Utility of changes in end-tidal carbon dioxide after volume expansion to assess fluid responsiveness in the operating room: a prospective observational study

Br J Anaesth. 2020 Nov;125(5):672-679. doi: 10.1016/j.bja.2020.07.018. Epub 2020 Aug 27.


Background: From a physiological viewpoint, changes in end-tidal carbon dioxide (EtCO2) could be a simple, noninvasive, and inexpensive way to monitor changes in cardiac index. This study aimed to assess the utility of changes in EtCO2 as a marker of fluid responsiveness after volume expansion in the operating room.

Methods: A prospective observational study was conducted in a tertiary university teaching hospital, from August 2018 to February 2019. A total of 109 non-consecutive, mechanically ventilated adults undergoing neurosurgery in the supine position with cardiac output monitors were included. Patients with major respiratory disease, arrhythmia, or heart failure were excluded. Volume expansion with 250 ml of saline 0.9% was performed over 10 min to maximise cardiac output during surgery, according to current guidelines. A positive fluid challenge was defined as an increase in stroke volume index of more than 10% from baseline. Changes in stroke volume index (monitored using pulse contour analysis) and EtCO2 were recorded before and after infusion.

Results: A total of 242 fluid challenges in 114 patients were performed, of which 26.9% were positive. Changes in EtCO2 > 1.1% induced by infusions had utility for identifying fluid responsiveness, with a sensitivity of 62.9% (95% confidence interval [CI], 62.5-63.3%) and a specificity of 77.8% (95% CI, 77.6-78.1%). The area under the receiver operating characteristic curve for changes in EtCO2 after volume expansion was 0.683 (95% CI, 0.680-0.686).

Conclusions: Changes in EtCO2 induced by rapid infusion of 250 ml saline 0.9% lacked accuracy for identifying fluid responsiveness in mechanically ventilated patients in the operating room.

Clinical trial registration: NCT03635307.

Keywords: cardiac output; end-tidal carbon dioxide; fluid responsiveness; haemodynamic; stroke volume.

Publication types

  • Observational Study

MeSH terms

  • Aged
  • Blood Volume*
  • Carbon Dioxide / blood*
  • Female
  • Fluid Therapy / methods*
  • Hemodynamics
  • Humans
  • Male
  • Middle Aged
  • Neurosurgical Procedures
  • Operating Rooms
  • Predictive Value of Tests
  • Prospective Studies
  • Respiration, Artificial
  • Stroke Volume
  • Supine Position


  • Carbon Dioxide

Associated data

  • ClinicalTrials.gov/NCT03635307