Interpretation of the tcPO2 curve in adult patients in an intensive care unit

From the data collected on 135 adult patients in an intensive care unit the following conclusions of the interpretation of the transcutaneous PO2 curve in this type of patient may be drawn: 1) One to four minutes after the electrode was attached a nadir (= the lowest initial point) was reached and then there was a gradual increase which ended with an initial plateau. This plateau could be predicted from the lowest initial point by adding 30 mm Hg. 2) If the lowest initial point was 35 mm Hg or less, it was expected that the final tcPO2 level would be lower than the actual PaO2. 3) No correlation was seen between the lowest initial point of the tcPO2 curve and the time until the initial plateau was reached. In 75% of the cases the plateau was reached within 20 minutes. 4) A slight positive correlation was found between arterial blood pressure and lowest initial point. The difference between the means of the lowest initial point for a group with blood pressure less than or equal to 90 mm Hg and another group with blood pressure greater than 120 mm Hg was highly significant. 5) Transcutaneous PO2 measurements were more likely to represent the arterial PO2 level if blood pressure was greater than 120 mm Hg than if it was less than or equal to 90 mm Hg. 6) The lower the initial tcPO2 level, the more likely it was that the arterial level was higher than the tcPO2 level (see also point 2). 7) The differences between PaO2 and tcPO2 were independent of the arterial PO2 level. 8) The overall correlation between PaO2 and tcPO2 in this material was 0.91; the slope was 0.90 and the intercept -8 mm Hg. The correlation coefficient within each individual patient was higher. 9) The correlation coefficient between PaO2 and tcPO2 for those patients in whom PaO2 was 60 mm Hg or less was comparatively low. This may be explained by the bad condition of these patients followed by a reduced blood flow. 10) An initial drop in tcPO2 to zero level indicates a reduced peripheral circulation, but this must be suspected when the initial drop is below 35 mm Hg.