Περίληψη:
Objective., To assess the effects of different positive end-expiratory
pressure (PEEP) levels (0, 5, 10, and 15 cm H2O) on tidal expiratory
flow limitation (FL), regional intrinsic positive end-expiratory
pressure (PEEPi) inhomogeneity, alveolar recruited volume (Vrec),
respiratory mechanics, and arterial blood gases in mechanically
ventilated patients with acute respiratory distress syndrome (ARDS).
Design: Prospective clinical study.
Setting. Multidisciplinary intensive care unit of a university hospital.
Patients: Thirteen sedated, mechanically ventilated patients during the
first 2 days of ARDS.
Interventions: Detection of tidal FL and evaluation of total dynamic
PEEP (PEEPt,dyn), total static PEEP (PEEPt,st), respiratory mechanics,
and Vrec from pressure, flow, and volume traces provided by the
ventilator. The average (+/-SD) tidal volume was 7.1 +/- 1.5 mL/kg, the
total cycle duration was 2.9 +/- 0.45 sees, and the duty cycle was 0.35
+/- 0.05.
Measurements: Tidal FL was assessed using the negative expiratory
pressure technique. Regional PEEPi inhomogeneity was assessed as the
ratio of PEEPt,dyn to PEEPt,st (PEEPi inequality index), and Vrec was
quantified as the difference in lung volume at the same airway pressure
between quasi-static inflation volume-pressure curves on zero
end-expiratory pressure (ZEEP) and PEEP.
Results. On ZEEP, seven patients exhibited FL amounting to 31 +/- 8% of
tidal volume. They had higher PEEPt,st and PEEPi,st (p < .001) and lower
PEEPi inequality index (p < .001) than the six nonflow-limited (NFL)
patients. Two FL patients became NFL with PEEP of 5 cm H2O and five with
PEEP of 10 cm H2O. In both groups, Pao(2) increased progressively with
PEEP. In the FL group, there was a significant correlation of Pao(2) to
PEEPi inequality index (p = .002). For a given PEEP, Vrec was greater in
NFL than FL patients, and a significant correlation of Pao(2) to Vrec
(p, < .001) was found only in the NFL group.
Conclusions: We conclude that on ZEEP, tidal FL is common in ARDS
patients and is associated with greater regional PEEPi inhomogeneity
than in NFL patients. With PEEP of 10 cm H2O, flow limitation with
concurrent cyclic dynamic airway compression and re-expansion and the
risk of “low lung volume injury” were absent in all patients. In FL
patients, PEEP induced a significant increase in Pao(2), mainly because
of the reduction of regional PEEPi inequality, whereas in the NFL group,
arterial oxygenation was improved satisfactorily because of alveolar
recruitment.
Συγγραφείς:
Koutsoukou, A
Bekos, B
Sotiropoulou, C
Koulouris, NG and
Roussos, C
Milic-Emili, J
