Diabetes and acute respiratory failure. Is the lung finally safe?

Dear Editor,

We read with great interest the article by Khatib et al.[1] regarding the factors related to the outcome of intensive care unit (ICU) patients in a real-life setting. The authors have analyzed, over 15 months period, the characteristics of 122 ICU patients intubated and mechanically ventilated, according to demographic data, indications for mechanical ventilation and the modality of ventilation. Interestingly, they observed a significant association between mortality and both preexisting (notably age, obesity, and heart failure) and subsequent factors (additional organ failure), as well as the severity of respiratory failure. In their cohort, almost one-quarter (23.8%) of patients with acute respiratory failure presented an acute respiratory distress syndrome (ARDS), and one-third (36.1%) had sepsis. Even though at the univariate analyses many factors resulted significantly associated with mortality (e.g., hypertension, central nervous system diseases), only a few were confirmed at the multivariate one. In particular, the presence of diabetes mellitus (DM) did not correlate with a worse outcome at the multivariate analysis.

We think that this study allows interesting considerations. The prognostic value of metabolic and endocrine diseases in critically ill patients has been widely investigated. As an example, Padhi et al.[2] have very recently shown that low T3 and T4 values are associated with a worse outcome compared to normal values in septic patients and that low T3 levels are independently associated with 28 days mortality.

Nevertheless, for DM the picture is not so clear. In fact, despite the widespread diffusion of the disease, responsible for very serious complications inside and outside the ICU,[34] most of the studies that investigated its role in the outcome of critically ill patients lead to contrasting results. On the one hand, in many studies, DM improved the prognosis, whereas, on the other hand, some papers found DM to be a predictor of mortality in the ICU population.[5]

In this context, the study of Khatib et al.[1] leans toward the former hypothesis, with no impact of DM on mortality, despite the reduced number of patients (acknowledged in the limitations). Nevertheless, their results have been confirmed very recently by the analysis performed by Boyle et al.[5] on a large-scale database of 4107 patients admitted to the ICU with respiratory failure. The authors observed no differences both in terms of ARDS development and in terms of mortality between diabetics and nondiabetics.

We think that the results of this study, with such a large sample size, are a strong confirmation that DM is not related to a worsening of prognosis in critically ill patients with acute respiratory failure. Furthermore, they can be seen as an external validation of all the previous studies that lead to the same conclusions, included the one of Khatib et al.[1]

In conclusion, a more definite picture has finally appeared in critical care medicine, enlightening the role of diabetes. The next challenge is, undoubtedly, to define how many shades of gray are present in this picture, giving a further contribution to the pathophysiological comprehension of these conclusions.

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