Subcutaneous glucose tracking during extreme perioperative perfusion stress: a prospective microdialysis study.

To determine whether the subcutaneous compartment retains an interpretable glucose signal during extreme perioperative perfusion stress and whether agreement with arterial glucose differs by anatomical site. In this prospective mechanistic observational study, 20 adults undergoing pulmonary endarterectomy with deep hypothermic circulatory arrest underwent subcutaneous microdialysis at upper thoracic and periumbilical sites. Recovery-corrected interstitial glucose was converted to calibrated subcutaneous glucose using one-point calibration. Agreement with arterial glucose was evaluated using absolute relative difference (ARD) and repeated-measures Bland-Altman analysis. Exploratory mixed-effects models examined associations of ARD with procedural phase and treatment-related variables. We analysed 743 paired measurements. Overall median ARD was 12.9% (IQR 5.9-21.9), and mean ARD was 17.2% (SD 17.2). The procedural phase was associated with ARD (global P < 0.001), with the greatest discordance during rewarming and early postoperative recovery rather than during the DHCA interval. Agreement was numerically more favourable at the upper thoracic site; however, this between-site difference did not reach statistical significance in the phase-adjusted analysis (P = 0.053). Under recovery-corrected and one-point-calibrated conditions, subcutaneous glucose retained interpretable tracking of arterial glucose during extreme perioperative perfusion stress. These findings argue against a uniform loss of subcutaneous glucose information in this setting and suggest that discordance is phase-dependent and may vary by anatomical site.