Association Between the Quantity of Subcutaneous Fat and the Inter-Device Agreement of 2 Tissue Oximeters

Abstract

Objective: This study aimed to evaluate the association between the quantity of subcutaneous fat (assessed by skinfold thickness) and the inter-device agreement of 2 tissue oximeters.

Design: This is a prospective cohort study.

Setting: This study was conducted in a tertiary care academic urban hospital.

Participants: Healthy volunteers were recruited.

Interventions: All patients recruited had their tissue saturations and skinfold thickness measured at 4 different sites (shoulder, forearm, knee, and calf) on both sides of the body using 2 tissue oximeters, the INVOS 5100C and the EQUANOX 7600.

Measurements and main results: Higher skinfold measures were associated with an increase in the difference between measures provided by both oximeters (slope = -0.59, Pearson correlation coefficient = -0.51, p < 0.001). This observed association persisted in a linear mixed model (-0.48 [95% confidence interval [CI] -0.61 to -0.36], p < 0.001). The sex of the volunteers also influenced the inter-oximeter agreement (women: -5.77 [95% CI -8.43 to -3.11], p < 0.001), as well as the forearm sites (left forearm: -7.16 [95% CI -9.85 to -4.47], p < 0.001; right forearm:-7.01 [95% CI -9.61 to -4.40], p < 0.001).

Conclusion: The inter-device agreement of the 2 studied oximeters is correlated to the quantity of subcutaneous fat. Monitoring using tissue oximetry should be interpreted with great care when sensors are placed on sites with a significant quantity of subcutaneous fat. In addition to the monitoring of cerebral oximetry, following the variations of saturations at the same peripheral site seems to remain the most secure way to use that technology for the monitoring of critically ill patients.

Keywords: inter-device agreement; near-infrared spectroscopy; subcutaneous fat; tissue oximetry.