Wound tissue oxygen tension predicts the risk of wound infection in surgical patients

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.

Obesity decreases perioperative tissue oxygenation

BACKGROUND

Obesity is an important risk factor for surgical site infections. The incidence of surgical wound infections is directly related to tissue perfusion and oxygenation. Fat tissue mass expands without a concomitant increase in blood flow per cell, which might result in a relative hypoperfusion with decreased tissue oxygenation. Consequently, the authors tested the hypotheses that perioperative tissue oxygen tension is reduced in obese surgical patients. Furthermore, they compared the effect of supplemental oxygen administration on tissue oxygenation in obese and nonobese patients.

METHODS

Forty-six patients undergoing major abdominal surgery were assigned to one of two groups according to their body mass index: body mass index less than 30 kg/m2 (nonobese) or 30 kg/m2 or greater (obese). Intraoperative oxygen administration was adjusted to arterial oxygen tensions of approximately 150 mmHg and approximately 300 mmHg in random order. Anesthesia technique and perioperative fluid management were standardized. Subcutaneous tissue oxygen tension was measured with a polarographic electrode positioned within a subcutaneous tonometer in the lateral upper arm during surgery, in the recovery room, and on the first postoperative day. Postoperative tissue oxygen was also measured adjacent to the wound. Data were compared with unpaired two-tailed t tests and Wilcoxon rank sum test; P < 0.05 was considered statistically significant.

RESULTS

Intraoperative subcutaneous tissue oxygen tension was significantly less in the obese patients at baseline (36 vs. 57 mmHg; P = 0.002) and with supplemental oxygen administration (47 vs. 76 mmHg; P = 0.014). Immediate postoperative tissue oxygen tension was also significantly less in subcutaneous tissue of the upper arm (43 vs. 54 mmHg; P = 0.011) as well as near the incision (42 vs. 62 mmHg; P = 0.012) in obese patients. In contrast, tissue oxygen tension was comparable in each group on the first postoperative morning.

CONCLUSION

Wound and tissue hypoxia were common in obese patients in the perioperative period and most pronounced during surgery. Even with supplemental oxygen tissue, oxygen tension in obese patients was reduced to levels that are associated with a substantial increase in infection risk.

Thoracic epidural anesthesia increases tissue oxygenation during major abdominal surgery

Intraoperative surgical stress may markedly increase adrenergic nerve activity and plasma catecholamine concentrations, which causes peripheral vasoconstriction and decreased tissue oxygen partial pressure possibly leading to tissue hypoxia. Tissue hypoxia is associated with an increased incidence of surgical wound infections. Thoracic epidural anesthesia blocks afferent neural stimuli and inhibits efferent sympathetic outflow in response to painful stimuli. Consequently, we tested the hypothesis that supplemental thoracic epidural anesthesia during major abdominal surgery improves tissue perfusion and subcutaneous oxygen tension. Thirty patients were randomly assigned to two groups: general (n = 15) or combined general and epidural anesthesia (n = 15). Anesthesia technique and fluid management were standardized. Subcutaneous tissue oxygen tension was measured continuously in the upper arm with a Clark type electrode. Data were compared with unpaired, two-tailed t-tests, Wilcoxon's ranked sum test, or repeated-measures analysis of variance and Scheffé F tests as appropriate; P < 0.05 was considered statistically significant. After 60 min, intraoperative tissue oxygen tension was significantly larger during combined anesthesia than during general anesthesia (54.3 +/- 7.4 mm Hg versus 42.1 +/- 8.6 mm Hg; P = 0.0002). Subcutaneous tissue oxygen tension remained significantly higher in the combined general/epidural anesthesia group throughout the observation period. Hemodynamic responses and global oxygen variables were similar in the groups. Thoracic epidural anesthesia improved intraoperative tissue oxygen tension outside the area of the epidural block. Thus, our results give evidence that supplemental neural nociceptive block blunts generalized vasoconstriction caused by surgical stress and adrenergic responses.

IMPLICATIONS

Thoracic epidural anesthesia blunts the decrease of subcutaneous tissue oxygen tension caused by surgical stress and adrenergic vasoconstriction during major abdominal surgery. Consequently, combined general and epidural anesthesia helps to provide sufficient tissue oxygenation.

Improved pain control after cardiac surgery: results of a randomized, double-blind, clinical trial

OBJECTIVE

We sought to determine whether a continuous regional infusion of a local anesthetic delivered to the operative site would result in decreased levels of postoperative pain and narcotic requirements for patients who undergo a standard median sternotomy for cardiac surgery.

METHODS

A double-blind, randomized, controlled trial was conducted at a single center. Patients who were undergoing elective coronary artery bypass graft surgery alone or combined with laser transmyocardial revascularization received bilateral intercostal nerve blocks with either ropivacaine or saline. At wound closure, 2 catheters with multiple side openings were inserted percutaneously and placed directly over the sternum. The same agent (ropivacaine vs saline) was then administered as a continuous regional infusion for 48 hours through an elastomeric pump. Requirements for postoperative systemic narcotic analgesics and pain assessment scores were recorded for 72 hours after the operation. Secondary outcome measures were hospital length of stay and pulmonary function test results. Pain scores and narcotic use on the second postoperative day were also compared to avoid the confounding influence of anesthesia administered at the time of the operation.

RESULTS

The total amount of narcotic analgesia required by the ropivacaine group was significantly less than that of the control group (47.3 vs 78.7 mg, respectively; P =.038). The ropivacaine group required less narcotics on postoperative day 2 as well (15.5 vs 29.4 mg, P =.025). The mean overall pain scores for the ropivacaine group were significantly less than the mean overall scores for the normal saline group (1.6 vs 2.6, respectively; P =.005). Patients receiving ropivacaine had a mean length of stay of 5.2 days compared with 8.2 days for patients in the normal saline group (P =.001). Excluding the data from outliers (length of stay = 39 days), the normal saline group mean length of stay was 6.3 days (P <.01). There was no difference in assessment of pulmonary function.

CONCLUSION

Continuous delivery of local anesthetics significantly improved postoperative pain control while decreasing the amount of narcotic analgesia required in patients who underwent standard median sternotomy. There was also a significant decrease in hospital length of stay, which is likely to result in significant cost reductions.

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.

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.

Molecular diagnostics of injury and repair responses in critical illness: what is the future of "monitoring" in the intensive care unit?

OBJECTIVE

To identify potential future means of monitoring injury and repair in critical illness.

DESIGN

Review of the literature.

RESULTS

Critically ill patients are monitored extensively and intensively by such means as hemodynamics, laboratory values, and radiologic studies. In general, however, the goal of monitoring has been to measure the degree of injury and to prevent further injury, rather than to measure repair. Measures of repair have been limited to phenotypic end points such as return of organ function, as measured by blood chemistry. In this article, I examine how it may be possible in the future to monitor the progress of repair using genomic and proteomic biomarkers. These types of monitors would enable clinicians to control the healing environment using real time, rapid biomarkers, and sophisticated techniques to target therapy to the patient's current inflammatory state, taking into account the genetic makeup of the patient and his or her likely response to a given drug.

CONCLUSIONS

The rapidly evolving sciences of genomics, proteomics, computational biology, and complex system theory can be used a) to model critical illness; b) to model adaptive and maladaptive responses to critical illness; c) to tailor treatments to create an ideal inflammatory environment for repair and regeneration, taking into account the individual genetic contribution; and d) to monitor the progress of repair. The major obstacles to reaching these goals are technological, and experience suggests that they will be overcome.

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.

Abstinence from smoking reduces incisional wound infection: a randomized controlled trial

OBJECTIVE

Clinical studies show that the incidence of postoperative wound complications is higher in smokers than nonsmokers. In this study, we evaluated the effect of abstinence from smoking on incisional wound infection.

METHODS

Seventy-eight healthy subjects (48 smokers and 30 never-smokers) were included in the study and followed for 15 weeks. In the first week of the study, the smokers smoked 20 cigarettes per day. Subsequently, they were randomized to continuous smoking, abstinence with transdermal nicotine patch (25 mg per day), or abstinence with placebo patch. At the end of the first week and 4, 8, and 12 weeks after randomization, incisional wounds were made lateral to the sacrum to excise punch biopsy wounds. At the same time identical wounds were made in 6 never-smokers. In 24 never-smokers a wound was made once. All wounds were followed for 2 weeks for development of wound complications.

RESULTS

A total of 228 wounds were evaluated. In smokers the wound infection rate was 12% (11 of 93 wounds) compared with 2% (1 of 48 wounds) in never-smokers (P <0.05). Wound infections were significantly fewer in abstinent smokers compared with continuous smokers after 4, 8, and 12 weeks after randomization. No difference between transdermal nicotine patch and placebo was found.

CONCLUSIONS

Smokers have a higher wound infection rate than never-smokers and 4 weeks of abstinence from smoking reduces the incidence of wound infections.

Short-term pre-operative smoking cessation intervention does not affect postoperative complications in colorectal surgery: a randomized clinical trial

BACKGROUND

Smokers have a higher risk of complicated tissue and wound healing after surgery than nonsmokers. We tested the hypothesis that short-term pre-operative cessation of smoking in colorectal surgery decreases the incidence of postoperative tissue and wound complications.

METHODS

From February 1998 to March 2001, 60 patients, who smoked daily, undergoing colorectal resection were randomly assigned 2-3 weeks before scheduled surgery to either abstinence from smoking, counselling and nicotine replacement therapy or maintenance of daily smoking habits. Postoperative tissue and wound complications necessitating surgical or medical treatment were evaluated at discharge and 30 days after surgery by blinded outcome assessment.

RESULTS

In the pre-operative period of 15 days (8-24) (median, interquartile range (IQR)), 89% of the patients in the intervention group vs. 13% in the control group abstained from smoking or reduced by more than half (P < 0.05). In the postoperative period of 11 days (10-13), the corresponding figures were 92% and 50%, respectively (P < 0.05). Postoperative tissue and wound complications occurred in 33% (9 of 27) of the patients in the intervention group compared to 27% (8 of 30) in the control group (NS). Likewise, no difference in overall postoperative complication rate was found between the groups.

CONCLUSION

Short-term cessation of smoking does not reduce the risk of complicated tissue and wound healing or other complications in colorectal surgery.

The effects of epidural and general anesthesia on tissue oxygenation

The risk of wound infections is inversely related to subcutaneous tissue oxygen tension. General anesthesia increases local blood flow by direct vasodilation and central inhibition of thermoregulatory vasoconstriction. Epidural anesthesia can increase perfusion in blocked regions by decreasing sympathetic tone. We therefore tested the hypothesis that epidural anesthesia increases tissue oxygen tension in awake and anesthetized subjects. Fifteen healthy volunteers underwent epidural, general, and combined epidural and general anesthesia. Subcutaneous tissue oxygen tension was measured using tonometers in the lateral upper arm and the lateral thigh. Epidural anesthesia to a T10 level was maintained with 0.75% mepivacaine. General anesthesia was maintained with 1.5% sevoflurane in 30% oxygen; 30% inspired oxygen was given via a sealed facemask during baseline and epidural anesthesia. Baseline subcutaneous tissue oxygen tensions for arm and thigh were 57 +/- 11 and 54 +/- 8 mm Hg, respectively. Epidural anesthesia significantly increased tissue oxygenation in the thigh by 9 mm Hg, to 63 +/- 7 mm Hg, without increasing arm oxygenation. Tissue oxygenation in the arm and thigh were similar during general anesthesia alone, 58 +/- 11 and 63 +/- 12 mm Hg. Arm oxygenation remained unchanged with the addition of epidural anesthesia; however, thigh subcutaneous oxygen partial pressure increased 8 +/- 3 mm Hg, from 63 +/- 12 to 71 +/- 9 mm Hg. Although epidural anesthesia increased tissue oxygenation significantly with and without general anesthesia, the magnitude of this increase might be of marginal clinical importance in regard to surgical wound infections.

IMPLICATIONS

Epidural anesthesia significantly increased subcutaneous tissue oxygenation in the thigh both with and without general anesthesia. Although each increase was statistically significant, previous work suggests that the magnitude of these changes is unlikely to markedly reduce the risk of surgical wound infection.

Effect of intra-operative end-tidal carbon dioxide partial pressure on tissue oxygenation

Postsurgical infection risk is correlated with subcutaneous tissue oxygenation. Mild hypercapnia augments cutaneous perfusion. We tested the hypothesis that peripheral tissue oxygenation increases as a function of arterial PCO2 in surgical patients. Twenty patients were randomly assigned to intra-operative end tidal PCO2 of 3.99 (control) or 5.99 kPa (hypercapnia). All other anaesthetic management was per protocol. Tissue oxygen partial pressure, transcutaneous oxygen tension, cerebral oxygen saturation, and cardiac output were measured. Mean (SD) subcutaneous tissue oxygen tension was 8.39 (1.86) kPa in control and 11.84 (2.53) kPa hypercapnia patients (p = 0.014). Cerebral oxygen saturation was 55 (4)% for control vs. 68 (9)% for hypercapnia (p = 0.004). Neither cardiac index nor transcutaneous tissue oxygen tension differed significantly between the groups. Mild intra-operative hypercapnia increased subcutaneous and cerebral oxygenation. Increases in subcutaneous tissue oxygen partial pressure similar to those observed in patients assigned to hypercapnia are associated with substantial reductions in wound infection risk.

Obesity: impediment to wound healing

Intrinsic and extrinsic factors affect wound healing. High risk factors for the obese patients include infection, seromas, anastomatic leaks, and incision dehiscence. Tissue perfusion is an issue of great concern and is a key factor in most assessments. Obesity adds another dimension to the needs of the patient and presents challenges to nurses. From routine evaluations to specialized assessments with attention to bariatric equipment needs, a thorough understanding of wound healing and potential problems of obese patients, and knowledge of interventions is needed. Nonjudgmental attitudes are imperative in planning care for the obese patients. Following a review of physiological needs and nursing interventions, a case study details one woman's surgical complications.

Optical Measurements of Tissue Oxygen Saturation in Lower Limb Wound Healing

This review has highlighted the role of oxygen in wound healing and in the mechanism of preventing infection. Optical measurements of tissue SO2 in wounds can provide valuable information, not only about the inflammatory state of the wound, but also about healing potential in ulcers and critical limb ischaemia. The technique is fast, non-invasive and can be used without the necessity for contact with the skin.

The clinical relevance of microbiology in acute and chronic wounds

PURPOSE

To improve clinical practice and the quality of patient care by providing a learning opportunity that enhances the participant's understanding of how wound microbiology affects healing.

TARGET AUDIENCE

This CME/CE activity is intended for physicians and nurses with an interest in interpreting the role of microorganisms in wound healing.

OBJECTIVES

At the conclusion of this course, participants should be able to: 1. Identify the microbiology of acute and chronic wounds, risk factors for infection, and advantages and disadvantages of wound culturing. 2. Identify methods of debridement and wounds for which they are appropriate. 3. Identify systemic antibiotic treatment options for acute and chronic wound infections.

Supplemental perioperative fluid administration increases tissue oxygen pressure

BACKGROUND

Wound infections are common and serious surgical complications. Wound perfusion delivers oxygen, inflammatory cells, growth factors, and cytokines to injured tissues. Hypoperfused regions experience low oxygen tensions that do not support adequate oxidative killing or wound healing. Clinicians may fail to recognize clinically important hypovolemia because hemodynamic stability and urine output are maintained after peripheral perfusion is compromised. We tested the hypothesis that supplemental fluid administration during and after elective colon resection increases tissue perfusion and tissue oxygen pressure.

METHODS

Fifty-six patients undergoing colon resection were randomly assigned to conservative (8 mL x kg(-1) x h(-1), n = 26) or aggressive (16 to 18 mL x kg(-1) x h(-1), n = 30) fluid management. Anesthetic technique was standardized. We used 60% nitrous oxide in 40% oxygen. During surgery and postanesthetic recovery, subcutaneous oxygen tension (P(sq)O(2)) was measured by using a polarographic sensor implanted subcutaneously into 1 upper arm. Capillary blood flow was evaluated postoperatively with a thermal diffusion system. Data were analyzed with 2-tailed t tests; P value less than.05 was considered statistically significant.

RESULTS

Hemodynamic and renal responses were similar in the groups. Intraoperative tissue oxygen tension was significantly greater in patients given supplemental fluid: 81 +/- 26 vs 67 +/- 18 mm Hg, P =.03. Postoperative P(sq)O(2) (77 +/- 26 vs 59 +/- 15 mm Hg, P =.009) and capillary blood flow (69 +/- 12 vs 53 +/- 12, P <.001) were also greater in the supplemental fluid patients.

CONCLUSIONS

Supplemental perioperative fluid administration significantly increases tissue perfusion and tissue oxygen partial pressure. Optimizing tissue perfusion will require providing more fluid than indicated by normal clinical criteria or use of invasive monitoring to guide treatment. The actual effect of supplemental fluid administration on incidence of wound infection requires further investigation.

Nonpharmacological prevention of surgical wound infections

Postoperative wound infection is a common and serious complication of surgery. This review will focus on 2 factors known to modulate perioperative immunity: maintenance of perioperative normothermia and provision of supplemental perioperative oxygen. Hypothermia causes numerous adverse outcomes, including morbid myocardial events, increased blood loss and transfusion requirement, postsurgical wound infections, and prolonged hospitalization. Perioperative normothermia should thus be maintained unless therapeutic hypothermia is specifically indicated. Supplemental perioperative oxygen (inspired fraction of 80% instead of 30%) significantly reduces postoperative nausea and vomiting, diminishes the decrease in phagocytosis and bacterial killing usually associated with anesthesia and surgery, and reduces the rate of postoperative wound infection among patients who undergo colon resection. Available data thus suggest that supplemental perioperative oxygen improves surgical outcome with little or no associated risk.

Update on the Epidemiology and Prevention of Surgical Site Infections

Surgical site infections contribute significantly to the morbidity and mortality of the individual patient and impose a burden on the health care resources of the community. With the shift toward streamlined hospitalizations and ambulatory surgery, a majority of surgical site infections are being diagnosed after discharge. There are several tools available for identifying and risk stratifying patients that include the National Nosocomial Infections Surveillance system and the Study on the Efficacy of Nosocomial Infection Control index. If patients can be identified preoperatively, appropriate prophylactic measures and postdischarge surveillance can be undertaken, an underemphasized task faced by hospital systems today.

Smoking as a risk factor for wound healing and infection in breast cancer surgery

AIM

Clinical studies suggest that smoking is associated with wound necrosis after breast cancer surgery. However, the significance of smoking as a risk factor for wound infection, skin flap necrosis, and epidermolysis when adjusting for other potential risk factors remains to be studied.

METHODS

From June 1994 through August 1996, 425 patients underwent breast cancer surgery as simple mastectomy, modified radical mastectomy, or breast conserving surgery. The patients were evaluated postoperatively for wound infection, skin flap necrosis, and epidermolysis. Association between these complications and 17 patient, operative, and postoperative variables were analysed by three separate multiple logistic regression analyses.

RESULTS

When compared to non-smoking, smoking was significantly associated with wound infection after all types of surgery (light smoking (1-14 grams per day): [odds ratio (OR)=2.95, 95% confidence interval (95% CI)=1.07-8.16], and heavy smoking (>/=15 grams per day): OR=3.46 (1.52-7.85). A similar significant association was found as regards skin flap necrosis and epidermolysis after simple mastectomy and modified radical mastectomy: both light and heavy smoking were predictive for skin flap necrosis: light smoking: OR=6.85 (1.96-23.90), heavy smoking: OR=9.22 (2.91-29.25) and for epidermolysis: light smoking: OR=3.98 (1.52-10.43) and heavy smoking: OR=4.28 (1.81-10.13). No significant dose-response relation was disclosed. Other risk factors and confounders associated with complicated wound healing were adjusted for in the analysis: diabetes, obesity, alcohol, NSAIDs, duration of surgery, and surgical experience.

CONCLUSION

Independent of other risk factors, smoking is predictive for post-mastectomy wound infection, skin flap necrosis, and epidermolysis.

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.

Mild hypothermia does not increase bacterial proliferation on implanted vascular grafts

BACKGROUND

Mild hypothermia may offer protection against spinal cord ischemia during aortic surgery. However, hypothermia also promotes postoperative infection via two mechanisms: peripheral vasoconstriction and impairment of various immune functions. If mild hypothermia aggravates graft infections, immune function impairment would presumably be the most important factor because thermoregulatory vasoconstriction does not appreciably reduce aortic blood flow. We therefore tested the hypothesis that resistance to vascular graft infection is not reduced by mild perioperative hypothermia in dogs.

METHODS

After colonization with a solution of Staphylococcus epidermidis, prostheses were used to replace the infrarenal aorta in 20 dogs. During surgery, the dogs were randomly assigned to maintain of normothermia or passive cooling. Seven days later, grafts were recovered for bacteriologic study.

RESULTS

Colony counts for the grafts removed from the normothermic and hypothermic dogs did not differ significantly.

CONCLUSIONS

Mild perioperative hypothermia does not increase proliferation of S epidermidis on aortic vascular grafts.

Wound pathophysiology, infection and therapeutic options

Wound healing is a complex and highly regulated process that can be compromised by both endogenous factors (pathophysiological) and exogenous factors (micro-organisms). Microbial colonisation of both acute and chronic wounds is inevitable, and in most situations endogenous bacteria predominate, many of which are potentially pathogenic in the wound environment. The risk of wound infection increases as local conditions favour bacterial growth rather than host defence. Consequently a primary objective in wound management is to redress the host-bacterial balance, and this is most effectively achieved by ensuring that the wound is cleared of devitalised tissue and foreign bodies, the bacterial load and inflammation are controlled, and that adequate tissue perfusion is maintained. Although surgical debridement is the most rapid and effective technique for removing devitalised tissue, topical enzymes, moisture-retentive dressings, biosurgical therapy and vacuum therapy have been used as alternative approaches to wound cleansing and preparation. Topical antimicrobial agents continue to be used widely for preventing wound infection and current interest is focused on alternatives to antibiotics, such as antimicrobial moisture-retentive dressings, honey, essential oils and cationic peptides. In addition to the need to control wound microflora, unregulated inflammation caused by both micro-organisms and underlying abnormal pathophysiological conditions is a major factor associated with poor healing in chronic wounds. Consequently, therapeutic strategies that target chronic inflammatory processes are critical to wound progression. The success of future therapies will be dependent on a growing understanding of the pathophysiological processes and the host-bacterial interactions that significantly influence wound healing.

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.

Infection control in the ICU

Nosocomial infections (NIs) now concern 5 to 15% of hospitalized patients and can lead to complications in 25 to 33% of those patients admitted to ICUs. The most common causes are pneumonia related to mechanical ventilation, intra-abdominal infections following trauma or surgery, and bacteremia derived from intravascular devices. This overview is targeted at ICU physicians to convince them that the principles of infection control in the ICU are based on simple concepts and that the application of preventive strategies should not be viewed as an administrative or constraining control of their activity but, rather, as basic measures that are easy to implement at the bedside. A detailed knowledge of the epidemiology, based on adequate surveillance methodologies, is necessary to understand the pathophysiology and the rationale of preventive strategies that have been demonstrated to be effective. The principles of general preventive measures such as the implementation of standard and isolation precautions, and the control of antibiotic use are reviewed. Specific practical measures, targeted at the practical prevention and control of ventilator-associated pneumonia, sinusitis, and bloodstream, urinary tract, and surgical site infections are detailed. Recent data strongly confirm that these strategies may only be effective over prolonged periods if they can be integrated into the behavior of all staff members who are involved in patient care. Accordingly, infection control measures are to be viewed as a priority and have to be integrated fully into the continuous process of improvement of the quality of care.

Effects of preoperative warming on the incidence of wound infection after clean surgery: a randomised controlled trial

BACKGROUND

Wound infection after clean surgery is an expensive and often underestimated cause of patient morbidity, and the benefits of using prophylactic antibiotics have not been proven. Warming patients during colorectal surgery has been shown to reduce infection rates. We aimed to assess whether warming patients before short duration, clean surgery would have the same effect.

METHODS

421 patients having clean (breast, varicose vein, or hernia) surgery were randomly assigned to either a non-warmed (standard) group or one of two warmed groups (local and systemic). We applied warming for at least 30 min before surgery. Patients were followed up and masked outcome assessments made at 2 and 6 weeks.

FINDINGS

Analysis was done on an intention-to-treat basis. We identified 19 wound infections in 139 non-warmed patients (14%) but only 13 in 277 who received warming (5%; p=0.001). Wound scores were also significantly lower (p=0.007) in warmed patients. There was no significant difference in the development of haematomas or seromas after surgery but the non-warmed group were prescribed significantly more postoperative antibiotics (p=0.002).

INTERPRETATION

Warming patients before clean surgery seems to aid the prevention of postoperative wound infection. If applied according to the manufacturers guidelines these therapies have no known side-effects and might, with the support of further studies, provide an alternative to prophylactic antibiotics in this type of surgery.

Surgical infections in patients with chronic renal failure

Patients with chronic renal failure and uremia have impaired host defenses and wound healing that can lead to an increased risk of infection in addition to a frequent need for surgical procedures with synthetic grafts and catheters. Antibiotic therapy plus timely surgical intervention in removal of infected grafts and catheters is crucial for infection control and patient survival. Other surgical infections, such as wound problems, intraabdominal infections, fungal infections, diabetic foot ulcers, and necrotizing soft tissue infections must be attended to promptly.

Hyperbaric medicine in soft tissue trauma

Severe crush injuries of the soft tissues can result in tears of the large vessels and destruction of the microcirculation. This produces ischaemia and tissue necrosis and contributes to the development of oedema and compartment syndromes. All these factors compromise tissue survival. Immediately following a crush injury some areas of tissue are obviously irreversibly damaged, and others undamaged. It is common to have a ‘grey area’ between these, where there is uncertainty as to what will survive. Management of crush injury must involve surgical repair of vessels and soft tissues, debridement of obviously dead tissue, and bone stabilization. At the same time tissue perfusion must be maintained by manoeuvres such as fluid replacement and diminution of oedema, and when necessary fasciotomy. It has been proposed that hyperbaric oxygen therapy has a role, as an adjunct, in the maintenance of tissue oxygenation under these conditions, and will improve survival of tissues in the grey area, and thus minimize tissue loss. Hyperbaric oxygen therapy involves breathing 100% oxygen at pressures greater than one atmosphere. Presently, the pressures most often used are in the range 2-3 atmospheres absolute.

Mild perioperative hypothermia and the risk of wound infection

BACKGROUND

Bacterial destruction caused by free radicals, which are synthesized by neutrophils in the presence of oxygen, depends on adequate tissue perfusion. Mild perioperative hypothermia causes vasoconstriction, reducing nutrient and oxygen supply to wounds and increasing frequency of surgical wound infection. However, the causal role of hypothermia in surgical wound infection is the subject of controversy. The present work proposes the hypothesis that mild perioperative hypothermia is associated with infection of the surgical wound.

METHODS

A prospective cohort of 290 surgical patients was studied in a second-level hospital; 261 (90%) of the patients concluded the follow-up. The relationship of hypothermia and of other confounding factors, such as diabetes mellitus, antibiotic treatment, and wound drains with infection outcome was evaluated. One physician, blinded to patient hypothermia, gathered the data. Surgical wound infection was defined as the surgeon's diagnosis with positive culture.

RESULTS

Twenty subjects (7.6%) showed infection of surgical wound; 18 (11.5%) of 156 hypothermics and two (2%) 105 normothermics (p = 0.004). Hypothermia proved to be a significant independent risk of infection with relative risk of 6.3 (p = 0.01).

CONCLUSIONS

Mild perioperative hypothermia is associated with infection of the surgical wound and its prevention is therefore justified.

Monitoring tissue oxygenation during resuscitation of major burns

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Tissue and wound healing effects of short duration postoperative oxygen therapy

The purpose of this study was to determine the effects of 28% oxygen given in the first 36 hours after surgery on tissue oxygen, collagen deposition, and clinical healing outcomes. Twenty-four subjects having cervical spine surgical procedures participated in a randomized, repeated-measures pilot study of tissue and healing effects of postoperative supplemental oxygen. The treatment group (n = 13) received 28% oxygen for the first 36 postoperative hours, whereas the control group (n = 11) was maintained on room air. Subcutaneous tissue oxygen and temperature were measured at intervals up to 36 hours postsurgery. Wound healing was evaluated by hydroxyproline content in a subcutaneous polytetrafluoroethylene tube removed on the 7th postoperative day. Clinical outcomes were evaluated for the 30 days post-hospital discharge. Subjects in the treatment group had significantly higher tissue oxygen tension overall, and at postoperative hours 1, 2, 18, and 36, with mean values 10 to 20 mm Hg higher than control subjects. Significant differences were not found in hydroxyproline levels or clinical wound outcome measures. Low level, short duration, supplemental oxygen increased and sustained wound tissue oxygen and was well tolerated by subjects. Larger studies of populations at risk for wound complications are needed to investigate variables of dose and duration of oxygen therapy in relation to clinical and cellular wound healing outcomes.

Wound closure technique and acute wound complications in gastric surgery for morbid obesity: a prospective randomized trial

BACKGROUND

During the past 10 years, numerous clinical studies have supported the use of continuous monofilament fascial closure after laparotomy. Because of the increased incidence of surgical-site infections and other acute wound complications in the morbidly obese, these patients are well suited for a study of technical factors that may affect the frequency of these wound complications.

STUDY DESIGN

A prospective, randomized study of the midline fascial closure technique in gastric bariatric operations was conducted between 1991 and 1998 in 331 consecutive morbidly obese patients. At the time of closure of the upper midline laparotomy wound, the patients were randomized into two groups: Group I patients (n = 172) underwent continuous fascial closure and group II patients (n = 159) underwent interrupted fascial closure. All patients received prophylactic antibiotics in a similar fashion. Wounds were monitored for 30 days postoperatively, and acute wound complications were classified as superficial or deep. Superficial complications included superficial surgical-site infections, seromas, and hematomas. In all superficial complications, the fascia remained uninvolved and intact. Deep wound complications included deep surgical-site infections and fascial dehiscence.

RESULTS

A total of 49 acute wound complications occurred (15%). There were 22 superficial (7%) and 27 deep (8%) wound complications in the 331 in the patients studied. Group I patients experienced fewer total wound complications than group II patients (18 versus 31; p=0.021). Group I patients also experienced fewer deep wound complications than group II (5 versus 22; p = 0.003).

CONCLUSIONS

Continuous fascial closure reduces major acute wound complications in morbidly obese patients undergoing gastric operations for obesity.

Supplemental perioperative oxygen to reduce the incidence of surgical-wound infection

BACKGROUND

Destruction by oxidation, or oxidative killing, is the most important defense against surgical pathogens and depends on the partial pressure of oxygen in contaminated tissue. An easy method of improving oxygen tension in adequately perfused tissue is to increase the concentration of inspired oxygen. We therefore tested the hypothesis that the supplemental administration of oxygen during the perioperative period decreases the incidence of wound infection.

METHODS

We randomly assigned 500 patients undergoing colorectal resection to receive 30 percent or 80 percent inspired oxygen during the operation and for two hours afterward. Anesthetic treatment was standardized, and all patients received prophylactic antibiotic therapy. With use of a double-blind protocol, wounds were evaluated daily until the patient was discharged and then at a clinic visit two weeks after surgery. We considered wounds with culture-positive pus to be infected. The timing of suture removal and the date of discharge were determined by the surgeon, who did not know the patient's treatment-group assignment.

RESULTS

Arterial oxygen saturation was normal in both groups; however, the arterial and subcutaneous partial pressure of oxygen was significantly higher in the patients given 80 percent oxygen than in those given 30 percent oxygen. Among the 250 patients who received 80 percent oxygen, 13 (5.2 percent; 95 percent confidence interval, 2.4 to 8.0 percent) had surgical-wound infections, as compared with 28 of the 250 patients given 30 percent oxygen (11.2 percent; 95 percent confidence interval, 7.3 to 15.1 percent; P=0.01). The absolute difference between groups was 6.0 percent (95 percent confidence interval, 1.2 to 10.8 percent). The duration of hospitalization was similar in the two groups.

CONCLUSIONS

The perioperative administration of supplemental oxygen is a practical method of reducing the incidence of surgical-wound infections.

Using the Veterans Administration National Surgical Quality Improvement Program to improve patient outcomes

BACKGROUND

The primary goal of collecting quality assurance data is to ultimately improve patient care. The VA National Surgical Quality Improvement Program (NSQIP) provides each station with risk-adjusted morbidity and mortality data on a regular basis. This report of one medical center's use of the risk-adjusted data shows how it can be used to improve patient care.

MATERIALS AND METHODS

Risk-adjusted surgical outcome data for Fiscal Year 1996 (FY96) was received from the NSQIP coordinating center. The Salt Lake City VA medical center was identified as a high outlier for morbidity in general surgery. Patient charts were reviewed and data analyzed to determine practice patterns and to determine if there were any provider issues. Data analysis revealed a large number of wound complications and uncovered a practice pattern of closure of contaminated wounds. Using these data and data from the literature, wound infection and disruption prevention protocols were instituted in the fall of 1997. Wound complications from January to December 1996 (preprotocol) and January to December 1998 (postprotocol) were compared using Student's t test.

RESULTS

The total number of operations in 1998 was 719 compared with 634 in 1996. Superficial wound infections dropped from 3.6 to 1.7%, while overall wound complications dropped from 5.5 to 2.9%. None of these changes were statistically significant.

CONCLUSIONS

Although introduction of wound infection and disruption prevention protocols did not result in a statistically significant decrease in wound complication, it did result in a clinically significant improvement in patient care.

Postoperative pain and subcutaneous oxygen tension

Surgical patients randomly assigned to standard pain control had postoperative subcutaneous oxygen partial pressures that were significantly less than patients given better pain treatment. Our data suggest that control of postoperative pain is a major determinant of surgical-wound infection and should be given the same consideration as maintaining adequate vascular volume and normothermia.

Hemorrhage decreases macrophage inflammatory protein 2 and interleukin-6 release: a possible mechanism for increased wound infection

OBJECTIVE

To determine whether alteration in wound exudate cell immune function occurs after trauma-hemorrhage.

BACKGROUND

Although clinical and experimental studies indicate that the rate of wound infection is increased after trauma and hemorrhagic shock, the underlying mechanism for this increased susceptibility remains unknown.

METHODS

Male C3H/HeN mice were subjected to a midline laparotomy and polyvinyl alcohol sponges were implanted subcutaneously in the abdominal wound before hemorrhage (35+/-5 mm Hg for 90 minutes and resuscitation) or sham operation. The wound exudate cells from the sponges were harvested on the first, third, and fifth postoperative day and cultured for 24 hours in the presence of lipopolysaccharide (10 microg/ml) or heat-killed Staphylococcus aureus. Interleukin (IL)-1beta, IL-6, monocyte chemotactic protein 1, macrophage inflammatory protein 2, and nitrite levels were determined in the supernatants. The distribution of macrophages and polymorphonuclear leukocytes was assessed in the sponge with and without in vivo injection of S. aureus. The phagocytic activity of isolated wound exudate cells was determined using fluorescent S. aureus.

RESULTS

The composition of exudate cells was unaltered by hemorrhagic shock; however, in vivo injection of S. aureus significantly decreased the percentage of macrophages under such conditions. Wound exudate cell phagocytic activity and the release of IL-1beta, IL-6, monocyte chemotactic protein 1, and macrophage inflammatory protein 2 was decreased on the first postoperative day. The release of IL-1beta and IL-6 was also decreased on the third postoperative day in hemorrhaged mice. On the fifth postoperative day, wound exudate cell cytokine production was comparable to that in shams.

CONCLUSIONS

Because most wound infections occur early after severe trauma, these results suggest that the dysfunction of wound exudate cells after hemorrhage might contribute to the increased incidence of wound infections. Therefore, attempts to enhance or restore wound cell immune function might be helpful for decreasing the incidence of wound infections in trauma victims.

Modifying perfusion, nutrition, and stress to promote wound healing in patients with acute wounds

Tissue injury is common among patients in acute care settings. The subsequent response to injury, wound healing, follows an intricate but well-defined sequence that, under normal conditions, proceeds to satisfactory repair. However, because of the complexity of the healing response, several factors can intervene to impair normal healing. As a better understanding of how diverse factors influence healing is gained, the use of interventions that modulate these factors becomes possible and potentially beneficial. This article reviews knowledge of perfusion, nutrition, and stress as they relate to healing in patients experiencing acute wounds. Therapeutic implications based on current research are discussed.

The effects of hyperbaric oxygen on normal and ischemic colon anastomoses

BACKGROUND

Leakage from colonic anastomoses is a major complication causing increased mortality and morbidity, and ischemia is a well-known cause of this event. Inadequate tissue oxygenation could be reversed by using hyperbaric oxygen. This study was designed to investigate the effects of hyperbaric oxygen on the healing of ischemic and normal colon anastomoses in the rat model.

METHODS

Standardized left colon resection 3 cm above the peritoneal reflection and colonic anastomosis were performed in 40 Wistar rats divided into four groups. The control group (I) received no further treatment. To mimic ischemia, 2 cm mesocolon was ligated on either site of the anastomosis in group II and IV rats. Hyperbaric oxygen therapy was started immediately after surgery in group III and IV rats (therapeutic groups). All animals were sacrificed on the fourth postoperative day. After careful relaparotomy, in situ bursting pressure was measured. The hydroxyproline contents of the anastomotic segments in equal length were determined.

RESULTS

The hydroxyproline assay revealed that rats in group II with ischemic colonic anastomosis have significantly lower levels (P <0.05). The highest levels are in the group III rats with normal colonic anastomosis treated by hyperbaric oxygen (P <0.05). There was no significant difference in hydroxyproline levels between group II and group IV animals (P >0.05). Group III animals had significantly higher bursting pressures than any other group (P <0.05). Group II rats had lowest bursting pressures (P <0.05). Group IV animals had significantly higher levels than group II (P <0.05). Mean bursting pressure values both in groups III and IV and hydroxyproline levels in group III were significantly increased by hyperbaric oxygen therapy (P <0.05).

CONCLUSIONS

Ischemia impairs anastomotic healing. Hyperbaric oxygen increases anastomotic healing of both normal and ischemic colonic anastomosis and reverses ischemic damage. This study demonstrated that hyperbaric oxygen improves anastomotic healing.