Judith West

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

Oxygen tension and collagen deposition were measured in standardized, subcutaneous wounds in 33 postoperative surgical patients. Pertinent clinical and wound parameters were analyzed by Pearsons correlation test and sequential linear regression analysis. Collagen deposition was directly and significantly proportional to wound oxygen tension and measures of perfusion. There were no significant correlations with hematocrit, estimated blood loss, length of operation, smoking, age, weight, sex, or urine output. This study in humans confirms animal experiments showing that collagen deposition and tensile strength in wounds are limited by perfusion and tissue oxygen tension. It appears unnecessary to maintain hemoglobin at normal levels to support repair, provided that peripheral perfusion can be maintained at a high level in compensation for anemia. These circumstances reflect the fact that although oxygen is essential to many aspects of healing, and must be delivered at adequate partial pressures, reparative tissue consumes relatively little of it.

Centrally and locally mediated thermoregulatory responses alter subcutaneous oxygen tension

Mild perianesthetic hypothermia decreases resistance to infections. Decreased resistance likely results in part from direct immune inhibition. However, decreased tissue oxygen partial pressure also decreases resistance to infection by impairing oxidative killing by neutrophils and collagen deposition. Thermoregulatory vasoconstriction decreases skin blood flow and may also decrease subcutaneous tissue oxygen tension. Accordingly, we determined the influence of centrally and locally mediated thermoregulatory vasomotion on subcutaneous oxygen tension. We also compared subcutaneous oxygen tension to other potential markers of tissue perfusion: laser Doppler flowmetry and transcutaneous oxygen tension. Arterial oxygen tension was maintained near 325 mm Hg in five volunteers. Control subcutaneous oxygen tension values were recorded after 1 hour of euthermia (no sweating or vasoconstriction). Volunteers were then cooled with a circulating‐water mattress positioned under the trunk and legs. After 1.5 hours of cooling sufficient to produce shivering, the right upper arm was covered for 1 hour with a small circulating water blanket set to 40° C while systemic cooling continued. The volunteers were then systematically warmed to produce sweating, and the right arm was locally cooled. There was no correlation among laser Doppler flowmetry, transcutaneous oxygen tension, and subcutaneous oxygen tension. Systemic cooling significantly decreased subcutaneous oxygen tension, but subcutaneous oxygen tension in the right arm returned to control values during local heating. Systemic warming significantly increased subcutaneous oxygen tension, and 1 hour of local cooling failed to fully reverse the increase. These data indicate that thermoregulatory vasoconstriction significantly decreases tissue oxygen availability. Decreased subcutaneous oxygen tension may be one mechanism by which mild perianesthetic hypothermia facilitates development of surgical wound infections.

Guidelines for the treatment of arterial insufficiency ulcers

1. Co-chaired panel 2. University of Utah, Salt Lake City, UT 3. University of Texas, San Antonio, TX 4. Sinai Hospital/Johns Hopkins Medical Institutions, Baltimore, MD 5. GKT School of Medicine, King’s College, London, UK 6. University of Texas Health Science Center at Houston, TX 7. Sequoia Hospital, Redwood City, CA 8. Maricopa Medical Center, Phoenix, AZ 9. Tufts-New England Medical Center, Boston, MA 10. Southampton University Hospitals Trust NHS, Southampton, UK 11. Penrose–St. Francis Health Services, Colorado Springs, CO 12. Beverly Surgical Associates, Beverly, MA 13. Saint Francis Memorial Hospital, San Francisco, CA 14. Northbay Center for Wound Care, Vacaville, CA, and 15. University of California, San Francisco, CA

Local radiant heating increases subcutaneous oxygen tension

BACKGROUND We evaluated a novel bandage that incorporates a thermostatically controlled radiant heater. We first determined optimal bandage temperature, based on increases in subcutaneous oxygen tension, a measure correlating well with resistance to infection and wound strength. We then tested the hypothesis that prolonged radiant heating would increase collagen deposition in experimental thigh wounds. METHODS The experimental bandages were positioned on the anterior thigh of 8 volunteers, and heated for 2 hours at 38 degrees C, 42 degrees C, or 46 degrees C, in a random order. Subcutaneous oxygen tension under the bandage was recorded from an electrode positioned within a subcutaneous tonometer. We studied 10 volunteers in the second protocol. For 1 week, the experimental bandage was continuously applied to one thigh, and heated to 38 degrees C using a 2-hour on/off cycle. On the alternate week, a standard gauze bandage was applied to the contralateral thigh. Treatment order was randomly assigned. Wound collagen deposition under each bandage was evaluated with subcutaneous polytetrafluoroethylene tubes, which were removed and assayed for hydroxyproline on the eighth day. Data are presented as means +/- SDs. RESULTS Skin temperature during heating ranged from 36 degrees C to 37.5 degrees C. Oxygen tension increased approximately 50% during heating, but the increase was comparable at the three tested temperatures. Even after heating was discontinued, subcutaneous oxygen tension remained elevated for the remaining 3 study hours. Collagen deposition after 1 week of active heating was 3.4 +/- 1.0 microg/ cm. After 1 week of control treatment, collagen deposition was 3.2 +/- 1.1 microg/cm (P = not significant). CONCLUSIONS Our data suggest that radiant heating at 38 degrees C significantly increases subcutaneous oxygen tension, and presumably resistance to infection. However, prolonged heating at this temperature does not increase wound collagen deposition.

Adjuncts to preparing wounds for closure ☆: Hyperbaric oxygen, growth factors, skin substitutes, negative pressure wound therapy (vacuum-assisted closure)

Achieving closure in a chronic wound requires provision of adequate oxygen delivery to the tissue, adequate protein and other nutritional factors, a moist environment, an appropriate inflammatory milieu, dèbridement, and correction of contributing medical diagnoses. In some patients, these conditions are achieved easily, whereas in others, greater effort is required. Adjunctive treatments, including HBO2, growth factors, skin substitutes, and negative-pressure wound therapy (e.g., V.A.C.) can provide the proper conditions for healing in appropriately selected patients.

The influence of a brief preoperative illness on postoperative healing.

In a study of wound healing at high altitude, subcutaneously implanted PTFE tubes were used to stimulate and measure accumulation of wound hydroxyproline (an index of collagen) in 26 patients who had appendectomy and in 38 patients who had cholecystectomy. Patient age, length of surgery, and postoperative recovery seemed to predict better healing in patients who had appendectomy, but there was a difference in the preoperative illness of the two groups: acute cholecystitis was treated medically and cholecystectomy performed after resolution of the acute phase of illness, whereas patients who had appendectomy were taken to surgery as soon as a diagnosis was made. It was observed that patients who had appendectomy accumulated 20% less hydroxyproline than patients who had cholecystectomy (p < 0.02), and that the depression of hydroxyproline accumulation was significantly related to length of preoperative illness (p = 0.008). This decrease in wound hydroxyproline accumulation is attributed to the acute preoperative illness. Conceptually, this is a unique situation since the brief illness did not produce lasting debility, and the source of illness, the inflamed appendix, was not present during healing. This indicates that even a brief preoperative illness has a more prolonged influence on postoperative healing than usually anticipated.

Guidelines for the prevention of lower extremity arterial ulcers

The Wound Healing Society (WHS) is a professional society of physicians, nurses, physical therapists, podiatrists, and other wound care specialists, basic scientists, clinical researchers, and industrial researchers dedicated to assuring that every patient receives optimal wound care. Its mission is to advance the science and practice of wound healing. To that end, the following comprehensive, evidence- and consensus-based guidelines were developed to address the Prevention of Lower Extremity Arterial Insufficiency Ulcers. The guidelines are presented in generic terms; the details of specific tests, therapies, and procedures are at the discretion of an interdisciplinary team of health care professionals who establish, implement, and evaluate policies and procedures directed at prevention of arterial ulcers.

Wound healing in the surgical patient: influence of the perioperative stress response on perfusion.

The clinical effect of surgical stress created by pain, cutting, cold, fear, and hypovolemia is peripheral vasoconstriction which limits wound perfusion and oxygenation and impairs wound healing. Correction of all factors as simultaneously as possible is the goal.

Measuring oxygen in wounds.

Publisher Summary The most important and commonly used methods for oxygen measurement, range from microelectrode measurements of wound oxygen gradients to clinically useful measurements in humans. Studies of the role of oxygen in wound healing turn on the ability to measure oxygen: in cell and tissue culture, in animal models, and in human wounds. The development of methods for the accurate measurement of wound oxygen tension has led to studies demonstrating that activation of the sympathetic nervous system by such common perioperative stressors as hypothermia, pain, and hypovolemia decreases wound oxygen tension and impairs wound healing. Tissue oxygen measurements are relatively simple to make, particularly with current highly stable probes. Concepts related to subcutaneous wound tissue oximetry and measurement of transcutaneous oxygen in patients with ulcers of the lower extremity are also discussed.