title: Correlation of central venous-arterial and mixed venous-arterial carbon dioxide tension gradient with cardiac output during neurosurgical procedures in the sitting position.
abstract: OBJECTIVE
  The study was conducted to evaluate the correlation of central venous-arterial and mixed venous-arterial pCO(2) gradient with cardiac output in patients being operated in the sitting position.
  
  
  METHODS
  Fifty-one patients, aged 41-69 years, classified as American Society of Anesthesiologists physical status II and III, scheduled to undergo elective neurosurgical procedures in the sitting position, were enrolled in this prospective cohort study. Simultaneous blood gas samples from arterial, central venous and pulmonary artery catheters were collected at four different time points during supine and sitting position. Cardiac index (CI) determination was accomplished simultaneously, with continuous cardiac output technique. The mixed venous-arterial pCO(2) and central venous-arterial pCO(2) gradients were calculated and related to CI at the specific time points, thus a total of 204 points of comparison were obtained.
  
  
  RESULTS
  Changing from the supine to the sitting position induced a significant deterioration of CI, right atrial pressure, mean pulmonary arterial pressure and pulmonary wedge pressure. The mean delta pCO(2) difference (bias) in the four time points ranged between -0.07 and -0.27. The upper (1.59-1.71 mmHg) and lower limits of agreement (-2.16 to -1.82 mmHg) were quite narrow, suggesting an acceptable overall agreement between the mixed and central venous pCO(2) differences. The coefficient of determination (R(2)) between the venous-arterial pCO(2) and CI for mixed and central venous circulations was 0.830 and 0.760 (P < 0.001 for both), respectively. In contrast, R(2) values between mixed and central venous oxygen saturation values and CI were 0.324 and 0.286, respectively (P < 0.001 for both), illustrating a rather weak relationship.
  
  
  CONCLUSIONS
  It seems that venous-arterial pCO(2) values obtained from mixed and central venous circulations can be reliably interchanged in estimating CI in patients undergoing neurosurgical procedures in the sitting position. Thus, central venous-arterial pCO(2) gradient could serve as a useful and simple method for estimating cardiac performance, in which further invasive monitoring is not strongly indicated.
authors.affiliation: Department of Anaesthesiology and Intensive Care, AHEPA University Hospital, Thessaloniki, Greece. tsaousig@otenet.gr
authors.forename: Georgia G
authors.initials: GG
authors.lastname: Tsaousi
authors.forename: Konstantinos A
authors.initials: KA
authors.lastname: Karakoulas
authors.forename: Ekaterini N
authors.initials: EN
authors.lastname: Amaniti
authors.forename: Ioanna D
authors.initials: ID
authors.lastname: Soultati
authors.forename: Maria D
authors.initials: MD
authors.lastname: Zouka
authors.forename: Dimitrios G
authors.initials: DG
authors.lastname: Vasilakos
mesh_terms: D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D001795:Blood Pressure Determination; D002245:Carbon Dioxide / Q000097:blood*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016343:Monitoring, Intraoperative / Q000379:methods*; D019635:Neurosurgical Procedures / Q000379:methods*; D011187:Posture; D011446:Prospective Studies; D011669:Pulmonary Wedge Pressure; D016683:Supine Position
chemical_list: D002245:Carbon Dioxide