title: Central venous-to-arterial carbon dioxide difference as a prognostic tool in high-risk surgical patients.
abstract: BACKGROUND
  The purpose of this study was to evaluate the clinical relevance of high values of central venous-to-arterial carbon dioxide difference (PCO2 gap) in high-risk surgical patients admitted to a postoperative ICU. We hypothesized that PCO2 gap could serve as a useful tool to identify patients still requiring hemodynamic optimization at ICU admission.
  
  
  METHODS
  One hundred and fifteen patients were included in this prospective single-center observational study during a 1-year period. High-risk surgical inclusion criteria were adapted from Schoemaker and colleagues. Demographic and biological data, PCO2 gap, central venous oxygen saturation, lactate level and postoperative complications were recorded for all patients at ICU admission, and 6 hours and 12 hours after admission.
  
  
  RESULTS
  A total of 78 (68%) patients developed postoperative complications, of whom 54 (47%) developed organ failure. From admission to 12 hours after admission, there was a significant difference in mean PCO2 gap (8.7 ± 2.8 mmHg versus 5.1 ± 2.6 mmHg; P = 0.001) and median lactate values (1.54 (1.1-3.2) mmol/l versus 1.06 (0.8-1.8) mmol/l; P = 0.003) between patients who developed postoperative complications and those who did not. These differences were maximal at admission to the ICU. At ICU admission, the area under the receiver operating characteristic curve for occurrence of postoperative complications was 0.86 for the PCO2 gap compared to Sequential Organ Failure Assessment score (0.82), Simplified Acute Physiology Score II score (0.67), and lactate level (0.67). The threshold value for PCO2 gap was 5.8 mmHg. Multivariate analysis showed that only a high PCO2 gap and a high Sequential Organ Failure Assessment score were independently associated with the occurrence of postoperative complications. A high PCO2 gap (≥6 mmHg) was associated with more organ failure, an increase in duration of mechanical ventilation and length of hospital stay.
  
  
  CONCLUSIONS
  A high PCO2 gap at admission in the postoperative ICU was significantly associated with increased postoperative complications in high-risk surgical patients. If the increase in PCO2 gap is secondary to tissue hypoperfusion then the PCO2 gap might be a useful tool complementary to central venous oxygen saturation as a therapeutic target.
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Lille, Lille, France. emmanuel.robin@chru-lille.fr.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Robin
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, Hospital Estaing, University Hospital of Clermont-Ferrand, Clermont-Ferrand, France. efutier@chu-clermontferrand.fr.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Futier
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Lille, Lille, France. oscarpires@hotmail.fr.
authors.forename: Oscar
authors.initials: O
authors.lastname: Pires
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Lille, Lille, France. maher.fleyfel@chru-lille.fr.
authors.forename: Maher
authors.initials: M
authors.lastname: Fleyfel
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Lille, Lille, France. benoit.tavernier@chru-lille.fr.
authors.forename: Benoit
authors.initials: B
authors.lastname: Tavernier
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Lille, Lille, France. gilles.lebuffe@chru-lille.fr.
authors.forename: Gilles
authors.initials: G
authors.lastname: Lebuffe
authors.affiliation: Department of Anaesthesiology and Intensive Care Medicine, University Hospital of Lille, Lille, France. benoit.vallet@sante.gouv.fr.
authors.forename: Benoit
authors.initials: B
authors.lastname: Vallet
mesh_terms: D000368:Aged; D001784:Blood Gas Analysis / Q000379:methods*; D002245:Carbon Dioxide / Q000097:blood*; D002405:Catheterization, Central Venous / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000097:blood* / Q000175:diagnosis* / Q000209:etiology; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D019616:Thoracic Surgical Procedures / Q000009:adverse effects
chemical_list: D002245:Carbon Dioxide