Oxygen as an isolated variable influences resistance to infection

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 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.

Preoperative Assessment: An Anesthesiologist's Perspective

Advances in anesthesia and surgery have made it so that almost any patient with a resectable lung malignancy is now an operative candidate given a full understanding of the risks and after appropriate investigation. This situation necessitates a change in the paradigm that anesthesiologists use for preoperative assessment. Understanding and stratifying the perioperative risks allows the anesthesiologist to develop a systematic focused approach to these patients at the time of the initial contact and immediately before induction, which can be used to guide anesthetic management.

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.

Prevention and treatment of postsurgical head and neck infections

Postoperative wound infection is an important cause of postsurgical morbidity. Efforts to reduce the incidence of wound infection are enhanced through appropriate preoperative preparation, adherence to excellent surgical technique, and the provision of outstanding postoperative care. Many head and neck surgical procedures are undertaken in an environment contaminated by saliva containing a large inoculum of potentially pathogenic bacteria. Prospective randomized clinical trials have demonstrated that perioperative antibiotic prophylaxis reduces the risk for postoperative wound infection. Effective antibiotic prophylaxis requires that the antibiotic be effective against normal oral flora. Antibiotics should be administered before wound contamination. The dose of the antibiotic should exceed the minimal inhibitory concentration needed for the normal flora. The antibiotic administration can cease within 24 hours of surgery.

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.

Is perioperative hypothermia a risk factor for post-Cesarean infection?

Objective: To determine whether hypothermia during Cesarean delivery is a risk factor for postoperative infection.

Methods: An historical cohort investigation was conducted on all women delivered by Cesarean at our center during 2001. Initial recovery-room temperature, taken via the oral or axillary route, was used as a surrogate for intraoperative temperature. Adding 0.5^°C to axillary temperatures generated oral temperature equivalents. Women with chorioamnionitis were excluded, as were those with an initial recovery-room temperature that exceeded 37.9^°C or was recorded more than 20 minutes after the end of surgery. Prophylactic antibiotics (cefazolin, 1 g) were given during Cesarean delivery.

Results: A total of 42 women (7.6%) were diagnosed with postoperative infections. Infections included endometritis (n= 25), wound abscess (n = 7), wound cellulitis (n = 7) and urinary tract infection (UTI) (n = 4). No cases of septic pelvic thrombophlebitis or pelvic abscess occurred. One woman had both endometritis and a UTI. Mean temperatures were higher, rather than lower, for women who subsequently had postoperative infections compared with those who did not (36.4 ± 0.8^°Cvs. 35.9 ± 0.7^°C; p < 0.001). Mean temperatures for the various postoperative infections were as follows: endometritis, 36.5 ± 0.8^°C (p < 0.001 vs. uninfected group); wound abscess 36.0 ± 0.8^°C (p = 0.63); wound cellulitis, 36.3 ± 0.6^°C (p = 0.14); UTI, 36.7 ± 0.9^°C (p = 0.04).

Conclusions: Women who develop post-Cesarean infections have higher initial recovery-room temperatures than those who do not develop such infections. This suggests the presence of subclinical infection at the time of Cesarean. Evaluating whether intraoperative warming has any role during Cesarean delivery requires a randomized clinical trial.

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.

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.

Hyperbaric oxygen and wound healing

Problem wounds, which fail to respond to traditional medical and surgical therapy, can be challenging to the plastic surgeon. Surgical, outpatient, and inpatient wound care costs can be exorbitant. Indirect costs, such as those related to patient productivity, disability, and premature death, can also be significant. The underlying problem in failure of a wound to heal is usually hypoxia and infection. HBO treatments in selected patients can facilitate healing by increasing tissue oxygen tension, thus providing the wound with a more favorable environment for repair. Therefore, HBO therapy can be an important component to any comprehensive wound care program.

A randomized controlled clinical trial to evaluate the effects of noncontact normothermic wound therapy on chronic full-thickness pressure ulcers

OBJECTIVE

To determine the effect of noncontact normothermic wound therapy (NNWT) versus standard wound care on chronic full-thickness pressure ulcers.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Veterans administration medical center and 7 long-term-care facilities.

PATIENTS

40 inpatients with 43 Stage III and IV pressure ulcers.

INTERVENTIONS

A sterile noncontact wound dressing was applied to 21 wounds for 24 hours per day, 7 days per week. Each day after the wound was irrigated and the noncontact dressing was changed, a heating element in the dressing was activated for 3 1-hour periods for 12 weeks or until wound closure. Twenty-two control wounds were treated with standard, moisture-retentive dressings 24 hours per day, 7 days per week for 12 weeks or until wound closure.

MAIN OUTCOME MEASURE

Measurement of wound surface area.

MAIN RESULTS

Healing rate for the NNWT group was significantly greater than for the control group (0.52 cm2 per week and 0.23 cm2 per week, respectively; P<.02). A clinically significant increase was seen among the NNWT group in the incidence of closure among wounds that completed the entire 12-week protocol compared with controls (11 of 14 or 79% and 8 of 16 or 50%, respectively; not significant). The mean slope of the individual regression analyses for the NNWT group was significantly different from the mean slope for the control group (-0.07 and -0.033, respectively; P<.05). Large wounds in the NNWT group demonstrated a significantly greater healing rate than large wounds in the control group (P <.05).

CONCLUSION

Wounds treated with NNWT healed significantly faster than wounds in the control group. The healing rate was greatest for larger wounds treated with NNWT.

Hypothermia induces T-cell production of immunosuppressive cytokines

BACKGROUND

Hypothermia is associated with increased postoperative infectious complications. We hypothesized that hypothermia suppresses the inflammatory response by altering T-cell cytokine production from a proinflammatory to an antiinflammatory profile, thus explaining the increased susceptibility to infectious complications associated with perioperative hypothermia.

METHODS

Forty rats were randomized to either a Hypothermia (30 degrees C) or Control (38 degrees C) group. Blood samples taken at baseline and after 8 h of thermoregulation were stimulated with phorbol 12-myristate 13-acetate and ionomycin. Interleukin (IL)-2 receptor expression and intracellular IL-10 production were measured using monoclonal antibodies and flow cytometry in CD4 and CD8 T cells. Differences in IL-10 production and IL-2 receptor expression for stimulated samples in the Hypothermia and Control groups were compared.

RESULTS

Stimulated CD4 cells demonstrated an antiinflammatory cytokine expression profile after hypothermia. Intracellular IL-10 production increased in the Hypothermia group but remained the same in the Control group (% change = 40 [3,87] and 2 [-36,26], respectively; P = 0.043). The increase in IL-2 receptor expression observed in the control group was suppressed after hypothermia (% change = 12[8,30] and 1 [-3,13], respectively; P = 0.026). We observed a greater increase in IL-10 production by CD8 cells from hypothermic animals than in those from control animals (% change = 41 [-8,90] and -4 [-40,5], respectively; P = 0.019). CD8 IL-2 receptor expression in hypothermic animals was similar to that of control animals (% change = 23 [-7,37] vs 25 [2,80], respectively; P = 0.32).

CONCLUSIONS

Hypothermia induced an antiinflammatory T-cell cytokine profile.

Preoperative assessment for pulmonary resection

Because of recent advances in anesthesia and surgery, almost any patient with a resectable lung malignancy is now an operative candidate, given a full understanding of the risks and provided he or she is investigated appropriately. This progress necessitates a change in the paradigm that one uses for preoperative assessment. Understanding and stratifying the perioperative risks allows the anesthesiologist to develop a systematic focused approach to these patients at the time of the initial contact and immediately before induction, which then can be used to guide anesthetic management (Fig. 7).

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.

Use of a noncontact radiant heat bandage and Staphylococcus aureus dermal infections in an ovine model

Diabetic foot wounds are difficult to manage due to relative tissue ischemia and high rates of soft tissue infection. One potential treatment modality is the application of local radiant heat to promote wound healing and control infection. However, there are concerns that local heat will spread rather than control infection. We determined in this study the effect of a noncontact radiant heat bandage in controlling an ischemic soft tissue infection. Bilateral 10 x 15 cm dermal flaps were created in 15 adult range sheep. The flaps were inoculated intradermally with 107 Staphylococcus aureus in 3 separate areas. The control flap was left open to air, while the treatment flap was covered with a noncontact radiant heat bandage and heated to 38 degrees C for three 1-hour periods separated by two 1-hour nonheating periods daily. After 10 days, both dermal flaps were harvested and sent for quantitative bacteriology. Due to operative complications, 12 of 15 sheep completed the study. The heated flap temperature was significantly higher 39.2 +/- 0.5 degrees C (+/- SE) vs. the control flap 36.1 +/- 0.1 degrees C (p < 0.00001) and bacterial counts were significantly smaller in the heated flap (median 1.0 x 107 colony-forming units per gm tissue) when compared to the control flap (median 7.5 x 107) (p = 0.001). This study shows the use of a noncontact radiant heat bandage controls ischemic soft tissue infections in an ovine model.

Vascular and epidermal effects of fibroblast growth factor on irradiated and nonirradiated skin flaps

Head and neck cancer surgeons are often faced with the challenge of managing previously irradiated soft tissue that has poor vascularity and slower epithelialization. This study investigates the effect of supplemental basic fibroblast growth factor (bFGF) on flap vascularity, tissue oxygenation, and epidermal regeneration in nonirradiated (n = 40) and irradiated porcine skin flaps (n = 40). Supplemental bFGF increased vascularity in nonirradiated flaps by 80% (p = .005), with a trend to a higher tissue oxygen level by day 14. The irradiated bFGF-treated flaps did not show increased vascularity or higher tissue oxygen levels 2 weeks after surgery. However, in both irradiated and nonirradiated groups, epidermal regeneration increased by greater than 70% with supplemental bFGF (p < .002). The results of this study suggest that supplemental bFGF can increase tissue vascularity in nonirradiated tissues and epidermal regeneration in both nonirradiated and irradiated conditions.

The effects of perioperative hypothermia and the duration of anesthesia on postoperative wound infection rate in clean wounds: a retrospective study

OBJECTIVE

To determine the effects of hypothermia and duration of anesthesia on the infection rate in clean wounds in dogs and cats.

STUDY DESIGN

Retrospective clinical study.

SAMPLE POPULATION

Seven hundred seventy-seven dogs and cats undergoing clean surgical procedures.

METHODS

Records of animals prospectively evaluated for postoperative wound infection were retrospectively evaluated for the prevalence of perioperative hypothermia. Body temperatures during the perioperative period and the duration of surgery and anesthesia were recorded. Data were analyzed to identify differences between animals with infected and uninfected wounds and multiple logistic regression modeling was used to evaluate the independent contribution of risk factors to the incidence of postoperative wound infection.

RESULTS

No statistically significant differences were found in the analysis of temperature data between animals with infected and uninfected wounds. Duration of anesthesia was significantly greater in animals with wound infections (P = .01). Multiple logistic regression modeling identified duration of anesthesia as a risk factor for postoperative wound infection independent of the duration of surgery.

CONCLUSIONS

In animals with clean surgical wounds, mild perioperative hypothermia is not a significant risk factor for postoperative wound infection. The duration of anesthesia, however, is a significant risk factor independent of the duration of surgery.

CLINICAL RELEVANCE

To decrease the incidence of postoperative wound infection, the duration of anesthesia should be minimized. Surgical time, as well as the time required for ancillary diagnostic tests while under anesthesia should, therefore, be kept to a reasonable minimum.

The effect of denervation on leukocyte function in soft tissue infection

BACKGROUND

The present study was undertaken to investigate the effect of denervation on leukocyte function in soft-tissue infection in an isolated in vivo ovine flap model.

METHODS

Fifteen adult ewes were divided into three groups. An island pedicle flap was raised on the right buttock. In group I (no denervation), the cutaneous nerve remained intact, whereas in group II (acute denervation) the nerve was divided acutely. In group III (prolonged denervation) the nerve was divided 7 days before flap elevation. All flaps received intradermal inoculation of 10(7) Staphylococcus aureus, and the animals were observed for 96 hours.

RESULTS

In both groups II and III, the leukocyte chemiluminescence and chemotaxis were significantly decreased when compared with group I. Furthermore, there was profound impairment of leukocyte functions in group III compared with group II. Group III also had significantly higher bacterial counts, larger septic foci, lower viable leukocyte ratios, and decreased bacterial killing compared with group I.

CONCLUSIONS

Denervation, particularly over a period of time, results in increased bacterial growth of soft-tissue septic foci. This appears to be due to decreased leukocyte function resulting in diminished bacterial killing.

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.

Guideline for Prevention of Surgical Site Infection, 1999. Centers for Disease Control and Prevention (CDC) Hospital Infection Control Practices Advisory Committee

EXECUTIVE SUMMARY The "Guideline for Prevention of Surgical Site Infection, 1999" presents the Centers for Disease Control and Prevention (CDC)'s recommendations for the prevention of surgical site infections (SSIs), formerly called surgical wound infections. This two-part guideline updates and replaces previous guidelines.1,2 Part I, "Surgical Site Infection: An Overview," describes the epidemiology, definitions, microbiology, pathogenesis, and surveillance of SSIs. Included is a detailed discussion of the pre-, intra-, and postoperative issues relevant to SSI genesis. Part II, "Recommendations for Prevention of Surgical Site Infection," represents the consensus of the Hospital Infection Control Practices Advisory Committee (HICPAC) regarding strategies for the prevention of SSIs.3 Whenever possible, the recommendations in Part II are based on data from well-designed scientific studies. However, there are a limited number of studies that clearly validate risk factors and prevention measures for SSI. By necessity, available studies have often been conducted in narrowly defined patient populations or for specific kinds of operations, making generalization of their findings to all specialties and types of operations potentially problematic. This is especially true regarding the implementation of SSI prevention measures. Finally, some of the infection control practices routinely used by surgical teams cannot be rigorously studied for ethical or logistical reasons (e.g., wearing vs not wearing gloves). Thus, some of the recommendations in Part II are based on a strong theoretical rationale and suggestive evidence in the absence of confirmatory scientific knowledge.It has been estimated that approximately 75% of all operations in the United States will be performed in "ambulatory," "same-day," or "outpatient" operating rooms by the turn of the century.4 In recommending various SSI prevention methods, this document makes no distinction between surgical care delivered in such settings and that provided in conventional inpatient operating rooms. This document is primarily intended for use by surgeons, operating room nurses, postoperative inpatient and clinic nurses, infection control professionals, anesthesiologists, healthcare epidemiologists, and other personnel directly responsible for the prevention of nosocomial infections. This document does not: Specifically address issues unique to burns, trauma, transplant procedures, or transmission of bloodborne pathogens from healthcare worker to patient, nor does it specifically address details of SSI prevention in pediatric surgical practice. It has been recently shown in a multicenter study of pediatric surgical patients that characteristics related to the operations are more important than those related to the physiologic status of the patients.5 In general, all SSI prevention measures effective in adult surgical care are indicated in pediatric surgical care. Specifically address procedures performed outside of the operating room (e.g., endoscopic procedures), nor does it provide guidance for infection prevention for invasive procedures such as cardiac catheterization or interventional radiology. Nonetheless, it is likely that many SSI prevention strategies also could be applied or adapted to reduce infectious complications associated with these procedures. Specifically recommend SSI prevention methods unique to minimally invasive operations (i.e., laparoscopic surgery). Available SSI surveillance data indicate that laparoscopic operations generally have a lower or comparable SSI risk when contrasted to open operations.6-11 SSI prevention measures applicable in open operations (e.g., open cholecystectomy) are indicated for their laparoscopic counterparts (e.g., laparoscopic cholecystectomy). Recommend specific antiseptic agents for patient preoperative skin preparations or for healthcare worker hand/forearm antisepsis. Hospitals should choose from products recommended for these activitie

Guideline for prevention of surgical site infection, 1999. Hospital Infection Control Practices Advisory Committee

The “Guideline for Prevention of Surgical Site Infection, 1999” presents the Centers for Disease Control and Prevention (CDC)'s recommendations for the prevention of surgical site infections (SSIs), formerly called surgical wound infections. This two-part guideline updates and replaces previous guidelines.

Part I, “Surgical Site Infection: An Overview,” describes the epidemiology, definitions, microbiology, pathogenesis, and surveillance of SSIs. Included is a detailed discussion of the pre-, intra-, and postoperative issues relevant to SSI genesis.

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.

Postoperative oxygen therapy

Much has been published in the medical literature concerning adverse events relating to the surgical patient. Among the notable disorders requiring the expertise of the postanesthesia care unit nurse are the diagnosis and management of respiratory dysfunction acutely attributable to the effects of surgery and anesthesia. Inhalational and/or intravenous anesthetic agents contribute to pathophysiological alterations that lend to the development of hypoxemia in the postoperative period. When patients present with preexisting respiratory disease, their care is frequently more complex and challenging. This review session will address the oxygenation component of respiration and the perioperative influences that alter it as well as treatment considerations for normalizing oxygenation.

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.

Use of tissue oxygen tension measurements during resuscitation from hemorrhagic shock

BACKGROUND

Tissue oxygen tension can be measured directly in selected organ beds, and these measurements may be more sensitive in assessing the adequacy of resuscitation than global physiologic parameters. We hypothesized that heart tissue oxygen tension would be an important marker for the severity of ischemic insult to the heart during hemorrhagic shock. We further hypothesized that gut oxygen tension measured in the jejunum would prove to be a better measure of splanchnic hypoperfusion than intramucosal pH (pHi).

METHODS

Tissue oxygen probes were inserted directly into the myocardium of the left ventricle and into the lumen of the proximal jejunum in 10 anesthetized swine. A pHi catheter was introduced into the stomach. The animals were subjected to a controlled hemorrhage of 50% of estimated blood volume. Gut and cardiac oxygen were monitored continuously during hemorrhage and resuscitation, which was performed with shed blood and crystalloid.

RESULTS

While gut O2 and pHi trended together, we were unable to establish a correlation between changes in these two variables during hemorrhage and resuscitation. Heart PO2 decreased significantly during hemorrhage, but surpassed baseline values after resuscitation, a finding not seen in gut PO2. No standard physiologic variables reliably predicted changes in heart PO2 during these experiments.

CONCLUSIONS

Tissue oxygen tensions measurements are highly responsive to changes induced during graded hemorrhagic shock and resuscitation. Gut PO2 and pHi appear to be measuring different physiologic processes in the gastrointestinal tract. The compensatory ability of the heart far exceeds that of the gut after ischemic insult. This hemorrhagic shock model appears feasible for the study of various methods of resuscitation.

Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. Study of Wound Infection and Temperature Group

BACKGROUND

Mild perioperative hypothermia, which is common during major surgery, may promote surgical-wound infection by triggering thermoregulatory vasoconstriction, which decreases subcutaneous oxygen tension. Reduced levels of oxygen in tissue impair oxidative killing by neutrophils and decrease the strength of the healing wound by reducing the deposition of collagen. Hypothermia also directly impairs immune function. We tested the hypothesis that hypothermia both increases susceptibility to surgical-wound infection and lengthens hospitalization.

METHODS

Two hundred patients undergoing colorectal surgery were randomly assigned to routine intraoperative thermal care (the hypothermia group) or additional warming (the normothermia group). The patient's anesthetic care was standardized, and they were all given cefamandole and metronidazole. In a double-blind protocol, their wounds were evaluated daily until discharge from the hospital and in the clinic after two weeks; wounds containing culture-positive pus were considered infected. The patients' surgeons remained unaware of the patients' group assignments.

RESULTS

The mean (+/- SD) final intraoperative core temperature was 34.7 +/- 0.6 degrees C in the hypothermia group and 36.6 +/- 0.5 degrees C in the normothermia group (P < 0.001) Surgical-wound infections were found in 18 of 96 patients assigned to hypothermia (19 percent) but in only 6 of 104 patients assigned to normothermia (6 percent, P = 0.009). The sutures were removed one day later in the patients assigned to hypothermia than in those assigned to normothermia (P = 0.002), and the duration of hospitalization was prolonged by 2.6 days (approximately 20 percent) in hypothermia group (P = 0.01).

CONCLUSIONS

Hypothermia itself may delay healing and predispose patients to wound infections. Maintaining normothermia intraoperatively is likely to decrease the incidence of infectious complications in patients undergoing colorectal resection and to shorten their hospitalizations.

Postoperative obstructive sleep apnoea. Haemodynamic effects of treatment with nasal CPAP

A 74-year-old man presenting for aortic reconstructive surgery showed severe, previously undiagnosed obstructive sleep apnoea during overnight oximetry monitoring before operation. Postoperatively, in the first 4 hours following extubation, he suffered 238 episodes of respiratory obstruction. These events were associated with frequent arousals, large fluctuations in systolic and diastolic blood pressure. Administration of nasal continuous positive airways pressure abolished the obstructions and allowed an uninterrupted night's sleep, with a significantly reduced blood pressure. Subsequent dips in oxygen saturation as a result of respiratory obstruction recurred on the fifth postoperative night. We conclude that pre-operative overnight oximetry may be useful in identifying those patients at risk of postoperative upper airway obstruction. Use of nasal continuous positive airway pressure may prevent the occurrence of early postoperative obstruction and the associated haemodynamic changes.

Dynamic properties of blood flow and leukocyte mobilization in infected flaps

Two aspects of the inflammatory response to infection--blood flow alteration and leukocyte mobilization--are investigated in the canine model. The elevation of paired musculocutaneous (MC) and random pattern (RP) flaps allowed comparison of healing flaps with significant differences in blood flow (lower in random pattern flaps) and resistance to infection (greater in musculocutaneous flaps). Blood flow changes as determined by radioactive xenon washout were compared in normal skin and distal flap skin both after elevation and following bacterial inoculation. Simultaneous use of In-111 labeled leukocytes allowed determination of leukocyte mobilization and subsequent localization in response to flap infection. Blood flow significantly improved in the musculocutaneous flap in response to infection. Although total leukocyte mobilization in the random pattern flap was greater, the leukocytes in the musculocutaneous flap were localized around the site of bacterial inoculation within the dermis. Differences in the dynamic blood flow and leukocyte mobilization may, in part, explain the greater reliability of musculocutaneous flaps when transposed in the presence of infection.