Hypoxia: developments in basic science, physiology and clinical studies

A New Methodology for the Oxygen Measurement in Lung Tissue of an Aged Ferret Model Proves Hypoxia during COVID-19

Oxygen as a key element has a high impact on cellular processes. Infection with a pathogen such as SARS-CoV-2 and after inflammation may lead to hypoxic conditions in tissue that impact cellular responses. To develop optimized translational in vitro models for a better understanding of physiologic and pathophysiologic oxygen conditions, it is a prerequisite to determine oxygen concentrations generated in vivo. Our study objective was the establishment of an invasive method for oxygen measurements using a luminescence-based microsensor to determine the dissolved oxygen in the lung tissue of ferrets as animal models for SARS-CoV-2 research. By way of analogy to humans, aged ferrets are more likely to show clinical signs after SARS-CoV-2 infection than are young animals. To investigate oxygen concentrations during a respiratory viral infection, we intratracheally infected nine aged (3-yr-old) ferrets with SARS-CoV-2. The aged SARS-CoV-2-infected ferrets showed mild to moderate clinical signs associated with prolonged viral RNA shedding until 14 days postinfection. SARS-CoV-2-infected ferrets showed histopathologic lung lesion scores that significantly negatively correlated with oxygen concentrations in lung tissue. At 4 days postinfection, oxygen concentrations in lung tissue were significantly lower (mean percentage O2, 3.89 ≙ ≈ 27.78 mm Hg) than in the negative control group (mean percentage O2, 8.65 ≙ ≈ 61.4 mm Hg). In summary, we succeeded in determining the pathophysiologic oxygen conditions in the lung tissue of aged SARS-CoV-2-infected ferrets.

High-flow nasal oxygen for children's airway surgery to reduce hypoxaemic events: a randomised controlled trial

BACKGROUND

Tubeless upper airway surgery in children is a complex procedure in which surgeons and anaesthetists share the same operating field. These procedures are often interrupted for rescue oxygen therapy. The efficacy of nasal high-flow oxygen to decrease the frequency of rescue interruptions in children undergoing upper airway surgery is unknown.

METHODS

In this multicentre randomised trial conducted in five tertiary hospitals in Australia, children aged 0-16 years who required tubeless upper airway surgery were randomised (1:1) by a web-based randomisation tool to either nasal high-flow oxygen delivery or standard oxygen therapy (oxygen flows of up to 6 L/min). Randomisation was stratified by site and age (<1 year, 1-4 years, and 5-16 years). Subsequent tubeless upper airway surgery procedures in the same child could be included if there were more than 2 weeks between the procedures, and repeat surgical procedures meeting this condition were considered to be independent events. The oxygen therapy could not be masked, but the investigators remained blinded until outcome data were locked. The primary outcome was successful anaesthesia without interruption of the surgical procedure for rescue oxygenation. A rescue oxygenation event was defined as an interruption of the surgical procedure to deliver positive pressure ventilation using either bag mask technique, insertion of an endotracheal tube, or laryngeal mask to improve oxygenation. There were ten secondary outcomes, including the proportion of procedures with a hypoxaemic event (SpO2 <90%). Analyses were done on an intention-to-treat (ITT) basis. Safety was assessed in all enrolled participants. This trial is registered in the Australian New Zealand Clinical Trials Registry, ACTRN12618000949280, and is completed.

FINDINGS

From Sept 4, 2018, to April 12, 2021, 581 procedures in 487 children were randomly assigned to high-flow oxygen (297 procedures) or standard care (284 procedures); after exclusions, 528 procedures (267 assigned to high-flow oxygen and 261 assigned to standard care) in 483 children (293 male and 190 female) were included in the ITT analysis. The primary outcome of successful anaesthesia without interruption for tubeless airway surgery was achieved in 236 (88%) of 267 procedures on high-flow oxygen and in 229 (88%) of 261 procedures on standard care (adjusted risk ratio [RR] 1·02, 95% CI 0·96-1·08, p=0·82). There were 51 (19%) procedures with a hypoxaemic event in the high-flow oxygen group and 57 (22%) in the standard care group (RR 0·86, 95% CI 0·58-1·24). Of the other prespecified secondary outcomes, none showed a significant difference between groups. Adverse events of epistaxis, laryngospasm, bronchospasm, hypoxaemia, bradycardia, cardiac arrest, hypotension, or death were similar in both study groups.

INTERPRETATION

Nasal high-flow oxygen during tubeless upper airway surgery did not reduce the proportion of interruptions of the procedures for rescue oxygenation compared with standard care. There were no differences in adverse events between the intervention groups. These results suggest that both approaches, nasal high-flow or standard oxygen, are suitable alternatives to maintain oxygenation in children undergoing upper airway surgery.

FUNDING

Thrasher Research Fund, the Australian and New Zealand College of Anaesthetists, the Society for Paediatric Anaesthesia in New Zealand and Australia.

Reduced hydrogen sulfide production contributes to adrenal insufficiency induced by hypoxia via modulation of NLRP3 inflammasome activation

Objective: Adrenocortical responsiveness is critical for maintaining glucocorticoids production and homeostasis during stress. We sought to investigate adrenocortical responsiveness during hypoxia in mice and the mechanisms responsible for the regulation of adrenal responsiveness.Methods: (1) Adult male WT mice were randomly divided into four groups: normoxia, hypoxia (24h), hypoxia (72h), hypoxia (72h) + GYY4137(hydrogen sulfide (H₂S) donor, 133mmol/kg/day); (2) WT mice were randomly divided into four groups: sham, adrenalectomy (ADX), sham+hypoxia, ADX+hypoxia; (3) Cse^-/- mice were randomly divided into two groups: Cse^-/-, Cse^-/- +GYY4137.Results: The circulatory level of corticosteroid induced by ACTH stimulation was significantly reduced in the mice with hypoxia compared with control mice. The mortality rate induced by lipopolysaccharide (LPS) increased during hypoxia. Cystathionine-γ-lyase (CSE) expression was significantly reduced in adrenal glands during hypoxia. GYY4137 treatment significantly increased adrenal responsiveness and attenuated NLRP3 inflammasome activation in mice treated by hypoxia and Cse^-/- mice. Furthermore, The sulfhydrated level of PSMA7 in adrenal gland was decreased in the mice with hypoxia and Cse^-/- mice. PSMA7 was S-sulfhydrated at cysteine 70. Blockage of S-sulfhydration of PSMA7 increased NLRP3 expression in adrenocortical cells.Conclusion: Reduced H₂S production mediated hypo-adrenocortical responsiveness and NLRP3 inflammasome activation via PAMA7 S-sulfhydration during hypoxia.

Early Titration of Oxygen During Mechanical Ventilation Reduces Hyperoxemia in a Pilot, Feasibility, Randomized Control Trial for Automated Titration of Oxygen Levels

Timely regulation of oxygen (Fio₂) is essential to prevent hyperoxemia or episodic hypoxemia. Exposure to excessive Fio₂ is often noted early after onset of mechanical ventilation. In this pilot study, we examined the feasibility, safety, and efficacy of a clinical trial to prioritize Fio₂ titration with electronic alerts to respiratory therapists.

Navigating Uncertainty in Respiratory Assessment: The Interaction of Culture and Technology During Phase I Postanesthetic Recovery

PURPOSE

To explore postanesthesia care unit (PACU) nurses' interactions with technology during the critical Phase I recovery period.

DESIGN

Interpretive description was used to understand nurses' experiences.

METHODS

Nine PACU nurses were recruited from three mid-sized hospitals within the same health authority in a Western Canadian province. Nurse participants were interviewed using a semistructured interview guide.

FINDINGS

Nurses' interactions with technology were significantly influenced by PACU culture, as they constantly navigated a level of uncertainly about their patient's respiratory status. Three themes from the study are described. Theme 1 described nurses' confidence and trust in a visual sensory respiratory assessment process and the influence of anesthesia providers. Theme 2 described PACU nurses' guarded trust or rationalized mistrust in technology. Theme 3 highlighted the contextual influences, which sustained nurses' approach to respiratory assessment.

CONCLUSIONS

PACU nurses practiced their intuitive sensory assessments with a projected strong sense of expert practice and minimal dependence on technology. PACU nurses expressed frustrations with current PACU bedside technology, particularly the respiratory module and described some experiences with delayed identification of hypoventilation and hypoxia. Rationalized behaviors with technology and alarm suppression were commonplace. Workplace culture sustained PACU nurses' respiratory assessment practices.

Which Anesthesia Regimen Is Best to Reduce Pulmonary Complications After Head and Neck Surgery?

OBJECTIVES/HYPOTHESIS

The differences between intravenous and inhalation anesthesia in clinical postoperative pulmonary complications (PPCs) have been studied in cardiac and lung resection surgery. Clinical evidence for the effects of these two anesthetics on PPCs in other types of surgery is still missing. We aimed to assess the impact of sevoflurane and propofol on the incidence of PPCs in patients undergoing surgery for head and neck cancer.

STUDY DESIGN

Double-blind, randomized, controlled trial.

METHODS

We assigned 220 adults at intermediate-to-high risk of PPCs scheduled for head and neck cancer surgery with radial forearm or fibular flap reconstruction to either propofol or sevoflurane as a general anesthetic. The occurrence of pulmonary complications according to the Clavien-Dindo score was defined as the primary (within 7 days after surgery) outcome.

RESULTS

The PPC incidence during 7 days after surgery was 32.4% and 18.2% in the propofol and sevoflurane groups, respectively (P = .027). The corresponding incidence of PPCs in patients who underwent tracheotomy at the end of surgery in the two groups was 44.8% and 24.5%, respectively (P = .030). In addition, the Clavien-Dindo classification showed significant differences between groups in minor complications (grades I and II) but not in major complications (grades III-V).

CONCLUSIONS

Compared with intravenous anesthesia, the administration of sevoflurane reduces the incidence of minor PPCs (grades I and II) in moderate- and high-risk patients who have undergone tracheotomy after head and neck cancer surgery with radial forearm or fibular flap reconstruction.

LEVEL OF EVIDENCE

2 Laryngoscope, 131:E108-E115, 2021.

Nasal high-flow oxygen in pediatric anesthesia and airway management

Nasal High-Flow (NHF) is weight-dependent in children, aimed to match peak inspiratory flow and thereby deliver an accurate FiO₂ with a splinting pressure of 4-6 cm H₂ O. During apnea in children, NHF oxygen can double the expected time to desaturation below 90% in well children but there is no ventilatory exchange; therefore, children do not "THRIVE". Total intravenous anesthesia competency to maintain spontaneous breathing is an important adjunct for successful NHF oxygenation technique during anesthesia. Jaw thrust to maintain a patent upper airway is paramount until surgical instrumentation occurs. There is no evidence to support safe use of NHF oxygen with LASER use due to increased risk of airway fire.

Ketamine ameliorates hypoxia-induced endothelial injury in human umbilical vein endothelial cells

OBJECTIVES

Hypoxia leads to endothelial cell inflammation, apoptosis, and damage, which plays an important role in the complications associated with ischemic cardiovascular disease. As an oxidoreductase, p66Shc plays an important role in the regulation of reactive oxygen species (ROS) production and apoptosis. Ketamine is widely used in clinics. This study was designed to assess the potential protective effect of ketamine against hypoxia-induced injury in human umbilical vein endothelial cells (HUVECs). Moreover, we explored the potential mechanism by which ketamine protected against hypoxia-induced endothelial injury.

METHODS

The protective effects of ketamine against hypoxia-induced injury was assessed using cell viability and adhesion assays, quantitative polymerase chain reaction, and western blotting.

RESULTS

Our data showed that hypoxia reduced HUVEC viability, increased the adhesion between HUVECs and monocytes, and upregulated the expression of endothelial adhesion molecules at the protein and mRNA levels. Moreover, hypoxia increased ROS accumulation and upregulated p66Shc expression. Furthermore, hypoxia downregulated sirt1 expression in HUVECs. Alternatively, ketamine was shown to reverse the hypoxia-mediated reduction of cell viability and increase in the adhesion between HUVECs and monocytes, ameliorate hypoxia-induced ROS accumulation, and suppress p66Shc expression. Moreover, EX527, a sirt1 inhibitor, reversed the protective effects of ketamine against the hypoxia-mediated reduction of cell viability and increase in adhesion between HUVECs and monocytes.

CONCLUSION

Ketamine reduces hypoxia-induced p66Shc expression and attenuates ROS accumulation via upregulating sirt1 in HUVECs, thus attenuating hypoxia-induced endothelial cell inflammation and apoptosis.

Apneic Oxygenation for Pediatric Endotracheal Intubation: A Narrative Review

Apneic oxygenation (ApOx) has shown to be effective in adult populations in a variety of settings, including prehospital, emergency departments, intensive care units, and elective surgery. This review aims to assess the available literature for ApOx in the pediatric population to determine its effects on hypoxemia, safe apnea times, and flow rates employed safely.

Effects of low-dose intraoperative fentanyl on postoperative respiratory complication rate: a pre-specified, retrospective analysis

BACKGROUND

Fentanyl is one of the most frequently administered intraoperative drugs and may increase the risk of postoperative respiratory complications (PRCs).

METHODS

We performed a pre-specified analysis of 145 735 adult non-cardiac surgical cases under general anaesthesia. Using multivariable logistic regression, we evaluated the association of intraoperative fentanyl dose and PRCs within 3 days after surgery (defined as reintubation, respiratory failure, pneumonia, pulmonary oedema, or atelectasis). We examined effect modification by patient characteristics, surgical site, and anaesthetics used.

RESULTS

PRCs within 3 days after surgery occurred in 18 839 (12.9%) patients. In comparison with high intraoperative fentanyl doses [median: 3.85; inter-quartile range (IQR): 3.42-4.50 μg kg^-1, quartile 4 (Q4)], low intraoperative fentanyl dose [median: 0.80, IQR: 0.00-1.14 μg kg^-1, quartile 1 (Q1)] was significantly associated with lower odds of PRCs [Q1 vs Q4: 10.9% vs 16.2%; adjusted odds ratio (aOR) 0.79; 95% confidence intervals (CI) 0.75-0.84; P<0.001; adjusted absolute risk difference (aARD) -1.7%]. This effect was augmented by thoracic surgery (P for interaction <0.001; aARD -6.2%), high doses of inhalation anaesthetics (P for interaction=0.016; aARD -2.2%) and neuromuscular blocking agents (NMBAs) (P for interaction=0.001; aARD -3.4%). Exploratory analysis demonstrated that compared with no fentanyl, low-dose fentanyl was associated with lower rates of PRCs (decile 2 vs decile 1: aOR 0.82, CI 0.75-0.89, P<0.001).

CONCLUSIONS

Intraoperative low-dose fentanyl (about 60-120 μg for a 70 kg patient) was associated with lower risk of postoperative respiratory complications compared with both no fentanyl and high-dose fentanyl. Beneficial effects of low-dose fentanyl were magnified in specific patient subgroups.

CLINICAL TRIAL REGISTRATION

NCT03198208.

Effects of Positive End-Expiratory Pressure on the Risk of Postoperative Pulmonary Complications in Patients Undergoing Elective Craniotomy

BACKGROUND

Intraoperative use of positive end-expiratory pressure (PEEP) has a protective effect in patients with acute lung injury and is recommended during anesthesia to minimize postoperative pulmonary complications. However, high levels of pressure might also cause harm to the lung because of overdistension. This retrospective study was designed to compare the effect of low and high levels of PEEP on the risk of postoperative pulmonary complications in patients with normal lung function who were undergoing an elective craniotomy.

METHODS

Two thousand four hundred thirty-seven patients without any pre-existing respiratory disease, who underwent an elective craniotomy, were hospitalized from January 1, 2008, to December 31, 2012. The patients were divided into 2 groups according to the application of an intraoperative PEEP < 5 or ≥ 5 cm H₂O, referred as low and high groups. Primary outcome was the odds of postoperative pneumonia and the requirement for either noninvasive ventilation (NIV) or reintubation and mechanical ventilation (MV).

RESULTS

One thousand twenty-three (42%) of 2437 patients were in the low group, and 1414 patients (58%) were in the high group. Patients in the low group did not show any difference in the incidence of postoperative pneumonia (P = 0.523) or the requirement of postoperative reintubation and MV (P = 0.999) compared with those in the high group. The incidence of reintubation and MV is significantly associated with postoperative pneumonia (P < 0.001).

CONCLUSIONS

Low and high levels of PEEP show similar incidences of postoperative pneumonia and requirement of postoperative NIV or invasive MV in patients with normal function of the lungs undergoing elective craniotomy.

Lung protective ventilation in patients undergoing major surgery: a systematic review incorporating a Bayesian approach

OBJECTIVE

Protective ventilation (PV) has been validated in patients with acute respiratory distress syndrome. However, the effect of PV in patients undergoing major surgery is controversial. The study aimed to explore the beneficial effect of PV on patients undergoing a major operation by systematic review and meta-analysis.

SETTING

Various levels of medical centres.

PARTICIPANTS

Patients undergoing general anaesthesia.

INTERVENTIONS

PV with low tidal volume.

PRIMARY AND SECONDARY OUTCOME MEASURES

Study end points included acute lung injury (ALI), pneumonia, atelectasis, mortality, length of stay (LOS) in intensive care unit (ICU) and hospital.

METHODS

Databases including PubMed, Scopus, EBSCO and EMBASE were searched from inception to May 2015. Search strategies consisted of terms related to PV and anaesthesia. We reported OR for binary outcomes including ALI, mortality, pneumonia, atelectasis and other adverse outcomes. Weighted mean difference was reported for continuous outcomes such as LOS in the ICU and hospital, pH value, partial pressure of carbon dioxide, oxygenation and duration of mechanical ventilation (MV).

MAIN RESULTS

A total of 22 citations were included in the systematic review and meta-analysis. PV had protective effect against the development of ALI as compared with the control group, with an OR of 0.41 (95% CI 0.19 to 0.87). PV tended to be beneficial with regard to the development of pneumonia (OR 0.46, 95% CI 0.16 to 1.28) and atelectasis (OR 0.68, 95% CI 0.46 to 1.01), but statistical significance was not reached. Other adverse outcomes such as new onset arrhythmia were significantly reduced with the use of PV (OR 0.47, 95% CI 0.48 to 0.93).

CONCLUSIONS

The study demonstrates that PV can reduce the risk of ALI in patients undergoing major surgery. However, there is insufficient evidence that such a beneficial effect can be translated to more clinically relevant outcomes such as mortality or duration of MV.

TRIAL REGISTRATION NUMBER

The study was registered in PROSPERO (http://www.crd.york.ac.uk/PROSPERO/) under registration number CRD42013006416.

TASK channels in arterial chemoreceptors and their role in oxygen and acid sensing

Arterial chemoreceptors play a vital role in cardiorespiratory control by providing the brain with information regarding blood oxygen, carbon dioxide, and pH. The main chemoreceptor, the carotid body, is composed of sensory (type 1) cells which respond to hypoxia or acidosis with a depolarising receptor potential which in turn activates voltage-gated calcium entry, neurosecretion and excitation of adjacent afferent nerves. The receptor potential is generated by inhibition of Twik-related acid-sensitive K(+) channel 1 and 3 (TASK1/TASK3) heterodimeric channels which normally maintain the cells' resting membrane potential. These channels are thought to be directly inhibited by acidosis. Oxygen sensitivity, however, probably derives from a metabolic signalling pathway. The carotid body, isolated type 1 cells, and all forms of TASK channel found in the type 1 cell, are highly sensitive to inhibitors of mitochondrial metabolism. Moreover, type1 cell TASK channels are activated by millimolar levels of MgATP. In addition to their role in the transduction of chemostimuli, type 1 cell TASK channels have also been implicated in the modulation of chemoreceptor function by a number of neurocrine/paracrine signalling molecules including adenosine, GABA, and serotonin. They may also be instrumental in mediating the depression of the acute hypoxic ventilatory response that occurs with some general anaesthetics. Modulation of TASK channel activity is therefore a key mechanism by which the excitability of chemoreceptors can be controlled. This is not only of physiological importance but may also offer a therapeutic strategy for the treatment of cardiorespiratory disorders that are associated with chemoreceptor dysfunction.

Oxygen supersaturated fluid using fine micro/nanobubbles

Microbubbles show peculiar properties, such as shrinking collapse, long lifetime, high gas solubility, negative electric charge, and free radical production. Fluids supersaturated with various gases can be easily generated using microbubbles. Oxygen microbubble fluid can be very useful for oxygen delivery to hypoxic tissues. However, there have been no reports of comparative investigations into adding fluids containing oxygen fine micro/nanobubbles (OFM-NBs) to common infusion solutions in daily medical care. In this study, it was demonstrated that OFMNBs can generate oxygen-supersaturated fluids, and they may be sufficiently small to infuse safely into blood vessels. It was found that normal saline solution is preferable for generating an oxygen-rich infusion fluid, which is best administered as a 30-minute intravenous infusion. It was also concluded that dextran solution is suitable for drug delivery substances packing oxygen gas over a 1-hour intravenous infusion. In addition, normal saline solution containing OFMNBs was effective for improving blood oxygenation. Thus, the use of OFMNB-containing fluids is a potentially effective novel method for improving blood oxygenation in cases involving hypoxia, ischemic diseases, infection control, and anticancer chemoradiation therapies.

Adverse respiratory events in a post-anesthesia care unit

INTRODUCTION

Adverse respiratory events (ARE) are a leading causes of postoperative morbidity and mortality. This study investigated the incidence and determinants of postoperative ARE.

METHODS

This observational prospective study was conducted in a post anesthesia care unit (PACU). A total of 340 adult subjects were admitted consecutively, and AREs were measured after elective surgery. Population demographics, perioperative parameters, ARE occurrence, and length of stay in the postoperative PACU and in hospital were recorded. Data were analyzed descriptively using the Mann-Whitney U-test and the Chi-square or Fisher's exact test. Multivariate analyses were carried outusing logistic binary regression, and the odds ratio (OR) and 95% confidence interval (CI) were calculated.

RESULTS

Postoperative AREs occurred in 67 subjects (19.7%). AREs were more frequent after high-risk procedures (42% vs 24%; P=.003), in patients undergoing major surgery (37% vs 25%; P=.041), those receiving general anesthesia (85% vs 67%; P=.004), and in patients administered intraoperative muscle relaxants (79% vs 55%; P<.001) and neostigmine (69% vs 49%; P=.002). Hypoactive emergence (13% vs 5%; P=.015) and residual neuromuscular blockade (46% versus 11%; P<.001) were more frequent in subjects with postoperative ARE. On multivariate analyses, residual neuromuscular blockade was an independent risk factor for ARE in the PACU (OR 6.4; CI 3.0-13.4; P<.001).

CONCLUSIONS

ARE is an important and common postoperative complication. Residual neuromuscular blockade was an independent risk factor for ARE in the PACU.

Blood oxygenation using microbubble suspensions

Microbubbles have been used in a variety of fields and have unique properties, for example shrinking collapse, long lifetime, efficient gas solubility, a negatively charged surface, and the ability to produce free radicals. In medicine, microbubbles have been used mainly as diagnostic aids to scan various organs of the body, and they have recently been investigated for use in drug and gene delivery. However, there have been no reports of blood oxygenation by use of oxygen microbubble fluids without shell reagents. In this study, we demonstrated that nano or microbubbles can achieve oxygen supersaturation of fluids, and may be sufficiently small and safe for infusion into blood vessels. Although Po(2) increases in fluids resulting from use of microbubbles were inhibited by polar solvents, normal saline solution (NSS) was little affected. Thus, NSS is suitable for production of oxygen-rich fluid. In addition, oxygen microbubble NSS effectively improved hypoxic conditions in blood. Thus, use of oxygen microbubble (nanobubble) fluids is a potentially effective novel method for oxygenation of hypoxic tissues, for infection control, and for anticancer treatment.