically important as an antioxidant of the respiratory tract, especially during the first days of life.