Spontaneous variability of arterial oxygenation in critically ill mechanically ventilated patients.
OBJECTIVE
To assess the magnitude of spontaneous variability of arterial oxygenation and oxygen tension-based indices over time in medical intensive care unit (ICU) patients and to study whether high positive end-expiratory pressure (PEEP) or inverse inspiratory-to-expiratory (I:E) ratio ventilation (IRV) results in a greater variability than low PEEP with conventional I:E ratio ventilation.


METHODS
Prospective study.


METHODS
Medical ICU in a tertiary medical center.


METHODS
23 patients requiring a pulmonary artery floating catheter for hemodynamic monitoring.


METHODS
After being completely sedated, patients were randomized to receive pressure-control ventilation at setting A: high PEEP (15 cm H2O) with conventional I:E ratio (1:2) and setting B: inverse I:E ratio (2:1) with low PEEP (5 cm H2O) alternately, and then at setting C: low PEEP (5 cm H2O) with conventional I:E ratio (1:2). Each ventilation setting lasted 1 h.


RESULTS
The arterial and mixed venous blood samples were measured simultaneously at baseline (time 0), and at 15, 30, 45, and 60 min thereafter. The coefficient of variation (CV) of arterial oxygen tension (PaO2) over time was 5.9 % for setting A, 7.2 % for setting B, and 6.9 % for setting C. ANOVA showed no significant differences in CVs of PaO2 between the three settings. Oxygen tension-based indices, alveolar-arterial oxygen difference (A-aDO2) and PaO2/ PAO2 (alveolar oxygen tension), displayed CVs equal to that of PaO2; the CV of A-aDO2/PaO2 was significantly greater than that of PaO2.


CONCLUSIONS
In critically ill medical ICU patients, despite sedation, the spontaneous variability in PaO2 over time is substantial. A high PEEP or IRV does not contribute to the increased variation in PaO2.
Tsai
Y H
YH
Department of Internal Medicine, Chang Gung Memorial Hospital, Taipei, Taiwan.
Lin
M C
MC
Hsieh
M J
MJ
Chen
N H
NH
Tsao
T C
TC
Lee
C H
CH
Huang
C C
CC
D018806:APACHE; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001784:Blood Gas Analysis; D002407:Catheterization, Swan-Ganz; D016001:Confidence Intervals; D016638:Critical Illness; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D012131:Respiratory Insufficiency / Q000097:blood* / Q000628:therapy