End-tidal carbon dioxide variation after a 100- and a 500-ml fluid challenge to assess fluid responsiveness

EtCO2 variation has been advocated replacing cardiac output measurements to evaluate fluid responsiveness (FR) during sepsis. The ability of EtCO2 variation after a fluid challenge to detect FR in the context of general anaesthesia has not been investigated. Forty patients were prospectively studied. They underwent general anaesthesia for major surgeries. CO was measured by transoesophageal Doppler, and EtCO2 was recorded as well as other haemodynamic parameters [heart rate (HR), mean arterial pressure (MAP), pulse pressure (PP)] at baseline, after 100-ml fluid load over 1 min, and at the end of the 500-ml fluid load. We measured the variation of EtCO2 at 100 (ΔEtCO2100) and 500 ml (ΔEtCO2500), and ROC curves were generated. A threshold for ΔEtCO2 to predict FR was determined with receiver operating curves (ROC) analysis. The primary end point was the ability of EtCO2 variation after a 500-ml fluid load to diagnose FR.

Fifteen patients (38 %) were fluid responders. ROC analysis showed that for a threshold of 5.8 % (ΔEtCO2500), sensitivity was 0.6 IC 95 % [0.33; 0.86] and specificity was 1.0 IC 95 % [1.0; 1.0]. An absolute increase of more than 2 mmHg of EtCO2 is specific to diagnose fluid responsiveness (spe = 96 [88-100] %, sens = 60 [33-88] %, AUC = 0.80 [0.96-0.65]). HR, MAP, and PP variations and ΔEtCO2100 did not bring information to predict or diagnose FR. During fluid challenge, the correlation between CI variation and EtCO2 variation was r = 0.566, p < 0.001.

During surgery, when alveolar ventilation and CO2 production are constant, ΔEtCO2500 is fairly reliable to assess FR. When the variation of EtCO2 is >5.8 %, all patients were responders, but no conclusion could be done when this variation was <5.8 %. ΔEtCO2100 failed to predict FR. Trial registration CPP Lyon Sud Est III ref: 2013-027 B, Number ID RCB: 2013-A00729-36 delivered by the ANSM).