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Improving Assisted Ventilation Immediately after Birth

2011; Elsevier BV; Volume: 160; Issue: 3 Linguagem: Inglês

10.1016/j.jpeds.2011.11.006

1097-6833

Tina A. Leone,

Congenital Diaphragmatic Hernia Studies

See related articles, p 372 and p 377The initiation of breathing at birth is a dynamic process that involves clearing the airways and lungs of fluid and filling the lungs with air. When the newborn does not initiate breathing or does not breathe adequately, care providers assist ventilation to stabilize the newborn’s cardiorespiratory status. Most of the time, the assisted ventilation is provided briefly and therefore most appropriately is provided non-invasively. Providing non-invasive ventilation is a skill that is not always easily mastered. Even for individuals with the highest skill level or for invasive ventilation, delivering the correct amount of ventilation for an individual infant is a difficult task. Two reports in this issue of The Journal have attempted to address the issue of how to best provide an appropriate amount of ventilation. Schmölzer et al1Schmölzer G.M. Morley C.J. Wong C. Dawson J.A. Kamlin C.O.F. Donath S.M. et al.Respiratory function monitor guidance of mask ventilation: a feasibility study.J Pediatr. 2012; 160: 377-381Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar evaluated a respiratory function monitor (RFM) as a method of improving the amount of ventilation being provided. Bowman et al2Bowman T.A. Paget-Brown A. Carroll J. Gurka M.J. Kattwinkel J. Sensing and responding to compliance changes during manual ventilation using a lung model: can we teach healthcare providers to improve?.J Pediatr. 2012; 160: 372-376Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar used a lung model and an educational intervention to evaluate an individual’s ability to provide a targeted tidal volume in response to changing lung compliance. See related articles, p 372 and p 377 Traditionally, the only tools clinicians have had to determine whether the amount of ventilation was adequate were the evaluation of chest rise and the assessment of clinical improvement. This is a one-sided approach because chest rise represents “adequate breaths,” but there is no clinical measure currently recommended to determine whether the breaths being provided are too large. Animal models have suggested that initiating ventilation at birth with high tidal volume may lead to lung injury.3Wada K. Jobe A.H. Ikegami M. Tidal volume effects on surfactant treatment responses with the initiation of ventilation in preterm lambs.J Appl Physiol. 1997; 83: 1054-1061PubMed Google Scholar Clinicians are not good at estimating tidal volume by assessing chest rise,4Poulton D.A. Schmölzer G.M. Morley C.J. Davis P.G. Assessment of chest rise during mask ventilation of preterm infants in the delivery room.Resuscitation. 2011; 82: 175-179Abstract Full Text Full Text PDF PubMed Scopus (100) Google Scholar and when chest rise is used in newborn infants to determine ventilator settings, infants frequently become hypocarbic,5Tracy M. Downe L. Holberton J. How safe is intermittent positive pressure ventilation in preterm babies ventilated from delivery to neonatal intensive care?.Arch Dis Child Fetal Neonatal Ed. 2004; 89: F84-F87Crossref PubMed Google Scholar indicating that these breaths are too large. It is, therefore, logical that monitoring the tidal volume of each breath could decrease the risk of lung injury caused by excessively large breaths. Delivering inadequate tidal volume is also a possible result of mask ventilation and can have harmful effects. Inadequate tidal volume could be the result of inadequate pressure being delivered to a poorly compliant lung, an obstructed airway resulting in the breaths not being delivered to the lungs, or mask leak resulting in gas escaping from the mask before reaching the airways. Immediately after birth, the process of filling the lungs with air occurs with the baby taking a spontaneous breath of varying but possibly very high inspiratory pressure. The volume of air that enters the lungs during the initial spontaneous breath of healthy term infants was previously measured to be approximately 12 mL/kg on average.6Vyas H. Field D. Milner A.D. Hopkin I.E. Determinants of the first inspiratory volume and functional residual capacity at birth.Pediatr Pulmonol. 1986; 2: 189-193Crossref PubMed Scopus (112) Google Scholar Newborn infants who are not spontaneously breathing or who have immature lungs may require different levels of assisted ventilation to establish good lung volumes. Inadequate breaths may deliver air only to the anatomic dead space of the airways rather than to the alveolar spaces.7Siew M.L. te Pas A.B. Wallace M.J. Kitchen M.J. Lewis R.A. Fouras A. et al.Positive end expiratory pressure enhances development of a functional residual capacity in preterm lambs ventilated from birth.J Appl Physiol. 2009; 65: 537-541Google Scholar The lack of expansion of the lungs may impair the normal increase in pulmonary blood flow, and when this is uncorrected, the newborn would remain hypoxemic and bradycardic. Monitoring, therefore, also has potential to improve the transition by decreasing the number of inadequate breaths. The paper by Schmölzer et al investigated a RFM to help clinicians decrease the amount of mask leak, with the idea that this would lead to improved ventilation. The trial protocol allowed for the RFM to be used in all infants, but for half the subjects the RFM screen was covered, and teams were instructed to adjust the ventilation clinically. In the RFM visible group, the clinical teams were instructed to minimize mask leak and target a tidal volume of 4 to 8 mL/kg. The authors found that use of the RFM did improve mask leak but was not associated with any statistical difference in the tidal volumes delivered in the two groups. The authors also found that the clinicians made more mask adjustments and more inspiratory pressure changes when the RFM was visible. Without a change in tidal volume delivered, is it possible to have any difference in clinical outcomes? The authors did find a decrease in the amount of oxygen used during resuscitation and a decrease in the frequency of delivery room intubation when the RFM was visible. Are these findings the result of more appropriate ventilation? The trial was a randomized controlled trial, which limited many of the biases that could result in such findings. However, the trial was by necessity unblinded, and therefore the unintentional but realistic possibility that treatment bias resulted in a more permissive approach in the RFM visible group cannot be ignored. The authors did show that fewer breaths greater than the target volume were delivered when the RFM was used. Perhaps limiting the number of very large breaths did allow for a more stable transition. This possibility needs to be further explored. The trial does reinforce the idea that paying closer attention to the assisted breaths that are given during resuscitation is likely to benefit the baby. In the trial by Bowman et al, clinicians of varying experience levels participated in a training session aimed at providing a targeted tidal volume to a test lung when the ventilating device was applied directly to the lung without a leak. The participants in the study received pre- and post-intervention testing. A portion of the participants were also tested 8 months after the intervention. The investigators found that targeted tidal volumes were more consistently provided when volume rather than pressure was displayed. There was some improvement in the ability to deliver a targeted tidal volume when pressure was displayed after the intervention. However, all improvements were lost after 8 months had passed. In this study, the participants were more successful at providing the targeted tidal volume when a self-inflating bag was used than when a flow-inflating bag was used. This is an unexpected finding, and the explanation for the finding is not clear. Perhaps the participants’ inexperience with flow-inflating bags (60% use self-inflating bags in practice) caused them to have more difficulty with this device during testing. Additionally, the changing compliance of the test lung may have been more difficult for those inexperienced with the flow-inflating bag to make rapid adjustments. We should use this information about bag type with caution because the results may not be generalizable to other groups. However, this study does strengthen the notion that tidal volume monitoring during resuscitation may be beneficial. Both of these studies have addressed the question of how to provide better ventilation to newborn infants. They suggest that tidal volume monitoring may be helpful in preventing mask leak or in achieving a desired tidal volume. Our group has been investigating end tidal carbon dioxide monitoring as an alternate method of determining whether ventilation is inadequate or excessive.8Kong JY, Rich W, Finer NN, Leone TA. Quantitative end tidal CO2 monitoring in the delivery room: can we prevent hypo/hypercapnia in babies upon admission to the NICU? E-PAS 20111660.1Google Scholar We have found that the presence of end tidal carbon dioxide is a very helpful indicator that ventilation is at least adequate enough that gas has reached the alveoli and that some amount of pulmonary blood flow is present.9Finer N.N. Rich W. Wang C. Leone T. Airway obstruction during mask ventilation of very low birth weight infants during neonatal resuscitation.Pediatrics. 2009; 123: 865-869Crossref PubMed Scopus (135) Google Scholar It may be that end tidal CO2 monitoring is more helpful at determining when ventilation is adequate, and tidal volume monitoring may be more helpful at determining when ventilation is excessive. Again, this needs more study. Despite ventilation being one of the most commonly used interventions in newborn resuscitation, several questions about how this intervention should best be delivered remain. A spontaneously breathing child is likely to need a different amount of support than a non-breathing child. How can clinicians best adjust to the needs of the child? What tidal volume is appropriate for a lung that is in the process of clearing fetal lung fluid? Which methods of providing artificial ventilation will cause the least injury to the lung during this time? Is the best monitoring for too little ventilation and too much ventilation the same? Can resuscitation teams use all this equipment and integrate all the information effectively to make good decisions during each resuscitation? These are only some of the many questions that are brought to mind when considering ventilation during neonatal resuscitation. These two papers shed a bit more light on this area than was previously known and, as with all good studies, raise more questions than answers. Sensing and Responding to Compliance Changes during Manual Ventilation Using a Lung Model: Can We Teach Healthcare Providers to Improve?The Journal of PediatricsVol. 160Issue 3PreviewTo test the hypothesis that an educational intervention would improve the resuscitator’s ability to provide on-target volume ventilation during pulmonary compliance changes. Full-Text PDF Respiratory Function Monitor Guidance of Mask Ventilation in the Delivery Room: A Feasibility StudyThe Journal of PediatricsVol. 160Issue 3PreviewTo investigate whether using a respiratory function monitor (RFM) during mask resuscitation of preterm infants reduces face mask leak and improves tidal volume (VT). Full-Text PDF