SUBCUTANEOUS OXYGEN AND CARBON-DIOXIDE TENSIONS DURING HEAD-UP TILT-INDUCED CENTRAL HYPOVOLEMIA IN HUMANS

The effect of hypovolaemic shock on subcutaneous oxygen and carbon dio xide tensions was studied in man. Subcutaneous oxygen (Psc,O-2) and ca rbon dioxide (Psc,CO2) tensions were monitored, during 50 degrees head -up tilt (anti-Trendelenburg's position)-induced central hypovolaemia, in two females and eight males, using a silicone tonometer on the lat eral upper aspect of the right arm. Ai cardiovascular variables remain ed stable at rest. Incremental tilting to 50 degrees increased heart r ate (HR) and mean arterial pressure (MAP) (p<0.01), while stroke volum e (SV), cardiac output (CO) and central venous saturation (SvO(2)) dec reased (p<0.05). Presyncopal symptoms appeared after 28 (8-48) min (me an 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 SvO(2) from 0.68 (0.56-0.76) to 0.58 (0.39-0.70) (p<0.01). On return of the tilt t able to the horizontal position HR, MAP, SV, CO and SvO(2) immediately re-established resting values. The Psc,O-2 was 83 (72-102)mmHg at res t and during tilting it increased to 89 (82-111)mmHg followed by a dec rease to 72 (58-97) mmHg (p<0.01) at the appearance of presyncopal sym ptoms. PscO(2) returned to the pretilt level over 45 (30-60) min of re covery. Arterial oxygen, carbon dioxide and Psc,CO2 did not change sig nificantly. Subcutaneous oxygen tension decreases during marked centra l hypovolaemia and it returns slowly to the resting level during recov ery. Psc,O-2 is a more sensitive marker of impaired tissue oxygenation than arterial oxygen pressure.