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

Therapeutic targeting of hypoxia inducible factor in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS) is characterized by bilateral chest infiltration and acute hypoxic respiratory failure. ARDS carries significant morbidity and mortality despite advancements in medical management, calling for the development of novel therapeutic targets. Hypoxia-inducible factor (HIF) is a heterodimeric protein involved in various essential pathways, including metabolic reprogramming, immune modulation, angiogenesis and cell cycle regulation. HIF is routinely degraded in homeostasis conditions via the prolyl hydroxylase domain/von Hippel-Lindau protein pathway. However, HIF is stabilized in ARDS via various mechanisms (oxygen-dependent and independent) as an endogenous protective pathway and plays multifaceted roles in different cell populations. This review focuses on the functional role of HIF and its target genes during ARDS, as well as how HIF has evolved as a therapeutic target in current medical management.

Alveolar Hyperoxia and Exacerbation of Lung Injury in Critically Ill SARS-CoV-2 Pneumonia

Acute hypoxic respiratory failure (AHRF) is a prominent feature of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) critical illness. The severity of gas exchange impairment correlates with worse prognosis, and AHRF requiring mechanical ventilation is associated with substantial mortality. Persistent impaired gas exchange leading to hypoxemia often warrants the prolonged administration of a high fraction of inspired oxygen (FiO2). In SARS-CoV-2 AHRF, systemic vasculopathy with lung microthrombosis and microangiopathy further exacerbates poor gas exchange due to alveolar inflammation and oedema. Capillary congestion with microthrombosis is a common autopsy finding in the lungs of patients who die with coronavirus disease 2019 (COVID-19)-associated acute respiratory distress syndrome. The need for a high FiO2 to normalise arterial hypoxemia and tissue hypoxia can result in alveolar hyperoxia. This in turn can lead to local alveolar oxidative stress with associated inflammation, alveolar epithelial cell apoptosis, surfactant dysfunction, pulmonary vascular abnormalities, resorption atelectasis, and impairment of innate immunity predisposing to secondary bacterial infections. While oxygen is a life-saving treatment, alveolar hyperoxia may exacerbate pre-existing lung injury. In this review, we provide a summary of oxygen toxicity mechanisms, evaluating the consequences of alveolar hyperoxia in COVID-19 and propose established and potential exploratory treatment pathways to minimise alveolar hyperoxia.

Exploration of the optimal pulse oximetry-derived oxygen saturation target for critically ill AECOPD patients: a retrospective cohort study

Background

Appropriate levels of blood oxygen are crucial for critically ill patients. However, the optimal oxygen saturation has not been confirmed for AECOPD patients during their ICU stays. The purpose of this study was to determine the optimal oxygen saturation range target to reduce mortality for those individuals.

Methods

Data of 533 critically ill AECOPD patients with hypercapnic respiratory failure from the MIMIC-IV database were extracted. The association between median SpO2 value during ICU stay and 30days mortality was analyzed by LOWESS curve, and an optimal range of SpO2(92-96%) platform was observed. Comparisons between subgroups and linear analyses of the percentage of SpO2 in 92-96% and 30days or 180 days mortality were performed to support our view further.

Methods

Although patients with 92-96% SpO2 had a higher rate of invasive ventilator than those with 88-92%, there was no significant increase in the adjusted ICU stay duration, non-invasive ventilator duration, or invasive ventilator duration while leading to lower 30days and 180days mortality in the subgroup with 92-96%. In addition, the percentage of SpO2 in 92-96% was associated with decreased hospital mortality.

Conclusion

In conclusion, SpO2 within 92-96% could lead to lower mortality than 88-92% and > 96% for AECOPD patients during their ICU stay.

A Comparison Between Selective Lobar Bronchial Blockade and Main Bronchial Blockade in Pediatric Thoracoscopic Surgery: A Retrospective Cohort Study

OBJECTIVE

The primary objective of this study was to assess the effect of selective lobar blockade on the risk of hypoxemia during one-lung ventilation in pediatric patients undergoing thoracoscopic surgery.

DESIGN

This was a retrospective matched case-control cohort study.

SETTING

The study was performed in a teaching hospital.

PARTICIPANTS

A total of 60 pediatric patients who underwent thoracoscopic surgery in the authors' hospital from March 2020 to March 2021 were analyzed.

INTERVENTIONS

The authors examined their electronic medical records and found 30 patients in whom selective lobar blockade was used. These patients then were matched to 30 other patients in whom routine main bronchial blockade was performed in the authors' center based on age, weight, sex, side of surgery, and type of surgery.

MEASUREMENTS AND MAIN RESULTS

The inclusion criteria were four-fold: (1) pediatric patients with scheduled thoracoscopic resection of the middle and lower lobe lesions; (2) no obvious anesthesia or surgical contraindications; (3) American Society of Anesthesiologists class I to II; and (4) age younger than one year old. The exclusion criteria were as follows: (1) pediatric patients whose trachea was intubated with a size less than 3.0 mm; (2) a difficult airway; (3) changes in ventilation patterns during surgery; and (4) severe pneumonia and respiratory and circulatory system dysfunction. The following patient data were collected: (1) general clinical information; (2) mean arterial blood pressure, heart rate, central venous pressure, airway peak pressure (Ppeak), oxygenation index (PaO₂/F_IO₂ ratio), and alveolar-arterial oxygen differential pressure (AaDO2) at different time points; that is, before one-lung ventilation (OLV) (T1), ten minutes after OLV (T2), and ten minutes after the end of OLV (T3); (3) degree of lung collapse ten minutes after OLV; (4) operative duration; and (5) the prevalence of hypoxemia, the number of adjustments required for intraoperative displacement of the bronchial blocker, and pulmonary atelectasis. A total of 135 patients were selected, and 60 pediatric patients (30 in group S and 30 in group R) were included in this study. There were no significant differences in age, sex, weight, general preoperative data, degree of lung collapse, or operative duration (p > 0.05). The perioperative hemodynamics between the two groups were not statistically significant (p > 0.05). The oxygenation index, AaDO2, and Ppeak were not significantly different between the two groups at the T1 time point (p > 0.05). However, the oxygenation index was higher, and AaDO2 and Ppeak were lower in group S than in group R at the T2 and T3 time points (p < 0.05). The incidence of atelectasis, the prevalence of hypoxemia, and the number of adjustments required for intraoperative displacement of the bronchial blocker in group S were lower than those in group R (p < 0.05).

CONCLUSION

Selective lobar bronchial blockade, using a bronchial blocker in pediatric thoracoscopic surgery, may represent an alternative to excluding the main bronchial blockade for patients undergoing middle and lower lobe procedures, which may improve intraoperative oxygenation and reduce postoperative atelectasis.

Oxygen therapy for critically Ill and post-operative patients

Nearly all patients receiving treatment in a peri-operative or intensive care setting receive supplemental oxygen therapy. It is biologically plausible that the dose of oxygen used might affect important patient outcomes. Most peri-operative research has focussed on oxygen regimens that target higher than normal blood oxygen levels. Whereas, intensive care research has mostly focussed on conservative oxygen regimens which assiduously avoid exposure to higher than normal blood oxygen levels. While such conservative oxygen therapy is preferred for spontaneously breathing patients with chronic obstructive pulmonary disease, the optimal oxygen regimen in other patient groups is not clear. Some data suggest that conservative oxygen therapy might be preferred for patients with hypoxic ischaemic encephalopathy. However, unless oxygen supplies are constrained, routinely aggressively down-titrating oxygen in either the peri-operative or intensive care setting is not necessary based on available data. Targeting higher than normal levels of oxygen might reduce surgical site infections in the perioperative setting and/or improve outcomes for intensive care patients with sepsis but further research is required and available data are not sufficiently strong to warrant routine implementation of such oxygen strategies.

Determining a safe upper limit of oxygen supplementation for adult patients: a systematic review

OBJECTIVE

This systematic review aimed to describe the connection between the inspired oxygen fraction and pulmonary complications in adult patients, with the objective of determining a safe upper limit of oxygen supplementation.

METHODS

MEDLINE and Embase were systematically searched in August 2019 (updated July 2020) for studies fulfilling the following criteria: intubated adult patients (Population); high fractions of oxygen (Intervention) versus low fractions of (Comparison); atelectasis, acute respiratory distress syndrome (ARDS), pneumonia and/or duration of mechanical ventilation (Outcome); original studies both observational and interventional (Studies). Screening, data extraction and risk of bias assessment was done by two independent reviewers.

RESULTS

Out of 6120 records assessed for eligibility, 12 were included. Seven studies were conducted in the emergency setting, and five studies included patients undergoing elective surgery. Eight studies reported data on atelectasis, two on ARDS, four on pneumonia and two on duration of mechanical ventilation. There was a non-significant increased risk of atelectasis if an oxygen fraction of 0.8 or above was used, relative risk (RR): 1.37 (95% CI 0.95 to 1.96). One study showed an almost threefold higher risk of pneumonia in the high oxygen fraction group (RR: 2.83 (95% CI 2.25 to 3.56)). The two studies reporting ARDS and the two studies with data on mechanical ventilation showed no association with oxygen fraction. Four studies had a high risk of bias in one domain.

CONCLUSIONS

In this systematic review, we found inadequate evidence to identify a safe upper dosage of oxygen, but the identified studies suggest a benefit of keeping inspiratory oxygen fraction below 0.8 with regard to formation of atelectases.

PROSPERO REGISTRATION NUMBER

CRD42020154242.

Conservative oxygen therapy for critically ill patients: a meta-analysis of randomized controlled trials

Objective

Conservative oxygen strategy is recommended in acute illness while its benefit in ICU patients remains controversial. Therefore, we sought to conduct a systematic review and meta-analysis to examine such oxygen strategies’ effect and safety in ICU patients.

Methods

We searched PubMed, Embase, and the Cochrane database from inception to Feb 15, 2021. Randomized controlled trials (RCTs) that compared a conservative oxygen strategy to a conventional strategy in critically ill patients were included. Results were expressed as mean difference (MD) and risk ratio (RR) with a 95% confidence interval (CI). The primary outcome was the longest follow-up mortality. Heterogeneity, sensitivity analysis, and publication bias were also investigated to test the robustness of the primary outcome.

Results

We included seven trials with a total of 5265 patients. In general, the conventional group had significantly higher SpO₂ or PaO₂ than that in the conservative group. No statistically significant differences were found in the longest follow-up mortality (RR, 1.03; 95% CI, 0.97–1.10; I²=18%; P=0.34) between the two oxygen strategies when pooling studies enrolling subjects with various degrees of hypoxemia. Further sensitivity analysis showed that ICU patients with mild-to-moderate hypoxemia (PaO₂/FiO₂ >100 mmHg) had significantly lower mortality (RR, 1.24; 95% CI, 1.05–1.46; I²=0%; P=0.01) when receiving conservative oxygen therapy. These findings were also confirmed in other study periods. Additional, secondary outcomes of the duration of mechanical ventilation, the length of stay in the ICU and hospital, change in sequential organ failure assessment score, and adverse events were comparable between the two strategies.

Conclusions

Our findings indicate that conservative oxygen therapy strategy did not improve the prognosis of the overall ICU patients. The subgroup of ICU patients with mild to moderate hypoxemia might obtain prognosis benefit from such a strategy without affecting other critical clinical results.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40560-021-00563-7.

Frequency of hyperoxaemia during and after major surgery

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

Benefits and harms of increased inspiratory oxygen concentrations

PURPOSE OF REVIEW

The topic of perioperative hyperoxia remains controversial, with valid arguments on both the 'pro' and 'con' side. On the 'pro' side, the prevention of surgical site infections was a strong argument, leading to the recommendation of the use of hyperoxia in the guidelines of the Center for Disease Control and the WHO. On the 'con' side, the pathophysiology of hyperoxia has increasingly been acknowledged, in particular the pulmonary side effects and aggravation of ischaemia/reperfusion injuries.

RECENT FINDINGS

Some 'pro' articles leading to the Center for Disease Control and WHO guidelines advocating perioperative hyperoxia have been retracted, and the recommendations were downgraded from 'strong' to 'conditional'. At the same time, evidence that supports a tailored, more restrictive use of oxygen, for example, in patients with myocardial infarction or following cardiac arrest, is accumulating.

SUMMARY

The change in recommendation exemplifies that despite much work performed on the field of hyperoxia recently, evidence on either side of the argument remains weak. Outcome-based research is needed for reaching a definite recommendation.

Conservative versus conventional oxygen therapy for cardiac surgical patients: A before-and-after study

Avoiding hypoxaemia is considered crucial in cardiac surgery patients admitted to the intensive care unit (ICU). However, avoiding hyperoxaemia may also be important. A conservative approach to oxygen therapy may reduce exposure to hyperoxaemia without increasing the risk of hypoxaemia. Using a before-and-after design, we evaluated the introduction of conservative oxygen therapy (target SpO₂ 88%-92% using the lowest FiO₂) for cardiac surgical patients admitted to the ICU. We studied 9041 arterial blood gas (ABG) datasets: 4298 ABGs from 245 'conventional' and 4743 ABGs from 298 'conservative' oxygen therapy patients. During mechanical ventilation (MV) and while in the ICU, compared to the conventional group, conservative group patients had significantly lower FiO₂ exposure and PaO₂ values ( P < 0.001 for each). Accordingly, using the mean PaO₂ during MV, more conservative group patients were classified as normoxaemic (226 versus 62 patients, P < 0.01), fewer as hyperoxaemic (66 versus 178 patients, P < 0.01) and no patient in either group as hypoxaemic or severely hypoxaemic. Moreover, more ABG samples were hyperoxaemic or severely hyperoxaemic during conventional treatment ( P < 0.001). Finally, there was no difference in ICU or hospital length of stay, ICU or hospital mortality or 30-day mortality between the groups. Our findings support the feasibility and physiological safety of conservative oxygen therapy in patients admitted to ICU after cardiac surgery.

A pilot study of hyperoxemia on neurological injury, inflammation and oxidative stress

BACKGROUND

Normobaric hyperoxia is used to alleviate secondary brain ischaemia in patients with traumatic brain injury (TBI), but clinical evidence is limited and hyperoxia may cause adverse events.

METHODS

An open label, randomised controlled pilot study comparing blood concentrations of reactive oxygen species (ROS), interleukin 6 (IL-6) and neuron-specific enolase (NSE) between two different fractions of inspired oxygen in severe TBI patients on mechanical ventilation.

RESULTS

We enrolled 27 patients in the Fi O₂ 0.40 group and 38 in the Fi O₂ 0.70 group; 19 and 23 patients, respectively, completed biochemical analyses. In baseline, there were no differences between Fi O₂ 0.40 and Fi O₂ 0.70 groups, respectively, in ROS (64.8 nM [22.6-102.1] vs. 64.9 nM [26.8-96.3], P = 0.80), IL-6 (group 92.4 pg/ml [52.9-171.6] vs. 94.3 pg/ml [54.8-133.1], P = 0.52) or NSE (21.04 ug/l [14.0-30.7] vs. 17.8 ug/l [14.1-23.9], P = 0.35). ROS levels did not differ at Day 1 (24.2 nM [20.6-33.5] vs. 29.2 nM [22.7-69.2], P = 0.10) or at Day 2 (25.4 nM [21.7-37.4] vs. 47.3 nM [34.4-126.1], P = 0.95). IL-6 concentrations did not differ at Day 1 (112.7 pg/ml [65.9-168.9) vs. 83.9 pg/ml [51.8-144.3], P = 0.41) or at Day 3 (55.0 pg/ml [34.2-115.6] vs. 49.3 pg/ml [34.4-126.1], P = 0.95). NSE levels did not differ at Day 1 (15.9 ug/l [9.0-24.3] vs. 15.3 ug/l [12.2-26.3], P = 0.62). There were no differences between groups in the incidence of pulmonary complications.

CONCLUSION

Higher fraction of inspired oxygen did not increase blood concentrations of markers of oxidative stress, inflammation or neurological injury or the incidence of pulmonary complications in severe TBI patients on mechanical ventilation.

Oxygen management in mechanically ventilated patients: A multicenter prospective observational study

PURPOSE

To observe arterial oxygen in relation to fraction of inspired oxygen (F_IO₂) during mechanical ventilation (MV).

MATERIALS AND METHODS

In this multicenter prospective observational study, we included adult patients required MV for >48h during the period from March to May 2015. We obtained F_IO₂, PaO₂ and SaO₂ from commencement of MV until the 7th day of MV in the ICU.

RESULTS

We included 454 patients from 28 ICUs in this study. The median APACHE II score was 22. Median values of F_IO₂, PaO₂ and SaO₂ were 0.40, 96mmHg and 98%. After day two, patients spent most of their time with a F_IO₂ between 0.3 and 0.49 with median PaO₂ of approximately 90mmHg and SaO₂ of 97%. PaO₂ was ≥100mmHg during 47.2% of the study period and was ≥130mmHg during 18.4% of the study period. F_IO₂ was more likely decreased when PaO₂ was ≥130mmHg or SaO₂ was ≥99% with a F_IO₂ of 0.5 or greater. When F_IO₂ was <0.5, however, F_IO₂ was less likely decreased regardless of the value of PaO₂ and SaO₂.

CONCLUSIONS

In our multicenter prospective study, we found that hyperoxemia was common and that hyperoxemia was not corrected.

Comparison of Mask Oxygen Therapy and High-Flow Oxygen Therapy after Cardiopulmonary Bypass in Obese Patients

Background

To clarify the efficiency of mask O₂ and high-flow O₂ (HFO) treatments following cardiopulmonary bypass (CPB) in obese patients.

Methods

During follow-up, oxygenization parameters including arterial pressure of oxygen (PaO₂), peripheral oxygen saturation (SpO₂), and arterial partial pressure of carbon dioxide (PaCO₂) and physical examination parameters including respiratory rate, heart rate, and arterial pressure were recorded respectively. Presence of atelectasia and dyspnea was noted. Also, comfort scores of patients were evaluated.

Results

Mean duration of hospital stay was 6.9 ± 1.1 days in the mask O₂ group, whereas the duration was significantly shorter (6.5 ± 0.7 days) in the HFO group (p=0.034). The PaO₂ values and SpO₂ values were significantly higher, and PaCO₂ values were significantly lower in patients who received HFO after 4th, 12th, 24th, 36th, and 48th hours. In postoperative course, HFO leads patients to achieve better postoperative FVC (p < 0.001). Also, dyspnea scores and comfort scores were significantly better in patients who received HFO in both postoperative day 1 and day 2 (p < 0.001, p < 0.001 and p=0.002, p=0.001, resp.).

Conclusion

Our study demonstrated that HFO following CPB in obese patients improved postoperative PaO₂, SpO₂, and PaCO₂ values and decreased the atelectasis score, reintubation, and mortality rates when compared with mask O₂.

Associations between intraoperative ventilator settings during one-lung ventilation and postoperative pulmonary complications: a prospective observational study

Background

The interest in perioperative lung protective ventilation has been increasing. However, optimal management during one-lung ventilation (OLV) remains undetermined, which not only includes tidal volume (V_T) and positive end-expiratory pressure (PEEP) but also inspired oxygen fraction (F_IO₂). We aimed to investigate current practice of intraoperative ventilation during OLV, and analyze whether the intraoperative ventilator settings are associated with postoperative pulmonary complications (PPCs) after thoracic surgery.

Methods

We performed a prospective observational two-center study in Japan. Patients scheduled for thoracic surgery with OLV from April to October 2014 were eligible. We recorded ventilator settings (F_IO₂, V_T, driving pressure (ΔP), and PEEP) and calculated the time-weighted average (TWA) of ventilator settings for the first 2 h of OLV. PPCs occurring within 7 days of thoracotomy were investigated. Associations between ventilator settings and the incidence of PPCs were examined by multivariate logistic regression.

Results

We analyzed perioperative information, including preoperative characteristics, ventilator settings, and details of surgery and anesthesia in 197 patients. Pressure control ventilation was utilized in most cases (92%). As an initial setting for OLV, an F_IO₂ of 1.0 was selected for more than 60% of all patients. Throughout OLV, the median TWA F_IO₂ of 0.8 (0.65-0.94), V_T of 6.1 (5.3-7.0) ml/kg, ΔP of 17 (15-20) cm H₂O, and PEEP of 4 (4-5) cm H₂O was applied. Incidence rate of PPCs was 25.9%, and F_IO₂ was independently associated with the occurrence of PPCs in multivariate logistic regression. The adjusted odds ratio per F_IO₂ increase of 0.1 was 1.30 (95% confidence interval: 1.04-1.65, P = 0.0195).

Conclusions

High F_IO₂ was applied to the majority of patients during OLV, whereas low V_T and slight degree of PEEP were commonly used in our survey. Our findings suggested that a higher F_IO₂ during OLV could be associated with increased incidence of PPCs.

Electronic supplementary material

The online version of this article (10.1186/s12871-018-0476-x) contains supplementary material, which is available to authorized users.

Relationship between hyperoxemia and ventilator associated pneumonia

Previous studies suggest a relationship between hyperoxemia and ventilator-associated pneumonia (VAP). Hyperoxemia is responsible for denitrogenation phenomena, and inhibition of surfactant production, promoting atelectasis in mechanically ventilated patients. Further, hyperoxemia impairs the efficacy of alveolar macrophages to migrate, phagocyte and kill bacteria. Oxygen can also cause pulmonary-specific toxic effect called hyperoxic acute lung injury leading to longer duration of mechanical ventilation. All these hyperoxic effects are well-known risk factors for VAP. A recent retrospective large single center study identified hyperoxemia as an independent risk factor for VAP. However, two recent randomized controlled trials evaluated the impact of conservative oxygen strategy versus a liberal strategy, but did not confirm the role of hyperoxemia in lower respiratory tract infection occurrence. In this review, we discuss animal and human studies suggesting a relationship between these two common conditions in mechanically ventilated patients and potential interventions that should be evaluated. Further large prospective studies in carefully selected groups of patients are required to confirm the potential role of hyperoxemia in VAP pathogenesis and to evaluate the impact of a conservative oxygen strategy vs. a conventional strategy on the incidence of VAP.

Patient Safety: Identifying and Managing Complications of Mechanical Ventilation

Mechanical ventilation is a fundamental aspect of critical care practice to help meet the respiratory needs of critically ill patients. Complications can occur though, as a direct result of being mechanically ventilated, or indirectly because of a secondary process. Preventing, identifying, and managing these complications significantly contribute to the role and responsibilities of critical care nurses in promoting patient safety. This article reviews common ventilator-associated events, including both infectious (eg, ventilator-associated pneumonia) and noninfectious causes (eg, acute respiratory distress syndrome, pulmonary edema, pleural effusion, and atelectasis).

Moderate hyperoxic versus near-physiological oxygen targets during and after coronary artery bypass surgery: a randomised controlled trial

Background

The safety of perioperative hyperoxia is currently unclear. Previous studies in patients undergoing coronary artery bypass surgery suggest reduced myocardial damage when avoiding extreme perioperative hyperoxia (>400 mmHg). In this study we investigated whether an oxygenation strategy from moderate hyperoxia to a near-physiological oxygen tension reduces myocardial damage and improves haemodynamics, organ dysfunction and oxidative stress.

Methods

This was a single-blind, single-centre, open-label, randomised controlled trial in patients undergoing elective coronary artery bypass surgery. Fifty patients were randomised to a partial pressure of oxygen in arterial blood (P_aO₂) target of 200–220 mmHg during cardiopulmonary bypass and 130–150 mmHg during intensive care unit (ICU) admission (control group) versus lower targets of 130–150 mmHg during cardiopulmonary bypass and 80–100 mmHg at the ICU (conservative group). Primary outcome was myocardial injury (CK-MB and Troponin-T) at ICU admission and 2, 6 and 12 hours thereafter.

Results

Weighted P_aO₂ during cardiopulmonary bypass was 220 mmHg (interquartile range (IQR) 211–233) vs. 157 (151–162) in the control and conservative group, respectively (P < 0.0001). During ICU admission, weighted P_aO₂ was 107 mmHg (86–141) vs. 90 (84–98) (P = 0.03), respectively. Area under the curve of CK-MB was median 23.5 μg/L/h (IQR 18.4–28.1) vs. 21.5 (15.8–26.6) (P = 0.35) and 0.30 μg/L/h (0.25–0.44) vs. 0.39 (0.24–0.43) (P = 0.81) for Troponin-T. Cardiac index, systemic vascular resistance index, creatinine, lactate and F2-isoprostane levels were not different between groups.

Conclusions

Compared to moderate hyperoxia, a near-physiological oxygen strategy does not reduce myocardial damage in patients undergoing coronary artery bypass surgery. Conservative oxygen administration was not associated with increased lactate levels or hypoxic events.

Trial registration

Netherlands Trial Registry NTR4375, registered on 30 January 2014

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-016-1240-6) contains supplementary material, which is available to authorized users.

Conservative oxygen therapy in mechanically ventilated patients following cardiac arrest: A retrospective nested cohort study

BACKGROUND

In mechanically ventilated (MV) cardiac arrest (CA) survivors admitted to the intensive care unit (ICU) avoidance of hypoxia is considered crucial. However, avoidance of hyperoxia may also be important. A conservative approach to oxygen therapy may reduce exposure to both.

METHODS

We evaluated the introduction of conservative oxygen therapy (target SpO2 88-92% using the lowest FiO2) during MV for resuscitated CA patients admitted to the ICU.

RESULTS

We studied 912 arterial blood gas (ABG) datasets: 448 ABGs from 50 'conventional' and 464 ABGs from 50 'conservative' oxygen therapy patients. Compared to the conventional group, conservative group patients had significantly lower PaO2 values and FiO2 exposure (p<0.001, respectively); more received MV in a spontaneous ventilation mode (18% vs 2%; p=0.001) and more were exposed to a FiO2 of 0.21 (19 vs 0 patients, p=0.001). Additionally, according to mean PaO2, more conservative group patients were classified as normoxaemic (36 vs 16 patients, p<0.01) and fewer as hyperoxaemic (14 vs 33 patients, p<0.01). Finally, ICU length of stay was significantly shorter for conservative group patients (p=0.04). There was no difference in the proportion of survivors discharged from hospital with good neurological outcome (14/23 vs 12/22 patients, p=0.67).

CONCLUSIONS

Our findings provide preliminary support for the feasibility and physiological safety of conservative oxygen therapy in patients admitted to ICU for MV support after cardiac arrest (Trial registration, NCT01684124).