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.

Doctors' and Nurses' Knowledge and Perceived Barriers Regarding Acute Oxygen Therapy in a Tertiary Care Hospital in Nigeria

PURPOSE

Oxygen may cause serious consequences when administered wrongly. This study aimed to assess doctors' and nurses' knowledge of acute oxygen therapy and perceived delivery barriers.

PARTICIPANTS AND METHODS

We conducted a cross sectional study among 202 healthcare providers (134 doctors and 68 nurses) in a Nigerian hospital. The validated Acute Oxygen Therapy Questionnaire (AOTQ), which consisted of 21 knowledge assessment questions, was self administered by participants. Provider's knowledge was classified as good if the score was≥80% and poor if < 60%.

RESULTS

Overall, 26.7% (37.3% doctors and 5.9% nurses) had good knowledge of acute oxygen therapy (AOT), 35.9% were aware, and 19.3% used the AOT guidelines. The commonest source of knowledge on oxygen therapy was medical /nursing school (75.2%). The participants' mean knowledge score was 14.75 ± 2.83(possible score of 0-21). Doctors in postgraduate (PG) training obtained the highest score (15.96±2.48) among the participants (F=12.45, df=4, p<0.001). Most doctors (62%) and 23.5% of nurses considered oxygen as a drug. More doctors (52.2%) than nurses (14.7%) believed that a doctor's order was mandatory before oxygen administration, contrary to guidelines recommendations. Most nurses did not know that breathlessness does not always signify hypoxemia and that asymptomatic anemia was not an indication for oxygen. Concerning oxygen prescription, 39.7% of nurses and 64.2% of doctors knew that it should be prescribed to achieve a target saturation range rather than a fixed dose. In acute oxygen delivery in COPD, doctors and nurses exhibited poor knowledge of the appropriate device and flow rate. The reported barriers to oxygen delivery were: a shortage of oxygen supply, inadequate delivery devices, power outages and out of pocket costs.

CONCLUSION

A significant proportion of doctors and nurses had poor knowledge of acute oxygen therapy, poor awareness and infrequently used AOT guidelines, and reported pertinent delivery barriers that warrant educational and administrative interventions.

Intraoperative Fractions of Inspiratory Oxygen Are Associated With Recurrence-Free Survival After Elective Cancer Surgery

Background: Choice of the fraction of inspiratory oxygen (FiO₂) is controversial. The objective of this analysis was to evaluate whether intraoperative FiO₂ was associated with recurrence-free survival after elective cancer surgery.

Methods and Analysis: In this single-center, retrospective study, we analyzed 1,084 patients undergoing elective resection of pancreatic (n = 652), colorectal (n = 405), or hepatic cancer (n = 27) at Heidelberg University Hospital between 2009 and 2016. Intraoperative mean FiO₂ values were calculated. For unstratified analyses, the study cohort was equally divided into a low- and a high-FiO₂ group. For cancer-stratified analyses, this division was done within cancer-strata. The primary outcome measure was recurrence-free survival until the last known follow-up. Groups were compared using Kaplan–Meier analysis. A stratified log rank test was used to control for different FiO₂ levels and survival times between the cancer strata. Cox-regression analyses were used to control for covariates. Sepsis, reoperations, surgical-site infections, and cardiovascular events during hospital stay and overall survival were secondary outcomes.

Results: Median FiO₂ was 40.9% (Q1–Q3, 38.3–42.9) in the low vs. 50.4% (Q1–Q3, 47.4–54.7) in the high-FiO₂ group. Median follow-up was 3.28 (Q1–Q3, 1.68–4.97) years. Recurrence-free survival was considerable higher in the high-FiO₂ group (p < 0.001). This effect was also confirmed when stratified for the different tumor entities (p = 0.007). In colorectal cancer surgery, increased FiO₂ was independently associated with increased recurrence-free survival. The hazard for the primary outcome decreased by 3.5% with every 1% increase in FiO₂. The effect was not seen in pancreatic cancer surgery and we did not find differences in any of the secondary endpoints.

Conclusions: Until definite evidence from large-scale trials is available and in the absence of relevant clinical conditions warranting specific FiO₂ values, perioperative care givers should aim for an intraoperative FiO₂ of 50% in abdominal cancer surgery as this might benefit oncological outcomes.

The Oxygen project: a prospective study to assess the effectiveness of a targeted intervention to improve oxygen management in hospitalised patients

BACKGROUND

Oxygen is commonly used in the acute care setting. However, used inappropriately, oxygen therapy can result in adverse consequences, including progressive respiratory failure and death.

AIM

To investigate the effectiveness of a targeted intervention to improve prescribing practice and therapeutic application of supplemental oxygen.

METHODS

Respiratory, Oncology and Surgery wards were targeted for the intervention. Nursing and junior medical staff from these wards undertook an education programme about safe use of oxygen. Cross-sectional data about oxygen prescribing, administration and monitoring were collected on inpatients in these wards at baseline, and at 3 and 6 months post-intervention, using a modified version of the British Thoracic Society Oxygen Audit Tool.

RESULTS

At baseline, there was a written prescription for oxygen in 56% of patients (n = 43) using oxygen and this increased to 75% (n = 44) at 3 months, and remained at 65% (n = 48) at 6 months. However, the increased prescription rates were not statistically significant when compared to baseline (χ² = 3.54, df = 1, P = 0.06 and χ² = 0.73, df = 1, P = 0.40, respectively). The observed increase in oxygen prescriptions was driven by the medical wards: Oncology ward at 3 months (χ² = 8.24, df = 1, P = 0.004); and Respiratory ward at 3 months (χ² = 3.31, df = 1, P = 0.069) and 6 months (χ² = 4.98, df = 1, P = 0.026).

CONCLUSION

The education programme intervention to improve oxygen prescription showed promise in the medical wards but did not impact outcomes in the surgical ward setting, where different strategies may be needed.

Oxygen reserve index, a new method of monitoring oxygenation status: what do we need to know?

The oxygen reserve index (ORI) is a new technology that provides real-time, non-invasive, and continuous monitoring of patients’ oxygenation status. This review aimed to discuss its clinical utility, prospect and limitations. A systematic literature search of PubMed, MEDLINE, Google Scholar, and ScienceDirect was performed with the keywords of “oxygen reserve index,” “ORI,” “oxygenation,” “pulse oximetry,” “monitoring,” and “hyperoxia.” Original articles, reviews, case reports, and other relevant articles were reviewed. All articles on ORI were selected. ORI can provide an early warning before saturation begins to decrease and expands the ability to monitor the human body's oxygenation status noninvasively and continuously with the combination of pulse oximetry so as to avoid unnecessary hyperoxia or unanticipated hypoxia. Although the technology is so new that it is rarely known and has not been applied to routine practices in hospitals, it shows good prospects for critical care, oxygen therapy, and intraoperative monitoring.

A nationwide survey of intraoperative management for one-lung ventilation in Taiwan: time to accountable for diversity in protective lung ventilation

BACKGROUND

There is a major paradigm shift for intraoperative mechanical ventilator support by the introduction of lung protective ventilation strategies to reduce postoperative pulmonary complications and improve overall clinical outcomes in non-thoracic surgeries. However, there is currently a lack of standardized practice guideline for lung protection during thoracic surgeries that require one-lung ventilation (OLV). This study aimed to collect the expert opinions of the thoracic anesthesiologists in perioperative care for OLV surgery in Taiwan.

METHODS

This prospective cross-sectional study was undertaken in 16 tertiary hospitals in Taiwan from January to February 2019. A structured survey form was distributed across the participating hospitals and the thoracic anesthesiologists were invited to complete the form voluntarily. The survey form consisted of three parts, including the basic information of the institutional anesthesia care standards, ventilatory settings for a proposed patient receiving OLV surgery and expert opinions on OLV.

RESULTS

A total of 71 thoracic anesthesiologists responded to the survey. Double-lumen tubes are the most commonly used (93.8%) airway devices for OLV. The most commonly recommended ventilator setting during OLV is a tidal volume of 6-7 ml/kg PBW (67.6%) and a PEEP level of 4-6 cmH₂O (73.5%). Dual controlled ventilator modes are used by 44.1% of the anesthesiologists. During OLV, high oxygen fraction (FiO₂ > 0.8) is more commonly supplemented to achieve an oxygen saturation higher than 94%. The consensus of anesthesiologists on the indices for lung protection in thoracic surgery is considerably low. Large majority of the anesthesiologists (91.5%) highly recommend that an international clinical practice guideline on the protective lung ventilation strategy for thoracic anesthesia should be established.

CONCLUSIONS

This study found that the thoracic anesthesiologists in Taiwan share certain common practices in ventilator support during OLV. However, they are concerned about the lack of fundamental clinical evidences to support the beneficial outcomes of the current lung protective strategies applicable to OLV. Large-scale trials are needed to form an evidence-based clinical practice guideline for thoracic anesthesia.

Oxygen targets in the intensive care unit during mechanical ventilation for acute respiratory distress syndrome: a rapid review

BACKGROUND

Supplemental oxygen is frequently administered to patients with acute respiratory distress syndrome (ARDS), including ARDS secondary to viral illness such as coronavirus disease 19 (COVID-19). An up-to-date understanding of how best to target this therapy (e.g. arterial partial pressure of oxygen (PaO2) or peripheral oxygen saturation (SpO2) aim) in these patients is urgently required.

OBJECTIVES

To address how oxygen therapy should be targeted in adults with ARDS (particularly ARDS secondary to COVID-19 or other respiratory viruses) and requiring mechanical ventilation in an intensive care unit, and the impact oxygen therapy has on mortality, days ventilated, days of catecholamine use, requirement for renal replacement therapy, and quality of life.

SEARCH METHODS

We searched the Cochrane COVID-19 Study Register, CENTRAL, MEDLINE, and Embase from inception to 15 May 2020 for ongoing or completed randomized controlled trials (RCTs).

SELECTION CRITERIA

Two review authors independently assessed all records in accordance with standard Cochrane methodology for study selection. We included RCTs comparing supplemental oxygen administration (i.e. different target PaO2 or SpO2 ranges) in adults with ARDS and receiving mechanical ventilation in an intensive care setting. We excluded studies exploring oxygen administration in patients with different underlying diagnoses or those receiving non-invasive ventilation, high-flow nasal oxygen, or oxygen via facemask.

DATA COLLECTION AND ANALYSIS

One review author performed data extraction, which a second review author checked. We assessed risk of bias in included studies using the Cochrane 'Risk of bias' tool. We used the GRADE approach to judge the certainty of the evidence for the following outcomes; mortality at longest follow-up, days ventilated, days of catecholamine use, and requirement for renal replacement therapy.

MAIN RESULTS

We identified one completed RCT evaluating oxygen targets in patients with ARDS receiving mechanical ventilation in an intensive care setting. The study randomized 205 mechanically ventilated patients with ARDS to either conservative (PaO2 55 to 70 mmHg, or SpO2 88% to 92%) or liberal (PaO2 90 to 105 mmHg, or SpO2 ≥ 96%) oxygen therapy for seven days. Overall risk of bias was high (due to lack of blinding, small numbers of participants, and the trial stopping prematurely), and we assessed the certainty of the evidence as very low. The available data suggested that mortality at 90 days may be higher in those participants receiving a lower oxygen target (odds ratio (OR) 1.83, 95% confidence interval (CI) 1.03 to 3.27). There was no evidence of a difference between the lower and higher target groups in mean number of days ventilated (14.0, 95% CI 10.0 to 18.0 versus 14.5, 95% CI 11.8 to 17.1); number of days of catecholamine use (8.0, 95% CI 5.5 to 10.5 versus 7.2, 95% CI 5.9 to 8.4); or participants receiving renal replacement therapy (13.7%, 95% CI 5.8% to 21.6% versus 12.0%, 95% CI 5.0% to 19.1%). Quality of life was not reported.

AUTHORS' CONCLUSIONS

We are very uncertain as to whether a higher or lower oxygen target is more beneficial in patients with ARDS and receiving mechanical ventilation in an intensive care setting. We identified only one RCT with a total of 205 participants exploring this question, and rated the risk of bias as high and the certainty of the findings as very low. Further well-conducted studies are urgently needed to increase the certainty of the findings reported here. This review should be updated when more evidence is available.

PROtective Ventilation with a low versus high Inspiratory Oxygen fraction (PROVIO) and its effects on postoperative pulmonary complications: protocol for a randomized controlled trial

BACKGROUND

Postoperative pulmonary complications (PPCs) are the most common perioperative complications following surgical site infection (SSI). They prolong the hospital stay and increase health care costs. A lung-protective ventilation strategy is considered better practice in abdominal surgery to prevent PPCs. However, the role of the inspiratory oxygen fraction (FiO₂) in the strategy remains disputed. Previous trials have focused on reducing SSI by increasing the inhaled oxygen concentration but higher FiO₂ (80%) was found to be associated with a greater incidence of atelectasis and mortality in recent research. The trial aims at evaluating the effect of different FiO₂ added to the lung-protective ventilation strategy on the incidence of PPCs during general anesthesia for abdominal surgery.

METHODS AND DESIGN

PROtective Ventilation with a low versus high Inspiratory Oxygen fraction trial (PROVIO) is a single-center, prospective, randomized controlled trial planning to recruit 252 patients undergoing abdominal surgery lasting for at least 2 h. The patients will be randomly assigned to (1) a low-FiO₂ (30% FiO₂) group and (2) a high-FiO₂ (80% FiO₂) group in the lung-protective ventilation strategy. The primary outcome of the study is the occurrence of PPCs within the postoperative 7 days. Secondary outcomes include the severity grade of PPCs, the occurrence of postoperative extrapulmonary complications and all-cause mortality within the postoperative 7 and 30 days.

DISCUSSION

The PROVIO trial assesses the effect of low versus high FiO₂ added to a lung-protective ventilation strategy on PPCs for abdominal surgery patients and the results should provide practical approaches to intraoperative oxygen management.

TRIAL REGISTRATION

www.ChiCTR.org.cn , identifier: ChiCTR18 00014901 . Registered on 13 February 2018.

Long-Term Cognitive Outcome and Brain Imaging in Adults After Extracorporeal Membrane Oxygenation

OBJECTIVES

To investigate the presence of cognitive dysfunction and brain lesions in long-term survivors after treatment with extracorporeal membrane oxygenation for severe respiratory failure, and to see whether patients with prolonged hypoxemia were at increased risk.

DESIGN

A single-center retrospective cohort study.

SETTING

Tertiary referral center for extracorporeal membrane oxygenation in Sweden.

PATIENTS

Long-term survivors treated between 1995 and July 2009. Seven patients from a previously published study investigated with a similar protocol were included.

INTERVENTIONS

Brain imaging, neurocognitive testing, interview.

MEASUREMENTS AND MAIN RESULTS

Thirty-eight patients (i.e., n = 31 + 7) were enrolled and investigated in median 9.0 years after discharge. Only memory tests were performed in 10 patients, mainly due to a lack of formal education necessary for the test results to be reliable. Median full-scale intelligence quotient, memory index, and executive index were 97, 101, and 104, respectively (normal, 100 ± 15). Cognitive function was not reduced in the group with prolonged hypoxemia. Brain imaging showed cerebrovascular lesions in 14 of 38 patients (37%), most commonly in the group treated with venoarterial extracorporeal membrane oxygenation (7/11, 64%). In this group, memory function and executive function were significantly reduced.

CONCLUSIONS

Patients treated with extracorporeal membrane oxygenation for respiratory failure may have normal cognitive function years after treatment, if not affected by cerebrovascular lesions. Permissive hypoxemia was not correlated with long-term cognitive dysfunction in the present study. Further prospective studies with minimal loss to follow-up are direly needed to confirm our findings.

Development and validation of a questionnaire to assess the doctors and nurses knowledge of acute oxygen therapy

BACKGROUND

Prescription and administration of oxygen in emergencies by healthcare providers are reported to be inappropriate in most settings. There is a huge gap in the knowledge of health care providers on various aspects of oxygen therapy, and this may be a barrier to optimal oxygen administration. Hence, it is essential to ascertain providers' knowledge of acute oxygen therapy so that appropriate educational interventions are instituted for better delivery. There is no available validated instrument to assess knowledge of acute oxygen therapy. The study aimed to develop, validate and evaluate the test-retest reliability of a questionnaire to determine the doctors and nurses understanding of acute oxygen therapy.

METHODS

This study involved the development of the questionnaire contents by a literature review, assessment of face validity (n = 5), content validity, using a panel of experts (n = 10), item analysis and test-retest reliability among a sample (n = 121) of doctors and nurses.

RESULTS

Face validity indicated that the questionnaire was quick to complete (10-15 min), most items were easy to follow and comprehensible. The global content validity index (S-CVI) was 0.85. The test-retest reliability statistics showed a kappa coefficient of 0.546-0.897 (all P<0.001) and percentage agreement of 80-98.3% indicating high temporal stability in the target population. In total, 90% of the items fulfilled the reliability acceptance criteria. Item discrimination analysis showed that most questions were at an acceptable level. The final questionnaire included 37 item questions and eight sections.

CONCLUSION

The designed questionnaire is a reliable and valid tool for assessing knowledge of acute oxygen therapy among doctors and nurses.

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

BACKGROUND

Evidence-based guidelines from the World Health Organization (WHO) have recommended a high (80%) fraction of inspired oxygen (FiO₂) to reduce surgical site infection in adult surgical patients undergoing general anaesthesia with tracheal intubation. However, there is ongoing debate over the safety of high FiO₂. We performed a systematic review to define the relative risk of clinically relevant adverse events (AE) associated with high FiO₂.

METHODS

We reviewed potentially relevant articles from the WHO review supporting the recommendation, including an updated (July 2018) search of EMBASE and PubMed for randomised and non-randomised controlled studies reporting AE in surgical patients receiving 80% FiO₂ compared with 30-35% FiO₂. We assessed study quality and performed meta-analyses of risk ratios (RR) comparing 80% FiO₂ against 30-35% for major complications, mortality, and intensive care admission.

RESULTS

We included 17 moderate-good quality trials and two non-randomised studies with serious-critical risk of bias. No evidence of harm with high FiO₂ was found for major AE in the meta-analysis of randomised trials: atelectasis RR 0.91 [95% confidence interval (CI) 0.59-1.42); cardiovascular events RR 0.90 (95% CI 0.32-2.54); intensive care admission RR 0.93 (95% CI 0.7-1.12); and death during the trial RR 0.49 (95% CI 0.17-1.37). One non-randomised study reported that high FiO₂ was associated with major respiratory AE [RR 1.99 (95% CI 1.72-2.31)].

CONCLUSIONS

No definite signal of harm with 80% FiO₂ in adult surgical patients undergoing general anaesthesia was demonstrated and there is little evidence on safety-related issues to discourage its use in this population.

Replicating measurements of total hemoglobin mass (tHb-mass) within a single day: precision of measurement; feasibility and safety of using oxygen to expedite carbon monoxide clearance

Hemoglobin concentration ([Hb]) is a function of total hemoglobin mass (tHb-mass) and plasma volume. [Hb] may fall by dilution due to plasma volume expansion and changes in the perioperative period may therefore correlate poorly with blood loss. A simple, reliable, repeatable way to measure plasma volume and tHb-mass would have substantial clinical utility. The "optimized carbon monoxide re-breathing method" (oCOR) meets these criteria. However, it is recommended that a minimum of 12 h (when breathing room air) is left between repeat measurements. Twenty-four subjects underwent 3 days of testing. Two oCOR tests were performed (T1 and T2), 3 h apart, with a different CO clearance method employed between tests aiming to keep the carboxyhemoglobin level below 10%. The primary aim was to ascertain whether tHb-mass testing could be safely repeated within 3 h if carboxyhemoglobin levels were actively reduced by breathing supplemental oxygen (PROCA ). Secondary aims were to compare two other clearance methods; moderate exercise (PROCB ), or a combination of the two (PROCC ). Finally, the reliability of the oCOR method was assessed. Mean (SD) tHb-mass was 807.9 ± (189.7 g) (for T1 on day 1). PROCA lowered the carboxyhemoglobin level from the end of T1 (mean 6.64%) to the start of T2 (mean 2.95%) by a mean absolute value of 3.69%. For PROCB and PROCC the mean absolute decreases in carboxyhemoglobin were 4.00% and 4.31%, respectively. The fall in carboxyhemoglobin between T1 and T2 was greatest in PROCC ; this was statistically significantly lower than that of PROCA (P = 0.0039) and PROCB (P = 0.0289). The test-retest reliability for the measurement of total hemoglobin mass was good with a mean typical error (TE) of 2.0%. The oCOR method is safe and can be repeated within 3 h when carbon monoxide is suitably cleared between tests. Using oxygen therapy alone adequately achieves this.

Exposure to 60% oxygen promotes migration and upregulates angiogenesis factor secretion in breast cancer cells

Peri-operative factors, including anaesthetic drugs and techniques, may affect cancer cell biology and clinical recurrence. In breast cancer cells, we demonstrated that sevoflurane promotes migration and angiogenesis in high fractional oxygen but not in air. Follow-up analysis of the peri-operative oxygen fraction trial found an association between high inspired oxygen during cancer surgery and reduced tumor-free survival. Here we evaluated effects of acute, high oxygen exposure on breast cancer cell viability, migration and secretion of angiogenesis factors in vitro. MDA-MB-231 and MCF-7 breast cancer cells were exposed to 21%, 30%, 60%, or 80% v/v O₂ for 3 hours. Cell viability at 24 hours was determined by MTT and migration at 24 hours with the Oris™ Cell Migration Assay. Secretion of angiogenesis factors at 24 hours was measured via membrane-based immunoarray. Exposure to 30%, 60% or 80% oxygen did not affect cell viability. Migration of MDA-MB-231 and MCF-7 cells was increased by 60% oxygen (P = 0.012 and P = 0.007, respectively) while 30% oxygen increased migration in MCF-7 cells (P = 0.011). These effects were reversed by dimethyloxaloylglycine. In MDA-MB-231 cells high fractional oxygen increased secretion of angiogenesis factors monocyte chemotactic protein 1, regulated on activation normal T-cell expressed and vascular endothelial growth factor. In MCF-7 cells, interleukin-8, angiogenin and vascular endothelial growth factor secretion was significantly increased by high fractional oxygen. High oxygen exposure stimulates migration and secretion of angiogenesis factors in breast cancer cells in vitro.

The oxygen reserve index (ORI): a new tool to monitor oxygen therapy

Supplemental oxygen is administered in the vast majority of patients in the perioperative setting and in the intensive care unit to prevent the potentially deleterious effects of hypoxia. On the other hand, the administration of high concentrations of oxygen may induce hyperoxia that may also be associated with significant complications. Oxygen therapy should therefore be precisely titrated and accurately monitored. Although pulse oximetry has become an indispensable monitoring technology to detect hypoxemia, its value in assessing the oxygenation status beyond the range of maximal arterial oxygen saturation (SpO₂ ≥97%) is very limited. In this hyperoxic range, we need to rely on blood gas analysis, which is intermittent, invasive and sometimes delayed. The oxygen reserve index (ORI) is a new continuous non-invasive variable that is provided by the new generation of pulse oximeters that use multi-wavelength pulse co-oximetry. The ORI is a dimensionless index that reflects oxygenation in the moderate hyperoxic range (PaO₂ 100-200 mmHg). The ORI may provide an early alarm when oxygenation deteriorates well before any changes in SpO₂ occur, may reflect the response to oxygen administration (e.g., pre-oxygenation), and may facilitate oxygen titration and prevent unintended hyperoxia. In this review we describe this new variable, summarize available data and preliminary experience, and discuss its potential clinical utilities in the perioperative and intensive care settings.

Acute oxygen therapy: a review of prescribing and delivery practices

Oxygen is a commonly used drug in the clinical setting and like other drugs its use must be considered carefully. This is particularly true for those patients who are at risk of type II respiratory failure in whom the risk of hypercapnia is well established. In recent times, several international bodies have advocated for the prescription of oxygen therapy in an attempt to reduce this risk in vulnerable patient groups. Despite this guidance, published data have demonstrated that there has been poor uptake of these recommendations. Multiple interventions have been tested to improve concordance, and while some of these interventions show promise, the sustainability of these interventions are less convincing. In this review, we summarize data that have been published on the prevalence of oxygen prescription and the accurate and appropriate administration of this drug therapy. We also identify strategies that have shown promise in facilitating changes to oxygen prescription and delivery practice. There is a clear need to investigate the barriers, facilitators, and attitudes of clinicians in relation to the prescription of oxygen therapy in acute care. Interventions based on these findings then need to be designed and tested to facilitate the application of evidence-based guidelines to support sustained changes in practice, and ultimately improve patient care.

Hyperoxic oxidative stress during abdominal surgery: a randomized trial

PURPOSE

The hypothesis of our study is that during anesthesia, administration of 80 % oxygen concentration increases oxidative stress more than 40 % oxygen.

METHODS

Forty ASA I-II patients were included in a randomized, single-blind study. Expiratory tidal volumes (ETV) were measured before induction and after extubation. After ventilation with 0.8 FiO2 and intubation, mini-bronchoalveolar lavage (mini-BAL), arterial blood gas (ABG), and blood samples were taken. Patients were randomly assigned to receive 0.8 (group I) or 0.4 (group II) FiO2 during management. Before extubation, mini-BAL, ABG, blood samples were taken. PaO2/FiO2, lactate, malondialdehyde (MDA), protein carbonyl (PCO), superoxide dismutase (SOD), total sulfhydryl (T-SH), non-protein sulfhydryl (NPSH), and protein sulfhydryl (PSH) were measured. In both groups, mean arterial pressure and heart rate values were recorded with 30-min intervals.

RESULTS

ETV values were higher in group II after extubation. PaO2/FiO2 values were higher in group II after extubation compared to group I. In both groups, plasma PCO, SOD, and T-SH levels increased significantly before extubation, whereas the increase in MDA was not significant between groups. Plasma PCO, T-SH, and lactate levels were higher in group I, and plasma SOD, and PSH were higher in group I before extubation. In both groups, MDA, SOD, T-SH, and NPSH levels in mini-BAL increased significantly before extubation. Between-group comparisons, PCO, T-SH, PSH, and NPSH were significantly higher in the BAL samples of group II, and MDA levels were higher in group I.

CONCLUSIONS

We found that 80 % FiO2 decreased ETV and PaO2/FiO2 and increased lactate levels and oxidative stress more, inhibiting antioxidant response compared to 40 % FiO2.

Cyclic and constant hyperoxia cause inflammation, apoptosis and cell death in human umbilical vein endothelial cells

BACKGROUND

Perioperative high-dose oxygen (O2 ) exposure can cause hyperoxia. While the effect of constant hyperoxia on the vascular endothelium has been investigated to some extent, the impact of cyclic hyperoxia largely remains unknown. We hypothesized that cyclic hyperoxia would induce more injury than constant hyperoxia to human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were exposed to cyclic hyperoxia (5-95% O2 ) or constant hyperoxia (95% O2 ), normoxia (21% O2 ), and hypoxia (5% O2 ). Cell growth, viability (Annexin V/propidium iodide and 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide, MTT) lactate dehydrogenase (LDH), release, cytokine (interleukin, IL and macrophage migration inhibitory factor, MIF) release, total antioxidant capacity (TAC), and superoxide dismutase activity (SOD) of cell lysate were assessed at baseline and 8, 24, and 72 h. A signal transduction pathway finder array for gene expression analysis was performed after 8 h.

RESULTS

Constant and cyclic hyperoxia-induced gradually detrimental effects on HUVECs. After 72 h, constant or cyclic hyperoxia exposure induced change in cytotoxic (LDH +12%, P = 0.026; apoptosis +121/61%, P < 0.01; alive cells -15%, P < 0.01; MTT -16/15%, P < 0.01), inflammatory (IL-6 +142/190%, P < 0.01; IL-8 +72/43%, P < 0.01; MIF +147/93%, P < 0.01), or redox-sensitive (SOD +278%, TAC-25% P < 0.01) markers. Gene expression analysis revealed that constant and cyclic hyperoxia exposure differently activates oxidative stress, nuclear factor kappa B, Notch, and peroxisome proliferator-activated receptor pathways.

CONCLUSIONS

Extreme hyperoxia exposure induces inflammation, apoptosis and cell death in HUVECs. Although our findings cannot be transferred to clinical settings, results suggest that hyperoxia exposure may cause vascular injury that could play a role in determining perioperative outcome.

Non-invasive monitoring of oxygen delivery in acutely ill patients: new frontiers

Hypovolemia, anemia and hypoxemia may cause critical deterioration in the oxygen delivery (DO₂). Their early detection followed by a prompt and appropriate intervention is a cornerstone in the care of critically ill patients. And yet, the remedies for these life-threatening conditions, namely fluids, blood and oxygen, have to be carefully titrated as they are all associated with severe side-effects when administered in excess. New technological developments enable us to monitor the components of DO₂ in a continuous non-invasive manner via the sensor of the traditional pulse oximeter. The ability to better assess oxygenation, hemoglobin levels and fluid responsiveness continuously and simultaneously may be of great help in managing the DO₂. The non-invasive nature of this technology may also extend the benefits of advanced monitoring to wider patient populations.

Atelectasis and mechanical ventilation mode during conservative oxygen therapy: A before-and-after study

PURPOSE

The purpose of the study is to assess the effect of a conservative oxygen therapy (COT) (target SpO2 of 90%-92%) on radiological atelectasis and mechanical ventilation modes.

MATERIALS AND METHODS

We conducted a secondary analysis of 105 intensive care unit patients from a pilot before-and-after study. The primary outcomes of this study were changes in atelectasis score (AS) of 555 chest radiographs assessed by radiologists blinded to treatment allocation and time to weaning from mandatory ventilation and first spontaneous ventilation trial (SVT).

RESULTS

There was a significant difference in overall AS between groups, and COT was associated with lower time-weighted average AS. In addition, in COT patients, change from mandatory to spontaneous ventilation or time to first SVT was shortened. After adjustment for baseline characteristics and interactions between oxygen therapy, radiological atelectasis, and mechanical ventilation management, patients in the COT group had significantly lower "best" AS (adjusted odds ratio, 0.28 [95% confidence interval {CI}, 0.12-0.66]; P=.003) and greater improvement in AS in the first 7 days (adjusted odds ratio, 0.42 [95% CI, 0.17-0.99]; P=.049). Moreover, COT was associated with significantly earlier successful weaning from a mandatory ventilation mode (adjusted hazard ratio, 2.96 [95% CI, 1.73-5.04]; P<.001) and with shorter time to first SVT (adjusted hazard ratio, 1.77 [95% CI, 1.13-2.78]; P=.013).

CONCLUSIONS

In mechanically ventilated intensive care unit patients, COT might be associated with decreased radiological evidence of atelectasis, earlier weaning from mandatory ventilation modes, and earlier first trial of spontaneous ventilation.

Variability in targeted arterial oxygenation levels in patients with severe sepsis or septic shock

BACKGROUND

Supplemental oxygen therapy is used for intensive care (ICU) patients with severe sepsis, but with no general guidelines and few safety data. The aim of this observational study was to describe the variability in oxygen administration as well as the association between partial pressure of arterial oxygen (PaO2 ) and mortality.

METHODS

We extracted data from two Scandinavian clinical trials of ICU patients with severe sepsis or septic shock. We calculated average PaO2 and fraction of inspired oxygen (FiO2 ) from trial inclusion and the following 5 days, and assessed the association between PaO2 and 90-day mortality.

RESULTS

The median PaO2 was 9.8 kPa [5-95% range 6.4-19.9] and FiO2 was 0.51 [5-95% range 0.27-1.00], respectively. Eight hundred and five of 1,770 patients (45%) died. The relative risk of mortality was 1.43 [95% CI: 1.19-1.65] in patients with average PaO2 < 8 kPa and 1.29 [95% CI: 0.84-1.68] in patients with average PaO2 ≥ 16 kPa, as compared to patients with average PaO2 10-12 kPa. The relative risk of mortality was 1.38 [95% CI: 1.17-1.58] in patients with an average FiO2 0.60-0.80 and 2.10 [95% CI: 1.88-2.23] in patients with an average FiO2  ≥ 0.80 as compared to patients with an average FiO2  ≤ 0.40.

CONCLUSION

Administration of oxygen in patients with severe sepsis resulted in a wide range of PaO2 . Significantly higher mortality was observed in patients with an average PaO2 < 8 kPa and FiO2 ≥ 0.60. The results do not imply causation and the associations between average PaO2 and adverse outcomes have to be assessed further.

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).