Predicting spinal hypotension during cesarean delivery: what is being predicted, and when

Spinal hypotension during cesarean delivery has generated a large prediction literature, but the term "prediction" is applied to signals obtained at very different points in the peri-spinal course. Most reviews group predictors by physiology or device. Here we organize them by when the signal becomes available and which clinical decision remains open. This changes how reported performance should be interpreted. A preoperative low-frequency/high-frequency heart rate variability threshold of 2.5, for example, showed only 35% sensitivity and discrimination around 0.60 in an independent cohort, whereas small development studies of other preoperative tools have reported areas under the receiver operating characteristic curve approaching 0.9. Pre-spinal provocation may improve discrimination while preserving time to adjust prophylaxis. Measurements obtained after intrathecal injection, and real-time algorithms operating minutes before hypotension, answer a different question because sympathetic blockade is already evolving and the decision window is narrower. Variation in hypotension definitions, treatment background, case mix, and small development samples further limits direct comparison. Routine vasopressor prophylaxis also changes what a useful predictor should do: rather than decide who receives prevention, it should help identify who needs earlier, stronger, or differently titrated treatment. Two randomized cesarean trials now support Hypotension Prediction Index-guided management, while treatment-impact evidence for true preoperative prediction remains limited.