200

1. PEEP 10-5 (∆LV20-rel = 0.9*∆LV20-abs – 73) r = 0.911 p<0.01 1200 PEEP 15-5 (∆LV20-rel = 0.87*∆LV20-abs – 85) r = 0.948 p<0.01 1000 800 ∆LV20-rel (ml) 600 ∆ EELV0 400 ∆LV20-rel 200 0 0 500 1000 1500 ∆LV20-abs (ml) Figure E2. Correlations of lung volume recruitment measurements at 20 cmH2O airway pressure. Recruitment assessed with the relative volume method did not include changes in EELV0 (∆LV20-rel) and recruitment assessed with the absolute volume method included EELV0 changes (∆LV20-abs). Open circles represent recruitment at PEEP 10 compared to PEEP 5, solid circles represent recruitment at PEEP 15 compared to PEEP 5. The dotted line is the reference line (a 1:1 correlation). The dashed line and solid line represent the correlations between the two methods. The vertical distance from the reference line to the correlation line is the amount that the relative volume method underestimated the absolute volume method; the underestimation corresponds to the changes in EELV0 (∆EELV0). There were no significant correlations between recruitment measured with the relative volume technique and the changes in EELV0 (Figure E3 [see Supplemental Digital Content 5, http://links.lww.com/CCM/A133]). The correlation between recruitment measured with the absolute volume method and the changes in EELV0 was only significant at PEEP 15 (Figure E3). It is important to remember that several factors may explain this lack of correlation. While EELV0 changes are measured at 0 cmH2O of airway pressure, LV20 is arbitrarily measured at 20 cmH2O of airway pressure. The volume at this pressure depends on several factors, including the compliance of the respiratory system (affected by both thoracic and pulmonary compliance), the open lung units that are distended, the lung units recruited between ZEEP and PEEP, and the different specific compliances of the recruited vs normal lung units. The lack of correlation indicates that changes in EELV0 cannot be predicted by the measured recruitment.