Tourniquet-induced tissue hypoxia characterized by near-infrared spectroscopy during ankle surgery: an observational study

BACKGROUND: Pneumatic tourniquet inflation during extremity surgery leads to profound and prolonged tissue ischemia. Its effect on tissue oxygenation is inadequately studied. METHODS: Patients undergoing elective ankle surgery with tourniquet application participated in this observational cohort study. Somatic and cerebral tissue oxygen saturation (SstO(2) and SctO(2)) were monitored using tissue near-infrared spectroscopy. Oxygenation was monitored distally (SstO(2)-distal) and proximally to the tourniquet, on the contralateral leg, and the forehead (a total of 4 tissue beds). Tissue oxygenation at different time points was compared. The magnitude, duration, and load (product of magnitude and duration) of tissue desaturation during tourniquet inflation were correlated with tissue resaturation and hypersaturation after tourniquet deflation. RESULTS: Data of 26 patients were analyzed. The tourniquet inflation time was 120 ± 31 mins. Following a rapid desaturation from 77 ± 8% pre-inflation to 38 ± 20% 10 mins post-inflation, SstO(2)-distal slowly and continuously desaturated and reach the nadir (16 ± 11%) toward the end of inflation. After deflation, SstO(2)-distal rapidly resaturated from 16 ± 11% to 91 ± 5% (i.e., hypersaturation); SstO(2) monitored proximally to the tourniquet and on contralateral leg had significant but small desaturation (~ 2–3%, p < 0.001); in contrast, SctO(2) remained stable. The desaturation load had a significant correlation with resaturation magnitude (p < 0.001); while the desaturation duration had a significant correlation with hypersaturation magnitude (p = 0.04). CONCLUSIONS: Tissue dys-oxygenation following tourniquet application can be reliably monitored using tissue oximetry. Its outcome significance remains to be determined.