Efficiency of ventilation in neonatal pulmonary maladaptation

Prenatal nicotine exposure transiently alters the lung mechanical response to hypoxia in young lambs

To test the hypothesis that fetal nicotine exposure alters the lung mechanical response to hypoxia (10% O(2)) 10 lambs were exposed during the last fetal trimester to a low dose nicotine (LN) and 10 to a moderate dose (MN) (maternal dose 0.5 and 1.5mg/(kgday) free base, respectively). There were 10 controls (C). At 12 days, minute ventilation increased significantly less in MN compared with LN but not with C. In contrast to C and LN, MN did not show anticipated increases in dynamic compliance, specific compliance and FRC or decrease in lung resistance but had signs of airway hyperreactivity during hypoxia. Nicotine exposure did not alter the cardiovascular response. These adverse effects decreased with advancing age. In summary, prenatal nicotine exposure alters the lung mechanical response to hypoxia. We speculate that prenatal nicotine-induced alterations of lung mechanics during hypoxia may contribute to an increased vulnerability to hypoxic stress during infancy.

Lung function tests in neonates and infants with chronic lung disease: global and regional ventilation inhomogeneity

This review considers measurement of global and regional ventilation inhomogeneity (VI) in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy (CLDI). We focus primarily on multiple-breath inert gas washout (MBW) and electrical impedance tomography (EIT). The literature is critically reviewed and the relevant methods, equipment, and studies are summarized, including the limitations and strengths of individual techniques, together with the availability and appropriateness of any reference data. There has been a recent resurgence of interest in using MBW to monitor lung function within individuals and between different groups. In the mechanically ventilated, sedated, and paralyzed patient, VI indices can identify serial changes occurring following exogenous surfactant. Similarly, global VI indices appear to be increased in infants with CLDI and to differentiate between infants without lung disease and those with mild, moderate, and severe lung disease following preterm birth. While EIT is a relatively new technique, recent studies suggest that it is feasible in newborn infants, and can quantitatively identify changes in regional lung ventilation following alterations to ventilator settings, positive end expiratory pressure (PEEP), and administration of treatments such as surfactant. As such, EIT represents one of the more exciting prospects for continuous bedside pulmonary monitoring. For both techniques, there is an urgent need to establish guidelines regarding data collection, analysis, and interpretation in infants both with and without CLDI.

Altered lung development after prenatal nicotine exposure in young lambs

There is compelling evidence that prenatal nicotine exposure permanently alters lung development and airway function. The aim of this study was to determine how prenatal nicotine exposure alters proximal and distal airway function. Thirteen lambs were continuously exposed during the last fetal trimester to low-dose nicotine (LN) and 12 to a moderate dose (MN) (maternal s.c. dose: 0.5 and 1.5 mg/kg/d, respectively). Ten lambs served as controls (C). Proximal airway function was measured by lung mechanics. A multiple-breath N2 washout technique was used to measure lung volume (functional residual capacity) and efficiency of gas mixing in distal airways, i.e. terminal respiratory units (moment ratio and nitrogen clearance). In comparison with C, both LN and MN had significantly reduced specific airway conductance to the same extent at a median study age of 12, 25, and 51 d, indicating signs of proximal airway obstruction. Distal airway function showed significant improvement in LN. Ventilation and functional residual capacity were unaffected. In summary, prenatal nicotine exposure induced airway obstruction in proximal airways and improved gas mixing in distal airways, possibly reflecting restriction in proximal airway growth and accelerated maturation of the acinar part of the lung, respectively. We speculate that prenatal nicotine exposure has a disparate impact on airway development and function. The effect on the distal airways seemed to be inversely related to dose, which was not the case in the large airways. The altered airway function persisted during the study period, indicating that the effects of prenatal nicotine exposure might be permanent.

Measurement of functional residual capacity through the transient phase of He dilution in newborns

Helium dilution maneuver is used to determine the functional residual capacity (FRC) 14 newborns ages 1-5 mo. The model equation describes the changing alveolar fractions of He and the ventilation promoted by a rebreathing procedure that does not exceed 40 s. The model does not involve the volume of the rebreathing bag usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to newborns. Results show a strong relationship between FRC and the biometrical indexes, and confirm those found in the literature featuring that the measurement duration of FRC can be considerably shortened.

Deadspace to tidal volume ratio predicts successful extubation in infants and children

OBJECTIVE

Using a modification of the Bohr equation, single-breath carbon dioxide capnography is a noninvasive technology for calculating physiologic dead space (V(D)/V(T)). The objective of this study was to identify a minimal V(D)/V(T) value for predicting successful extubation from mechanical ventilation in pediatric patients.

DESIGN

Prospective, blinded, clinical study.

SETTING

Medical and surgical pediatric intensive care unit of a university hospital.

PATIENTS

Intubated children ranging in age from 1 wk to 18 yrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Forty-five patients were identified by the pediatric intensive care unit clinical team as meeting criteria for extubation. Thirty minutes before the planned extubation, each patient was begun on pressure support ventilation set to deliver an exhaled tidal volume of 6 mL/kg. After 20 mins on pressure support ventilation, an arterial blood gas was obtained, V(D)/V(T) was calculated, and the patient was extubated. Over the next 48 hrs, the clinical team managed the patient without knowledge of the preextubation V(D)/V(T) value. Of the 45 patients studied, 25 had V(D)/V(T) < or =0.50. Of these patients, 24 of 25 (96%) were successfully extubated without needing additional ventilatory support. In an intermediate group of patients with V(D)/V(T) between 0.50 and 0.65, six of ten patients (60%) successfully extubated from mechanical ventilation. However, only two of ten patients (20%) with a V(D)/V(T) > or =0.65 were successfully extubated. Logistic regression analysis revealed a significant association between lower V(D)/V(T) and successful extubation.

CONCLUSIONS

A V(D)/V(T) < or =0.50 reliably predicts successful extubation, whereas a V(D)/V(T) >0.65 identifies patients at risk for respiratory failure following extubation. There appears to be an intermediate V(D)/V(T) range (0.51-0.65) that is less predictive of successful extubation. Routine V(D)/V(T) monitoring of pediatric patients may permit earlier extubation and reduce unexpected extubation failures.

Determination of diffusing capacity by modeling the dynamics of C18O uptake in newborns

Dynamic modeling of lung C18O diffusion is used to measure the C18O transfer factor (TLCO) of 14 newborns aged 1-4 mo. The model equation is based on the alveolar fractions of C18O and on changing alveolar ventilation induced by the rebreathing conditions. The model does not involve the volume of the rebreathing bag which is usually needed when applying rebreathing technique and which is a source of error. The equation is discretized and solved for recorded data obtained with equipment adapted to use in newborns. A least-square parameter calculation technique is applied to estimate TLCO. Results show a strong relationship between this index and the biometrical ones and confirm those found in the literature featuring that the measurement duration can be considerably shortened.