Subcutaneous oxygen and carbon dioxide tensions during head-up tilt-induced central hypovolaemia in humans

The effect of hypovolaemic shock on subcutaneous oxygen and carbon dioxide tensions was studied in man. Subcutaneous oxygen (Psc O2) and carbon dioxide (Psc, CO2) tensions were monitored, during 50° head-up tilt (anti-Trendelenburg's position)-induced central hypovolaemia, in two females and eight males, using a silicone tonometer on the lateral upper aspect of the right arm. All cardiovascular variables remained stable at rest. Incremental tilting to 50° increased heart rate (HR) and mean arterial pressure (MAP) (p<0.01), while stroke volume (SV), cardiac output (CO) and central venous saturation (SvO2) decreased (p<0.05). Presyncopal symptoms appeared after 28 (8–48) min (mean and range) as HR decreased from 82 (63–108) to 52 (36–70) beats min−1 (p<0.05), MAP from 88 (61–106) to 46 (37–54) mmHg and SvO2 from 0.68 (0.56–0.76) to 0.58 (0.39–0.70) (p<0.01). On return of the tilt table to the horizontal position HR, MAP, SV, CO and SvO2 immediately re-established resting values. The Psc, O2 was 83 (72–102) ...