Mechanisms for episodes of hypoxemia in preterm infants undergoing mechanical ventilation

Etiology and Mechanism of Intermittent Hypoxemia Episodes in Spontaneously Breathing Extremely Premature Infants

OBJECTIVE

To evaluate the mechanisms leading to intermittent hypoxemia (IH) episodes in spontaneously breathing extremely premature infants at 32 weeks and 36 weeks postmenstrual age (PMA).

METHODS

We studied spontaneously breathing premature infants born at 23-28 weeks of gestational age who presented with IH episodes while on noninvasive respiratory support at 32 or 36 weeks PMA. Daytime recordings of arterial oxygen saturation (SpO2), esophageal pressure, respiratory inductive plethysmography of the abdomen, chest wall, and their sum were obtained during 4 hours at 32 weeks and 36 weeks PMA. IH episodes (SpO2 <90% for ≥5 seconds) and severe IH episodes (SpO2 < 80% for ≥5 seconds) were classified as resulting from apnea, active exhalation and breath holding, reduced tidal volume (VT), or reduced respiratory rate (RR) during the preceding 60 seconds.

RESULTS

Fifty-one infants with a mean gestational age of 25.9 ± 1.5 weeks and a mean birth weight of 846 ± 185 g were included. Of these, 31 and 41 were included in the analysis at 32 weeks and 36 weeks PMA, respectively. At both 32 weeks and 36 weeks PMA, greater proportions of all IH episodes and severe IH episodes were associated with active exhalation and breath holding than with apnea, reduced RR, or reduced VT. The severity and duration of the IH episodes did not differ between mechanisms.

CONCLUSIONS

In this group of premature infants, the predominant mechanism associated with daytime IH was active exhalation and breath holding. This etiology is more closely associated with behavioral factors than abnormal respiratory control and can have implications for prevention.

Late permissive hypercapnia and respiratory stability among very preterm infants: a pilot randomised trial

OBJECTIVE

Determine if targeting higher transcutaneous carbon dioxide improves respiratory stability among very preterm infants on ventilatory support.

DESIGN

Single-centre pilot randomised clinical trial.

SETTING

The University of Alabama at Birmingham.

PATIENTS

Very preterm infants on ventilatory support after postnatal day 7.

INTERVENTIONS

Infants were randomised to two different transcutaneous carbon dioxide levels targeting 5 mm Hg (0.67 kPa) changes with four sessions each lasting 24 hours for 96 hours: baseline-increase-baseline-increase or baseline-decrease-baseline-decrease.

MAIN OUTCOME MEASURES

We collected cardiorespiratory data evaluating episodes of intermittent hypoxaemia (oxygen saturations (SpO2)<85% for ≥10 s), bradycardia (<100 bpm for ≥10 s), and cerebral and abdominal hypoxaemia on near-infrared spectroscopy.

RESULTS

We enrolled 25 infants with a gestational age of 24 w 6 d±11 d (mean±SD) and birth weight 645±142 g on postnatal day 14±3. Continuous transcutaneous carbon dioxide values (56.8±6.9 in the higher group vs 54.5±7.8 in the lower group; p=0.36) did not differ significantly between groups during the intervention days. There were no differences in intermittent hypoxaemia (126±64 vs 105±61 per 24 hours; p=0.30) or bradycardia (11±16 vs 15±23 per hour; p=0.89) episodes between groups. The proportion of time with SpO2<85%, SpO2<80%, cerebral hypoxaemia or abdominal hypoxaemia did not differ (all p>0.05). There was moderate negative correlation between mean transcutaneous carbon dioxide and bradycardia episodes (r=-0.56; p<0.001).

CONCLUSION

Targeting 5 mm Hg (0.67 kPa) changes in transcutaneous carbon dioxide did not improve respiratory stability among very preterm infants on ventilatory support but the intended carbon dioxide separation was difficult to achieve and maintain.

TRIAL REGISTRATION NUMBER

NCT03333161.

Unstable SpO2 in preterm infants: The key role of reduced ventilation to perfusion ratio

Introduction: Instability of peripheral oxyhemoglobin saturation (SpO₂) in preterm infants is correlated with late disability and is poorly understood. We hypothesised that a reduced ventilation to perfusion ratio (V_A/Q) is the key predisposing factor for SpO₂ instability. Methods: We first used a mathematical model to compare the effects of reduced V_A/Q or shunt on SaO₂ stability (SaO₂ and SpO₂ are used for model and clinical studies respectively). Stability was inferred from the slope of the SaO₂ vs. inspired oxygen pressure (P _IO₂) curve as it intersects the 21 kPa P _IO₂ line (breathing air). Then, in a tertiary neonatal intensive care unit, paired hourly readings of SpO₂ and P _IO₂ were recorded over a 24 h period in week old extremely preterm infants. We noted SpO₂ variability and used an algorithm to derive V_A/Q and shunt from the paired SpO₂ and P _IO₂ measurements. Results: Our model predicted that when V_A/Q < 0.4, a 1% change in P _IO₂ results in >8% fluctuation in SaO₂ at 21 kPa P _IO₂. In contrast, when a 20% intrapulmonary shunt was included in the model, a 1% change in P _IO₂ results in <1% fluctuation in the SaO₂. Moreover, further reducing the V_A/Q from 0.4 to 0.3 at 21 kPa P _IO₂ resulted in a 24% fall in SaO₂. All 31 preterm infants [mean gestation (±standard deviation) 26.2 (±1) week] had V_A/Q < 0.74 (normal >0.85) but only two infants had increased shunt at 1.1 (±0.5) weeks' postnatal age. Median (IQR) SpO₂ fluctuation was 8 (7)%. The greatest SpO₂ fluctuations were seen in infants with V_A/Q < 0.52 (n = 10): SpO₂ fluctuations ranged from 11%-17% at a constant P _IO₂ when V_A/Q < 0.52. Two infants had reduced V_A/Q and increased shunt (21% and 27%) which resolved into low V_A/Q after 3-6 h. Discussion: Routine monitoring of P _IO₂ and SpO₂ can be used to derive a hitherto elusive measure of V_A/Q. Predisposition to SpO₂ instability results from reduced V_A/Q rather than increased intrapulmonary shunt in preterm infants with cardiorespiratory disease. SpO₂ instability can be prevented by a small increase in P _IO₂.

Pulse oximetry reliability for detection of hypoxemia under motion in extremely premature infants

BACKGROUND

Episodes of intermittent hypoxemia (IH) in extremely premature infants are detected by pulse oximetry (SpO₂) but motion artifact can cause falsely low readings.

OBJECTIVES

To evaluate the reliability of SpO₂ during IH episodes associated with motion in premature infants of ≤28 weeks GA monitored with 2 pulse oximeters.

METHODS

IH episodes (defined as SpO₂ < 90%, >10 s and SpO₂ < 80%, >10 s) were classified by an analytic tool based on distortion caused by motion in the pulse plethysmograph (Pleth) as: A (true hypoxemia), both SpO₂ decreased (only one Pleth showed motion); B (false hypoxemia), one SpO₂ decreased (Pleth showed motion) and the other didn't (Pleth didn't show motion); C (suspected hypoxemia), both SpO₂ decreased (both Pleth showed motion); D (true hypoxemia-motion free), both SpO₂ decreased (neither Pleth showed motion).

RESULTS

In 24-72 h data from 20 infants of 25.4 ± 1.5 weeks GA, 14.1 ± 5.7 episodes with SpO₂ < 90% and 7.9 ± 5.5 episodes with SpO₂ < 80% per infant were identified. 29 ± 15% of episodes with SpO₂ < 90% were type A, 1 ± 2% B, 43 ± 21% C and 27 ± 23% D, while 26 ± 22% of episodes with SpO₂ < 80% were type A, 0.3 ± 1.2% B, 45 ± 29% C, and 19 ± 25% D [p < 0.001 type B vs. rest (GLM-repeated measures)].

CONCLUSION

In extremely premature infants SpO₂ with motion artifact is more likely to indicate true- than false hypoxemia.

IMPACT

Uncertainty on the effect of motion on SpO₂ accuracy during hypoxemia episodes in premature infants can influence the caregiver's trust on SpO₂ and influence their response. This study evaluated data from two pulse oximeters used simultaneously in different extremities to determine the reliability of SpO₂ during motion artifact in premature infants. Data from this study showed that in extremely premature infants SpO₂ is more likely to indicate true- than false hypoxemia during episodes of hypoxemia associated with motion artifact.

Automated control of oxygen titration in preterm infants on non-invasive respiratory support

OBJECTIVE

To evaluate the performance of a rapidly responsive adaptive algorithm (VDL1.1) for automated oxygen control in preterm infants with respiratory insufficiency.

DESIGN

Interventional cross-over study of a 24-hour period of automated oxygen control compared with aggregated data from two flanking periods of manual control (12 hours each).

SETTING

Neonatal intensive care unit.

PARTICIPANTS

Preterm infants receiving non-invasive respiratory support and supplemental oxygen; median birth gestation 27 weeks (IQR 26-28) and postnatal age 17 (12-23) days.

INTERVENTION

Automated oxygen titration with the VDL1.1 algorithm, with the incoming SpO₂ signal derived from a standard oximetry probe, and the computed inspired oxygen concentration (FiO₂) adjustments actuated by a motorised blender. The desired SpO₂ range was 90%-94%, with bedside clinicians able to make corrective manual FiO₂ adjustments at all times.

MAIN OUTCOME MEASURES

Target range (TR) time (SpO₂ 90%-94% or 90%-100% if in air), periods of SpO₂ deviation, number of manual FiO₂ adjustments and oxygen requirement were compared between automated and manual control periods.

RESULTS

In 60 cross-over studies in 35 infants, automated oxygen titration resulted in greater TR time (manual 58 (51-64)% vs automated 81 (72-85)%, p<0.001), less time at both extremes of oxygenation and considerably fewer prolonged hypoxaemic and hyperoxaemic episodes. The algorithm functioned effectively in every infant. Manual FiO₂ adjustments were infrequent during automated control (0.11 adjustments/hour), and oxygen requirements were similar (manual 28 (25-32)% and automated 26 (24-32)%, p=0.13).

CONCLUSION

The VDL1.1 algorithm was safe and effective in SpO₂ targeting in preterm infants on non-invasive respiratory support.

TRIAL REGISTRATION NUMBER

ACTRN12616000300471.

Effect of the Target Range on Arterial Oxygen Saturation Stability in Extremely Premature Infants

OBJECTIVE

The aim of this study was to compare the effect of targeting arterial oxygen saturation (SpO2) in the high (93-95%) versus the low portion (90-92%) of the recommended range of 90-95% on oxygenation stability in extremely premature infants.

METHODS

Premature infants of ≤28 weeks of gestational age who received a fraction of inspired oxygen (FiO2) > 0.21 after day 14 were eligible. FiO2 was adjusted by a dedicated investigator to keep SpO2 between 90-92% and 93-95% for 2 h each in random sequence. Episodes of intermittent hypoxemia (IH) were defined as SpO2 <90% for ≥10 s; severe IH episodes were defined as SpO2 <80% for ≥10 s. Hyperoxemia was defined as SpO2 >95% or >98%.

RESULTS

Eighteen premature infants were enrolled. Their (mean ± SD) GA was 26 ± 1.5 w. Seven infants were on mechanical ventilation, 4 infants on nasal ventilation, and 7 infants on nasal cannula. They were on a mean FiO2 0.38 ± 0.12 at study entry. Episodes of IH and severe IH were more frequent during the low compared to the high target (36.6 [27.0-41.3] vs. 16.0 [7.8-19.0], p < 0.001; 8.4 ± 9.3 vs. 3.2 ± 4.3, p = 0.002). The proportions of time with SpO2 >95% and >98% were greater with the high target (13.9 ± 11 vs. 34.1 ± 15.4%, p < 0.001; 0.9 [0-5.7] vs. 3.4 [0.5-16.1]%, p = 0.002).

CONCLUSION

In this group of extremely premature infants, targeting SpO2 at the lower portion of the recommended range resulted in more frequent episodes of IH. However, targeting the higher SpO2 range led to more hyperoxemia. This trade-off warrants further investigation.

New Modes of Respiratory Support for the Premature Infant: Automated Control of Inspired Oxygen Concentration

Most extremely premature infants have respiratory instability that can manifest as frequent episodes of intermittent hypoxemia. Although caregivers target clinically recommended ranges of arterial oxygen saturation (oxygen saturation as measured by pulse oximetry [Spo₂]), consistent maintenance of these ranges is not always achieved. Excessive administration of supplemental oxygen combined with limited staff resources increases exposure to extreme Spo₂ levels. In this population, exposure to hyperoxemia and prolonged episodes of intermittent hypoxemia have been associated with damage to the eye and lung and impaired neurodevelopment. To improve Spo₂ targeting, various systems for automated control of inspired oxygen have been developed recently.

Mechanical Ventilation During Chronic Lung Disease

For infants with the most severe forms of chronic lung disease, regardless of etiology, chronic mechanical ventilation can provide stability, reduce acute respiratory events, and alleviate increased work of breathing. This approach prioritizes the baby's growth and development during early life. Once breathing comfortably, these infants can tolerate developmental therapies with the goal of achieving the best neurocognitive outcomes possible.

Infant inclined sleep product safety: A model for using biomechanics to explore safe infant product design

Over 450 adverse incidents have been reported in infant inclined sleep products over the past 17 years, with many infants found dead in both the supine and prone positions. The unique design of inclined sleep products may present unexplored suffocation risks related to how these products impact an infant's ability to move. The purpose of this study was to assess body movement and muscle activity of healthy infants when they lie supine and prone on different inclined sleep products. Fifteen healthy full-term infants (age: 17.7 ± 4.9 weeks) were recruited for this IRB-approved study. Three inclined sleep products with unique features, representative of different sleeper designs, were included. Surface electromyography (EMG) was recorded from infants' cervical paraspinal, abdominal, and lumbar erector spinae muscles for 60 s during supine and prone positioning. Neck and trunk sagittal plane movements were evaluated for each testing condition. Paired t-tests and Wilcoxon signed-rank tests were performed to compare each inclined sleeper to a flat crib mattress (0° baseline condition). During prone positioning, abdominal muscle activity significantly nearly doubled for all inclined sleep products compared to the flat crib mattress, while erector spinae muscle activity decreased by up to 48%. Trunk movement significantly increased compared to the flat crib mattress during prone lying. During prone lying, inclined sleep products resulted in significantly higher muscle activity of the trunk core muscles (abdominals) and trunk movement, which has the potential to exacerbate fatigue and contribute to suffocation if an infant cannot self-correct to the supine position.

Chronic respiratory failure in bronchopulmonary dysplasia

Although survival has improved dramatically for extremely preterm infants, those with the most severe forms of bronchopulmonary dysplasia (BPD) fail to improve in the neonatal period and go on to develop chronic respiratory failure. When careful weaning of respiratory support is not tolerated, the difficult decision of whether or not to pursue chronic ventilation via tracheostomy must be made. This requires shared decision-making with an interdisciplinary medical team and the child's family. Although they suffer from increased morbidity and mortality, the majority of these children will survive to tolerate ventilator liberation and tracheostomy decannulation. Care coordination for the technology-dependent preterm infant is complex, but there is a growing consensus that chronic ventilation can best support neurodevelopmental progress and improve long-term outcomes.

Automated versus manual oxygen control in preterm infants receiving respiratory support: a systematic review and meta-analysis

BACKGROUND

Ventilated preterm infants are exposed to deviations from the intended arterial oxygen saturation range. Therefore, an automated control system was developed to rapidly modulate the fraction of inspired oxygen. The aim of this review is to compare the efficacy and safety of automated versus manual oxygen delivery control.

METHODS

In December 2020, we systematically searched four electronic databases; PubMed, Cochrane Library, Scopus, and Web of Science for eligible randomized controlled trials. We extracted and pooled data as mean difference and 95% confidence interval in an inverse variance method using RevMan software.

RESULTS

Thirteen trials were included in this systematic review and meta-analysis, enrolling 343 preterm infants on respiratory support. Automated oxygen control increased the time spent within the target arterial oxygen saturation range of 85-96% (MD = 8.96; 95% CI [6.26, 11.67], p<.00001), and 90-95% (MD = 18.25; 95% CI [4.58, 31.65], p = .008). In addition, it reduced the time of hypoxia (<80%); (MD = -1.24; 95% CI [-2.05, -0.43], p = .003), (MD = -0.82; 95% CI [-1.23, -0.41], p<.0001) with predetermined ranges of 85-96% and 90-95%, respectively. Automated control system reduced as well the time of hyperoxia (>98%) (MD = -0.99; 95% CI [-1.74, -0.25], p = .009) at intended range of 90-95%, and number of manual inspired oxygen fraction adjustments (MD = -2.82; 95% CI [-4.56, -1.08], p = .002).

CONCLUSIONS

Automated oxygen delivery is rapid and effective in controlling infants' oxygen saturation. It can be used to reduce the load over the nurses, but not to substitute the clinical supervision. Further long-term trials of large-scale are required to evaluate the prolonged clinical outcomes.

An overview of developmental dysregulation of autonomic control in infants

In this short review, we provide an overview of developmental disorders causing autonomic nervous system dysregulation. We briefly discuss perinatal conditions that adversely impact developmental outcomes including apnea of prematurity, sudden infant death syndrome, and Rett syndrome. We provide a brief clinical description, an overview of known or hypothesized mechanisms for the disorder, and current standard of practice for treatment of each condition. Additionally, we consider preventative measures and complications of these disorders to provide further insight into the pathogenesis of specific autonomic dysregulation in neonates. The goal of this short review is to provide an updated understanding of the impact of autonomic dysregulation on development of brainstem circuits and to briefly highlight promising future treatment options and controversies.

Do inclined sleeping surfaces impact infants' muscle activity and movement? A safe sleep product design perspective

The design of inclined sleep products may be associated with an increased risk of suffocation when an infant finds themselves prone in the product. It is important to understand how different inclined sleep surface angles impact infants' muscle activity when considering a safe sleep environment. The purpose of this study was to assess muscle activity of healthy infants when they lie supine and prone on different inclined crib mattress surfaces (0° vs. 10° vs. 20°). Fifteen healthy infants were recruited for this study. Surface EMG was recorded from cervical paraspinal, abdominal, lumbar erector spinae, and triceps muscles for 60 s during supine and prone positioning. Repeated measures ANOVAs and Bonferroni post-hoc adjustments were performed to test the effect of incline angles. Paired t-tests were performed to test the effect of position (supine vs. prone). During prone lying, abdominal muscle activity increased by 33% and 71% for 10° and 20° compared to 0°, while erector spinae and triceps muscle activity decreased for 20° compared to 0°. Lumbar erector spinae and cervical paraspinal muscle activity increased by 185% and 283% for prone compared to supine lying. During prone positioning, the 20° inclined surface resulted in significantly higher muscle activity of the trunk core muscles (abdominals), which may exacerbate fatigue and contribute to suffocation if an infant cannot self-correct to the supine position. Compared to supine positioning, prone lying requires higher musculoskeletal effort to maintain a safe posture to prevent suffocation, and babies likely fatigue faster when lying prone.

Clinical quantification of SpO2 instability using a new histogram classification system: a clinical study

BACKGROUND

Oxygenation instability is not quantified or documented despite being common and correlated with neonatal morbidities, retinopathy of prematurity, and adverse 18-month outcomes.

METHODS

We developed a five-type SpO₂ histogram classification system based on the SpO₂ difference within the 10-90th cumulative time percentile (A) and the time percentage with SpO₂ ≤80% (B). In type 1, A is <5% and in type 5, A and B are ≥10%. We then studied consecutive 12-h SpO₂ frequency histograms in all infants ≤34 weeks gestation receiving respiratory support on day 1, over 6 months.

RESULTS

Six thousand and sixteen histograms were obtained in 73 infants, 28.9 ± 3.0 weeks gestation, and birth weight (BW) 1318.5 ± 495 g. All types were common and did not overlap. Type 3-5 ("unstable") histograms were more common in oxygen or any intubated support. Time in SpO₂ <85% and <80% progressively increased in types 3-5. Among histograms in oxygen, the mean (±SD) of SpO₂ medians was 92.8 ± 1.9. Infants ≤28 weeks exhibited three phases of SpO₂ instability (stable-unstable-stable). Those developing unstable histograms during the first week received longer ventilatory support (median [IQR], 101 [66] vs. 62 [28] days) and supplemental oxygen (62.5 [72] vs. 40.5 [40] days), and more were on ventilatory support at 40 weeks (7/15 vs. 0/10).

CONCLUSIONS

Classified SpO₂ histograms quantify and document SpO₂ instability and identify early infants at risk of prolonged respiratory support, while median SpO₂ does not.

Effects of closed-loop automatic control of the inspiratory fraction of oxygen (FiO2-C) on outcome of extremely preterm infants - study protocol of a randomized controlled parallel group multicenter trial for safety and efficacy

Background

Most extremely low gestational age neonates (ELGANS, postmenstrual age at birth (PMA) < 28 completed weeks) require supplemental oxygen and experience frequent intermittent hypoxemic and hyperoxemic episodes. Hypoxemic episodes and exposure to inadequately high concentrations of oxygen are associated with an increased risk of retinopathy of prematurity (ROP), chronic lung disease of prematurity (BPD), necrotizing enterocolitis (NEC), neurodevelopmental impairment (NDI), and death beyond 36 weeks PMA.

Closed-loop automated control of the inspiratory fraction of oxygen (FiO₂-C) reduces time outside the hemoglobin oxygen saturation (SpO₂) target range, number and duration of hypo- and hyperoxemic episodes and caregivers’ workload. Effects on clinically important outcomes in ELGANs such as ROP, BPD, NEC, NDI and mortality have not yet been studied.

Methods

An outcome-assessor-blinded, randomized controlled, parallel-group trial was designed and powered to study the effect of FiO₂-C (in addition to routine manual control (RMC) of FiO₂), compared to RMC only, on death and severe complications related to hypoxemia and/or hyperoxemia. 2340 ELGANS with a GA of 23 + 0/7 to 27 + 6/7 weeks will be recruited in approximately 75 European tertiary care neonatal centers. Study participants are randomly assigned to RMC (control-group) or FiO₂-C in addition to RMC (intervention-group). Central randomization is stratified for center, gender and PMA at birth (< 26 weeks and ≥ 26 weeks).

FiO₂-C is provided by commercially available and CE-marked ventilators with an FiO₂-C algorithm intended for use in newborn infants. The primary outcome variable (composite of death, severe ROP, BPD or NEC) is assessed at 36 weeks PMA (or, in case of ROP, until complete vascularization of the retina, respectively). The co-primary outcome variable (composite outcome of death, language/cognitive delay, motor impairment, severe visual impairment or hearing impairment) is assessed at 24 months corrected age.

Discussion

Short-term studies on FiO₂-C showed improved time ELGANs spent within their assigned SpO₂ target range, but effects of FiO₂-C on clinical outcomes are yet unknown and will be addressed in the FiO₂-C trial. This will ensure an appropriate assessment of safety and efficacy before FiO₂-C may be implemented as standard therapy.

Trial registration

The study is registered at www.ClinicalTrials.gov: NCT03168516, May 30, 2017.

Mechanistic actions of oxygen and methylxanthines on respiratory neural control and for the treatment of neonatal apnea

Apnea remains one of the most concerning and prevalent respiratory disorders spanning all ages from infants (particularly those born preterm) to adults. Although the pathophysiological consequences of apnea are fairly well described, the neural mechanisms underlying the etiology of the different types of apnea (central, obstructive, and mixed) still remain incompletely understood. From a developmental perspective, however, research into the respiratory neural control system of immature animals has shed light on both central and peripheral neural pathways underlying apnea of prematurity (AOP), a highly prevalent respiratory disorder of preterm infants. Animal studies have also been fundamental in furthering our understanding of how clinical interventions (e.g. pharmacological and mechanical) exert their beneficial effects in the clinical treatment of apnea. Although current clinical interventions such as supplemental O₂ and positive pressure respiratory support are critically important for the infant in respiratory distress, they are not fully effective and can also come with unfortunate, unintended (and long-term) side-effects. In this review, we have chosen AOP as one of the most common clinical scenarios involving apnea to highlight the mechanistic basis behind how some of the interventions could be both beneficial and also deleterious to the respiratory neural control system. We have included a section on infants with critical congenital heart diseases (CCHD), in whom apnea can be a clinical concern due to treatment with prostaglandin, and who may benefit from some of the treatments used for AOP.

Targeting Arterial Oxygen Saturation by Closed-Loop Control of Inspired Oxygen in Preterm Infants

Exposure to hyperoxemia from excessive oxygen supplementation and episodes of intermittent hypoxemia have been associated with damage to the eye, lung, and central nervous system in premature infants. The inherent respiratory instability of the premature infant combined with limited staffing or equipment resources often affect SpO₂ targeting and increase exposure to extreme SpO₂ levels. Multiple systems for closed loop control of inspired oxygen have been developed to improve SpO₂ targeting. This article reviews the evidence provided by clinical studies evaluating the efficacy of these systems in extreme premature infants.

Early hypoxemia burden is strongly associated with severe intracranial hemorrhage in preterm infants

OBJECTIVES

The objective of this study was to define the association between the burden of severe hypoxemia (SpO₂ ≤70%) in the first week of life and development of severe ICH (grade III/IV) in preterm infants.

STUDY DESIGN

Infants born at <32 weeks or weighing <1500 g underwent prospective SpO₂ recording from birth through 7 days. Severe hypoxemia burden was calculated as the percentage of the error-corrected recording where SpO₂ ≤70%. Binary logistic regression was used to model the relationship between hypoxemia burden and severe ICH.

RESULTS

A total of 163.3 million valid SpO₂ data points were collected from 645 infants with mean EGA = 27.7 ± 2.6 weeks, BW = 1005 ± 291 g; 38/645 (6%) developed severe ICH. There was a greater mean hypoxemia burden for infants with severe ICH (3%) compared to those without (0.1%) and remained significant when controlling for multiple confounding factors.

CONCLUSION

The severe hypoxemia burden in the first week of life is strongly associated with severe ICH.

Hypoxemia Episodes during Day and Night and Their Impact on Oxygen Saturation Targeting in Mechanically Ventilated Preterm Infants

BACKGROUND

Hypoxemia episodes (HE) occur frequently in ventilated preterm infants and hinder the achievement of arterial oxygen saturation (SpO2) targets. These episodes may increase the risk for retinopathy of prematurity and neurodevelopmental disability. There are no data on the variation in HE and SpO2 targeting between day and night.

OBJECTIVE

The aim of this study was to evaluate the difference between day and night on the frequency and severity of HE and achievement of SpO2 targets.

METHODS

Twenty-four mechanically ventilated preterm infants with ≥4 episodes of SpO2 <75% over an 8-h period were enrolled. The fraction of inspired oxygen (FiO2), SpO2, and ventilator parameters were recorded over 24 h. Data from the day (9 a.m. to 5 p.m.) were compared to the night (9 p.m. to 5 a.m.) for the frequency of HE and proportion of time within and outside the target SpO2 range (90-95%).

RESULTS

The frequency of severe HE (SpO2 <75, ≥20 s) and prolonged severe HE (SpO2 <75, ≥60 s) was lower during the night compared to the day (1.6 ± 1.0 vs. 2.4 ± 1.3 episodes/h, p = 0.008, and 0.53 ± 0.35 vs. 0.90 ± 0.54 episodes/h, p = 0.018). There was no difference in mean episode duration. The frequency and duration of mild HE (SpO2 <85, ≥20 s) were lower during the night compared to the day (5.9 ± 2.7 vs. 7.1 ± 2.5 episodes/h, p = 0.003, and 72 ± 15 vs. 87 ± 25 s, p = 0.01, respectively). The proportion of time in severe hypoxemia (SpO2 <75%) was smaller, whereas time in hyperoxemia (SpO2 >95%) was greater, during the night compared to the day. The mean FiO2 did not differ between day and night.

CONCLUSION

In this group of infants with frequent HE, nighttime was associated with fewer episodes when compared to daytime. This is likely due to less handling and sensory stimulation during the night. The increase in time spent with hyperoxemia during the night is likely to be due to more tolerance of high SpO2 with less proactive weaning of FiO2.

Development and preclinical testing of an adaptive algorithm for automated control of inspired oxygen in the preterm infant

OBJECTIVE

To assess the performance of a novel algorithm for automated oxygen control using a simulation of oxygenation founded on in vivo data from preterm infants.

METHODS

A proportional-integral-derivative (PID) control algorithm was enhanced by (i) compensation for the non-linear SpO₂-PaO₂ relationship, (ii) adaptation to the severity of lung dysfunction and (iii) error attenuation within the target range. Algorithm function with and without enhancements was evaluated by iterative linking with a computerised simulation of oxygenation. Data for this simulation (FiO₂ and SpO₂ at 1 Hz) were sourced from extant recordings from preterm infants (n=16), and converted to a datastream of values for ventilation:perfusion ratio and shunt. Combination of this datastream second by second with the FiO₂ values from the algorithm under test produced a sequence of novel SpO₂ values, allowing time in the SpO₂ target range (91%-95%) and in various degrees of hypoxaemia and hyperoxaemia to be determined. A PID algorithm with 30 s lockout after each FiO₂ adjustment, and a proportional-derivative (PD) algorithm were also evaluated.

RESULTS

Separate addition of each enhancing feature to the PID algorithm showed a benefit, but not with uniformly positive effects. The fully enhanced algorithm was optimal for the combination of targeting the desired SpO₂ range and avoiding time in, and episodes of, hypoxaemia and hyperoxaemia. This algorithm performed better than one with a 30 s lockout, and considerably better than PD control.

CONCLUSIONS

An enhanced PID algorithm was very effective for automated oxygen control in a simulation of oxygenation, and deserves clinical evaluation.

Oxygen requirement as a screening tool for the detection of late pulmonary hypertension in extremely low birth weight infants

BACKGROUND

Many extremely low birth weight infants develop pulmonary hypertension late in their clinical course, and over 60% go undetected by early screening echocardiography. At present, no standardised screening protocol exists for detecting late pulmonary hypertension in extremely low birth weight infants. We assessed the utility of oxygen supplementation as a predictor of late pulmonary hypertension.

METHODS

A retrospective single-centre review of extremely low birth weight infants with no evidence of CHD and those surviving for >30 days was performed. The association between oxygen ⩾30% at day of life 30 and diagnosis of late pulmonary hypertension was estimated with an odds ratio and 95% confidence interval using logistic regression. Doppler echocardiography was used to diagnose pulmonary hypertension in the infants.

RESULTS

A total of 230 infants met the study criteria. The incidence of late pulmonary hypertension was 8.3% (19/230). Infants with late pulmonary hypertension were more likely to have a lower mean birth weight (667.1±144 versus 799.3±140 g, p=0.001) and more likely to be small for gestational age (47.4 versus 14.2%, p=0.004). Oxygen requirement ⩾30% at day of life 30 was associated with increased risk of late pulmonary hypertension (odds ratio=3.77, 95% confidence interval=1.42-10.00, p=0.008) in univariate analysis and after adjusting for birth weight (odds ratio=2.47, 95% confidence interval=0.89-6.84, p=0.08).

CONCLUSIONS

The need of oxygen supplementation ⩾30% at day of life 30 may be a good screening tool for detecting late pulmonary hypertension in extremely low birth weight infants.

Volume Guarantee Ventilation: Effect on Preterm Infants with Frequent Hypoxemia Episodes

BACKGROUND

Preterm infants on mechanical ventilation have spontaneous hypoxemia episodes (HE) triggered by decreases in lung volume and tidal volume (VT). Volume guarantee (VG) is a mode where the ventilator peak pressure is adjusted to keep the exhaled VT at a target level. The effect of VG on HE under routine clinical conditions has not been fully evaluated.

OBJECTIVE

To evaluate the effect of VG on HE in preterm infants in comparison to pressure control (PC) ventilation under routine clinical conditions.

METHODS

Twenty-four mechanically ventilated preterm infants with ≥4 HE of arterial oxygen saturation (SpO2) <75% over 8 h were enrolled. They were studied over 2 consecutive 24-hour periods of VG and PC, in random order.

RESULTS

While the frequency of HE (SpO2 <85% for ≥20 s) did not differ, their duration was reduced during VG. The frequency or duration of severe HE (SpO2 <75% for ≥20 s) did not differ between PC and VG. The proportion of time in severe hypoxemia (SpO2 <75%) during VG did not differ from PC [median: 4.4 (IQR 2.9-5.0) vs. 5.0% (IQR 3.9-6.9), p = 0.44]. The fraction of inspired oxygen (FiO2) was lower during VG compared to PC.

CONCLUSION

The use of VG during routine clinical conditions resulted in a modest reduction in the duration of HE (SpO2 <85%) and FiO2 compared to PC. The use of VG did not reduce the more severe HE.

Fully automated predictive intelligent control of oxygenation (PRICO) in resuscitation and ventilation of preterm lambs

BACKGROUND

Hyperoxia and hypoxia influence morbidity and mortality of preterm infants. Automated closed-loop control of the fraction of inspired oxygen (FiO(2)) has been shown to facilitate oxygen supplementation in the neonatal intensive care unit (NICU), but has not yet been tested during preterm resuscitation. We hypothesized that fully automated FiO(2) control based on predefined oxygen saturation (SpO(2)) targets was applicable in both preterm resuscitation and ventilation.

METHODS

Twenty-two preterm lambs were operatively delivered and intubated in a modified EXIT procedure. They were randomized to receive standardized resuscitation with either automated or manual FiO(2) control, targeting SpO(2) according to the Dawson curve in the first 10 min and SpO(2) 90-95% hereafter. Automated FiO(2) control also was applied during surfactant replacement therapy and subsequent ventilation.

RESULTS

Time within target range did not differ significantly between manual and automated FiO(2) control during resuscitation, however automated FiO(2) control significantly avoided hyperoxia. Automated FiO(2) control was feasible during surfactant replacement and kept SpO(2) within target range significantly better than manual control during subsequent ventilation.

CONCLUSION

In our model, fully automated FiO(2) control was feasible in rapidly changing physiologic conditions during postnatal resuscitation and prevented hyperoxia. We conclude that closed loop FiO(2) control is a promising tool for the delivery room.

Closed-loop control of inspired oxygen in premature infants

Systems for closed-loop control of inspired oxygen have been developed to improve the maintenance of oxygenation targets in premature infants and reduce hyperoxemia, hypoxemia, and exposure to high inspired oxygen levels. This review describes some of the clinical studies that have evaluated the efficacy of these systems in oxygen targeting.

Newborn hypoxia/anoxia inhibits cardiomyocyte proliferation and decreases cardiomyocyte endowment in the developing heart: role of endothelin-1

In the developing heart, cardiomyocytes undergo terminal differentiation during a critical window around birth. Hypoxia is a major stress to preterm infants, yet its effect on the development and maturation of the heart remains unknown. We tested the hypothesis in a rat model that newborn anoxia accelerates cardiomyocyte terminal differentiation and results in reduced cardiomyocyte endowment in the developing heart via an endothelin-1-dependent mechanism. Newborn rats were exposed to anoxia twice daily from postnatal day 1 to 3, and hearts were isolated and studied at postnatal day 4 (P4), 7 (P7), and 14 (P14). Anoxia significantly increased HIF-1α protein expression and pre-proET-1 mRNA abundance in P4 neonatal hearts. Cardiomyocyte proliferation was significantly decreased by anoxia in P4 and P7, resulting in a significant reduction of cardiomyocyte number per heart weight in the P14 neonates. Furthermore, the expression of cyclin D2 was significantly decreased due to anoxia, while p27 expression was increased. Anoxia has no significant effect on cardiomyocyte binucleation or myocyte size. Consistently, prenatal hypoxia significantly decreased cardiomyocyte proliferation but had no effect on binucleation in the fetal heart. Newborn administration of PD156707, an ET_A-receptor antagonist, significantly increased cardiomyocyte proliferation at P4 and cell size at P7, resulting in an increase in the heart to body weight ratio in P7 neonates. In addition, PD156707 abrogated the anoxia-mediated effects. The results suggest that hypoxia and anoxia via activation of endothelin-1 at the critical window of heart development inhibits cardiomyocyte proliferation and decreases myocyte endowment in the developing heart, which may negatively impact cardiac function later in life.

Effects of automated adjustment of the inspired oxygen on fluctuations of arterial and regional cerebral tissue oxygenation in preterm infants with frequent desaturations

OBJECTIVE

To assess the effect of automated adjustment of the inspired oxygen fraction (FiO2) on arterial oxygen saturation (SpO2) and cerebral tissue oxygen saturation (SctO2) in very low birth weight infants with frequent fluctuations in oxygenation.

STUDY DESIGN

Fifteen infants (median gestational age, 25 weeks [range, 23-28 weeks]; median age, 34 days [range, 19-74 days]) were assigned in random sequence to 24 hours of automated adjustment of FiO2 or manual adjustment of FiO2. Primary outcome measurements were time within the SpO2 target range and the area under the curve above and below a defined SctO2 range.

RESULTS

Percentage of time within the SpO2 target range increased during automated FiO2 control (76.3% ± 9.2% vs 69.1% ± 8.2% for manual; P < .01). Prolonged episodes with SpO2 <88% of >60 seconds duration (median, 115 episodes [range, 67-240] vs 54 episodes [range, 7-184]; P < .01) and of >180 seconds duration (median, 13 episodes [range, 6-39] vs 2 episodes [range, 0-5]; P < .01) decreased significantly during the automated period. Percentage of time with SpO2 >96% decreased during automated control (6.6% ± 4.4% vs 10.4% ± 3.3%; P < .02). There was no significant difference in FiO2 exposure. The area (deviation × time) below and above the defined SctO2 threshold did not differ between the 2 periods (median, 59.7%*seconds [range, 17.2%-208.3%] for manual vs 49.0%*seconds [range, 4.3%-193.7%] for automated; P = .36).

CONCLUSION

Automated FiO2 control in preterm infants with frequent SpO2 fluctuations significantly increased the time within the SpO2 target range and reduced the incidence of prolonged hypoxemic events compared with manual FiO2 adjustment, but did not significantly affect cerebral tissue oxygenation.

Acute Neonatal Respiratory Failure

Acute respiratory failure requiring assisted ventilation is one of the most common reasons for admission to the neonatal intensive care unit. Respiratory failure is the inability to maintain either normal delivery of oxygen to the tissues or normal removal of carbon dioxide from the tissues. It occurs when there is an imbalance between the respiratory workload and ventilatory strength and endurance. Definitions are somewhat arbitrary but suggested laboratory criteria for respiratory failure include two or more of the following: PaCO₂ > 60 mmHg, PaO₂ < 50 mmHg or O₂ saturation <80 % with an FiO₂ of 1.0 and pH < 7.25 (Wen et al. 2004).

Setting the Ventilator in the NICU

Success in providing respiratory support to the neonate requires a clear understanding of the context in which it is being applied. Perhaps more than for any other age group, the array of different situations in which ventilation is applied to the newborn infant is extremely broad, with in each case different pathophysiological disturbances and often the need to use a specific approach to apply ventilation optimally. Table 42.1 provides a list of the more common situations in which conventional ventilation is used in the neonate and includes some considerations regarding ventilator settings for each situation. For each situation, a suggested mode of ventilation is indicated, along with target ranges for positive end-expiratory pressure (PEEP) and tidal volume (V_T). Further discussion of the physiological rationale and available evidence for ventilator settings is set out below.

Apnea of prematurity--perfect storm

With increased survival of preterm infants as young as 23 weeks gestation, maintaining adequate respiration and corresponding oxygenation represents a clinical challenge in this unique patient cohort. Respiratory instability characterized by apnea and periodic breathing occurs in premature infants because of immature development of the respiratory network. While short respiratory pauses and apnea may be of minimal consequence if oxygenation is maintained, they can be problematic if accompanied by chronic intermittent hypoxemia. Underdevelopment of the lung and the resultant lung injury that occurs in this population concurrent with respiratory instability creates the perfect storm leading to frequent episodes of profound and recurrent hypoxemia. Chronic intermittent hypoxemia contributes to the immediate and long term co-morbidities that occur in this population. In this review we discuss the pathophysiology leading to the perfect storm, diagnostic assessment of breathing instability in this unique population and therapeutic interventions that aim to stabilize breathing without contributing to tissue injury.

Low oxygen saturation target range is associated with increased incidence of intermittent hypoxemia

OBJECTIVE

To test the hypothesis that preterm infants randomized to a low vs high O(2) saturation target range have a higher incidence of intermittent hypoxemia.

STUDY DESIGN

A subcohort of 115 preterm infants with high resolution pulse oximetry enrolled in the Surfactant, Positive Pressure, and Oxygenation Randomized Trial were randomized to low (85%-89%) or high (91%-95%) O(2) saturation target ranges. Oxygen saturation was monitored until 36 weeks postmenstrual age or until the infant was breathing room air without respiratory support for ≥72 hours.

RESULTS

The low target O(2) saturation group had a higher rate of intermittent hypoxemia (≤80% for ≥10 seconds and ≤3 minutes) prior to 12 days and beyond 57 days of life (P < .05). The duration shortened (P < .0001) and the severity increased (P < .0001) with increasing postnatal age with no differences between target saturation groups. The higher rate of intermittent hypoxemia events in the low target group was associated with a time interval between events of <1 minute.

CONCLUSION

A low O(2) saturation target was associated with an increased rate of intermittent hypoxemia events that was dependent on postnatal age. The duration and severity of events was comparable between target groups. Further investigation is needed to assess the role of intermittent hypoxemia and their timing on neonatal morbidity.

Volume-limited and volume-targeted ventilation

This article shows that volume-targeted ventilation is physiologically more logical than pressure-limited ventilation, and is associated with a reduced risk of pneumothorax, hypocarbia, duration of ventilation, death or bronchopulmonary dysplasia, and severe intraventricular hemorrhage. Therefore, it should now be adopted as the main mode for mechanical ventilation of preterm neonates.

Control of oxygenation during mechanical ventilation in the premature infant

Maintenance of oxygen saturation targets is a demanding and tedious task because of the frequency with which oxygenation changes, especially in small infants receiving prolonged respiratory support. It is clear that the achievement of oxygenation targets can be improved by a higher nurse-to-patient ratio and by intense staff training. Automated control systems can also improve target maintenance, and this is achieved mainly by reducing exposure to hyperoxemia. The long-term benefits and safety of this strategy are yet to be determined in clinical trials.

Prospective analysis of pulmonary hypertension in extremely low birth weight infants

OBJECTIVES

Pulmonary hypertension is associated with bronchopulmonary dysplasia in extremely low birth weight (ELBW) infants and contributes to morbidity and mortality. The objective was to determine the prevalence of pulmonary hypertension among ELBW infants by screening echocardiography and evaluate subsequent outcomes.

METHODS

All ELBW infants admitted to a regional perinatal center were evaluated for pulmonary hypertension with echocardiography at 4 weeks of age and subsequently if clinical signs suggestive of right-sided heart failure or severe lung disease were evident. Management was at discretion of the clinician, and infants were evaluated until discharge from the hospital or pre-discharge death occurred.

RESULTS

One hundred forty-five ELBW infants (birth weight: 755 ± 144 g; median gestational age: 26 weeks [interquartile range: 24-27]) were screened from December 2008 to February 2011. Overall, 26 (17.9%) were diagnosed with pulmonary hypertension at any time during hospitalization (birth weight: 665 ± 140 g; median gestational age: 26 weeks [interquartile range: 24-27]): 9 (6.2%) by initial screening (early pulmonary hypertension) and 17 (11.7%) who were identified later (late pulmonary hypertension). Infants with pulmonary hypertension were more likely to receive oxygen treatment on day 28 compared with those without pulmonary hypertension (96% vs 75%, P < .05). Of the 26 infants, 3 died (all in the late group because of cor pulmonale) before being discharged from the hospital.

CONCLUSIONS

Pulmonary hypertension is relatively common, affecting at least 1 in 6 ELBW infants, and persists to discharge in most survivors. Routine screening of ELBW infants with echocardiography at 4 weeks of age identifies only one-third of the infants diagnosed with pulmonary hypertension. Further research is required to determine optimal detection and intervention strategies.

Multicenter crossover study of automated control of inspired oxygen in ventilated preterm infants

OBJECTIVE

To determine the efficacy and safety of automated adjustment of the fraction of inspired oxygen (Fio(2)) adjustment in maintaining arterial oxygen saturation (Spo(2)) within an intended range for mechanically ventilated preterm infants with frequent episodes of decreased Spo(2).

METHODS

Thirty-two infants (gestational age [median and interquartile range]: 25 weeks [24-27 weeks]; age: 27 days [17-36 days]) were studied during 2 consecutive 24-hour periods, one with Fio(2) adjusted by clinical staff members (manual) and the other by an automated system (automated), in random sequence.

RESULTS

Time with Spo(2) within the intended range (87%-93%) increased significantly during the automated period, compared with the manual period (40% ± 14% vs 32% ± 13% [mean ± SD]). Times with Spo(2) of >93% or >98% were significantly reduced during the automated period (21% ± 20% vs 37% ± 12% and 0.7% vs 5.6% [interquartile ranges: 0.1%-7.2% and 2.7%-11.2%], respectively). Time with Spo(2) of <87% increased significantly during the automated period (32% ± 12% vs 23% ± 9%), with more-frequent episodes with Spo(2) between 80% and 86%, whereas times with Spo(2) of <80% or <75% did not differ between periods. Hourly median Fio(2) values throughout the automated period were lower and there were substantially fewer manual Fio(2) changes (10 ± 9 vs 112 ± 59 changes per 24 hours; P < .001), compared with the manual period.

CONCLUSIONS

In infants with fluctuations in Spo(2), automated Fio(2) adjustment improved maintenance of the intended Spo(2) range led to reduced time with high Spo(2) and more-frequent episodes with Spo(2) between 80% and 86%.

A higher incidence of intermittent hypoxemic episodes is associated with severe retinopathy of prematurity

OBJECTIVE

Retinopathy of prematurity (ROP), a vasoproliferative disorder of the retina in preterm infants, is associated with multiple factors, including oxygenation level. We explored whether the common intermittent hypoxemic events in preterm infants are associated with the development of ROP.

STUDY DESIGN

Oxygen desaturation events were quantified in 79 preterm infants (gestational age, 24 to 27-6/7 weeks) during the first 8 weeks of life. Infants were classified as requiring laser treatment for ROP versus having less severe or no ROP. A linear mixed model was used to study the association between the incidence of intermittent hypoxia and laser treatment of ROP, controlling for gestational age, sex, race, multiple births, and initial severity of illness.

RESULTS

For all infants, hypoxemic events increased with postnatal age (P<.001). Controlling for all covariates, a higher incidence of oxygen desaturation events was found in the infants undergoing laser therapy for ROP (P<.001), males (P<.02), and infants of younger gestational age (P<.003).

CONCLUSIONS

The incidence of hypoxemic events was higher in infants with ROP requiring laser therapy. Therapeutic strategies to optimize oxygenation in preterm infants should include minimization of desaturation episodes, which may in turn decrease serious morbidity in this high-risk population.

Automated adjustment of inspired oxygen in preterm infants with frequent fluctuations in oxygenation: a pilot clinical trial

OBJECTIVE

To assess the efficacy of a system for automated fraction of inspired oxygen (FiO(2)) adjustment in maintaining oxygen saturation (SpO(2)) within an intended range in preterm infants with spontaneous fluctuations in SpO(2).

STUDY DESIGN

Sixteen infants (gestational age, 24.9 +/- 1.4 weeks; birth weight, 678 +/- 144 g; age, 33 +/- 15 days) with frequent hypoxemia episodes underwent two 4-hour periods of FiO(2) adjustment by clinical personnel (routine) and the automated system (automated).

RESULTS

Compared with the routine period, the percent time within intended SpO(2) range (88%-95%) increased during the automated period (58% +/- 10% versus 42% +/- 9%; P < .001), whereas the percent time with SpO(2) higher than the intended range and >or=98% were reduced (9% +/- 10% versus 31% +/- 8% [P < .001] and 3% +/- 5% versus 16% +/- 9% [P < .001], respectively). Percent time with SpO(2) < 88% increased during the automated period (33% +/- 7% versus 27% +/- 9%; P = .003) because of more frequent episodes, whereas the time with SpO(2) < 75% did not differ. The 4-hour median FiO(2) was lower during the automated period (29% +/- 4% versus 34% +/- 5%; P < .001).

CONCLUSION

Automated FiO(2) adjustment improved maintenance of SpO(2) within the intended range and reduced hyperoxemia and FiO(2). These findings should be examined in longer periods with standard clinical conditions and, eventually, in the context of randomized trials powered to detect clinically important effects on outcome.

Automated respiratory support in newborn infants

A considerable proportion of premature infants requires mechanical ventilatory support and supplemental oxygen. Due to their immaturity, exposure to these forms of respiratory support contributes to the development of lung injury, oxidative stress and abnormal retinal development. These conditions are associated with poor long-term respiratory and neurological outcome. Mechanically ventilated preterm infants present with frequent fluctuations in ventilation and gas exchange. Currently available ventilatory modes and manual adjustment to the ventilator or supplemental oxygen cannot effectively adapt to these recurrent fluctuations. Moreover, the respiratory support often exceeds the infant's real needs. Techniques that adapt the mechanical ventilatory support and supplemental oxygen to the changing needs of preterm infants are being developed in order to improve stability of gas exchange, to minimise respiratory support and to reduce personnel workload. This article describes the preliminary evidence on the application of these new techniques in preterm infants and animal models.

Methods and evidence on volume-targeted ventilation in preterm infants

PURPOSE OF REVIEW

Several modalities of volume-targeted ventilation have been developed for the premature infant or were adopted from those used in older populations. The article describes these modalities, their clinical application in preterm infants and reviews the evidence for the possible beneficial effects in this population.

RECENT FINDINGS

Evidence from physiologic studies indicates increased stability of tidal volume and gas exchange while requiring less ventilatory support. Randomized trials of volume-targeted ventilation indicate faster weaning and shorter duration of mechanical ventilation, but this has not resulted in better respiratory outcome.

SUMMARY

The proposed benefits of volume-targeted ventilation on respiratory outcome have not been fully confirmed by the existing data. Some trends suggest possible benefits, but these need to be further explored. The efficacy of volume-targeted ventilation may be method dependent and may also be influenced by the magnitude of the volume targeted.

Outcomes of extremely low birth weight (<1 kg) and extremely low gestational age (<28 weeks) infants with bronchopulmonary dysplasia: effects of practice changes in 2000 to 2003

OBJECTIVE

The goal was to evaluate whether changes in neonatal intensive care have improved outcomes for children with bronchopulmonary dysplasia (oxygen dependence at corrected age of 36 weeks).

METHODS

We compared outcomes of extremely low birth weight (<1 kg) and extremely low gestational age (<28 weeks) infants with bronchopulmonary dysplasia between 2 periods (period I, 1996-1999: extremely low birth weight, n = 122; extremely low gestational age, n = 118; period II, 2000-2003: extremely low birth weight, n = 109; extremely low gestational age, n = 107).

RESULTS

For both groups, significant practice changes between period I and period II included increased prenatal and decreased postnatal steroid therapy and increased surfactant therapy, indomethacin therapy, and patent ductus arteriosus ligation. Significant morbidity changes included decreased rates of severe cranial ultrasound abnormalities and increased rates of ventilator dependence. Rates of bronchopulmonary dysplasia did not change (52% vs 53%). Follow-up evaluation revealed significantly lower rates of neurosensory abnormalities during period II (extremely low birth weight: 29% vs 16%; extremely low gestational age: 31% vs 16%). There were no changes in rates of Mental Developmental Index scores of <70 (extremely low birth weight: 42% vs 42%; extremely low gestational age: 37% vs 45%) or overall developmental impairment (extremely low birth weight: 51% vs 49%; extremely low gestational age: 50% vs 51%). For the extremely low gestational age group, predictors of neurosensory abnormalities were severe cranial ultrasound abnormality and postnatal steroid therapy. Predictors of overall impairment included severe cranial ultrasound abnormalities, ventilator dependence, postnatal steroid therapy, and patent ductus arteriosus ligation. For the extremely low birth weight group, the only predictor of neurosensory abnormalities was severe cranial ultrasound abnormality. Predictors of overall impairment included multiple birth, ventilator dependence, and severe cranial ultrasound abnormalities.

CONCLUSIONS

Neurosensory outcomes of infants with bronchopulmonary dysplasia improved during 2000 to 2003 but overall neurodevelopmental outcomes did not change.

Mechanisms of hypoxemia episodes in spontaneously breathing preterm infants after mechanical ventilation

BACKGROUND

Preterm infants often present with recurrent episodes of hypoxemia after mechanical ventilation.

OBJECTIVE

To evaluate the role of abdominal muscle activity and central apnea on the frequency and severity of hypoxemia episodes (HEs) in preterm infants with a history of mechanical ventilation.

METHODS

Continuous recordings of arterial oxygen saturation (SpO(2)), gastric pressure, respiratory inductance plethysmography and abdominal surface electromyography were obtained during 4 h from spontaneously breathing preterm infants who had recently been extubated and presented with frequent HEs.

RESULTS

Ten infants (gestational age 26.4 +/- 1.1 weeks, body weight 816 +/- 128 g, age 44 +/- 21 days, FiO2 0.31 +/- 0.09, mechanically ventilated for 33 +/- 37 days) were studied 12 +/- 7 (mean +/- SD) days after extubation. These infants presented with 10.2 +/- 9.3 HEs/h (SpO2 <88%, > or =10 s). Of these, 8.2 +/- 6.2 HEs/h were associated with abdominal muscle contraction while only 2.0 +/- 4.5 HEs/h were associated with > or =10 s apnea (p < 0.05). Of the more severe HEs (SpO(2) <75%, > or =10 s), 2.7 +/- 3.1 HEs/h were associated with abdominal contraction and only 0.7 +/- 2.1 HEs/h with apnea (p < 0.05). Resting lung volume decreased by 69 +/- 16% of tidal volume in HEs associated with abdominal contraction.

CONCLUSIONS

In this group of premature infants who presented with frequent HEs after mechanical ventilation, most HEs were associated with abdominal muscles contraction and a loss in lung volume. These findings provide an alternate mechanism to explain these episodes in spontaneously breathing preterm infants with a history of mechanical ventilation.

Do ventilated neonates require pain management?

Mechanical ventilation is a stressful experience in neonates resulting in changes in neuroendocrine parameters, pain scores, and physiologic responses. Assisted ventilation in neonates is presumed to be associated with chronic repetitive pain, which in turn is associated with adverse long-term sequelae. Reasons to routinely sedate ventilated neonates include improved ventilator synchrony, improved pulmonary function, and decreased neuroendocrine responses, including cortisol, beta-endorphine, and catecholamines. Reasons not to treat include the well-known adverse side effects of pain medication, especially the opiates, including hypotension from morphine, chest wall rigidity from fentanyl, and tolerance, dependence, and withdrawal from both opiates and benzodiazepines. Additionally, adverse effects such as death and IVH are not improved with preemptive treatment. Chronic pain assessment is poorly validated and difficult to assess in this population, and most studies have evaluated only acute pain scores. If patients are treated, opiates are the most common class of drugs, with morphine the most well studied. Fentanyl may be advantageous in hypotensive, younger neonates because it has fewer cardiovascular effects. The benzodiazepines, midazolam and lorazepam, have been used in ventilated neonates, but midazolam has been associated with adverse effects in one small study so concern remains regarding its use. Significant gaps in our knowledge exist, especially in regard to long-term effects of treatment, or lack thereof, and in the assessment of the chronic pain associated with assisted ventilation.

Hybrid algorithm for automatic regulation of mechanical ventilation in premature infants based on expert rules and proportional differential control

Mechanically ventilated premature infants present with fluctuations in ventilation that cannot be addressed by conventional mechanical ventilation with fixed positive pressure and constant frequency. A hybrid algorithm for automatic targeting of minute ventilation and tidal volume by individual or combined closed loop control of the ventilator frequency and peak inspiratory pressure was developed. The objective of this system is to minimize the mechanical support and adapt to changes in ventilatory need. Under the most challenging conditions, the combined controller is more efficient than individual control.

Role of abdominal muscles activity on duration and severity of hypoxemia episodes in mechanically ventilated preterm infants

BACKGROUND

Episodes of hypoxemia are often observed in ventilated preterm infants. The factors that determine their duration, severity and the failure of the mechanical breaths to maintain ventilation have not been fully defined.

OBJECTIVE

To determine the relation between activity of the abdominal muscles and the duration and severity of hypoxemia episodes in ventilated preterm infants.

METHODS

Clinically stable ventilated preterm infants weighing between 500 and 1,000 g at birth, who presented with frequent episodes of hypoxemia, were studied. Recordings of arterial oxygen saturation (SpO(2)), tidal volume and abdominal surface electromyography were obtained during 4 h to assess the temporal relationship between activation of abdominal musculature with the onset, duration and severity of hypoxemia episodes.

RESULTS

In 15 infants, GA (mean +/- SD) 25 +/- 1.5 weeks, BW 697 +/- 141 g, age 37 +/- 14 days, synchronized intermittent mandatory ventilation rate 17 +/- 6 breaths/min, peak inspiratory pressure 18 +/- 1.9 cm H(2)O, positive end-expiratory pressure 4.8 +/- 0.6 cm H(2)O, and fraction of inspired oxygen (FiO(2)) 0.4 +/- 0.1 were studied. These infants presented with 7.2 +/- 4.4 episodes of hypoxemia (SpO(2) <88%) per hour. The number of abdominal muscle contractions per episode correlated with the duration and severity of the episodes of hypoxemia. The episode duration increased by 14 +/- 18 s per abdominal muscle contraction. The lowest SpO(2) reached during an episode of hypoxemia decreased by 1.7 +/- 1.4% for every abdominal muscle contraction.

CONCLUSIONS

These data document a relationship between abdominal muscles contraction and the duration and severity of hypoxemia episodes in ventilated preterm infants. These findings can explain the failure of mechanical ventilation to prevent their occurrence or decrease their severity.