Abstract
Background Exhaled carbon dioxide (CO2) reflects cardiac output (CO) provided stable ventilation and metabolism. Detecting CO changes may help distinguish hypovolemia or cardiac dysfunction from other causes of haemodynamic instability. We investigated whether CO2 measured as end-tidal concentration (EtCO2) and eliminated volume per breath (VtCO2) reflect sudden changes in cardiac output (CO). Methods We measured changes in CO, VtCO2, and EtCO2 during right ventricular pacing and passive leg raise in 33 ventilated patients after open heart surgery. CO was measured with oesophageal Doppler. Results During right ventricular pacing, CO was reduced by 21% (CI 18–24; p < 0.001), VtCO2 by 11% (CI 7.9–13; p < 0.001), and EtCO2 by 4.9% (CI 3.6–6.1; p < 0.001). During passive leg raise, CO increased by 21% (CI 17–24; p < 0.001), VtCO2 by 10% (CI 7.8–12; p < 0.001), and EtCO2 by 4.2% (CI 3.2–5.1; p < 0.001). Changes in VtCO2 were significantly larger than changes in EtCO2 (ventricular pacing: 11% vs. 4.9% (p < 0.001); passive leg raise: 10% vs. 4.2% (p < 0.001)). Relative changes in CO correlated with changes in VtCO2 (ρ=0.53; p=0.002) and EtCO2 (ρ=0.47; p=0.006) only during reductions in CO. When dichotomising CO changes at 15%, only EtCO2 detected a CO change as judged by area under the receiver operating characteristic curve. Conclusion VtCO2 and EtCO2 reflected reductions in cardiac output, although correlations were modest. The changes in VtCO2 were larger than the changes in EtCO2, but only EtCO2 detected CO reduction as judged by receiver operating characteristic curves. The predictive ability of EtCO2 in this setting was fair. This trial is registered with NCT02070861.
Highlights
Haemodynamic deteriorations are frequent in many clinical situations but may initially be subtle and difficult to detect
There were statistically signi cant reductions in mean scores from BL to right ventricular pacing (RVP) and statistically signi cant increases from RVP to BL and from BL to passive leg raise (PLR) (Table 2, Figure 3). e con dence intervals of the line plots in Figure 3 indicate that the study was not underpowered for the presented analyses
From BL to RVP, cardiac output (CO) was reduced by 21.0% (CI 18–24; p < 0.001), VtCO2 by 11% (CI 7.9–13; p < 0.001), and EtCO2 by 4.9% (CI 3.6–6.1; p < 0.001)
Summary
Exhaled carbon dioxide (CO2) reflects cardiac output (CO) provided stable ventilation and metabolism. We investigated whether CO2 measured as end-tidal concentration (EtCO2) and eliminated volume per breath (VtCO2) reflect sudden changes in cardiac output (CO). We measured changes in CO, VtCO2, and EtCO2 during right ventricular pacing and passive leg raise in 33 ventilated patients after open heart surgery. Changes in VtCO2 were significantly larger than changes in EtCO2 (ventricular pacing: 11% vs 4.9% (p < 0.001); passive leg raise: 10% vs 4.2% (p < 0.001)). When dichotomising CO changes at 15%, only EtCO2 detected a CO change as judged by area under the receiver operating characteristic curve. VtCO2 and EtCO2 reflected reductions in cardiac output, correlations were modest. E changes in VtCO2 were larger than the changes in EtCO2, but only EtCO2 detected CO reduction as judged by receiver operating characteristic curves. VtCO2 and EtCO2 reflected reductions in cardiac output, correlations were modest. e changes in VtCO2 were larger than the changes in EtCO2, but only EtCO2 detected CO reduction as judged by receiver operating characteristic curves. e predictive ability of EtCO2 in this setting was fair. is trial is registered with NCT02070861
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