Transcutaneous oximetry: variability in normal values for the upper and lower limb.

INTRODUCTION

Published normal transcutaneous oxygen partial pressures (PO) for the chest and lower limb have defined tissue hypoxia as a value of < 40 mmHg (< 30 mmHg in some patients, < 50 mmHg in others).

AIM

To determine 'normal' PO for the upper and lower limb in healthy, non-smoking adults using the Radiometer® TCM400 with tc Sensor E5250.

METHOD

Thirty-two volunteers had transcutaneous oxygen measurements (TCOM) performed on the chest, upper and lower limbs breathing air, with leg then arm elevated and whilst breathing 100% oxygen.

RESULTS

Room-air PO (mmHg, mean (95% confidence interval)) were: chest: 53.6 (48.7-58.5); upper arm: 60.0 (56.1-64.0); forearm: 52.3 (44.8-55.8); dorsum of hand: 50.2 (46.1-54.3); thenar eminence: 70.8 (67.7-73.8); hypothenar eminence: 77.9 (75.1-80.7); lateral leg: 50.2 (46.2-54.2); lateral malleolus: 50.5 (46.6-54.3); medial malleolus: 48.9 (45.6-52.1); dorsum, between first and second toe: 53.1 (49.2-57.0); dorsum, proximal to fifth toe: 58.5 (55.0 - -62.0); plantar, 1st MTP: 73.7 (70.3-77.1). Nineteen subjects had at least one room-air PO below 40 mmHg (nine upper limb, 13 lower limb, four chest). Approximately 10% lower limb PO were < 100 mmHg on normobaric oxygen. Only one subject at one site had an upper limb PO < 100 mmHg breathing oxygen.

CONCLUSION

The broad dispersion in PO in our healthy cohort reflects the inherent biologic variability in dermal perfusion and oxygen delivery, making it difficult to define narrow, rigid 'normal' values. Thus, we cannot recommend a single PO value as 'normal' for the upper or lower limb. A thorough patient assessment is essential to establish appropriateness for hyperbaric oxygen therapy, with TCOM used as an aid to guide this decision and not as an absolute.