Genetic predisposition of RSV infection-related respiratory morbidity in preterm infants

The aim of this study was to assess whether prematurely born infants have a genetic predisposition to respiratory syncytial virus (RSV) infection-related respiratory morbidity. One hundred and forty-six infants born at less than 36 weeks of gestation were prospectively followed. Nasopharygeal aspirates were obtained on every occasion the infants had a lower respiratory tract infection (LRTI) regardless of need for admission. DNA was tested for 11 single-nucleotide polymorphisms (SNPs). Chronic respiratory morbidity was assessed using respiratory health-related questionnaires, parent-completed diary cards at a corrected age of 1 year and review of hospital notes. Lung function was measured at a post menstrual age (PMA) of 36 weeks and corrected age of 1 year. A SNP in ADAM33 was associated with an increased risk of developing RSV LRTIs, but not with significant differences in 36-week PMA lung function results. SNPs in several genes were associated with increased chronic respiratory morbidity (interleukin 10 (IL10), nitric oxide synthase 2A (NOS2A), surfactant protein C (SFTPC), matrix metalloproteinase 16 (MMP16) and vitamin D receptor (VDR)) and reduced lung function at 1 year (MMP16, NOS2A, SFTPC and VDR) in infants who had had RSV LRTIs.

CONCLUSIONS

Our results suggest that prematurely born infants may have a genetic predisposition to RSV LRTIs and subsequent respiratory morbidity which is independent of premorbid lung function.

Airways obstruction and pulmonary capillary blood volume in children with sickle cell disease

OBJECTIVES AND WORKING HYPOTHESIS

Airways obstruction occurs in young children with sickle cell disease (SCD). Our aim was to test the hypothesis that increased pulmonary capillary blood volume at least in part explained the increased airways obstruction as this would inform which therapy might be most appropriate to treat the airway obstruction.

STUDY DESIGN

Observational study.

PATIENT-SUBJECT SELECTION

Twenty-five SCD children and 25 ethnic origin matched controls were recruited.

METHODOLOGY

Respiratory system resistance, using impulse oscillometry at 5 Hz (R5 %pred), pulmonary capillary blood volume (Vc), alveolar volume (VA), and spirometry were assessed before and after bronchodilator (ipratropium bromide). Lung volume measurements were also made.

RESULTS

The SCD children compared to the controls had a higher R5 %pred before (median 133 (range 88-181)% vs. 102 (83-184)%, P = 0.0046) and after (105 (79-150)% vs. 91 (64-147)%, P = 0.0489) bronchodilator and their median Vc/VA (ml/L) was higher before (26 (18-38) vs. 18 (14-28) P < 0.0001) and after (26 (19-41) vs. 18 (13-27) P < 0.0001) bronchodilator. There were similar decreases in R5 %pred post-bronchodilator in the two groups, but no significant changes in Vc/VA in either group. Vc/VA correlated significantly with R5 %pred in the SCD children only.

CONCLUSIONS

Increased pulmonary capillary blood volume contributes to the increased airways obstruction in children with SCD, hence, bronchodilators may be of limited benefit in reducing their airways obstruction.

Respiratory outcome of prematurely born infants following human rhinovirus A and C infections

Human rhinoviruses (HRVs) are a common cause of lower respiratory tract infections (LRTIs) and are associated with chronic respiratory morbidity. Our aim was to determine whether HRV species A or C were associated with chronic respiratory morbidity and increased health care utilisation in prematurely born infants. A number of 153 infants with a median gestational age of 34 (range 23-35) weeks were prospectively followed. Nasopharyngeal aspirates were collected whenever the infants had LRTIs regardless of hospitalisation status. Parents completed a respiratory diary card and health questionnaire about their infant when they were 11 and 12 months corrected age, respectively. The health-related cost of care during infancy was calculated from the medical records using the National Health Service (NHS) reference costing scheme and the British National Formulary for children. There were 32 infants that developed 40 HRV LRTIs; samples were available from 23 of the 32 infants for subtyping. Nine infants had HRV-A LRTIs, 13 HRV-C LRTIs, and one infant had a HRV-B LRTI. Exclusion of infants who also had RSV LRTIs revealed that the infants who had a HRV-C LRTI were more likely to wheeze (p < 0.0005) and use respiratory medications (p < 0.0005) and had more days of wheeze (p = 0.01) and used an inhaler (p = 0.02) than the no LRTI group. In addition, the respiratory cost of care was greater for the HRV-C LRTI than the no LRTI group (p < 0.0005).

CONCLUSION

Our results suggest HRV-C is associated with chronic respiratory morbidity during infancy in prematurely born infants.

Ankle dorsiflexor muscle size, composition and force with ageing and chronic obstructive pulmonary disease

Loss of skeletal muscle strength is a well-recognized feature of ageing and chronic obstructive pulmonary disease (COPD). Reductions in muscle size provide only a partial explanation for this loss of strength, and additional contributory factors remain undetermined. We hypothesized that reductions in skeletal muscle strength, as measured in the ankle dorsiflexor muscles, would be reduced with ageing and COPD as a result of changes in both size and composition of the tibialis anterior muscle. Twenty healthy young subjects, 18 healthy elderly subjects and 17 patients with COPD were studied. Ankle dorsiflexor muscle strength was assessed by maximal voluntary contraction (ADMVC) and 100 Hz supramaximal electrical stimulation of the peroneal nerve (100 HzAD). Tibialis anterior cross-sectional area (TACSA) and composition, as assessed by echo intensity (TAEI), were measured using ultrasonography. Despite a lack of differences in TACSA between groups, ADMVC and 100 HzAD were significantly reduced in COPD patients compared with both healthy elderly and healthy young subjects, when expressed as absolute values and when normalized to TACSA (P < 0.01). The TAEI was, however, higher in COPD patients compared with healthy elderly (P = 0.025) and healthy young subjects (P = 0.0008), suggesting increased levels of non-contractile tissue. Across all participants, ADMVC and 100 HzAD correlated positively with TACSA (r = 0.78, P < 0.0001) and negatively with TAEI (r = -0.46, P < 0.0005). The variance in 100 HzAD was best explained with a regression model incorporating TACSA, TAEI, age and COPD status (r(2) = 0.822, P = 0.001). These data demonstrate that the loss of skeletal muscle strength in COPD is related to changes in muscle composition, with infiltration of non-contractile tissue beyond that seen during normal ageing.

Sleeping position and responses to a carbon dioxide challenge in convalescent prematurely born infants studied post-term

OBJECTIVES

To test the hypothesis that the ventilatory response to a carbon dioxide (CO2) challenge would be lower in the prone compared to the supine position in prematurely born infants studied post-term. To determine whether there were postural-related differences in respiratory drive, respiratory muscle strength, thoracoabdominal synchrony and/or lung volume.

DESIGN

Prospective cohort study.

SETTING

Tertiary neonatal unit.

PATIENTS

Eighteen infants (median gestational age 31 (range 22-32) weeks) were studied at a median of 5 (range 2-11) weeks post-term.

INTERVENTIONS

The ventilatory responses to three added carbon dioxide (CO2) levels (0% baseline, 2% and 4%) were assessed in the prone and supine positions.

MAIN OUTCOME MEASURES

The airway pressure change after the first 100 ms of an occluded inspiration (P0.1) (respiratory drive) and the maximum inspiratory pressure during crying with an occluded airway (Pimax) (respiratory muscle strength) were measured. The P0.1/Pimax ratio at each CO2 level and slope of the P0.1/Pimax response were calculated.

RESULTS

The mean P0.1 (p<0.05) and P0.1/Pimax (p<0.05) were higher and the functional residual capacity (p=0.031) lower in the supine compared to the prone position. The mean P0.1 and P0.1/Pimax increased independently of position as the percentage CO2 increased (p<0.001). There was no tendency for the differences in P0.1 and P0.1/Pimax between the prone and supine position to vary by CO2 level.

CONCLUSIONS

Convalescent, prematurely born infants studied post-term have a reduced respiratory drive, but not a lower ventilatory response to a CO2 challenge, in the prone compared to the supine position.

Rhinovirus infection and healthcare utilisation in prematurely born infants

Our aim was to determine whether rhinovirus (RV) lower respiratory tract infections (LRTIs) in prematurely born infants increase health-related cost of care during infancy. 153 infants born at <36 weeks of gestation were prospectively followed to 1 year. Cost of care was calculated from the National Health Service reference costing scheme and healthcare utilisation determined by examining hospital/general practitioner records. 20 infants developed RV LRTIs (RV group), 17 respiratory syncytial virus (RSV) LRTIs (RSV group), 12 both RV and RSV LRTIs (RV/RSV group) and 74 had no LRTI (no LRTI group). Compared with the no LRTI group, the RV/RSV LRTI group had the greatest increase in adjusted mean cost (difference GBP 5769), followed by the RV LRTI group (difference GBP 278) and, finally, the RSV LRTI group (difference GBP 172) (p=0.045). The RV group had more outpatient (p<0.05) and respiratory-related general practitioner (p<0.05) attendances, more wheezed at follow-up (p<0.001) than the no LRTI group and more had respiratory-related outpatient attendances than the RSV LRTI group (p<0.05). We conclude that RV LRTIs were associated with increased health-related cost of care during infancy; our results suggest that the RV group compared with the RSV group suffered greater chronic respiratory morbidity.

Neural respiratory drive measured during inspiratory threshold loading and acute hypercapnia in healthy individuals

Understanding the effects of respiratory load on neural respiratory drive and respiratory pattern are key to understanding the regulation of load compensation in respiratory disease. The aim of the study was to examine and compare the recruitment pattern of the diaphragm and parasternal intercostal muscles when the respiratory system was loaded using two methods. Twelve subjects performed incremental inspiratory threshold loading up to 50% of their maximal inspiratory pressure, and 10 subjects underwent incremental, steady-state hypercapnia to a maximal inspired CO2 of 5%. The diaphragmatic electromyogram (EMGdi) was measured using a multipair oesophageal catheter, and the parasternal intercostal muscle EMG (sEMGpara) was recorded from bipolar surface electrodes positioned in the second intercostal space. The EMGdi and sEMGpara were analysed over the last minute of each increment of both protocols, normalized using the peak EMG recorded during maximal respiratory manoeuvres and expressed as EMG%max. The EMGdi%max and sEMGpara%max increased in parallel during the two loading methods, although EMGdi%max was consistently greater than sEMGpara%max in both conditions, inspiratory threshold loading [bias (SD) 9 (3)%, 95% limits of agreement 4-15%] and hypercapnia [bias (SD) 6 (3)%, 95% limits of agreement -0.05 to 12%]. Inspiratory threshold loading resulted in more pronounced increases in mean (SD) EMGdi%max [10 (7)-45 (28)%] and sEMGpara%max [5.3 (3.1)-40 (28)%] from baseline compared with EMGdi%max [7 (4)-21 (8)%] and sEMGpara%max [4.7 (2.3)-10 (4)%] during hypercapnia, despite comparable levels of ventilation. These data support the use of sEMGpara%max, as a non-invasive alternative to EMGdi%max recorded with an invasive oesophageal electrode catheter, for the quantification of neural respiratory drive. This technique should make evaluation of respiratory muscle function easier to undertake and therefore more readily acceptable in patients with respiratory disease, in whom transduction of neural respiratory drive to pressure generation can be compromised.

Randomised trial of volume-targeted ventilation versus pressure-limited ventilation in acute respiratory failure in prematurely born infants

BACKGROUND

During volume-targeted ventilation (VTV), a constant volume is delivered with each ventilator inflation.

OBJECTIVES

To determine whether VTV compared to pressure-limited ventilation (PLV) reduced the time to reach weaning criteria in prematurely born infants with acute respiratory distress, and if any difference was explained by better respiratory muscle strength and/or a lower work of breathing (WOB).

METHODS

Infants of <34 weeks of gestational age ventilated for <24 h in the first week after birth were randomised to receive either VTV or PLV. The primary outcome was the time to achieve pre-specified weaning criteria. Respiratory muscle strength was assessed by the measurement of the maximum inflation and expiratory pressures, and the WOB assessed by the transdiaphragmatic pressure time product. Other outcomes reported are the duration of ventilation, occurrence of patent ductus arteriosus, pneumothorax, intraventricular haemorrhage, periventricular leukomalacia and episodes of hypocarbia.

RESULTS

Forty infants, median gestational age 27 (range 23-33) weeks, were recruited. The time taken to achieve weaning criteria was similar in the two groups [median 14 h (VTV) vs. 23 h (PLV)]. There were no significant differences between the groups with regard to respiratory muscle strength, WOB or other outcomes, except that fewer of the VTV compared to the PLV group had episodes of hypocarbia (8 vs. 19; p < 0.001).

CONCLUSION

In prematurely born infants with acute respiratory failure, use of VTV did not reduce the time to reach weaning criteria, but was associated with a reduction in episodes of hypocarbia.

Quadriceps and ankle dorsiflexor strength in chronic obstructive pulmonary disease

INTRODUCTION

Quadriceps strength and size are commonly reduced in chronic obstructive pulmonary disease (COPD). We wished to assess volitional and nonvolitional ankle dorsiflexor strength in COPD.

METHODS

Quadriceps and ankle dorsiflexor strength were measured by maximum voluntary contraction (MVC) and by twitch responses to supramaximal femoral and fibular nerve stimulation. Cross-sectional areas of the tibialis anterior (TA(CSA)) and rectus femoris muscles (RF(CSA)) were measured by ultrasound.

RESULTS

Eighteen elderly subjects and 20 COPD patients [mean(SD) %predictedFEV(1) 50(20)%] participated. No significant difference in fat-free mass index, ankle dorsiflexor strength, or TA(CSA) were observed in the presence of reduced quadriceps strength and size in COPD [mean MVC difference: -10.9 kg (95% confidence interval {CI}: -17.1 kg to -4.8 kg, P < 0.01; mean RF(CSA) difference -119 mm(2), 95% CI: -180 mm(2) to -58 mm(2), P < 0.01)].

CONCLUSIONS

Ankle dorsiflexor strength is less attenuated than quadriceps strength in COPD patients with moderate airflow obstruction. Direct quadriceps assessment may be more relevant than measurement of lower limb fat-free mass.

Randomised weaning trial comparing assist control to pressure support ventilation

OBJECTIVES

To determine if the work of breathing was lower, respiratory muscle strength greater, but the degree of asynchrony higher during weaning by assist control ventilation (ACV) rather than pressure support ventilation (PSV) and if any differences were associated with a shorter duration of weaning.

DESIGN

Randomised trial

SETTING

Tertiary neonatal unit

PATIENTS

Thirty-six infants, median gestational age 29 (range 24 to 39) weeks

INTERVENTION

Weaning by either ACV or PSV.

MAIN OUTCOME MEASURES

At baseline, 24 hours after entering the study and immediately prior to extubation, the work of breathing (PTPdi), thoracoabdominal asynchrony (TAA) and respiratory muscle strength (Pimax) were assessed and weaning duration recorded.

RESULTS

There were no significant differences in the median PTPdi, TAA and Pimax results at any time point. The inflation times during ACV and PSV were similar. The median duration of weaning was 34 (range 7-100) hours in the ACV group and 27 (range 10-169) hours in the PSV group (p=0.88).

CONCLUSION

No significant differences were found between weaning by PSV and ACV when similar inflation times were used.

Lung function at follow-up of infants with surgically correctable anomalies

Infants with congenital diaphragmatic hernia (CDH) or anterior wall defects (AWD) can suffer abnormal antenatal lung growth, the risk, however, may be greater for CDH infants. The objectives of this study were to test the hypothesis that following surgical correction, CDH infants would have worse lung function at follow-up than AWD infants and to determine whether fetal lung volume (FLV) results correlated with the lung function results at follow-up. Thirteen infants with CDH and 13 infants with AWD had lung function measurements at a median age of 11 (range 6-24) months; 17 of the infants had had their FLV assessed. Lung function was assessed by plethysmographic measurement of lung volume (FRCpleth) and airway resistance (Raw). In addition, functional residual capacity was assessed by a helium gas dilution technique (FRCHe); tidal breathing parameters (T(PTEF) :Te) and compliance and resistance of the respiratory system (Crs and Rrs, respectively) were also determined. FLV was assessed using three-dimensional (3D) ultrasound and virtual organ computer aided analysis. The CDH compared to the AWD infants had a higher median FRCpleth (41 ml/kg vs. 37 ml/kg, P = 0.043) and a lower median Crs (1.45 ml/cm H(2) O/kg vs. 2.78 ml/cm H(2) O/kg, P = 0.041). FRCpleth results correlated significantly with FLV results (r = 0.721, P < 0.001). In conclusion, infants with CDH had significantly different lung function at follow-up than AWD infants. Our findings suggest FLV results may predict lung function abnormalities at follow-up in infants with surgically correctable anomalies.

Measurement of parasternal intercostal electromyogram during an infective exacerbation in patients with cystic fibrosis

The parasternal intercostal muscle electromyogram (sEMGpara) is a measure of neural respiratory drive and reflects lung disease severity in stable cystic fibrosis (CF). The aim of the study was to measure sEMGpara in acute infective exacerbations of CF and compare changes in sEMGpara with those in conventional lung function measures. 12 patients with CF admitted to hospital with an acute chest infection were studied. There was a significant reduction in mean ± SD sEMGpara (ΔsEMGpara -38 ± 19%, p<0.001) between admission and discharge. Spirometery also improved significantly from admission to discharge; Δforced expiratory volume in 1 s % predicted 39 ± 30%, p<0.001 and Δvital capacity % pred 22 ± 18%, p<0.001. sEMGpara has potential value as a nonvolitional measure of change in respiratory function in CF.

Volume-targeted ventilation in infants born at or near term

OBJECTIVES

To determine the impact of different volume-targeted (VT) levels during volume-targeted ventilation (VTV) on the work of breathing (WOB) of infants born at or near term and to investigate whether a level of VT reduced the WOB below that experienced on respiratory support without VT.

DESIGN

Prospective crossover study.

PATIENTS

Sixteen infants, median gestational age of 38 (range 34-41) weeks, birth weight of 3.1 (range 1.5-4.1) kg and postnatal age of 5 (range 2-17) days were studied. The infants were receiving time-cycled, pressure-limited ventilation in a continuous mandatory or in a triggered mode.

INTERVENTIONS

The infants were studied first without VT (baseline) and then at VT levels of 4, 5 and 6 ml/kg delivered in a random order. After each VT level, the infants were returned to baseline.

MAIN OUTCOME MEASURE

The WOB was assessed by measuring the transdiaphragmatic pressure-time product (PTPdi).

RESULTS

One infant became apnoeic at VT of 6 ml/kg. At a VT level of 4 ml/kg, four infants were making such vigorous respiratory efforts that no inflations were delivered. The median PTPdi was higher at a VT level of 4 ml/kg than at 5 ml/kg (p<0.01) or 6 ml/kg (p<0.001). Only at a VT level of 6 ml/kg was the median PTPdi lower than that at baseline (p<0.01).

CONCLUSION

Low VT levels (4 ml/kg) during VTV increase the WOB in ventilated infants born at term or near term. The results suggest that a VT level of 6 ml/kg could be used to reduce the WOB.

Prediction of bronchopulmonary dysplasia

OBJECTIVE

To determine whether elevation of a biological marker of inflammation would be a better predictor of bronchopulmonary dysplasia (BPD) development than lung function measurement results.

DESIGN

Prospective study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

78 prematurely born infants (median gestational age 29 (range 24-32) weeks) were studied; 39 developed BPD.

INTERVENTIONS

BPD was diagnosed as oxygen dependence at 28 days.

MAIN OUTCOME MEASURES

Levels of a biological marker of inflammation (carbon monoxide) were assessed by measurement of end-tidal carbon monoxide (ETCO) and lung function by measurement of functional residual capacity (FRC) and compliance (Crs) and resistance (Rrs) of the respiratory system on days 3 and 14 after birth. Possible predictive factors were modelled for BPD and for BPD severity.

RESULTS

Gestational age, birth weight, ETCO, FRC and Crs results on days 3 and 14 differed significantly between infants who did and did not develop BPD. In multifactorial logistic regression, only birth weight and ETCO results (on day 14) remained significant predictors of BPD with an area under the curve of 0.97. The final multifactorial model for the severity of BPD included those two factors, plus septic episodes.

CONCLUSION

These results emphasise the importance of ongoing inflammation in the development of BPD; ETCO levels, rather than lung function test results, were the more accurate predictor of BPD development.

Lung function abnormalities in infants developing bronchopulmonary dysplasia

OBJECTIVE

To determine if infants developing bronchopulmonary dysplasia (BPD), particularly mild BPD, initially had minimal lung function abnormalities, which then worsened throughout the neonatal period.

DESIGN

Prospective observational study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

74 infants with a median gestational age of 30 weeks (24-32) and birth weight of 1200 g (474-2000) were studied; 35 had no BPD, 12 developed mild BPD and 23 developed moderate/severe BPD.

INTERVENTIONS

BPD was diagnosed in infants who were oxygen dependent beyond 28 days after birth.

MAIN OUTCOME MEASURES

Lung function was assessed by measurement of functional residual capacity (FRC) by helium gas dilution and compliance and resistance of the respiratory system. Measurements were attempted on days 3, 5, 7, 14, 21 and 28.

RESULTS

Infants developing BPD, particularly moderate/severe BPD, had lower mean FRC (p=0.009) and mean compliance (p=0.005) throughout the 28-day period than those who did not develop BPD. Lung function improved over the neonatal period in all three groups, but the rate of improvement in FRC (p=0.004) and compliance (p=0.002) results over the first 28 days varied by BPD status, being greatest in infants developing moderate/severe BPD (all p values <0.05).

CONCLUSIONS

Overall, in infants who did and did not develop BPD, lung function improved throughout the neonatal period. Infants with more severe initial lung disease were more likely to develop moderate/severe BPD.

Chorioamnionitis, lung function and bronchopulmonary dysplasia in prematurely born infants

OBJECTIVE

To determine whether prematurely born infants exposed to chorioamnionitis compared to those not exposed have poorer lung function and are more likely to develop severe bronchopulmonary dysplasia (BPD).

DESIGN

Results were analysed from consecutive infants born at <33 weeks gestation with placental histology results and lung function measurement results on days 2 and/or 7 after birth and/or at 36 weeks postmenstrual age (PMA).

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

120 infants with a median gestational age of 29 (range 23-32) weeks were studied, 76 (63%) developed BPD and 41 (34%) had been exposed to chorioamnionitis and/or funisitis.

INTERVENTIONS

Chorioamnionitis was diagnosed histologically.

MAIN OUTCOME MEASURES

Lung function was assessed by measurement of lung volume and compliance and resistance of the respiratory system. If the infants remained oxygen dependent beyond 28 days, they were diagnosed at 36 weeks PMA to have mild BPD (no longer oxygen dependent), moderate BPD (required less than 30% oxygen) or severe BPD (required more than 30% oxygen and/or positive pressure support).

RESULTS

No significant differences were found in the lung function results between the chorioamnionitis and non-chorioamnionitis groups at any postnatal age. There was no significant relationship between chorioamnionitis and the occurrence or severity of BPD. Regression analysis demonstrated BPD was significantly related only to birth weight, gestational age and use of surfactant.

CONCLUSION

In prematurely born infants, routinely exposed to antenatal steroids and postnatal surfactant, chorioamnionitis was not associated with worse lung function or more severe BPD.

Prediction of extubation outcome in infants using the tension time index

OBJECTIVE

Approximately one-third of ventilated infants fail extubation. The objective of this study was to determine whether assessment of the load relative to the capacity of respiratory muscles by measurement of the tension time index (TTI) successfully predicted extubation outcome in infants.

DESIGN

Prospective study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

Twenty ventilated infants, with a median gestational age of 31 (range 24-39) weeks, were studied at a median postnatal age of 2.5 (range 1-37) days.

INTERVENTIONS

The diaphragm tension time index (TTdi) was derived from measurements of transdiaphragmatic pressure using a dual-pressure transducer tipped catheter. The respiratory muscle tension time index (TTmus) was derived from non-invasive airway pressure measurements. Measurements were made within the 6 h prior to extubation.

MAIN OUTCOME MEASURES

Extubation failure was defined as the need for reintubation within 48 h of extubation.

RESULTS

Five infants failed extubation; their median TTdi (p=0.001) and TTmus (p=0.001) were significantly higher than those of the successfully extubated infants. A TTdi of >0.15 and a TTmus of >0.18 were 100% sensitive and 100% specific in predicting extubation failure

CONCLUSION

In ventilated infants, invasive and non-invasive measurements of the TTI could provide an accurate prediction of extubation outcome.

Lung function prior to viral lower respiratory tract infections in prematurely born infants

OBJECTIVE

Prematurely born infants who develop respiratory syncytial virus (RSV) lower respiratory tract infections (LRTIs) have lung function abnormalities at follow-up. The aim of this study was to determine whether prematurely born infants who developed symptomatic RSV, or other viral LRTI(s), had poorer premorbid lung function than infants who did not develop LRTIs during the RSV season.

METHODS

Lung function (functional residual capacity (FRC), compliance (Crs) and resistance (Rrs) of the respiratory system) was measured at 36 weeks postmenstrual age. After neonatal unit discharge, nasopharyngeal aspirates were obtained whenever the infants had an LRTI, regardless of whether this was in the community or in hospital. Nasopharyngeal aspirates were examined for RSV A and B, rhinovirus, influenza A and B, parainfluenza 1, 2 and 3, human metapneumovirus and adenovirus.

RESULTS

159 infants with a median gestational age of 34 (range 23-36) weeks were prospectively followed. 73 infants developed LRTIs: 27 had at least one RSV LRTI and 31 had at least one other viral LRTI, but not an RSV LRTI. Overall, there were no significant differences in the FRC (p=0.54), Crs (p=0.11) or Rrs (p=0.12) results between those who developed an RSV or other viral LRTI and those who did not develop an LRTI. Infants with RSV or other viral LRTIs who were admitted to hospital compared with those who were not had higher Rrs results (p=0.033 and p=0.039, respectively).

CONCLUSION

Diminished premorbid lung function may predispose prematurely born infants to severe viral LRTIs in infancy.

Ventilatory response to added dead space and position in preterm infants at high risk age for SIDS

OBJECTIVE

The vulnerability of prematurely born infants to sudden infant death syndrome (SIDS) in the prone position might be explained by a reduced ability to respond to a stress, such as hypercarbia, in that position; our objective, therefore, was to further explore the influence of position on the response to a stress.

WORKING HYPOTHESIS

The ability of prematurely born infants to respond to added dead space in the prone compared to the supine position would be impaired at the high risk age for SIDS.

PATIENTS

Twenty infants, median gestational age of 30 (range 24-32) weeks were studied at a median postmenstrual age (PMA) of 45 weeks. In addition, comparisons were made to the results of 25 infants studied at 36 weeks PMA.

METHODOLOGY

Infants were studied supine and prone. Breath by breath minute volume was measured at baseline and after a dead space was incorporated into the breathing circuit; the time constant of the response was calculated. The pressure generated in the first 100 msec of an occlusion (P0.1 ), the maximum inspiratory pressure during an airway occlusion and functional residual capacity (FRC) were also measured in both positions.

RESULTS

The median time constant was longer (38 (range 15-85) vs. 26 (range 2-40) sec (P = 0.002)). P0.1 lower (P = 0.003) and FRC higher (P = 0.031) in the prone compared to the supine position. In the prone position, the time constant correlated with PMA (P = 0.047), that is, the rate of response to added dead space was significantly damped with increasing postnatal age up to the critical age for SIDS.

CONCLUSIONS

The dampened rate of response to added dead space in the prone compared to the supine position lends support to the hypothesis that a poorer response to a stress may contribute to prematurely born infants increased risk of SIDS in the prone position.

Three-dimensional ultrasound fetal lung volumes and infant respiratory outcome: a prospective observational study

OBJECTIVE

To determine if fetal lung volumes (FLVs), determined by three-dimensional rotational ultrasound and virtual organ computer-aided analysis software (vocal), correlated with neonatal respiratory outcomes in surviving infants who had a high risk [fetuses with congenital diaphragmatic hernia (CDH)], lower risk [fetuses with anterior wall defects (AWDs)] and no risk (controls) of abnormal antenatal lung growth.

DESIGN

Prospective observational study.

SETTING

Tertiary fetal medicine and neonatal intensive care units.

POPULATION

Sixty fetuses (25 with CDH, 25 with AWDs and ten controls).

METHODS

FLVs were measured and expressed as the percentage of the observed compared with the expected for gestational age.

MAIN OUTCOME MEASURES

Neonatal respiratory outcome was determined by the duration of supplemental oxygen, mechanical ventilation and dependencies, and assessment of lung volume using a gas dilution technique to measure functional residual capacity (FRC).

RESULTS

The infants with CDH had lower FLV results than both the infants with AWDs (P=0.05) and the controls (P<0.05). The infants with CDH had longer durations of mechanical ventilation (P<0.001) and supplementary oxygen (P<0.001) dependence, compared with infants with AWDs. The infants with CDH had a lower median FRC than both the infants with AWDs (P<0.001) and the controls (P<0.001). FLV results correlated significantly with the durations of dependency on ventilation (r= -0.744, P<0.01) and oxygen (r= -0.788, P<0.001), and with FRC results (r=0.429, P=0.001).

CONCLUSIONS

These results suggest that FLVs obtained using three-dimensional rotational ultrasound might be useful in predicting neonatal respiratory outcome in surviving infants who had varying risks of abnormal lung growth. Larger and more comprehensive studies are needed to clarify the role that lung volume measurements have in assessing lung function and growth.

Survey of sleeping position recommendations for prematurely born infants

The risk of sudden infant death syndrome is increased in prematurely born infants compared to those born at term, particularly if they are either slept prone or on their side. The aim of this study was to determine whether a national campaign "Time to get back to sleep" had influenced the recommendations made by neonatal practitioners regarding the sleeping position for prematurely born babies prior to and after neonatal unit discharge. A questionnaire survey was sent to all UK neonatal units, of which 90% responded. The results were compared to those of a survey carried out prior to the national campaign. Analysis of the responses demonstrated that there was no significant difference in the proportion of units which recommended supine sleeping at least 1-2 weeks before discharge (78% versus 83%). Still, a minority of units provided written information for staff (26% versus 33%), but a greater proportion of units provided written information for parents (95% versus 90%, p = 0.047). All units recommended supine sleeping following discharge, and compared to the results of the previous survey, a smaller proportion of units additionally recommended side sleeping after discharge (8% versus 17%, p =0.01) and a greater proportion actively discouraged prone sleeping (62% versus 38%, p < 0.0001).

CONCLUSIONS

The majority but, importantly, not all neonatal units are giving appropriate recommendations regarding sleeping position following neonatal unit discharge. These results highlight that further education of neonatal staff regarding appropriate sleeping position for prematurely born babies remains imperative.

Neural respiratory drive, pulmonary mechanics and breathlessness in patients with cystic fibrosis

BACKGROUND

Neural respiratory drive (NRD) measured from the diaphragm electromyogram (EMGdi) reflects the load/capacity balance of the respiratory muscle pump and is a marker of lung disease severity. EMGdi measurement is invasive, but recording the EMG from the parasternal intercostal muscles using surface electrodes (sEMGpara) could provide a non-invasive method of assessing NRD and disease severity. Objectives To test the hypothesis that NRD measured by sEMGpara correlates with EMGdi, to provide an index of disease severity in cystic fibrosis (CF) and to relate to exercise-induced breathlessness.

METHODS

15 patients with CF (mean forced expiratory volume in 1&emsp14;s (FEV(1)) 53.5% predicted) and 15 age-matched healthy controls were studied. sEMGpara and EMGdi were recorded at rest and during exercise. sEMGpara was recorded using surface electrodes and EMGdi using a multipair oesophageal electrode catheter. Signals were normalised using the peak EMG recorded during maximum respiratory manoeuvres and expressed as EMG%max. The respiratory pattern, metabolic data, oesophageal and gastric pressures and Borg scores were also recorded.

RESULTS

Mean (SD) resting sEMGpara%max and EMGdi%max were higher in patients with CF than in controls (13.1 (7)% and 18.5 (7.5)% vs 5.8 (3)% and 7.5 (2)%, respectively, p<0.001). In the patients with CF, resting sEMGpara%max and EMGdi%max were related to the degree of airways obstruction (FEV(1)) (r = -0.91 and r = -0.82, both p<0.001), hyperinflation (r = 0.63 and r = 0.56, both p<0.001) and dynamic lung compliance (r = -0.53 and r = -0.59, both p<0.001). During exercise, sEMGpara%max and EMGdi%max were strongly correlated with breathlessness in the patients with CF before (r = 0.906, p<0.001) and after (r = 0.975, p<0.001) the onset of neuromechanical dissociation.

CONCLUSION

sEMGpara%max provides a non-invasive marker of neural drive, which reflects disease severity and exercise-induced breathlessness in CF.

Work of breathing and volume targeted ventilation in respiratory distress

OBJECTIVE

To determine the level of volume targeting (VT) associated with the lowest work of breathing (WOB) for prematurely born infants being ventilated with acute respiratory distress.

DESIGN

Prospective study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

18 infants, median gestational age 29 (range 25-34) weeks, being ventilated for acute respiratory distress.

INTERVENTIONS

Infants were studied first without VT (baseline). Volume targeted levels of 4 ml/kg, 5 ml/kg and 6 ml/kg were then delivered in random order. After each VT level, the infants were returned to baseline. Each step was maintained for 20 minutes.

MAIN OUTCOME MEASURE

The transdiaphragmatic pressure time product (PTPdi) as an estimate of the WOB.

RESULTS

The mean PTPdi was higher at a VT level of 4 ml/kg (median 154 cm H(2)O·s/min) compared to baseline (median 112 cm H(2)O·s/min) (p<0.001) and a VT level of 6 ml/kg (median 89 cm H(2)O·s/min) (p<0.001).

CONCLUSION

A low level of VT increased the WOB in infants with acute respiratory distress syndrome. The authors' results suggest that, during acute respiratory distress, a VT level of at least 5 ml/kg rather than a lower level might avoid an increased WOB. The most appropriate level of VT needs to be determined in a randomised controlled trial with long-term outcomes.

The effects of sleeping position on ventilatory responses to carbon dioxide in premature infants

BACKGROUND

The prone sleeping position, particularly in prematurely born infants, is associated with an increased risk of sudden infant death syndrome. A possible mechanism is an impaired ability to respond to respiratory compromise. The hypothesis that the ventilatory response to a carbon dioxide (CO(2)) challenge in convalescent, prematurely born infants would be lower in the prone compared with the supine position was therefore tested.

METHODS

In each position, ventilatory responses to increasing levels of inspired CO(2) were assessed. The airway pressure change after the first 100 ms of an occluded inspiration (P(0.1)) and the maximum inspiratory pressure with an occluded airway during crying (P(imax)) were measured; the ratio of the P(0.1) to the P(imax) at each inspired CO(2) level and the slope of the P(0.1)/P(imax) response were calculated. Chest and abdominal wall asynchrony was assessed using inductance plethysmography and functional residual capacity (FRC) measured using a helium gas dilution technique.

RESULTS

Eighteen infants with a median postmenstrual age of 35 (range 35-37) weeks were studied. In the prone versus the supine position, the mean P(0.1) (p=0.002), the mean P(imax) (p=0.006), the increase in P(0.1) with increasing CO(2) (p=0.007) and the P(0.1)/P(imax) response slope (p=0.007) were smaller. Thoracoabdominal asynchrony was not significantly influenced by position or inspired CO(2). FRC was higher in the prone position (p=0.019).

CONCLUSIONS

Convalescent, prematurely born infants have a reduced ventilatory response to CO(2) challenge in the prone position, suggesting they may have an impaired ability to respond to respiratory compromise in that position.

In vitro assessment of proportional assist ventilation

OBJECTIVE

During proportional assist ventilation (PAV) the timing and frequency of inflations are controlled by the patient and the patient's work of breathing may be relieved by elastic and/or resistive unloading. It is important and the authors' objective to determine whether ventilators delivering PAV function well in situations mimicking neonatal respiratory conditions.

DESIGN

In vitro laboratory study.

SETTING

Tertiary neonatal ICU.

INTERVENTIONS

Dynamic lung models were developed which mimicked respiratory distress syndrome, bronchopulmonary dysplasia and meconium aspiration syndrome to assess the performance of the Stephanie neonatal ventilator.

MAIN OUTCOME MEASURES

The effects of elastic and resistive unloading on inflation pressures and airway pressure wave forms and whether increasing unloading was matched by an 'inspiratory' load reduction.

RESULTS

During unloading, delivered pressures were between 1 and 4 cm H(2)O above those expected. Oscillations appeared in the airway pressure wave form when the elastic unloading was greater than 0.5 cm H(2)O/ml with a low resistance model and 1.5 cm H(2)O/ml with a high resistance model and when the resistive unloading was greater than 100 cm H(2)O/l/s. There was a time lag in the delivery of airway pressure of at least 60 ms, but increasing unloading was matched by an inspiratory load reduction.

CONCLUSIONS

During PAV, unloading does reduce inspiratory load, but there are wave form abnormalities and a time lag in delivery of the inflation pressure. The impact of these problems needs careful evaluation in the clinical setting.

Diaphragm electromyogram in infants with abdominal wall defects and congenital diaphragmatic hernia

Measurement of the diaphragm electromyogram (EMGdi) elicited by phrenic nerve stimulation could be useful to assess neonates suffering from respiratory distress due to diaphragm dysfunction, as observed in infants with abdominal wall defects (AWD) or congenital diaphragmatic hernia (CDH). The study aims were to assess the feasibility of recording EMGdi using a multipair oesophageal electrode catheter and examine whether diaphragm muscle and/or phrenic nerve function was compromised in AWD or CDH infants. Diaphragm compound muscle action potentials elicited by magnetic phrenic nerve stimulation were recorded from 18 infants with surgically repaired AWD (n = 13) or CDH (n = 5), median (range) gestational age 36.5 (34-40) weeks. Diaphragm strength was assessed as twitch transdiaphragmatic pressure (TwP(di)). One AWD patient had prolonged phrenic nerve latency (PNL) bilaterally (left 9.31 ms, right 9.49 ms) and two CDH patients had prolonged PNL on the affected side (10.1 ms and 10.08 ms). There was no difference in left and right TwP(di) in either group. PNL correlated significantly with TwP(di) in CDH (r = 0.8; p = 0.009). Oesophageal EMG and magnetic stimulation of the phrenic nerves can be useful to assess phrenic nerve function in infants. Reduced phrenic nerve conduction accompanies the reduced diaphragm force production observed in infants with CDH.

Effect of caffeine on respiratory muscle strength and lung function in prematurely born, ventilated infants

The aims of this study were to determine whether caffeine administration increased respiratory muscle function and if this was associated with lung function improvement in prematurely born infants being weaned from mechanical ventilation. Respiratory muscle function was assessed by measurement of the maximum pressures generated during occlusions at end inspiration (Pemax) and end expiration (Pimax) and lung function by measurement of lung volume (functional residual capacity (FRC)) and respiratory system compliance (CRS) and resistance (RRS) in 18 infants with a median gestational age of 28 (range 24-36) weeks. Measurements were made immediately prior to caffeine administration (baseline) and 6 h later. Six hours after caffeine administration compared to baseline, the median Pemax (p = 0.017), Pimax (p = 0.004), FRC (p < 0.001), CRS (p = 0.002) and RRS (p = 0.004) had significantly improved. Our results suggest that caffeine administration facilitates weaning of prematurely born infants from mechanical ventilation by improving respiratory muscle strength.

Tension-time index as a predictor of extubation outcome in ventilated children

RATIONALE

Indices that assess the load on the respiratory muscles, such as the tension-time index (TTI), may predict extubation outcome.

OBJECTIVES

To evaluate the performance of a noninvasive assessment of TTI, the respiratory muscle tension time index (TTmus), by comparison to that of the diaphragm tension time index (TTdi) and other predictors of extubation outcome in ventilated children.

METHODS

Eighty children (median [range] age 2.1 yr [0.15-16]) admitted to pediatric intensive care units at King's College and St Mary's Hospitals who required mechanical ventilation for more than 24 hours were studied.

MEASUREMENTS AND MAIN RESULTS

TTmus, maximal inspiratory pressure, respiratory drive, respiratory system mechanics, and functional residual capacity using a helium dilution technique, the rapid shallow breathing and CROP indices (compliance, rate, oxygenation, and pressure) indexed for body weight were measured and standard clinical data recorded in all patients. TTdi was measured in 28 of the 80 children using balloon catheters. Eight children (three in the TTdi group) failed extubation. TTmus (0.199 vs. 0.09) and TTdi (0.157 vs. 0.07) were significantly higher in children who failed extubation. TTmus greater than 0.18 (n = 80) and TTdi greater than 0.15 (n = 28) had sensitivities and specificities of 100% in predicting extubation failure. The other predictors performed less well.

CONCLUSIONS

Invasive and noninvasive measurements of TTI may provide accurate prediction of extubation outcome in mechanically ventilated children.

Work of breathing during SIMV with and without pressure support

OBJECTIVE

In a randomised trial, pressure support with synchronised intermittent mandatory ventilation (SIMV) compared to SIMV alone was associated with a significant reduction in supplementary oxygen duration. The hypothesis that the addition of pressure support to SIMV compared to SIMV alone would reduce the work of breathing was examined.

DESIGN

Prospective study.

SETTING

Perinatal service.

PATIENTS

20 infants, with a mean gestational age of 31 weeks, being weaned from mechanical ventilation were studied.

INTERVENTIONS

1 h periods of SIMV and SIMV with pressure support at 50% of the difference between the peak inflating pressure and positive end expiratory pressures.

MAIN OUTCOME MEASURES

The work of breathing was assessed by measurement of the transdiaphragmatic pressure time product (PTPdi).

RESULTS

The mean PTPdi on SIMV plus pressure support was 112 cm H(2)Oxs/min, approximately 20% lower than that on SIMV alone (141 cm H(2)Oxs/min) (p<0.001).

CONCLUSION

The addition of pressure support to SIMV reduces the work of breathing in infants being weaned from the ventilator.

Relation of exhaled nitric oxide levels to development of bronchopulmonary dysplasia

OBJECTIVE

To test the hypothesis that exhaled nitric oxide levels on day 28 and changes in exhaled nitric oxide levels in the neonatal period would differ according to whether infants developed bronchopulmonary dysplasia (BPD) and its severity.

DESIGN

Prospective observational study.

SETTING

Tertiary neonatal intensive care unit.

PATIENTS

80 infants (median gestational age 28, range 24-32 weeks), 46 of whom developed BPD.

INTERVENTIONS

Exhaled nitric oxide measurements were attempted on days 3, 5, 7, 14, 21 and 28.

MAIN OUTCOME MEASURES

BPD (oxygen dependency at 28 days), mild BPD (oxygen dependent at 28 days, but not 36 weeks postmenstrual age (PMA)); moderate BPD (oxygen dependent at 36 weeks PMA) and severe BPD (respiratory support dependent at 36 weeks PMA).

RESULTS

On day 28, exhaled nitric oxide levels were higher in infants with BPD compared to those without BPD (p<0.001) and there was a linear trend in exhaled nitric oxide results as BPD severity increased (p = 0.006). No significances in the change in exhaled nitric oxide levels over the neonatal period were found between the four groups.

CONCLUSION

Exhaled nitric oxide levels are raised in infants with established BPD, particularly in those developing moderate or severe BPD, and may reflect ongoing inflammation.

Work of breathing and different levels of volume-targeted ventilation

OBJECTIVES

The objectives of this study were to determine the impact of different volume-targeted levels on the work of breathing and to investigate whether a level that reduced the work of breathing below that experienced during ventilatory support without volume targeting could be determined.

METHODS

The transdiaphragmatic pressure-time product, as an estimate of the work of breathing, was measured for 20 infants (median gestational age: 28 weeks) who were being weaned from respiratory support by using patient-triggered ventilation (either assist-control ventilation or synchronous intermittent mandatory ventilation). The transdiaphragmatic pressure-time product was measured first without volume targeting (baseline) and then at volume-targeted levels of 4, 5, and 6 mL/kg, delivered in random order. After each volume-targeted level, the infants were returned to baseline. Each step was maintained for 20 minutes.

RESULTS

The mean transdiaphragmatic pressure-time product was higher with volume targeting at 4 mL/kg in comparison with baseline, regardless of the patient-triggered mode. The transdiaphragmatic pressure-time product was higher at a volume-targeted level of 4 mL/kg in comparison with 5 mL/kg and at 5 mL/kg in comparison with 6 mL/kg. The mean work of breathing was below that at baseline only at a volume-targeted level of 6 mL/kg.

CONCLUSIONS

Low volume-targeted levels increase the work of breathing during volume-targeted ventilation. Our results suggest that, during weaning, a volume-targeted level of 6 mL/kg, rather than a lower level, could be used to avoid an increase in the work of breathing.

Position and ventilatory response to added dead space in prematurely born infants

OBJECTIVES

Prematurely born infants are at increased risk of sudden infant death syndrome (SIDS) if slept prone.

WORKING HYPOTHESIS

Prematurely born infants would have an impaired response to an added dead space and lower respiratory muscle strength in the prone compared to the supine position.

STUDY DESIGN

Prospective study. PATIENT-SUBJECT SELECTION: Twenty-five infants, median gestational age of 30 (range 26-32) weeks.

METHODOLOGY

The infants were studied supine and prone at a median of 36 weeks postmenstrual age. Breath by breath minute volume was measured at baseline and after a dead space was incorporated into the breathing circuit; the time constant of the response was calculated. The maximum inspiratory occlusion pressure generated (MIOP) and the pressure generated over the first 100 msec (P(0.1)) during airway occlusion were assessed.

RESULTS

The median time constant was longer (26 (range 8-106) sec vs. 22 (range 6-92) sec (P = 0.045)) and the median MIOP (P = 0.001) and P(0.1) (P = 0.003) were lower in the prone compared to the supine position.

CONCLUSION

Prematurely born infants have a dampened response to tube breathing and reduced respiratory muscle strength in the prone compared to the supine position, which may contribute to their increased vulnerability to SIDS in the prone position.

Sleeping position, oxygenation and lung function in prematurely born infants studied post term

OBJECTIVE

To determine the effect of sleeping position on the lung function of prematurely born infants when post term, whether any effect was similar to that before discharge from the neonatal unit, and if it differed according to bronchopulmonary (BPD) status.

DESIGN

Prospective study.

SETTING

Tertiary neonatal unit.

PATIENTS

Twenty infants, median gestational age 30 weeks (range 25-32); 10 had BPD.

INTERVENTIONS

Before neonatal unit discharge (median age 36 weeks postmenstrual age (PMA)) and when post term, infants were studied prone and supine, each position maintained for 3 h.

MAIN OUTCOME MEASURES

Oxygen saturation was monitored continuously and, at the end of each 3 h period, functional residual capacity (FRC) and compliance (CRS) and resistance (RRS) of the respiratory system were measured.

RESULTS

At a median of 36 weeks PMA and 6 weeks later (post term), respectively, oxygen saturation (98% vs 96%, p = 0.001; 98% vs 97%, p = 0.011), FRC (26 vs 24 ml/kg, p<0.0001; 35 vs 31 ml/kg, p = 0.001) and CRS (3.0 vs 2.4 ml/cm H(2)O, p = 0.034; 3.7 vs 2.5 ml/cm H(2)O, p = 0.015) were higher in the prone than the supine position. In the prone position, both BPD and non-BPD infants had significantly greater FRCs on both occasions and oxygen saturation at 36 weeks PMA, but oxygen saturation was significantly better post term only in non-BPD infants. Twelve infants had superior oxygen saturation and 17 superior FRCs in the prone compared with the supine position at both 36 weeks PMA and post term.

CONCLUSIONS

These results suggest that lung function impairment does not explain why prematurely born infants are at increased risk of sudden infant death syndrome in the prone compared with the supine position.

Chest radiograph thoracic areas and lung volumes in infants developing bronchopulmonary dysplasia

OBJECTIVES

To determine whether chest radiograph (CXR) thoracic areas and lung volumes differed between infants who did and did not develop BPD and according to the severity of BPD developed.

WORKING HYPOTHESIS

Infants developing BPD, particularly if moderate or severe, would have low CXR thoracic areas and lung volumes in the perinatal period.

STUDY DESIGN

Prospective study. PATIENT-SUBJECT SELECTION: 53 infants with a median gestational age of 28 (range 24-32) weeks.

METHODOLOGY

CXR thoracic areas were calculated using a Picture Archiving and Communicating System (PACS) and lung volume assessed by measurement of functional residual capacity (FRC) in the first 72 hr after birth. BPD was diagnosed if the infants were oxygen dependent beyond 28 days, mild BPD in infants no longer oxygen dependent at 36 weeks post-menstrual age (PMA) and moderate/severe BPD in infants who required supplementary oxygen with or without respiratory support at 36 weeks PMA.

RESULTS

Thirty two infants developed BPD, 21 had moderate/severe BPD. The median CXR thoracic areas were higher (P < 0.0001) and FRCs were lower (P < 0.0001) in the BPD compared to no BPD infants. The median CXR thoracic areas of the moderate/severe group (P < 0.001) and the mild group (P < 0.05) were greater than that of the no BPD group and the median FRC of the moderate/severe BPD group was lower than the no BPD group (<0.001) and the mild BPD group (P < 0.05).

CONCLUSION

These results highlight that in the perinatal period infants developing BPD, particularly if moderate/severe, have low functional lung volumes and may have gas trapping, which likely reflects ventilation inhomogeneity.

Measurement of maximal inspiratory pressure in ventilated children

Maximal inspiratory pressure (PIMAX), the maximum negative pressure generated during temporary occlusion of the airway, is commonly used to measure inspiratory muscle strength in mechanically ventilated infants and children. There are, however, no guidelines as to how the PIMAX measurement should be made. We compared the maximum inspiratory pressure generated during airway occlusion (PIMAX(OCC)) to that when a unidirectional valve (PIMAX(UNI)), which allowed expiration, but not inspiration was used. Twenty-two mechanically ventilated children (mean (SD) age 4.8 (4.5) years) were studied. Three sets of end expiratory occlusions were performed for each method in random order. The expired volume during PIMAX(UNI) was assessed and related to the functional residual capacity (FRC) measured using a helium dilution technique.The mean (SD) PIMAX(UNI) (45.5 (15.2) cmH(2)O) was significantly greater than mean (SD) PIMAX(OCC) (30.9 (9.0) cmH(2)O) (P < 0.0001). The mean (SD) expired volume during PIMAX(UNI), was 98 ml (62.3), a mean reduction in FRC of 33.1% (SD 13.9). There were no significant differences between techniques in the baseline respiratory drive, the number of efforts required and the time to reach PIMAX. Regardless of technique, PIMAX was reached in 10 inspiratory efforts or 15 sec of airway occlusion.A unidirectional valve allowing expiration, but not inspiration yields greater PIMAX values in children. Occlusions should be maintained for 12 sec or eight breaths (99% CI of mean).

Neural respiratory drive in healthy subjects and in COPD

The aim of the present study was to use the diaphragm electromyogram (EMG(di)) to compare levels of neural respiratory drive (NRD) in a cohort of healthy subjects and chronic obstructive pulmonary disease (COPD) patients, and to investigate the relationship between NRD and pulmonary function in COPD. EMG(di) was recorded at rest and normalised to peak EMG(di) recorded during maximum inspiratory manoeuvres (EMG(di) % max) in 100 healthy subjects and 30 patients with COPD, using a multipair oesophageal electrode. EMG(di) was normalised to the amplitude of the diaphragm compound muscle action potential (CMAP(di,MS)) in 64 healthy subjects. The mean+/-sd EMG(di) % max was 9.0+/-3.4% in healthy subjects and 27.9+/-9.9% in COPD patients, and correlated with percentage predicted forced expiratory volume in one second, vital capacity and inspiratory capacity in patients. EMG(di) % max was higher in healthy subjects aged 51-80 yrs than in those aged 18-50 yrs (11.4+/-3.4 versus 8.2+/-2.9%, respectively). Observations in the healthy group were similar when peak EMG(di) or CMAP(di,MS) were used to normalise EMG(di). Levels of neural respiratory drive were higher in chronic obstructive pulmonary disease patients than healthy subjects, and related to disease severity. Diaphragm compound muscle action potential could be used to normalise diaphragm electromyogram if volitional inspiratory manoeuvres could not be performed, allowing translation of the technique to critically ill and ventilated patients.

Hering-Breuer reflex, lung volume and position in prematurely born infants

OBJECTIVES

To investigate the effect of position on the strength of the Hering-Breuer reflex in prematurely born infants and determine whether any differences seen were related to differences in lung or tidal volume between positions.

WORKING HYPOTHESIS

Position related differences in the strength of the Hering-Breuer reflex relate to differences in lung or tidal volume.

STUDY DESIGN

Prospective observational study. PATIENT/SUBJECT SELECTION: Eighteen infants, median gestational age 30 (range 25-32) weeks were studied.

METHODOLOGY

Infants were examined in the supine and prone position, each position was maintained for 2 hr. At the end of each 2-hr period, the strength of the Hering-Breuer reflex was assessed by determining the prolongation of expiration following an end inspiratory occlusion. In addition, tidal volume and functional residual capacity (FRC) were assessed in each position.

RESULTS

The strength of the Hering-Breuer reflex was greater (P = 0.01) and the mean FRC was higher (P < 0.0001) in the prone compared to the supine position. The position related differences in the strength of the reflex correlated significantly with position related differences in FRC (P = 0.05).

CONCLUSIONS

The Hering-Breuer reflex is stronger in the prone compared to the supine position. Our results suggest this is explained by position related differences in lung volume.

Ventilator assessment of respiratory mechanics in paediatric intensive care

Many modern "paediatric" mechanical ventilators have in-built features for estimation of respiratory mechanics which could be useful in the management of ventilated infants and children. The aim of this study was to determine if such measurements were reproducible and accurate. Ventilator (Draeger Evita 4) displayed compliance (Cvent) and resistance (Rvent) values were assessed and compared to the results of respiratory system mechanics (respiratory system compliance (Crs) and resistance (Rrs)) measurements obtained using a single breath occlusion technique. Seventeen children (median age 5.1; range 0.3 to 16 yrs) were studied on 24 occasions. The mean coefficients of variations for the techniques were similar (Cvent 13%; Crs 11%; Rvent 16%; Rrs 14%). The mean (SD) Crs (22.8 (12.3) ml/cmH2O) did not differ significantly from Cvent (22.1 (12.7) ml/cm H2O) but the mean Rrs 21.0 (12.7) cmH2O/l/s was significantly higher than the mean Rvent 32.0 (32.0) cmH2O/l/s (p = 0.03). Bland and Altman analysis demonstrated a mean difference of -10.94 cmH2O/l/s (SD 24.1) between Rrs and Rvent; the agreement between Rrs and Rvent decreased as Rrs increased (p = 0.008).

CONCLUSIONS

Ventilator assessment of compliance, but not resistance, using the Evita 4 is reproducible and reliable.

Acid gastroesophageal reflux in convalescent preterm infants: effect of posture and relationship to apnea

Concerns regarding gastroesophageal reflux (GER) and associated apnea episodes result in some practitioners having convalescent, prematurely born infants sleep in the prone position. We have tested the hypothesis that such infants would not suffer from clinically important acid GER or associated apnea episodes more in the supine compared with the prone position. Lower esophageal pH was measured and videopolysomnographic recordings of nasal airflow, chest and abdominal wall movements, electrocardiographic activity, and oxygen saturation were made on two successive days of 21 premature infants (median gestational age 28 wk) at a median postmenstrual age (PMA) of 36 wk. On each day, the infants were studied prone and supine. The acid reflux index was higher in the supine compared with the prone position (median 3% versus 0%, p = 0.002), but was low in both positions. The number of obstructive apnea episodes per hour was higher in the supine position (p = 0.008). There were, however, no statistically significant correlations between the amount of acid GER and the number of either obstructive or total apnea episodes in either the supine or prone position. Supine compared with prone sleeping neither increases clinically important acid GER nor obstructive apnea episodes associated with acid GER in asymptomatic, convalescent, prematurely born infants.

Sleeping position, oxygen saturation and lung volume in convalescent, prematurely born infants

OBJECTIVE

To determine whether the effects of sleeping position on lung volume and oxygenation are influenced by postmenstrual age (PMA) and oxygen dependency in convalescent prematurely born infants.

DESIGN

Prospective study.

SETTING

Tertiary neonatal unit.

PATIENTS

41 infants (21 oxygen dependent), median gestational age 28 weeks (range 24-31 weeks) and birth weight 1120 g (range 556-1780 g).

INTERVENTION

Infants were studied both supine and prone at two-weekly intervals from 32 weeks' PMA until discharge. Each posture was maintained for 1 h.

MAIN OUTCOME MEASURES

Pulse oximeter oxygen saturation (Spo(2)) was monitored continuously, and at the end of each hourly period functional residual capacity (FRC) was measured.

RESULTS

Overall, lung volumes were higher in the prone position throughout the study period; there was no significant effect of PMA on lung volumes. Overall, Spo(2) was higher in the prone position (p = 0.02), and the effect was significant in the oxygen-dependent infants (p = 0.03) (mean difference in Spo(2) between prone and supine was 1.02%, 95% CI 0.11% to 1.92%), but not in the non-oxygen-dependent infants. There was no significant influence of PMA on Spo(2).

CONCLUSION

In the present study, prone sleeping did not improve oxygenation in prematurely born infants, 32 weeks' PMA or older and with no ongoing respiratory problems. However, the infants were monitored in each position for an hour, thus it is recommended that oxygen saturation should continue to be monitored after 32 weeks' PMA to be certain that longer periods of supine sleeping are not associated with loss of lung volume and hypoxaemia.

Peak expiratory flow in Afro-Caribbean children with and without sickle cell anaemia

AIMS

To create a reference range of peak expiratory flow (PEF) results of Afro-Caribbean children and determine whether interpretation of PEF results in children with sickle cell anaemia (SCA) differed according to whether comparison was made of results obtained from children of similar age or height.

METHODS

A prospective observational study was carried out in two specialist sickle cell disease clinics. Seventy-eight nonasthmatic African and Caribbean (AC) controls (age range 2.6-17.8 years), and 99 nonasthmatic SCA children (age range 3.4-17.3 years) were recruited. PEF was measured using a dry rolling sealed spirometer before and after bronchodilator therapy.

RESULTS

PEF results in the AC controls correlated with height (r = 0.88, p< 0.0001). Comparison of similarly aged children demonstrated that pre- (p = 0.02) and post- (p = 0.04) bronchodilator PEF results were lower in the SCA children, but comparison of children of similar height revealed no statistically significant differences in PEF results between children with SCA and controls. The SCA children tended to be shorter than the controls.

CONCLUSION

The results suggest PEF measurements are not a useful method of monitoring the respiratory status of children with sickle cell disease.

Very prematurely born infants wheezing at follow-up: lung function and risk factors

OBJECTIVES

To determine whether abnormalities of lung volume and/or airway function were associated with wheeze at follow-up in infants born very prematurely and to identify risk factors for wheeze.

DESIGN

Lung function data obtained at 1 year of age were collated from two cohorts of infants recruited into the UKOS and an RSV study, respectively.

SETTING

Infant pulmonary function laboratory.

PATIENTS

111 infants (mean gestational age 26.3 (SD 1.6) weeks).

INTERVENTIONS

Lung function measurements at 1 year of age corrected for gestational age at birth. Diary cards and respiratory questionnaires were completed to document wheeze.

MAIN OUTCOME MEASURES

Functional residual capacity (FRC(pleth) and FRC(He)), airways resistance (R(aw)), FRC(He):FRC(pleth) and tidal breathing parameters (T(PTEF):T(E)).

RESULTS

The 60 infants who wheezed at follow-up had significantly lower mean FRC(He), FRC(He):FRC(pleth) and T(PTEF):T(E), but higher mean R(aw) than the 51 without wheeze. Regression analysis demonstrated that gestational age, length at assessment, family history of atopy and a low FRC(He):FRC(pleth) were significantly associated with wheeze.

CONCLUSIONS

Wheeze at follow-up in very prematurely born infants is associated with gas trapping, suggesting abnormalities of the small airways.

Effect of electronic compensation on plethysmographic airway resistance measurements

OBJECTIVES

To compare the performance of a plethysmograph which incorporated electronic compensation (Jaeger) to one which incorporated a heated humidified breathing system (Hammersmith plethysmograph).

WORKING HYPOTHESIS

The performance of a plethysmograph which incorporated electronic compensation would be impaired compared to that which incorporated a heated humidified system.

STUDY DESIGN

In vitro and in vivo comparison.

PATIENT SELECTION

Eleven children, median postnatal age 13 (range 5-15) months.

METHODS

In vitro, the plethysmographs were assessed using known resistances (1.94, 4.85, and 6.80 kPa, equivalent to 20, 50, and 70 cm H(2)O/L/sec, respectively). In vivo, comparison was made of the results of children studied in both plethysmographs.

RESULTS

In vitro, the resistance results of the two plethysmographs were similar to each other and to the known resistances. In vivo, the median "effective" airways resistance result of the Jaeger (4.15 kPa/L/sec) was significantly higher than the inspiratory resistance of the Hammersmith plethysmograph (3.0 kPa/L/sec), but the median inspiratory resistances of the Jaeger were significantly lower than those of the Hammersmith plethysmograph (2.8 kPa/L/sec vs. 3.0 kPa/L/sec). The mean within patient coefficient of variability for inspiratory resistance of the Jaeger plethysmograph (16.7%) was significantly higher than that of the Hammersmith plethysmograph (11.6%) (P = 0.014).

CONCLUSION

These results suggest plethysmographs which incorporate electronic compensation may be inappropriate for use in infants and very young children.

Survey of sleeping position recommendations for prematurely born infants on neonatal intensive care unit discharge

INTRODUCTION

Prematurely born infants are at an increased risk of sudden infant death syndrome (SIDS), particularly when sleeping prone. Parents are strongly influenced in their choice of sleeping position for their infant by practitioners. The aim of this study was to determine the neonatal units' recommendations regarding the sleeping position for premature infants prior to and after discharge and ascertain whether there had been changes from those recorded in a survey performed in 2001-2002.

MATERIALS AND METHODS

A questionnaire survey was sent to all 229 neonatal units in the United Kingdom; 80% responded.

RESULTS AND DISCUSSION

The majority (83%) of units utilized the supine sleep position for infants at least 1-2 weeks prior to discharge, but after discharge, only 38% of the units actively discouraged prone sleeping and 17% additionally recommended side sleeping. Compared to the previous survey, significantly more units started infants with supine sleeping 1-2 weeks prior to discharge (p < 0.0001) and fewer recommended side sleeping after discharge (p = 0.0015). However, disappointingly, less actively discouraged prone sleeping after discharge (p = 0.0001).

CONCLUSION

Recommendations regarding sleeping position for prematurely born infants after neonatal discharge by some practitioners remain inappropriate. Evidence-based guidelines are required as these would hopefully inform all neonatal units' recommendations.