The impact of hyperoxia on outcomes after cardiac surgery: a systematic review and narrative synthesis

The Effects of Different Doses of Sufentanil on Intraoperative Cardiovascular Response and Postoperative Recovery in Patients Undergoing Cardiac Surgery: A Retrospective Cohort Study

Objective

To investigate the correlation between the amount of sufentanil used during anesthesia and intraoperative hemodynamic fluctuation and postoperative recovery in patients undergoing cardiopulmonary bypass (CPB).

Materials and Methods

A retrospective analysis was performed on 454 patients undergoing elective heart surgery under CPB. Patients were divided into two groups according to the amount of sufentanil used during anesthesia: Group L (induced sufentanil 0.4-0.6 ug /kg, maintained sufentanil 0.01-0.02 ug/kg/min, n = 223) and Group H (induced sufentanil 4-6 ug/kg, maintained sufentanil 0.02-0.03 ug/kg/min, n = 231). Propensity score matching (PSM) was used at a 1:1 nearest-neighbor ratio to compare the two groups. Intraoperative use of vasoactive drugs, spontaneous heart rebound, secondary endotracheal intubation, postoperative mechanical ventilation time, the length of stay (LOS) in ICU, postoperative LOS in hospital, postoperative in-hospital mortality were analyzed.

Results

After matching, a total of 144 patients were included (72 patients in Group L, and 72 patients in Group H). Multivariate logistic regression analysis showed that the dosage of sufentanil during anesthesia was significantly correlated with the utilization rate of intraoperative vasoactive drugs (P < 0.001) and the success rate of spontaneous heart rebound (p = 0.001). The utilization rate of vasoactive drugs decreased significantly in Group H (OR, 0.062; 95% CI, 0.019-0.200) compared to that of Group L. The success rate of spontaneous heart rebound (OR, 0.187; 95% CI, 0.071-0.491) was higher in Group H. There were no differences on postoperative recovery outcomes between the two groups.

Conclusion

On the basis of our data, the use of high-dose sufentanil is beneficial to keep the cardiovascular response of patients in a stable state, but there is no significant effect on the quality of early postoperative recovery.

Hypobaric type oxygenators - physics and physiology

Brain injury is still a serious complication after cardiac surgery. Gaseous microemboli (GME) are known to contribute to both short and longer-term brain injury after cardiac surgery. Hypobaric and novel dual-chamber oxygenators use the physical behaviors and properties of gases to reduce GME. The aim of this review was to present the basic physics of the gases, the mechanism in which the hypobaric and dual-chamber oxygenators reduce GME, their technical performance, the preclinical studies, and future directions. The gas laws are reviewed as an aid to understanding the mechanisms of action of oxygenators. Hypobaric-type oxygenators employ a high oxygen, no nitrogen environment creating a steep concentration gradient of nitrogen out of the blood and into the oxygenator, reducing the risk of GMEs forming. Adequately powered clinical studies have never been carried out with a hypobaric or dual-chamber oxygenator. These are required before such technology can be recommended for widespread clinical use.

Effects of intraoperative inspired oxygen fraction (FiO2 0.3 vs 0.8) on patients undergoing off-pump coronary artery bypass grafting: the CARROT multicenter, cluster-randomized trial

BACKGROUND

To maintain adequate oxygenation is of utmost importance in intraoperative care. However, clinical evidence supporting specific oxygen levels in distinct surgical settings is lacking. This study aimed to compare the effects of 30% and 80% oxygen in off-pump coronary artery bypass grafting (OPCAB).

METHODS

This multicenter trial was conducted in three tertiary hospitals from August 2019 to August 2021. Patients undergoing OPCAB were cluster-randomized to receive either 30% or 80% oxygen intraoperatively, based on the month when the surgery was performed. The primary endpoint was the length of hospital stay. Intraoperative hemodynamic data were also compared.

RESULTS

A total of 414 patients were cluster-randomized. Length of hospital stay was not different in the 30% oxygen group compared to the 80% oxygen group (median, 7.0 days vs 7.0 days; the sub-distribution hazard ratio, 0.98; 95% confidence interval [CI] 0.83-1.16; P = 0.808). The incidence of postoperative acute kidney injury was significantly higher in the 30% oxygen group than in the 80% oxygen group (30.7% vs 19.4%; odds ratio, 1.94; 95% CI 1.18-3.17; P = 0.036). Intraoperative time-weighted average mixed venous oxygen saturation was significantly higher in the 80% oxygen group (74% vs 64%; P < 0.001). The 80% oxygen group also had a significantly greater intraoperative time-weighted average cerebral regional oxygen saturation than the 30% oxygen group (56% vs 52%; P = 0.002).

CONCLUSIONS

In patients undergoing OPCAB, intraoperative administration of 80% oxygen did not decrease the length of hospital stay, compared to 30% oxygen, but may reduce postoperative acute kidney injury. Moreover, compared to 30% oxygen, intraoperative use of 80% oxygen improved oxygen delivery in patients undergoing OPCAB. Trial registration ClinicalTrials.gov (NCT03945565; April 8, 2019).

Hyperoxemia During Cardiac Surgery Is Associated With Postoperative Pulmonary Complications

The use of hyperoxemia during cardiac surgery remains controversial. We hypothesized that intraoperative hyperoxemia during cardiac surgery is associated with an increased risk of postoperative pulmonary complications.

DESIGN

Retrospective cohort study.

SETTING

We analyzed intraoperative data from five hospitals within the Multicenter Perioperative Outcomes Group between January 1, 2014, and December 31, 2019. We assessed intraoperative oxygenation of adult patients undergoing cardiac surgery with cardiopulmonary bypass (CPB). Hyperoxemia pre and post CPB was quantified as the area under the curve (AUC) of Fio₂ above 0.21 in minutes when the corresponding peripheral oxygen saturation was greater than 92% measured by pulse oximetry. We quantified hyperoxemia during CPB as the AUC of Pao₂ greater than 200 mm Hg measured by arterial blood gas. We analyzed the association of hyperoxemia during all phases of cardiac surgery with the frequency of postoperative pulmonary complications within 30 days, including acute respiratory insufficiency or failure, acute respiratory distress syndrome, need for reintubation, and pneumonia.

PATIENTS

Twenty-one thousand six hundred thirty-two cardiac surgical patients.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

During 21,632 distinct cardiac surgery cases, 96.4% of patients spent at least 1 minute in hyperoxemia (99.1% pre-CPB, 98.5% intra-CPB, and 96.4% post-CPB). Increasing exposure to hyperoxemia was associated with an increased risk of postoperative pulmonary complications throughout three distinct surgical periods. During CPB, increasing exposure to hyperoxemia was associated with an increased odds of developing postoperative pulmonary complications (p < 0.001) in a linear manner. Hyperoxemia before CPB (p < 0.001) and after CPB (p = 0.02) were associated with increased odds of developing postoperative pulmonary complications in a U-shaped relationship.

CONCLUSIONS

Hyperoxemia occurs almost universally during cardiac surgery. Exposure to hyperoxemia assessed continuously as an AUC during the intraoperative period, but particularly during CPB, was associated with an increased incidence of postoperative pulmonary complications.

ARTERIAL HYPEROXIA AND MORTALITY IN PATIENTS UNDERGOING VENOARTERIAL EXTRACORPOREAL MEMBRANE OXYGENATION

ABSTRACT

Background: Venoarterial extracorporeal membrane oxygenation (VA-ECMO) can easily lead to supranormal oxygenation. The impact of hyperoxygenation beyond the early VA-ECMO support phase is unexplored. We sought to investigate its association with short- and long-term mortality. Methods: A total of 10,615 arterial blood gases of 179 patients undergoing VA-ECMO between 2013 and 2018 in our cardiosurgical tertiary center were analyzed for partial pressure of oxygen (PaO2) and its association with in-hospital, 90-day, and 1-year mortality. Patients were stratified into terciles (T) based on PaO2. Results: The median systemic PaO2 during VA-ECMO was 122 mm Hg (Q1-Q3, 111-158 mm Hg) and was significantly higher in 90-day nonsurvivors versus survivors (134 mm Hg [Q1-Q3, 114-175 mm Hg] vs. 114 mm Hg [Q1-Q3, 109-136 mm Hg]; P < 0.001). The incidence of mortality increased at all time points tested after VA-ECMO implantation along with the increasing terciles of PaO2. The lowest mortality rates were noted for patients with median PaO2 values of <115 mm Hg (T1), whereas patients with median PaO2 values of >144 mm Hg (T3) had the highest mortality rates. Bonferroni multiple testing analysis found the T3 of PaO2 to be a predictor of decreased 90-day survival in comparison with T1 (P < 0.001) and T2 (P = 0.002). Multivariable Cox regression analyses for in-hospital, 90-day, and 1-year mortality showed a significant association of the T3 compared with the T2 and the T1 of PaO2 to mortality across all endpoints. Conclusion: Hyperoxygenation during VA-ECMO might be associated with increased all-cause mortality. The results of our study further document the known toxicity of hyperoxygenation in general critical care patients and mark the need to focus specifically on VA-ECMO patients.

Intraoperative mild hyperoxia may be associated with improved survival after off-pump coronary artery bypass grafting: a retrospective observational study

Background

The effect of hyperoxia due to supplemental oxygen administration on postoperative outcomes in patients undergoing cardiac surgery remains unclear. This retrospective study aimed to evaluate the relationship between intraoperative oxygen tension and mortality after off-pump coronary artery bypass grafting (OPCAB).

Methods

The study included adult patients who underwent isolated OPCAB between July 2010 and June 2020. Patients were categorised into three groups based on their intraoperative time-weighted average arterial oxygen partial pressure (PaO₂): normoxia/near-normoxia (< 150 mmHg), mild hyperoxia (150–250 mmHg), and severe hyperoxia (> 250 mmHg). The risk of in-hospital mortality was compared using weighted logistic regression analysis. Restricted cubic spline analysis was performed to analyse intraoperative PaO₂ as a continuous variable. The risk of cumulative all-cause mortality was compared using Cox regression analysis.

Results

The normoxia/near-normoxia, mild hyperoxia, and severe hyperoxia groups included 229, 991, and 173 patients (n = 1393), respectively. The mild hyperoxia group had a significantly lower risk of in-hospital mortality than the normoxia/near-normoxia (odds ratio [OR], 0.12; 95% confidence interval [CI], 0.06–0.22) and severe hyperoxia groups (OR, 0.06; 95% CI, 0.03–0.14). Intraoperative PaO₂ exhibited a U-shaped relationship with in-hospital mortality in the non-hypoxic range. The risk of cumulative all-cause mortality was significantly lower in the mild hyperoxia group (hazard ratio, 0.72; 95% CI, 0.52–0.99) than in the normoxia/near-normoxia group.

Conclusions

Maintaining intraoperative PaO₂ at 150–250 mmHg was associated with a lower risk of mortality after OPCAB than PaO₂ at < 150 mmHg and at > 250 mmHg. Future randomised trials are required to confirm if mildly increasing arterial oxygen tension during OPCAB to 150–250 mmHg improves postoperative outcomes.

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

BACKGROUND

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

METHODS

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

DISCUSSION

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

Year in Review 2021: Noteworthy Literature in Cardiothoracic Anesthesia

In 2021, progress in clinical science related to Cardiac Anesthesiology continued, but at a slower rate due to the ongoing pandemic and disruptions to clinical research. Most progress was incremental and addressed persistent questions related to our field. To identify articles for this review, we completed a structured review using our previously reported methods (1). Specifically, we used the search terms: "cardiac anesthesiology and outcomes" (n = 177), "cardiothoracic anesthesiology" (n = 34), "cardiac anesthesia," and "clinical outcomes" (n = 42) filtered on clinical trials and the year 2021 in PubMed. We also reviewed clinical trials from the most prominent clinical journals to identify additional studies for a narrative review. We then selected the most noteworthy publications for inclusion in this review and identified key themes.

Hyperoxia and Acute Kidney Injury: A Tale of Oxygen and the Kidney

Although oxygen supplementation is beneficial to support life in the clinic, excessive oxygen therapy also has been linked to damage to organs such as the lung or the eye. However, there is a lack of understanding of whether high oxygen therapy directly affects the kidney, leading to acute kidney injury, and what molecular mechanisms may be involved in this process. In this review, we revise our current understanding of the mechanisms by which hyperoxia leads to organ damage and highlight possible areas of investigation for the scientific community interested in novel mechanisms of kidney disease. Overall, we found a significant need for both animal and clinical studies evaluating the role of hyperoxia in inducing kidney damage. Thus, we urge the research community to further investigate oxygen therapy and its impact on kidney health with the goal of optimizing oxygen therapy guidelines and improving patient care.

Outcomes and Predictors of Severe Hyperoxemia in Patients Receiving Mechanical Ventilation: A Single-Center Cohort Study

RATIONALE

Supplemental oxygen is among the most commonly administered therapies in intensive care units. High supplemental oxygen exposure has been associated with harm in observational human studies and animal models. Yet no consensus exists regarding which dose and duration of high oxygen constitutes harmful hyperoxemia, and little is known regarding the clinical factors that predict potentially injurious exposure.

OBJECTIVES

To determine the level and duration of arterial oxygen (PaO2) associated with mortality among mechanically ventilated patients, and to identify the clinical factors that predict this exposure.

METHODS

We performed a retrospective cohort study of patients who received invasive mechanical ventilation at a single academic institution in 2017 and 2018. We used a generalized additive model to visualize the relationship between the measured PaO2 via arterial blood gases (ABGs) and 30-day mortality. We used multivariable logistic regression to identify patient- and hospital-level factors that predict exposure to harmful hyperoxemia.

RESULTS

We analyzed 2,133 patients with 33,310 ABGs obtained during mechanical ventilation. We identified a U-shaped relationship between PaO2 and mortality, where PaO2 was positively correlated with mortality above a threshold of 200 mmHg. 1,184 patients (55.5%) had at least one PaO2 level above this threshold. If patients spent an entire day exposed to PaO2 > 200 mmHg, they had 2.19 (95% CI 1.33 - 3.60, p = 0.002) greater odds of 30-day mortality in an adjusted analysis. Any exposure to severe hyperoxemia (PaO2 > 200 mmHg), was associated with mortality (OR 1.29, 95% CI 1.04 - 1.59, p = 0.021). The strongest clinical predictor of severe hyperoxemia exposure was the identity of the ICU in which mechanical ventilation was delivered.

CONCLUSIONS

Exposure to high arterial oxygen concentrations is common among mechanically ventilated patients, and the dose and duration of PaO2 ≥ 200 mmHg is associated with mortality. Severe hyperoxemia is highly variable across ICUs, and is far more common in clinical practice than in recent randomized trials of oxygen targeting strategies. Efforts to minimize this common and injurious exposure level are needed.

Impact of partial pressure of oxygen trajectories on the incidence of acute kidney injury in patients undergoing cardiopulmonary bypass

BACKGROUND

To investigate the impact of the dynamic oxygenation status on the incidence of acute kidney injury (AKI) in patients undergoing cardiopulmonary bypass.

METHODS

This retrospective study was performed using data extracted from the Medical Information Mart for Intensive Care III database. A group-based trajectory approach was used to identify partial pressure of oxygen (PaO₂) trajectories using dynamic change in PaO₂ within 48 hours after intensive care unit admission.

RESULTS

In total, 5,824 patients were included. Four PaO₂ trajectories were identified: Trajectory 1 (Traj-1), hyperoxia and rapid decrease; Trajectory 2 (Traj-2), hyperoxia and rapid decrease similar to that of Traj-1; Trajectory 3 (Traj-3), normoxemia and rapid increase in PaO₂; and Trajectory 4 (Traj-4), hyperoxia and gradual decrease. Compared with the Traj-1 group, the Traj-3 group had a significantly lower initial Sequential Organ Failure Assessment score, similar vasopressor use rate, and a higher fraction of inspired oxygen. However, the risk of developing AKI was significantly higher in the Traj-3 [adjusted odds ratio (OR): 1.7, 95% confidence interval (CI): 1.1-2.7] and Traj-4 groups (OR: 1.9, 95% CI: 1.4-2.5) than in the Traj-1 group.

CONCLUSIONS

Patients with persistent hyperoxia had a higher incidence of AKI than those with transient hyperoxia. Further studies are required to determine potential underlying mechanisms.

Efficacy of a glucagon-like peptide-1 agonist and restrictive versus liberal oxygen supply in patients undergoing coronary artery bypass grafting or aortic valve replacement: study protocol for a 2-by-2 factorial designed, randomised clinical trial

INTRODUCTION

Coronary artery bypass grafting (CABG) and/or aortic valve replacement (AVR) are associated with risk of death, as well as brain, heart and kidney injury. Glucagon-like peptide-1 (GLP-1) analogues are approved for treatment of type 2 diabetes, and GLP-1 analogues have been suggested to have potential organ-protective and anti-inflammatory effects. During cardiopulmonary bypass (CPB), consensus on the optimal fraction of oxygen is lacking. The objective of this study is to determine the efficacy of the GLP-1-analogue exenatide versus placebo and restrictive oxygenation (50% fractional inspired oxygen, FiO2) versus liberal oxygenation (100% FiO2) in patients undergoing open heart surgery.

METHODS AND ANALYSIS

A randomised, placebo-controlled, double blind (for the exenatide intervention)/single blind (for the oxygenation strategy), 2×2 factorial designed single-centre trial on adult patients undergoing elective or subacute CABG and/or surgical AVR. Patients will be randomised in a 1:1 and 1:1 ratio to a 6-hour and 15 min infusion of 17.4 µg of exenatide or placebo during CPB and to a FiO2 of 50% or 100% during and after weaning from CPB. Patients will be followed until 12 months after inclusion of the last participant. The primary composite endpoint consists of time to first event of death, renal failure requiring renal replacement therapy, hospitalisation for stroke or heart failure. In addition, the trial will include predefined sub-studies applying more advanced measures of cardiac- and pulmonary dysfunction, renal dysfunction and cerebral dysfunction. The trial is event driven and aims at 323 primary endpoints with a projected inclusion of 1400 patients.

ETHICS AND DISSEMINATION

Eligible patients will provide informed, written consent prior to randomisation. The trial is approved by the local ethics committee and is conducted in accordance with Danish legislation and the Declaration of Helsinki. The results will be presented in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

NCT02673931.

Effect of changes in inspired oxygen fraction on oxygen delivery during cardiac surgery: a substudy of the CARROT trial

When hemoglobin (Hb) is fully saturated with oxygen, the additional gain in oxygen delivery (DO2) achieved by increasing the fraction of inspired oxygen (FiO2) is often considered clinically insignificant. In this study, we evaluated the change in DO2, interrogated by mixed venous oxygen saturation (SvO2), in response to a change in FiO2 of 0.5 during cardiac surgery. When patients were hemodynamically stable, FiO2 was alternated between 0.5 and 1.0 in on-pump cardiac surgery patients (pilot study), and between 0.3 and 0.8 in off-pump coronary artery bypass grafting patients (substudy of the CARROT trial). After the patient had stabilized, a blood gas analysis was performed to measure SvO2. The observed change in SvO2 (ΔSvO2) was compared to the expected ΔSvO2 calculated using Fick's equation. A total 106 changes in FiO2 (two changes per patient; total 53 patients; on-pump, n = 36; off-pump, n = 17) were finally analyzed. While Hb saturation remained near 100% (on-pump, 100%; off-pump, mean [SD] = 98.1% [1.5] when FiO2 was 0.3 and 99.9% [0.2] when FiO2 was 0.8), SvO2 changed significantly as FiO2 was changed (the first and second changes in on-pump, 7.7%p [3.8] and 7.6%p [3.5], respectively; off-pump, 7.9%p [4.9] and 6.2%p [3.9]; all P < 0.001). As a total, regardless of the surgery type, the observed ΔSvO2 after the FiO2 change of 0.5 was ≥ 5%p in 82 (77.4%) changes and ≥ 10%p in 31 (29.2%) changes (mean [SD], 7.5%p [3.9]). Hb concentration was not correlated with the observed ΔSvO2 (the first changes, r =  - 0.06, P = 0.677; the second changes, r =  - 0.21, P = 0.138). The mean (SD) residual ΔSvO2 (observed - expected ΔSvO2) was 0%p (4). Residual ΔSvO2 was more than 5%p in 14 (13.2%) changes and exceeded 10%p in 2 (1.9%) changes. Residual ΔSvO2 was greater in patients with chronic kidney disease than in those without (median [IQR], 5%p [0 to 7] vs. 0%p [- 3 to 2]; P = 0.049). DO2, interrogated by SvO2, may increase to a clinically significant degree as FiO2 is increased during cardiac surgery, and the increase of SvO2 is not related to Hb concentration. SvO2 increases more than expected in patients with chronic kidney disease. Increasing FiO2 can be used to increase DO2 during cardiac surgery.

Hyperoxia During Cardiopulmonary Bypass Is Associated With Mortality in Infants Undergoing Cardiac Surgery

OBJECTIVES

Patients undergoing cardiac surgery using cardiopulmonary bypass have variable degrees of blood oxygen tension during surgery. Hyperoxia has been associated with adverse outcomes in critical illness. Data are not available regarding the association of hyperoxia and outcomes in infants undergoing cardiopulmonary bypass. We hypothesize that among infants undergoing cardiac surgery, hyperoxia during cardiopulmonary bypass is associated with greater odds of morbidity and mortality.

DESIGN

Retrospective study.

SETTING

Single center at an academic tertiary children's hospital.

PATIENTS

All infants (< 1 yr) undergoing cardiopulmonary bypass between January 1, 2015, and December 31, 2017, excluding two patients who were initiated on extracorporeal membrane oxygenation in the operating room.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The study included 469 infants with a median age of 97 days (interquartile range, 14-179 d), weight 4.9 kg (interquartile range, 3.4-6.4 kg), and cardiopulmonary bypass time 128 minutes (interquartile range, 91-185 min). A Pao2 of 313 mm Hg (hyperoxia) on cardiopulmonary bypass had highest sensitivity with specificity greater than 50% for association with operative mortality. Approximately, half of the population (237/469) had hyperoxia on cardiopulmonary bypass. Infants with hyperoxia were more likely to have acute kidney injury, prolonged postoperative length of stay, and mortality. They were younger, weighed less, had longer cardiopulmonary bypass times, and had higher Society of Thoracic Surgeons and the European Association for Cardio-Thoracic Surgery mortality scores. There was no difference in sex, race, preoperative creatinine, single ventricle physiology, or presence of genetic syndrome. On multivariable analysis, hyperoxia was associated with greater odds of mortality (odds ratio, 4.3; 95% CI, 1.4-13.2) but failed to identify an association with acute kidney injury or prolonged postoperative length of stay. Hyperoxia was associated with greater odds of mortality in subgroup analysis of neonatal patients.

CONCLUSIONS

Hyperoxia occurred in a substantial portion of infants undergoing cardiopulmonary bypass for cardiac surgery. Hyperoxia during cardiopulmonary bypass was an independent risk factor for mortality and may be a modifiable risk factor. Furthermore, hyperoxia during cardiopulmonary bypass was associated with four-fold greater odds of mortality within 30 days of surgery. Hyperoxia failed to identify an association with development of acute kidney injury or prolonged postoperative length of stay when controlling for covariables. Validation of our data among other populations is necessary to better understand and elucidate potential mechanisms underlying the association between excess oxygen delivery during cardiopulmonary bypass and outcome.

Pathophysiology and clinical consequences of arterial blood gases and pH after cardiac arrest

Post cardiac arrest syndrome is associated with high morbidity and mortality, which is related not only to a poor neurological outcome but also to respiratory and cardiovascular dysfunctions. The control of gas exchange, and in particular oxygenation and carbon dioxide levels, is fundamental in mechanically ventilated patients after resuscitation, as arterial blood gases derangement might have important effects on the cerebral blood flow and systemic physiology.

In particular, the pathophysiological role of carbon dioxide (CO₂) levels is strongly underestimated, as its alterations quickly affect also the changes of intracellular pH, and consequently influence metabolic energy and oxygen demand. Hypo/hypercapnia, as well as mechanical ventilation during and after resuscitation, can affect CO₂ levels and trigger a dangerous pathophysiological vicious circle related to the relationship between pH, cellular demand, and catecholamine levels. The developing hypocapnia can nullify the beneficial effects of the hypothermia. The aim of this review was to describe the pathophysiology and clinical consequences of arterial blood gases and pH after cardiac arrest.

According to our findings, the optimal ventilator strategies in post cardiac arrest patients are not fully understood, and oxygen and carbon dioxide targets should take in consideration a complex pattern of pathophysiological factors. Further studies are warranted to define the optimal settings of mechanical ventilation in patients after cardiac arrest.

Association Between Intraoperative Hyperoxia and Acute Kidney Injury After Cardiac Surgery: A Retrospective Observational Study

OBJECTIVE

Optimal oxygen management during cardiac surgery has not been established, and studies on the effects of perioperative hyperoxia on postoperative acute kidney injury (AKI) are scarce. The association between intraoperative hyperoxia and AKI after cardiac surgery involving cardiopulmonary bypass was evaluated for the present study.

DESIGN

Retrospective observational study.

SETTING

A tertiary teaching hospital.

PARTICIPANTS

Adult patients who underwent cardiac surgery with cardiopulmonary bypass from November 2006-December 2018.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The area above arterial oxygen partial pressure (PaO₂) threshold of 300 mmHg (AOT₃₀₀, mmHg × h) was used as a metric of intraoperative hyperoxia and was associated with postoperative AKI, using the logistic regression analysis. Data also were fitted using the restricted cubic spline model. Sensitivity analyses were conducted using different PaO₂ thresholds (150, 200, 250, and 350 mmHg). A total of 2,926 patients were analyzed. Intraoperative AOT₃₀₀ independently was associated with the risk of AKI (odds ratio 1.0009; 95% confidence interval 1.0002-1.0015). A PaO₂ increment of 100 mmHg above PaO₂ 300 mmHg for an hour was associated with an increased risk of AKI by 9.4% (1.0009¹⁰⁰ ≈ 1.094). In the spline model, the log-odds of AKI increased as AOT₃₀₀ increased. In the sensitivity analyses, AOT₂₅₀ and AOT₃₅₀ also significantly were associated with the risk of AKI, whereas AOT₁₅₀ and AOT₂₀₀ were not. As the PaO₂ threshold increased from 150 to 350 mmHg, the odds ratio gradually increased.

CONCLUSIONS

Intraoperative hyperoxia significantly was associated with the risk of AKI after cardiac surgery involving cardiopulmonary bypass.

Oxygen Management During Cardiopulmonary Bypass: A Single-Center, 8-Year Retrospective Cohort Study

OBJECTIVE

To characterize the institutional oxygen management practices during cardiopulmonary bypass (CPB) in patients undergoing cardiac surgery, including any potential changes during an 8-year study period.

DESIGN

A retrospective cohort study.

SETTING

A tertiary care cardiac surgical program.

PARTICIPANTS

Patients who underwent cardiac surgery involving CPB, with or without hypothermic circulatory arrest (HCA), between January 1, 2010, and December 31, 2017.

MEASUREMENTS AND MAIN RESULTS

In addition to baseline patient characteristics, the authors recorded the partial pressures of arterial oxygen (Pao₂), fraction of inspired oxygen, and mixed venous oxygen saturation during CPB of 696 randomly selected patients during an 8-year study period. The overall mean Pao₂ was 255 ± 48 mmHg, without any significant change during the 8-year study period (p = 0.30). The mean Pao₂ of HCA patients was significantly higher than in patients without HCA (327 ± 93 mmHg v 252 ± 45 mmHg, respectively; p < 0.001).

CONCLUSIONS

The current approach to oxygen management during CPB at the authors' institution is within the range of hyperoxemic levels, and these practices have not changed over time. The impact of these practices on patients' outcomes is not fully understood, and additional studies are needed to establish firm evidence to guide optimal oxygen management practice during CPB.

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.

Hyperoxia during cardiopulmonary bypass does not decrease cardiovascular complications following cardiac surgery: the CARDIOX randomized clinical trial

PURPOSE

Data on the benefit or or harmful effects of oxygen level on ischemic reperfusion injuries in cardiac surgery are insufficient. We hypothesized that hyperoxia during cardiopulmonary bypass decreases the incidence of postoperative atrial fibrillation (POAF) and ventricular fibrillation, and therefore decreases cardiovascular morbidity (CARDIOX study).

METHODS

An open-label, randomized clinical trial including adults undergoing elective cardiac surgery, i.e. cardiopulmonary bypass (CPB) randomized 1:1 to an intervention group or standard group at two French University Hospitals from June 2016 to October 2018. The intervention consisted in delivering of an inspired fraction of oxygen of one to one during CPB. The standard care consisted in delivering oxygen to achieve a partial arterial blood pressure less than 150 mmHg. The primary endpoint was the occurrence of POAF and/or ventricular tachycardia/ventricular fibrillation (VT/VF) within the 15 days following cardiac surgery. The secondary endpoint was the occurrence of major adverse cardiovascular events (MACCE: in-hospital mortality, stroke, cardiac arrest, acute kidney injury, and mesenteric ischemia).

RESULTS

330 patients were randomly assigned to either the intervention group (n = 161) or the standard group (n = 163). Mean PaO₂ was 447 ± 98 mmHg and 161 ± 60 mmHg during CPB, for the intervention and standard group (p < 0.0001) respectively. The incidence of POAF or VT/VF were similar in the intervention group and the standard group (30% [49 of 161 patients] and 30% [49 of 163 patients], absolute risk reduction 0.4%; 95% CI, - 9.6-10.4; p = 0.94). MACCE was similar between groups with, an occurrence of 24% and 21% for the intervention group and the standard groups (absolute risk reduction 3.4%; 95% CI, - 5.7-12.5; p = 0.47) respectively. After adjustment, the primary and secondary endpoints remained similar for both groups.

CONCLUSION

Hyperoxia did not decrease POAF and cardiovascular morbidity following cardiac surgery with CPB. CLINICALTRIAL.

GOV IDENTIFIER

NCT02819739.

Ventilation strategies with different inhaled Oxygen conceNTration during CardioPulmonary Bypass in cardiac surgery (VONTCPB): study protocol for a randomized controlled trial

Background

There is no consensus on the ventilation management during cardiopulmonary bypass (CPB), and the anesthesiologists or the surgeons usually ventilate the lungs with different ventilation strategies or keep them static. Better outcomes are more likely to occur when the ventilation is administered during CPB according to the existing literatures. However, the use of high fraction of inspired oxygen (FiO₂) is debatable in cardiac surgery. And the potential effects of strategies combining low tidal volume (V_T) ventilation with different FiO₂ during CPB on postoperative pulmonary complications (PPCs) are unclear.

Design

The VONTCPB trial is a single-center, prospective, double-blinded, randomized, controlled trial. We are going to recruit total 420 elective cardiac surgery patients with median sternotomy under CPB, who will be equally randomized into three different ventilation strategy groups: NoV, LOV and HOV. (1) The NoV group receives no mechanical ventilation during CPB; (2) the LOV group receives a low V_T of 3-4 ml/kg of ideal body weight (IBW) with the respiratory rate (RR) of 10–12 acts/min, and the positive end-expiratory pressure (PEEP) of 5–8 cmH₂O during CPB; the FiO₂ is 30%; (3) the HOV group receives a low V_T of 3-4 ml/kg of IBW with the RR of 10–12 acts/min, and the PEEP of 5–8 cmH₂O during CPB; the FiO₂ is 80%. The primary endpoints are the incidence of the composite of PPCs and the PPCs score. The secondary endpoints refer to the incidence of the oxygenation index (PaO₂/FiO₂ ratio) < 300 mmHg at three time points (the moment arriving in the ICU, 6 and 12 h after arrival in the ICU), the surgical incision healing grade, the intubation time, the stay of ICU, the length of hospital stay, and mortality at 30 days after the surgery.

Discussion

The VONTCPB trial is the first study to assess the effects of strategies combining low tidal volume (V_T) ventilation with different FiO₂ during CPB on patients’ outcomes.

Trial registration

ChiCTR1800015261. Registered on 20 March 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3335-2) contains supplementary material, which is available to authorized users.

Routine practice in mechanical ventilation in cardiac surgery in Italy

BACKGROUND

Management of mechanical ventilation is a key issue in the prevention of postoperative pulmonary complications (PPCs) and the improvement of surgical outcome. This is especially true in cardiac surgery where the use of the cardiopulmonary bypass (CPB) increases the risk of lung injury. In the last years a growing number of studies have shown that protective ventilation has led to excellent results. However, the literature in this regard is lacking in cardiac surgery and there are no univocal guidelines in this sense. The aim of this survey was to investigate the actual clinical practice about ventilation techniques used in the Italian cardiac surgery centers.

METHODS

A questionnaire of 32-item was sent to 69 Italian cardiac surgery centers, 56 of which return a completed form (81.2%). The questionnaire was assembled by three independent researchers and the final version was e-mailed to all members of the SIAARTI (Italian society of anesthesia resuscitation and intensive care medicine) Study Group on Cardiothoracic and Vascular Anesthesia. The answers were collected using a Google Forms sheet. In case of multiple questionnaires returned from the same center (i.e., different physicians from the same center responded) the head of department was asked to give a definite answer. Furthermore, for the 17 centers who reported multiple questionnaires, no large differences were found between the responses of different doctors belonging to the same center (12.3%±4.2% of discordant answers).

RESULTS

Intraoperatively, patients were ventilated with a tidal volume (TV) of 6-8 mL/kg (91.1% of centers), a positive end-expiration pressure of 3-5 cmH2O (76.8% of centers) and a fraction of inspired oxygen (FiO2) of 50-80% (60.7% of centers). During the CPB, the "stop ventilation" technique was frequently adopted (73.2%). Before the discharge from the intensive care unit (ICU) non-invasive ventilation (NIV) was never applied in 32.1% of the centers, but it was used in 46.4% of patients with postoperative complications.

CONCLUSIONS

This study shows a significant heterogeneity in ventilatory techniques among the Italian centers during CPB, whereas in the other surgical time the majority of the responding centers adopted a protective mechanical ventilation strategy.

MALAT1 promoted cell proliferation and migration via MALAT1/miR-155/MEF2A pathway in hypoxia of cardiac stem cells

Accumulating evidence revealed that hypoxia contributed to many human diseases, including ischemic myocardium and heart failure (HF). In recent years, the roles of hypoxia in stem cell survival and cardiac biology have been studied extensively. However, the underlying molecular mechanisms remain to be elucidated. As a leading cause of HF, ischemic heart disease was correlated with hypoxia. In this study, we firstly constructed the hypoxia cell model by CoCl₂ in cardiac stem cells (CSCs) and found that hypoxia induced the cell proliferation and migration potential in CSCs. Then, we demonstrated that the expression of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) was promoted in CoCl₂ -induced CSCs hypoxia model. Furthermore, we found that knockdown of MALAT1 inhibited the cell proliferation and migration in CoCl₂ -induced CSCs hypoxia model. In addition, we revealed that MALAT1 regulated the microRNA-155 (miR-155) expression in CSCs under both the normal and hypoxia conditions and further, manipulation of the miR-155 expression affected the role of MALAT1 in CoCl₂ -induced CSCs hypoxia cell model. We then illustrated that miR-155 regulated the myocyte enhancer factor 2A (MEF2A) expression in CSCs under both the normal and hypoxia conditions and further, changing the expression of MEF2A affected the role of miR-155. Finally, we demonstrated that MALAT1 regulated the MEF2A expression and exerted its role via modulation of the MALAT1/miR-155/MEF2A pathway. Taken together, our study illustrated that MALAT1 promoted the cell proliferation and migration in CoCl₂ -induced CSCs hypoxia model, acting mechanistically by promoting MEF2A expression via "sponging" miR-155.