Study Finds Change in End-Tidal CO2 Accurately Predicts Fluid Responsiveness in Major Abdominal Surgery

When managing fluid therapy during major abdominal cancer surgery, how can anaesthesiologists quickly and accurately predict who will respond to a fluid bolus? Traditional measures like pulse pressure variation (PPV) and stroke volume variation (SVV) are useful, but not always reliable or readily available. Could a simple, non-invasive parameter—end-tidal carbon dioxide (ETCO₂)—be the answer?

Study Design: Testing a Non-Invasive Marker

Recently published prospective observational study enrolled 22 adults undergoing major abdominal oncosurgery. All patients were mechanically ventilated and monitored with advanced haemodynamic systems. When clinical signs suggested hypovolaemia, patients received a 4 mL/kg crystalloid bolus over 10 minutes. The researchers measured ETCO₂, cardiac index (CI), stroke volume index (SVI), PPV, and SVV both before and after the fluid challenge. Fluid responsiveness was defined as a ≥10% increase in CI.

Key Findings: ETCO₂ as a Predictor of Fluid Response

Diagnostic Accuracy: A rise in ETCO₂ (ΔETCO₂) of at least 1.5 mmHg after a fluid bolus predicted fluid responsiveness with an area under the ROC curve (AUROC) of 0.823, 68.8% sensitivity, and 90% specificity.

Comparison with Other Indices: ΔETCO₂ outperformed pre-bolus PPV and SVV, with both of these traditional indices showing lower predictive value for fluid responsiveness.

Clinical Relevance: The high specificity means a ΔETCO₂ ≥1.5 mmHg is particularly useful in confirming true fluid responders, making it a strong positive predictor when present.

How Does This Help in Practice?

ETCO₂ monitoring is already standard in modern anaesthesia workstations and is non-invasive. These findings suggest that, when ventilatory and metabolic factors are stable, a simple rise in ETCO₂ after a fluid bolus can serve as a surrogate for cardiac output monitoring. This can be especially valuable in settings where advanced monitoring is unavailable or as an adjunct to guide intraoperative fluid therapy.

Limitations and Considerations

While ΔETCO₂ is promising, the test is best used as a confirmatory tool due to its high specificity but modest sensitivity. It is less effective in ruling out fluid responsiveness when negative. The method requires metabolic and ventilatory parameters to remain unchanged during assessment. The study’s small sample and its focus on a specific surgical population limit generalizability, and larger trials are needed for validation.

Conclusion

A change in end-tidal CO₂ of 1.5 mmHg or more following a 4 mL/kg fluid bolus is a strong predictor of fluid responsiveness in major abdominal surgery. Incorporating ETCO₂ monitoring into intraoperative fluid management may improve decision-making and patient outcomes, especially when advanced cardiac output monitoring is unavailable.

KEY points

A rise in ETCO₂ of ≥1.5 mmHg after a fluid bolus predicts fluid responsiveness with high specificity.

ETCO₂ outperforms PPV and SVV in this setting for detecting fluid responders.

This method is non-invasive and leverages standard capnography already in use in operating rooms.

ETCO₂ is best used as a confirmatory (rule-in) test rather than for ruling out fluid responsiveness.

Stable ventilatory and metabolic conditions are essential for accurate interpretation.

Citation:

Chawathey SA, Solanki SL, Divatia JV. Detecting if change in end-tidal carbon dioxide signifies change in cardiac output for the prediction of fluid responsiveness in patients undergoing major abdominal oncosurgery: An observational study. Indian Journal of Anaesthesia. 2026;70(8):905-12. DOI: 10.4103/ija.ija_557_26