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Figure 1 | Critical Care

Figure 1

From: Overdistension in ventilated children

Figure 1

Detection of overdistension using the C20/C ratio and c coefficient on the same dynamic volume–pressure curves of two representative patients. The C20/C ratio was calculated on the inspiratory part of the V-P loop obtained during mechanical ventilation. It is the ratio of the compliance calculated from the last 20% of the inspiratory V-P curve (C20) to the total compliance calculated from the entire slope of the inspiratory curve (C) between zero flow points. A C20/C ratio below 0.80 is indicative of overdistension [20]. The nonlinear coefficient c of a SOPE (see Equation 5) was fitted to the V-P data obtained during a period of constant flow. The sign of this coefficient c describes the curvature of the V-P curve. When a convex shape with a progressive decrease in slope with increasing inflation volume is observed, the coefficient c is negative, indicating overdistension; when a concave shape with a progressive increase in slope with increasing inflation volume is observed, the coefficient c is positive [23]. For patient A, the positive value of coefficient c and the C20/C ratio in excess of 0.80 were not indicative of overdistension. For patient B, the negative value of coefficient c and the C20/C ratio below 0.80 were both indicative of overdistension.

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