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Volume control: A logical solution to volutrauma?

2006; Elsevier BV; Volume: 149; Issue: 3 Linguagem: Inglês

10.1016/j.jpeds.2006.06.032

1097-6833

Peter G. Davis, Colin J. Morley,

Trauma and Emergency Care Studies

Management of respiratory failure in small infants is a key function of modern neonatal intensive care. The mainstay of respiratory support over many years has been time-cycled, pressure-limited ventilation through an endotracheal tube. Although potentially life-saving, ventilation is costly and associated with acute and chronic complications, including air leak and bronchopulmonary dysplasia. Accumulating evidence from animal models1Hernandez L.A. Peevy K.J. Moise A.A. Parker J.C. Chest wall restriction limits high airway pressure-induced lung injury in young rabbits.J Appl Physiol. 1989; 66: 2364-2368PubMed Google Scholar as well as adult human studies2Acute Respiratory Distress Syndrome NetworkVentilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome.N Engl J Med. 2000; 342: 1301-1308Crossref PubMed Scopus (10570) Google Scholar indicates that excessive tidal volume (volutrauma) rather than high inspiratory pressure is the primary determinant of lung injury. Infants with respiratory distress syndrome are at particular risk of volutrauma, as lung compliance (and therefore volumes delivered by pressure-limited ventilators) may change rapidly with disease progression or surfactant therapy. Inability to accurately deliver the small tidal volumes has resulted in delayed use of volume-targeted ventilation in neonatal intensive care. The development of very sensitive and accurate flow sensors has allowed many new-generation ventilators to include volume targeting as an option. There is strong biological plausibility for the belief that such ventilators might improve outcomes in neonatal intensive care. Unfortunately, many such “good ideas” in neonatology subsequently have been proven disastrous or at best unhelpful.See related article, p 308 See related article, p 308 In this issue of The Journal, Singh et al3Singh J. Sinha S. Byrne S. Donn S. Mechanical ventilation of very low birth weight infants is volume or pressure a better target variable?.J Pediatr. 2006; 149: 308-313Abstract Full Text Full Text PDF PubMed Scopus (91) Google Scholar report the results of a single-center clinical trial comparing volume-controlled (VC) ventilation with time-cycled, pressure-limited ventilation. The study has a number of strengths; it is randomized with a permuted block design, preventing selection bias at study entry. The eligibility criteria are clearly described and the babies studied are representative of those in neonatal units throughout the Western world, that is, high rates of antenatal steroid use and early postnatal surfactant therapy. A priori stratification of the study population by birth weight was performed and serves two important purposes. It ensures balance between the groups for an important risk factor, and, particularly for this study, strengthens inferences from the subgroup analysis. Neither the caregivers nor those measuring the outcomes in this trial were masked to the group of random assignment. The authors argue that to do so was impracticable in this “pragmatic” trial. In an effort to minimize bias arising from inequality of care given to the two groups as well as the risk of differential measurement of the primary outcome, a rigorous protocol was used. This has led to the choice of a somewhat idiosyncratic primary outcome: time to achieve an alveolar-arterial oxygen gradient (>100 mm Hg) or mean airway pressure (<8 cm H2O). Although less clinically important than the more conventional measures of time to extubation, incidence of chronic lung disease, and time on respiratory support, this outcome is less subject to bias from caregivers making decisions about extubation. The sample size calculation (n = 90) is based on a large treatment effect but is similar to other trials in the field. The headline result of this trial is a trend toward shorter time to reach the success criteria in the VC group as a whole, which was statistically significant in the subgroup of infants with birth weight <1000 g. The time difference (10 hours for all subjects) is approximately 5% of the total ventilation time. Therefore, the result, even if it were statistically significant, is of modest clinical importance. On the other hand, death is a very important outcome; the probability value favoring the VC group does not reach statistical significance (.064). The authors are appropriately cautious in commenting on these trends. This study meets the inclusion criteria and will appear in updated versions of our systematic review of volume-targeted versus pressure-limited ventilation in the Cochrane Library.4McCallion N. Davis P. Morley C. Volume-targeted versus pressure-limited ventilation in the neonate.Cochrane Database Syst Rev. 2005; (;CD003666)PubMed Google Scholar The review currently comprises four studies and a total of 178 infants; two studies evaluated VC ventilation and two, volume-guarantee ventilation. Despite the differences between the modes of ventilation, we found the results across the four studies remarkably consistent; in statistical terms, there was no evidence of heterogeneity for most of the important outcomes. Pooled analyses showed significant reductions in duration of ventilation, rates of severe intraventricular hemorrhage, and pneumothorax for infants receiving volume-targeted ventilation. A trend toward reduced mortality rates in infants receiving volume-targeted ventilation did not reach statistical significance. Therefore, the findings of Singh et al3Singh J. Sinha S. Byrne S. Donn S. Mechanical ventilation of very low birth weight infants is volume or pressure a better target variable?.J Pediatr. 2006; 149: 308-313Abstract Full Text Full Text PDF PubMed Scopus (91) Google Scholar are largely consistent with other studies, and the strong methodology and numbers recruited mean that their study makes a substantial contribution to the field. There are at least three reasons to be cautious in applying the results of these trials to all very premature newborn infants. The numbers of babies randomly assigned, even in a subsequent pooled analysis of studies, are quite small. Although the authors claim “safety and efficacy” for the technique, the ability to detect even relatively common unwanted effects is limited. Second, the outcomes assessed are the common ones measured in trials of neonatal ventilation; they are short-term and predominantly lung-related. Improved survival free of neurodevelopmental impairment is the goal of modern neonatal intensive care and therefore should be the primary outcome of clinical trials preceding widespread uptake of any new therapy. Third, the groups of Sunil Sinha and Martin Keszler have made major contributions both to the randomized trials and the broader literature in this area.5Sinha S.K. Donn S.M. Gavey J. McCarty M. Randomised trial of volume controlled versus time cycled, pressure limited ventilation in preterm infants with respiratory distress syndrome.Arch Dis Child Fetal Neonatal Ed. 1997; 77: F202-F205Crossref PubMed Google Scholar, 6Sinha S.K. Donn S.M. Volume-controlled ventilation variations on a theme.Clin Perinatol. 2001; 28: 547-560Abstract Full Text Full Text PDF PubMed Scopus (27) Google Scholar, 7Sinha S.K. Donn S.M. Gavey J. McCarty M. Randomised trial of volume controlled versus time cycled, pressure limited ventilation in preterm infants with respiratory distress syndrome.Arch Dis Child Fetal Neonatal Ed. 1997; 77: F202-F205Crossref PubMed Scopus (112) Google Scholar, 8Abubakar K. Keszler M. Effect of volume guarantee combined with assist/control vs synchronized intermittent mandatory ventilation.J Perinatol. 2005; 25: 638-642Crossref PubMed Scopus (53) Google Scholar, 9Keszler M. Volume-targeted ventilation.J Perinatol. 2005; 25: S19-S22Crossref PubMed Scopus (34) Google Scholar They are experts in the practical application of the technique of volume-targeted ventilation. It is vital to determine whether the wider, less experienced neonatal community can replicate their results. The groundwork has been well laid for a multicentric trial of volume-targeted ventilation with sufficient power to evaluate long-term respiratory and neurodevelopmental outcomes.10Keszler M. Abubakar K. Volume guarantee stability of tidal volume and incidence of hypocarbia.Pediatr Pulmonol. 2004; 38: 240-245Crossref PubMed Scopus (128) Google Scholar Mechanical ventilation of very low birth weight infants: Is volume or pressure a better target variable?The Journal of PediatricsVol. 149Issue 3PreviewTo compare the efficacy and safety of volume-controlled (VC) ventilation to time-cycled pressure-limited (TCPL) ventilation in very low birth weight infants with respiratory distress syndrome (RDS). Full-Text PDF