Influence of respiratory dead space on lung clearance index in preterm infants

Long-term pulmonary outcomes of young adults born prematurely: a Polish prospective cohort study PREMATURITAS 20

BACKGROUND

The long-term consequences of prematurity are often not sufficiently recognized. To address this gap, a prospective cohort study, which is a continuation of the multicenter Polish study PREMATURITAS, was conducted, utilizing unique clinical data from 20 years ago.

OBJECTIVE

The main goal was to evaluate lung function, detect any structural abnormalities using lung ultrasound, and assess psychological well-being in young adults born between 24 and 34 weeks of gestational age (GA). Additionally, the study aimed to investigate potential associations between perinatal risk factors and abnormalities observed in pulmonary function tests (PFTs) during adulthood.

METHODS

The young survivors underwent a comprehensive set of PFTs, a lung ultrasound, along with the quality of life assessment. Information regarding the neonatal period and respiratory complications was obtained from the baseline data collected in the PREMATURITAS study.

RESULTS

A total of 52 young adults, with a mean age of 21.6 years, underwent PFTs. They were divided into two groups based on GA: 24-28 weeks (n = 12) and 29-34 weeks (n = 40). The subgroup born more prematurely had significantly higher lung clearance index (LCI), compared to the other subgroup (p = 0.013). LCI ≥ 6.99 was more frequently observed in the more premature group (50% vs. 12.5%, p = 0.005), those who did not receive prenatal steroids (p = 0.020), with a diagnosis of Respiratory Distress Syndrome (p = 0.034), those who received surfactant (p = 0.026), and mechanically ventilated ≥ 7 days (p = 0.005). Additionally, elevated LCI was associated with the diagnosis of asthma (p = 0.010).

CONCLUSIONS

The findings suggest pulmonary effects due to prematurity persist into adulthood and their insult on small airway function. Regular follow-up evaluations of young survivors born preterm should include assessments of PFTs. Specifically, the use of LCI can provide valuable insights into long-term pulmonary impairment.

Instrumental dead space: A glass ceiling for extremely low birth weight preterm infants? A dead space washout bench study

BACKGROUND

When ventilating extremely low birth weight infants, clinicians face the problem of instrumental dead space, which is often larger than tidal volume. Hence, aggressive ventilation is necessary to achieve CO₂ removal. Continuous tracheal gas insufflation can wash out CO₂ from dead space and might also have an impact on O₂ and water vapor transport. The objective of this bench study is to test the impact of instrumental dead space on the transport of CO₂ , O₂ , and water vapor and the ability of continuous tracheal gas insufflation to remedy this problem during small tidal volume ventilation.

METHODS

A test-lung located in an incubator at 37°C was ventilated with pressure levels needed to reach different tidal volumes from 1.5 to 5 mL. End-tidal CO₂ at the test-lung exit, O₂ concentration, and relative humidity in the test-lung were measured for each tidal volume with and without a 0.2 L/min continuous tracheal gas insufflation flow.

RESULTS

CO₂ clearance was improved by continuous tracheal gas insufflation allowing a 28%-44% of tidal volume reduction. With continuous tracheal gas insufflation, time to reach desired O₂ concentration was reduced from 20% to 80% and relative humidity was restored. These results are inversely related to tidal volume and are particularly critical below 3 mL.

CONCLUSION

For the smallest tidal volumes, reduction of instrumental dead space seems mandatory for CO₂ , O₂ , and water vapor transfer. Continuous tracheal gas insufflation improved CO₂ clearance, time to reach desired O₂ concentration and humidification of airways and, thus, may be an option to protect lung development.

Palivizumab Following Extremely Premature Birth Does Not Affect Pulmonary Outcomes in Adolescence

BACKGROUND

Prematurity is a risk factor for impaired lung function. We sought to assess the long-term effect of palivizumab immunization and extreme prematurity (<29 weeks gestation) on respiratory symptoms and pulmonary function in adolescence.

RESEARCH QUESTION

What is the long-term effect of palivizumab immunization and extreme prematurity (<29 weeks) on respiratory symptoms and pulmonary function in adolescence?

STUDY DESIGN AND METHODS

We examined survivors of extreme prematurity (<29 weeks gestation) at 13 to 18 years of age (study group). Study group babies who were born immediately before palivizumab immunization (nonpalivizumab group [NPG]) were compared with those babies who were born just after implementation (PG) and with a control group. For study group patients, lung function in adolescence was further compared longitudinally with that at primary school age.

RESULTS

Sixty-four adolescents aged 15.76 ± 1.52 years were included: 46 in the study group (17 PG and 29 NPG) and 18 in the control group. For the study group, wheezing episodes, inhaler use, and hospitalizations were uncommon. For the study group compared with the control group, FEV₁ percent predicted was 82.60% ± 13.54% vs 105.83% ± 13.12% (P < .001), and the lung clearance index was 7.67 ± 1.02 vs 7.46 ± 0.70 (P = .48), respectively. Study group adolescents with bronchopulmonary dysplasia had a higher lung clearance index than did adolescents with no bronchopulmonary dysplasia (7.94 ± 1.11 vs 7.20 ± 0.60; P = .002). PG and NPG adolescents were not significantly different. Comparing the study group in adolescence with primary school age, we found improvement in mean FEV₁ percent predicted bronchodilator response (0.37% ± 9.98% vs 5.67% ± 9.87%; P = .036) and mean provocative concentration causing 20% decline in FEV₁ (12.16 ± 4.71 mg/mL vs 4.14 ± 4.51 mg/mL, respectively; P < .001).

INTERPRETATION

Palivizumab did not provide any discernable long-term protective effect. Nevertheless, adolescent survivors of extreme prematurity showed good clinical and physiologic outcomes, except for mildly raised lung clearance index in patients with bronchopulmonary dysplasia. Airway hyperreactivity detected at primary school age, decreased by adolescence.

Small for gestational age birth may increase airflow limitation in bronchopulmonary dysplasia

OBJECTIVES

To determine significant indices for assessing the pulmonary function of infants according to bronchopulmonary dysplasia (BPD) severity and to evaluate whether small for gestational age (SGA) could affect pulmonary function in BPD.

METHODS

We evaluated 117 preterm infants who had undergone tidal breathing flow-volume loop and multiple-breath washout analyses within 7 months after birth. We categorized preterm infants according to BPD severity into mild/moderate BPD (n = 86), severe BPD (n = 21), and without BPD (n = 10) and the presence of SGA or appropriate gestational age (AGA) using the Fenton growth chart. We evaluated nine healthy term infants as controls.

RESULTS

The tidal breathing ratio (time to peak expiratory flow/expiratory time [t_PEF /t_E ]) was significantly lower in infants with severe BPD than in those with mild/moderate BPD. Lung clearance index (LCI) was not different based on BPD severity. In the correlation analysis after adjusting for gestational age and sex, t_PEF /t_E was correlated with the duration of mechanical ventilation (r = -0.347, P < .001) and the duration of oxygen supply (r = -0.248, P = .013) in infants with BPD. The proportion of "lower t_PEF /t_E ," defined as below the cut-off value, was greater in SGA infants (P = .017), while no significant difference was seen in the percentage of "higher LCI," defined as above the cut-off value between SGA and AGA infants.

CONCLUSIONS

In infants with BPD, t_PEF /t_E could be a useful pulmonary index which shows lower values in severe BPD. The finding of SGA in infants with BPD could be associated with poor pulmonary function related to the t_PEF /t_E values.

Generalized estimation of the ventilatory distribution from the multiple-breath washout: a bench evaluation study

BACKGROUND

The multiple-breath washout (MBW) is able to provide information about the distribution of ventilation-to-volume (v/V) ratios in the lungs. However, the classical, all-parallel model may return skewed results due to the mixing effect of a common dead space. The aim of this work is to examine whether a novel mathematical model and algorithm is able to estimate v/V of a physical model, and to compare its results with those of the classical model. The novel model takes into account a dead space in series with the parallel ventilated compartments, allows for variable tidal volume (VT) and end-expiratory lung volume (EELV), and does not require a ideal step change of the inert gas concentration.

METHODS

Two physical models with preset v/V units and a common series dead space (vd) were built and mechanically ventilated. The models underwent MBW with N2 as inert gas, throughout which flow and N2 concentration signals were acquired. Distribution of v/V was estimated-via nonnegative least squares, with Tikhonov regularization-with the classical, all-parallel model (with and without correction for non-ideal inspiratory N2 step) and with the new, generalized model including breath-by-breath vd estimates given by the Fowler method (with and without constrained VT and EELV).

RESULTS

The v/V distributions estimated with constrained EELV and VT by the generalized model were practically coincident with the actual v/V distribution for both physical models. The v/V distributions calculated with the classical model were shifted leftwards and broader as compared to the reference.

CONCLUSIONS

The proposed model and algorithm provided better estimates of v/V than the classical model, particularly with constrained VT and EELV.

Determinants of pulmonary dead space in ventilated newborn infants

BACKGROUND

Pulmonary dead space (V_D) is an index of ventilation inhomogeneity and one of the determinants of the magnitude of tidal volume to maintain optimal blood gases.

AIMS

To identify the determinants of V_D in ventilated newborns and to investigate differences in V_D between prematurely born and term infants and those prematurely born infants who did or did not develop bronchopulmonary dysplasia (BPD).

METHODS

Sixty-one mechanically ventilated infants (15 term, 46 preterm) were studied at a median age of 8 (IQR 2-31) days; 32 of the preterm infants developed BPD. V_D was determined from the difference between arterial and end tidal carbon dioxide (CO₂) using a low dead space CO₂ detector using the Bohr/Enghoff equation and was related to body weight (V_D/kg) at the time of study. The time to peak tidal expiratory flow/expiratory time (T_PTEF/T_E) was measured during spontaneous breathing using a fixed orifice pneumotachograph.

RESULTS

V_D/kg was related to gestational age (r=-0.285, p=0.001), birth weight (r=-0.356, p<0.001), weight (r=-0.316, p<0.001) and postmenstrual age (r=-0.205, p=0.020) at measurement, days of ventilation (r=0.322, p<0.001) and T_PTEF/T_E (r=-0.397, p=0.003). The median V_D/kg was higher in prematurely born infants [2.3 (IQR: 1.7-3.0) ml/kg] compared to term infants [1.5 (1.3-2.1) ml/kg, (p=0.003)] and in premature infants that developed BPD [2.6 (IQR 1.8-3.4) ml/kg] compared to those who did not [1.7 (IQR 1.1-1.9) ml/kg], (p<0.001).

CONCLUSIONS

Numerous factors influence pulmonary dead space and thus an optimum tidal volume will differ according to the underlying demographics and respiratory status.