Thalassemia minor presents unique challenges in intraoperative hemodynamic management due to chronically low hemoglobin and altered oxygen-carrying capacity. While pleth variability index (PVi) is an established surrogate of volume responsiveness, its behavior in hemoglobinopathies remains underexplored. This pilot case investigates the relationship between PVi and co-oximetry-derived parameters to assess perfusion trends when plethysmographic signals may be unreliable.

A 36-year-old female with thalassemia minor undergoing parasagittal craniotomy was monitored using Masimo Radical-7 co-oximeter (spectral hemoglobin [SpHb], perfusion index [Pi], spectrophotometric oxygen content [SpOC], PVi) and GE Centricity hemodynamic records. Data were time-synchronized using POSIX conversion and down-sampled to 1-minute intervals. Multivariate regression and LOESS (locally estimated scatterplot smoothing) curve fitting were used to explore relationships among SpHb, SpOC, Pi, and PVi.

Regression modeling yielded:

PVi = 0.45 × SpHb + 0.15 × SpOC + 1.57 × Pi − 1.04,

with an adjusted R2 of 0.92. Pi emerged as the strongest predictor of PVi. LOESS plots revealed nonlinear associations, especially between PVi and Pi. SpHb showed minimal early-phase variability, consistent with limited responsiveness to acute blood loss.

This exploratory model highlights physiologically grounded inter-variable behavior of co-oximetry parameters in thalassemia. It provides a foundation for redundant trend monitoring and decision support during neurosurgery in patients with hematologic disorders.

Article published online:
21 August 2025

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