A Functional and Morphologic Analysis of Pressure-Controlled Inverse Ratio Ventilation in Oleic Acid-Induced Lung Injury: Computed Tomography

End-expiratory mean lung density during VCV ZEEP (—167 HU) was significantly larger than densities registered during ventilation with VCV PEEP (-333 [pCO.OOl]) and PCIRV (-357 (pCO.OOl). End-expiratory lung densities were equal between VCV PEEP and PCIRV.
Mean lung density at end-inspiration was not significantly different among VCV ZEEP, VCV PEEP, and PCIRV.
Dynamic mean lung density during VCV ZEEP (—260 HU) was significantly larger than densities registered during ventilation with VCV PEEP (—419 HU [pCO.Ol]) and PCIRV (-488 HU [pCO.OOl]). Dynamic mean lung density was equal between VCV PEEP and PCIRV. Figure 1 summarizes the CT density data. purchase antibiotics online

The amount of poorly aerated regions (—200 to —100 HU) was 14 percent at end-expiration with VCV ZEEP and 11 and 12 percent with VCV PEEP and PCIRV, respectively (p<0.001). At end-inspira-tion, poorly aerated regions constituted 7 percent with VCV ZEEP and 5 percent with VCV PEEP and PCIRV (p<0.05). The amount of nonaerated area (—100 to +100 HU) was 54 and 21 percent with VCV ZEEP and considerably smaller with VCV PEEP (28 (pCO.OOl) and 10 percent [pCO.OOl]) and PCIRV (29 (pCO.Ol) and 12 percent [pC0.05]). Thus, at end-ex-piration during VCV ZEEP, almost 70 percent of the lung area was poorly aerated or nonaerated. VCV PEEP and PCIRV both resulted in improved aeration with corresponding percentages of 39 percent (VCV PEEP, pCO.Ol) and 42 percent (PCIRV, pCO.Ol). There was no difference between VCV PEEP and PCIRV (Fig 2). Mean density increased from top to bottom in all three ventilatory modes. This was true both during static and dynamic conditions. VCV PEEP and PCIRV resulted in significantly lower density values in all three zones than did VCV ZEEP.

Figure-1

Figure 1. Computed density values of the right lung during expiratory hold (static expiration), inspiratory hold (static inspiration), and during a full dynamic ventilatory cycle (ventilation frequency 15, scan time 4 ss). Values expressed as mean+1 SD. VCV ZEEP=volume=controlled zero PEEP ventilation; VCV PEEP=volume=controlled PEEP ventilation; PCIRV=pres-sure=controlled inverse ratio ventilation (two asterisks=p<0.01; three asterisks=p<0.001).

Figure-2

Figure 2. Distribution of nonaerated (—100 to +100 HU) and poorly aerated (—200 to —100 HU) regions expressed as percent of total right lung area (percent of ROI)+l SD. Insp=static inspiration; Exp=static expiration; VCV ZEEP=volume-controlled zero PEEP ventilation; VCV PEEP=volume-controlled PEEP ventilation; PCIRV=pressure-controlled inverse ratio ventilation (two asterisks=p<0.01; ns=not significant).

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