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BackgroundThe purpose of the study was to analyze the characteristics and evolution of non-invasive mechanical ventilation (NIV) in the postoperative period of heart surgery in children.MethodsRetrospective observational study including all children requiring NIV after heart surgery in a single center pediatric intensive care unit (PICU) between 2001 and 2012. Demographic characteristics, ventilation parameters and outcomes were registered, comparing the first 6 years of the study with the last 6 years.Results935 children required invasive or non-invasive mechanical ventilation, of which 200 (21.4) received NIV. The median duration of NIV was 3 days. Mortality rate was 3.9%. The use of NIV increased from 13.2% in the first period to 29.2% in the second period (p <0.001). Continuous positive airway pressure (CPAP) was the most common modality of NIV (65.5%). The use of bilevel positive airway pressure mode (BIPAP) increased from 15% in the first period to 42.9% in the second period (p < 0.001). The nasopharyngeal tube was the most common interface (66%), but the use of nasal cannula increased from 3.3 to 41.4% in the second period (p < 0.001). NIV failed in 15% of patients. The mortality rate did not change, the duration of NIV decreased and the PICU length of stay increased throughout the study.ConclusionsNIV is increasingly being used in the postoperative period of heart surgery in our center with an 85% success rate and is associated with a lesser need for invasive mechanical ventilation. CPAP was the most common modality and the “nasopharyngeal tube” was the most common interface in our study although, in the latter years, the use of BIPAP and nasal cannula has increased significantly.

The equation of state (ES) is a subject of the greatest interest in Statistical Mechanics and Chemical Physics. In this paper we present a simple and rigorous method by which the ES of simple systems can be obtained. The derivation requires at most the knowledge of the Maxwell distribution. The well known formula for the ES of a one-dimensional system of hard rods is derived exactly, as an illustration. The method can be generalized to higher dimensionality and to include other types of potential.