E. Roupie et al., TITRATION OF TIDAL VOLUME AND INDUCED HYPERCAPNIA IN ACUTE RESPIRATORY-DISTRESS SYNDROME, American journal of respiratory and critical care medicine, 152(1), 1995, pp. 121-128
Citations number
35
Categorie Soggetti
Emergency Medicine & Critical Care","Respiratory System
Mechanical ventilation may promote overdistension-induced pulmonary le
sions in patients with acute respiratory distress syndrome (ARDS). The
static pressure-volume (P-V) curve of the respiratory system can be u
sed to determine the lung volume and corresponding static airway press
ure at which lung compliance begins to diminish (the upper inflection
point, or UIP). This fall in compliance may indicate overdistension of
lung units. We prospectively studied 42 patients receiving mechanical
ventilation with an FIO2 of 0.5 or more for at least 24 h. According
to the Lung Injury Score (LIS), 25 patients were classified as having
ARDS (LIS > 2.5), while 17 patients constituted a non-ARDS control gro
up. The P-V curve was obtained every 2 d. Mechanical ventilation initi
ally used standard settings (volume-control mode, a positive end-expir
atory pressure [PEEP] adjusted to the lower inflection point on the P-
V curve, and a tidal volume [VT] of 10 ml/kg). The end-inspiratory pla
teau pressure (Pplat) was compared to the UIP, and VT was lowered when
the Pplat was above the UIP. In the range of lung volume studied on t
he P-V curves (up to 1600 mi), a UIP could be shown in only one contro
l patient (at 23 cm H2O). By contrast, a UIP was present on the P-V cu
rve obtained from all patients with ARDS, corresponding to a mean airw
ay pressure of 26 +/- 6 cm H2O, a lung volume of 850 +/- 200 ml above
functional residual capacity and 610 +/- 235 ml above PEEP. During the
course of ARDS, Pplat rose above the UIP in 20 (80%) of the 25 patien
ts (Pplat of 31 +/- 5 cm H2O, range 22 to 48, compared with UIP of 24
+/- 4 cm H2O, range 18 to 37, p < 0.001). In these patients, VT was re
duced by 2.2 +/- 0.9 ml/kg (1 to 4.2 ml/kg) in an attempt to keep Ppla
t below the UIP. This induced a rise in Pa-CO2 from 44 +/- 10 to 77 +/
- 25 mm Hg (p < 0.01) but no change in the Pa-O2/FIO2 ratio. We conclu
de that a UIP can be demonstrated in all patients with ARDS and that 8
0% of them would need a reduction in VT based on this criterion; this
strategy may result in marked hypercapnia, without a significant chang
e in oxygenation.