title: Comparison of Minimally and More Invasive Methods of Determining Mixed Venous Oxygen Saturation.
abstract: OBJECTIVE
  To investigate the accuracy of a minimally invasive, 2-step, lookup method for determining mixed venous oxygen saturation compared with conventional techniques.
  
  
  METHODS
  Single-center, prospective, nonrandomized, pilot study.
  
  
  METHODS
  Tertiary care hospital, university setting.
  
  
  METHODS
  Thirteen elective cardiac and vascular surgery patients.
  
  
  METHODS
  All participants received intra-arterial and pulmonary artery catheters. Minimally invasive oxygen consumption and cardiac output were measured using a metabolic module and lithium-calibrated arterial waveform analysis (LiDCO; LiDCO, London), respectively. For the minimally invasive method, Step 1 involved these minimally invasive measurements, and arterial oxygen content was entered into the Fick equation to calculate mixed venous oxygen content. Step 2 used an oxyhemoglobin curve spreadsheet to look up mixed venous oxygen saturation from the calculated mixed venous oxygen content. The conventional "invasive" technique used pulmonary artery intermittent thermodilution cardiac output, direct sampling of mixed venous and arterial blood, and the "reverse-Fick" method of calculating oxygen consumption.
  
  
  RESULTS
  LiDCO overestimated thermodilution cardiac output by 26%. Pulmonary artery catheter-derived oxygen consumption underestimated metabolic module measurements by 27%. Mixed venous oxygen saturation differed between techniques; the calculated values underestimated the direct measurements by between 12% to 26.3%, this difference being statistically significant.
  
  
  CONCLUSIONS
  The magnitude of the differences between the minimally invasive and invasive techniques was too great for the former to act as a surrogate of the latter and could adversely affect clinical decision making.
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine and Health Sciences, Stellenbosch University and Tygerberg Hospital, Cape Town, South Africa. Electronic address: smitmarli@yahoo.com.
authors.forename: Marli
authors.initials: M
authors.lastname: Smit
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine and Health Sciences, Stellenbosch University and Tygerberg Hospital, Cape Town, South Africa.
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Levin
authors.affiliation: Department of Anesthesiology and Critical Care, Faculty of Medicine and Health Sciences, Stellenbosch University and Tygerberg Hospital, Cape Town, South Africa.
authors.forename: Johan F
authors.initials: JF
authors.lastname: Coetzee
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002302:Cardiac Output; D006348:Cardiac Surgical Procedures / Q000379:methods; D005260:Female; D006801:Humans; D008094:Lithium / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010108:Oxyhemoglobins / Q000032:analysis; D010865:Pilot Projects; D011446:Prospective Studies; D063128:Tertiary Health Care; D013815:Thermodilution; D014656:Vascular Surgical Procedures / Q000379:methods; D058067:Wavelet Analysis
chemical_list: D010108:Oxyhemoglobins; D008094:Lithium; D010100:Oxygen
keywords: cardiac output; minimally invasive; mixed venous oxygenation; oxygen consumption; pulmonary artery catheter