Ventilation inhomogeneity is one criterion among many in multidimensional PEEP titration

Amato [1] on our recent study [2], 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 [1]. Especially in patients with normal lungs, inhomogeneity of lung perfusion and venti lation along the gravity axis match each other – a match that is essential to optimize gas exchange. Little attention was paid, however, to isogravitational inhomo-geneity of pulmonary perfusion and ventilation. When isogravitational inhomogeneity is included in the estimation , the infl uence 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 fi nd a balance between overdistension and atelectasis. Physiological hetero geneity (good heterogeneity) may be preserved at the selected PEEP level. Th e global inhomogeneity index [2] can be independently combined with any region-of-interest-defi nition method, if appropriate. Given that no perfect method exists currently for identifi cation of collapsed lung areas by electrical impedance tomography, our approach [5] guarantees to include as much of the collapsed lung regions as is detectable in the analysis of ventilation in-homo geneity and provides satisfactory results, as shown in a preliminary study by comparison with computed tomography. Th e titration of PEEP actually requires a multi-dimensional 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. Abbreviations PEEP, positive end-expiratory pressure. Competing interests The authors declare that they have no competing interests. PEEP titration guided by ventilation homogeneity: a feasibility study using electrical impedance tomography. Crit Care 2010, 14:R8. 3. Glenny R: Counterpoint: Gravity is not the major factor determining the distribution of blood fl ow in the healthy human lung. Ventilation inhomogeneity in upright and supine position assessed by electrical impedance tomography. A lung area estimation method for analysis of ventilation inhomogeneity based on electrical impedance tomography.