High Inspired Oxygen Fraction Research Articles

First real-time imaging of bronchoscopic lung volume reduction by electrical impedance tomography

BackgroundBronchoscopic lung volume reduction (BLVR) with one-way endobronchial valves (EBV) has better outcomes when the target lobe has poor collateral ventilation, resulting in complete lobe atelectasis. High-inspired oxygen fraction (FIO2) promotes atelectasis through faster gas absorption after airway occlusion, but its application during BLVR with EBV has been poorly understood. We aimed to investigate the real-time effects of FIO2 on regional lung volumes and regional ventilation/perfusion by electrical impedance tomography (EIT) during BLVR with EBV.MethodsSix piglets were submitted to left lower lobe occlusion by a balloon-catheter and EBV valves with FIO2 0.5 and 1.0. Regional end-expiratory lung impedances (EELI) and regional ventilation/perfusion were monitored. Local pocket pressure measurements were obtained (balloon occlusion method). One animal underwent simultaneous acquisitions of computed tomography (CT) and EIT. Regions-of-interest (ROIs) were right and left hemithoraces.ResultsFollowing balloon occlusion, a steep decrease in left ROI-EELI with FIO2 1.0 occurred, 3-fold greater than with 0.5 (p < 0.001). Higher FIO2 also enhanced the final volume reduction (ROI-EELI) achieved by each valve (p < 0.01). CT analysis confirmed the denser atelectasis and greater volume reduction achieved by higher FIO2 (1.0) during balloon occlusion or during valve placement. CT and pocket pressure data agreed well with EIT findings, indicating greater strain redistribution with higher FIO2.ConclusionsEIT demonstrated in real-time a faster and more complete volume reduction in the occluded lung regions under high FIO2 (1.0), as compared to 0.5. Immediate changes in the ventilation and perfusion of ipsilateral non-target lung regions were also detected, providing better estimates of the full impact of each valve in place.Trial registrationNot applicable.

Lung ultrasound imaging and clinical consequences of intraoperative high inspired oxygen fraction in healthy mechanically ventilated children

Study objectiveHigh inspired oxygen concentrations (FiO2) are claimed to cause resorption atelectasis increasing the risk for perioperative hypoxemia and postoperative pulmonary complications. Pediatric physicians are still reluctant to accomplish low FiO2 strategies in children. We investigated the association between lung ultrasound score (LUS) and arterial oxygenation (PaO2/FiO2 ratio)in anesthetized mechanically ventilated children undergoing non-abdominal surgery using different FiO2 fractions. Study designObservational cohort. Study settingsOperative rooms and post-anesthesia care unit. PatientsThirty-three patients aged (3–12 years) of both sexes. InterventionPatients were anesthetized while receiving high FIO2 protocol (preoxygenation 1.0, induction and recovery 0.8, maintenance 0.6, post-extubation 1.0 and 0.21 for 2h postoperative). Measurements: LUS was performed after intubation and initiation of mechanical ventilation, after the end of surgery, and 2h postoperatively. Arterial blood gas analysis was performed at the same time points and respiratory mechanics were recorded intraoperatively. LUS scores were tested for probability of bivariate correlation with PaO2/FiO2 ratio (primary endpoint), age, weight, operation time, PaO2, and dynamic compliance. Main resultsAfter intubation, the median LUS score was 2 (Range: 0–14) which significantly decreased after surgery to 1 (0–8), (P = 0.010). At 2- hours postoperatively, it was 0 (0–6) which was significantly lower than both after intubation (P = 0.001) and after surgery (P = 0.007). No significant Correlation was found between the LUS score and any investigated parameters. ConclusionsEven though we found no significant correlation between LUS and PaO2, or PaO2/FiO2 ratio, the high values of LUS after intubation necessitate caution when administering high FiO2 levels in pediatrics. Trial registrationClinicalTrials.gov ID: NCT04581226.

The effect of high perioperative inspiratory oxygen fraction for abdominal surgery on surgical site infection: a systematic review and meta-analysis

Guidelines from the World Health Organization strongly recommend the use of a high fraction of inspired oxygen (FiO2) in adult patients undergoing general anesthesia to reduce surgical site infection (SSI). However, previous meta-analyses reported inconsistent results. We aimed to address this controversy by focusing specifically on abdominal surgery with relatively high risk of SSI. Medline, EMBASE, and Cochrane CENTRAL databases were searched. Randomized trials of abdominal surgery comparing high to low perioperative FiO2 were included, given that the incidence of SSI was reported as an outcome. Meta-analyses of risk ratios (RR) were performed using a fixed effects model. Subgroup analysis and meta-regression were employed to explore sources of heterogeneity. We included 27 trials involving 15977 patients. The use of high FiO2 significantly reduced the incidence of SSI (n = 27, risk ratio (RR): 0.87; 95% confidence interval (CI): 0.79, 0.95; I2 = 49%, Z = 3.05). Trial sequential analysis (TSA) revealed that z-curve crossed the trial sequential boundary and data are sufficient. This finding held true for the subgroup of emergency operations (n = 2, RR: 0.54; 95% CI: 0.35, 0.84; I2 = 0%, Z = 2.75), procedures using air as carrier gas (n = 9, RR: 0.79; 95% CI: 0.69, 0.91; I2 = 60%, Z = 3.26), and when a high level of FiO2 was maintained for a postoperative 6 h or more (n = 9, RR: 0.68; 95% CI: 0.56, 0.83; I2 = 46%, Z = 3.83). Meta-regression revealed no significant interaction between SSI with any covariates including age, sex, body-mass index, diabetes mellitus, duration of surgery, and smoking. Quality of evidence was assessed to be moderate to very low. Our pooled analysis revealed that the application of high FiO2 reduced the incidence of SSI after abdominal operations. Although TSA demonstrated sufficient data and cumulative analysis crossed the TSA boundary, our results should be interpreted cautiously given the low quality of evidence.Registration: https://www.crd.york.ac.uk/prospero (CRD42022369212) on October 2022.

Impact of hyperoxia and phenylephrine on cerebral oxygenation: An experimental clinical study.

Oxygen supply to the brain is of special importance during intracranial surgery because it may be compromised by intracranial pathology. A high arterial blood pressure (mean arterial pressure above 80 mmHg) and a high arterial oxygen tension (PaO2 above 12 kPa) is therefore often targeted in these patients, when for example intracranial pressure is increased or when a mass effect on brain tissue from a tumour is present, and it is pursued by administering vasopressors such as phenylephrine and by increasing inspiratory oxygen fraction (FiO2 ). However, whether these interventions increase cerebral oxygenation remains uncertain. We aimed to investigate the effect of hyperoxia and phenylephrine on brain tissue oxygen tension (PbtO2 ) in patients undergoing craniotomy. In this experimental study, we included 17 adult patients scheduled for elective craniotomy. After securing a stable baseline of the oxygen probe, PbtO2 was measured in white matter peripherally in the surgical field during general anaesthesia. Primary comparisons were PbtO2 before versus after an increase in FiO2 from 0.30 to 0.80 as well as before versus after a bolus dose of phenylephrine (0.1-0.2mg depending on patient haemodynamics). Data were analysed with the Wilcoxon signed rank test. We obtained complete data sets in 11 patients undergoing the FiO2 increase and six patients receiving the phenylephrine bolus. PbtO2 was 22 (median; 5%-95% range, 4.6-54) mmHg during 30% oxygen, 68 (8.4-99) mmHg during 80% oxygen (p=.004 compared to 30% oxygen), 21 (4.5-81) mmHg before phenylephrine, and 19 (4.2-56) mmHg after phenylephrine (p=.56 compared to before phenylephrine). In patients undergoing craniotomy under general anaesthesia, brain tissue oxygen tension increased with a high inspiratory oxygen fraction but remained unchanged after a bolus dose of phenylephrine.

High Perioperative Inspiratory Oxygen Fraction for High-Risk Orthopaedic Trauma: Commentary on an article by the Major Extremity Trauma Research Consortium (METRC): "Effect of Supplemental Perioperative Oxygen on SSI Among Adults with Lower-Extremity Fractures at Increased Risk for Infection. A Randomized Clinical Trial".

Commentary Surgical site infection (SSI) complicates care and worsens outcomes among orthopaedic trauma patients. Despite efforts to reduce postoperative infection in this population, the incidence of SSI remains unacceptably high. The study by the Major Extremity Trauma Research Consortium (METRC) is a randomized investigation into the impact of a high versus low perioperative inspiratory oxygen fraction in reducing SSI among orthopaedic trauma patients considered at high risk for infection based on their injury characteristics. The authors should be commended for completing a rigorous investigation of this perioperative intervention. The study was well designed and required a high degree of coordination, and the authors have expertly communicated their results. This multidisciplinary and multicenter collaboration stands as an example to be emulated. Generally, SSI risk can be mitigated through interventions such as perioperative patient optimization, efficient and meticulous surgical technique, appropriate perioperative antibiotics, and the avoidance of autologous blood transfusion when possible. However, given the deleterious effect of infection on treatment outcomes, the search continues for discrete interventions that can further reduce infection risk. Ideal interventions would also be cost-effective and easily scalable to permit expedient widespread implementation. Perioperative supplemental oxygen is a particularly appealing candidate for prophylaxis against infection as it is relatively safe, inexpensive, and ubiquitous. The study results generally favor the perioperative use of a high fraction of inspired oxygen in the treatment of high-risk orthopaedic trauma, although the authors note that the apparent benefit of the intervention was primarily driven by a reduction in superficial infections. Reliably defining superficial infection is inherently difficult as it primarily relies on clinical evaluation. The authors employed a practical method, defining superficial infection by antibiotic administration prompted by a concerning wound evaluation. However, antibiotic administration does not confirm the presence of an infection. For example, a moderately ischemic but uninfected wound may trigger some providers to prescribe antibiotics while others would continue close surveillance or institute other wound-care interventions. Nevertheless, whether the reduction in antibiotic administration in the intervention group was entirely related to the reduction in superficial infection or was more broadly related to improved perfusion and the subjective appearance of wounds, the results suggest that supplemental oxygen has a beneficial effect on wound healing. It is inherently more difficult to demonstrate that an intervention reduces the rate of deep infection, and it is common to employ a combined outcome of superficial and deep infection in research. Given deep infection rates of 5.6% and 6.6% in the treatment and control groups, respectively, a massive study population would be required to appropriately power an investigation into a potential 1% difference in deep infection. However, there is considerable benefit to preventing 1 patient in 100 from developing a deep SSI, and the results of this study generate optimism that such an effect could exist with this low-cost intervention. As discussed above, relatively few discrete interventions have been demonstrated to reduce the rate of SSI in orthopaedic trauma. Identifying interventions that safely contribute to improved wound healing and infection risk is critical to optimizing care. Candidate interventions should be iteratively introduced into established protocols and monitored for their effect on outcomes and interaction with other aspects of care. This study’s results support the consideration of augmenting standard perioperative protocols with high perioperative oxygen supplementation for high-risk cases given its safety, low cost, and availability.

The Renin-Angiotensin System as a Component of Biotrauma in Acute Respiratory Distress Syndrome.

Acute respiratory distress syndrome (ARDS) is a major concern in critical care medicine with a high mortality of over 30%. Injury to the lungs is caused not only by underlying pathological conditions such as pneumonia, sepsis, or trauma, but also by ventilator-induced lung injury (VILI) resulting from high positive pressure levels and a high inspiratory oxygen fraction. Apart from mechanical factors that stress the lungs with a specific physical power and cause volutrauma and barotrauma, it is increasingly recognized that lung injury is further aggravated by biological mediators. The COVID-19 pandemic has led to increased interest in the role of the renin-angiotensin system (RAS) in the context of ARDS, as the RAS enzyme angiotensin-converting enzyme 2 serves as the primary cell entry receptor for severe acute respiratory syndrome (SARS) coronavirus (CoV)-2. Even before this pandemic, studies have documented the involvement of the RAS in VILI and its dysregulation in clinical ARDS. In recent years, analytical tools for RAS investigation have made major advances based on the optimized precision and detail of mass spectrometry. Given that many clinical trials with pharmacological interventions in ARDS were negative, RAS-modifying drugs may represent an interesting starting point for novel therapeutic approaches. Results from animal models have highlighted the potential of RAS-modifying drugs to prevent VILI or treat ARDS. While these drugs have beneficial pulmonary effects, the best targets and application forms for intervention still have to be determined to avoid negative effects on the circulation in clinical settings.

Haemodynamic instability during hip prothesis removal due to metallosis: An acute chrome/cobalt intoxication? A case report.

IntroductionMetallosis is produced by friction between prothesis pieces, release of metal particles that can enter systemic circulation provoking cobalt or chromium poisoning. No studies have been found in which the mobilization of metal particles causes haemodynamic instability.Case presentationWe present the case of an 85 years old male with metallosis, programmed for washing and prothesis extraction (Girldlestone procedure). During pseudotumor drainage and washing, patient presented sudden desaturation and hypotension refractory to volume and phenylephrine administration. Echocardiogram showed overall hypocontractility. Situation was controlled with high inspired oxygen fraction and noradrenaline perfusion. In postoperative period E. coli grew in pseudotumor samples and metal particles could be seen in soft parts as the testicles. Plasma metal concentration showed high levels of chromium, but no chelator treatment was needed.DiscussionIntraoperative hypotension raises several differential diagnoses. Echocardiography was useful to rule out hypovolaemia, pulmonary embolism and cardiac ischaemia. The results of analytical tests are often delayed, especially cultures and plasma metal levels; therefore, if metal poisoning is suspected, supportive treatment should be performed. Chelation and plasmapheresis should be used once the diagnosis is certain and are therefore not useful in the acute phase.ConclusionIntraoperative hemodynamic instability during hip prosthesis explant may be due to bleeding, release of inflammatory or infectious detritus, acute pulmonary thromboembolism, etc. However, the sudden increase of cobalt or chromium ions should be considered as a feasible option in patients with metallosis, despite not presenting previous clinical manifestations of intoxication.

Hyperoxia and Antioxidants for Myocardial Injury in Noncardiac Surgery: A 2 × 2 Factorial, Blinded, Randomized Clinical Trial.

Hyperoxia and oxidative stress may be associated with increased risk of myocardial injury. The authors hypothesized that a perioperative inspiratory oxygen fraction of 0.80 versus 0.30 would increase the degree of myocardial injury within the first 3 days of surgery, and that an antioxidant intervention would reduce degree of myocardial injury versus placebo. A 2 × 2 factorial, randomized, blinded, multicenter trial enrolled patients older than 45 yr who had cardiovascular risk factors undergoing major noncardiac surgery. Factorial randomization allocated patients to one of two oxygen interventions from intubation and at 2 h after surgery, as well as antioxidant intervention or matching placebo. Antioxidants were 3 g IV vitamin C and 100 mg/kg N-acetylcysteine. The primary outcome was the degree of myocardial injury assessed by the area under the curve for high-sensitive troponin within the first 3 postoperative days. The authors randomized 600 participants from April 2018 to January 2020 and analyzed 576 patients for the primary outcome. Baseline and intraoperative characteristics did not differ between groups. The primary outcome was 35 ng · day/l (19 to 58) in the 80% oxygen group; 35 ng · day/l (17 to 56) in the 30% oxygen group; 35 ng · day/l (19 to 54) in the antioxidants group; and 33 ng · day/l (18 to 57) in the placebo group. The median difference between oxygen groups was 1.5 ng · day/l (95% CI, -2.5 to 5.3; P = 0.202) and -0.5 ng · day/l (95% CI, -4.5 to 3.0; P = 0.228) between antioxidant groups. Mortality at 30 days occurred in 9 of 576 patients (1.6%; odds ratio, 2.01 [95% CI, 0.50 to 8.1]; P = 0.329 for the 80% vs. 30% oxygen groups; and odds ratio, 0.79 [95% CI, 0.214 to 2.99]; P = 0.732 for the antioxidants vs. placebo groups). Perioperative interventions with high inspiratory oxygen fraction and antioxidants did not change the degree of myocardial injury within the first 3 days of surgery. This implies safety with 80% oxygen and no cardiovascular benefits of vitamin C and N-acetylcysteine in major noncardiac surgery.

Perioperative high inspired oxygen fraction induces atelectasis in patients undergoing abdominal surgery: A randomized controlled trial

Study objectiveWe evaluated the feasibility of use and effects on postoperative atelectasis and complications of lower inspired oxygen fraction (FIO2) compared to conventional oxygen therapy. DesignSingle center, randomized clinical trial. SettingUniversity hospital, operating room and postoperative recovery area. PatientsOne hundred ninety patients aged ≥50 with an American Society of Anesthesiologists physical status of I-III who underwent abdominal surgery with general anesthesia. InterventionsParticipants were randomly assigned to either the low FIO2 group (intraoperative: FIO2 0.35, during induction and recovery: FIO2 0.7) or the conventional FIO2 group (intraoperative: FIO2 0.6, during induction and recovery: FIO2 1.0). MeasurementsThe primary outcome was postoperative atelectasis measured with lung ultrasonography at postoperative 30 min in the post-anesthesia care unit (consolidation score: each region 0–3, 12 region, total score range of 0 to 36, a lower score indicating better aeration). Main resultsSeven patients in the low FIO2 group were omitted from the study due to changing FIO2 during intervention (7/95 (8.4%) vs. 2/95 (2.1%), p = 0.088; low FIO2 group vs. conventional FIO2 group). Overall, atelectasis was detected in 29.7% (51/172) of patients 30 min after surgery by lung ultrasound and 40.1% (69/172) of patients after 2 days after surgery by chest X-ray. The scores of lung ultrasonography and the incidence of significant atelectasis (consolidation score ≥ 2 at any region) were lower in the low FIO2 group than in the conventional FIO2 group (median [IQR]: 3 [1,6] vs. 7 [3,9], p < 0.001 and 17/85 (20%) vs. 34/87 (39%), RR: 0.512 [95% CI: 0.311–0.843], p = 0.006, respectively). The incidence of surgical site infection and length of hospitalization were not significantly different between the two groups. ConclusionsBased on our findings, decreased inspired oxygen fraction during anesthesia and recovery did not cause hypoxic events, but instead reduced immediate postoperative atelectasis. The use of intraoperative conventional higher inspired oxygen did not afford any clinical advantages for postoperative recovery in abdominal surgery.

Maintaining a high inspired oxygen fraction with the Elisée 350 turbine transport ventilator connected to two portable oxygen concentrators in an austere environment.

Management of critically ill patients requiring mechanical ventilation in austere environments or during disaster response is a logistic challenge. Availability of oxygen cylinders for mechanically ventilated patient may be difficult in such a context. A solution to ventilate patients requiring high fraction of inspired oxygen (FiO2) is to use a ventilator able to be supplied by a low-pressure oxygen source connected with two oxygen concentrators (OCs). We tested the Elisée 350 (ResMedBella Vista, Australia) ventilator paired with two Newlife Intensity 10 (Airsep, Ball Ground, Georgia) OCs and evaluated the delivered FiO2 across a range of minute volumes and combinations of ventilator settings. The ventilators were attached to a test lung, OC flow was adjusted with a Certifier FA ventilator test systems from 2 to 10 L/min and injected into the oxygen inlet port of the Elisée 350. The FiO2 was measured by the analyzer integrated in the ventilator, controlled by the ventilator test system. Several combinations of ventilator settings were evaluated to determine the factors affecting the delivered FiO2. The Elisée 350 ventilator is a turbine ventilator able to deliver high FiO2 when functioning with two OCs. However, modifications of the ventilator settings such as an increase in minute ventilation affect delivered FiO2 even if oxygen flow is constant on the OC. The ability of two OCs to deliver high FiO2 when used with a turbine ventilator makes this method of oxygen delivery a viable alternative to cylinders to ventilate patients requiring an FiO2 of ≥80% in austere place or during disaster response. Feasibility study on test bench, level V.

Comparison of low and high inspiratory oxygen fraction added to lung-protective ventilation on postoperative pulmonary complications after abdominal surgery: A randomized controlled trial

Study objectiveIntraoperative lung-protective ventilation strategy has been recommended to reduce postoperative pulmonary complications (PPCs). However, the role of inspiratory oxygen fraction (FiO2) in this protection remains highly uncertain. We aimed to evaluate the effect of intraoperative low (30%) versus high (80%) FiO2 in the context of lung-protective ventilation strategy on PPCs in patients undergoing abdominal surgery. DesignProspective, two-arm, randomized controlled trial. SettingTertiary university hospital in China. PatientsA total of ASA I-III 252 patients aged ≥18, who were scheduled for elective abdominal surgery under general anesthesia were included in the study. InterventionPatients were randomly assigned to receive either 30% or 80% FiO2 during the intraoperative period. All patients received volume-controlled mechanical ventilation with lung-protective ventilation approach, which included a tidal volume of 8 ml kg−1 of predicted body weight, a positive end-expiratory pressure level of 6–8 cmH2O, and repeated recruitment maneuvers. MeasurementsThe primary outcome was a composite of postoperative pulmonary complications within the first 7 postoperative days, consisting of respiratory infection, respiratory failure, bronchospasm, atelectasis, pleural effusion, pneumothorax, and aspiration pneumonitis. The severity grade of PPCs was measured as a key secondary outcome. Main resultsTwo hundred and fifty-one patients completed the trial. PPCs occurred in 43 of 125 (34.4%) patients assigned to receive 30% FiO2 compared with 59 of 126 (46.8%) patients receiving 80% FiO2 (relative risk 0.74, 97.5% confidence interval, 0.51–1.02, p = 0.045, > 0.025). The severity of PPCs within the first 7 days following surgery was attenuated significantly in the low (30%) FiO2 group (p = 0.001). ConclusionsAmong patients undergoing abdominal surgery under general anesthesia, an intraoperative lung-protective ventilation strategy with 30% FiO2 compared with 80% FiO2 did not reduce the incidence of PPCs. And the use of 30% FiO2 resulted in less severe pulmonary complications.

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

BackgroundPostoperative 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 designPROtective 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.DiscussionThe 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 registrationwww.ChiCTR.org.cn, identifier: ChiCTR18 00014901. Registered on 13 February 2018.

High oxygen fraction during airway opening is key to effective airway rescue in obese subjects.

Apnea is common after induction of anesthesia and may produce dangerous hypoxemia, particularly in obese subjects. Optimal management of airway emergencies in obese, apneic subjects is complex and controversial, and clinical studies of rescue strategies are inherently difficult and ethically-challenging to perform. We investigated rescue strategies in various degrees of obesity, using a highly-integrated, computational model of the pulmonary and cardiovascular systems, configured against data from 8 virtual subjects (body mass index [BMI] 24-57 kg m-2). Each subject received pre-oxygenation with 100% oxygen for 3 min, and then apnea with an obstructed airway was simulated until SaO2 reached 40%. At that time, airway rescue was simulated, opening of the airway with the provision of various patterns of tidal ventilation with 100% oxygen. Rescue using tidal ventilation with 100% oxygen provided rapid re-oxygenation in all subjects, even with small tidal volumes in subjects with large BMI. Overall, subjects with larger BMI pre-oxygenated faster and, after airway obstruction, developed hypoxemia more quickly. Our results indicate that attempts to achieve substantial tidal volumes during airway rescues are probably not worthwhile (and may be counter-productive); rather, it is the assurance of a high-inspired oxygen fraction that will prevent critical hypoxemia.

Benefits and risks of oxygen therapy during acute medical illness: Just a matter of dose!

Oxygen therapy is used to reverse hypoxemia since more than a century. Current usage is broader and includes routine oxygen administration despite normoxemia which may result in prolonged periods of hyperoxemia. While systematic oxygen therapy was expected to be of benefit in some ischemic diseases such as stroke or acute myocardial infarction, recent randomised controlled trials (RCTs) have challenged this hypothesis by showing the absence of clinical improvement. Although oxygen is known to be toxic at high inspired oxygen fractions, a recent meta-analysis of RCTs revealed the life-threatening effect of hyperoxemia, with a dose-dependent relationship. Several recommendations have therefore been updated: (i) to monitor peripheral oxygen saturation (SpO2) as a surrogate for arterial oxygen saturation (SaO2); (ii) to initiate oxygen only when the lower SpO2 threshold is crossed; (iii) to titrate the delivered oxygen fraction to maintain SpO2 within a target range; and (iv) to stop supplying oxygen when the upper limit of SpO2 is surpassed, in order to prevent hyperoxemia. The lower and upper limits of SpO2 depend on the presence of risk factors for oxygen-induced hypercapnia (Chronic obstructive pulmonary disease, asthma, and obesity-associated hypoventilation). For patients at risk, oxygen therapy should be started when SpO2 is≤88% and stopped when it is>92%. For patients without risk factors, oxygen therapy should be started when SpO2 is≤92% and stopped when it is >96%. High-flow oxygen should only be used in a few diseases such as carbon monoxide poisoning, cluster headaches, sickle cell crisis and pneumothorax.

The Effects of Intraoperative Inspired Oxygen Fraction on Postoperative Pulmonary Parameters in Patients with General Anesthesia: A Systemic Review and Meta-Analysis.

High intraoperative inspired oxygen concentration is applied to prevent desaturation during induction and recovery of anesthesia. However, high oxygen concentration may lead to postoperative pulmonary complications. The purpose of this study is to compare the postoperative pulmonary parameters according to intraoperative inspired oxygen fraction in patients undergoing general anesthesia. We identified all randomized controlled trials investigating postoperative differences in arterial gas exchange according to intraoperative fraction of inspired oxygen (FiO2). A total of 10 randomized controlled trials were included, and 787 patients were analyzed. Postoperative PaO2 was lower in the high FiO2 group compared with the low FiO2 group (mean difference (MD) −4.97 mmHg, 95% CI −8.21 to −1.72, p = 0.003). Postoperative alveolar-arterial oxygen gradient (AaDO2) was higher (MD 3.42 mmHg, 95% CI 0.95 to 5.89, p = 0.007) and the extent of atelectasis was more severe (MD 2.04%, 95% CI 0.14 to 3.94, p = 0.04) in high intraoperative FiO2 group compared with low FiO2 group. However, postoperative SpO2 was comparable between the two groups. The results of this meta-analysis suggest that high inspired oxygen fraction during anesthesia may impair postoperative pulmonary parameters. Cautious approach in intraoperative inspired oxygen fraction is required for patients susceptible to postoperative pulmonary complications.

High inspired oxygen fraction impairs lung volume and ventilation heterogeneity in healthy children: a double-blind randomised controlled trial

BackgroundAlthough a high inspired oxygen fraction (FiO2) is commonly used in paediatric anaesthesia, the impact on postoperative lung function is unclear. We compared lung volume, ventilation heterogeneity, and respiratory mechanics in anaesthetised children randomised to receive low or high FiO2 intraoperatively. MethodsIn a double-blind randomised controlled trial, children scheduled for elective surgery were randomly assigned FiO2 100% (n=29) or FiO2 80% (n=29) during anaesthesia induction and emergence. During maintenance of anaesthesia, participants assigned FiO2=100% at induction/emergence received FiO2=80% (FiO2>0.8 group); those randomised to FiO2=80% at induction/emergence received FiO2=35% intraoperatively (FiO2 [0.8→0.35 group]). During spontaneous breathing, we measured the (i) functional residual capacity (FRC) and lung clearance index (ventilation inhomogeneity) by multiple-breath nitrogen washout; and (ii) airway resistance and respiratory tissue elastance by forced oscillations, before operation, after discharge from the recovery room, and 24 h after operation. Mean (95% confidence intervals) are reported. ResultsFifty eight children (12.9 [12.3–13.5] yr) were randomised; 22/29 (high group) and 21/29 (low group) children completed serial multiple-breath nitrogen washout measurements. FRC decreased in the FiO2>0.8 group after discharge from recovery (–12.0 [–18.5 to –5.5]%; P=0.01), but normalised 24 h later. Ventilation inhomogeneity increased in both groups after discharge from recovery, but persisted in the FiO2>0.8 group 24 h after surgery (6.1 [2.5–9.8%]%; P=0.02). Airway resistance and respiratory elastance did not differ between the groups at any time point. ConclusionsFiO2>0.8 decreases lung volume in the immediate postoperative period, accompanied by persistent ventilation inhomogeneity. These data suggest that FiO2>0.8 should be avoided in anaesthetised children with normal lungs. Clinical trial registrationNCT02384616.

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

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

Hyperintensity of Cerebrospinal Fluid on T2-Weighted Fluid-Attenuated Inversion Recovery Magnetic Resonance Imaging Caused by High Inspired Oxygen Fraction.

In veterinary medicine, patients undergo magnetic resonance imaging (MRI) under general anesthesia to enable acquisition of artifact-free images. The fraction of inspired oxygen (FiO2) ranges between 30 and 95%. In humans, a high FiO2 is associated with incomplete signal suppression of peripheral cerebrospinal fluid (CSF) spaces on T2-weighted fluid-attenuated inversion recovery (T2w-FLAIR) sequences. The influence of FiO2 on T2w-FLAIR images remains unreported in small animals. The aim of this prospective study was to investigate whether a high FiO2 is associated with hyperintensity in peripheral CSF spaces on T2w-FLAIR images in dogs and cats. Client-owned patients undergoing brain MRI were prospectively enrolled. Animals with brain parenchymal abnormalities and/or meningeal contrast enhancement on MRI images and/or abnormal CSF analysis were excluded. Consequently, twelve patients were enrolled. Anesthesia was maintained by isoflurane 0.5–1 minimal alveolar concentration in 30% oxygen. After acquisition of transverse and dorsal T2w-FLAIR images, the FiO2 was increased to 95%. The T2w-FLAIR sequences were then repeated after 40 min. Arterial blood gas analysis was performed in six patients at the same time as T2w-FLAIR sequence acquisition. Plot profiles of the signal intensity (SI) from CSF spaces of three cerebral sulci and adjacent gray and white matter were generated. SI ratios of CSF space and white matter were compared between the T2w-FLAIR images with 30 and 95% FiO2. An observer blinded to the FiO2, subjectively evaluated the SI of peripheral CSF spaces on T2w-FLAIR images as high or low. There was significant difference in the partial pressure of oxygen between the two arterial samples (P < 0.001). The SI ratios obtained from the T2w-FLAIR images with 95% FiO2 were significantly higher compared with those obtained from the T2w-FLAIR images with 30% FiO2 (P < 0.05). The peripheral CSF spaces were subjectively considered hyperintense in 11 of 12 cases on T2w-FLAIR images with 95% FiO2 (P < 0.005). A clear difference in SI, dependent on the FiO2 was seen in the peripheral CSF spaces on T2w-FLAIR images. In conclusion, the influence of FiO2 must be considered when differentiating pathological and normal CSF spaces on T2w-FLAIR images in dogs and cats.

Effect of High Inspiratory Oxygen Fraction on Endothelial Function in Healthy Volunteers: A Randomized Controlled Crossover Pilot Study.

It has been suggested that high inspiratory oxygen concentrations during anesthesia may be associated with higher postoperative mortality due to endothelial dysfunction. A randomized controlled crossover study was conducted with 25 healthy male volunteers. They inhaled an oxygen concentration of 30% and 80%. The endothelial function was assessed using noninvasive digital pulse amplitude tonometry (EndoPAT) supported by endothelial biomarkers. The difference in endothelial function between the 2 treatments was 0.05 (95% confidence interval, -0.36 to 0.27; P = .77). Endothelial biomarkers were unaffected. Inhalation of a high oxygen fraction in healthy volunteers did not result in a significant reduction of endothelial function.

The New World Health Organization Recommendations on Perioperative Administration of Oxygen to Prevent Surgical Site Infections: A Dangerous Reductionist Approach?

In October 2016, the World Health Organization (WHO) published recommendations for preventing surgical site infections (SSIs). Among those measures is a recommendation to administer oxygen at an inspired fraction of 80% intra- and postoperatively for up to 6 hours. SSIs have been identified as a global health problem, and the WHO should be commended for their efforts. However, this recommendation focuses only on the patient's "wound," ignores other organ systems potentially affected by hyperoxia, and may ultimately worsen patient outcomes.The WHO advances a "strong recommendation" for the use of a high inspired oxygen fraction even though the quality of evidence is only moderate. However, achieving this goal by disregarding other potentially lethal complications seems inappropriate, particularly in light of the weak evidence underpinning the use of high fractions of oxygen to prevent SSI. Use of such a strategy thus should be intensely discussed by anesthesiologists and perioperative physicians.Normovolemia, normotension, normoglycemia, normothermia, and normoventilation can clearly be safely applied to most patients in most clinical scenarios. But the liberal application of hyperoxemia intraoperatively and up to 6 hours postoperatively, as suggested by the WHO, is questionable from the viewpoint of anesthesia and perioperative medicine, and its effects will be discussed in this article.