Skin Oxygen Research Articles

Use of lightguide spectrophotometry to quantify skin oxygenation in a variable model of venous hypertension.

A variable model of venous hypertension was used to examine the immediate effect on skin oxygenation and blood flow. Measurements were carried out using laser Doppler flowmetry, transcutaneous oximetry and both macro- and micro-lightguide spectrophotometry to measure haemoglobin saturation (SO2). Assessments were performed on 20 normal subjects and in ten patients with deep venous insufficiency lying supine with a pressure cuff left uninflated (P0), then inflated to 40 mmHg (P40), 60 mmHg (P60) and 80 mmHg (P80). All measurements were performed at the gaiter area of the leg. In normal subjects median Doppler values fell significantly at P40 (P < 0.001) but further pressure increases had no more effect. Mean values of transcutaneous partial pressure of oxygen (PtcO2) fell steadily (P < 0.001), although the initial fall at P40 was small. Median SO2 fell with increasing occlusion pressure with both macro- and micro-lightguide spectrophotometry (P < 0.001), although the main reduction occurred predominantly at lower occlusion pressures. Higher levels of SO2 were obtained with local heating up to 44 degrees C, with a pattern similar to that of PtcO2. In patients, the same pattern of response to increased venous pressure occurred in areas of clinically normal skin. These data suggest that small increases in venous hypertension have an immediate and profound influence on skin blood flow and oxygen availability in normal skin.

Oxygen tension on the skin of the gaiter area of limbs with venous disease.

We examined the levels of oxygen on the skin of the gaiter areas of limbs with venous disease using a Roche Transcutaneous pO2 Monitor to determine whether hypoxia contributes to the skin changes and ulceration associated with severe venous disease. We studied patients with superficial varicose veins and no skin changes (Group 1: n = 25), patients with skin changes and healed ulcers (Group 2: n = 15), and an age matched normal control group (controls: n = 25). TcpO2 measurements were taken 5 cm above the medial malleolus with the limb both horizontal and vertical using a Roche Transcutaneous pO2 Monitor. A standard heel-raising test using a Medisonics Photoplethysmograph indicated the degree of venous insufficiency present. Results show that Group 1 patients and controls have similar skin oxygen levels (Group 1: TcpO2 66.48 + 14.12 mmHg; controls: TcpO2 61.60 +/- 11.02 mmHg) whereas those with skin changes and ulceration have significantly lower oxygen levels (Group 2: TcpO2 46.57 +/- 9.70 mmHg, t = 4.29, P less than 0.001). Group 2 patients did not show a significant rise in TcpO2 levels in the standing position whereas Group 1 patients and controls did (t = 2.6, P less than 0.02). PPG post-exercise recovery times confirmed differences between the three groups. These findings show that significant skin hypoxia occurs on the gaiter area of limbs with severe venous disease and support the concept of an oxygen diffusion block.

Rheopheresis in Patients with Critical Limb Ischemia––Results of an Open Label Prospective Pilot Trial

Rheopheresis is a specifically designed application of double filtration plasmapheresis, for extracorporeal treatment of microcirculatory disorders. Safety and efficacy of Rheopheresis for wound healing and skin oxygenation were investigated in patients with critical limb ischemia. Twelve patients of Fontaine stage III-IV were treated with a series of 10 Rheopheresis sessions over 17 weeks. Transcutaneous oxygen pressure (tcpO(2)) and ankle-brachial index (ABI) were repeatedly determined to monitor the effects of the Rheopheresis treatment series on microcirculation and skin blood flow. Laboratory parameters of blood rheology were measured in addition to safety parameters and course of the pain syndrome was documented. In four patients (baseline Fontaine stage III) Rheopheresis was associated with an improvement of Fontaine stage, a pronounced increase in tcpO(2) and complete regression of the rest pain. As an adjunct therapeutic option, Rheopheresis may preserve a functional lower extremity, delay amputation or reduce the extent of amputation.

Measurement of critical lower limb tissue hypoxia by coupling chemical and optical techniques.

It has been a long-term goal to develop non-invasive methods that can detect critical levels of tissue hypoxia to help in the management of chronic lower limb ischaemia. In the present study, skeletal muscle oxygenation was measured using a new Clark-type TCPO2 [transcutaneous PO2 (partial pressure of O2)]/PCO2 (partial pressure of CO2) monitoring system and optical NIRS (near-infrared spectroscopy) at graded levels of hypoxaemia using a rabbit model (n=6). The TCPO2/PCO2 probe was placed on the shaved hindlimb to record SPO2 (skin PO2) and SPCO2 (skin PCO2) continuously. A pair of NIRS probes were placed on the limb to monitor HbO2 (oxyhaemoglobin) and Hb (deoxyhaemoglobin). Graded hypoxaemia was achieved by stepwise reductions of FiO2 (fraction of inspired O2) from 30% to 6%. Animals were allowed to recover after each episode of hypoxia at an FiO2 of 30% as indicated by normalized arterial blood PO2. There was a significant (P<0.05) decrease in SPO2 with all grades of hypoxaemia and no significant changes in SPCO2. There was a significant (P<0.05) increase in muscle Hb with all grades of hypoxaemia and a significant (P<0.05) decrease in HbO2 when FiO2 was below 15%. A significant correlation was found between the SPO2 and HbO2 (r=0.92, P<0.001) and both were significantly correlated with arterial blood PO2 (P<0.001). The new TCPO2/PCO2 system, in addition to its application for the assessment of conditions such as chronic venous insufficiency where alteration in skin oxygenation occurs solely, also has potential in conditions such as peripheral vascular disease where both skin and muscle oxygenation may be affected.

Evaluation of the parameters of total, nutritive, and shunt blood flows in the skin microvasculature using laser Doppler flowmetry

Examination of 28 healthy subjects and 66 patients was performed using laser Doppler flowmetry (LDF) of the skin of fingers in the red and infrared ranges and wavelet analysis of microvascular blood flow oscillations. Formulas were suggested for the total (TF), nutritive (NF), and shunt (SF) local blood flows. TF = MI × Ac × An /(Pm × σ), where MI is the microcirculation index in perfusion units (PU), An and Ac are the averaged maximum amplitudes of the neurogenic and cardiac rhythms (in PU), Pm is the mean arterial pressure (in mm Hg), and σ is the mean square deviation of the amplitude of blood flow oscillations (in PU). NF = TF/SP, where SP is the shunting parameter. SP = An/Am, where Am is the averaged maximum amplitude of the myogenic rhythm (in PU). SF = TF - NF. Significant positive relationships between the skin oxygenation and NF (red), temperature and TF (red), and blood flow measured by hydrogen clearance and TF (infrared) were revealed by comparison of the LDF parameters with polarographic and thermographic data. The advantages of the LDF parameters compared with the MI were shown, especially in skin denervation syndromes. The TF decreased in the case of complete anatomic rupture of the median nerve and increased in reflex sympathetic dystrophy, with both cases being accompanied by a deficit of the NF (red).

Emerging Technology: Hyperspectral Imaging

Clinical decision-making in managing the patient with peripheral vascular disease is dependent upon patient history, physical examination, and noninvasive and invasive testing. Noninvasive testing currently includes the ankle-brachial index, pulse volume recordings, and transcutaneous oximetry. Each test yields information regarding perfusion and tissue oxygenation, but has limitations. The ankle-brachial index compares lower extremity blood pressure with the upper extremity, but it must be interpreted with caution in a patient with calcified atherosclerotic vessels, as is seen with diabetic patients, which can lead to an overestimation of actual pressure. Pulse volume recordings are mainly a qualitative estimation of distal perfusion and are highly dependent on the operator, which introduces both intraobserver and interobserver variability. Duplex ultrasound evaluation looses sensitivity in the small vessels of the limb and can be limited by instrument and operator. Transcutaneous oximetry is a quantitative measure of skin (end organ) oxygenation, but is limited by only evaluating one small area of the foot at a given time. Hyperspectral imaging was developed to possibly provide quantitative information regarding the spatial tissue oxygen saturation in patients with peripheral vascular disease.

Systemic effects of shock and resuscitation monitored by visible hyperspectral imaging.

Hyperspectral imaging (HSI) has been useful in monitoring several medical conditions, which to date have generally involved local changes in skin oxygenation of isolated regions of interest such as skin flaps or small burns. Here, by contrast, we present a study in which HSI was used to assess the local cutaneous manifestations of significant systemic events. HSI of the ventral surface of the lower jaw was used to monitor changes in skin oxygenation during hypovolemic shock induced by hemorrhage with additional pulmonary contusion injury in a porcine model, and to monitor the subsequent recovery of oxygenation with resuscitation. Quantitative and qualitative changes were observed in the level of skin oxygenation during shock and recovery. Quantitative values were obtained by fitting reference spectra of oxyhemoglobin and deoxyhemoglobin to sample spectra. Qualitative changes included changes in the observed spatial distribution or pattern of skin oxygenation. A mottled pattern of oxygen saturation was observed during hemorrhagic shock, but not observed during hypovolemic shock or following resuscitation. Historically, the assessment of skin color and mottling has been an important, albeit inexact, component of resuscitation algorithms. Now, it is possible to analyze these variables during shock and resuscitation in an objective manner. The clinical utility of these advances needs to be determined.

Oxygenation and microcirculation during skin stretching in undermined and nonundermined skin.

The aim of this experimental study was to assess the skin microcirculation of undermined and nonundermined wound edges closed with a skin-stretching device. In eight piglets, 9 x 9-cm wounds were created on both flanks by excision of the skin and the subcutaneous layer down to the muscular fascia, with general anesthesia. On one flank, the surrounding skin was completely undermined. For a period of 30 minutes, wound closure was performed with a stretching device, using the principle of load cycling. The device stretched the skin and moved the opposing wound edges toward each other. During this period, laser Doppler flowmetry and transcutaneous oximetry were simultaneously used to monitor microcirculation and oxygenation in the stretched skin of both flanks. Undermining of the surrounding skin produced a 12 percent decrease in the laser Doppler flowmetry signal and a 21 percent decrease in the transcutaneous oximetry value. Skin stretching resulted in decreases in the laser Doppler flowmetry signals and the transcutaneous oximetry values, whether or not the skin was undermined. Releasing the stretching device resulted in rapid normalization of the laser Doppler flowmetry values in undermined and nonundermined skin and a slow return of the transcutaneous oximetry values to close to baseline levels in nonundermined skin. The transcutaneous oximetry values in undermined skin did not return to baseline levels; each period of skin stretching resulted in an additional decrease in the transcutaneous oximetry values. Stretching of undermined skin for 30 minutes produced a significant (p < 0.0001) decrease in skin oxygenation. As a result, 50 percent of the undermined stretched skin demonstrated skin necrosis at the wound edges, which was still present after 1 week. Wound healing in the nonundermined stretched skin proceeded without problems. It is concluded from these experiments that the viability of undermined skin becomes compromised as a result of significantly decreased oxygen availability in the skin during and after stretching. Consequently, it is recommended that skin stretching be performed on nonundermined skin, rather than undermined skin. In addition, when skin is stretched to close a large defect, it is logical to use cyclic loading, so that recuperation of the skin circulation can occur. Furthermore, laser Doppler flowmetry seemed to produce atypical signals in monitoring of skin viability of wound edges closed with a skin-stretching device.

Rheopheresis in patients with ischemic diabetic foot syndrome: results of an open label prospective pilot trial.

Rheopheresis is a specific application of membrane differential filtration, synonymous with double filtration plasmapheresis, for extracorporeal hemorheotherapy. Safety and efficacy of Rheopheresis for wound healing and skin oxygenation were investigated in patients with ischemic diabetic foot syndrome. Eight patients with type 2 diabetes mellitus and non-healing foot ulcers caused by severe ischemic diabetic foot syndrome were treated by a series of seven Rheopheresis sessions in a time span of 11 weeks. Wound healing had not been detectable under conditions of standardized wound care during at least 2 months. Wound status was classified by its morphology, severity and location, according to the criteria of Wagner. Transcutaneous oxygen pressure (tcPO2), laser Doppler flowmetry and vital capillary microscopy were repeatedly performed to monitor the effects of the Rheopheresis treatment series on microcirculation and skin blood flow. Laboratory parameters of blood rheology, endothelial function and inflammatory state were measured in addition to safety parameters. In four patients (baseline Wagner stage 2), Rheopheresis accelerated wound healing of foot ulcers and was associated with an improvement of Wagner stage and a pronounced increase in tcPO2. In two patients (baseline Wagner stage 2), wound healing was unchanged but mean tcPO2 increased, allowing successful minor amputation. Values of tcPO2 remained stable and enhanced for the 3 months follow-up period. In two patients (baseline Wagner stage 4 or 5), no improvements in foot lesions were observed within the treatment period. As an adjunct therapeutic option, Rheopheresis may preserve a functional lower extremity, delay amputation or reduce the extent of amputation.

Skin oxygenation after topical application of liposome-entrapped benzyl nicotinate as measured by EPR oximetry in vivo: Influence of composition and size

New and improved drug delivery systems are the important subject of much scientific research. The development of formulations that increase skin oxygenation and of methods for measuring oxygen levels in skin are important for dealing with healing processes affected by the level of oxygen. We have use EPR oximetry in vivo to compare the influence of liposomal formulations of different size and composition with that of hydrogel with respect to the action of the entrapped benzyl nicotinate (BN). Following the topical application of BN onto the skin of mice, pO2 increase was measured by low-frequency EPR as a function of time. The effect of BN was evaluated by 3 different parameters: lag-time, time needed for maximum pO2 increase, and overall effectiveness expressed by the area under the response-time curve. An increase in skin oxygenation was observed after BN application. The results show that the effect of BN incorporated in liposomes is achieved more rapidly than the effect from hydrophilic gel. The composition of the liposomes significantly affects the time at which BN starts to act and, to a lesser extent, the maximum increase of pO2 in skin and the effectiveness of BN action. However, the size of the liposomes influences both the effectiveness of BN action and the time at which BN starts to act. After repeated application of liposomes, the pO2 baseline increased and the response of the skin tissue was faster. Our results demonstrate that EPR oximetry is a useful method for evaluating oxygen changes after drug application and for following the time course of their action.

Can motor nerve conduction velocity predict foot problems in diabetic subjects over a 6-year outcome period?

This study examined motor nerve conduction velocity (MNCV) and other peripheral nerve and vascular tests as predictors for foot ulceration, amputation, and mortality in diabetes over a 6-year follow-up period. We recruited 169 diabetic subjects (without significant peripheral vascular disease with an ankle brachial pressure index [ABPI] >/=0.75) for the study and separated them into groups (to ensure diversity of nerve function). The control group consisted of 22 nondiabetic people. At baseline, all subjects underwent assessment of MNCV; vibration, pressure, and temperature perception thresholds; peripheral vascular function; and other diabetes assessments. Over the 6-year outcome period, 37.3% of the diabetic subjects developed at least one new ulcer, 11.2% had a lower-limb amputation (LLA) (minor or major), and 18.3% died. Using multivariate Cox's regression analysis (RR [95% CI] and removing previous ulcers as a confounding variable, MNCV was found to be the best predictor of new ulceration (0.90 [0.84-0.96], P = 0.001) and the best predictors of amputation were pressure perception threshold (PPT) (5.18 [1.96-13.68], P = 0.001) and medial arterial calcification (2.88 [1.13-7.35], P = 0.027). Creatinine (1.01 [1.00-1.01], P < 0.001), MNCV (0.84 [0.73-0.97], P = 0.016), and skin oxygen levels (14.32 [3.04-67.52], P = 0.001) were the best predictors of mortality. This study shows that MNCV, which is often assessed in clinical trials of neuropathy, can predict foot ulceration and death in diabetes. In addition, tests of PPT and medial arterial calcification can be used in the clinic to predict LLA in diabetic subjects.

Physiologically low oxygen concentrations in fetal skin regulate hypoxia-inducible factor 1 and transforming growth factor-beta3.

In the first-trimester mammalian fetus, skin wounds heal with perfect reconstitution of the dermal architecture without scar formation. Understanding environmental molecular regulation in fetal wound healing may reveal scar-limiting therapeutical strategies for the prevention of postnatal scarring wound repair. Therefore, we performed studies on fetal skin oxygenation and skin and wound expression of hypoxia-inducible factor 1alpha (HIF-1alpha) in the sheep model in vivo and performed studies on the potential relevance of HIF-1alpha during wound healing in vitro. Skin oxygen partial pressure levels were hypoxic throughout normal development. In nonscarring fetal skin at gestation day (GD)60, HIF-1alpha could be detected neither in healthy nor in wounded tissue. At GD100, in wounds with minimal scar formation, HIF-1alpha was expressed in fibroblasts and was markedly up-regulated at the wound edge. In scarring fetal wounds at GD120, HIF-1alpha was predominantly expressed in inflammatory cells. Expression of transforming growth factor beta3 (TGF-beta3), a potent antiscarring cytokine, overlapped with HIF-1a expression at GD100. HIF-1alpha-deficient mouse embryonic fibroblasts showed impaired migratory capabilities and demonstrated that TGF-beta3, but not proscarring TGF-beta1, manifests hypoxia- and HIF-1alpha-dependent regulation. In conclusion, HIF-1alpha-dependent regulation of a potent antiscarring cytokine may provide new strategies for antiscarring manipulation of wound healing.

Early detection of microcirculatory impairment in diabetic patients with foot at risk.

To assess microcirculatory impairment and alterations of the skin oxygen supply in diabetic patients with foot at risk. This study evaluated skin blood flow in 21 type 2 diabetic patients with a foot at risk (defined as a foot with neuropathy but without ulceration or previous ulcerations), 20 type 2 diabetic patients without foot lesions or neuropathy, and 21 normal subjects as a control group. The skin blood flow was determined by measuring the transcutaneous oxygen pressure (TcPO(2)) at the dorsum of the foot in supine and sitting position. The clinical assessment included standard measures of peripheral and autonomic neuropathy, but peripheral vascular disease was excluded by Doppler ultrasound. In supine position, TcPO(2) was significantly reduced (means +/- SE) in diabetic patients with foot at risk (6.04 +/- 0.52 kPa) compared with diabetic (7.14 +/- 0.43 kPa, P = 0.035) and nondiabetic (8.10 +/- 0.44 kPa, P = 0.01) control subjects. The sitting/supine TcPO(2) difference was higher in diabetic subjects with foot at risk (3.13 +/- 0.27 kPa) compared with both diabetic (2.00 +/- 0.18, P = 0.004) and nondiabetic (1.77 +/- 0.15 kPa, P = 0.0003) control subjects. The mean sitting/supine ratio was 1.70 +/- 0.12 in diabetic patients with foot at risk, 1.32 +/- 0.04 in diabetic control subjects, and 1.25 +/- 0.03 in nondiabetic control subjects (P = 0.007). The sitting/supine TcPO(2) ratio was negatively correlated with the heart rate variation coefficient at rest (r = -0.32, P = 0.044) and at deep respiration (r = -0.31, P = 0.046). Our data indicate that skin oxygen supply is reduced in type 2 diabetic patients with foot at risk. This is probably due to an impaired neurogenic blood flow regulation and may contribute to capillary hypertension, followed by disturbed endothelial function leading to edema and skin damage of the foot. The determination of TcPO(2) appears to be a useful tool in screening type 2 diabetic patients for foot at risk.

An analysis of skin perfusion over the achilles tendon in varying degrees of plantarflexion.

Delayed wound healing and, less commonly, wound breakdown are significant complications following open Achilles tendon repair. Skin perfusion over the Achilles tendon may be reduced when the ankle is plantarflexed. The aim of this study was to analyse skin perfusion over the Achilles tendon with the ankle in varying degrees of plantarflexion in 20 volunteers. Skin perfusion was determined by measuring the transcutaneous skin oxygen pressure (tcPO2) using the Novametrix TcO2M 860 monitor. Measurements were taken at the medial edge of the Achilles tendon in 20 volunteers. Skin perfusion was maximal with the ankle plantarflexed to 20 degrees. With plantarflexion beyond this skin perfusion was reduced. At 40 degrees plantarflexion skin perfusion was reduced by up to 49% (mean 35%, range 27% to 49%). We conclude plantarflexion beyond 20 degrees reduces skin perfusion in the region of the Achilles tendon. Though this study was performed on non-operated cases, and is thus limited, the findings may have clinical implications with regard to cast position following Achilles tendon repair.

Transcutaneous oxygen tension in patients with calciphylaxis

Calciphylaxis is a severe complication of chronic renal failure, confined almost exclusively to patients on dialysis therapy. Histological characteristics of calciphylaxis include small-vessel calcifications of skin, subcutaneous tissue, and visceral organs. These vascular changes promote tissue ischemia that often results in tissue necrosis. In this study, we investigated the extent of skin ischemia in patients with calciphylaxis by means of transcutaneous oxygen tension (TCPo2) measurement, a noninvasive test that accurately assesses skin oxygenation. TCPo2 levels were measured in 21 patients with calciphylaxis and 21 age- and sex-matched patients without evidence of calciphylaxis (controls). TCPo2 levels were measured bilaterally at the chest, anterior abdomen, and upper thigh while patients breathed room air and after a 30-minute exposure to 100% fraction of inspired oxygen (Fio2). Compared with controls, patients with calciphylaxis showed significantly lower TCPo2 levels at each body region. In both controls and patients with calciphylaxis, lower TCPo2 levels correlated with increased weight and use of hemodialysis. No correlation with serum parathyroid hormone (PTH), serum calcium, or serum phosphorus values was present, although 39% of the patients with calciphylaxis had markedly elevated PTH values (sixfold greater than normal; >300 pg/dL). Low TCPo2 levels in patients with calciphylaxis were documented in body regions with and without skin lesions. In patients with calciphylaxis, extremely low TCPo2 values (≤30 mm Hg while patients breathed room air) were present in 62% of the body regions with skin lesions and 26% of the body regions without lesions. Room-air TCPo2 levels ≤30 mm Hg were present in only 0.8% of the body regions of control patients. TCPo2 levels obtained while patients breathed 100% Fio2 remained lower in patients with calciphylaxis than in controls. In conclusion, TCPo2 levels are abnormally low in patients with calciphylaxis, indicating that severe and diffuse skin ischemia exists, even at areas free of skin lesions. Low TCPo2 values did not substantially increase with 100% Fio2 in many patients with calciphylaxis, suggesting a fixed insufficiency of the skin vessels. This study shows that TCPo2 measurements may allow rapid and noninvasive screening for skin ischemia before the development of skin lesions in patients with calciphylaxis.

Monitoring tissue oxygenation during resuscitation of major burns.

Because subcutaneous and splanchnic oxygenation indices are sensitive indicators of evolving hemorrhagic shock and adequacy of resuscitation, we postulated that these indices might have an equivalent role in the monitoring of severely burned patients. This observational study was undertaken to examine changes in tissue oxygenation indices during burn resuscitation. Seven patients with major burns (54 +/- 21% total body surface area) were studied during the first 36 hours of fluid resuscitation. Silastic tubing was placed in the subcutaneous tissue just beneath both normal skin and deep partial thickness burn. Fiberoptic sensors inserted into the tubing measured subcutaneous oxygen and carbon dioxide tensions in the burnt skin (PO2scb and PCO2scb) and normal skin (PO2scn and PCO2scn) continuously. Gastric intramucosal pH (pHi) and the mucosal CO2 (PCO2m) gap were calculated using gastric tonometers. Mean arterial pressure, arterial pH, lactate, and pHi measurements were obtained for 36 hours. There were no significant differences in mean arterial pressure, arterial pH, or lactate concentrations throughout the study period, whereas indices of tissue oxygenation showed deterioration: pHi decreased from 7.2 +/- 0.1 to 6.7 +/- 0.3 (p = 0.06), the PCO2m gap increased from 12 +/- 17 to 108 +/- 123 mm Hg (p < 0.01), PO2scn decreased from 112 +/- 18 to 50 +/- 11 mm Hg (p < 0.01), PO2scb decreased from 62 +/- 23 to 29 +/- 16 mm Hg (p < 0.01), PCO2scn increased from 42 +/- 4 to 46 +/- 10 mm Hg (p = 0.2), and PCO2scb increased from 42 +/- 10 to 52 +/- 5 mm Hg (p = 0.05). Despite adequate global indices of tissue perfusion after 36 hours of resuscitation, tissue monitoring indicated significant deterioration in the splanchnic circulation and in the normal and burnt skin.

Improved skin oxygenation after benzyl nicotinate application in different carriers as measured by EPR oximetry in vivo

The development of formulations, which increase skin oxygenation and of methods for measuring oxygen levels in skin are important for dealing with processes affected by the level of oxygen, e.g., rate of healing and efficiency of radiation oncology. In this study we have investigated the role of carriers on the efficacy of benzyl nicotinate (BN) action in skin after dermal application in different formulations by EPR oximetry in vivo. The time course of pO 2 in the skin after application of rubefacient is followed directly for the first time. The results obtained proved the applicability of in vivo EPR oximetry as a sensitive method by which small alterations in pO 2 can be detected. We have found that the type of vehicle significantly influences the time when BN starts to act, the duration of its action, and the maximal increase in pO 2. The ranking of vehicle efficiency was: lipid nanoparticles in hydrophilic gel>liposomes in hydrophilic gel>hydrophilic gel>hydrophobic ointment>hydrophobic cream. Primarily the semi-solid vehicle determines the lag-time of action, but the maximal oxygen level is influenced decisively by the particulate carrier systems. BN effectiveness was dose dependent. 2.5% w/w concentration of BN appears to be the most appropriate for therapeutic application. After repeated application a successive increase of pO 2 base line in skin and of the maximal pO 2 was noticed.

Transcutaneous oxygen and CO2 as early warning of tissue hypoxia and hemodynamic shock in critically ill emergency patients.

Although cardiac and pulmonary function can be measured precisely, evaluation of tissue perfusion remains elusive because it usually is inferred from subjective symptoms and imprecise signs of shock. The latter are indirect criteria used to assess the overall circulatory status as well as tissue perfusion but are not direct quantitative measures of perfusion. However, noninvasive transcutaneous oxygen (PtcO2) and carbon dioxide (PtcCO2) tensions, which directly measure skin oxygenation and CO2 retention, may be used to objectively evaluate skin oxygenation and perfusion in emergency patients beginning with resuscitation immediately after hospital admission. This study was a preliminary evaluation of tissue oxygenation and perfusion by objective PtcO2 and PtcCO2 patterns in severely injured surviving and nonsurviving patients; specifically, the aim was to describe time patterns that may be used as early warning signs of circulatory dysfunction and death. Prospective descriptive study of a consecutive series of severely injured emergency patients. University-affiliated Level I trauma center and intensive care unit. Forty-eight consecutive severely injured patients were prospectively monitored by PtcO2 and PtcCO2 sensors immediately after emergency admission. Compared with survivors, patients who died had significantly lower PtcO2 and higher PtcCO2 values beginning with the early stage of resuscitation. All patients who maintained PtcO2 >150 torr (19.99 kPa) throughout monitoring survived. Periods of PtcO2 <50 torr (6.66 kPa) for >60 mins or PtcCO2 >60 torr (8.00 kPa) for >30 mins were associated with 90% mortality and 100% morbidity. PtcO2 and PtcCO2 monitoring continuously evaluate tissue perfusion and serve as early warning in critically injured patients during resuscitation immediately after hospital admission.

Decubitus Risk: Is Shear More Important than Pressure?

A mechanical load through which the capillaries are closed causes tissue ischaemia of the skin. Most authors agree that it is this tissue ischaemia that is the main factor in the cause of pressure sores. Different combinations of mechanical load on the skin may have the same effect within the skin. The aim of this study is to evaluate the effect that different combinations of pressure and shear have on blood flow within the skin. The skin blood flow was measured by means of skin oxygen tension. Different load combinations on the skin surface, for which the maximum shear stress within the skin remained equal, showed no significant difference in skin blood flow. Research should therefore focus on load situations within the skin instead of pressure measurements on the skin surface only.

Effects of vacuum compression therapy on skin microcirculation in patients suffering from lower limb ischaemia.

We investigated the short-term effect of vacuum compression (VC) treatment on skin microcirculatory perfusion in the foot of patients with lower limb ischaemia and healthy controls. Ten patients with intermittent claudication or rest pain and 5 healthy controls underwent vacuum-compression treatment for half an hour. The leg was positioned in an air-tight plexiglass cylinder in which hypobaric (-115 mm Hg) and hyperbaric (75 mm Hg) pressure could be generated alternately, in order to improve peripheral circulation. The effect on skin microcirculation was investigated using nailfold capillary microscopy (measuring nutritive perfusion), laser Doppler fluxmetry (LDF) (total skin perfusion) and transcutaneous oxygen tension measurements (TcpO2). A few patients experienced ischaemic symptoms during VC, probably because the leg was pinched off through inflation of the cuff. In both patients and controls capillary microscopic parameters did not change significantly. In some cases, microcirculatory perfusion decreased because the leg had cooled during the treatment. Application of a heating matrass annihilated this effect. Only in the patient group a few LDF- and TcpO2 parameters improved slightly, but significantly. Vacuum-compression therapy only slightly improves total skin perfusion and oxygenation, but not the nutritive microcirculation, being an essential factor in the occurrence of ischaemic symptoms. We therefore conclude that this instrument in its present form is not an aid in the treatment of lower limb ischaemia.