Oxygen as an isolated variable influences resistance to infection

Prepectoral Direct-to-Implant versus Staged Tissue Expander Breast Reconstruction: A Comparison of Complications

BACKGROUND

Direct-to-implant (DTI) reconstruction has multiple advantages over a staged tissue expander (TE) approach. However, its use may be limited by concerns of increased complications. This study is the largest series to date comparing postoperative outcomes for DTI versus TE reconstruction in the prepectoral plane.

METHODS

The authors retrospectively reviewed 348 patients who underwent 536 total immediate, prepectoral implant-based breast reconstructions between January of 2018 and December of 2021. The authors compared the presence of risk factors and the rate of six separate complications between patients who underwent DTI versus TE reconstruction up to 1 year after surgery.

RESULTS

Of 348 patients, 147 (42%) and 201 (58%) underwent TE and DTI reconstruction ( P = 0.1813), respectively. The overall infection rate was 16.4% ( n = 57). DTI patients had a significantly greater incidence of wounds ( P < 0.0001), including minor ( P < 0.0011) and major wounds ( P < 0.0053). Significantly greater mastectomy resection weights were found for DTI patients who experienced any complication ( P < 0.0076), postoperative wounds ( P < 0.0001), and major wounds specifically ( P < 0.0035). Compared with medium-thickness acellular dermal matrix (ADM), extra thick ADM was associated with significantly increased rates of infection ( P < 0.0408) and wounds ( P < 0.0001).

CONCLUSIONS

Prepectoral DTI reconstruction in patients with adequate flap perfusion may have complication rates comparable to staged TE reconstruction, apart from a higher incidence of postoperative wounds. Greater mastectomy resection weights and thickness of ADM may specifically contribute to infection and wound-healing complications. Prepectoral DTI reconstruction is encouraged in the patients with adequate flap perfusion and moderate to low mastectomy resection weights who desire comparable or smaller implant volumes.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Therapeutic, III.

Skull Base Osteomyelitis: A 5-Year Review and Prognostic Outcome in a Single Tertiary Institution

Objective

The primary objective of this study is to review the clinical parameters associated with skull base osteomyelitis (SBO), with a secondary aim of studying their association with patient outcomes 1 and 6 months after treatment initiation.

Study Design

This is a single-center restrospective observational study.

Setting

The study was conducted from January 2018 to December 2022 at the University Malaya Medical Center in Kuala Lumpur.

Methods

Patients aged over 15 years with a diagnosis of SBO were included in the study. Clinical parameters, investigations, and follow-up records were recorded. The disease outcomes were analyzed at 1 and 6 months after treatment initiation using multivariable analyses.

Results

The study identified 31 patients with SBO, the majority of whom were elderly males with comorbidities such as diabetes and hypertension. Otalgia and otorrhea were the most common symptoms, and computed tomography scans were used for diagnosis. Pseudomonas aeruginosa was the most commonly identified pathogen, and intravenous broad-spectrum antimicrobials were used to treat all patients. Surgical intervention was required for 25% of patients, and underlying ischemic heart disease, anemia, and single nerve palsy were significantly associated with an unfavorable prognosis. Patients with higher body mass index and elevated C-reactive protein showed poorer outcomes after 1 and 6 months of treatment, respectively.

Conclusion

Early recognition, prompt treatment, better control of comorbidities, nutrition, and monitoring can improve SBO outcomes and reduce complications. Therefore, as the prevalence of SBO increases, diagnostic criteria or management guidelines should be established to guide the best clinical practice.

Oxygen-Generating Hydrogels as Oxygenation Therapy for Accelerated Chronic Wound Healing

Hypoxia in chronic wounds impairs the activities of reparative cells, resulting in tissue necrosis, bacterial infections, decreased angiogenesis, and delayed wound healing. To achieve effective oxygenation therapy and restore oxygen homeostasis, oxygen-generating hydrogels based on different oxygen sources have been developed to release dissolved oxygen in the wound bed, which not only alleviate hypoxia, but also accelerate chronic wound healing. This review first discusses the vital role of oxygen and hypoxia in the wound healing process. The advancements in oxygen-generating hydrogels, which produce oxygen through the decomposition of hydrogen peroxide, metal peroxides, glucose-activated cascade reactions, and photosynthesis of algae microorganisms for chronic wound healing, are discussed and summarized. The therapeutic effects and challenges of using oxygen-generating hydrogels for the clinical treatment of chronic wounds are concluded and prospected.

Real-world evidence of hyperbaric oxygen therapy on cardiovascular outcomes in patients with chronic osteomyelitis

BACKGROUND

The effectiveness of hyperbaric oxygen (HBO) therapy for chronic osteomyelitis remains inconclusive. In particular, recent studies have shown that chronic osteomyelitis is a crucial risk factor for cardiovascular diseases. However, the preventive effect of HBO on cardiovascular events has not been reported in patients with chronic osteomyelitis.

METHODS

We conducted a population-based cohort study to evaluate the impact of HBO on patients with chronic osteomyelitis. Overall, 5312 patients with chronic osteomyelitis were selected from the Taiwan National Health Insurance Database to evaluate the impact of HBO in patients with chronic osteomyelitis. Propensity-score (PS) matching and inverse probability weighting (IPTW) were employed to balance covariates between the HBO and non-HBO groups. The primary outcome was all-cause mortality. The secondary outcomes were myocardial infarction (MI) and stroke hospitalisation. Furthermore, we evaluated the appropriate timing for HBO intervention by the restricted cubic spline (RCS) functions.

RESULTS

After 1:4 PS-matching, the HBO group (n = 265) was associated with lower 1-year mortality (hazard ratio [HR], 0.49; 95 % confidence interval [CI], 0.25-0.95) than the non-HBO group (n = 994); this was consistent with the IPTW weighting results (HR, 0.25; 95 % CI, 0.20-0.33). The risk of stroke was lower in the HBO group (HR, 0.46; 95 % CI, 0.34-0.63) than that in the non-HBO group. However, HBO therapy failed to reduce the risk of MI. Using the RCS model, patients with intervals within 90 days (HR, 1.38; 95 % CI, 1.04-1.84) presented a significant risk of 1-year mortality. After 90 days, as the length of interval increased, the risk gradually decreased and became insignificant.

CONCLUSION

The present study revealed that adjunctive HBO could benefit the 1-year mortality and stroke hospitalisation in patients with chronic osteomyelitis. HBO was recommended to be initiated within 90 days of chronic osteomyelitis hospitalisation.

Peri-anesthetic hypothermia in rodents: A factor to consider for accurate and reproducible outcomes in orthopedic device-related infection studies

Orthopedic device-related infection (ODRI) preclinical models are widely used in translational research. Most ODRI models require induction of general anesthesia, which frequently results in hypothermia in rodents. This study aimed to evaluate the impact of peri-anesthetic hypothermia in rodents on outcomes in preclinical ODRI studies. A retrospective analysis of all rodents that underwent surgery under general anesthesia to induce an ODRI model with inoculation of Staphylococcus epidermidis between 2016 and 2020 was conducted. A one-way multivariate analysis of covariance (one-way MANCOVA) was used to determine the fixed effect of peri-anesthetic hypothermia (hypothermic defined as rectal temperature <35°C) on the combined harvested tissue and implant colony-forming unit (CFU) counts, and having controlled for the study groups including treatments received, duration of surgery and anesthesia, and study period. The results showed a significant effect of peri-anesthetic hypothermia on the post-mortem combined CFU counts from the harvested tissue and implant(s) (p = 0.01) when comparing normo- versus hypothermic rodents. Using Wilks' Λ as a criterion to determine the contribution of independent variables to the model, peri-anesthetic hypothermia was the most significant, though still a weak predictor, of increased harvested CFU counts. Altogether, the data corroborate the concept that bacterial colonization is affected by abnormal body temperature during general anesthesia at the time of bacterial inoculation in rodents, which needs to be taken into consideration to decrease infection data variability and improve experimental reproducibility.

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

The advent of implanted medical devices has greatly improved the quality of life and increased longevity. However, infection remains a significant risk because bacteria can colonize device surfaces and form biofilms that are resistant to antibiotics and the host's immune system. Several factors contribute to this resistance, including heterogeneous biochemical and pH microenvironments that can affect bacterial growth and interfere with antibiotic biochemistry; dormant regions in the biofilm with low oxygen, pH, and metabolites; slow bacterial growth and division; and poor antibody penetration through the biofilm, which may also be regions with poor acid product clearance. Measuring pH in biofilms is thus key to understanding their biochemistry and offers potential routes to detect and treat latent infections. This review covers the causes of biofilm pH changes and simulations, general findings of metabolite-dependent pH gradients, methods for measuring pH in biofilms, effects of pH on biofilms, and pH-targeted antimicrobial-based approaches.

Vastus lateralis vs rectus femoris muscle flaps for recalcitrant hip joint infection: an anatomical study comparing the effectiveness of acetabular dead space control

Eliminating recalcitrant prosthetic hip joint infections remains one of the greatest challenges in orthopedic surgery. In such cases, the salvage procedure of femoral head excision (the Girdlestone procedure) is often performed. There has been emerging surgical interest in filling the resulting acetabular dead space with a pedicled muscle flap, to enable antibiotic delivery. Both vastus lateralis (VL) and rectus femoris (RF) muscle flaps have been described for this purpose with good success. This study is the first anatomical investigation comparing VL and RF as candidates for interposition myoplasty following hip joint excision. Following standard surgical technique, the Girdlestone procedure and interposition myoplasty of both RF and VL were performed on 10 cadavers. The primary aim was to determine which muscle flap eliminated a greater volume of acetabular dead space. Secondary aims were to characterize the blood supply to RF and assess additional metrics indicative of the likelihood of flap success. The VL flap eliminated more dead space than RF. However, the use of the RF flap was feasible in all cases and has several benefits, including ease of harvest, mobility, and aesthetics. The location of the inferior vascular pedicle into RF was relatively consistent and the most effective predictor of flap success. Both VL and RF are effective in reducing acetabular dead space. While VL can fill a greater volume, the RF flap has technical advantages, related to the predictability of the blood supply.

Dissolved oxygen technologies as a novel strategy for non-healing wounds: A critical review

Non-healing wounds are steadily becoming a global-health issue. Prolonged hypoxia propagates wound chronicity; yet, oxygenating treatments are considered inadequate to date. Dissolved oxygen (DO) in aqueous solutions introduces a novel approach to enhanced wound oxygenation, and is robustly evaluated for clinical applications. A systematic literature search was conducted, whereby experimental and clinical studies of DO technologies were categorized per engineering approach. Technical principles, methodology, endpoints and outcomes were analysed for both oxygenating and healing effects. Forty articles meeting our inclusion criteria were grouped as follows: DO solutions (17), oxygen (O₂ ) dressings (9), O₂ hydrogels (11) and O₂ emulsions (3). All technologies improved wound oxygenation, each to a variable degree. They also achieved at least one statistically significant outcome related to wound healing, mainly in epithelialization, angiogenesis and collagen synthesis. Scarcity in clinical data and methodological variability precluded quantitative comparisons among the biotechnologies studied. DO technologies warrantee further evaluation for wound oxygenation in the clinical setting. Standardised methodologies and targeted research questions are pivotal to facilitate global integration in healthcare.

Perioperative Hypothermia-A Narrative Review

Unintentional hypothermia (core temperature < 36 °C) is a common side effect in patients undergoing surgery. Several patient-centred and external factors, e.g., drugs, comorbidities, trauma, environmental temperature, type of anaesthesia, as well as extent and duration of surgery, influence core temperature. Perioperative hypothermia has negative effects on coagulation, blood loss and transfusion requirements, metabolization of drugs, surgical site infections, and discharge from the post-anaesthesia care unit. Therefore, active temperature management is required in the pre-, intra-, and postoperative period to diminish the risks of perioperative hypothermia. Temperature measurement should be done with accurate and continuous probes. Perioperative temperature management includes a bundle of warming tools adapted to individual needs and local circumstances. Warming blankets and mattresses as well as the administration of properly warmed infusions via dedicated devices are important for this purpose. Temperature management should follow checklists and be individualized to the patient's requirements and the local possibilities.

Intraoperative surgical site infection control and prevention: a position paper and future addendum to WSES intra-abdominal infections guidelines

BACKGROUND

Surgical site infections (SSI) represent a considerable burden for healthcare systems. They are largely preventable and multiple interventions have been proposed over past years in an attempt to prevent SSI. We aim to provide a position paper on Operative Room (OR) prevention of SSI in patients presenting with intra-abdominal infection to be considered a future addendum to the well-known World Society of Emergency Surgery (WSES) Guidelines on the management of intra-abdominal infections.

METHODS

The literature was searched for focused publications on SSI until March 2019. Critical analysis and grading of the literature has been performed by a working group of experts; the literature review and the statements were evaluated by a Steering Committee of the WSES.

RESULTS

Wound protectors and antibacterial sutures seem to have effective roles to prevent SSI in intra-abdominal infections. The application of negative-pressure wound therapy in preventing SSI can be useful in reducing postoperative wound complications. It is important to pursue normothermia with the available resources in the intraoperative period to decrease SSI rate. The optimal knowledge of the pharmacokinetic/pharmacodynamic characteristics of antibiotics helps to decide when additional intraoperative antibiotic doses should be administered in patients with intra-abdominal infections undergoing emergency surgery to prevent SSI.

CONCLUSIONS

The current position paper offers an extensive overview of the available evidence regarding surgical site infection control and prevention in patients having intra-abdominal infections.

Effectiveness of 80% vs 30-35% fraction of inspired oxygen in patients undergoing surgery: an updated systematic review and meta-analysis

BACKGROUND

In 2016, the World Health Organization (WHO) strongly recommended the use of a high fraction of inspired oxygen (FiO₂) in adult patients undergoing general anaesthesia to reduce the risk of surgical site infection (SSI). Since then, further trials have been published, trials included previously have come under scrutiny, and one article was retracted. We updated the systematic review on which the recommendation was based.

METHODS

We performed a systematic literature search from January 1990 to April 2018 for RCTs comparing the effect of high (80%) vs standard (30-35%) FiO₂ on the incidence of SSI. Studies retracted or under investigation were excluded. A random effects model was used for meta-analyses; the sources of heterogeneity were explored using meta-regression.

RESULTS

Of 21 RCTs included, six were newly identified since the publication of the WHO guideline review; 17 could be included in the final analyses. Overall, no evidence for a reduction of SSI after the use of high FiO₂ was found [relative risk (RR): 0.89; 95% confidence interval (CI): 0.73-1.07]. There was evidence that high FiO₂ was beneficial in intubated patients [RR: 0.80 (95% CI: 0.64-0.99)], but not in non-intubated patients [RR: 1.20 (95% CI: 0.91-1.58); test of interaction; P=0.048].

CONCLUSIONS

The WHO updated analyses did not show definite beneficial effect of the use of high perioperative FiO₂, overall, but there was evidence of effect of reducing the SSI risk in surgical patients under general anaesthesia with tracheal intubation. However, the evidence for this beneficial effect has become weaker and the strength of the recommendation needs to be reconsidered.

Normothermia in Arthroplasty

BACKGROUND

Since the initial design of surgical theatres, the thermal environment of the operating suite itself has been an area of concern and robust discussion. In the 1950s, correspondence in the British Medical Journal discussed the most suitable design for a surgeon's cap to prevent sweat from dripping onto the surgical field. These deliberations stimulated questions about the effects of sweat-provoking environments on the efficiency of the surgical team, not to mention the effects on the patient. Although these benefits translate to implant-based orthopedic surgery, they remain poorly understood and, at times, ignored.

METHODS

A review and synthesis of the body of literature on the topic of maintenance of normothermia was performed.

RESULTS

Maintenance of normothermia in orthopedic surgery has been proven to have broad implications from bench top to bedside. Normothermia has been shown to impact everything from nitrogen loss and catabolism after hip fracture surgery to infection rates after elective arthroplasty.

CONCLUSION

Given both the physiologic impact this has on patients, as well as a change in the medicolegal environment around this topic, a general understanding of these concepts should be invaluable to all surgeons.

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

Staphylococcal infection and neutrophilic inflammation can act in concert to establish a profoundly hypoxic environment. In this review we summarise how neutrophils and Staphylococcus aureus are adapted to function under hypoxic conditions, with a particular focus on the impaired ability of hypoxic neutrophils to effect Staphylococcus aureus killing.

Immunological properties of oxygen-transport proteins: hemoglobin, hemocyanin and hemerythrin

It is now well documented that peptides with enhanced or alternative functionality (termed cryptides) can be liberated from larger, and sometimes inactive, proteins. A primary example of this phenomenon is the oxygen-transport protein hemoglobin. Aside from respiration, hemoglobin and hemoglobin-derived peptides have been associated with immune modulation, hematopoiesis, signal transduction and microbicidal activities in metazoans. Likewise, the functional equivalents to hemoglobin in invertebrates, namely hemocyanin and hemerythrin, act as potent immune effectors under certain physiological conditions. The purpose of this review is to evaluate the true extent of oxygen-transport protein dynamics in innate immunity, and to impress upon the reader the multi-functionality of these ancient proteins on the basis of their structures. In this context, erythrocyte-pathogen antibiosis and the immune competences of various erythroid cells are compared across diverse taxa.

Rational Hyperoxia in the Perioperative Period: a Safe and Effective Tool in the Reduction of SSI

Oxygen supplemented at a concentration higher than 40-50 % for at least 2 h perioperatively is expected to reduce surgical site infections (SSI). Although supplementation of 80 % of oxygen perioperatively has shown to reduce SSI in various studies, this concentration is known to be associated with airway complications. This study was taken up to assess the efficacy of 60 %, i.e. <80 and >50 %, inspired oxygen supplemented perioperatively in reducing SSI. One hundred and eighty-eight patients who underwent elective class I and II surgeries were studied. Patients were divided equally into two groups and subgroups and matched for age, sex, type of surgeries, etc. The control group received 30 % and the study group received 60 % oxygen supplementation perioperatively for 2 h. Wounds were observed for the development of SSI. 8/94 patients in the study group and 13/94 patients in the control group developed SSI (p < 0.01). The results indicate a relative risk of 1.62, risk difference of 0.0531 and attributable risk of 38.42 %. Hence, it may be concluded that perioperative oxygen supplementation at 60 % concentration reduces SSI.

Endogenous bone regeneration is dependent upon a dynamic oxygen event

Amputation of the digit tip within the terminal phalangeal bone of rodents, monkeys, and humans results in near-perfect regeneration of bone and surrounding tissues; however, amputations at a more proximal level fail to produce the same regenerative result. Digit regeneration is a coordinated, multifaceted process that incorporates signaling from bioactive growth factors both in the tissue matrix and from several different cell populations. To elucidate the mechanisms involved in bone regeneration we developed a novel multi-tissue slice-culture model that regenerates bone ex vivo via direct ossification. Our study provides an integrated multi-tissue system for bone and digit regeneration and allows us to circumvent experimental limitations that exist in vivo. We used this slice-culture model to evaluate the influence of oxygen on regenerating bone. Micro-computed tomography (µCT) and histological analysis revealed that the regenerative response of the digit is facilitated in part by a dynamic oxygen event, in which mutually exclusive high and low oxygen microenvironments exist and vacillate in a coordinated fashion during regeneration. Areas of increased oxygen are initially seen in the marrow and then surrounding areas of vasculature in the regenerating digit. Major hypoxic events are seen at 7 days postamputation (DPA 7) in the marrow and again at DPA 12 in the blastema, and manipulation of oxygen tensions during these hypoxic phases can shift the dynamics of digit regeneration. Oxygen increased to 21% oxygen tension can either accelerate or attenuate bone mineralization in a stage-specific manner in the regenerative timeline. These studies not only reveal a circumscribed frame of oxygen influence during bone regeneration, but also suggest that oxygen may be one of the primary signaling influences during regeneration.

Infection control hazards associated with the use of forced-air warming in operating theatres

A review is presented of the published experimental and clinical research into the infection control hazards of using forced air-warming (FAW) in operating theatres to prevent inadvertent hypothermia. This evidence has been reviewed with emphasis on the use of ultra-clean ventilation, any interaction it has with different types of patient warming (and FAW in particular), and any related increased risk of surgical site infection (SSI). We conclude that FAW does contaminate ultra-clean air ventilation; however, there appears to be no definite link to an increased risk of SSI based on current research. Nevertheless, whereas this remains unproven, we recommend that surgeons should at least consider alternative patient-warming systems in areas where contamination of the operative field may be critical. Although this is not a systematic review of acceptable randomized controlled clinical trials, which do not exist, it does identify that there is a need for definitive research in this field.

Obesity and surgical wound healing: a current review

Objective. The correlation between obesity and deficient wound healing has long been established. This review examines the current literature on the mechanisms involved in obesity-related perioperative morbidity. Methods. A literature search was performed using Medline, PubMed, Cochrane Library, and Internet searches. Keywords used include obesity, wound healing, adipose healing, and bariatric and surgical complications. Results. Substantial evidence exists demonstrating that obesity is associated with a number of postoperative complications. Specifically in relation to wound healing, explanations include inherent anatomic features of adipose tissue, vascular insufficiencies, cellular and composition modifications, oxidative stress, alterations in immune mediators, and nutritional deficiencies. Most recently, advances made in the field of gene array have allowed researchers to determine a few plausible alterations and deficiencies in obese individuals that contribute to their increased risk of morbidity and mortality, especially wound complications. Conclusion. While the literature discusses how obesity may negatively affect health on various of medical fronts, there is yet to be a comprehensive study detailing all the mechanisms involved in obesity-related morbidities in their entirety. Improved knowledge and understanding of obesity-induced physiological, cellular, molecular, and chemical changes will facilitate better assessments of surgical risks and outcomes and create efficient treatment protocols for improved patient care of the obese patient population.

Store-operated Ca²⁺ entry mediated regulation of polarization in differentiated human neutrophil-like HL-60 cells under hypoxia

The regulation of neutrophil polarization by calcium entry is critical for maintaining an effective host response. Hypoxia has a major effect on the apoptosis of neutrophils, however the role of store-operated Ca2+ entry (SOCE) in neutrophil polarization under hypoxia remains to be elucidated. In the present study, we examined the polarization of differentiated human neutrophil-like HL-60 (dHL-60) cells exposed to hypoxia (3% O2) and the results demonstrated that the percentage of polarized cells following exposure to an N-formyl-Met-Leu-Phe (fMLP) gradient in the Zigmond chamber was increased. We examined stromal interaction molecule 1 (STIM1) and Orai1 expression in dHL-60 cells during hypoxia, and it was observed that the expression of STIM1 and Orai1 was significantly reduced at day 2. However, no apparent change was observed on the first day, indicating that this effect is dependent on stimulation time. Fluo-4/acetoxymethyl (AM) ester imaging also demonstrated that SOCE was decreased in dHL-60 cells. The plasmid overexpression assay demonstrated that the response of polarization was returned to the control level. We demonstrated the inhibitory role of SOCE on the polarization of dHL-60 cells under hypoxic conditions, which may be the mechanism for the adaptation of neutrophils to hypoxia. SOCE is also suggested to be a key modulator of immune deficiency under hypoxic conditions and is potentially a therapeutic target.

Abdominal surgical site infections: a prospective study of determinant factors in Harare, Zimbabwe

Surgical site infections (SSIs) are reported in lower frequencies in the developed countries than in the developing world. A prospective evaluation of risk factors in 285 patients undergoing abdominal surgery procedures in Zimbabwe was therefore undertaken. Overall infection rate was 26%. The age group 30-39 years had the highest number of dirty wounds and the highest rate of human immunodeficiency virus (HIV) infection. Multivariate regression analysis showed a correlation between wound class and SSI (P < 0·05). This was also noted for American Society of Anesthesiologists (ASA) score (P < 0·05). HIV-infected patients had 52% SSIs and non-infected patients had 26% (P < 0·05). Patients receiving blood transfusion had 51% SSIs and those not transfused had 17% (P < 0·01). Patients receiving pre- and intra-operative prophylactic antibiotics had 18% SSIs and those receiving postoperative administration had 37% (P < 0·01). Treatment ranged from dressings only in 11% to surgical intervention in 30% resulting in prolongation of median hospital stay from 8 to 18 days (P < 0·001). Mortality was 7%. High wound class, high ASA score, blood transfusion, HIV infection and delayed use of prophylactic antibiotics were risk factors for SSIs, resulting in surgical interventions, prolonged hospital stay and mortality.

Regulation of IDO activity by oxygen supply: inhibitory effects on antimicrobial and immunoregulatory functions

Tryptophan is an essential amino acid for human beings as well as for some microorganisms. In human cells the interferon-γ (IFN-γ) inducible enzyme indoleamine 2,3-dioxygenase (IDO) reduces local tryptophan levels and is therefore able to mediate broad-spectrum effector functions: IDO activity restricts the growth of various clinically relevant pathogens such as bacteria, parasites and viruses. On the other hand, it has been observed that IDO has immunoregulatory functions as it efficiently controls the activation and survival of T-cells. Although these important effects have been analysed in much detail, they have been observed in vitro using cells cultured in the presence of 20% O₂ (normoxia). Such high oxygen concentrations are not present in vivo especially within infected and inflamed tissues. We therefore analysed IDO-mediated effects under lower oxygen concentrations in vitro and observed that the function of IDO is substantially impaired in tumour cells as well as in native cells. Hypoxia led to reduced IDO expression and as a result to reduced production of kynurenine, the downstream product of tryptophan degradation. Consequently, effector functions of IDO were abrogated under hypoxic conditions: in different human cell lines such as tumour cells (glioblastoma, HeLa) but also in native cells (human foreskin fibroblasts; HFF) IDO lost the capacity to inhibit the growth of bacteria (Staphylococcus aureus), parasites (Toxoplasma gondii) or viruses (herpes simplex virus type 1). Additionally, IDO could no longer efficiently control the proliferation of T-cells that have been co-cultured with IDO expressing HFF cells in vitro. In conclusion, the potent antimicrobial as well as immunoregulatory functions of IDO were substantially impaired under hypoxic conditions that pathophysiologically occurs in vivo.

Nonsteady state oxygen transport in engineered tissue: implications for design

Engineered tissue constructs are limited in size, and thus clinical relevance, when diffusion is the primary mode of oxygen transport. Understanding the extent of oxygen diffusion and cellular consumption is necessary for the design of engineered tissues, particularly those intended for implantation into hypoxic wound sites. This study presents a combined experimental and computation model to predict design constraints for cellularized fibrin tissues subjected to a step change in the oxygen concentration to simulate transplantation. Nonsteady state analysis of oxygen diffusion and consumption was used to estimate the diffusion coefficient of oxygen (mean±SD, 1.7×10(-9)±8.4×10(-11) m(2)/s) in fibrin hydrogels as well as the Michaelis-Menten parameters, Vmax (1.3×10(-17)±9.2×10(-19) mol·cell(-1)·s(-1)), and Km (8.0×10(-3)±3.5×0(-3) mol/m(3)), of normal human lung fibroblasts. Nondimensionalization of the governing diffusion-reaction equation enabled the creation of a single dimensionless parameter, the Thiele modulus (φ), which encompasses the combined effects of oxygen diffusion, consumption, and tissue dimensions. Tissue thickness is the design parameter with the most pronounced influence on the distribution of oxygen within the system. Additionally, tissues designed such that φ<1 achieve a near spatially uniform and adequate oxygen concentration following the step change. Understanding and optimizing the Thiele modulus will improve the design of engineered tissue implants.

Temperature preference during forelimb regeneration in the red-spotted newt Notophthalmus viridescens

Red-spotted newts (Notophthalmus viridescens) are model organisms for regenerative research. These animals can regenerate limbs, tails, jaws, spinal cords, as well as the lens of the eye. Newts are small ectotherms that are aquatic as adults; as ectotherms, they naturally conform to the temperature of their surroundings. Environmental temperatures, however, can increase or decrease the red-spotted newt's metabolic processes, including their rate of tissue regeneration; whether an optimal temperature for this rate of regeneration exists is unknown. However, newts do exhibit behavioral preferences for certain temperatures, and these thermal preferences can change with season or with acclimation. Given this flexibility in behavioral thermoregulation, we hypothesized that the process of tissue regeneration could also affect thermal preference, given the metabolic costs or altered temperature sensitivities of tissue regrowth. It was predicted that regenerating newts would select an environmental temperature that maximized the rate of regeneration, however, this prediction was not fully supported. Thermal preference trials revealed that newts consistently selected temperatures between 24 and 25°C throughout regeneration. This temperature selection was warmer than that of uninjured conspecifics, but was lower than temperatures that would have further augmented the rate of regeneration. Interestingly, regenerating newts maintained a more stable temperature preference than sham newts, suggesting that accuracy in thermoregulation may be more important to regenerating individuals, than to noninjured individuals.

Hypoxia-mediated impairment of the mitochondrial respiratory chain inhibits the bactericidal activity of macrophages

In infected tissues oxygen tensions are low. As innate immune cells have to operate under these conditions, we analyzed the ability of macrophages (Mφ) to kill Escherichia coli or Staphylococcus aureus in a hypoxic microenvironment. Oxygen restriction did not promote intracellular bacterial growth but did impair the bactericidal activity of the host cells against both pathogens. This correlated with a decreased production of reactive oxygen intermediates (ROI) and reactive nitrogen intermediates. Experiments with phagocyte NADPH oxidase (PHOX) and inducible NO synthase (NOS2) double-deficient Mφ revealed that in E. coli- or S. aureus-infected cells the reduced antibacterial activity during hypoxia was either entirely or partially independent of the diminished PHOX and NOS2 activity. Hypoxia impaired the mitochondrial activity of infected Mφ. Inhibition of the mitochondrial respiratory chain activity during normoxia (using rotenone or antimycin A) completely or partially mimicked the defective antibacterial activity observed in hypoxic E. coli- or S. aureus-infected wild-type Mφ, respectively. Accordingly, inhibition of the respiratory chain of S. aureus-infected, normoxic PHOX(-/-) NOS2(-/-) Mφ further raised the bacterial burden of the cells, which reached the level measured in hypoxic PHOX(-/-) NOS2(-/-) Mφ cultures. Our data demonstrate that the reduced killing of S. aureus or E. coli during hypoxia is not simply due to a lack of PHOX and NOS2 activity but partially or completely results from an impaired mitochondrial antibacterial effector function. Since pharmacological inhibition of the respiratory chain raised the generation of ROI but nevertheless phenocopied the effect of hypoxia, ROI can be excluded as the mechanism underlying the antimicrobial activity of mitochondria.

Perioperative normothermia during major surgery: is it important?

PH caused by anesthesia-induced thermoregulatory inhibition and exposure to cold operating room environments still occurs in a significant proportion of patients undergoing major surgery. Although the association between specific perioperative temperatures (in and of themselves) and postoperative morbidity remains unclear, there is fair evidence to suggest that perioperative active warming may reduce the risk of postoperative cardiac events, bleeding, and SSIs. As such, proactive efforts by surgical teams to prevent PH are warranted and have become the standard of care at many institutions. Continued intraoperative monitoring of core temperature (ideally using esophageal probes) is recommended in all cases lasting more than 30 minutes, both to detect malignant hyperthermia and to maintain normothermia. Preoperative and/or intraoperative use of warmed forced-air devices is an effective way to minimize redistribution hypothermia following induction, whereas intraoperative use of warmed i.v. fluids helps reduce the potential for fluid-induced hypothermia and, in turn, optimizes rates of perioperative normothermia.

Successful management of recalcitrant infection related to total hip replacement using pedicled rectus femoris or vastus lateralis muscle flaps

Deep prosthetic joint infection remains an uncommon but serious complication of total hip replacement. We reviewed 24 patients with recalcitrant hip wounds following infected total hip replacement treated with either pedicled rectus femoris or vastus lateralis muscle flaps between 1998 and 2009. The mean age of the patients was 67.4 years (42 to 86) with ten men and 14 women.

There had been a mean of four (1 to 8) previous attempts to close the wound. A total of 20 rectus femoris and five vastus lateralis flaps were used, with one of each type of flap failing and requiring further reconstruction. All patients had positive microbiology. At a mean follow-up of 47 months (9 to 128), 22 patients had a healed wound and two had a persistent sinus. The prosthesis had been retained in five patients. In the remainder it had been removed, and subsequently re-implanted in nine patients. Six patients continued to take antibiotics at final follow-up.

This series demonstrates the effectiveness of pedicled muscle flaps in healing these infected wounds. The high number of previous debridements suggests that these flaps could have been used earlier.

Hypoxia selectively inhibits respiratory burst activity and killing of Staphylococcus aureus in human neutrophils

Neutrophils play a central role in the innate immune response and a critical role in bacterial killing. Most studies of neutrophil function have been conducted under conditions of ambient oxygen, but inflamed sites where neutrophils operate may be extremely hypoxic. Previous studies indicate that neutrophils sense and respond to hypoxia via the ubiquitous prolyl hydroxylase/hypoxia-inducible factor pathway and that this can signal for enhanced survival. In the current study, human neutrophils were shown to upregulate hypoxia-inducible factor (HIF)-1α-dependent gene expression under hypoxic incubation conditions (3 kPa), with a consequent substantial delay in the onset of apoptosis. Despite this, polarization and chemotactic responsiveness to IL-8 and fMLP were entirely unaffected by hypoxia. Similarly, hypoxia did not diminish the ability of neutrophils to phagocytose serum-opsonized heat-killed streptococci. Of the secretory functions examined, IL-8 generation was preserved and elastase release was enhanced by hypoxia. Hypoxia did, however, cause a major reduction in respiratory burst activity induced both by the soluble agonist fMLP and by ingestion of opsonized zymosan, without affecting expression of the NADPH oxidase subunits. Critically, this reduction in respiratory burst activity under hypoxia was associated with a significant defect in the killing of Staphylococcus aureus. In contrast, killing of Escherichia coli, which is predominantly oxidase independent, was fully preserved under hypoxia. In conclusion, these studies suggest that although the NADPH oxidase-dependent bacterial killing mechanism may be compromised by hypoxia, neutrophils overall appear extremely well adapted to operate successfully under severely hypoxic conditions.

Normothermia to prevent surgical site infections after gastrointestinal surgery: holy grail or false idol?

OBJECTIVE

To analyze the association between perioperative normothermia (temperature ≥36°C) and surgical site infections (SSIs) after gastrointestinal (GI) surgery.

SUMMARY OF BACKGROUND DATA

Although active warming during colorectal surgery reduces SSIs, there is limited evidence that perioperative normothermia is associated with lower rates of SSI. Nonetheless, hospitals participating in the Surgical Care Improvement Project must report normothermia rates during major surgery.

METHODS

We conducted a nested, matched, case-control study; cases consisted of GI surgery patients enrolled in our National Surgical Quality Improvement Program database between March 2006 and March 2009 who developed SSIs. Patient/surgery risk factors for SSI were obtained from the National Surgical Quality Improvement Program database. Perioperative temperature/antibiotic/glucose data were obtained from medical records. Cases/controls were compared using univariate/random effects/logistic regression models. Independent risk factors for SSIs were identified using multivariate/random effects/logistic regression models.

RESULTS

A total of 146 cases and 323 matched controls were identified; 82% of patients underwent noncolorectal surgery. Cases were more likely to have final intraoperative normothermia compared with controls (87.6% vs. 77.8%, P = 0.015); rates of immediate postoperative normothermia were similar (70.6% vs. 65.3%, respectively, P = 0.19). Emergent surgery/higher wound class were associated with higher rates of intraoperative normothermia. Independent risk factors for SSI were diabetes, surgical complexity, small bowel surgery, and nonlaparoscopic surgery. There was no independent association between perioperative normothermia and SSI (adjusted odds ratio, 1.05; 95% confidence interval, 0.48-2.33; P = 0.90).

CONCLUSIONS

Pay-for-reporting measures focusing on perioperative normothermia may be of limited value in preventing SSI after GI surgery. Studies to define the benefit of active warming after noncolorectal GI surgery are warranted.

Surgical site infection prevention: how we do it

BACKGROUND

Efforts to prevent surgical site infection (SSI) employ methods that are valid scientifically, but each institution and each surgeon also incorporates methods believed to be useful although this has not been proved by clinical trials.

METHODS

The surgical literature was reviewed, as were practices at the University of Virginia that the authors believe are of value for the prevention of SSI.

RESULTS

Preventive antibiotics are established measures. A case can be made for increasing the dose in patients with a large body mass, and antibiotics probably should be re-administered during procedures lasting longer than 3 h. Chlorhexidine showers for the patient are not proven; however, they are inexpensive and of potential benefit. Hair removal is always done with clippers and in the operating room at the time of the procedure. No scientific case can be made specifically for using antiseptic at the surgical site before the incision. Keeping the blood glucose concentration and the core body temperature near normal probably are important, but how close to normal is unclear. Transfusion enhances SSI, but leukocyte reduction of transfused blood may be of benefit. Some evidence supports the value of antibacterial suture in preventing SSI.

CONCLUSIONS

Many proven and potentially valid methods are employed to prevent SSI. Coordinated and standardized protocols with good data collection can assist the multi-disciplinary efforts to reduce SSI within the unique practices of a given institution.

Effects of sevoflurane on collagen production and growth factor expression in rats with an excision wound

BACKGROUND

Sevoflurane is a widely used inhalation anesthetic, but there are no studies on its effect on the wound-healing process. This study was undertaken to evaluate the effect of exposure time to sevoflurane on wound healing.

METHOD

Male Sprague-Dawley rats were used. Two circular full-thickness skin defects 8 mm in diameter were made on the dorsum of the rats. The animals were divided into six groups according to exposed gas type and time: S1 (sevoflurane, 1 h), S4 (sevoflurane, 4 h), S8 (sevoflurane, 8 h), O1 (oxygen, 1 h), O4 (oxygen, 4 h), and O8 (oxygen, 8 h). The surface area of the wounds was measured 0, 1, 3, and 7 days after surgery. Separately, the mean blood pressures (MBP) and arterial oxygen pressures (PaO(2)) were monitored during the sevoflurane exposure. Collagen type I production and transforming growth factor-beta1 (TGF-beta1) and basic fibroblast growth factor (bFGF) expression on the wound surface were analyzed. Routine histological analysis was also performed.

RESULT

Exposure duration to sevoflurane had no influence on MBP and PaO(2). The reduction in wound size and collagen type I production was delayed in S8. The expression of TGF-beta1 and bFGF on the wound surface in S8 was significantly attenuated in S8. The histology of the S8 demonstrated a delayed healing status.

CONCLUSIONS

Prolonged exposure to sevoflurane might alter the inflammatory phase of the wound-healing process by attenuation of growth factor expression such as TGF-beta1 and bFGF and subsequently by reduced collagen production.

Thermotherapy in dermatologic infections

The use of local induced hyperthermia or thermotherapy for dermatologic infections has not been fully explored in the more recent medical literature. Herein, we discuss the rationale behind the use of thermotherapy and review reported clinical experience with its use in the management of cutaneous infections.

Evidence-based recommendations for the use of topical oxygen therapy in the treatment of lower extremity wounds

Topical oxygen therapy provides another tool in the armamentarium of clinicians treating refractory lower extremity wounds. Devices suitable for providing topical oxygen therapy in a clinical setting have recently become available. This article reviews the evidence to justify the use of this treatment modality, including in vitro, preclinical data, and clinical data. It also provides a protocol for how to administer topical oxygen therapy as well as guidance on patient selection and management to optimize outcomes. Randomized controlled trials are not yet reported and clearly necessary. The current body of evidence suggests that topical oxygen therapy may be considered as a second line of therapy for refractory wounds.

Wounds: an overview of the role of oxygen

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

Supplemental l-arginine enhances wound healing following trauma/hemorrhagic shock

To determine whether parenteral L-arginine supplementation enhances the impaired wound healing of rats subjected to trauma/hemorrhagic shock. Impaired wound healing after trauma and shock has been documented experimentally and clinically. L-arginine has been shown to enhance wound strength and collagen synthesis in rodents and humans. Its efficacy under conditions of impaired wound healing is less well defined. Forty-eight male Lewis rats were used in this study. Using a well-defined model, 24 rats underwent trauma/hemorrhagic shock before wounding. Twenty-four untreated rats served as controls. All animals underwent a dorsal skin incision with implantation of polyvinyl-alcohol sponges. Half of the animals in each group were assigned to receive 1 g/kg/day of L-arginine by intraperitoneal injection in three divided doses, while the other half received saline injections only. Animals were sacrificed 10 days postwounding, and wound-breaking strength (WBS) and wound sponge total hydroxyproline (OHP) and nitrite/nitrate (NO(x)) content were determined. Wound sponge RNA was collected and subjected to Northern blot analysis for procollagens I and III. Trauma/hemorrhage greatly decreased WBS with a concomitant diminution in collagen (OHP) deposition. L-arginine significantly enhanced WBS (19%) and increased OHP (21%) levels in control animals as well as in rats subjected to trauma/hemorrhage (WBS +29%, OHP 40%) compared with their saline-treated counterparts. Procollagen I and III mRNA levels were elevated by L-arginine treatment in both trauma/hemorrhage and control rats. Arginine treatment had no effect on wound fluid and plasma NO(x). The data demonstrate that the impaired healing subsequent to trauma/hemorrhage can be greatly alleviated by L-arginine supplementation.

Using Physiology to Improve Surgical Wound Outcomes

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

Hyperoxia and angiogenesis

We hypothesized that tissue hyperoxia would enhance and hypoxia inhibit neovascularization in a wound model. Therefore, we used female Swiss-Webster mice to examine the influence of differential oxygen treatment on angiogenesis. One milliliter plugs of Matrigel, a mixture of matrix proteins that supports but does not itself elicit angiogenesis, were injected subcutaneously into the mice. Matrigel was used without additive or with added vascular endothelial growth factor (VEGF) or anti-VEGF antibody. Animals were maintained in hypoxic, normoxic, or one of four hyperoxic environments: hypoxia -- 13 percent oxygen at 1 atmosphere absolute (ATA); normoxia -- 21 percent oxygen at 1 ATA; hyperoxia -- (groups a-d) 100 percent oxygen for 90 minutes twice daily at the following pressures: Group a, 1 ATA; Group b, 2 ATA; Group c, 2.5 ATA; Group d, 3.0 ATA. Subcutaneous oxygen tension was measured in all groups. The Matrigel was removed 7 days after implantation. Sections were graded microscopically for the extent of neovascularization. Angiogenesis was significantly greater in all hyperoxic groups and significantly less in the hypoxic group compared with room air-exposed controls. Anti-VEGF antibody abrogated the angiogenic effect of both VEGF and increased oxygen tension. We conclude that angiogenesis is proportional to ambient pO(2) over a wide range. This confirms the clinical impression that angiogenesis requires oxygen. Intermittent oxygen exposure can satisfy the need for oxygen in ischemic tissue.

Supplemental intravenous crystalloid administration does not reduce the risk of surgical wound infection

Wound perfusion and oxygenation are important determinants of the development of postoperative wound infections. Supplemental fluid administration significantly increases tissue oxygenation in surrogate wounds in the subcutaneous tissue of the upper arm in perioperative surgical patients. We tested the hypothesis that supplemental fluid administration during and after elective colon resections decreases the incidence of postoperative wound infections. Patients undergoing open colon resection were randomly assigned to small-volume (n = 124, 8 mL.kg(-1).h(-1)) or large-volume (n = 129, 16-18 mL.kg(-1).h(-1)) fluid management. Our major outcomes were two distinct criteria for diagnosis of surgical wound infections: 1) purulent exudate combined with a culture positive for pathogenic bacteria, and 2) Center for Disease Control criteria for diagnosis of surgical wound infections. All wound infections diagnosed using either criterion by a blinded observer in the 15 days after surgery were considered in the analysis. Wound healing was evaluated with the ASEPSIS scoring system. Of the patients given small fluid administration, 14 had surgical wound infections; 11 given large fluid therapy had infections, P = 0.46. ASEPSIS wound-healing scores were similar in both groups: 7 +/- 16 (small volume) versus 8 +/- 14 (large volume), P = 0.70. Our results suggest that supplemental hydration in the range tested does not impact wound infection rate.

Tissue oxygenation in obese and non-obese patients during laparoscopy

BACKGROUND

Wound infection risk is inversely related to subcutaneous tissue oxygenation, which is reduced in obese patients and may be reduced even more during laparoscopic procedures.

METHODS

We evaluated subcutaneous tissue oxygenation (PsqO(2)) in 20 patients with a body mass index (BMI) > or=40 kg/m(2) (obese group) and 15 patients with BMI <30 kg/m(2) (non-obese group) undergoing laparoscopic surgery with standardized anaesthesia technique and fluid administration. Arterial oxygen tension was maintained near 150 mmHg. PsqO(2) was measured from a surrogate wound on the upper arm.

RESULTS

A mean FIO(2) of 51% (13%) was required in obese patients to reach an arterial oxygen tension of 150 mmHg; however, a mean FIO(2) of only 40% (7%) was required to reach the same oxygen tension in non-obese patients (P=0.007). PsqO(2) was significantly less in obese patients: 41 (10) vs 57 (15) mmHg (P<0.001).

CONCLUSION

Obese patients having laparoscopic surgery require a significantly greater FIO(2) to reach an arterial oxygen tension of about 150 mmHg than non-obese patients; they also have significantly lower subcutaneous oxygen tensions. Both factors probably contribute to an increased infection risk in obese patients.