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

Abstract

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) mmHg at rest and during tilting it increased to 89 (82–111) mmHg followed by a decrease to 72 (58–97)mmHg (p<0.01) at the appearance of presyncopal symptoms. Psc, O₂ returned to the pretilt level over 45 (30–60) min of recovery. Arterial oxygen, carbon dioxide and Psc, CO₂ did not change significantly. Subcutaneous oxygen tension decreases during marked central hypovolaemia and it returns slowly to the resting level during recovery. Psc, O₂ is a more sensitive marker of impaired tissue oxygenation than arterial oxygen pressure.

Key Words:

• arterial oxygen saturation
• blood pressure
• cardiac output
• central venous pressure
• heart rate
• stroke volume
• venous oxygen saturation