Rational use of oxygen in medical disease and anesthesia

Predicting intraoperative hypoxemia in lung resection surgery: assessing the utility of oxygen reserve index measurements during one-lung ventilation before pleural opening

One-lung ventilation (OLV) is crucial for collapsing the lung and improving access to the operative field during lung surgery. Intraoperative OLV may increase the intrapulmonary shunt, potentially leading to intraoperative hypoxemia. The Oxygen Reserve Index (ORI) is a continuous, noninvasive parameter that provides a broader range of oxygen reserve data than conventional oxygen saturation measurements. We aimed to determine whether ORI values measured during OLV before pleural opening are reliable predictors of intraoperative hypoxemia. We included 113 adult patients who underwent lung resection surgery at a tertiary medical center between January 2024 and April 2024. Patients were positioned laterally for surgery, and preemptive OLV was performed with a tidal volume of 5 mL/kg and a fraction of inspired oxygen (FiO2) of 60% for at least 5 min before pleural opening, with concurrent ORI measurements. ORI values obtained during this period were analyzed using ROC curve analysis to predict intraoperative hypoxemia (SaO2 ≤ 90%). AUC values were compared using DeLong's test. Among the 113 patients, 13 (11.5%) developed intraoperative hypoxemia. The predictive power of ORI measured 5 min after initiating OLV for intraoperative hypoxemia was reflected by an AUC of 0.955 (95% CI: 0.899-1.000). Additionally, the predictive power of the change in ORI over 5 min for intraoperative hypoxemia was demonstrated by an AUC of 0.966 (95% CI: 0.935-0.997). The optimal cut-off values for the ORI and its change measured 5 min after preemptive OLV to predict intraoperative hypoxemia were 0.040 and 0.110, respectively. In patients receiving OLV during lung surgery, ORI values and their changes measured during preemptive OLV before pleural opening can predict intraoperative hypoxemia. These findings support an individualized approach to intraoperative FiO2 management, which may help prevent unnecessary oxygen overdose and enable early identification and intervention in patients at high risk of hypoxemia during OLV.

Correlation between oxygen reserve index monitoring and blood gas oxygen values during anesthesia in robotic total prostatectomy surgery

INTRODUCTION-OBJECTIVE

Hyperoxia is associated with acute lung injury and atelectasis. Arterial blood gas measurement is an invasive method. The Oxygen Reserve Index (ORI) was developed to monitor the oxygen values of patients. In this study, we aimed to find out whether safe monitoring against hyperoxia could be achieved in Robotic-Assisted Radical Prostatectomy (RARP) operations by using ORI, which is an easier measurement method compared to arterial blood gas measurements.

MATERIALS AND METHODS

The study was carried out with adult male patients over the age of 18 who underwent RARP with the diagnosis of prostate cancer. An ORI pulse oximeter was additionally attached to their index fingers for ORI monitoring. The moment when ORI values were first read was considered the baseline, and arterial blood gas and ORI values were recorded simultaneously at the baseline (T1), 30 min later (T2), 1 h later (T3), 3 h later (T4), and 5 h later (T5). The correlations between the simultaneously recorded ORI and arterial blood gas values were analyzed.

RESULTS

The sample of the study included 24 male patients. The mean age of the patients was 63.30 ± 7.74, their mean BMI (kg/m2) was 26.64 ± 2.84, and their mean duration of operation was 351.52 ± 48.72 min. The mean ORI value in all measurements was 0.36 (median: 0.28, SD: 0.3694). In the ROC curve analysis conducted to determine the optimal cut-off point for ORI to detect PaO2 ≥ 150 mmHg, the AUC was 0.901 (95% CI: 0.821-0.981), and the cut-off value obtained based on the ROC curve (cut point ORI) was 0.220 (sensitivity: 0.826, specificity: 0.771). The results of the linear regression analysis showed a strong relationship between ORI and PaO2 (PaO2 < 240 mmHg) [simple linear regression, n = 90; r2 = 0.505, p < 0.001].

CONCLUSION

The results of this study demonstrated a significant connection between ORI and PO2 values in their simultaneous interpretation at PO2 values lower than 240. Because the sensitivity of ORI to PO2 is low in cases of severe hyperoxia, blood gas analyses will be needed.

A modified screening protocol for ARDS in patients with respiratory support based on SpO2 and FiO2: A single-center prospective, observational study

Background

The purpose is to formulate a modified screening protocol for acute respiratory distress syndrome (ARDS) in patients with respiratory support based on saturation of pulse oximetry (SpO2) and inspired oxygen concentration (FiO2).

Methods

This prospective observational study was conducted from August to October 2020 at the Department of Critical Care Medicine of Yijishan Hospital Affiliated with Wannan Medical College. All patients admitted during the study period and required arterial blood gas analysis and electrocardiogram monitoring were included in this study. Patients with contraindications to arterial puncture, methemoglobinemia, carbon monoxide poisoning, and other factors that could affect data collection were excluded. The demographic and clinical data, immediate percutaneous SpO2, FiO2, arterial oxygen partial pressure (PaO2), and respiratory rate were recorded; and the SpO2/FiO2 ratio (SFR) and PaO2/FiO2 ratio (PFR) values were calculated according to the above information. The patients were divided into two cohorts by random number table: the establishment cohort and the verification cohort. In the established part, data were divided into group H and group N according to whether SpO2 >97 %. For group H (SpO2 ≤97 %), the regression equation was established between SFR and PFR. For group N (SpO2 >97 %), the correlation between each observation data and PFR was analyzed. Then, a new diagnostic process was established, and the reliability was verified with the Berlin definition set as the gold standard for diagnosis and classification.

Results

There were 341 patients were included. Among them, 161 patients were used to establish the model, and 180 patients were used to verify the validity of the model. In this new diagnosis progress, when SpO2 ≤97 %, if SFR ≤352, ARDS may exist; when SpO2 >97 %, if FiO2min >39 %, there may be ARDS. The sensitivity, specificity, negative predictive value, positive predictive value, and accuracy of the new diagnosis progress for ARDS were 91.1 %, 76.7 %, 89.6 %, 79.6 %, and 83.9 %, respectively.

Conclusion

The SpO2/FiO2 ratio demonstrates notable sensitivity and specificity in diagnosing ARDS, presenting as a credible alternative to PFR.Trail Registration Chinese Clinical Trial Registry Identifier: ChiCTR2000029217.

Tale of Two Cities: narrative review of oxygen

The human brain contributes 2% of the body weight yet receives 15% of cardiac output and demands a constant supply of oxygen (O ₂) and nutrients to meet its metabolic needs. Cerebral autoregulation is responsible for maintaining a constant cerebral blood flow that provides the supply of oxygen and maintains the energy storage capacity. We selected oxygen administration-related studies published between 1975-2021 that included meta-analysis, original research, commentaries, editorial, and review articles. In the present narrative review, several important aspects of the oxygen effects on brain tissues and cerebral autoregulation are discussed, as well the role of exogenous O ₂ administration in patients with chronic ischemic cerebrovascular disease: We aimed to revisit the utility of O ₂ administration in pathophysiological situations whether or not being advantageous. Indeed, a compelling clinical and experimental body of evidence questions the utility of routine oxygen administration in acute and post-recovery brain ischemia, as evident by studies in neurophysiology imaging. While O ₂ is still part of common clinical practice, it remains unclear whether its routine use is safe.

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.

The utility of gradient of end-tidal carbon dioxide between two lungs in lateral decubitus position in predicting a drop in oxygenation during one-lung ventilation in elective thoracic surgery- A prospective observational study

Background and Aims:

Baseline difference in the perfusion of two lungs is the cause of intra-operative shunt during one-lung ventilation (OLV). This study aimed to test the hypothesis that the gradient of end-tidal carbon dioxide (EtCO₂) between two lungs in lateral position (D-EtCO_2lateral) would predict the quantity of shunt and hence the drop in the oxygenation during OLV.

Methods:

An observational study was conducted to include consecutive 70 patients undergoing thoracic surgery using a double-lumen tube in a lateral position. D-EtCO_2lateral was calculated by subtracting EtCO₂ from the non-dependent lung from that of the dependent lung when ventilation parameters are the same for each lung. Oxygenation was assessed by measuring PaO₂/FiO₂ ratios (P/F ratio) at 10, 20 and 40 min after OLV. Correlations between D-EtCO_2lateral and P/F ratios were calculated. Receiver operating curves were analysed to test the ability of D-EtCO_2lateral to identify patients with a P/F ratio of <100 during OLV.

Results:

A moderate correlation was found between D-EtCO_2lateral and P/F ratios at 10 and 20 min of OLV. Among lung resection cases (n = 61), correlation was moderate at 10 (r = 0.64), and 20 min (r = 0.65) (P < 0.001) and became weak at 40 min (r = 0.489, P < 0.001). Areas under curve for D-EtCO_2lateral to predict the drop in P/F ratio <100 at 10, 20 and 40 min after OLV were 0.90 (cut-off: 2.5), 0.78 (cut-off: 3.5) and 0.78 (cut-off: 4.5), respectively.

Conclusion:

D-EtCO_2lateral could predict the drop in oxygenation in the early part of OLV in lung resection surgeries.

Intraoperative Anesthetic Management of the Thoracic Patient

The intraoperative anesthetic management for thoracic surgery can impact a patient's postoperative course, especially in patients with significant lung disease. One-lung ventilation poses an inherent risk to patients, including hypoxemia, acute lung injury, and right ventricular dysfunction. Patient-specific ventilator management strategies during one-lung ventilation can reduce postoperative morbidity.

Short-duration hyperoxia causes genotoxicity in mouse lungs: protection by volatile anesthetic isoflurane

High concentrations of oxygen (hyperoxia) are routinely used during anesthesia, and supplemental oxygen is also administered in connection with several other clinical conditions. Although prolonged hyperoxia is known to cause acute lung injury (ALI), whether short-duration hyperoxia causes lung toxicity remains unknown. We exposed mice to room air (RA or 21% O₂) or 60% oxygen alone or in combination with 2% isoflurane for 2 h and determined the expression of oxidative stress marker genes, DNA damage and DNA repair genes, and expression of cell cycle regulatory proteins using quantitative PCR and Western analyses. Furthermore, we determined cellular apoptosis using TUNEL assay and assessed the DNA damage product 8-hydroxy-2'-deoxyguanosine (8-Oxo-dG) in the urine of 60% hyperoxia-exposed mice. Our study demonstrates that short-duration hyperoxia causes mitochondrial and nuclear DNA damage and that isoflurane abrogates this DNA damage and decreases apoptosis when used in conjunction with hyperoxia. In contrast, isoflurane mixed with RA caused significant 8-Oxo-dG accumulations in the mitochondria and nucleus. We further show that whereas NADPH oxidase is a major source of superoxide anion generated by isoflurane in normoxia, isoflurane inhibits superoxide generation in hyperoxia. Additionally, isoflurane also protected the mouse lungs against ALI (95% O₂ for 36-h exposure). Our study established that short-duration hyperoxia causes genotoxicity in the lungs, which is abrogated when hyperoxia is used in conjunction with isoflurane, but isoflurane alone causes genotoxicity in the lung when delivered with ambient air.

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.

High intraoperative inspiratory oxygen fraction and risk of major respiratory complications

Background

High inspiratory oxygen fraction ( FIO2 ) may improve tissue oxygenation but also impair pulmonary function. We aimed to assess whether the use of high intraoperative FIO2 increases the risk of major respiratory complications.

Methods

We studied patients undergoing non-cardiothoracic surgery involving mechanical ventilation in this hospital-based registry study. The cases were divided into five groups based on the median FIO2 between intubation and extubation. The primary outcome was a composite of major respiratory complications (re-intubation, respiratory failure, pulmonary oedema, and pneumonia) developed within 7 days after surgery. Secondary outcomes included 30-day mortality. Several predefined covariates were included in a multivariate logistic regression model.

Results

The primary analysis included 73 922 cases, of whom 3035 (4.1%) developed a major respiratory complication within 7 days of surgery. For patients in the high- and low-oxygen groups, the median FIO2 was 0.79 [range 0.64-1.00] and 0.31 [0.16-0.34], respectively. Multivariate logistic regression analysis revealed that the median FIO2 was associated in a dose-dependent manner with increased risk of respiratory complications (adjusted odds ratio for high vs low FIO2 1.99, 95% confidence interval [1.72-2.31], P -value for trend <0.001). This finding was robust in a series of sensitivity analyses including adjustment for intraoperative oxygenation. High median FIO2 was also associated with 30-day mortality (odds ratio for high vs low FIO2 1.97, 95% confidence interval [1.30-2.99], P -value for trend <0.001).

Conclusions

In this analysis of administrative data on file, high intraoperative FIO2 was associated in a dose-dependent manner with major respiratory complications and with 30-day mortality. The effect remained stable in a sensitivity analysis controlled for oxygenation.

Clinical trial registration

NCT02399878.

The nasal oxygen practice in intensive care units in China: A multi-centered survey

Background

Nurses frequently administer nasal oxygen therapy for patients in intensive care units (ICUs). However, little is known about the current status, nurses’ management and perception on the nasal oxygen therapy in China. Therefore, we aimed to investigate the nasal oxygen practice of ICUs in China to provide insights into future direction.

Methods

A cross-sectional survey on 10 hospitals was conducted. A self-designed questionnaire was administered to ICU nurses. Descriptive statistics, univariate, and multiple stepwise regression analyses were performed to analyze the respondents’ questionnaires.

Results

A total of 580 respondents with a response rate of 96.67% were included in this study. The average correct answer rate was 58.28%. The current status of nasal oxygen administration in ICUs in Chinese hospitals lagged behind the recommendations of related guidelines. Nurses in China were eager to learn about the updated knowledge on oxygen therapy. The gender, age, clinical experience, degree, job title, and classification of working hospitals were not related to the oxygen therapy-related knowledge scores (all P>0.05).

Conclusion

Many deficiencies are observed regarding the nasal oxygen practice in ICUs of Chinese hospitals. Increased efforts by authorities and medical staff are required to narrow the gap between the current status of oxygen practice and the recommendations from related guidelines.

Intraoperative factors associated with postoperative complications in body contouring surgery

BACKGROUND

Several preoperative factors have been shown to influence outcome of body contouring surgeries. The effect of intraoperative features, including fluid volume administered, hemodynamic and respiratory parameters, and body temperature on postoperative complication, has not been reported to date.

MATERIALS AND METHODS

All subsequent patients undergoing body contouring surgery in the Tel Aviv Medical Center between 2007 and 2012 were enrolled. Demographic and intraoperative data were collected and analyzed for possible associations with postoperative complications, including formation of seroma, hematoma/bleeding, other surgical site complications (infection, adhesiolysis, or need for debridement), formation of a hypertrophic scar, any documented, infection or a composite outcome of any of the previously mentioned.

RESULTS

Data of 218 patients were assessed. Mean (standard deviation) age of patients was 41(14) y. Intraoperative administration of higher volumes of fluids was significantly associated with formation of seroma (P = 0.01), hematoma/bleeding (P = 0.03), hypertrophic scar (P = 0.01), surgical site complications (P = 0.01), and a composite outcome (P < 0.001). Development of hematoma/bleeding was associated with longer periods of low (<35.6°C) intraoperative core temperature (72% versus 50% of surgery duration in patients who did not develop this complication, P < 0.05). Surgical site complications were associated with longer periods of intraoperative oxygen desaturation (saturation ≤92%, 4.2% versus 0.9% of surgery duration in patients who did not develop surgical site complications, P < 0.01).

CONCLUSIONS

Intraoperative moderate hypothermia, hypoxemia, and liberal fluid administration are associated with worse surgical outcome in patients undergoing body contouring surgery. Increased awareness of the potential adverse effects of these factors in body contouring surgery will enhance interventions aimed at avoiding and promptly treating such events.

Technological aided assessment of the acutely ill patient - The case of postoperative complications

Surgical interventions come with complications and highly reported mortality after major surgery. The mortality may be a result of delayed detection of severe complications due to lower monitoring frequency in the general wards. Several studies have shown that continuous monitoring is superior to the manually intermittent recorded monitoring in terms of detecting abnormal physiological signs. Hopefully improved observations may result in earlier detection and clinical intervention. This narrative review will describe current monitoring possibilities for postoperative patients and how it may prevent complications. Several wireless systems are being developed for monitoring vital parameters, but many of these are not yet validated for critically ill patients. The ultimate goal with patient monitoring and detect of events is to prevent postoperative complications, death and costs in the health care system. A few studies indicate that monitoring systems detect deteriorating patients earlier than the nurses, and this was associated with less clinical instability. An important caveat of future devices is to assess their effect in relevant patient populations and not only in healthy test-subjects. Implementation of novel technologies is expensive although expected to be cost-effective if just few adverse events can be prevented. The future is here with promising devices and the possibility to give an unprecedented precise risk estimation of adverse post-surgical events. Next step is to integrate existing evidence based treatment algorithms to demonstrate the clinical efficacy of implementing the new technology.

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.

Ovine platelet function is unaffected by extracorporeal membrane oxygenation within the first 24 h

This study investigated platelet dysfunction during short-term extracorporeal membrane oxygenation (ECMO) and secondarily to determine if hyperoxaemia contributes to this dysfunction. Healthy sheep were anaesthetized and maintained on ECMO for either 2 or 24 h, with or without induction of smoke inhalation acute lung injury. A specialized animal-operating theatre was used to conduct the experimentation. Forty-three healthy female sheep were randomized into either a test or a control group. Following anaesthesia, test groups received ECMO ± smoke inhalation acute lung injury (SALI), whereas control groups were maintained with ventilation only ± SALI. Physiological, biochemical and coagulation data were obtained throughout via continuous monitoring and blood sampling. Platelet function was quantified through whole blood impedance aggregometry using Multiplate. Ovine platelet activity induced by adenosine diphosphate (ADP) and collagen was unaffected during the first 24 h of ECMO. However, progressive divergence of ADP-induced platelet activity was noted at cessation of the experiment. PaO2 was inversely related to ADP-dependent platelet activity in the ECMO groups--a relationship not identified in the control groups. ADP and collagen-dependent platelet activity are not significantly affected within the first 24 h of ECMO in sheep. However, dysfunction in ADP-dependent platelet activity may have continued to develop if observed beyond 24 h. Hyperoxaemia during ECMO does appear to affect how platelets react to ADP and may contribute to this developing dysfunction. Long-term animal models and investigation in clinical animals are warranted to fully investigate platelet function during ECMO.

Oxigenoterapia inalatória em idosos internados em um hospital público

Resumo Objetivos: Descrever as características da oxigenoterapia inalatória (OI) utilizada em idosos internados no setor de clínica médica de um hospital público brasileiro, bem como verificar o conhecimento dos acompanhantes sobre esta terapia. Método: Estudo observacional, transversal e descritivo. A amostra foi composta por 52 idosos internados no setor de clínica médica de um hospital público de Minas Gerais por dois meses. As características da aplicação da OI, os aspectos sociodemográficos e características gerais de saúde do grupo foram avaliados pela análise dos prontuários, prescrições médicas e observação in loco. O conhecimento dos acompanhantes sobre a OI foi avaliado por meio de entrevista estruturada. A análise estatística contemplou análises univariadas exploratórias, com frequências das variáveis categóricas e estatísticas descritivas das variáveis contínuas. Resultados: Houve predomínio do sexo feminino (53,8%); idade média 75 anos; baixa escolaridade (dois anos) e renda per capita (entre um e três salários mínimos); situação conjugal casado (42,2%); não tabagistas (48,1%); 67,3% não estavam em ventilação mecânica anterior e 61,5% estavam em tratamento fisioterapêutico. A principal evolução foi alta sem OI (53,8%). O cateter nasal foi o dispositivo mais utilizado (51,9%); 42,0% das prescrições não foram documentadas; a monitorização esteve presente em 76,9%; 81,8% dos acompanhantes não sabiam o que era o dispositivo da OI e 27,0% relataram ter alterado o dispositivo de oferta de oxigênio. Conclusão: Este estudo mostrou características relevantes da aplicação da OI em idosos internados em um hospital público, demonstrando a necessidade de padronização das indicações, prescrições e monitorização dos idosos em OI, com medidas para a educação da equipe de saúde e acompanhantes.

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.

How much oxygen in adult cardiac arrest?

Although experimental studies have suggested that a high arterial oxygen pressure (PaO₂) might aggravate post-anoxic brain injury, clinical studies in patients resuscitated from cardiac arrest (CA) have given conflicting results. Some studies found that a PaO₂ of more than 300 mm Hg (hyperoxemia) was an independent predictor of poor outcome, but others reported no association between blood oxygenation and neurological recovery in this setting. In this article, we review the potential mechanisms of oxygen toxicity after CA, animal data available in this field, and key human studies dealing with the impact of oxygen management in CA patients, highlighting some potential confounders and limitations and indicating future areas of research in this field. From the currently available literature, high oxygen concentrations during cardiopulmonary resuscitation seem preferable, whereas hyperoxemia should be avoided in the post-CA care. A specific threshold for oxygen toxicity has not yet been identified. The mechanisms of oxygen toxicity after CA, such as seizure development, reactive oxygen species production, and the development of organ dysfunction, need to be further evaluated in prospective studies.

Intensive care clinicians' opinion of conservative oxygen therapy (SpO₂ 90-92%) for mechanically ventilated patients

BACKGROUND

In the ICU, SpO2≥96% are regularly targeted implying that more oxygen may be given than desirable. To reduce exposure to hyperoxia a conservative oxygen therapy protocol (targeted SpO2 90-92% using lowest FiO2) for mechanically ventilated patients was introduced in a single tertiary ICU in September 2012.

OBJECTIVES

To describe intensive care clinicians' opinion of conservative oxygen therapy for mechanically ventilated adult patients.

METHODS

A structured multi-choice questionnaire of intensive care clinicians was conducted between February and March 2013.

RESULTS

Responses were received from 90 staff members: 81 intensive care nurses and 9 medical doctors. A majority of respondents (60.7%) considered oxygen related lung injury as 'a major concern'. Most respondents (81/89; 91.1%) felt conservative oxygen therapy was easy to perform and few respondents (6/88; 8%) considered performing conservative oxygen therapy to be stressful. Most respondents (58%) reported not performing more arterial blood gases to monitor PaO2 during conservative oxygen therapy and 90% (81/90) of respondents indicated a desire to continue conservative oxygen therapy. Free text comments indicated adoption of this protocol was a paradigm shift yet more education and research to elucidate the benefits/harm of lower oxygen saturation targeting is needed.

CONCLUSIONS

Intensive care clinicians readily accepted the introduction of a conservative oxygen therapy protocol into their practice. Most respondents found conservative oxygen therapy easy and not stressful to perform. Further evaluation the administration of oxygen therapy, its management by intensive care clinicians and possible impact on outcome for mechanically ventilated patients appears well accepted by clinical staff.

Is hyperoxaemia helping or hurting patients during extracorporeal membrane oxygenation? Review of a complex problem

Extracorporeal membrane oxygenation (ECMO) facilitates organ support in patients with refractory cardiorespiratory failure whilst disease-modifying treatments can be administered. Improvements to the ECMO process have resulted in its increased utilisation. However, iatrogenic injuries remain, with bleeding and thrombosis the most significant concerns. Many factors contribute to the formation of thrombi, with the hyperoxaemia experienced during ECMO a potential contributor. Outside of ECMO, emerging evidence associates hyperoxaemia with increased mortality. Currently, no universal definition of hyperoxaemia exists, a gap in clinical standards that may impact patient outcomes. Hyperoxaemia has the potential to induce platelet activation, aggregation and, subsequently, thrombosis through markedly increasing the production of reactive oxygen species. There are minimal data in the current literature that explore the relationship between ECMO-induced hyperoxaemia and the production of reactive oxygen species – a putative link towards pathology. Furthermore, there is limited research directly linking hyperoxaemia and platelet activation. These are areas that warrant investigation as definitive data regarding the nascence of these pathological processes may delineate and define the relative risk of supranormal oxygen tension. These data could then assist in defining optimal oxygenation practice, reducing the risks associated with extracorporeal support.

Influence of perioperative oxygen fraction on pulmonary function after abdominal surgery: a randomized controlled trial

Background

A high perioperative inspiratory oxygen fraction (FiO₂) may reduce the frequency of surgical site infection. Perioperative atelectasis is caused by absorption, compression and reduced function of surfactant. It is well accepted, that ventilation with 100% oxygen for only a few minutes is associated with significant formation of atelectasis. However, it is still not clear if a longer period of 80% oxygen results in more atelectasis compared to a low FiO₂.

Our aim was to assess if a high FiO₂ is associated with impaired oxygenation and decreased pulmonary functional residual capacity (FRC).

Methods

Thirty-five patients scheduled for laparotomy for ovarian cancer were randomized to receive either 30% oxygen (n = 15) or 80% oxygen (n = 20) during and for 2 h after surgery. The oxygenation index (PaO₂/FiO₂) was measured every 30 min during anesthesia and 90 min after extubation. FRC was measured the day before surgery and 2 h after extubation by a rebreathing method using the inert gas SF₆.

Results

Five min after intubation, the median PaO₂/FiO₂ was 69 kPa [53-71] in the 30%-group vs. 60 kPa [47-69] in the 80%-group (P = 0.25). At the end of anesthesia, the PaO₂/FiO₂ was 58 kPa [40-70] vs. 57 kPa [46-67] in the 30%- and 80%-group, respectively (P = 0.10). The median FRC was 1993 mL [1610-2240] vs. 1875 mL [1545-2048] at baseline and 1615 mL [1375-2318] vs. 1633 mL [1343-1948] postoperatively in the 30%- and 80%-group, respectively (P = 0.70).

Conclusion

We found no significant difference in oxygenation index or functional residual capacity between patients given 80% and 30% oxygen for a period of approximately 5 hours.

Trial registration

ClinicalTrials.gov Identifier: NCT00637936.