137. The Evaluation of Skin Pigmentation Effects on Pulse Oximetry Monitoring Using a Novel Porcine Deoxygenation Model

BACKGROUND: We have previously demonstrated that skin pigmentation affects the performance of NIRS based flap monitoring devices (Vioptix T.Ox). There is now increasing concern that similar issues may affect pulse-oximetry, which has far-reaching impact beyond the niche application of flap monitoring. The lack of an appropriate animal model has limited systematic investigation of this critical question. In this study, we modified our previously validated porcine dual-pigmentation flap model to include controlled systemic deoxygenation of animals with alternately pigmented ears. This provides an optimal platform for an internally controlled investigation skin pigmentation’s impact upon pulse oximetry. We hypothesized that pulse oximeters overestimate arterial oxygen saturation (SaO2) in the presence of pigmentation. METHODS: Two Hampshire pigs with naturally occurring oppositely pigmented ears were utilized. Ear pigmentation levels was quantified colorimetrically using the Individual Typology Angle (ITA, Konica Minolta CM700d spectrophotometer). Pulse-oximetry (SpO2) data was continuously and simultaneously collected from each ear using research grade open data stream (reflectance-mode Maxim 86171 pulse oximeter) and clinical standard proprietary pulse oximeters (Masimo-K181956). Starting from normoxemia, progressive hypoxemia (SaO2 60-100%) was induced by decreasing the fraction of inhaled oxygen in a stepwise manner. Arterial blood gas samples were intermittently drawn from in indwelling catheter, and co-oximetry was used to define the gold standard SaO2. RESULTS: During normoxemia, both types of pulse-oximeters showed good correspondence between measurements taken on the pigmented and non-pigmented ears. As hypoxemia was induced, there was diversion of the SpO2 curves measured in the pigmented and non-pigmented ears. The oximeter on the non-pigmented ear measured lower SpO2 values, which corresponded closely with the arterial blood gas values, while the oximeters on the pigmented ear overestimated the true oxygenation. At 70% SaO2, the mean discrepancy in measured SpO2 was +1% in non-pigmented skin and +16% in pigmented skin. This discrepancy was recapitulated in the Maxim oximetry data where the slope of the modulation ratio (R) vs SaO2 curve was 5.9% steeper in the non-pigmented compared to the pigmented ear. CONCLUSION: This study presents the first internally controlled animal model demonstrating that skin pigmentation significantly influences the accuracy of pulse oximetry. In normoxemic conditions, oximetry readings were comparable between pigmented and non-pigmented ears. However during hypoxemia, devices overestimated oxygen saturation in pigmented skin. This was observed with both a commercial device using proprietary calculation algorithms and a modular oximetry research device which allowed direct analysis of raw optical data streams. This means that pulse-oximetry may underestimate the degree of hypoxemia in ill patients with dark pigmentation. There is an urgent need for research to address pigmentation-related inaccuracies in pulse oximetry.