Diagnostic Performance and Trending Ability of Continuous Non-Invasive Hemoglobin Monitoring During Elective Intracranial Neurosurgery with Invasive Arterial Monitoring: Influence of Anesthetic Technique

<b>Background:</b> Continuous non-invasive hemoglobin monitoring (SpHb) may provide real-time information during surgery, but its accuracy in neurosurgery remains uncertain. We evaluated the agreement, trending ability, and diagnostic performance of SpHb compared with arterial blood gas hemoglobin during elective intracranial neurosurgery. <b>Methods:</b> In this prospective observational study, 60 adults undergoing elective neurosurgery with invasive arterial monitoring were included. SpHb (Masimo Radical-7) was compared with paired arterial hemoglobin values. Agreement was assessed using repeated-measures Bland-Altman analysis and mixed-effects modeling. Trending ability was evaluated using four-quadrant concordance with an exclusion zone of ±0.5 g/dL. Discrimination for severe anemia (Hb < 8 g/dL) was assessed using ROC analysis with patient-level cluster bootstrapping. <b>Results:</b> A total of 190 paired measurements were analyzed. Mean bias was +0.23 g/dL, with wide limits of agreement (-3.26 to +3.72 g/dL). Agreement was worse under low-perfusion-index conditions. Trending performance was preserved, with an overall concordance rate of 85.5%. SpHb showed moderate discrimination for severe anemia (AUC 0.78; 95% CI 0.61-0.93), although severe anemia events were infrequent. <b>Conclusions:</b> SpHb showed limited reliability for absolute hemoglobin quantification during neurosurgery but provided useful trend information. SpHb should not replace invasive hemoglobin measurements for clinical decision-making.