The Role of Perioperative High Inspired Oxygen Therapy in Reducing Surgical Site Infection

Systematic Review of Surgical Site Infection Prevention Guideline Recommendations for Maintenance of Homeostasis in the Perioperative Period

Surgical site infections are common, result in increased patient morbidity and mortality, and increase the economic burden to society. Anesthesiologists play a key role in perioperative infection prevention, with data suggesting that evidence-based measures can significantly reduce the incidence of these infections. This systematic review aimed to identify and compare current recommendations for the maintenance of homeostasis in surgical site infection prevention guidelines. Eight surgical site infection prevention guidelines published in the past 10 yr were identified. There was broad consensus regarding the importance of optimizing intraoperative homeostasis to reduce infections. However, there was substantial heterogeneity in both the studies cited and the specific recommendations provided regarding maintenance of oxygenation, normovolemia, normothermia and glycemic targets. High-quality randomized controlled trials are required to close existing knowledge gaps, with adaptive platform trials likely to play a key role in improving the current evidence base for preventing surgical site infection.

Current Approaches on Nurse-Performed Interventions to Prevent Healthcare-Acquired Infections: An Umbrella Review

To analyze nursing interventions for preventing healthcare-associated infections (HAIs), major complications in acute care impacting length of stay, costs, morbidity, and mortality, an umbrella review was conducted between 1 February and 26 February 2024, following the Joanna Briggs Institute methodology and PRISMA reporting guidelines, resulting in the inclusion of 22 articles. The 22 final articles obtained addressed the following Centers for Disease Control and Prevention (CDC) categories: surgical site infections (e.g., skin antisepsis, antibiotic prophylaxis), catheter-related bloodstream infections (e.g., taurolidine lock solutions), ventilator-associated pneumonia (e.g., oral hygiene, semi-recumbent positioning), and catheter-associated urinary tract infections (e.g., catheter duration management). Using Neuman's holistic framework, the review emphasized patient-environment interactions. Further primary research is needed to refine these interventions and enhance interprofessional care. The protocol was registered in PROSPERO (CRD42024506801).

Do the results of the OXYGEN trial change if analyzed as "as-treated?": A secondary analysis of the OXYGEN trial

OBJECTIVE

To determine if the results of the OXYGEN trial changed using an "as-treated" approach instead of the original "intention-to-treat" approach. The multi-center randomized controlled OXYGEN trial aimed to determine the effectiveness of high FiO2 in decreasing infection rates for high-risk tibial plateau, tibial pilon, and calcaneus fractures.

METHODS

A secondary analysis of a multi-center randomized controlled trial conducted at 29 US trauma centers was performed. A total of 1231 patients aged 18-80 years with tibial plateau, tibial pilon, or calcaneus fractures thought to be at elevated risk of infection were enrolled. Patients were randomly assigned to receive inspired oxygen at a concentration of 80 % FiO2 (treatment) or 30 % FiO2 (control). Adherence was defined using two different criteria. Criterion 1 required at least 80 % of the surgery time ≤40 % FiO2 for the control group or ≥70 % FiO2 for the treatment group. Criterion 2 required at least 80 % of surgery time within 20-40 % (control) or 70-90 % FiO2 (treatment). The primary outcome was surgical site infection (SSI) within 182 days of definitive fracture fixation. Secondary outcomes were deep and superficial surgical site infections within 90, 182, and 365 days of definitive fixation.

RESULTS

Under Criterion 1, the primary outcome occurred in 7 % (38/523) and 10 % (49/471) of patients in the treatment and control groups, respectively (p = 0.10). Deep infection occurred in 30 (6 %) treatment and 30 (6 %) control patients (p = 0.75). Superficial infection occurred in 9 (2 %) treatment and 20 (4 %) control patients (RR, 0.41; p = 0.03). Using Criterion 2, the primary outcome occurred in 7 % (36/498) of treatment and 10 % (48/468) of control patients (p = 0.12). Deep infection occurred in 28 (6 %) treatment and 29 (6 %) control patients (p = 0.81). Superficial infection occurred in 9 (2 %) treatment and 20 (4.3 %) control patients (RR = 0.43; p = 0.03).

CONCLUSIONS

When re-analyzing based on which patients actually received high or control levels of perioperative oxygen fraction, the results are somewhat consistent with the original "intent-to-treat" analysis. Specifically, high perioperative oxygen lowered the risk of superficial SSI but did not affect deep infections.

Perioperative hyperoxia and myocardial injury after surgery: a randomized controlled trial

BACKGROUND

The World Health Organization recommends hyperoxia (80% fraction of inspired oxygen, FiO2) during and for 2-6 hours following surgery to reduce surgical site infection (SSI). However, some studies suggest increased cardiovascular complications with such a high perioperative FiO2. The goal of our study was to compare the appearance of cardiovascular complications in elective adult colorectal surgery comparing the use of FiO2>0.8 versus conventional therapy (FiO2<0.4).

METHODS

We performed a randomized controlled trial in intubated patients undergoing elective major colorectal surgery. Patients were randomly assigned to receive perioperative FiO2>0.8 or FiO2<0.4. The primary outcome, expressed as Odds Ratio (OR) ±95% Confidence Interval (95%CI), was the incidence of MINS (myocardial injury after noncardiac surgery evaluated for the first 4 postoperative days). Secondary outcomes included MACCE (major adverse cardiovascular and cerebral events) up to 30 postoperative days, SSI, other postoperative complications (according to Clavien-Dindo classification) and length of stay.

RESULTS

We included in the final analyses 403 patients. Comparing the FiO2>0.8 and FiO2<0.4 groups, there was no difference in the appearance of MINS (6.0% vs. 10.4%; OR 0.55; 95% CI: 0.26-1.14; P=0.945). There were no differences between the groups for important secondary outcomes including MACCE to 30 days, SSI, postoperative complications or length of stay.

CONCLUSIONS

Perioperative hyperoxia therapy (FiO2>0.8) with the aim of decreasing SSI did not increase cardiovascular complications after elective colorectal surgery in a general population.

Perioperative oxygen therapy: a protocol for an overview of systematic reviews and meta-analyses

BACKGROUND

Oxygen is routinely given to patients during and after surgery. Perioperative oxygen administration has been proposed as a potential strategy to prevent and treat hypoxaemia and reduce complications, such as surgical site infections, pulmonary complications and mortality. However, uncertainty exists as to which strategies in terms of amount, delivery devices and timing are clinically effective. The aim of this overview of systematic reviews and meta-analyses is to answer the research question, 'For which types of surgery, at which stages of care, in which sub-groups of patients and delivered under what conditions are different types of perioperative oxygen therapy clinically effective?'.

METHODS

We will search key electronic databases (MEDLINE, EMBASE, the Cochrane Database of Systematic Reviews, CENTRAL, Epistemonikos, PROSPERO, the INAHTA International HTA Database and DARE archives) for systematic reviews and randomised controlled trials comparing perioperative oxygen strategies. Each review will be mapped according to type of surgery, surgical pathway timepoints and clinical comparison. The highest quality reviews with the most comprehensive and up-to-date coverage of relevant literature will be chosen as anchoring reviews. Standardised data will be extracted from each chosen review, including definition of oxygen therapy, summaries of interventions and comparators, patient population, surgical characteristics and assessment of overall certainty of evidence. For clinical outcomes and adverse events, the overall pooled findings and results of subgroup and sensitivity analyses (where available) will be extracted. Trial-level data will be extracted for surgical site infections, mortality, and potential trial-level effect modifiers such as risk of bias, outcome definition and type of surgery to facilitate quantitative data analysis. This analysis will adopt a multiple indication review approach with panoramic meta-analysis using review-level data and meta-regression using trial-level data. An evidence map will be produced to summarise our findings and highlight any research gaps.

DISCUSSION

There is a need to provide a panoramic overview of systematic reviews and meta-analyses describing peri-operative oxygen practice to both inform clinical practice and identify areas of ongoing uncertainty, where further research may be required. SYSTEMATIC REVIEW REGISTRATION: PROSPERO CRD42021272361.

Prevention of Surgical Site Infections in Neonates and Children: Non-Pharmacological Measures of Prevention

A surgical site infection (SSI) is an infection that occurs in the incision created by an invasive surgical procedure. Although most infections are treatable with antibiotics, SSIs remain a significant cause of morbidity and mortality after surgery and have a significant economic impact on health systems. Preventive measures are essential to decrease the incidence of SSIs and antibiotic abuse, but data in the literature regarding risk factors for SSIs in the pediatric age group are scarce, and current guidelines for the prevention of the risk of developing SSIs are mainly focused on the adult population. This document describes the current knowledge on risk factors for SSIs in neonates and children undergoing surgery and has the purpose of providing guidance to health care professionals for the prevention of SSIs in this population. Our aim is to consider the possible non-pharmacological measures that can be adopted to prevent SSIs. To our knowledge, this is the first study to provide recommendations based on a careful review of the available scientific evidence for the non-pharmacological prevention of SSIs in neonates and children. The specific scenarios developed are intended to guide the healthcare professional in practice to ensure standardized management of the neonatal and pediatric patients, decrease the incidence of SSIs and reduce antibiotic abuse.

Effects of high versus low inspiratory oxygen fraction on postoperative clinical outcomes in patients undergoing surgery under general anesthesia: A systematic review and meta-analysis of randomized controlled trials

OBJECTIVES

To determine whether high perioperative inspired oxygen fraction (FiO₂) compared with low FiO₂ has more deleterious postoperative clinical outcomes in patients undergoing non-thoracic surgery under general anesthesia.

DESIGN

Meta-analysis of randomized controlled trials.

SETTING

Operating room, postoperative recovery room and surgical ward.

PATIENTS

Surgical patients under general anesthesia.

INTERVENTION

High perioperative FiO₂ (≥0.8) vs. low FiO₂ (≤0.5).

MEASUREMENTS

The primary outcome was mortality within 30 days. Secondary outcomes were pulmonary outcomes (atelectasis, pneumonia, respiratory failure, postoperative pulmonary complications [PPCs], and postoperative oxygen parameters), intensive care unit (ICU) admissions, and length of hospital stay. A subgroup analysis was performed to explore the treatment effect by body mass index (BMI).

MAIN RESULTS

Twenty-six trials with a total 4991 patients were studied. The mortality in the high FiO₂ group did not differ from that in the low FiO₂ group (risk ratio [RR] 0.91, 95% confidence interval [CI] 0.42-1.97, P = 0.810). Nor were there any significant differences between the groups in such outcomes as pneumonia (RR 1.19, 95% CI 0.74-1.92, P = 0.470), respiratory failure (RR 1.29, 95% CI 0.82-2.04, P = 0.270), PPCs (RR 1.05, 95% CI 0.69-1.59, P = 0.830), ICU admission (RR 0.94, 95% CI 0.55-1.60, P = 0.810), and length of hospital stay (mean difference [MD] 0.27 d, 95% CI -0.28-0.81, P = 0.340). The high FiO₂ was associated with postoperative atelectasis more often (risk ratio 1.27, 95% CI 1.00-1.62, P = 0.050), and lower postoperative arterial partial oxygen pressure (MD -5.03 mmHg, 95% CI -7.90- -2.16, P < 0.001)_. In subgroup analysis of BMI >30 kg/m², these parameters were similarly affected between the groups.

CONCLUSIONS

The use of high FiO₂ compared to low FiO₂ did not affect the short-term mortality, although it may increase the incidence of atelectasis in adult, non-thoracic patients undergoing surgical procedures. Nor were there any significant differences in other secondary outcomes.

Effect of Peri-Operative Hyperoxygenation on Surgical Site Infection in Patients Undergoing Emergency Abdominal Surgery: A Randomized Controlled Trial

Background: The rationale for hyperoxygenation in controlling surgical site infection (SSI) has been described in many studies yet has not been defined clearly. Some studies in colorectal surgery have reported beneficial effects, whereas studies in gynecologic surgery have reported either no effect or a deleterious effect. This study assessed the effectiveness of hyperoxygenation on the reduction of SSI in patients undergoing emergency abdominal surgery. Patients and Methods: Eligible patients were assigned randomly to two groups (study group, 80% oxygen or control group, 30% oxygen). The patients in the study group received 80% oxygen and the patients in the control group received 30% oxygen intra-operatively and for two hours after surgery. Arterial blood gas analysis was done after resuscitation, at the end of the surgery, and at two hours after extubation. All patients were assessed for SSI, post-operative nausea and vomiting, and respiratory complications. Patients were followed post-operatively for 14 days. Surgical site infection was diagnosed according to U.S. Centers for Disease Control and Infection (CDC) criteria and by aerobic wound cultures. Results: After exclusion, 85 patients in the control group and 93 patients in the study group were analyzed. There was no difference for baseline, intra-operative, and post-operative characteristics between the two groups, except for higher oxygen saturation at closure and two hours post-operatively, in the 80% group (p = 0.01). Surgical site infection occurred in 29 patients (34.11%) in 30% fraction of inspired oxygen (F_IO₂) group and in 19 patients (20.43%) in 80% F_IO₂ group (p = 0.04). The risk of SSI was 59% lower in the 80% F_IO₂ group (adjusted odds ratio, 0.41; 95% confidence interval [CI], 0.19-0.88 vs. the 30% F_IO₂ group). There were no differences in post-operative nausea and vomiting and respiratory complications between the two treatment groups. Conclusions: Administration of 80% peri-operative hyperoxygenation in emergency abdominal surgery reduces SSI and is a cost-effective method.

Automated closed-loop versus standard manual oxygen administration after major abdominal or thoracic surgery: an international multicentre randomised controlled study

Introduction

Hypoxaemia and hyperoxaemia may occur after surgery, with related complications. This multicentre randomised trial evaluated the impact of automated closed-loop oxygen administration after high-risk abdominal or thoracic surgeries in terms of optimising the oxygen saturation measured by pulse oximetry time within target range.

Methods

After extubation, patients with an intermediate to high risk of post-operative pulmonary complications were randomised to “standard” or “automated” closed-loop oxygen administration. The primary outcome was the percentage of time within the oxygenation range, during a 3-day frame. The secondary outcomes were the time with hypoxaemia and hyperoxaemia under oxygen.

Results

Among the 200 patients, time within range was higher in the automated group, both initially (≤3 h; 91.4±13.7% versus 40.2±35.1% of time, difference +51.0% (95% CI −42.8–59.2%); p<0.0001) and during the 3-day period (94.0±11.3% versus 62.1±23.3% of time, difference +31.9% (95% CI 26.3–37.4%); p<0.0001). Periods of hypoxaemia were reduced in the automated group (≤3 days; 32.6±57.8 min (1.2±1.9%) versus 370.5±594.3 min (5.0±11.2%), difference −10.2% (95% CI −13.9–−6.6%); p<0.0001), as well as hyperoxaemia under oxygen (≤3 days; 5.1±10.9 min (4.8±11.2%) versus 177.9±277.2 min (27.0±23.8%), difference −22.0% (95% CI −27.6–−16.4%); p<0.0001). Kaplan–Meier analysis depicted a significant difference in terms of hypoxaemia (p=0.01) and severe hypoxaemia (p=0.0003) occurrence between groups in favour of the automated group. 25 patients experienced hypoxaemia for >10% of the entire monitoring time during the 3 days within the standard group, as compared to the automated group (p<0.0001).

Conclusion

Automated closed-loop oxygen administration promotes greater time within the oxygenation target, as compared to standard manual administration, thus reducing the occurrence of hypoxaemia and hyperoxaemia.

Frequency of hyperoxaemia during and after major surgery

The oxygen concentration (FiO₂) and arterial oxygen tension (PaO₂) delivered in patients undergoing major surgery is poorly understood. We aimed to assess current practice with regard to the delivered FiO₂ and the resulting PaO₂ in patients undergoing major surgery. We performed a retrospective cohort study in a tertiary hospital. Data were collected prospectively as part of a larger randomised controlled trial but were analysed retrospectively. Patients were included if receiving controlled mandatory ventilation and arterial line monitoring. Anaesthetists determined the FiO₂ and the oxygenation saturation (SpO₂) targets. An arterial blood gas (ABG) was obtained 15-20 minutes after induction of anaesthesia, immediately before the emergence phase of anaesthesia and 15 minutes after arrival in the post-anaesthesia care unit (PACU). We defined hyperoxaemia as a PaO₂ of >150 mmHg and included a further threshold of PaO₂ >200 mmHg. We studied 373 patients. The median (interquartile range (IQR)) lowest intraoperative FiO₂ and SpO₂ values were 0.45 (IQR 0.4-0.5) and 97% (IQR 96-98%), respectively, with a median PaO₂ on the first and second ABG of 237 mmHg (IQR 171-291 mmHg) and 189 mmHg (IQR 145-239 mmHg), respectively. In the PACU, the median lowest oxygen flow rate was 6 L/min (IQR 3-6 L/min), and the PaO₂ was 158 mmHg (IQR 120-192 mmHg). Hyperoxaemia occurred in 82%, 73% and 54% of participants on the first and second intraoperative and postoperative ABGs respectively. A PaO₂ of >200 mmHg occurred in 64%, 41% and 21% of these blood gases, respectively. In an Australian tertiary hospital, a liberal approach to FiO₂ and PaO₂ was most common and resulted in a high incidence of perioperative hyperoxaemia.

A mathematical model of the use of supplemental oxygen to combat surgical site infection

Infections are a common complication of any surgery, often requiring a recovery period in hospital. Supplemental oxygen therapy administered during and immediately after surgery is thought to enhance the immune response to bacterial contamination. However, aerobic bacteria thrive in oxygen-rich environments, and so it is unclear whether oxygen has a net positive effect on recovery. Here, we develop a mathematical model of post-surgery infection to investigate the efficacy of supplemental oxygen therapy on surgical-site infections. A 4-species, coupled, set of non-linear partial differential equations that describes the space-time dependence of neutrophils, bacteria, chemoattractant and oxygen is developed and analysed to determine its underlying properties. Through numerical solutions, we quantify the efficacy of different supplemental oxygen regimes on the treatment of surgical site infections in wounds of different initial bacterial load. A sensitivity analysis is performed to investigate the robustness of the predictions to changes in the model parameters. The numerical results are in good agreement with analyses of the associated well-mixed model. Our model findings provide insight into how the nature of the contaminant and its initial density influence bacterial infection dynamics in the surgical wound.

Automated oxygen administration versus conventional oxygen therapy after major abdominal or thoracic surgery: study protocol for an international multicentre randomised controlled study

INTRODUCTION

Hypoxemia and hyperoxia may occur after surgery with potential related complications. The FreeO₂ PostOp trial is a prospective, multicentre, randomised controlled trial that evaluates the clinical impact of automated O₂ administration versus conventional O₂ therapy after major abdominal or thoracic surgeries. The study is powered to demonstrate benefits of automated oxygen titration and weaning in term of oxygenation, which is an important surrogate for complications after such interventions.

METHODS AND ANALYSIS

After extubation, patients are randomly assigned to the Standard (manual O₂ administration) or FreeO₂ group (automated closed-loop O₂ administration). Stratification is performed for the study centre and a medical history of chronic obstructive pulmonary disease (COPD). Primary outcome is the percentage of time spent in the target zone of oxygen saturation, during a 3-day time frame. In both groups, patients will benefit from continuous oximetry recordings. The target zone of oxygen saturation is SpO₂=88%-92% for patients with COPD and 92%-96% for patients without COPD. Secondary outcomes are the nursing workload assessed by the number of manual O₂ flow adjustments, the time spent with severe desaturation (SpO₂ <85%) and hyperoxia area (SpO₂ >98%), the time spent in a hyperoxia area (SpO₂ >98%), the VO₂, the duration of oxygen administration during hospitalisation, the frequency of use of mechanical ventilation (invasive or non-invasive), the duration of the postrecovery room stay, the hospitalisation length of stay and the survival rate.

ETHICS AND DISSEMINATION

The FreeO₂ PostOp study is conducted in accordance with the declaration of Helsinki and was registered on 11 September 2015 (http://www.clinicaltrials.gov). First patient inclusion was performed on 14 January 2016. The results of the study will be presented at academic conferences and submitted to peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT02546830.

Effect of Perioperative High Oxygen Concentration on Postoperative SSI in Elective Colorectal Surgery-A Randomized Controlled Trial

BACKGROUND

This study was carried out to investigate the effect of perioperative high oxygen concentration on surgical site infection (SSI) in patients undergoing elective colorectal surgery.

METHODS

This was a single-center, prospective, parallel arm, double-blind, superiority randomized controlled trial. All patients more than 18 years of age undergoing elective colorectal surgery were included as per the inclusion criteria. Patients were randomized at the time of induction of anesthesia into high concentration and standard concentration oxygen group based on the concentration of oxygen. Incidence of SSI, day of the detection of SSI, grade of SSI, incidence of anastomotic leak, postoperative day of return of bowel functions, day of starting oral feeds, day of ambulation, and length of hospitalization were studied in both the groups.

RESULTS

A total of 94 patients were included in the study, 47 patients each in high concentration oxygen group and standard concentration oxygen group respectively. The SSI rates were comparable between the two groups [55.3% (95% CI-4.012-69.83) vs. 40.4% (95% CI-26.37-55.73); p = 0.215]. There was no significant difference found with respect to mean day of detection of SSI [4.5(IQR-3.0-7.5) vs. 6.0 (IQR-3.0-9.0; p = 0.602], postoperative day of return of bowel functions (2.20 ± 0.542 vs. 2.13 ± 0.582; p = 0.540), oral feeds (3.62 ± 0.945 vs. 3.46 ± 1.048; p = 0.544), ambulation (4.17 ± 0.868 vs. 4.17 ± 1.270; p = 0.987), and the length of hospitalization [15(IQR-10-19) vs. 15(IQR-10.75-18.25); p = 0.862] between the two groups.

CONCLUSION

There was no significant difference in the rate of SSI with the use of perioperative high oxygen concentration in patients undergoing elective colorectal surgery.

Current Ventilator and Oxygen Management during General Anesthesia

Background

Intraoperative oxygen management is poorly understood. It was hypothesized that potentially preventable hyperoxemia and substantial oxygen exposure would be common during general anesthesia.

Methods

A multicenter, cross-sectional study was conducted to describe current ventilator management, particularly oxygen management, during general anesthesia in Japan. All adult patients (16 yr old or older) who received general anesthesia over 5 consecutive days in 2015 at 43 participating hospitals were identified. Ventilator settings and vital signs were collected 1 h after the induction of general anesthesia. We determined the prevalence of potentially preventable hyperoxemia (oxygen saturation measured by pulse oximetry of more than 98%, despite fractional inspired oxygen tension of more than 0.21) and the risk factors for potentially substantial oxygen exposure (fractional inspired oxygen tension of more than 0.5, despite oxygen saturation measured by pulse oximetry of more than 92%).

Results

A total of 1,786 patients were found eligible, and 1,498 completed the study. Fractional inspired oxygen tension was between 0.31 and 0.6 in 1,385 patients (92%), whereas it was less than or equal to 0.3 in very few patients (1%). Most patients (83%) were exposed to potentially preventable hyperoxemia, and 32% had potentially substantial oxygen exposure. In multivariable analysis, old age, emergency surgery, and one-lung ventilation were independently associated with increased potentially substantial oxygen exposure, whereas use of volume control ventilation and high positive end-expiratory pressure levels were associated with decreased potentially substantial oxygen exposure. One-lung ventilation was particularly a strong risk factor for potentially substantial oxygen exposure (adjusted odds ratio, 13.35; 95% CI, 7.24 to 24.60).

Conclusions

Potentially preventable hyperoxemia and substantial oxygen exposure are common during general anesthesia, especially during one-lung ventilation. Future research should explore the safety and feasibility of a more conservative approach for intraoperative oxygen therapy.

Intra-Operative Inspired Fraction of Oxygen and the Risk of Surgical Site Infections in Patients with Type 1 Surgical Incisions

BACKGROUND

Whether the fraction of inspired oxygen (F_IO₂) influences the risk of surgical site infection (SSI) is controversial. The World Health Organization and the World Federation of Societies of Anesthesiologists offer conflicting recommendations. In this study, we evaluate simultaneously three different definitions of F_IO₂ exposure and the risk of SSI in a large surgical population.

PATIENTS AND METHODS

Patients with clean (type 1) surgical incisions who developed superficial and deep organ/space SSI within 30 days after surgery from January 2003 through December 2012 in five surgical specialties were matched to specialty-specific controls. Fraction of inspired oxygen exposure was defined as (1) nadir F_IO₂, (2) percentage of operative time with F_IO₂ greater than 50%, and (3) cumulative hyperoxia exposure, calculated as the area under the curve (AUC) of F_IO₂ by time for the duration in which F_IO₂ greater than 50%. Stratified univariable and multivariable logistic regression models tested associations between F_IO₂ and SSI.

RESULTS

One thousand two hundred fifty cases of SSI were matched to 3,248 controls. Increased oxygen exposure, by any of the three measures, was not associated with the outcome of any SSI in a multivariable logistic regression model. Elevated body mass index (BMI; 35+ vs. <25, odds ratio [OR] 1.78, 95% confidence interval [CI] 1.43-2.24), surgical duration (250+ min vs. <100 min, OR 1.93, 95% CI 1.48-2.52), diabetes mellitus (OR 1.37, 95% CI 1.13-1.65), peripheral vascular disease (OR 1.52, 95% CI 1.10-2.10), and liver cirrhosis (OR 2.48, 95% CI 1.53-4.02) were statistically significantly associated with greater odds of any SSI. Surgical sub-group analyses found higher intra-operative oxygen exposure was associated with higher odds of SSI in the neurosurgical and spine populations.

CONCLUSION

Increased intra-operative inspired fraction of oxygen was not associated with a reduction in SSI. These findings do not support the practice of increasing F_IO₂ for the purpose of SSI reduction in patients with clean surgical incisions.

Alternatives to antibiotics for prevention of surgical infection

BACKGROUND

Surgical-site infection (SSI) is still the second most common healthcare-associated infection, after respiratory tract infection. SSIs are associated with higher morbidity and mortality rates, and result in enormous healthcare costs. In the past decade, several guidelines have been developed that aim to reduce the incidence of SSI. Unfortunately, there is no consensus amongst the guidelines, and some are already outdated. This review discusses the recent literature regarding alternatives to antibiotics for prevention of SSI.

METHODS

A literature search of PubMed/MEDLINE was performed to retrieve data on the prevention of SSI. The focus was on literature published in the past decade.

RESULTS

Prevention of SSI can be divided into preoperative, perioperative and postoperative measures. Preoperative measures consist of showering, surgical scrubbing and cleansing of the operation area with antiseptics. Perioperative factors can be subdivided as: environmental factors, such as surgical attire; patient-related factors, such as plasma glucose control; and surgical factors, such as the duration and invasiveness of surgery. Postoperative measures consist mainly of wound care.

CONCLUSION

There is a general lack of evidence on the preventive effectiveness of perioperative measures to reduce the incidence of SSI. Most measures are based on common practice and perceived effectiveness. The lack of clinical evidence, together with the stability of the high incidence of SSI (10 per cent for colorectal procedures) in recent decades, highlights the need for future research.

Supplemental Perioperative Oxygen to Reduce Surgical Site Infection After High-Energy Fracture Surgery (OXYGEN Study)

Supplemental perioperative oxygen (SPO) therapy has been proposed as one approach for reducing the risk of surgical site infection (SSI). Current data are mixed regarding efficacy in decreasing SSI rates and hospital inpatient stays in general and few data exist for orthopaedic trauma patients. This study is a phase III, double-blind, prospective randomized clinical trial with a primary goal of assessing the efficacy of 2 different concentrations of perioperative oxygen in the prevention of SSIs in adults with tibial plateau, pilon (tibial plafond), or calcaneus fractures at higher risk of infection and definitively treated with plate and screw fixation. Patients are block randomized (within center) in a 1:1 ratio to either treatment group (FiO2 80%) or control group (FiO2 30%) and stratified by each study injury location. Secondary objectives of the study are to compare species and antibacterial sensitivities of the bacteria in patients who develop SSIs, to validate a previously developed risk prediction model for the development of SSI after fracture surgery, and to measure and compare resource utilization and cost associated with SSI in the 2 study groups. SPO is a low cost and readily available resource that could be easily disseminated to trauma centers across the country and the world if proved to be effective.

Perioperative high inspired oxygen fraction therapy reduces surgical site infection with Pseudomonas aeruginosa in rats

Surgical site infection (SSI) remains one of the most important causes of healthcare-associated infections, accounting for ~17 % of all hospital-acquired infections. Although short-term perioperative treatment with high fraction of inspired oxygen (FiO2) has shown clinical benefits in reducing SSI in colorectal resection surgeries, the true clinical benefits of FiO2 therapy in reducing SSI remain unclear because randomized controlled trials on this topic have yielded disparate results and inconsistent conclusions. To date, no animal study has been conducted to determine the efficacy of short-term perioperative treatments with high (FiO2>60 %) versus low (FiO2<40 %) oxygen in reducing SSI. In this report, we designed a rat model for muscle surgery to compare the effectiveness of short-term perioperative treatments with high (FiO2=80 %) versus a standard low (FiO2=30 %) oxygen in reducing SSI with Pseudomonas aeruginosa - one of the most prevalent Gram-negative pathogens, responsible for nosocomial SSIs. Our data demonstrate that 5 h perioperative treatment with 80 % FiO2 is significantly more effective in reducing SSI with P. aeruginosa compared to 30 % FiO2 treatment. We further show that whilst 80 % FiO2 treatment does not affect neutrophil infiltration into P. aeruginosa-infected muscles, neutrophils in the 80 % FiO2-treated and infected animal group are significantly more activated than neutrophils in the 30 % FiO2-treated and infected animal group, suggesting that high oxygen perioperative treatment reduces SSI with P. aeruginosa by enhancing neutrophil activation in infected wounds.

Intra-operative adherence to lung-protective ventilation: a prospective observational study

BACKGROUND

Lung-protective ventilation in patients with acute respiratory distress syndrome improves mortality. Adopting this strategy in the perioperative period has been shown to reduce lung inflammation and postoperative pulmonary and non-pulmonary sepsis complications in patients undergoing major abdominal surgery. We conducted a prospective observational study into the intra-operative ventilation practice across the West Midlands to assess the use of lung-protective ventilation.

METHODS

Data was collected from all adult ventilated patients undergoing surgery across 14 hospital trusts in the West Midlands over a 2-day period in November 2013. Data collected included surgical specialty, patient's biometric data, duration of procedure, grade of anesthetist, and ventilatory parameters. Lung-protective ventilation was defined as the delivery of a tidal volume between 6 and 8 ml/kg/predicted body weight, a peak pressure of less than 30 cmH2O, and the use of positive end expiratory pressure of 6-8 cmH2O. Categorical data are presented descriptively, while non-parametric data are displayed as medians with statistical tests from Mann-Whitney U tests or Kruskal-Wallis tests for independent samples while paired samples are represented by Wilcoxon signed rank tests.

RESULTS

Four hundred six patients with a median age of 56 years (16-91) were included. The majority of operations (78 %) were elective procedures with the principal anesthetist being a consultant. The commonest surgical specialties were general (29 %), trauma and orthopedic (19 %), and ENT (17 %). Volume-controlled ventilation was the preferred ventilation strategy in 70 % of cases. No patients were ventilated using lung-protective ventilation. Overall peak airway pressure (pPeak) was low (median 20 cmH2O (inter-quartile range [IQR] 10-43 cmH2O)) with median delivered tidal volumes of 8.4 ml/kg/predicted body weight (PBW) (IQR 3.5-14.5 ml/kg/PBW). The median positive end expiratory pressure (PEEP) was only 4 cmH2O (0-5 cmH2O) with PEEP not used in 152 cases.

CONCLUSIONS

Perioperative lung protection ventilation can improve patient outcomes from major surgery. This large prospective study demonstrates that within the West Midlands lung-protective ventilation during the perioperative period is uncommon, especially in relation to the use of PEEP, and that perhaps further trials are required to promote wider adoption of practice.

Enhanced Recovery After Surgery (ERAS) for gastrointestinal surgery, part 2: consensus statement for anaesthesia practice

Background

The present interdisciplinary consensus review proposes clinical considerations and recommendations for anaesthetic practice in patients undergoing gastrointestinal surgery with an Enhanced Recovery after Surgery (ERAS) programme.

Methods

Studies were selected with particular attention being paid to meta‐analyses, randomized controlled trials and large prospective cohort studies. For each item of the perioperative treatment pathway, available English‐language literature was examined and reviewed. The group reached a consensus recommendation after critical appraisal of the literature.

Results

This consensus statement demonstrates that anaesthesiologists control several preoperative, intraoperative and postoperative ERAS elements. Further research is needed to verify the strength of these recommendations.

Conclusions

Based on the evidence available for each element of perioperative care pathways, the Enhanced Recovery After Surgery (ERAS ^®) Society presents a comprehensive consensus review, clinical considerations and recommendations for anaesthesia care in patients undergoing gastrointestinal surgery within an ERAS programme. This unified protocol facilitates involvement of anaesthesiologists in the implementation of the ERAS programmes and allows for comparison between centres and it eventually might facilitate the design of multi‐institutional prospective and adequately powered randomized trials.

High inspired oxygen versus low inspired oxygen for reducing surgical site infection: a meta-analysis

To perform a meta-analysis of published literature to assess the role of high-concentration inspired oxygen in reducing the incidence of surgical site infections (SSIs) following all types of surgery, a comprehensive search for published randomized controlled trials (RCTs) comparing high- with low-concentration inspired oxygen for SSIs was performed. The related data were extracted by two independent authors. The fixed and random effects methods were used to combine data. Twelve RCTs involving 6750 patients were included. Our pooled result found that no significant difference in the incidence of SSIs was observed between the two groups, but there was high statistic heterogeneity across the studies [risk ratio (RR): 0·91; 95% confidence interval (CI): 0·72-1·14; P = 0·40; I² = 54%]. The sensitivity analysis revealed the superiority of high-concentration oxygen in decreasing the SSI rate (RR: 0·86; 95% CI: 0·75-0·98; P = 0·02). Moreover, a subgroup analysis of studies with intestinal tract surgery showed that patients experienced less SSI when high-concentration inspired oxygen was administrated (RR: 0·53; 95% CI: 0·37-0·74; P = 0·0003). Our study provided no direct support for high-concentration inspired oxygen in reducing the incidence of SSIs in patients undergoing all types of surgery.

Short-term hyperoxia does not exert immunologic effects during experimental murine and human endotoxemia

Oxygen therapy to maintain tissue oxygenation is one of the cornerstones of critical care. Therefore, hyperoxia is often encountered in critically ill patients. Epidemiologic studies have demonstrated that hyperoxia may affect outcome, although mechanisms are unclear. Immunologic effects might be involved, as hyperoxia was shown to attenuate inflammation and organ damage in preclinical models. However, it remains unclear whether these observations can be ascribed to direct immunosuppressive effects of hyperoxia or to preserved tissue oxygenation. In contrast to these putative anti-inflammatory effects, hyperoxia may elicit an inflammatory response and organ damage in itself, known as oxygen toxicity. Here, we demonstrate that, in the absence of systemic inflammation, short-term hyperoxia (100% O2 for 2.5 hours in mice and 3.5 hours in humans) does not result in increased levels of inflammatory cytokines in both mice and healthy volunteers. Furthermore, we show that, compared with room air, hyperoxia does not affect the systemic inflammatory response elicited by administration of bacterial endotoxin in mice and man. Finally, neutrophil phagocytosis and ROS generation are unaffected by short-term hyperoxia. Our results indicate that hyperoxia does not exert direct anti-inflammatory effects and temper expectations of using it as an immunomodulatory treatment strategy.

Hyperoxia in intensive care, emergency, and peri-operative medicine: Dr. Jekyll or Mr. Hyde? A 2015 update

This review summarizes the (patho)-physiological effects of ventilation with high FiO₂ (0.8–1.0), with a special focus on the most recent clinical evidence on its use for the management of circulatory shock and during medical emergencies. Hyperoxia is a cornerstone of the acute management of circulatory shock, a concept which is based on compelling experimental evidence that compensating the imbalance between O₂ supply and requirements (i.e., the oxygen dept) is crucial for survival, at least after trauma. On the other hand, “oxygen toxicity” due to the increased formation of reactive oxygen species limits its use, because it may cause serious deleterious side effects, especially in conditions of ischemia/reperfusion. While these effects are particularly pronounced during long-term administration, i.e., beyond 12–24 h, several retrospective studies suggest that even hyperoxemia of shorter duration is also associated with increased mortality and morbidity. In fact, albeit the clinical evidence from prospective studies is surprisingly scarce, a recent meta-analysis suggests that hyperoxia is associated with increased mortality at least in patients after cardiac arrest, stroke, and traumatic brain injury. Most of these data, however, originate from heterogenous, observational studies with inconsistent results, and therefore, there is a need for the results from the large scale, randomized, controlled clinical trials on the use of hyperoxia, which can be anticipated within the next 2–3 years. Consequently, until then, “conservative” O₂ therapy, i.e., targeting an arterial hemoglobin O₂ saturation of 88–95 % as suggested by the guidelines of the ARDS Network and the Surviving Sepsis Campaign, represents the treatment of choice to avoid exposure to both hypoxemia and excess hyperoxemia.

Cardiovascular effects of hyperoxia during and after cardiac surgery

During and after cardiac surgery with cardiopulmonary bypass, high concentrations of oxygen are routinely administered, with the intention of preventing cellular hypoxia. We systematically reviewed the literature addressing the effects of arterial hyperoxia. Extensive evidence from pre-clinical experiments and clinical studies in other patient groups suggests predominant harm, caused by oxidative stress, vasoconstriction, perfusion heterogeneity and myocardial injury. Whether these alterations are temporary and benign, or actually affect clinical outcome, remains to be demonstrated. In nine clinical cardiac surgical studies in low-risk patients, higher oxygen targets tended to compromise cardiovascular function, but did not affect clinical outcome. No data about potential beneficial effects of hyperoxia, such as reduction of gas micro-emboli or post-cardiac surgery infections, were reported. Current evidence is insufficient to specify optimal oxygen targets. Nevertheless, the safety of supraphysiological oxygen suppletion is unproven. Randomised studies with a variety of oxygen targets and inclusion of high-risk patients are needed to identify optimal oxygen targets during and after cardiac surgery.

Perioperative ventilatory strategies in cardiac surgery

Recent data promote the utilization of prophylactic protective ventilation even in patients without acute respiratory distress syndrome (ARDS), and especially after cardiac surgery. The implementation of specific perioperative ventilatory strategies in patients undergoing cardiac surgery can improve both respiratory and extra-pulmonary outcomes. Protective ventilation is not limited to tidal volume reduction. The major components of ventilatory management include assist-controlled mechanical ventilation with low tidal volumes (6-8 mL kg(-1) of predicted body weight) associated with higher positive end-expiratory pressure (PEEP), limitation of fraction of inspired oxygen (FiO2), ventilation maintenance during cardiopulmonary bypass, and finally recruitment maneuvers. In order for such strategies to be fully effective, they should be integrated into a multimodal approach beginning from the induction and continuing over the postoperative period.

Bench-to-bedside review: the effects of hyperoxia during critical illness

Oxygen administration is uniformly used in emergency and intensive care medicine and has life-saving potential in critical conditions. However, excessive oxygenation also has deleterious properties in various pathophysiological processes and consequently both clinical and translational studies investigating hyperoxia during critical illness have gained increasing interest. Reactive oxygen species are notorious by-products of hyperoxia and play a pivotal role in cell signaling pathways. The effects are diverse, but when the homeostatic balance is disturbed, reactive oxygen species typically conserve a vicious cycle of tissue injury, characterized by cell damage, cell death, and inflammation. The most prominent symptoms in the abundantly exposed lungs include tracheobronchitis, pulmonary edema, and respiratory failure. In addition, absorptive atelectasis results as a physiological phenomenon with increasing levels of inspiratory oxygen. Hyperoxia-induced vasoconstriction can be beneficial during vasodilatory shock, but hemodynamic changes may also impose risk when organ perfusion is impaired. In this context, oxygen may be recognized as a multifaceted agent, a modifiable risk factor, and a feasible target for intervention. Although most clinical outcomes are still under extensive investigation, careful titration of oxygen supply is warranted in order to secure adequate tissue oxygenation while preventing hyperoxic harm.

The Effects of Local Warming on Surgical Site Infection

BACKGROUND

Surgical site infections (SSI) account for a major proportion of hospital-acquired infections. They are associated with longer hospital stay, readmissions, increased costs, mortality, and morbidity. Reducing SSI is a goal of the Surgical Care Improvement Project and identifying interventions that reduce SSI effectively is of interest. In a single-blinded randomized controlled trial (RCT) we evaluated the effect of localized warming applied to surgical incisions on SSI development and selected cellular (immune, endothelial) and tissue responses (oxygenation, collagen).

METHODS

After Institutional Review Board approval and consent, patients having open bariatric, colon, or gynecologic-oncologic related operations were enrolled and randomly assigned to local incision warming (6 post-operative treatments) or non-warming. A prototype surgical bandage was used for all patients. The study protocol included intra-operative warming to maintain core temperature ≥36°C and administration of 0.80 FIO2. Patients were followed for 6 wks for the primary outcome of SSI determined by U.S. Centers for Disease Control (CDC) criteria and ASEPSIS scores (additional treatment; presence of serous discharge, erythema, purulent exudate, and separation of the deep tissues; isolation of bacteria; and duration of inpatient stay). Tissue oxygen (PscO2) and samples for cellular analyses were obtained using subcutaneous polytetrafluoroethylene (ePTFE) tubes and oxygen micro-electrodes implanted adjacent to the incision. Cellular and tissue ePTFE samples were evaluated using flow cytometry, immunohistochemistry, and Sircol™ collagen assay (Biocolor Ltd., Carrickfergus, United Kingdom).

RESULTS

One hundred forty-six patients participated (n=73 per group). Study groups were similar on demographic parameters and for intra-operative management factors. The CDC defined rate of SSI was 18%; occurrence of SSI between groups did not differ (p=0.27). At 2 wks, warmed patients had better ASEPSIS scores (p=0.04) but this difference was not observed at 6 wks. There were no significant differences in immune, endothelial cell, or collagen responses between groups. On post-operative days one to two, warmed patients had greater PscO2 change scores with an average PscO2 increase of 9-10 mm Hg above baseline (p<0.04).

CONCLUSIONS

Post-operative local warming compared with non-warming followed in this study, which included intra-operative warming to maintain normothermia and FIO2 level of 0.80, did not reduce SSI and had no effect on immune, endothelial cell presence, or collagen synthesis. PscO2 increased significantly with warming, however, the increase was modest and less than expected or what has been observed in studies testing other interventions.

The effects of high perioperative inspiratory oxygen fraction for adult surgical patients

BACKGROUND

Available evidence on the effects of a high fraction of inspired oxygen (FIO2) of 60% to 90% compared with a routine fraction of inspired oxygen of 30% to 40%, during anaesthesia and surgery, on mortality and surgical site infection has been inconclusive. Previous trials and meta-analyses have led to different conclusions on whether a high fraction of supplemental inspired oxygen during anaesthesia may decrease or increase mortality and surgical site infections in surgical patients.

OBJECTIVES

To assess the benefits and harms of an FIO2 equal to or greater than 60% compared with a control FIO2 at or below 40% in the perioperative setting in terms of mortality, surgical site infection, respiratory insufficiency, serious adverse events and length of stay during the index admission for adult surgical patients.We looked at various outcomes, conducted subgroup and sensitivity analyses, examined the role of bias and applied trial sequential analysis (TSA) to examine the level of evidence supporting or refuting a high FIO2 during surgery, anaesthesia and recovery.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, BIOSIS, International Web of Science, the Latin American and Caribbean Health Science Information Database (LILACS), advanced Google and the Cumulative Index to Nursing and Allied Health Literature (CINAHL) up to February 2014. We checked the references of included trials and reviews for unidentified relevant trials and reran the searches in March 2015. We will consider two studies of interest when we update the review.

SELECTION CRITERIA

We included randomized clinical trials that compared a high fraction of inspired oxygen with a routine fraction of inspired oxygen during anaesthesia, surgery and recovery in individuals 18 years of age or older.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data independently. We conducted random-effects and fixed-effect meta-analyses, and for dichotomous outcomes, we calculated risk ratios (RRs). We used published data and data obtained by contacting trial authors.To minimize the risk of systematic error, we assessed the risk of bias of the included trials. To reduce the risk of random errors caused by sparse data and repetitive updating of cumulative meta-analyses, we applied trial sequential analyses. We used Grades of Recommendation, Assessment, Development and Evaluation (GRADE) to assess the quality of the evidence.

MAIN RESULTS

We included 28 randomized clinical trials (9330 participants); in the 21 trials reporting relevant outcomes for this review, 7597 participants were randomly assigned to a high fraction of inspired oxygen versus a routine fraction of inspired oxygen.In trials with an overall low risk of bias, a high fraction of inspired oxygen compared with a routine fraction of inspired oxygen was not associated with all-cause mortality (random-effects model: RR 1.12, 95% confidence interval (CI) 0.93 to 1.36; GRADE: low quality) within the longest follow-up and within 30 days of follow-up (Peto odds ratio (OR) 0.99, 95% CI 0.61 to 1.60; GRADE: low quality). In a trial sequential analysis, the required information size was not reached and the analysis could not refute a 20% increase in mortality. Similarly, when all trials were included, a high fraction of inspired oxygen was not associated with all-cause mortality to the longest follow-up (RR 1.07, 95% CI 0.87 to 1.33) or within 30 days of follow-up (Peto OR 0.83, 95% CI 0.54 to 1.29), both of very low quality according to GRADE. Neither was a high fraction of inspired oxygen associated with the risk of surgical site infection in trials with low risk of bias (RR 0.86, 95% CI 0.63 to 1.17; GRADE: low quality) or in all trials (RR 0.87, 95% CI 0.71 to 1.07; GRADE: low quality). A high fraction of inspired oxygen was not associated with respiratory insufficiency (RR 1.25, 95% CI 0.79 to 1.99), serious adverse events (RR 0.96, 95% CI 0.65 to 1.43) or length of stay (mean difference -0.06 days, 95% CI -0.44 to 0.32 days).In subgroup analyses of nine trials using preoperative antibiotics, a high fraction of inspired oxygen was associated with a decrease in surgical site infections (RR 0.76, 95% CI 0.60 to 0.97; GRADE: very low quality); a similar effect was noted in the five trials adequately blinded for the outcome assessment (RR 0.79, 95% CI 0.66 to 0.96; GRADE: very low quality). We did not observe an effect of a high fraction of inspired oxygen on surgical site infections in any other subgroup analyses.

AUTHORS' CONCLUSIONS

As the risk of adverse events, including mortality, may be increased by a fraction of inspired oxygen of 60% or higher, and as robust evidence is lacking for a beneficial effect of a fraction of inspired oxygen of 60% or higher on surgical site infection, our overall results suggest that evidence is insufficient to support the routine use of a high fraction of inspired oxygen during anaesthesia and surgery. Given the risk of attrition and outcome reporting bias, as well as other weaknesses in the available evidence, further randomized clinical trials with low risk of bias in all bias domains, including a large sample size and long-term follow-up, are warranted.

Pure oxygen ventilation during general anaesthesia does not result in increased postoperative respiratory morbidity but decreases surgical site infection. An observational clinical study

Background. Pure oxygen ventilation during anaesthesia is debatable, as it may lead to development of atelectasis. Rationale of the study was to demonstrate the harmlessness of ventilation with pure oxygen.

Methods. This is a single-centre, one-department observational trial. Prospectively collected routine-data of 76,784 patients undergoing general, gynaecological, orthopaedic, and vascular surgery during 1995–2009 were retrospectively analysed. Postoperative hypoxia, unplanned ICU-admission, surgical site infection (SSI), postoperative nausea and vomiting (PONV), and hospital mortality were continuously recorded. During 1996 the anaesthetic ventilation for all patients was changed from 30% oxygen plus 70% nitrous oxide to 100% oxygen in low-flow mode. Therefore, in order to minimize the potential of confounding due to a variety of treatments being used, we directly compared years 1995 (30% oxygen) and 1997 (100%), whereas the period 1998 to 2009 is simply described.

Results. Comparing 1995 to 1997 pure oxygen ventilation led to a decreased incidence of postoperative hypoxic events (4.3 to 3.0%; p < 0.0001) and hospital mortality (2.1 to 1.6%; p = 0.088) as well as SSI (8.0 to 5.0%; p < 0.0001) and PONV (21.6 to 17.5%; p < 0.0001). There was no effect on unplanned ICU-admission (1.1 to 0.9; p = 0.18).

Conclusions. The observed effects may be partly due to pure oxygen ventilation, abandonment of nitrous oxide, and application of low-flow anesthesia. Pure oxygen ventilation during general anaesthesia is harmless, as long as certain standards are adhered to. It makes anaesthesia simpler and safer and may reduce clinical morbidity, such as postoperative hypoxia and surgical site infection.

Oxygen Therapy in Critical Illness: Friend or Foe? A Review of Oxygen Therapy in Selected Acute Illnesses

In recent years there has been a gradual shift away from using uncontrolled high concentrations of inspired oxygen in some acute illnesses. Oxygen is perhaps the most frequently used drug in medicine, and understanding the balance of benefits and harms is essential knowledge for all anaesthetists and intensivists. While current teaching and practice emphasise avoiding hypoxaemia over concerns about hyperoxaemia, it may transpire that oxygen excess is more harmful than previously thought. As with many interventions in intensive care medicine, striving to achieve physiological normality may sometimes do more harm than good, and tolerance of abnormal values may on occasion be in patients' best interests. Incorporating Single Best Answers (see page 197: answers on page 237).