Detecting if Change in End tidal Carbon dioxide (delta ETCO2) signifies change in Cardiac Output for the preDiction of fluid rEsponsiveness in adult patients undergoing major non-thoracic oncosurgery: DECODE, An observational study

Major oncosurgeries entail significant fluid shifts, adding to considerable patient morbidity and affecting intraoperative and post operative outcomes, hence requiring prompt and adequate replacement of fluid and electrolytes. Understanding fluid responsiveness is thus key to make rational clinical decisions to appropriately replace fluid losses, because excessive fluid loading may cause peripheral and/or pulmonary oedema secondary to volume overload, while inadequately replaced fluid significantly affects intraoperative hemodynamic stability and end organ perfusion, portending to end organ injury.

The current Gold standard to assess fluid responsiveness as per prevailing guidelines is based on an increase in stroke volume (SV) by >=10% after a fluid bolus of crystalloid of 4ml/kg of actual body weight (ABW) over 10 minutes. Directly monitoring Cardiac output (CO) and thus cardiac index (the ratio of Cardiac output (L/min) and Body surface area (BSA;m2) [CI =  CO/BSA])

requires invasive and expensive devices which may increase perioperative morbidity and may not be financially viable and/or readily available in a number of settings, and require expertise for troubleshooting and interpretation of results these devices show. In patients with invasive continuous arterial pressure and SV monitoring, the Pulse Pressure variation (PPV) and stroke volume variation (SVV) are used as predictors of fluid responsiveness, and is based on a change in PPV (delta PPV) and that in SVV (delta SVV) observed after fluid bolusing.

End tidal Carbon dioxide concentration (ETCO2) is related to arterial CO.2 If ventilator and metabolic parameters are maintained constant, any change in ETCO2 indicateds a corresponding change in the cardiac output, for example, an increase in ETCO2 suggests that cardiac output has increased and vice versa. ETCO2 is a non-invasive, easily interpretable and routinely used parameter in mechanically ventilated adult patients undergoing major non-thoracic oncosurgeries. Recently, there has been a growing interest in understanding whether a change in End-tidal Carbon dioxide (delta ETCO2) may be useful as a surrogate parameter for detecting a change in SV brought about by a fluid challenge test. A systematic review of seven studies conducted in sedated and mechanically ventilated patients in intensive care and intraoperative settings, and various studies in patients undergoing a number of procedures, such as neurosurgery and cardiac surgery, have attempted to understand the utility of delta ETCO2  to aid in the prediction of fluid responsiveness in comparison to changes in SV and/or other surrogate parameters used for detecting fluid responsiveness, such as passive leg raising and/or using 2D echocardiography, among other methods, and these have given conflicting results. Utility of the latter aids, such as 2D echocardiography may not be always feasible for use in an operating room setting, whereas passive leg raising (PLR) may not provide the anaesthesiologist with the exact volume of fluid given as a bolus, and though physiologically sound, thus does not provide information to the anaesthesiologist about the exact amount of volume brought to the circulation in the great vessels and the heart so as to quantify the extent of the change in the CO caused by the PLR maneuvre. Also, PLR may also not be feasible in certain cohorts of patients, such as in those with trauma or those requiring a stable position during surgery.

If the delta ETCO2 in response to a fluid challenge is useful in determining fluid responsiveness, it can be used as a non-invasive alternative when invasive arterial pressure or stroke volume monitoring are not available. Thus, it is interesting to explore a possible correlation between delta ETCO2 and changes in cardiac index (delta CI), and compare the changes between delta ETCO2 with delta PPV and delta SVV, to know what is the diagnostic accuracy of these to detect fluid responsiveness

in patients undergoing major non thoracic oncosurgeries.

Aims and Objectives

1. The primary aim of the study is to determine whether the delta ETCO2 after a fluid challenge test identifies fluid responsiveness, i.e., increase in stroke volume index (dSVI) and Cardiac Index (dCI) > 10%.
2. The secondary aim will be to compare the ability to delta ETCO2 to discriminate between fluid responders and non-responders with that of PPV and Stroke Volume Variation (SVV)