Letter | Open | Published:
Ventilation inhomogeneity is one criterion among many in multidimensional PEEP titration
Critical Carevolume 14, Article number: 424 (2010)
We appreciate the commentary from Dr Costa and Dr Amato  on our recent study , in which we proposed that ventilation inhomogeneity should be regarded as an additional prospective index along with blood gases, lung mechanics and hemodynamics in a multifactorial method to optimize positive end-expiratory pressure (PEEP) at the bedside.
We agree with Costa and Amato that some ventilation heterogeneity may be good . Especially in patients with normal lungs, inhomogeneity of lung perfusion and ventilation along the gravity axis match each other - a match that is essential to optimize gas exchange. Little attention was paid, however, to isogravitational inhomogeneity of pulmonary perfusion and ventilation. When isogravitational inhomogeneity is included in the estimation, the influence of gravity is no longer dominant [3, 4]. Minimizing the ventilation inhomogeneity during PEEP titration is not intended to eliminate inhomogeneity at all (which is impossible by PEEP alone), but rather to find a balance between overdistension and atelectasis. Physiological hetero geneity (good heterogeneity) may be preserved at the selected PEEP level.
The global inhomogeneity index  can be independently combined with any region-of-interest-definition method, if appropriate. Given that no perfect method exists currently for identification of collapsed lung areas by electrical impedance tomography, our approach  guarantees to include as much of the collapsed lung regions as is detectable in the analysis of ventilation inhomogeneity and provides satisfactory results, as shown in a preliminary study by comparison with computed tomography.
The titration of PEEP actually requires a multidimensional approach. A single ideal PEEP level, satisfying all clinical objectives and situations, may even not exist. A weighted combination of lung mechanics, blood gas analysis and imaging techniques to titrate PEEP therefore seems appealing and promising.
positive end-expiratory pressure.
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Glenny R: Counterpoint: Gravity is not the major factor determining the distribution of blood flow in the healthy human lung. J Appl Physiol 2008, 104: 1533-1535. discussion 1535-1536 10.1152/japplphysiol.01092.2007a
Zhao Z, Kiefer N, Kulcsar M, Lang S, Möller K: Ventilation inhomogeneity in upright and supine position assessed by electrical impedance tomography. In XII Mediterranean Conference on Medical and Biological Engineering and Computing. 27-30 May, 2010; Chalkidiki, Greece. Edited by: Bamidis PD, Konstantindis ST, Bliznakova K and Pallikarakis N. Springer; 2010:84. ISBN 978-960-99365-0-7
Zhao Z, Steinmann D, Müller-Zivkovic D, Martin J, Frerichs I, Guttmann J, Möller K: A lung area estimation method for analysis of ventilation inhomogeneity based on electrical impedance tomography. J Xray Sci Technol 2010, 18: 171-182.
The authors declare that they have no competing interests.