In Reply:
Koepke et al.1 raise three issues, first regarding the evidence supporting the hypotension prediction index alert threshold for future trials. Selection of a hypotension prediction index alert threshold must balance sensitivity and specificity, with the goal of predicting meaningful hypotension while avoiding false alerts. Preferably, sensitivity and specificity should be high for an optimal alert threshold. However, evaluating hypotension prediction index sensitivity is challenging because clinician responses to alerts can prevent impending hypotension that might otherwise have occurred. The prediction window also changes sensitivity and specificity, with predictions being less accurate over longer event horizons. For example, two minutes before hypotensive events, a hypotension prediction index threshold of 47 can be considered optimal, whereas it is 32 five minutes before events (table 1). Therefore, choosing the alert threshold based only on sensitivity and specificity is not desirable. We need to consider clinical input and the time-to-event analysis presented in our article2 in choosing an optimal threshold. We are considering a lower hypotension prediction index threshold for our forthcoming trial to provide adequate warning time and avoid unnecessary alerts.
We agree that automating recommendations, currently under development, will decrease cognitive burden and presumably improve clinical workflow. However, incomplete implementation research and strict regulatory requirements for physiologic closed-loop controllers3 will limit adoption of automated recommendations anytime soon. Finally, many clinicians did not act on hypotension prediction index alerts because blood pressure, heart rate, and other hemodynamic indicators appeared reasonable. Other times, hypotension developed quickly, limiting adequate intervention—especially when fluid administration was the selected treatment.
Competing Interests
Dr. Maheshwari and Dr. Sessler are consultants with Edwards Lifesciences (Irvine, California). Dr. Zhongping is an employee of Edwards Lifesciences.