Sir
I read with interest the article by Mr Stacey et al. on changes in the apparently normal limb in unilateral venous ulceration ( B r J Surg 1987; 74: 936-9). However, I must take issue with both the method of measurement of percutaneous oxygen tension and the interpretation of the results which imply that a low cutaneous oxygen tension reflects poor diffusion of oxygen from the capillaries. Most equipment used for percutaneous oxygen measurement is designed for use in neonates who have very thin skin and can give unreliable results when used in adults'.
The actual measured oxygen tension will be a function of the amount of blood flowing into the limb, the amount of blood leaving the limb and the skin thickness. In a limb with already diseased venous circulation and a defective pump mechanism as stated in the paper, venous pooling and increased oxygen dissociation may allow for a lower measured oxygen tension. Defective arterial inflow into the limb will also give low readings and although the authors state that ank1e:brachial ratios were measured, no reference to this is made in interpretation of the measured results.
In the evaluation of identical equipment I found that more reliable information was gained by having the patients breathe 100 per cent oxygen for 5 min. The gradient of the increase in oxygen tension in the limb compared with the gradient at the sternal ankle was measured rather than a static value. This method may give differing results from those obtained in the study particularly if arterial insufficiency is excluded.