Fig. 3. Example of 6.2-h recordings in a 68-yr-old patient undergoing right hepatectomy in whom pulse pressure variation (ΔPP) and variation of the plethysmographic waveform of pulse oximetry (ΔPOP) were well correlated (r = 0.52). (A ) Variations in ΔPOP, ΔPP, and systolic arterial pressure (SAP). Salient events are indicated at the bottom: insertion of upper abdominal wall retractor (filled upward arrow ), bolus phenylephrine administration (plus sign ), and volume loading (open upward arrow ). Variations of ΔPP and ΔPOP were roughly parallel. (B ) Bland and Altman analysis for ΔPP and ΔPOP showed a bias of 1.2% according to the following equation y = 0.19x − 1.90 (r = 0.03 –P  value less than 0.0001). (C ) Polar plot showing relation between variations of ΔPP and ΔPOP. The angle was 16.3 ± 14.4°.