Please see Bibliography of References for a list of abstracts, manuscripts and posters.
Torres PA, Polanco P, Pinsky M, Kim, Puyana JC. J Surg Res. 2006;130(2):279. Abstract 323.
Presently, the bedside assessment of cardiovascular adequacy in the critically ill trauma patient is not practical. Compensatory mechanisms often restore blood pressure and vital organ blood flow despite ongoing hypovolemia and hypoperfusion. We reasoned that delay in the restoration of tissue oxygenation following vascular occlusion would identify impaired cardiovascular reserve. The InSpectra® near infrared sensor measures tissue O2 saturation (StO2) in a continuous and non-invasive fashion. We hypothesized that dynamic changes in StO2 may assess cardiovascular reserve, if coupled to a defined circulatory stress. We measured the time course of thenar eminence StO2 in 7 normal volunteers (controls) and 3 trauma patients during blood pressure cuff-induced total vascular occlusion (cuff inflation to 20mmHg > systolic pressure until StO2 < 35%) and release. This procedure was repeated four times in controls and twice in patients. Controls exercised their thenar muscles during the final occlusion maneuver to assess for the effect of changing metabolic rate on this response. We found that 1) the decrease in thenar StO2 within subjects during baseline occlusion and recovery were highly reproducible across repeated occlusions; 2) at rest, the decrease in StO2 started 20-30 seconds post-occlusion and reached < 35% by 2.2 to 4 min; 3) post-deflation recovery occurred rapidly in all controls (<8 sec); 4) exercise markedly increased the rate of StO2 decrease during occlusion (<30 sec) but did not alter the rate of recovery (fig 1). In one trauma patient following resuscitation, recovery was also < 10 sec. However, in the remaining 2 patients with circulatory shock without hypotension (lactate>3 mmol/l, MAP>70mm Hg), the slope of recovery post-occlusion was markedly decreased requiring >2 min to return to baseline (fig 2). These preliminary data suggest that the real-time StO2 response to transient vascular occlusion may identify subjects with compensated circulatory shock.