Transcutaneous Oxygen Tension in Imminent Foot Gangrene

Transcutaneous oxygen tension at 44C and maximal isotope clearance (⁹⁹ m Tcpertechnetate + histramine) just proximal to the 1st toe and systolic toe blood pressure (strain gauge) were studied on a tilt table in patients with various degrees of obstructive arteriosclerotic disease. In legs with moderate obstruction, the oxygen tension reached zero at a toe systolic blood pressure of 5–10 mmHg (tilt toe up) and reached arterial oxygen tension at about 50 to 70 mmHg (tilt toe down). In legs with severe arterial obstruction and ischaemic rest pain, oxygen tension rose from zero not before systolic toe blood pressure reached 20–50 mmHg. Significant isotope clearance was seen at pressures below the limits just mentioned for both types of patients.
This phenomenon here seen of a perfusion without oxygen supply is explained by a gas leak (rendered significant because of the slow flow rate) from the arterioles into the tissue sink and counter current gas shunting. The hypoxia in spite of a positive perfusion pressure up to 50 mmHg explains our experience that ischaemic ulcers in feet with such low pressures never heal.