Benefits and harms of increased inspiratory oxygen concentrations

Transitions from Aerobic to Anaerobic Metabolism and Oxygen Debt during Elective Major and Emergency Non-Cardiac Surgery

INTRODUCTION

Intraoperative hemodynamic and metabolic optimization of both the high-risk surgical patients and critically ill patients remains challenging. Reductions in oxygen delivery or increases in oxygen consumption can initiate complex cellular processes precipitating oxygen debt (OXD).

METHODS

This study tested the hypothesis that intraoperative changes in sublingual microcirculatory flow reflect clinically relevant transitions from aerobic to anaerobic metabolism (TRANAM). We included patients undergoing elective major and emergency non-cardiac surgery. Macro- and microcirculatory variables, oxygen extraction, and transitions of metabolism were assessed in both cohorts.

RESULTS

In the elective group, OXD was progressively increased over time, with an estimated 2.24 unit increase every 30 min (adjusted p < 0.001). Also, OXD was negatively correlated with central venous pressure (ρ = -0.247, adjusted p = 0.006) and positively correlated with stroke volume variation (ρ = 0.185, adjusted p = 0.041). However, it was not significantly correlated with sublingual microcirculation variables. In the emergency surgery group, OXD increased during the first two intraoperative hours and then gradually decreased until the end of surgery. In that cohort, OXD was positively correlated with diastolic arterial pressure (ρ = 0.338, adjpatients and the critically ill patients remains challengingsted p = 0.015). Also, OXD was negatively correlated with cardiac index (ρ = -0.352, adjusted p = 0.003), Consensus Proportion of Perfused Vessels (PPV) (ρ = -0.438, adjusted p < 0.001), and Consensus PPV (small) (ρ = -0.434, adjusted p < 0.001).

CONCLUSIONS

TRANAM were evident in both the elective major and emergency non-cardiac surgery cohorts independent of underlying alterations in the sublingual microcirculation.

Oxygenation during general anesthesia in pediatric patients: A retrospective observational study

STUDY OBJECTIVE

Protocols are used in intensive care and emergency settings to limit the use of oxygen. However, in pediatric anesthesiology, such protocols do not exist. This study aimed to investigate the administration of oxygen during pediatric general anesthesia and related these values to PaO2, SpO2 and SaO2.

DESIGN

Retrospective observational study.

SETTING

Tertiary pediatric academic hospital, from June 2017 to August 2020.

PATIENTS

Patients aged 0-18 years who underwent general anesthesia for a diagnostic or surgical procedure with tracheal intubation and an arterial catheter for regular blood withdrawal were included. Patients on cardiopulmonary bypass or those with missing data were excluded. Electronic charts were reviewed for patient characteristics, type of surgery, arterial blood gas analyses, and oxygenation management.

INTERVENTIONS

No interventions were done.

MEASUREMENTS

Primary outcome defined as FiO2, PaO2 and SpO2 values were interpreted using descriptive analyses, and the correlation between PaO2 and FiO2 was determined using the weighted Spearman correlation coefficient.

MAIN RESULTS

Data of 493 cases were obtained. Of these, 267 were excluded for various reasons. Finally, 226 cases with a total of 645 samples were analyzed. The median FiO2 was 36% (IQR 31 to 43), with a range from 20% to 97%, and the median PaO2 was 23.6 kPa (IQR 18.6 to 28.1); 177 mmHg (IQR 140 to 211). The median SpO2 level was 99% (IQR 98 to 100%). The study showed a moderately positive association between PaO2 and FiO2 (r = 0.52, p < 0.001). 574 of 645 samples (89%) contained a PaO2 higher than 13.3 kPa; 100 mmHg.

CONCLUSIONS

Oxygen administration during general pediatric anesthesia is barely regulated. Hyperoxemia is observed intraoperatively in approximately 90% of cases. Future research should focus on outcomes related to hyperoxemia.

Association between mean arterial pressure and sublingual microcirculation during major non-cardiac surgery: Post hoc analysis of a prospective cohort

OBJECTIVE

To test the hypothesis that there is an association between mean arterial pressure (MAP) and sublingual perfusion during major surgery, and perhaps an identifiable harm threshold.

METHODS

This post hoc analysis of a prospective cohort included patients who had elective major non-cardiac surgery with a duration of ≥2 h under general anesthesia. We assessed sublingual microcirculation every 30 min using SDF+ imaging and determined the De Backer score, Consensus Proportion of Perfused Vessels (Consensus PPV), and the Consensus PPV (small). Our primary outcome was the relationship between MAP and sublingual perfusion which was evaluated with linear mixed effects modeling.

RESULTS

A total of 100 patients were included, with MAP ranging between 65 mmHg and 120 mmHg during anesthesia and surgery. Over a range of intraoperative MAPs between 65 and 120 mmHg, there were no meaningful associations between blood pressure and various measures of sublingual perfusion. There were also no meaningful changes in microcirculatory flow over 4.5 h of surgery.

CONCLUSIONS

In patients having elective major non-cardiac surgery with general anesthesia, sublingual microcirculation is well maintained when MAP ranges between 65 and 120 mmHg. It remains possible that sublingual perfusion will be a useful marker of tissue perfusion when MAP is lower than 65 mmHg.

Nanotechnological strategies to increase the oxygen content of the tumor

Hypoxia is a negative prognostic indicator of solid tumors, which not only changes the survival state of tumors and increases their invasiveness but also remarkably reduces the sensitivity of tumors to treatments such as radiotherapy, chemotherapy and photodynamic therapy. Thus, developing therapeutic strategies to alleviate tumor hypoxia has recently been considered an extremely valuable target in oncology. In this review, nanotechnological strategies to elevate oxygen levels in tumor therapy in recent years are summarized, including (I) improving the hypoxic tumor microenvironment, (II) oxygen delivery to hypoxic tumors, and (III) oxygen generation in hypoxic tumors. Finally, the challenges and prospects of these nanotechnological strategies for alleviating tumor hypoxia are presented.

The use of mean circulatory filling pressure analogue for monitoring hemodynamic coherence: A post-hoc analysis of the SPARSE data and proof-of-concept study

BACKGROUND

Dissociation between macrocirculation and microcirculation is often observed in surgical patients.

OBJECTIVE

To test the hypothesis that the analogue of mean circulatory filling pressure (Pmca) can monitor hemodynamic coherence during major non-cardiac surgery.

METHODS

In this post-hoc analysis and proof-of-concept study, we used the central venous pressure (CVP), mean arterial pressure (MAP), and cardiac output (CO) to calculate Pmca. Efficiency of the heart (Eh), arterial resistance (Rart), effective arterial elastance (Ea), venous compartment resistance (Rven), oxygen delivery (DO2), and oxygen extraction ratio (O2ER) were also calculated. Sublingual microcirculation was assessed using SDF + imaging, and the De Backer score, Consensus Proportion of Perfused Vessels (Consensus PPV), and Consensus PPV (small) were determined.

RESULTS

Thirteen patients were included, with a median age of 66 years. Median Pmca was 16 (14.9-18) mmHg and was positively associated with CO [p <  0.001; a 1 mmHg increase in Pmca increases CO by 0.73 L  min - 1 (p <  0.001)], Eh (p <  0.001), Rart (p = 0.01), Ea (p = 0.03), Rven (p = 0.005), DO2 (p = 0.03), and O2ER (p = 0.02). A significant correlation was observed between Pmca and Consensus PPV (p = 0.02), but not with De Backer Score (p = 0.34) or Consensus PPV (small) (p = 0.1).

CONCLUSION

Significant associations exist between Pmca and several hemodynamic and metabolic variables including Consensus PPV. Adequately powered studies should determine whether Pmca can provide real-time information on hemodynamic coherence.

Inspiratory hyperoxia suppresses lung cancer metastasis through a MYC/SLC1A5-dependent metabolic pathway

The lack of knowledge about the effect of inspiratory hyperoxia on the lung-specific tumour microenvironment and progression of lung cancer has attracted considerable attention. This study proposes that inspiratory hyperoxia has special significance for the malignant phenotype of lung cancer cells. The effects of different oxygenation parameters on the proliferation, apoptosis, invasion and migration of lung cancer cells were systematically evaluated in vitro and in vivo Our results reveal that inspiratory hyperoxia treatment (60% oxygen, 6 h·day^-1) not only has no tumour progression-promoting effects, but also suppresses lung cancer metastasis and promotes long-term survival. In addition, we combined transcriptome, proteome and metabolome analysis and found that hyperoxia treatment induced significant intracellular metabolic changes in lung cancer cells. Overall, we established that MYC/SLC1A5-induced metabolic reprogramming and glutamine addiction is a new mechanism that drives lung cancer metastasis, which can be significantly suppressed by inspiratory hyperoxia treatment. These findings are relevant to the debate on the perils, promises and antitumour effect of inspiratory hyperoxia, especially for patients with lung cancer.

Oxygen administration during surgery and postoperative organ injury: observational cohort study

OBJECTIVE

To examine whether supraphysiological oxygen administration during surgery is associated with lower or higher postoperative kidney, heart, and lung injury.

DESIGN

Observational cohort study.

SETTING

42 medical centers across the United States participating in the Multicenter Perioperative Outcomes Group data registry.

PARTICIPANTS

Adult patients undergoing surgical procedures ≥120 minutes' duration with general anesthesia and endotracheal intubation who were admitted to hospital after surgery between January 2016 and November 2018.

INTERVENTION

Supraphysiological oxygen administration, defined as the area under the curve of the fraction of inspired oxygen above air (21%) during minutes when the hemoglobin oxygen saturation was greater than 92%.

MAIN OUTCOMES

Primary endpoints were acute kidney injury defined using Kidney Disease Improving Global Outcomes criteria, myocardial injury defined as serum troponin >0.04 ng/mL within 72 hours of surgery, and lung injury defined using international classification of diseases hospital discharge diagnosis codes.

RESULTS

The cohort comprised 350 647 patients with median age 59 years (interquartile range 46-69 years), 180 546 women (51.5%), and median duration of surgery 205 minutes (interquartile range 158-279 minutes). Acute kidney injury was diagnosed in 19 207 of 297 554 patients (6.5%), myocardial injury in 8972 of 320 527 (2.8%), and lung injury in 13 789 of 312 161 (4.4%). The median fraction of inspired oxygen was 54.0% (interquartile range 47.5%-60.0%), and the area under the curve of supraphysiological inspired oxygen was 7951% min (5870-11 107% min), equivalent to an 80% fraction of inspired oxygen throughout a 135 minute procedure, for example. After accounting for baseline covariates and other potential confounding variables, increased oxygen exposure was associated with a higher risk of acute kidney injury, myocardial injury, and lung injury. Patients at the 75th centile for the area under the curve of the fraction of inspired oxygen had 26% greater odds of acute kidney injury (95% confidence interval 22% to 30%), 12% greater odds of myocardial injury (7% to 17%), and 14% greater odds of lung injury (12% to 16%) compared with patients at the 25th centile. Sensitivity analyses evaluating alternative definitions of the exposure, restricting the cohort, and conducting an instrumental variable analysis confirmed these observations.

CONCLUSIONS

Increased supraphysiological oxygen administration during surgery was associated with a higher incidence of kidney, myocardial, and lung injury. Residual confounding of these associations cannot be excluded.

TRIAL REGISTRATION

Open Science Framework osf.io/cfd2m.

Relationship of Effective Circulating Volume with Sublingual Red Blood Cell Velocity and Microvessel Pressure Difference: A Clinical Investigation and Computational Fluid Dynamics Modeling

The characteristics of physiologic hemodynamic coherence are not well-investigated. We examined the physiological relationship between circulating blood volume, sublingual microcirculatory perfusion, and tissue oxygenation in anesthetized individuals with steady-state physiology. We assessed the correlation of mean circulatory filling pressure analogue (Pmca) with sublingual microcirculatory perfusion and red blood cell (RBC) velocity using SDF+ imaging and a modified optical flow-based algorithm. We also reconstructed the 2D microvessels and applied computational fluid dynamics (CFD) to evaluate the correlation of Pmca and RBC velocity with the obtained pressure and velocity fields in microvessels from CFD (pressure difference, (Δp)). Twenty adults with a median age of 39.5 years (IQR 35.5−44.5) were included in the study. Sublingual velocity distributions were similar and followed a log-normal distribution. A constant Pmca value of 14 mmHg was observed in all individuals with sublingual RBC velocity 6−24 μm s−1, while a Pmca < 14 mmHg was observed in those with RBC velocity > 24 μm s−1. When Pmca ranged between 11 mmHg and 15 mmHg, Δp fluctuated between 0.02 Pa and 0.1 Pa. In conclusion, the intact regulatory mechanisms maintain a physiological coupling between systemic hemodynamics, sublingual microcirculatory perfusion, and tissue oxygenation when Pmca is 14 mmHg.

Association of Preoperative Basal Inflammatory State, Measured by Plasma suPAR Levels, with Intraoperative Sublingual Microvascular Perfusion in Patients Undergoing Major Non-Cardiac Surgery

It remains unknown whether chronic systemic inflammation is associated with impaired microvascular perfusion during surgery. We evaluated the association between the preoperative basal inflammatory state, measured by plasma soluble urokinase-type plasminogen activator receptor (suPAR) levels, and intraoperative sublingual microcirculatory variables in patients undergoing major non-cardiac surgery. Plasma suPAR levels were determined in 100 non-cardiac surgery patients using the suPARnostic® quick triage lateral flow assay. We assessed sublingual microcirculation before surgical incision and every 30 min during surgery using Sidestream Darkfield (SDF+) imaging and determined the De Backer score, the Consensus Proportion of Perfused Vessels (Consensus PPV), and the Consensus PPV (small). Elevated suPAR levels were associated with lower intraoperative De Backer score, Consensus PPV, and Consensus PPV (small). For each ng mL−1 increase in suPAR, De Backer score, Consensus PPV, and Consensus PPV (small) decreased by 0.7 mm−1, 2.5%, and 2.8%, respectively, compared to baseline. In contrast, CRP was not significantly correlated with De Backer score (r = −0.034, p = 0.36), Consensus PPV (r = −0.014, p = 0.72) or Consensus PPV Small (r = −0.037, p = 0.32). Postoperative De Backer score did not change significantly from baseline (5.95 ± 3.21 vs. 5.89 ± 3.36, p = 0.404), while postoperative Consensus PPV (83.49 ± 11.5 vs. 81.15 ± 11.8, p < 0.001) and Consensus PPV (small) (80.87 ± 13.4 vs. 78.72 ± 13, p < 0.001) decreased significantly from baseline. In conclusion, elevated preoperative suPAR levels were associated with intraoperative impairment of sublingual microvascular perfusion in patients undergoing elective major non-cardiac surgery.

Soluble Urokinase Receptor Levels Are Not Affected by the Systemic Inflammatory Response to Anesthesia and Operative Trauma

INTRODUCTION

Soluble urokinase plasminogen activator receptor (suPAR) is an emerging biomarker of the level of chronic systemic inflammation and the general condition of the patient. We aimed to investigate the impact of general anesthesia and major surgery on perioperative suPAR and C-reactive protein (CRP) levels.

METHODS

This study included patients undergoing elective major noncardiac surgery with an expected duration of ≥2 h under general anesthesia. Inclusion criteria were age ≥18 years and American Society of Anesthesiologists' physical status I-IV. Blood was drawn 30 min prior to induction of anesthesia (preoperatively), as well as 30 min after emergence from anesthesia (postoperatively). Plasma suPAR levels were determined using the suPARnostic® Quick Triage lateral flow assay. CRP measurements were performed by particle-enhanced immunoturbidimetric assay.

RESULTS

The difference in preoperative and postoperative suPAR levels was not statistically significant (7.7 [5.28-10.4] ng/mL vs. 7.15 [5.68-9.8] ng/mL, p = 0.462). CRP levels increased significantly during surgery (0.81 [0.24-2.1] mg/dL vs. 5.76 [2.2-8.75] mg/dL, p < 0.001). No correlation was observed between CRP and suPAR levels, both preoperatively (rho = 0.127; p = 0.208) and postoperatively (rho = 0.017; p = 0.87). A statistically significant increase was also observed in postoperative white blood cell count (7.576 vs. 10.711, p < 0.001).

CONCLUSION

General anesthesia and operative trauma did not affect perioperative suPAR levels despite the activation of systemic inflammatory response.

Association of Passive Lung Insufflation Oxygen Fraction in Adult Patients on Cardiopulmonary Bypass with Postoperative Pulmonary Outcomes: A Retrospective Cohort Study

OBJECTIVES

To determine whether F_IO₂ of passive lung insufflation during cardiopulmonary bypass correlates with postoperative pulmonary function.

DESIGN

A retrospective, observational study SETTING: A single-center, university-affiliated, specialist cardiothoracic center in the United Kingdom.

PARTICIPANTS

Adult patients presenting for nonemergency, nontransplant cardiac surgery requiring cardiopulmonary bypass without the need for deep hypothermic circulatory arrest between January 1, 2018, and December 31, 2018.

INTERVENTIONS

Passive insufflation of the lungs during cardiopulmonary bypass with fresh gas flow of varying F_IO₂. Patients were sorted retrospectively into low F_IO₂ (0.21-0.44), intermediate F_IO₂ (0.45-0.69), and high F_IO₂ (0.7-1.0) groups. The primary outcome was the difference between the PaO₂:F_IO₂ on the first postinduction blood gas and on the first blood gas recorded postoperatively in the intensive care unit (ICU) (delta PaO₂:F_IO₂). Secondary outcomes were ICU and hospital lengths of stay, requirement for respiratory support, and 30-day mortality.

MEASUREMENTS AND MAIN RESULTS

Nine hundred patients were included in the authors' analysis (low F_IO₂ n = 307, intermediate F_IO₂ n = 459, high F_IO₂ n = 134). There was no significant difference in delta PaO₂:F_IO₂ among the groups (low F_IO₂ = 52.5 [-38.8 to 152.4], intermediate F_IO₂ = 71.8 [-39.4 to 165.1], high F_IO₂ = 60.2 [-19.2 to 184.0], p = 0.25). There were no significant differences among groups for any secondary outcomes.

CONCLUSION

Fresh gas flow with a low F_IO₂ delivered to the lungs without positive airway pressure during cardiopulmonary bypass was not associated with improved postoperative pulmonary function when compared to higher F_IO₂ levels.

Thinking Out-of-the-Box: A Non-Standard Application of Standard Pulse-Oximetry and Standard Near-Infrared Spectroscopy in a COVID-19 Patient

PURPOSE

Purpose of this report is to describe the feasibility of lingual pulse oximetry and lingual near-infrared spectroscopy (NIRS) in a COVID-19 patient to assess lingual tissue viability after several days of mechanical ventilation in the prone position.

MATERIALS & METHODS

In a COVID-19 ICU-patient, the tongue became grotesquely swollen, hardened and protruding from the oral cavity after 20 h of mechanical ventilation uninterrupted in the prone position. To assess the doubtful viability of the tongue, pulse-oximetric hemoglobin O2-saturation (SpO2; Nellcor, OxiMax MAX-NI, Covidien, MA, USA) and NIRS-based, regional tissue O2-saturation measurements (rSO2; SenSmart, Nonin, MN, USA) were performed at the tongue.

RESULTS

At the tongue, regular pulse-oximetric waveforms with a pulse-oximetric hemoglobin O2-saturation (SpO2) of 88% were recorded, i.e. only slightly lower than the SpO2 reading at the extremities at that time (90%). Lingual NIRS-based rSO2 measurements yielded stable tissue rSO2-values of 76-78%, i.e. values expected also in other adequately perfused and oxygenated (muscle-) tissues.

CONCLUSION

Despite the alarming, clinical finding of a grotesquely swollen, rubber-hard tongue and clinical concerns on the adequacy of the tongue perfusion and oxygenation, our measurements of both arterial pulsatility (SpO2) and NIRS-based tissue oxygenation (rSO2) suggested adequate perfusion and oxygenation of the tongue, rendering non-vitality of the tongue, e.g. by lingual venous thrombosis, unlikely. To our knowledge, this is the first clinical report of lingual rSO2 measurement.

Oxygen for interstitial lung diseases

PURPOSE OF REVIEW

Supplemental oxygen therapy is prescribed for management of hypoxaemia in patients with interstitial lung disease (ILD). This review summarizes current evidence and implications of the use of supplemental oxygen therapy at home and during exercise training in ILD.

RECENT FINDINGS

Despite the significance of hypoxaemia in patients with ILD, there is a lack of high-quality evidence to guide the use of oxygen therapy in this population. Recent studies suggest that ambulatory oxygen may improve symptoms and health-related quality of life in patients with ILD. Long-term oxygen therapy for resting hypoxaemia in ILD is recommended by international guidelines. Supplemental oxygen during exercise may augment training effects, whereas therapeutic effects of nocturnal oxygen therapy are yet to be evaluated in patients with ILD. Nevertheless, it is important to consider the potential burden imposed by oxygen therapy on patients' daily activities of living.

SUMMARY

Ambulatory oxygen may be considered in ILD patients with exertional hypoxaemia, with long-term oxygen therapy being a standard care for resting hypoxaemia. Trials are currently underway to clarify therapeutic potentials of supplemental oxygen for exertional hypoxaemia and during exercise training in ILD patients, with additional research needed for the evaluation of nocturnal oxygen therapy.