title: End-tidal carbon dioxide is better than arterial pressure for predicting volume responsiveness by the passive leg raising test.
abstract: OBJECTIVE
  In stable ventilatory and metabolic conditions, changes in end-tidal carbon dioxide (EtCO(2)) might reflect changes in cardiac index (CI). We tested whether EtCO(2) detects changes in CI induced by volume expansion and whether changes in EtCO(2) during passive leg raising (PLR) predict fluid responsiveness. We compared EtCO(2) and arterial pulse pressure for this purpose.
  
  
  METHODS
  We included 65 patients [Simplified Acute Physiology Score (SAPS) II = 57 ± 19, 37 males, under mechanical ventilation without spontaneous breathing, 15 % with chronic obstructive pulmonary disease, baseline CI = 2.9 ± 1.1 L/min/m(2)] in whom a fluid challenge was decided due to circulatory failure and who were monitored by an expiratory-CO(2) sensor and a PiCCO2 device. In all patients, we measured arterial pressure, EtCO(2), and CI before and after a fluid challenge. In 40 patients, PLR was performed before fluid administration. The PLR-induced changes in arterial pressure, EtCO(2), and CI were recorded.
  
  
  RESULTS
  Considering the whole population, the fluid-induced changes in EtCO(2) and CI were correlated (r (2) = 0.45, p = 0.0001). Considering the 40 patients in whom PLR was performed, volume expansion increased CI ≥ 15 % in 21 "volume responders." A PLR-induced increase in EtCO(2) ≥ 5 % predicted a fluid-induced increase in CI ≥ 15 % with sensitivity of 71 % (95 % confidence interval: 48-89 %) and specificity of 100 (82-100) %. The prediction ability of the PLR-induced changes in CI was not different. The area under the receiver-operating characteristic (ROC) curve for the PLR-induced changes in pulse pressure was not significantly different from 0.5.
  
  
  CONCLUSIONS
  The changes in EtCO(2) induced by a PLR test predicted fluid responsiveness with reliability, while the changes in arterial pulse pressure did not.
authors.affiliation: AP-HP, Hôpital de Bicêtre, Service de Réanimation Médicale, 78, rue du Général Leclerc, 94270, Le Kremlin-Bicêtre, France. xavier.monnet@bct.aphp.fr
authors.forename: Xavier
authors.initials: X
authors.lastname: Monnet
authors.forename: Aurélien
authors.initials: A
authors.lastname: Bataille
authors.forename: Eric
authors.initials: E
authors.lastname: Magalhaes
authors.forename: Jérôme
authors.initials: J
authors.lastname: Barrois
authors.forename: Marine
authors.initials: M
authors.lastname: Le Corre
authors.forename: Clément
authors.initials: C
authors.lastname: Gosset
authors.forename: Laurent
authors.initials: L
authors.lastname: Guerin
authors.forename: Christian
authors.initials: C
authors.lastname: Richard
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Teboul
mesh_terms: D062186:Arterial Pressure; D002245:Carbon Dioxide / Q000032:analysis*; D002302:Cardiac Output / Q000502:physiology*; D005260:Female; D006801:Humans; D035002:Lower Extremity / Q000098:blood supply*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology; D012680:Sensitivity and Specificity; D013990:Tidal Volume
chemical_list: D002245:Carbon Dioxide