Differential cardiovascular responses during weaning failure: effects on tissue oxygenation and lactate.
OBJECTIVE
To test the following two hypotheses during weaning failure: (a) mixed venous oxygen saturation (SvO2) does not decrease in patients whose oxygen consumption does not increase, and (b) blood lactate may increase in patients who demonstrate substantial decreases in SvO2.


METHODS
A prospective observational and physiological study in a 30-bed university intensive care unit.


METHODS
18 patients who failed weaning and 12 patients who succeeded weaning (controls).


RESULTS
Hemodynamics, global tissue oxygenation, cardiovascular response (cardiac index/oxygen extraction diagram), and blood lactate were measured in ventilator-supported patients undergoing a spontaneous breathing trial. In patients who failed without having increased their oxygen consumption (n=9) the increase in oxygen delivery was accompanied by a decrease in oxygen extraction (by 15+/-4%). In patients who failed (n=9) having increased their oxygen consumption (by>10%) this increase was met mainly by an increase in oxygen extraction (by 30+/-7%). SvO2 increased by 2+/-1% in the former patients, whereas it decreased by 20+/-5% in the latter. Arterial lactate increased (range 2.3-3.1 mM/l) in only three patients who failed to have increased oxygen consumption and exhibited heart failure and the highest decreases in SvO2 (by 12-39%).


CONCLUSIONS
Patients whose SvO2 does not decrease during weaning failure do not have increased oxygen consumption probably due to respiratory center depression in some of them. Patients whose SvO2 decreases have increased oxygen consumption.
Zakynthinos
Spyros
S
Department of Critical Care and Pulmonary Services, University of Athens Medical School, Evangelismos Hospital, 45-47 Ipsilandou Str., 10675, Athens, Greece. szakynthinos@yahoo.com
Routsi
Christina
C
Vassilakopoulos
Theodoros
T
Kaltsas
Panagiotis
P
Zakynthinos
Epaminondas
E
Kazi
Danai
D
Roussos
Charis
C
D000368:Aged; D000369:Aged, 80 and over; D002302:Cardiac Output; D002303:Cardiac Output, Low / Q000503:physiopathology; D016022:Case-Control Studies; D005260:Female; D006333:Heart Failure / Q000503:physiopathology; D006439:Hemodynamics; D006801:Humans; D019344:Lactic Acid / Q000097:blood*; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood*; D011446:Prospective Studies; D017211:Treatment Failure; D015300:Ventilator Weaning
D019344:Lactic Acid; D010100:Oxygen