Prone position ameliorates lung elastance and increases functional residual capacity independently from lung recruitment

BACKGROUND: Prone position is used to recruit collapsed dependent lung regions during severe acute respiratory distress syndrome, improving lung elastance and lung gas content. We hypothesised that, in the absence of recruitment, prone position would not result in any improvement in lung mechanical properties or gas content compared to supine position. METHODS: Ten healthy pigs under general anaesthesia and paralysis underwent a pressure-volume curve of the respiratory system, chest wall and lung in supine and prone positions; the respective elastances were measured. A lung computed tomography (CT) scan was performed in the two positions to compute gas content (i.e. functional residual capacity (FRC)) and the distribution of aeration. Recruitment was defined as a percentage change in non-aerated lung tissue compared to the total lung weight. RESULTS: Non-aerated (recruitable) lung tissue was a small percentage of the total lung tissue weight in both positions (4\u2009\ub1\u20093 vs 1\u2009\ub1\u20091 %, supine vs prone, p\u2009=\u20090.004). Lung elastance decreased (20.5\u2009\ub1\u20091.8 vs 15.5\u2009\ub1\u20091.6 cmH2O/l, supine vs prone, p\u2009<\u20090.001) and functional residual capacity increased (380\u2009\ub1\u200982 vs 459\u2009\ub1\u200960 ml, supine vs prone, p\u2009=\u20090.025) in prone position; specific lung elastance did not change (7.0\u2009\ub1\u20090.5 vs 6.5\u2009\ub1\u20090.5 cmH2O, supine vs prone, p\u2009=\u20090.24). Lung recruitment was low (3\u2009\ub1\u20092 %) and was not correlated to increases in functional residual capacity (R (2) 0.2, p\u2009=\u20090.19). A higher amount of well-aerated and a lower amount of poorly aerated lung tissue were found in prone position. CONCLUSIONS: In healthy pigs, prone position ameliorates lung mechanical properties and increases functional residual capacity independently from lung recruitment, through a redistribution of lung aeration

High positive end-expiratory pressure : only a dam against edema formation?

Introduction Healthy piglets ventilated with Tidal Volume (VT) close to inspiratory capacity (IC; maximal physiological lung inflation) always largely increase their lung weight within 24-36 hours [1], as for fluid filtration through a disrupted blood-gas barrier. We have recently noted that when a similar degree of lung inflation is mainly due to high Positive End-Expiratory Pressure (PEEP), lung weight never changes. Aim To clarify whether PEEP acts only as a dam, preventing fluid filtration through a blood-gas barrier that is invariably damaged when lungs are inflated up to their physiological limit. If that is the case, removal of PEEP will rapidly lead to lung edema formation. Methods Three healthy piglets (21\ub12 Kg) had their IC measured with lung computed tomography (CT). They were then ventilated with high PEEP (around 75% of IC) and low VT (25% of IC). After 36 hours, PEEP was removed and ventilation continued with low VT for 18 hours. Lung weight was measured at the beginning (CT) and end (balance, following autopsy) of the study. Results IC was 1023\ub1136 ml. Accordingly, animals were initially ventilated with PEEP 19\ub11 cmH2O (volume of gas 898\ub1211 ml) and VT 213\ub112 ml. Following PEEP removal, VT was 217\ub121 ml. As shown in figure, lung weight never increased. InitialFinalLung Weight ( g)200300400 Figure. Individual changes in lung weight. p = 0.13 ( Paired t-test ) Conclusion Our preliminary findings suggest that high PEEP does not merely act as a dam, as its removal is not followed by an increase in lung weight. We therefore hypothesize that ventilation with high PEEP and low VT somehow protects the blood-gas barrier. [1]: Protti et al. AJRCCM, 2011; 183(10):1354-1362

Role of tidal volume and positive end-expiratory pressure in the development of Ventilator-Induced Lung Injury

Puede afirmarse que cuando en el Mercurio Peruano y en marzo de 1829 (es decir apenas ocho años después de la declaración de la independencia nacional), Felipe Pardo y Aliaga publica la sátira en verso "El carnaval de Lima", se inicia la historia del Costumbrismo en sentido estricto en el Perú O si se prefiere tomar como referencia una obra de mayor entidad, puede sostenerse mejor que el hito inicial está dado por el estreno de Frutos de la Educación, la primera comedia del mismo Pardo (6 de ..