title: Effects of inspired oxygen fraction in discriminating venous from arterial blood in percutaneous central venous catheterization under general anesthesia.
abstract: BACKGROUND
  A low fraction of inspired oxygen (FiO(2)) increases venous deoxygenated hemoglobin concentrations, making the color of the blood darker. The present study was aimed to determine the effects of FiO(2) on the ability to discriminate venous from arterial blood.
  
  
  METHODS
  One-hundred and sixty surgical patients undergoing percutaneous central venous access of the internal jugular vein were randomly assigned to receive an FiO(2) of 0.2, 0.4, 0.6, or 1.0 (n = 40 each) for at least 20 min prior to central line placement under general anesthesia. Vascular access was achieved with a 22-gauge needle; 2 ml of blood was withdrawn and shown to three physicians including the operator. Each of them was asked to identify the blood as 'arterial', 'venous' or 'not sure'. Simultaneous blood gas analysis of the samples was performed on blood taken from the puncture site and the artery after visual comparison to confirm blood's origin and hemodynamic measurements.
  
  
  RESULTS
  Lowering FiO(2) progressively increased venous deoxygenated hemoglobin concentrations (2.24 ± 1.12, 3.30 ± 1.08, 3.66 ± 1.15, and 3.71 ± 1.33 g/dl) in groups having an FiO(2) of 1.0, 0.6, 0.4 and 0.2, respectively (P < 0.001), thereby facilitating the 'venous' blood identification (P < 0.001). Neither heart rate nor mean arterial pressure differed among the groups. None developed hypoxemia (percutaneous hemoglobin oxygen saturation < 90%) in any group during the study period.
  
  
  CONCLUSIONS
  A low FiO(2) increases venous deoxygenated hemoglobin levels, thereby facilitating the recognition by clinicians of its venous origin in percutaneous central venous catheterization under general anesthesia.
authors.affiliation: Department of Anesthesiology and Pain Medicine, Chonnam National University Medical School, Gwangju, Korea.
authors.forename: Dong Yun
authors.initials: DY
authors.lastname: Lim
authors.forename: Dae Wook
authors.initials: DW
authors.lastname: Lee
authors.forename: Eun Ah
authors.initials: EA
authors.lastname: Jang
authors.forename: Seong Heon
authors.initials: SH
authors.lastname: Lee
authors.forename: Hye Jin
authors.initials: HJ
authors.lastname: Jeong
authors.forename: Cheol Won
authors.initials: CW
authors.lastname: Jeong
authors.forename: Seong Wook
authors.initials: SW
authors.lastname: Jeong
authors.forename: Kyung Yeon
authors.initials: KY
authors.lastname: Yoo