Proof of concept of noninvasive detection of norepinephrine induced stroke volume changes using perfusion index in cardiac surgery

Intraoperative arterial hypotension (IAH) increases the risk of complications. Norepinephrine is often used to treat IAH, but its effects on stroke volume (SV) are highly variable. The perfusion index (PI), a non-invasive marker measured via pulse oximetry, may help monitor hemodynamic changes. This study aims to evaluate the ability of changes in the perfusion index (∆PI), a non-invasive marker measured via pulse oximetry, to identify patients experiencing a decrease in SV in response to norepinephrine bolus. This is a prospective observational study in the cardiac surgery. Hemodynamic variables, including SV assessed via transesophageal echocardiography and PI, were measured before and after a 4–8 μg norepinephrine bolus. The relationship between ΔPI and ΔSV was assessed using Pearson’s correlation test, and the ability of ΔPI to detect a ≥ 10% decrease in SV was evaluated using receiver operating characteristics curve (ROC) analysis (DeLong method). Twenty-seven patients undergoing cardiac surgery who required norepinephrine for IAH were included. Thirty-one measurements were analyzed. A > 10% decrease in SV was observed in 45% of the cases. The ROC curve for ∆PI detecting a ≥ 10% decrease in SV had an area under the curve of 0.94 (95% CI 0.86–1). A correlation was found between ∆PI and ∆SV, with a Pearson correlation coefficient of 0.81 (95% CI 0.65–0.91, p < 0.001). This prospective study confirms that some cardiac surgery patients experience SV fall in response to NE bolus and is a proof-of-concept that the PI might be a useful tool for tracking these patients. Further research is needed to confirm these findings in larger cohort and broader surgical populations.