Use of tissue oxygenation saturation in association with skin temperature as an indicator of the peripheral tissue perfusion in critically ill patients

Introduction

Studies have suggested that tissue oxygenation saturation (StO₂) values are insensitive in assessing peripheral perfusion. StO₂ measurements may be more correctly interpreted if measured in association with the forearm-to-fingertip skin-temperature gradient (Tskin-diff). A Tskin-diff threshold of 0°C has been showed to reflect vasoconstriction. We aimed to propose a different approach for the interpretation of StO₂ by adding Tskin-diff monitoring and to characterize the pattern of StO₂ dynamics in patients with peripheral vasoconstriction and vasodilation. We hypothesize that monitoring StO₂ with Tskin-diff can more adequately predict ICU complications than StO₂ itself.

Methods

StO₂ was continuously monitored on the thenar with an InSpectra Model 325 probe (Hutchinson Technology Inc., Hutchinson, MN, USA). The Tskin-diff was obtained from two skin probes (Hewlett Packard 21078A; Phips Medical Systems, Eindhoven, the Netherlands) attached to the index finger and on the radial side of the forearm. To describe the effect of variations in skin temperature on StO₂, we compared StO₂ in survivors and nonsurvivors stratified by the condition of peripheral circulation (vasoconstriction, Tskin-diff >0; vasodilation, Tskin-diff < 0). The first measurement was registered within 24 hours and then every 24 hours until day 3. Differences between group means were tested by the Mann–Whitney U test. P < 0.05 was considered statistically significant.

Results

We prospectively studied 41 consecutive critically ill patients (survivors = 29; nonsurvivors = 12): age: 49 ± 16 years; 20 septic shock, 14 nonseptic shock, seven other. No differences in StO₂ were seen between survivors and nonsurvivors (day 1: 73 ± 9 vs. 78 ± 10; day 2: 74 ± 11 vs. 75 ± 11; day 3: 76 ± 10 vs. 77 ± 9). In survivors, StO₂ values were significantly lower in peripheral vasoconstriction than in vasodilation (day 1: 69 ± 8 vs. 76 ± 8; day 2: 68 ± 13 vs. 78 ± 7; day 3: 71 ± 10 vs. 80 ± 9; P < 0.05). In nonsurvivors, this association was seen only on day 1 (71 ± 8 vs. 86 ± 4; P < 0.05). Compared with survivors on day 3, nonsurvivors had lower StO₂ values in peripheral vasodilation (69 ± 6 vs. 80 ± 9, P = 0.02) and higher StO2 values in peripheral vasoconstriction (83 ± 7 vs. 71 ± 10, P = 0.02).

Conclusion

Dissociation between StO₂ and skin temperature was seen more often in nonsurvivors. StO₂ measured in association with skin temperature can more adequately predict ICU death than StO₂ itself.