title: Tissue oxygen saturation as an early indicator of delayed lactate clearance after cardiac surgery: a prospective observational study.
abstract: BACKGROUND
  In this observational study near infrared spectroscopy (NIRS) was evaluated as a non-invasive monitor of impaired tissue oxygenation (StO2) after cardiac surgery. StO2, cardiac output, mixed venous oxygen saturation and mean arterial pressure were compared with lactate clearance as established measure for sufficient tissue perfusion and oxygen metabolism.
  
  
  METHODS
  Forty patients after cardiac surgery (24 aortocoronary bypass grafting, 5 heart valve, 3 ascending aorta and 8 combined procedures) were monitored until postoperative day 1 with NIRS of the thenar muscle (InSpectra™ StO2-monitor, Hutchinson Technology), a pulmonary-artery catheter and intermittent blood gas analyses for the assessment of lactate clearance.
  
  
  RESULTS
  StO2 was reduced 4 h after surgery (75 ± 6 %), but recovered at day 1 (84 ± 5 %), while lactate concentration remained increased. Using uni- and multivariate regression analysis, minimum StO2 (r = 0.46, p <0.01) and cardiac index (r = 0.40, p <0.05) correlated with lactate clearance at day 1, while minimum mixed venous saturation and mean arterial pressure did not. In a receiver-operating characteristics (ROC) analysis, minimum StO2 (with a threshold of 75 %) predicted a lactate clearance <10 % at day 1 with an area under the ROC-curve of 0.83, a sensitivity of 78 % and a specificity of 88 %. In the subgroup with StO2  <75 %, troponin and creatine kinase MB were significantly increased at day 1.
  
  
  CONCLUSIONS
  StO2 below 75 % in the first hours after surgery was a better early indicator of persistent impaired lactate clearance at day 1 than cardiac index, mixed venous oxygen saturation or mean arterial pressure.
authors.affiliation: Department of Intensive Care, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. rkopp@ukaachen.de.
authors.forename: Rüdger
authors.initials: R
authors.lastname: Kopp
authors.affiliation: Department of Intensive Care, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. dommann@gmx.com.
authors.forename: Katja
authors.initials: K
authors.lastname: Dommann
authors.affiliation: Department of Intensive Care, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. rrossaint@ukaachen.de.|Department of Anaesthesiology, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. rrossaint@ukaachen.de.
authors.forename: Rolf
authors.initials: R
authors.lastname: Rossaint
authors.affiliation: Department of Anaesthesiology, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. gschaelte@ukaachen.de.
authors.forename: Gereon
authors.initials: G
authors.lastname: Schälte
authors.affiliation: Department of Anaesthesiology, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. ogrottke@ukaachen.de.
authors.forename: Oliver
authors.initials: O
authors.lastname: Grottke
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. jspillner@ukaachen.de.
authors.forename: Jan
authors.initials: J
authors.lastname: Spillner
authors.affiliation: Department of Anaesthesiology, University Hospitals Leuven, Herestraat 49, 3000 Leuven, Belgium. steffen.rex@uzleuven.be.|Department of Cardiovascular Sciences, Katholieke Universiteit Leuven, Herestraat 49, 3000, Leuven, Belgium. steffen.rex@uzleuven.be.
authors.forename: Steffen
authors.initials: S
authors.lastname: Rex
authors.affiliation: Department of Intensive Care, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. gmarx@ukaachen.de.|Department of Anaesthesiology, University Hospital RWTH Aachen, RWTH Aachen University, Pauwelsstr. 30, 52074, Aachen, Germany. gmarx@ukaachen.de.
authors.forename: Gernot
authors.initials: G
authors.lastname: Marx
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D062186:Arterial Pressure / Q000502:physiology; D001784:Blood Gas Analysis; D002302:Cardiac Output / Q000502:physiology; D006348:Cardiac Surgical Procedures / Q000379:methods*; D002407:Catheterization, Swan-Ganz / Q000379:methods; D005260:Female; D006801:Humans; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010100:Oxygen / Q000378:metabolism*; D011446:Prospective Studies; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D019265:Spectroscopy, Near-Infrared / Q000379:methods*; D013997:Time Factors
chemical_list: D019344:Lactic Acid; D010100:Oxygen