Comparison of airway pressure and airflow triggering systems using a single type of neonatal ventilator

The performances of two triggering systems using a single neonatal ventilator type (SLE) were compared. Eight infants, gestational age 27-30 wk, were each recorded during two 1-h periods of patient-triggered ventilation (PTVs), one with airway pressure and one with airflow triggering. The airflow trigger had a shorter trigger delay (p < 0.02), higher sensitivity (p < 0.02) and lower asynchrony rate (p < 0.02). Conclusion: In immature infants with mild respiratory distress syndrome using the SLE ventilator with inflation times of 0.3 to 0.36 sec, airflow triggering is more appropriate than airway pressure triggering.     

Comparison of body surface and airway triggered ventilation in extremely premature infants

Failure of patient triggered ventilation in very premature infants may reflect the use of inappropriate triggering systems. We have therefore compared the performance of an airway and a body surface trigger in 12 infants of median gestational age 26 weeks (range 24–27). Airway flow and oesophageal and ventilator pressure changes were recorded during two periods of patient triggered ventilation. From the traces, the degree of asynchrony (inflation extending beyond inspiration), triggering rate, sensitivity (proportion of the infant's breaths detected) and trigger delay (response time) were calculated. Although with both triggering systems there was a high rate of asynchrony, the triggering rate ( p < 0.05), sensitivity ( p < 0.05) and trigger delay ( p < 0.01) were all better with the body surface trigger. These results suggest that the body surface trigger is the more appropriate system for very immature infants.     

Causes of failure of neonatal patient triggered ventilation

Causes of failure of patient triggered ventilation (PTV) in neonates have been determined. In particular we have investigated the importance of the timing of ventilator inflation in the spontaneous respiratory cycle and hence the respiratory interaction provoked during PTV. Fifty-six infants (median gestational age 29 weeks) were studied on 63 occasions using two different trigger systems, changes in airway pressure and airflow. After one hour of PTV, only 26 infants were synchronous (inflation coinciding with and occurring only in inspiration), 8 were apnoeic. In the remaining 29 infants, inflation extended into expiration, five of whom were actively expiring. The timing of inflation in the spontaneous respiratory cycle and the interaction provoked was significantly related to the trigger delay, but not the inflation time or type of trigger used. Oxygenation after one hour of PTV improved in infants in whom inflation occurred in inspiration only and in some when it extended beyond. Failure of long term PTV was more common, however, in infants in whom inflation extended beyond inspiration (i.e. asynchronous), but this did not relate to the type of trigger used. Failure was also associated with a long trigger delay (P less than 0.01), a very short inflation time (P less than 0.01) and commencement of PTV early in the infant's illness (P less than 0.05). We conclude that synchrony is the most beneficial respiratory interaction during PTV. Our data suggest that this interaction would be more consistently provoked by the use of a sensitive triggering system which ensured a short trigger delay.     

Evaluation of triggering systems for patient triggered ventilation for neonates ventilator-dependent beyond 10 days of age

The performance of two triggering systems was compared during patient triggered ventilation (PTV) of infants ventilator-dependent beyond 10 days of age. Ten infants were studied who had a median gestational age of 26.5 weeks and a postnatal age of 15.5 days. PTV was administered via the SLE ventilator and the two triggering systems, an airway pressure monitor and the MR10 respiration monitor, were used in random order each for 30 min. The airway pressure trigger had a superior performance in that, although it did not differ significantly in delivered inflation volume or sensitivity to the MR10 respiration monitor, it had a shorter trigger delay (P<0.01). Oxygenation improved in eight of the ten infants on the airway pressure trigger, but only in three on the MR10 respiration monitor. The reduction in PaCO₂ was greater during PTV with the airway pressure trigger compared with the MR10 respiration monitor (P<0.01). We conclude that the airway pressure trigger has a superior performance compared to the MR10 respiration monitor trigger in infants who are ventilator-dependent beyond 10 days of age.     

Airway and body surface sensors for triggering in neonatal ventilation

Failure of neonatal patient triggered ventilation may reflect a delay in delivery of flow relative to the inspiratory effort of the infant. Transmission of diaphragmatic contraction to the sensor site (patient delay) and further transmission to and within the sensing device (device delay) both contribute to the delay in triggering. Patient and device delays were studied for different sensing systems in 36 infants, 24 of whom were intubated. Device delay was long (<40 ms) with a conventional apnoea monitor compared with sensors placed at the airway opening (2 ms), the inspiratory (12 ms) and expiratory (3 ms) pressure transducers of the ventilator, the Graseby capsule (8 ms), strain gauges (3 ms) and oesophageal pressure (6 ms). In near normal infants, the sum of patient and device delays for the latter sensors was less than 20 ms and a minor component of the total delay. However, in severe lung disease the total delay may be more than 100ms even for airway sensors.     

Nasal and lower airway levels of nitric oxide in prematurely born infants

BACKGROUND: Nitric oxide (NO) is produced by various cells in the respiratory tract, but the majority is released from the paranasal sinuses in adults. The paranasal sinuses in infants are only partially pneumatised. Thus, nasal NO would be predicted to be low in infants measured soon after birth and/or born very prematurely; this has implications for the measurement of exhaled NO and interpretation of the results obtained. OBJECTIVES: To determine whether nasal NO could be detected in very immature infants, particularly soon after birth, and whether nasal or lower airway NO levels were influenced by gestational age or postnatal age. PATIENTS: Fifteen infants, with median gestational age of 27 weeks (range 25-32 weeks). METHODS: Nasal and lower airway NO measurements were attempted on days 1, 3, 5, 7, 14, 21, and 28 after birth. Measurements were only made while the infants remained ventilated. Nasal NO was sampled directly from the nasal space and lower airway. NO was sampled from a catheter positioned so that its tip lay at the lower end of the endotracheal tube. RESULTS: Nasal NO was detected in all infants on all study occasions and the levels were greater than those from the lower airway. Nasal and lower airway NO levels did not correlate significantly with gestational age, but lower airway NO levels correlated with postnatal age (r=0.86, p=0.014). CONCLUSION: Even in very immature infants examined in the first day after birth, care must be taken to avoid contamination with nasal NO, if lower airway levels are to be accurately assessed.     

Patient triggered ventilation in chronically ventilator-dependent infants

Patient triggered ventilation (PTV) has been assessed as a method of respiratory support in infants remaining ventilator-dependent beyond the 1st week of life. Sixteen preterm infants were studied who had a median gestational age of 26 weeks and postnatal age of 22 days. PTV was delivered using a ventilator incorporating an airway pressure trigger. PTV was only successfully maintained until extubation in 3 infants, failing to provide a satisfactory method of respiratory support in the remaining 13 infants after a median of 1 h (range 1–10). One of the 13 infants was persistently asynchronous at 1 h despite manipulation of inflation time. The other 12 infants, at failure of PTV, were making respiratory efforts which were inadequate to consistently trigger the ventilator. Infants in whom PTV was successful were older, more mature and of greater birth weight; the trigger delay at 1 h was significantly shorter in this group (P<0.05). A predictor of failure of PTV was asynchrony in the 1st h after commencing PTV (P<0.02). We conclude PTV incorporating an airway pressure trigger infrequently provides a useful method of respiratory support in infants who are chronically ventilator-dependent.     

Inflation times during resuscitation of preterm infants

Data on the effects of a prolonged inflation time during the resuscitation of very prematurely born infants are limited; one study showed no effect, and in another, although lower bronchopulmonary dysplasia (BPD) rates were seen, that effect could have been due to the prolonged inflation time, the positive end expiratory pressure applied or the combination of the two. The aims of our study were to assess the length of inflation times used during face mask and t-piece resuscitation of prematurely born infants in the labour suite and determine whether prolonged inflations led to longer inflation flow times. A respiration monitor (NM3 respiratory profile monitor) was used to record flow, airway pressure and tidal volume changes. The first five inflations for each baby were analysed. Forty prematurely born infants (median gestational age 30, range 26–32 weeks) were examined. Their median inflation pressure was 17.6 (range 12.2–27.4) cm H₂O, inflation time 0.89 (range 0.33–2.92) s, expiratory tidal volume 1.01 (range 0.02–11.41) ml/kg and inflation flow time 0.11 (range 0.04–0.54) s. There was no significant relationship between the inflation time and the inflation flow time, but there was a significant relationship between the inflation pressure and the inflation flow time (p = 0.024). Conclusion: These results suggest that prolonging inflation times during face mask resuscitation of prematurely born infants would not improve ventilation as prolonged inflation did not lead to longer inflation flow times.     

Neonatal patient triggered ventilation.

Patient triggered ventilation was assessed in 14 neonates (gestational age 24-40 weeks). Inspiratory changes in airflow, monitored by a pneumotachograph, were used to trigger the ventilator and this was not associated with complications. Patient triggered ventilation was maintained for up to eight hours (mean duration five hours). In 13 of 14 infants oxygenation improved and this was associated in most with an increase in rate of delivered positive pressure inflations and inflating volumes. A greater improvement in oxygenation was shown when trigger mode was used during the recovery phase of respiratory distress syndrome. Only one infant, who made very little respiratory effort, failed to improve. We conclude that patient triggered ventilation may be used as an effective form of neonatal ventilation.     

In vivo mechanical properties of the developing airway

The inherent mechanical characteristics of the airways are determined in part by their elastic and viscoelastic properties. As compliant structures during early development, the airways are susceptible to significant distention and collapse, depending on the proportionality between airway volume and transmural pressure. To characterize the age-related changes in airway mechanical properties, the elastic and viscoelastic behavior of in vivo tracheal segments were evaluated in preterm and newborn lambs over a wide range of developmental age (108 to 154 days postconceptional age). Tracheal pressure-vol relationships and concomitant airway compliance measurements were used to determine elastic behavior. Calculations of the tracheal relaxation time constant on the same tracheal segments were used to evaluate airway viscoelastic behavior. Data demonstrated a significant (p less than 0.01) correlation with developmental age. With increasing age, the airways were found to be less compliant, and the tracheal relaxation time constant was observed to decrease. The difference in elastic properties of the trachea, in vivo compared to in vitro, suggest that neural-humoral and surrounding connective tissue factors may affect the elasticity of the developing airway. Although the modulating effects of smooth muscle tone and supporting connective tissue assist in the control of airway dimension and resistance to airflow in the intact airway, the age-related differences in the elastic properties may be a factor that predisposes the more immature airway to positive pressure-induced damage.     

Airflow limitation during respiratory syncytial virus lower respiratory tract infection predicts recurrent wheezing

BACKGROUND: Respiratory syncytial virus (RSV) lower respiratory tract infection (LRTI) is frequently followed by recurrent wheezing. Thus far no clinical risk factors have been identified to predict which infants will have wheezing episodes subsequent to RSV LRTI. OBJECTIVE: To determine clinical predictors for airway morbidity after RSV LRTI. METHODS: In a 1-year follow-up study we investigated the predictive value of auscultatory findings characteristic of airflow limitation (wheezing) during RSV LRTI for subsequent airway morbidity. Clinical characteristics, including the presence or absence of signs of airflow limitation, of hospitalized infants with RSV LRTI were prospectively recorded during 2 winter epidemics. During a 1-year follow-up period parents of 130 infants recorded daily airway symptoms. OUTCOME MEASURE: Recurrent wheezing defined as > or = 2 episodes of wheezing. RESULTS: Signs of airflow limitation during RSV LRTI were absent in 47 (36%) infants and present in 83 (64%) infants. Recurrent wheezing was recorded in 10 (21%) infants without signs of airflow limitation and in 51 (61%) with signs of airflow limitation during initial RSV LRTI (relative risk, 0.29, P < 0.001). In a multiple logistic regression model, airflow limitation during initial RSV LRTI proved independent from other clinical parameters, including age, parental history of asthma and smoke exposure. CONCLUSIONS: A sign of airflow limitation during RSV LRTI is the first useful clinical predictor for subsequent recurrent wheezing.     

Upper airway measurements during inspiration and expiration in infants

Accurate measurements of the upper airway of the infant are important but are difficult to obtain reliably because of the normal variation that occurs during respiration. X-ray films of the lateral upper airway were obtained during inspiration and expiration in healthy infants, by using as a timing device a respiration monitor which was wired to the x-ray machine and was attached to the abdominal wall of the infant. Cephalometric measurements were made of 44 "normal" full-term neonates and 29 infants at 6 weeks of age. Despite significant differences in head circumference between the sexes, only the nasion to sella length was significantly longer in the boys (P less than .01). The lateral upper airway measurements were independent of weight, head circumference, and sex in the neonates and infants at 6 weeks of age but were significantly smaller during inspiration than expiration (P less than .01). The measurements progressively increased from the middle to the posterior airway space at both ages. The middle airway space behind the caudal end of the hard palate was smaller during inspiration at 6 weeks of age compared to the neonate (P less than .01). During expiration, the posterior airway space was larger at 6 weeks compared to the neonate (P less than .01). The method described in this report enables reliable roentgenographic measurements to be made of the upper airway of the infant; normal values for the changes during inspiration and expiration are provided. This may assist in the evaluation of infants with suspected upper airway obstruction.     

The effect of a low continuous positive airway pressure on the reflex control of respiration in the preterm infant

The airway occlusion technique was used to measure the strength of the Hering-Breuer inflation reflex before and during the administration of low pressure CPAP. In five of 12 preterm infants studied in the first two weeks of life, CPAP did not alter the inflation reflex. In the other seven premature infants, shortened rather than lengthened inspiratory efforts were observed on occlusion 32 times of CPAP but only twice on CPAP. In seven term infants at 1 to 2.5 hours of age this shortening was noted only twice in 58 occlusions. In the preterm infants exhibiting short responses, the peak inspiratory pressure generated in response to occlusion rose on CPAP from 3.4 to 7.1 cm H2O (p less than 0.005), while respiratory rate fell from 61 to 49 breaths/minute (p less than 0.025). This data suggests that CPAP enhances these infants' ability to adjust to increased respiratory loads, possibly by the elimination of a Hering-Breuer deflation reflex.     

Influence of breastfeeding and complementary food on growth between 5 and 10 months

The aim of this study was to examine the nature of the association between breastfeeding, complementary feeding and growth in a random sample of infants from Denmark, where the prevalence of breastfeeding is high. A semiquantitative food frequency questionnaire and a questionnaire on breastfeeding duration and on weight and length measurements taken at the infant welfare visit at 5 and 10 months were sent to 590 families with 10-month-old infants. A total of 339 infants with complete growth data were included in the analyses. When controlling for mid-parental height and birth weight infants breastfed for ≥ 7 months gained 198 g less in weight ( p < 0:01) and 7 mm less in length ( p < 0:01) during the period from 5 to 10 months than infants breastfed for < 7 months. Controlling for these effects, the 10% of the sample with the highest protein intake (i.e. ≥16 energy percentage) gained 262g more than those with a lower protein intake ( p = 0:03). Infants breastfed for ≥ 7 months received significantly less cow's milk ( p < 0:01), and fewer meat-containing dishes ( p < 0:05) and sweets or cakes ( p < 0:01), which may partly explain the effect of breastfeeding. The long-term consequences of this moderate difference in growth velocity are unknown and the findings should not be used to advocate against breastfeeding during late infancy.     

Sustained pressure—controlled inflation or intermittent mandatory ventilation in preterm infants in the delivery room? A randomized,controlled trial on initial respiratory support via nasopharyngeal tube

AIM: To prove the hypothesis that sustained pressure-controlled inflation compared to intermittent mandatory ventilation for lung recruitment via nasopharyngeal tube after delivery is more effective in reducing the rate of endotracheal intubation and mechanical ventilation in very preterm infants. METHODS: The study was designed as a randomized, controlled trial. The setting was the delivery room and neonatal intensive care unit of a university hospital in Germany. Subjects were 61 infants (25.0-28.9 wk of gestation) with signs of respiratory distress immediately after birth. The infants were randomized in the delivery room to two different respiratory interventions: either to sustained pressure-controlled inflation (15 s) or to intermittent mandatory ventilation (rate 60 min(-1)). This respiratory support was given by a nasopharyngeal tube. The inflation pressure or peak inspiratory pressure was increased stepwise (20-25-30 cm H2O) according to the response of heart rate and oxygenation. RESULTS: The main outcome measure was treatment failure, i.e., endotracheal intubation and mechanical ventilation according to given intubation criteria. Treatment failure occurred in 61% (95% CI, sustained pressure-controlled inflation: 42-78) and 70% (95% CI, intermittent mandatory ventilation: 51-85) (p = 0.59). The rates of mortality (3/61), severe intraventricular haemorrhage (5/61) and chronic lung disease (10/58) were not different between groups. CONCLUSION: Sufficient spontaneous breathing within the first 48 h of life without endotracheal intubation and mechanical ventilation was achieved in about 30% with both methods of initial respiratory support.     

The influence of timing of elective cesarean section on neonatal resuscitation risk.

OBJECTIVE: Cesarean section has negative effects on the physiologic responses to birth, including the development of lung volumes, pulmonary vascular resistance, and biochemical responses. The objective of this study was to examine the association between the timing of delivery between 37 and 42 wks gestation and neonatal resuscitation risk in elective cesarean section. DESIGN: Observational, cohort study. SETTING: Maternity Department of Padua University, Italy. SUBJECTS: All pregnant women who delivered by elective cesarean section at term during a 3-yr period were identified from a perinatal database and compared retrospectively with pregnant women who delivered vaginally and matched for week of gestation. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Comparative neonatal resuscitation risk (odds ratio, OR; confidence interval, CI) was analyzed. During this time, 1,284 (13%) elective cesarean section deliveries occurred at or after 37 wks of gestation. Forty-four (3.4%) newborns delivered by elective cesarean section and 18 (1.4%) newborns vaginally delivered needed positive pressure ventilation resuscitation by laryngeal mask airway or tracheal tube. Positive pressure ventilation resuscitation risk was significantly higher in the infant group delivered by elective cesarean section compared with vaginal delivery (OR, 2.05; CI, 1.25-5.67; p < .01) and involved both laryngeal mask airway and tracheal tube resuscitation maneuvers (OR, 2.77 CI, 1.26-5.8; p < .01 and OR, 2.9; CI, 1.02-7.81; p < .01, respectively). In the period of weeks 37(+0) to 38(+6), positive pressure ventilation resuscitation risk and single laryngeal mask airway and tracheal tube resuscitation maneuver risk were significantly greatly increased (OR, 4.25; CI, 1.46-16.12; p < .01; OR, 2.25; CI, 1.46-6.12; p < .01; and OR, 11.3; CI, 2.15-16.0; p < .01, respectively). After 38(+6) weeks, there was no significant difference in positive pressure ventilation resuscitation risk. CONCLUSIONS: Elective cesarean section at term, in an obstetric population without prenatally identified risk factors, remains associated with increased resuscitation risk with related implications for the neonate compared with vaginal delivery. A significant reduction in neonatal resuscitation risk would be obtained by waiting until week 39(+0) before performing elective cesarean section.     

Surfactant substitution in ventilated very low birth weight infants: factors related to response types.

We investigated factors than may influence the response to surfactant substitution. Thirty-five very low birth weight infants with respiratory distress syndrome were treated with Curosurf at 3-12 h of age. From the changes in oxygenation, the therapeutic response was categorized as rapid and sustained, rapid with relapse, or poor. Phospholipids and surfactant protein A were quantified in gastric aspirate samples obtained immediately after birth. They showed that 16 infants had accelerated lung maturity, despite clinical and radiologic signs of respiratory distress syndrome. Ten of them had suffered from birth asphyxia or connatal infection. Nevertheless, 12 of these 16 infants responded rapidly to surfactant substitution. Poor response was seen in four infants with connatal infection. Of 19 infants with immature lung profile, 18 showed a rapid initial response to surfactant substitution. Dynamic compliance of the respiratory system or arterial blood pressure before substitution, the ultrastructure of the surfactant preparation, or persistence of the ductus arteriosus did not influence the response type, but fraction of inspired oxygen was higher before surfactant substitution in infants with poor response. Prognosis was related to short-term response: Of 17 infants who showed a rapid and sustained response, none died, whereas eight of 18 infants with relapse after rapid initial response or poor response died (p less than 0.05). We conclude that surfactant substitution may be beneficial not only in babies with primary surfactant deficiency but also in other pulmonary disorders that are common in very low birth weight infants. The type of response may be of prognostic value.     

Sodium and potassium in red blood cells of premature infants during the first few days: risk of hyperkalaemia.

Erythrocyte sodium and potassium were studied in 64 newborn infants including 21 very low birthweight infants (birthweight less than 1500 g) during the first three days after birth. Erythrocyte sodium showed a positive correlation with gestational age (r = 0.63, p less than 0.01) and birthweight (r = 0.66, p less than 0.01). Erythrocyte potassium was negatively correlated with birthweight (r = -0.33, p less than 0.05). The Na/K ratio in red blood cells showed a positive correlation with gestational age (r = 0.60, p less than 0.01) and birthweight (r = 0.65, p less than 0.01). In VLBW infants plasma potassium rose significantly (p less than 0.01) from 0-6 h to 12-30 h and decreased from 12-30 h to 30-60 h (p less than 0.05). Erythrocyte potassium decreased slightly from 0-6 h to 12-30 h, but not significantly. A new finding that "more immature infants have higher potassium and lower sodium concentration in RBC" may suggest a potential risk of hyperkalaemia in tiny infants.     

Effect of ventilation on mechanical properties and pressure-flow relationships of immature airways

Ventilation of immature airways has been shown to result in pressure-induced deformation and alteration of mechanical properties. These changes in mechanical properties may alter the effect of compressive pressures on pressure-flow relationships. To test this hypothesis, unventilated (Group I, n = 8) and ventilated (group II, n = 8; mean pressures of 8-12 cm H2O for 2 h duration) tracheal segments were excised from preterm lambs approximately 118 days gestation and mounted in a Krebs-filled chamber for determination of compliances and pressure-flow relationships. Compliance data were obtained for both the inflation loop (inflation compliance) and the collapsing loop (collapsing compliance) of the pressure-volume curve for each segment. Flow (V = 2-10 liter/min.) was introduced through the lumen of each segment at different chamber pressures (Pc = 5-30 mm Hg). Driving pressure (Pd) was recorded for each V and Pc. Airway resistance (R) was calculated as Pd/V. Group II had significantly greater (p less than 0.005) radii than Group I, suggesting ventilation-induced deformation. Group II had significantly lower (p less than 0.05) inflation compliance but significantly greater (p less than 0.05) collapsing compliance than group I. Two-factor analysis of variance demonstrated significantly greater (p less than 0.05) R in group II at each value of V and each Pc. These data may help to explain the flow limitation and gas-trapping observed in preterm infants who have been mechanically ventilated.     

Trends in outcomes for very preterm infants in the southern region of Sweden over a 10-year period

Aim: To investigate trends in mortality and morbidity in very preterm infants.
Methods: Population-based perinatal register; liveborn infants 22 + 0 to 31 + 6 gestational weeks were investigated (time period 1995–2004). Time trends for mortality and common morbidities were explored using logistic regression analyses.
Results: Data from 1614 liveborn infants were included. There was an increase in live born infants below 25 gestational weeks, annual odds ratio (OR) 1.15 (95% CI: 1.08–1.23) and a decrease in mortality annual OR 0.82 (95% CI: 0.69–0.98). The rates of bronchopulmonary dysplasia (BPD) and sepsis increased during the study period, annual ORs of 1.10 (95% CI: 1.04–1.17) and 1.09 (95% CI: 1.03–1.16). The duration of mechanical ventilation increased for surviving infants <25 gestational weeks (p = 0.003), while the duration of continuous positive airway pressure (CPAP) increased for infants <28 gestational weeks (p = <0.001). There were no changes in the rates of intraventricular haemorrhages (IVH, 3–4), retinopathy of prematurity (ROP, 3–5), seizures or necrotizing enterocolitis (NEC).
Conclusion: During the 10-year period changes in mortality and morbidity were most pronounced for infants with GA <28 gestational weeks. The increasing rate of sepsis was present in infants <28 gestational weeks, whereas the increase in BPD was demonstrated in the whole study population <32 gestational weeks.