Problems of Transcutaneous Measurement of Arterial Blood Gases
Applying the dropping mercury electrode is has been previously tried to measure the arterial Po2 by measuring the Po2 of heated water which was brought in close contactwith the skin (1,11) Using solid electrodes, Po measurements on the skin surface turned out to be extremely difficult to perform, since even a rather light electrode had the tendency to compress some of the skin capillaries. Therefore, Evans and Naylor (3) mounted the electrode on a spring balance. We succeeded in reducing the pressure by increasing the contact area of the electrode using plastic material (Xantopren). Similar to Evans and Naylor (4) we found that the blood of the normal skin is regulated in such a way that the oxygen pressure on the skin surface covered by an oxygen-impermeable layer is only a few Torr (4,6). The highest value measured so far was 7 Torr, more frequently the values ranged between 0 and 2.5 Torr. During O respiration skin Po did not rise. Interruption of blood flow deceased the skin O2 ti zero; after releasing the cuff, the skin O2 rose up to 10 Tor, and then fell to the starting point again. Thus, under normal physiological conditions, skin blood flow is so regulated that it supplies just the amount of oxygen needed for the O2 consumption of the akin. Since all these experiments had shown that O diffuses through the skin, the question arose to which degree it would be possible to measure arterial Po2 through the intact skin. Fig. 1 shows schematically which way the oxygen must diffuse in order to reach the Po2 electrode. It leaves the ca-pillary and permeates through the resiring skin (shown by the mitochondrium) and then through the upper part of the epidermis together with the membranes of the electrode. It can be easily predicted that vasodilatation without changing skin respiration must increase the skin surface Po But haw close this value will reach the arterial Po2 depends on the composition of blood, on the blood flow, and on the O2 consumption of the skin.
KeywordsSkin Surface Intact Skin Drop Mercury Electrode Arterial Oxygen Tension Local Blood Flow
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