Tissue oxygenation, anemia, and perfusion in relation to wound healing in surgical patients

Mechanisms governing the effects of vacuum-assisted closure in cardiac surgery

SUMMARY

: Vacuum-assisted closure has been adopted as the first-line treatment for poststernotomy mediastinitis as a result of the excellent clinical outcome achieved with its use. Scientific evidence regarding the mechanisms by which vacuum-assisted closure promotes wound healing has started to emerge, although knowledge regarding the effects on heart and lung function is still limited. The organs in the mediastinum are hemodynamically crucial, and in patients with poststernotomy mediastinitis, vulnerable bypass grafts and reduced cardiac function must be taken into consideration during vacuum-assisted closure therapy. This article provides an overview of the effects of vacuum-assisted closure on heart and lung function and summarizes the current knowledge on the mechanisms by which vacuum-assisted closure therapy promotes wound healing.

Perioperative Hypothermie

Mild perioperative hypothermia is a common complication of anesthesia and surgery associated with several adverse effects including impaired wound healing and more frequently leads to wound infections. Perioperative hypothermia affects the hemostasis and various immune functions and therefore interferes with the initial phases of the wound healing process. Furthermore, perioperative hypothermia contributes to wound complications by inhibition of deposition of collagen and prolongation of postoperative catabolism. Wound complications prolong hospitalization and substantially increase medical costs. Thus, maintaining normothermia perioperatively is essential to reduce the number of wound complications.

Incidence and Risk Factors of Stomal Complications in Patients Undergoing Cystectomy With Ileal Conduit Urinary Diversion for Bladder Cancer

PURPOSE

In this study we examined the incidence and associated factors of stomal complications in patients undergoing radical cystectomy with ileal conduit urinary diversion for bladder cancer. In addition, we evaluated the treatment and outcomes of surgical procedures in patients in whom stoma related complications developed.

MATERIALS AND METHODS

From 2001 to 2005 a total of 137 patients underwent ileal conduit diversion after cystectomy or exploration for bladder cancer, had complete clinical followup and were followed for at least 12 months after surgery. The incidence of stomal complications (including parastomal hernia, stomal stenosis and stomal prolapse) is reported with correlations made to age, race, gender, body mass index, smoking history, alcohol consumption, preoperative laboratory values (creatinine, hematocrit), operative estimated blood loss and surgical complications. In addition, management of stomal complications is reported.

RESULTS

Of the 137 patients 21 stomal complications (15.3%) occurred in 20 patients (14.6%). The most common complication was parastomal hernia in 19 patients (13.9 %). Stomal stenosis developed in 1 patient (0.7%) and stomal prolapse developed in 1 patient with a parastomal hernia (0.7%). There were no significant differences in gender, age, race, preoperative laboratory values or history of abdominal/pelvic radiation therapy between patients with or without complications. However, patients in whom complications developed had a significantly higher mean body mass index compared to those without complications (30.8 vs 26.5 kg/m(2), respectively, p = 0.012). Operative outcomes, extent of disease and length of postoperative followup were also similar between patients with or without stomal complications. In addition, there were no significant differences in lifestyle factors (eg smoking, alcohol abuse) in patients in whom complications developed.

CONCLUSIONS

Stomal complications associated with ileal conduit urinary diversion are not uncommon and occur in almost 15% of patients, with the most common problem being parastomal hernia. Evaluation of possible risk factors demonstrates that obesity may be a contributing factor in the development of stomal complications, particularly in the elderly. Furthermore, our experience suggests that subsequent repairs of parastomal hernias are only moderately successful.

Determinanten des insensiblen Flüssigkeitsverlustes

Accurate perioperative fluid balance is the basis of a targeted infusion regimen. However, neither the initial status nor perioperative changes of the fluid compartments can be reliably measured in daily routine. In particular, insensible losses are not consistently assessed, so that substitution therapy is generally empirical. The object of this paper is to communicate the scientific data on this topic. Preoperative fasting (10 h) does not per se cause intravascular hypovolemia. In adults, total basal evaporation by way of the skin and airways and of any wounds during major abdominal interventions is usually less than 1 ml/kg/h. An inconstant fluid and protein shift towards the interstitial space perioperatively seems to be associated with hypervolemia, which suggests it should be preventable. The decisive factor in this context seems to be deterioration of the endothelial glycocalyx, whose further patho-physiological impact is currently only partially known. Clinical studies have revealed a link between fluid restriction and improved outcome after major abdominal surgery.

Wounds: an overview of the role of oxygen

We sought to review the role of oxygen in wound healing, with an emphasis on the role tissue oximetry has played in clinical advances in the care of patients with wounds. Oxygen is required for wound healing. Hypoxia sufficient to impair healing is common in wounds, frequently resulting from sympathetically induced vasoconstriction. Correction or prevention of vasoconstriction, as well as provision of increased inspired oxygen in well-perfused patients, has been shown in randomized, controlled clinical trials to improve wound outcomes. Our understanding of the role of oxygen in wound healing has been fueled by tissue oximetry. Advances in technology will lead to further advances in the management of patients with wounds.

Photobiomodulation on the Angiogenesis of Skin Wounds in Rats Using Different Light Sources

OBJECTIVE

The aim of this study was to compare the angiogenic effects of laser and light-emitting diode (LED) illumination on wounds induced in rats, with varied fluence.

BACKGROUND DATA

The LED is an alternative light source that accelerates wound healing, and its efficiency concerning the angiogenic effect was compared to low-level laser therapy (LLLT).

METHODS

The experimental model consisted of a circular wound inflicted on the quadriceps of 120 rats, using a 15-mm-diameter "punch." Animals were divided randomly into five groups: two groups of laser, with dosages of 5 and 20 J/cm(2), respectively, two groups of LED, also with dosages of 5 and 20 J/cm(2), and a control group. Six hours after wound infliction, the treated groups received the diverse applications accordingly and were irradiated every 24 h. Angiogenesis was studied through histomorphometry on days 3, 7, 14, and 21 after the wounds were inflicted.

RESULTS

On days 3, 7, and 14, the proliferation of blood vessels in all irradiated groups was superior in comparison to those of the control group (p < 0.05). Treatment with fluence of 5 J/cm(2) was better than the laser group with 20 J/cm(2) on day 21.

CONCLUSION

Red LLLT and LED demonstrated expressive results in angiogenesis. Light coherence was shown not to be essential to angiogenesis. However, further studies are needed in order to investigate the photobiomodulatory effects of LED in relation to LLLT in various biological tissues.

Effect of oral hydration on skin microcirculation in healthy young and midlife and older adults

Clinically undetected underhydration lowers subcutaneous tissue oxygen, impairs healing and increases wound infection. This study examined the effect of supplemental oral hydration on noninvasive measures of skin temperature (T(s)), transcutaneous skin O(2) (PtcO(2)), and CO(2) (PtcCO(2)), and skin blood flow (laser Doppler fluxmetry [Flux]=concentration of moving blood cells [CMBC] x Velocity) in healthy adults. Nineteen Control and 18 Test (Hydrated) subjects participated. Ad libitum fluid intake was allowed before the experiment. Sensors were placed on the chest, lower legs, and feet. Time 1 resting supine T(s), PtcO(2)/PtcCO(2), and Flux/CMBC/Velocity were obtained. Then, the Test group ingested 500 mL of H(2)O. Time 2 measures were obtained 30 minutes later. Data were analyzed using ANOVA. Change in T(s), PtcO(2), PtcCO(2), and Velocity did not differ between groups. Flux increased more in the Test than in the Control group (p<0.01). The Flux change was explained by a CMBC increase (p<0.05). For midlife/older subjects only, the CMBC change was greater in the Test than in the Control group (p<0.01). Flux may be sufficiently sensitive to detect microvascular changes in response to supplemental oral hydration. These data also suggest that subtle levels of hypoperfusion due to underhydration may exist in community-dwelling healthy midlife/older adults in their natural state.

Lactate stimulates endothelial cell migration

The significance of the high lactate levels that characterize healing wounds is not fully understood. Lactate has been shown to enhance collagen synthesis by fibroblasts and vascular endothelial growth factor (VEGF) production by macrophages and endothelial cells. VEGF has been shown to induce endothelial cell migration. However, it has not been shown whether accumulated lactate correlates with the biological activity of VEGF. Therefore, we investigated the effect of lactate on migration of endothelial cells. Human umbilical vein endothelial cells and human microvascular endothelial cells were cultured to subconfluent monolayers in standard six-well tissue culture plates. Following a 24-hour serum starvation, cells were treated with the indicated concentrations of l-lactate. Cell migration was assessed using a modified Boyden chamber. VEGF protein in the cell culture supernatant was measured by enzyme-linked immunoassay. Lactate-enhanced VEGF protein synthesis in a time- and dose-dependent manner. Lactate added into the bottom well did not stimulate cellular migration from the upper well. However, lactate when added together with endothelial cells to the bottom well of the Boyden chamber increased cellular migration in a dose-dependent manner. This effect was blocked by anti-VEGF and by cycloheximide. Lactate enhances VEGF production in endothelial cells, although lactate, itself, is not a chemoattractant. We conclude that the lactate-mediated increase in cellular migration is regulated by VEGF.

Incisional vacuum-assisted closure therapy

Postoperative swelling and prolonged drainage from surgical incisions result in both practical and medical burdens, such as increased need for dressing changes and potentially higher rates of surgical wound infection. This article presents a technique to apply a vacuum-assisted closure therapy sponge as a postoperative dressing to provide a clean, dry wound environment in the immediate postoperative period.

Laparoscopy and collagen metabolism

The collagens represent a vital component within the wound healing process and physiological scar formation. Therefore, analysing the influence of new operative procedures on collagen metabolism is of great surgical interest. As the endoscopic technique has, nowadays, become routinely applied for diverse abdominal diseases worldwide, we present a review of literature facing its impact on collagen biology.

Continuous Muscle Tissue Oxygenation in Critically Injured Patients: A Prospective Observational Study

BACKGROUND

Despite normalization of vital signs, critically injured patients may remain in a state of occult underresuscitation that sets the stage for sepsis, organ failure, and death. A continuous, sensitive, and accurate measure of resuscitation after injury remains elusive.

METHODS

In this pilot study, we evaluated the ability of two continuous measures of peripheral tissue oxygenation in their ability to detect hypoperfusion: the Licox polarographic tissue oxygen monitor (PmO2) and the InSpectra near-infrared spectrometer (StO2). We hypothesized that deltoid muscle tissue oxygenation measurements could detect patients in "occult shock" who are at increased risk for post-injury complications. The study was designed to (1) define values for PmO2 and StO2 in patients who by all standard measures appeared to be clinically resuscitated; (2) evaluate the relationship between PmO2, StO2 and other physiologic variables including mean arterial pressure (MAP), lactate and base deficit (BD); and (3) examine the relationship between early low tissue oxygen values and the subsequent development of infections and organ dysfunction. Licox probes were inserted into the deltoid muscle of critically injured patients after initial surgical and radiologic interventions, and transcutaneous StO2 monitors were applied over the same muscle bed. PmO2, StO2, and standard physiologic data were collected continuously using a multimodal bioinformatics system.

RESULTS

Twenty-eight critically injured patients were enrolled in this study at admission to the intensive care unit (ICU). For patients who appeared to be well resuscitated (defined as MAP > or = 70 mm Hg, heart rate [HR] < or = 110 bpm, BD > or = -2, and partial pressure of arterial oxygen (PaO2) = 80 and 150 mm Hg), the mean PmO2 was 34 +/- 11 mm Hg and StO2 was 63 +/- 27%. There was a strong relationship between PmO2 and BD (p < 0.001) but no significant relationship between StO2 and BD. The relationship between PmO2 and StO2 was weak but statistically significant. Early low values of both PmO2 and StO2 identified patients at risk for infectious complications or multiple organ failure (MOF). In patients who were well resuscitated by standard continuous parameters (HR and MAP), low PmO2 during the first 24 hours after admission (PmO2 < or = 25 for at least 2 hours) was strongly associated with the development of infectious complications (Odds Ratio = 16.5, 95% CI 1.49 to 183, p = 0.02).

CONCLUSIONS

PmO2 is a responsive, reliable and continuous monitor of changes in base deficit. Initial low values for either PmO2 or StO2 were associated with post-injury complications. PmO2 monitoring may be useful in identifying patients in the state of occult underresuscitation who remain at risk for developing infection and MOF.

Differences in cutaneous wound healing between dogs and cats

Regardless of the species involved, wound healing follows a predictable course of overlapping phases. In spite of these commonalities, significant species differences in cutaneous wound healing have been uncovered in the Equidae and, more recently, between the dog and cat. It has also recently been shown that the subcutaneous tissues play an important supporting role in cutaneous wound healing, which may help to ex-plain healing differences between cats and dogs. These discoveries may improve veterinarians' understanding of problem wound healing in the cat and, hopefully, lead to better strategies for wound management in this sometimes troublesome species.

Blood flow responses in the peristernal thoracic wall during vacuum-assisted closure therapy

BACKGROUND

Vacuum-assisted closure (VAC) therapy is a recently introduced method for the treatment of poststernotomy mediastinitis. The aim of this study was to examine the effects of negative pressure on peristernal soft tissue blood flow and metabolism because the mechanisms by which vacuum-assisted closure therapy promotes wound healing are not known in detail.

METHODS

Microvascular blood flow was examined by laser Doppler velocimetry in an uninfected porcine sternotomy wound model. Microvascular blood flow was examined in the muscular and subcutaneous tissue, at different distances from the wound edge, after the application of -50 to -200 mm Hg. Wound fluid pH, partial pressures of oxygen and carbon dioxide, bicarbonate, and lactate were analyzed after 0, 30, and 60 minutes of continuous negative pressure.

RESULTS

Vacuum-assisted closure therapy induced an increase in the microvascular blood flow a few centimeters from the wound edge. In muscular tissue, the distance from the wound edge to the position at which the blood flow was increased was shorter than that in subcutaneous tissue. Close to the wound edge, relative hypoperfusion was observed. The hypoperfused zone was larger at high negative pressures and was especially prominent in subcutaneous tissue. Wound fluid partial pressure of oxygen and lactate levels were increased after 60 minutes of vacuum-assisted closure therapy, which may be the result of changes in the microvascular blood flow.

CONCLUSIONS

Vacuum-assisted closure therapy induces a change in microvascular blood flow that is dependent on the pressure applied, the distance from the wound edge, and the tissue type. It may be beneficial to tailor the negative pressure used for vacuum-assisted closure therapy according to the wound tissue composition. Wound fluid partial pressure of oxygen and lactate levels increased during vacuum-assisted closure therapy. This combination is known to promote wound healing.

Fluid management of patients undergoing abdominal surgery – more questions than answers *

The 'wet vs. dry' philosophy in patients undergoing abdominal surgery is a subject of substantial debate. It has been suggested that restricting fluid input would significantly reduce complications and improve outcome following abdominal surgery. Keeping the patients dry may be a two-edged sword because the resulting hypovolaemia may result in compromised organ perfusion and poor tissue oxygenation. A review of the literature from 1990 to 2004 revealed that only very few studies on this subject have been published. Unfortunately, most of the 'dry'-supporting studies used fixed amounts of volume instead of a fluid concept adapted to the patients' need ('goal-directed') and there is no generally accepted definition of 'restricted', 'dry' or 'overload'. Not only the amount but also the kind of administered fluid appears to be important. Current evidence indicates that using crystalloids exclusively may cause overloading of the interstitial compartment with considerable negative sequelae, whereas using colloids may improve microperfusion and tissue oxygenation. This review shows that the meagre literature on a restricted volume replacement strategy in abdominal surgery patients cannot clearly support the 'dry' approach. Further well-performed studies are necessary to elucidate the ideal amount and type of fluid replacement and determine how to guide fluid therapy.

Extending the limits of fingertip composite grafting with moist-exposed dressing

We introduced the concept of moist wound healing to extend the limits of fingertip composite grafting. In this retrospective study, we assessed the success of fingertip composite grafting with moist-exposed ointment dressing, which has been shown to maintain adequate moisture for optimal healing by frequent ointment application without the need for a secondary overlying dressing. We reviewed the outcome of composite graft replacement of 60 amputated fingertips in 56 consecutive patients over a period of 3 years and 3 months. Forty-two fingertips had survived completely and 18 had failed. Twelve of 15 fingers among patients younger than 15 years of age and 30 of 45 fingers among those 16 years of age and older had survived completely. We believe that our use of antibiotic ointment to maintain a moist environment was an important factor in improving the survival of composite grafts.

Topical and Systemic Medications for Wounds

There are a plethora of topical and systemic medications available to the veterinary practitioner today that aid the wound healing process. Some of these help to maintain a moist environment. Others increase growth factors, provide local energy sources, control infection, provide for debridement, increase wound blood flow and temperature, or reduce wound edema. Modern wound care requires that the proper products(s)be used, depending on the condition of the wound and the phase of wound healing. This article discusses various wound care products and provides guidelines on their use.

Non-pharmacologic Prevention of Surgical Wound Infection

Surgical site infections are among the most common serious perioperative complications. Infections are established during a decisive period that lasts a few hours after contamination. Adequacy of host immune defenses is the primary factor that determines whether inevitably wound contamination progresses into a clinical infection. As it turns out, many determinants of infection risk are under the direct control of anesthesiologists; factors that are at least as important as prophylactic antibiotics. Major outcome studies demonstrate that the risk of surgical wound infection is reduced threefold simply by keeping patients normothermic. Infection risk is reduced by an additional factor of two by if supplemental oxygen is provided (80% versus 30%) during surgery and for the initial hours after surgery. The contribution, if any, of other factors including, tight glucose control, fluid management, and mild hypercapnia have yet to be suitably tested.

Using Physiology to Improve Surgical Wound Outcomes

Despite major advances in surgical management and approaches, including aseptic techniques, prophylactic antibiotics, and laparoscopic surgery, surgical wound infection and wound failure remain common complications of surgery. In a review of the literature, the authors found that a growing body of literature supports the concept that patient factors are a major determinant of wound outcome after surgery. In particular, wounds are exquisitely sensitive to hypoxia, which is both common and preventable. Perioperative management can be adapted to promote postoperative wound healing and resistance to infection. The most important factors are fluid management, temperature management, pain control, increased arterial oxygen tension, and, as has been long recognized, appropriate sterile techniques and administration of prophylactic antibiotics. This article reviews how knowledge of and attention to physiology can improve quality of care in both acute and chronic wounds.

Wound Healing: An Overview

Understanding wound healing today involves much more than simply stating that there are three phases: inflammation, proliferation, and maturation. Wound healing is a complex series of reactions and interactions among cells and "mediators." Each year, new mediators are discovered and our understanding of inflammatory mediators and cellular interactions grows. This article will attempt to provide a concise overview on wound healing and wound management.

Risk factors related to recurrence in inguinal hernia repair: a retrospective analysis

The aim of this study was to analyze and evaluate the long-term recurrence rate and risk factors for inguinal hernia recurrence in patients treated by the Shouldice suture repair. A total of 293 hernias treated by Shouldice suture technique in 1992 were studied retrospectively. After a 10-year follow-up, 15 potential risk factors for recurrence were assessed in 142 patients undergoing 171 Shouldice repairs. Recurrent hernias showed a significantly higher (22.0%) recurrence rate than primary inguinal hernias (7.7%). Furthermore, an age of more than 50 years, smoking, and the presence of two or more similarly affected relatives were found to be independent risk factors for recurrence. The present study underlines the importance of patient-related risk factors for the development of a recurrent inguinal hernia. Patients at risk should preoperatively be identified in order to improve treatment by, for example, the application of mesh techniques.

Randomized clinical trial to evaluate the effects of perioperative supplemental oxygen administration on the colorectal anastomosis

Background

Perioperative supplemental oxygen therapy may have beneficial effects on wound healing following colorectal surgery. The aim of this study was to evaluate the effects of such therapy on colorectal anastomotic pH and partial pressure of carbon dioxide (Pco2) gap.

Methods

Forty-five patients undergoing anterior resection for rectal or sigmoid cancer were randomized to receive 30 or 80 per cent perioperative oxygen. Administration was commenced after induction of anaesthesia and maintained for 6 h after surgery. Intragastric and anastomotic tonometric catheters were placed in each patient and intramucosal pH (pHi) was measured immediately after operation, and 6 and 24 h later. Gastric and anastomotic pHi and Pco2 gap in each group were compared.

Results

There was a significantly lower anastomotic pHi and wider Pco2 gap for gastric readings in the 30 per cent O2 group, both 30 min (pHi, P = 0·006; Pco2 gap, P = 0·006) and 6 h (pHi, P = 0·024; Pco2 gap, P = 0·036) after surgery. There were no differences 24 h after surgery while breathing room air (pHi, P = 0·131; Pco2 gap P = 0·139). No difference was found between gastric and anastomotic readings at any time point in the 80 per cent O2 group.

Conclusion

Perioperative administration of 80 per cent O2 both during surgery and for 6 hours afterwards is associated with an improvement in relative anastomotic hypoperfusion as assessed by the measurement of pHi and Pco2 gap.

Effects of hyperbaric oxygen and Pgg-glucan on ischemic colon anastomosis

AIM: In colorectal surgery, anastomotic failure is still a problem in ischemia. Here, we analyzed the effects of hyperbaric oxygen and beta-glucan on colon anastomoses in ischemic condition.

METHODS: Colonic resection and anastomosis in rectosigmoid region were done in forty Wistar-Albino rats of four groups of equal number. Colon mesentery was ligated to induce ischemia. The first group was the control group. The subjects of second group were treated with hyperbaric oxygen; the third group with glucan and the forth group were treated with both. At the forth day, rats were sacrificed, anastomotic segment was resected and burst pressures and hydroxyproline levels of anastomotic line were measured.

RESULTS: The burst pressure difference of second and third groups from the control group were meaningful (P < 0.01); the forth group differed significantly from the control (P < 0.001). There was no difference between the treated groups on burst pressure level (P > 0.05). The hydroxyproline levels in all treated groups were different from the control group significantly (P < 0.001). Hydroxyproline levels in the forth group were higher than those of the second and the third groups (P < 0.001). There were no significant differences between the second and the fourth groups in burst pressure and hydroxyproline levels (P > 0.05).

CONCLUSION: Hyperbaric oxygen and glucan improve healing in ischemic colon anastomoses by anti-microbic, immune stimulating properties and seem to act synergistically when combined together.

Dermal excisional wound healing in pigs following treatment with topically applied pure oxygen

Hypoxia, caused by disrupted vasculature and peripheral vasculopathies, is a key factor that limits dermal wound healing. Factors that can increase oxygen delivery to the regional tissue, such as supplemental oxygen, warmth, and sympathetic blockade, can accelerate healing. Clinical experience with adjunctive hyperbaric oxygen therapy (HBOT) in the treatment of chronic wounds have shown that wound hyperoxia may increase granulation tissue formation and accelerate wound contraction and secondary closure. However, HBOT is not applicable to all wound patients and may pose the risk of oxygen toxicity. Thus, the efficacy of topical oxygen treatment in an experimental setting using the pre-clinical model involving excisional dermal wound in pigs was assessed. Exposure of open dermal wounds to topical oxygen treatment increased tissue pO2 of superficial wound tissue. Repeated treatment accelerated wound closure. Histological studies revealed that the wounds benefited from the treatment. The oxygen treated wounds showed signs of improved angiogenesis and tissue oxygenation. Topically applied pure oxygen has the potential of benefiting some wound types. Further studies testing the potential of topical oxygen in pre-clinical and clinical settings are warranted.

Abnormal Extracellular Matrix Metabolism in Chronically Ischemic Skin: A Mechanism for Dermal Failure in Leg Ulcers

Extracellular matrix (ECM) metabolism and homeostasis is sensitive to changes in oxygen tension manifest in ischemia. We hypothesize that in chronically ischemic limbs, abnormalities in uninjured skin, secondary to hypoxia, predispose to dermal breakdown. Paired biopsies of uninjured distal ischemic and proximal non-ischemic skin were harvested at below knee amputation from 14 patients with peripheral vascular disease following quantification of ischemia. Age- and site-matched controls were taken at total knee replacement (TKR) and varicose vein (VV) operations. Matrix metalloproteinase (MMP)-2 and -9 expression was determined using gelatin zymography, MMP-1 by western blotting and ELISA and tissue inhibitor of MMP (TIMP) by reverse zymography. Collagen content was measured by determining hydroxyproline levels, and collagen type I synthesis by ELISA. Collagen type I synthesis was upregulated in ischemic tissue compared with non-ischemic matched pairs (p<0.001) and both TKR and VV controls, however, there was no increase in collagen deposition. Levels of MMP-2 (p<0.0005) and TIMP-2 (p<0.01), were elevated in ischemic samples. MMP-9 was unaltered, signifying no inflammatory changes. Tissue ischemia was linked to elevated ECM turnover, associated with matrix failure when compounded with problems of matrix stabilization, likely in ischemia. This represents a potential mechanism for ulcer formation.

The effect of preoperative radiotherapy on systemic collagen deposition and postoperative infective complications in rectal cancer patients

PURPOSE

Preoperative, high-dose radiotherapy for rectal cancer reduces local recurrence rates and improves overall survival. However, adverse effects in varying degrees include impaired wound healing and local infection. This study investigates the influence of preoperative, high-dose radiotherapy on subcutaneous accumulation of collagen in a primary rectal cancer group operated on with or without adjuvant radiotherapy.

METHODS

Forty-two eligible patients who underwent total mesorectal excision surgery with or without radiotherapy were included in the study. Polytetrafluoroethylene tubings were implanted in the arm ten days before surgery (three days before the start of radiotherapy). Implants were extracted the day before surgery. New implants were inserted before surgery and were extracted ten days after surgery. The hydroxyproline and proline contents of the implants were measured and the hydroxyproline/proline ratio was calculated as a measure for deposited collagen relative to protein. Blood loss, postoperative complications, and blood levels of hemoglobin, leukocytes, and albumin were recorded.

RESULTS

The two groups were similar in relation to Dukes stage, age, and body mass index. Infectious complications developed in 39 percent of patients after radiotherapy compared with 16 percent in the nonirradiated group. In the irradiated patients with infective complications we found a significant decrease in the hydroxyproline/proline ratio compared with that of irradiated patients without infections (P = 0.037). There was a significant decrease in the leukocyte count preoperatively and postoperatively in the irradiated group compared with surgery alone.

CONCLUSIONS

High-dose, short-term radiotherapy does not have a systemic effect on collagen accumulation, but a significant reduction is manifested in infected patients. Radiotherapy also impairs leukocyte production and increases the postoperative infective complication rate.

The effects of systemic hypoxia on colon anastomotic healing: an animal model

PURPOSE

Acute postoperative systemic hypoxia occurs frequently in the clinical setting following intestinal resection, as a result of complications such as pneumonia, pulmonary edema, or the acute respiratory distress syndrome. Although it is well established that oxygen is essential for metabolism in general and intestinal anastomotic healing, the mechanisms by which systemic hypoxia affect this process are not clear. The purpose of this study was to establish an animal model to simulate acute systemic hypoxia and to examine the effects on anastomotic healing. We investigated the hypothesis that systemic hypoxia impairs anastomotic healing in the colon by disrupting revascularization via changes in the expression of two putative angiogenic factors: inducible nitric oxide synthase and vascular endothelial growth factor.

METHODS

Phase I: Juvenile male Sprague-Dawley rats underwent carotid artery cannulation. In a controlled environment the FiO2 was incrementally decreased from 21 to 9 percent and the resultant PaO2 measured. Phase II: Animals underwent colonic transection with immediate reanastomosis and were placed in either a normoxic (FiO2 21 percent) or hypoxic (FiO2 11 percent) environment for seven days. Perianastomotic in vivo tissue oxygen saturation was measured before segmental colon resection in each of the animals and at seven days before measurement of anastomotic bursting pressure. Perianastomotic tissue samples were assessed by Western blot assay for the expression of vascular endothelial growth factor and inducible nitric oxide synthase protein. Sections from each tissue sample were taken and evaluated by a pathologist blinded to treatment group for determination of anastomotic healing score.

RESULTS

Phase I: Incrementally decreasing the FiO2 resulted in a progressive decrease in PaO2 (r2 = 0.77). Phase II: Animals maintained in a hypoxic environment had a significant decrease in tissue oxygen saturation (73 +/- 9 percent vs. 94 +/- 3 percent; P < 0.0001) and anastomotic bursting pressure (118 +/- 18 mmHg vs. 207 +/- 30 mmHg; P < 0.0001) compared with normoxic controls. Systemic hypoxia induced a significant increase, when compared with normoxic controls, in vascular endothelial growth factor (247.1 +/- 9.5 vs. 142.2 +/- 10.6; P < 0.0001) and inducible nitric oxide synthase (259.6 +/- 21.1 vs. 120.2 +/- 10.9; P < 0.0001) protein expression and led to a significant decrease in the overall wound-healing score.

CONCLUSION

This study validates a new animal model to study the effects of acute systemic hypoxia on colonic anastomotic healing. In this model, systemic hypoxia directly translated into local tissue hypoxia, and anastomotic healing was impaired. Contrary to our original hypothesis, hypoxia led to a significant increase in vascular endothelial growth factor and inducible nitric oxide synthase protein expression at the colonic anastomotic site. Impairment in anastomotic integrity despite upregulation of these angiogenic factors could be a result of the inability of wounded tissue to respond to vascular endothelial growth factor and inducible nitric oxide synthase or alternatively, hypoxia may adversely affect collagen synthesis and deposition directly.

Acute wounds

The most important factors in the management of acute wounds are the history and physical examination. The goals of wound care are fivefold: avoid further tissue damage, achieve wound closure as rapidly as possible, restore function to the injured tissue, facilitate the patient's expedient return to normal daily activities, and restore the patient's quality of life. The treating physician must have a good understanding of the wound healing mechanism. One must rule out all associated occult injuries that may be life threatening. Proper wound assessment and management with minimal discomfort to the patient are crucial. The primary goal is to facilitate the healing process to achieve a cosmetically pleasing and functional result.

Hyperoxia improves microvascular perfusion in a murine wound model

There is a need for a noninvasive method that measures wound angiogenesis. Hyperoxia is known to increase the appearance of new blood vessels in wounds, yet no study has confirmed increases in wound bed perfusion with periodic hyperbaric oxygen (HBO) exposure. This study investigates whether laser Doppler imaging is able to detect and quantify the enhancement of wound angiogenesis that is known to occur with intermittent HBO treatments. Full-thickness dorsal dermal wounds were created on mice randomized to hyperoxic (n = 14) and control (n = 15) groups. Hyperbaric oxygen was administered twice daily for 90 minutes each at 2.1 atmospheres for 7 days. Wound bed perfusion was measured by laser Doppler imaging on days 0, 7, and 10 postwounding. Wound blood flow increased significantly over baseline on day 7 and 10 in the hyperoxic group, but only on day 10 in the control group. Comparison between groups showed a 20% statistically significant increase in wound perfusion in HBO-treated animals compared to control on day 10 (p = 0.05). Laser Doppler imaging was able to detect and quantify the increase in wound bed perfusion resulting from intermittent HBO treatments and shows promise as a noninvasive measure of angiogenesis and wound healing.

Effects of vacuum-assisted closure therapy on inguinal wound edge microvascular blood flow

Vacuum-assisted closure (VAC) therapy has been shown to facilitate wound healing. Data on the mechanisms are scarce, although beneficial effects on blood flow and granulation tissue formation have been presented. In the current study, laser Doppler was used to measure microvascular blood flow to an inguinal wound in pigs during VAC therapy (-50 to -200 mmHg), including consideration of the different tissue types and the distance from the wound edge. VAC treatment induced an increase in microvascular blood flow a few centimeters from the wound edge. The increase in blood flow occurred closer to the wound edge in muscular as compared to subcutaneous tissue (1.5 cm and 3 cm, at -75 mmHg). In the immediate proximity to the wound edge, blood flow was decreased. This hypoperfused zone was increased with decreasing pressure and was especially prominent in subcutaneous as compared to muscular tissue (0-1.9 cm vs. 0-1.0 cm, at -100 mmHg). When VAC therapy was terminated, blood flow increased multifold, which may be due to reactive hyperemia. In conclusion, VAC therapy affects microvascular blood flow to the wound edge and may thereby promote wound healing. A low negative pressure during treatment may be beneficial, especially in soft tissue, to minimize possible ischemic effects. Intermittent VAC therapy may further increase blood flow.

Effects of warming on healing

Systemic and local warming may accelerate wound healing and minimise postoperative wound infection, although more research is needed to confirm this. The existing evidence of the benefits of warming therapies is outlined here.

[Anastomotic leakage in the gastrointestinal tract-repair and prognosis]

Anastomotic leakage is still a serious complication in surgery, resulting in increased morbidity and mortality. The reasons for its onset are various and due to two main reasons: general risk factors of the individual patient and technical surgical factors influencing the outcome after gastrointestinal anastomoses. Changes in the extracellular matrices, particularly due to collagen metabolism, and related disturbances are assumed to be important factors influencing wound healing processes. The technique chosen and the surgical skill are important with regard to inflammation and tissue necroses at the anastomotic line. Analysis of data obtained by clinical studies that concern clinical risk factors for anastomotic leakage reveal an inhomogeneous picture. Attempts to develop risk profiles or scores based on these results have failed until now. Problems encompass the complexity of wound healing processes, and it is questionable whether our current knowledge about them is complete. Therefore, profound understanding of anastomotic leakage requires in-depth analysis of the interaction of extracellular matrix components. Preliminary results indicate the presence of a risk population with collagen metabolism disturbances that have a major effect on wound healing after gastrointestinal anastomosis.

Topical radiant heating in wound healing: an experimental study in a donor site wound model*

The importance of temperature in the wound-healing process is rapidly being recognised as a novel way in which to manipulate the wound-healing environment. In this study, we aimed to investigate the direct effect of topical radiant heating (TRH), using a novel bandaging system (Warm-Up, Arizant Health care Inc., Eden Prairie MN, USA; Augustine Medical, USA), on wound healing at a physiological and cellular level. Experimental bandages were positioned over split-thickness skin graft donor site wounds of 12 patients undergoing graft harvesting from the anterior thigh. The experimental group (n=6) underwent intermittent heating for 5 hours (three 1-hour heating cycles at 38 degrees C, separated by two 1-hour rest periods), whilst the control group (n=6) received no radiant heating. Physiological blood-flow recordings both in the control group and the topical radiant heat cohort were undertaken using Laser Doppler Imaging (LDI). Skin biopsies were obtained at identical time points, and immunohistochemical analysis was undertaken using antibodies against neutrophils (NP57), lymphocytes (CD3) and macrophages (CD68). We found that TRH significantly increased local dermal blood flow (P<0.001) by up to 100% in both injured and intact skin. Furthermore, this increase in flow was associated with a significant (P<0.05) increase in CD3 immunoreactivity on day 1 postoperatively. This study demonstrates that TRH increases local blood flow and lymphocyte (CD3) extravasation, and we postulate that these changes may enhance local innate immunity within the healing wound environment.

Cutaneous Wound Healing in the Cat: A Macroscopic Description and Comparison with Cutaneous Wound Healing in the Dog

OBJECTIVE

To describe the macroscopic features of first and second intention cutaneous wound healing in the cat and compare with the dog.

STUDY DESIGN

Experimental study.

ANIMALS

Domestic shorthaired cats (6) and beagle dogs (6).

METHODS

Square, open cutaneous wounds created on the dorsal aspect of the thorax were evaluated for 21 days for temporal and spatial development of granulation tissue, wound contraction, epithelialization, and total healing. To evaluate first intention healing, breaking strength of sutured linear cutaneous wounds was measured at 7 days post-wounding. Laser-Doppler perfusion imaging was used to measure cutaneous perfusion.

RESULTS

First intention healing: sutured wounds in cats were only half as strong as those in dogs at day 7 (0.406 versus 0.818 kg breaking strength). Second intention healing: cats produced significantly less granulation tissue than dogs, with a peripheral, rather than central distribution. Wound epithelialization and total wound healing (total reduction in open wound area from contraction and epithelialization) were greater for dogs than for cats over 21 days. Wound contraction on day 7 was greater for dogs, but not on day 14 or 21. Cutaneous perfusion was initially greater for dogs than for cats, but no differences were detected after day 7.

CONCLUSIONS

Significant, previously unreported differences in cutaneous wound healing exist between cats and dogs. In general, cutaneous wounds in cats are slower to heal. Cats and dogs also appear to use different mechanisms of second intention healing. In cats wounds close mainly by contraction of the wound edges, whereas in dogs wounds close more from central pull, and epithelialization.

CLINICAL RELEVANCE

Surgeons should view the cat as a unique species, which presents its own special challenges in wound healing, and should take this into account when planning treatment of feline wounds, either by primary closure, or by second intention healing.

Supplemental Oxygen and Carbon Dioxide Each Increase Subcutaneous and Intestinal Intramural Oxygenation

Oxidative killing by neutrophils, a primary defense against surgical pathogens, is directly related to tissue oxygenation. We tested the hypothesis that supplemental inspired oxygen or mild hypercapnia (end-tidal PCO2 of 50 mm Hg) improves intestinal oxygenation. Pigs (25 +/- 2.5 kg) were used in 2 studies in random order: 1) Oxygen Study: 30% versus 100% inspired oxygen concentration at an end-tidal PCO2 of 40 mm Hg, and 2) Carbon Dioxide Study: end-tidal PCO2 of 30 mm Hg versus 50 mm Hg with 30% oxygen. Within each study, treatment order was randomized. Treatments were maintained for 1.5 h; measurements were averaged over the final hour. A tonometer inserted in the subcutaneous tissue of the left upper foreleg measured subcutaneous oxygen tension. Tonometers inserted into the intestinal wall measured intestinal intramural oxygen tension from the small and large intestines. Oxygen 100% administration doubled subcutaneous oxygen partial pressure (PO2) (57 +/- 10 to 107 +/- 48 mm Hg, P = 0.006) and large intestine intramural PO2 (53 +/- 14 to 118 +/- 72 mm Hg, P = 0.014); intramural PO2 increased 40% in the small intestine (37 +/- 10 to 52 +/- 25 mm Hg, P = 0.004). An end-tidal PCO2 of 50 mm Hg increased large intestinal PO2 approximately 16% (49 +/- 10 to 57 +/- 12 mm Hg, P = 0.039), whereas intramural PO2 increased by 45% in the small intestine (31 +/- 12 to 44 +/- 16 mm Hg, P = 0.002). Supplemental oxygen and mild hypercapnia each increased subcutaneous and intramural tissue PO2, with supplemental oxygen being most effective.

Oxygen in wound healing and infection

It is a fundamental clinical observation that wounds do not heal in tissue that does not bleed, and they almost always heal in tissue that bleeds extensively. Continuous supply of oxygen to the tissue through microcirculation is vital for the healing process and for resistance to infection. Evaluation of tissue perfusion and oxygenation is important in all types of wound patients. Monitoring systems should measure the hemodynamic situation and the ability of the cardiovascular system to deliver an adequate volume of oxygen to meet the metabolic demands of the peripheral tissue. Oxygen therapy is important in relation to both healing and resistance to infections. External factors have been shown to significantly decrease the peripheral oxygen supply, and supplementary perioperative oxygen to reduce the surgical wound infection rate by one- half in patients undergoing colorectal resection. Hyperbaric oxygen therapy may be beneficial in situations where the nutritive flow and oxygen supply to the healing tissue are compromised by local injury, and particularly if anaerobic infection is present. However, the definitive proof for the effect and indications of this therapy in wound healing still has to be established. It can be concluded that adequate delivery of oxygen to the wound tissue is vital for optimal healing and resistance to infection. Assessment of perfusion and oxygenation is essential for the wound patient, as well as the treating personnel. The indication for hyperbaric oxygen treatment still needs to be defined. During wound healing the continuity and function of the damaged tissue are re-established. This is only possible through a restoration of the microcirculation and thereby the nutrition to the tissue. The main component of the nutrition is oxygen, which is critically important for healing a wound by production of granulation tissue and for ensuring resistance against infection. This has been shown experimentally, but recently a short period of supplementary oxygen has been shown to decrease wound complications in clinical practice as well.

Supplemental perioperative oxygen and fluids to improve surgical wound outcomes: Translating evidence into practice

Numerous reports support the concept that tissues require an adequate oxygen supply to heal well and to prevent complications of infection. Adequate oxygen supply to tissue depends on perfusion as well as arterial oxygen tension, and tissue oxygen tension, particularly in peripheral tissues, is dependent on adequate vascular volume. Therefore, potential benefits to wound healing and reduction in infection in postsurgical patients might be attained by judicious manipulation of supplemental oxygen and/or fluids in the perioperative period. This article reviews evidence that suggests such manipulations are beneficial and proposes that integrated care pathways be developed that include these interventions.

Use of hypoxia-inducible factor signal transduction pathway to measure O2 levels and modulate growth factor pathways

Tissue PO2 levels are known to directly modulate numerous processes involved in the reparative response to cutaneous tissue injury, including cell differentiation and migration, extracellular matrix synthesis and maturation, and effectiveness of endogenous and exogenous growth factors. Oxygen is therefore likely the critical variable determining the healing capabilities of any tissue. Significant advances in the understanding of cutaneous wound healing progressed with advances in the measurement of tissue PO2, which has advanced over the past several decades from implantable probes to now include molecular tools such as the transcription factor hypoxia inducible factor-1 (HIF-1). HIF-1 modulates the expression of genes that drive the cellular adaptive response to hypoxia and possess the HIF-1 binding sequence named hypoxia response element within their promoter sequence. Molecular biology techniques are now allowing exploitation of the HIF-1/hypoxia response element pathway to drive the expression of potential vulnerary ectopic genes. Here we show the utility of the hypoxia response element for hypoxia-driven expression of the transforming growth factor-beta-signaling component Smad3 in vitro and the in vivo detection of ischemic hypoxia using luciferase. Smad3 is a positive effector of transforming growth factor-beta superfamily signal transduction. Such approaches are the latest evolution of work championed by Hunt and colleagues over the past 4 decades.

Revisiting the essential role of oxygen in wound healing

Hypoxemia, caused by disrupted vasculature, is a key factor that limits wound healing. Correcting hypoxemia through the administration of supplemental oxygen (O(2)) can have significant beneficial impact on wound healing in the perioperative and outpatient settings. Beyond its role as a nutrient and antibiotic, O(2) may support vital processes such as angiogenesis, cell motility, and extracellular matrix formation. Recent discoveries highlight a novel aspect, addressing the role of O(2) in wound healing via the production of reactive oxygen species (ROS). Almost all wound-related cells possess specialized enzymes that generate ROS (including free radicals and H(2)O(2)) from O(2). Defect in these enzymes is associated with impaired healing. Low wound pO(2) is expected to compromise the function of these enzymes. At low concentrations, ROS serve as cellular messengers to support wound healing. The use of systemic hyperbaric O(2) therapy presents potential advantages, as well as risks. There is evidence to suspect that the use of pressure and systemic pure O(2) may not be essential in wound care. Elimination of these factors by using sub-pure systemic O(2) under normobaric conditions may significantly minimize the risk of O(2) toxicity. Furthermore, opportunities to treat dermal wounds using topical O(2) therapy warrant further investigation. Given that many growth factors require ROS for their function, it is reasonable to assume that approaches to correct wound pO(2) will serve as an effective adjunct in treating chronic wounds.

Healing responses of skin and muscle in critical illness

OBJECTIVE

Many aspects of the care and underlying pathologies in patients suffering critical illness can detrimentally influence the normal healing processes of skin and soft tissues. Although a great diversity of pathologies exists, some aspects of the diseases and their treatments are common in critically ill patients. We aimed to identify some features, both common and specific, that could influence wound healing and the mechanisms by which they may do so.

DESIGN

In this review, we first outline the biology of normal skin and muscle healing and then explore how critical illness may influence the normal healing cascade.

FINDINGS

The healing of skin and skeletal muscle in critical illness is influenced by both underlying disease processes and the intensive care environment. Local and systemic factors can contribute to impaired healing, with the potential to prolong functional disability and increase the likelihood of wound complications. The frequency and number of soft tissue injuries derived from accidental injury, surgical intervention, and the need for invasive monitoring and therapies in the intensive care unit setting are likely to compromise the innate immunity and potentially further jeopardize the patient's ability to heal. Alterations in coagulation, tissue perfusion, inflammation, immune functioning, metabolism, nutrition, and drug therapies will influence healing responses by modifying the biological responses to tissue disruption. Locally, wound contamination, sepsis, tissue hypoxia, edema, and excessive or prolonged local pressure all have the potential to compromise soft tissue healing. One or more of these factors may be present at any time.

CONCLUSION

The skin and soft tissues are vulnerable to both injury and compromised healing when a patient is critically ill and exposed to a critical care environment. The identification of risk factors may aid in forming and modifying treatment strategies when caring for the critically ill patient with soft tissue injuries.

Repair of full-thickness bowel injury

OBJECTIVE

Colon surgery is more and more often performed in complex situations such as after trauma, under immunosuppression, or in the elderly. Even under optimal conditions, anastomosis fails in certain situations. The objective of this study was to demonstrate the normal phases of bowel healing and to review the local and systemic factors affecting healing with special attention to critical care variables such as major surgery, acute hemorrhage, and infections.

DATA SOURCE

MEDLINE cited and/or published articles.

DESIGN

Review analysis.

RESULTS

Colon healing is a structured cascade of different phases that can be affected by a multitude of local (infection, ischemia) and systemic (diabetes, malnutrition, anemia, hypothermia, trauma) factors. The normal phases of repair, the resulting bursting pressure as an experimental index of healing, and the available published data on local and systemic factors affecting healing are summarized.

CONCLUSION

Several local and systemic factors negatively affect bowel healing; there is still a small portion of patients who fail to heal, suggesting that intrinsic factors need to be analyzed.

Lesões pulmonares provocadas pela nicotina por via subcutânea em ratos

OBJETIVO: Estudo com o objetivo de observar a influência da nicotina, aplicada pela via subcutânea, em pulmões de ratos. MÉTODOS: Foram utilizados 20 ratos Wistar pesando 235± 35g, separados aleatoriamente em 2 grupos iguais. O grupo I (n=10) recebeu nicotina na dose de 2 mg/Kg/dia pela via subcutânea durante 20 dias e o grupo II (n=10) recebeu placebo pela mesma via de administração. RESULTADOS: Os resultados mostraram que no grupo I ocorreu broncopneumonia em 3 (30%) ratos, leucocitose alveolar em 10 (100%) e leucocitose septal em 7 (70%). Atelectasia foi encontrada em 2 (20%). Transformados em escores, os dados totalizaram 52 pontos. Os escores das alterações observadas nos pulmões do grupo II atingiram 11 pontos (p<0,05). CONCLUSÃO: Os dados permitiram concluir que o uso da nicotina por via subcutânea contribuiu para o aparecimento de lesões pulmonares em ratos, em número e intensidade significativamente maiores do que nos animais considerados controles.

Topical oxygen as an adjunct to wound healing: a clinical case series

BACKGROUND: Disrupted vasculature and high energy-demand to support processing and regeneration of wounded tissue are typical characteristics of a wound site. Oxygen delivery is a critical element for the healing of wounds. Clinical experience with adjunctive hyperbaric oxygen therapy in the treatment of chronic wounds have shown that wound hyperoxia increases wound granulation tissue formation and accelerates wound contraction and secondary closure. Nevertheless, the physiologic basis for this modality remains largely unknown. Also, systemic hyperbaric oxygen therapy is associated with risks related to oxygen toxicity. Topical oxygen therapy represents a less explored modality in wound care. The advantages of topical oxygen therapy include low cost, lack of systemic oxygen toxicity, and the ability to receive treatment at home, making the benefits of oxygen therapy available to a much larger population of patients. MATERIALS AND METHODS: Over 9 months, seven surgeons treated 58 wounds in 32 patients with topical oxygen with follow-up ranging from 1 to 8 months. The data presented herein is a retrospective analysis of the results we have achieved using topical oxygen on complex wounds. RESULTS: Thirty-eight wounds in 15 patients healed while on topical oxygen. An additional five wounds in five patients had preoperative oxygen therapy; all wounds initially healed postoperatively. In two patients, wounds recurred post-healing. In ten wounds, topical oxygen had no effect; and two of those patients went on to require limb amputation. There were no complications attributable to topical oxygen. Three patients died during therapy and one died in the first postoperative month from underlying medical problems. Two patients were lost to follow-up. CONCLUSIONS: In this case series, topical oxygen had no detrimental effects on wounds and showed beneficial indications in promoting wound healing.

Effects of an Augmented Postoperative Fluid Protocol on Wound Healing in Cardiac Surgery Patients

• Background Cardiac surgery patients are vulnerable to hypoperfusion postoperatively and often have subcutaneous tissue oxygen tension less than 50 mm Hg. Hypovolemia most likely contributes to this hypoperfusion and may lead to impaired wound healing.

• Objective To determine if a modified postoperative fluid replacement protocol would result in improved tissue oxygen tension, blood flow, and healing in cardiothoracic surgery patients.

• Methods A total of 166 cardiac surgery patients, 18 to 90 years old, participated in a randomized, 2-group, repeated-measures study. The experimental group received fluid augmentation during the first 36 hours after surgery; the control group received standard postoperative replacement fluids. Subcutaneous tissue oxygen tension and temperature were measured 8, 18, and 36 hours after surgery. Tissue cellularity and accumulation of hydroxyproline were evaluated in tissue obtained from subcutaneous expanded polytetrafluoroethylene tubes. Wound complications were evaluated by using the ASEPSIS Wound Scoring System.

• Results Tissue oxygen levels, tissue cellularity, and accumulation of hydroxyproline were similar in the 2 groups. A negative correlation (P = .01) existed between higher tissue oxygen values and lower (better) ASEPSIS leg wound scores. More than 80% of the patients had tissue oxygen levels of 50 mm Hg or less at each time of measure. Many values were 30 to 40 mm Hg less than the ideal for control of bacteria and healing.

• Conclusions The frequency of low oxygen levels is consistent with data from earlier studies. Determination of other interventions to improve subcutaneous tissue perfusion in cardiac surgery patients is needed.