Confounding effects of blood hemoglobin and hematocrit levels on flap perfusion measurement with the Oxygen-to-see (O2C) analysis system in microvascular head and neck reconstruction- a retrospective study.

[BACKGROUND] The Oxygen-2-see (O2C) analysis system can measure flap perfusion, which is a prerequisite for flap viability, and it is therefore commonly used in flap monitoring for microvascular head and neck reconstruction. However, in the context of predefined threshold values for perfusion parameters indicating vascular flap compromise, it is unclear whether blood hemoglobin and hematocrit levels are confounding variables. The aim of this study was to investigate the influence of blood hemoglobin and hematocrit levels on flap perfusion parameters.

[METHODS] Perfusion parameters (i.e., flap blood flow, hemoglobin concentration, and hemoglobin oxygen saturation) measured intraoperatively and postoperatively with the O2C analysis system at 8- and 2-mm tissue depths were retrospectively analyzed in 125 patients reconstructed with a radial free forearm flap (RFFF), an anterolateral thigh flap (ALTF), or a fibula free flap (FFF) between 2011 and 2020. Associations between perfusion parameters and blood hemoglobin and hematocrit levels were analyzed using Spearman correlation coefficient and multiple linear regression models.

[RESULTS] Postoperative hemoglobin concentration at a 2-mm tissue depth was associated with blood hemoglobin and hematocrit levels in RFFFs (r = 0.259, p = 0.031; and r = 0.268, p = 0.026; respectively). Both associations persisted in multivariable regression analysis (p = 0.040 and p = 0.036). No other associations between perfusion parameters and blood hemoglobin and hematocrit levels were observed for RFFFs, ALTFs or FFFs (all p > 0.05).

[CONCLUSIONS] For the perfusion parameters flap blood flow and hemoglobin oxygen saturation no association with blood hemoglobin or hematocrit levels was observed. This underlines the validity of absolute threshold levels for indicating vascular flap compromise in the context of flap monitoring with the O2C analysis system.