PURPOSE: Pulse oximetry readings are of utmost importance in Intensive Care Units but in low peripheral perfusion states the readings become unreliable. Our purpose was to compare tissue perfusion and tissue oxygen saturation at low flow states.
METHODS: We studied the effect of cuff inflation to a pressure of 20mm Hg above systolic blood pressure and sustained for 2 to 3 minutes on the trend of tissue oxygenation (StO2, Hutchinson) and perfusion index (PI).
RESULTS: In a patient with high PI, cuff inflation caused the StO2 to first increase by 5% before falling steeply to 10% below baseline StO2, at a rate faster than a patient who had a low baseline PI. On cuff deflation, the rate of increase of StO2 was faster than the rate of fall and was accompanied with an overshoot of about 5%. On the contrary, in a patient with low PI of less than 1.4 there was a very gradual return of StO2 to the baseline on cuff deflation with no overshoot noted. The trend of PI also showed a fall and rise with cuff inflation and deflation in the patient with the high PI. However the change in PI preceded the change in StO2 by about a minute and the nadir of the PI readings preceded the nadir of the StO2 readings. In the patient with the PI of less than 1.4, cuff inflation failed to produce any further fall of PI.
CONCLUSION: The perfusion index is a less sensitive estimate of tissue perfusion versus StO2. The rapidity of recovery of StO2 following temporary cuff occlusion provides a more accurate estimate of tissue hypoxia compared to a single reading of StO2.
CLINICAL IMPLICATIONS: For noninvasive estimation of tissue oxygenation in low perfusion states, StO2 is more sensitive than the perfusion index. StO2 recovery rates following arterial occlusion by cuff is a better estimate of hypoxia than the perfusion index.
DISCLOSURE: Parijat Joy, No Financial Disclosure Information; No Product/Research Disclosure Information