title: The marked reduction in mixed venous oxygen saturation during early mobilization after cardiac surgery: the effect of posture or exercise?
abstract: Early mobilization after cardiac surgery induces a marked reduction in mixed venous oxygen saturation (Svo2). Using pulmonary artery catheters and indirect calorimetry, we investigated the effects of exercise and postural change on cardiac index (CI) and Svo2 before and on the first morning after coronary artery bypass surgery. Sixteen patients with an ejection fraction >0.50 were studied at rest, during supine bicycle exercise, and during passive standing. Supine cycling at 30 W increased CI by 1.5 +/- 0.8 L x min(-1) x m(-2) before and 0.9 +/- 0.7 L x min(-1) x m(-2) after surgery (P < 0.05), whereas Svo2 was reduced from 80% +/- 4% at rest to 63 +/- 6% preoperatively (P < 0.05) and from 71% +/- 5% to 46% +/- 11% postoperatively (P < 0.05). Passive standing reduced CI by 0.8 +/- 0.5 L x min(-1) x m(-2) before and 0.3 +/- 0.4 L x min(-1) x m(-2) after surgery (P < 0.05). Svo2 was reduced from 79% +/- 5% to 64% +/- 7% preoperatively (P < 0.05) and from 72% +/- 6% to 60% +/- 6% postoperatively (P < 0.05). The exercise challenge revealed an altered cardiovascular response after surgery, causing a larger reduction in Svo2 for the same workload. Passive standing significantly reduced Svo2 both days, but this effect was less pronounced after surgery. The response to postural change and exercise was altered after surgery and may both contribute to the reduction in Svo2 during postoperative mobilization.
authors.affiliation: Department of Cardiothoracic Anesthesia and Intensive Care, St. Olav University Hospital, Hans Nissens gt 3, N 7018 Trondheim, Norway. Idar.Kirkeby-Garstad@ntnu.no
authors.forename: Idar
authors.initials: I
authors.lastname: Kirkeby-Garstad
authors.forename: Ulrik
authors.initials: U
authors.lastname: Wisløff
authors.forename: Eirik
authors.initials: E
authors.lastname: Skogvoll
authors.forename: Tomas
authors.initials: T
authors.lastname: Stølen
authors.forename: Arnt-Erik
authors.initials: AE
authors.lastname: Tjønna
authors.forename: Roar
authors.initials: R
authors.lastname: Stenseth
authors.forename: Olav F M
authors.initials: OF
authors.lastname: Sellevold
mesh_terms: D000328:Adult; D000368:Aged; D002153:Calorimetry, Indirect; D002302:Cardiac Output; D002407:Catheterization, Swan-Ganz; D001026:Coronary Artery Bypass / Q000534:rehabilitation; D004434:Early Ambulation; D015444:Exercise; D006439:Hemodynamics; D006801:Humans; D019344:Lactic Acid / Q000097:blood; D008297:Male; D008875:Middle Aged; D010100:Oxygen; D010101:Oxygen Consumption; D011187:Posture; D013318:Stroke Volume; D014680:Veins
chemical_list: D019344:Lactic Acid; D010100:Oxygen