The Effect of Vacuum-assisted Closure on the Tissue Oxygenation of Venous Ulcers: A Pilot Study
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Individual TcPO2 measurements and clinical details are outlined in Table 1. Figure 1 shows the mean ± standard deviation of TcPO2 at the reference point and periwound area on day 1 and day 6. There was no significant difference in mean TcPO2 within the periulcer region (41.5 mmHg ± 14.6 and 40.0± 15.9 mmHg, respectively [P = 0.67]). There was a significant difference in TcPO2 between the reference site and the periulcer area (P < 0.001). The TCOM periulcer values on day 1 and 6 were on average, less than the reference TCOM by 18.3 mmHg (P < 0.005) and 20.6 mmHg (P < 0.0005), respectively. The mean of the TCOM reference point on day 1 and 6 were 59.8 ± 12.4 and 60.6 ± 12.9.
This prospective pilot study suggests that TcPO2 is lower around chronic venous ulcers than in normal tissues and that VAC applied over a 6-day period does not increase tissue oxygenation.
The 6-day study period was chosen for two reasons: a prospective trial on patients with venous ulcers used this regimen and showed that most ulcers formed granulation tissue within this period14; and because animal models revealed maximum increase in capillary density on the sixth day.9
We strictly adhered to the application of TCOM in the recommended manner as described by Sheffield15 to reduce the limitations of this tool. However, one limitation with the device might be that TCOM estimates oxygen around the wound not the wound base and a 6-day period might not be sufficient to stimulate neoangiogenesis. In addition, the adjacent tissue is likely to have a higher PO2 than the wound itself.5 Therefore, the values measured might be overestimating the TcPO2 levels. TCOM has some limitations in venous ulcer measurements, as there are several skin changes present on the limbs. Jünger et al16 showed that the greater the severity of trophic skin changes, the lower the TcPO2 and the number of nutritive capillaries observed.
A limitation of this experiment was its small number of participants. If TCOM were taken from the unaffected limb, an interesting dimension would have been added to this study, as this might reveal if the microcirculation was affected bilaterally. Cina et al17 showed TcPO2 in healthy subjects decreased with an increase in age. Both foot and calf TcPO2 values of healthy controls were more than 60 mmHg. Patients with peripheral arterial occlusive disease had TcPO2 values more than 50 mmHg in the asymptomatic lower limb.
Several other studies have shown that TcPO2 is low in patients with venous skin changes and ulcers when compared to normal controls, which provides support for the theory that hypoxia is a contributing factor.18,19 Moosa et al20 showed that perivenous ulcers had a mean TcPO2 of 10 mmHg, which was similar to the mean value of 5.6 mmHg reported by Nemeth et al.21 Older models of TCOM devices only had 2 sensors (reference and periulcer) and studies reported a single periulcer figure rather than a circumferential representation of the skin, as was the case in the present study. This might explain why our periulcer values were higher than published studies.
We improved the seal of the electrode and the semipermeable patch by stripping excess scale and any remains of topical moisturizing products applied before compression bandaging. In some instances, the patch did not have an adequate seal and the skin had to be prepped several times before an adequate seal was achieved.
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