Electric Cell-Substrate Impedance Sensing (ECIS) as a Platform for Evaluating Barrier-Function Susceptibility and Damage from Pulmonary Atelectrauma.

Biophysical insults that either reduce barrier function (COVID-19, smoke inhalation, aspiration, and inflammation) or increase mechanical stress (surfactant dysfunction) make the lung more susceptible to atelectrauma. We investigate the susceptibility and time-dependent disruption of barrier function associated with pulmonary atelectrauma of epithelial cells that occurs in acute respiratory distress syndrome (ARDS) and ventilator-induced lung injury (VILI). This in vitro study was performed using Electric Cell-substrate Impedance Sensing (ECIS) as a noninvasive evaluating technique for repetitive stress stimulus/response on monolayers of the human lung epithelial cell line NCI-H441. Atelectrauma was mimicked through recruitment/derecruitment (RD) of a semi-infinite air bubble to the fluid-occluded micro-channel. We show that a confluent monolayer with a high level of barrier function is nearly impervious to atelectrauma for hundreds of RD events. Nevertheless, barrier function is eventually diminished, and after a critical number of RD insults, the monolayer disintegrates exponentially. Confluent layers with lower initial barrier function are less resilient. These results indicate that the first line of defense from atelectrauma resides with intercellular binding. After disruption, the epithelial layer community protection is diminished and atelectrauma ensues. ECIS may provide a platform for identifying damaging stimuli, ventilation scenarios, or pharmaceuticals that can reduce susceptibility or enhance barrier-function recovery.

Perioperative Pulmonary Atelectasis: Part II. Clinical Implications.

The development of pulmonary atelectasis is common in the surgical patient. Pulmonary atelectasis can cause various degrees of gas exchange and respiratory mechanics impairment during and after surgery. In its most serious presentations, lung collapse could contribute to postoperative respiratory insufficiency, pneumonia, and worse overall clinical outcomes. A specific risk assessment is critical to allow clinicians to optimally choose the anesthetic technique, prepare appropriate monitoring, adapt the perioperative plan, and ensure the patient's safety. Bedside diagnosis and management have benefited from recent imaging advancements such as lung ultrasound and electrical impedance tomography, and monitoring such as esophageal manometry. Therapeutic management includes a broad range of interventions aimed at promoting lung recruitment. During general anesthesia, these strategies have consistently demonstrated their effectiveness in improving intraoperative oxygenation and respiratory compliance. Yet these same intraoperative strategies may fail to affect additional postoperative pulmonary outcomes. Specific attention to the postoperative period may be key for such outcome impact of lung expansion. Interventions such as noninvasive positive pressure ventilatory support may be beneficial in specific patients at high risk for pulmonary atelectasis (e.g., obese) or those with clinical presentations consistent with lung collapse (e.g., postoperative hypoxemia after abdominal and cardiothoracic surgeries). Preoperative interventions may open new opportunities to minimize perioperative lung collapse and prevent pulmonary complications. Knowledge of pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should provide the basis for current practice and help to stratify and match the intensity of selected interventions to clinical conditions.

Perioperative Pulmonary Atelectasis: Part I. Biology and Mechanisms.

Pulmonary atelectasis is common in the perioperative period. Physiologically, it is produced when collapsing forces derived from positive pleural pressure and surface tension overcome expanding forces from alveolar pressure and parenchymal tethering. Atelectasis impairs blood oxygenation and reduces lung compliance. It is increasingly recognized that it can also induce local tissue biologic responses, such as inflammation, local immune dysfunction, and damage of the alveolar-capillary barrier, with potential loss of lung fluid clearance, increased lung protein permeability, and susceptibility to infection, factors that can initiate or exaggerate lung injury. Mechanical ventilation of a heterogeneously aerated lung (e.g., in the presence of atelectatic lung tissue) involves biomechanical processes that may precipitate further lung damage: concentration of mechanical forces, propagation of gas-liquid interfaces, and remote overdistension. Knowledge of such pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should guide optimal clinical management.

Prevalence and clinical consequences of atelectasis in SARS-CoV-2 pneumonia: a computed tomography retrospective cohort study.

BACKGROUND: The aim of the study is to estimate the prevalence of atelectasis assessed with computer tomography (CT) in SARS-CoV-2 pneumonia and the relationship between the amount of atelectasis with oxygenation impairment, Intensive Care Unit admission rate and the length of in-hospital stay. PATIENTS AND METHODS: Two-hundred thirty-seven patients admitted to the hospital with SARS-CoV-2 pneumonia diagnosed by clinical, radiology and molecular tests in the nasopharyngeal swab who underwent a chest computed tomography because of a respiratory worsening from Apr 1 to Apr 30, 2020 were included in the study. Patients were divided into three groups depending on the presence and amount of atelectasis at the computed tomography: no atelectasis, small atelectasis (< 5% of the estimated lung volume) or large atelectasis (> 5% of the estimated lung volume). In all patients, clinical severity, oxygen-therapy need, Intensive Care Unit admission rate, the length of in-hospital stay and in-hospital mortality data were collected. RESULTS: Thirty patients (19%) showed small atelectasis while eight patients (5%) showed large atelectasis. One hundred and seventeen patients (76%) did not show atelectasis. Patients with large atelectasis compared to patients with small atelectasis had lower SatO2/FiO2 (182 vs 411 respectively, p = 0.01), needed more days of oxygen therapy (20 vs 5 days respectively, p = 0,02), more frequently Intensive Care Unit admission (75% vs 7% respectively, p < 0.01) and a longer period of hospitalization (40 vs 14 days respectively p < 0.01). CONCLUSION: In patients with SARS-CoV-2 pneumonia, atelectasis might appear in up to 24% of patients and the presence of larger amount of atelectasis is associated with worse oxygenation and clinical outcome.

Driving Pressure-Guided Individualized Positive End-Expiratory Pressure in Abdominal Surgery: A Randomized Controlled Trial.

BACKGROUND: The optimal positive end-expiratory pressure (PEEP) to prevent postoperative pulmonary complications (PPCs) remains unclear. Recent evidence showed that driving pressure was closely related to PPCs. In this study, we tested the hypothesis that an individualized PEEP guided by minimum driving pressure during abdominal surgery would reduce the incidence of PPCs. METHODS: This single-centered, randomized controlled trial included a total of 148 patients scheduled for open upper abdominal surgery. Patients were randomly assigned to receive an individualized PEEP guided by minimum driving pressure or an empiric fixed PEEP of 6 cm H2O. The primary outcome was the incidence of clinically significant PPCs within the first 7 days after surgery, using a χ2 test. Secondary outcomes were the severity of PPCs, the area of atelectasis, and pleural effusion. Other outcomes, such as the incidence of different types of PPCs (including hypoxemia, atelectasis, pleural effusion, dyspnea, pneumonia, pneumothorax, and acute respiratory distress syndrome), intensive care unit (ICU) admission rate, length of hospital stay, and 30-day mortality were also explored. RESULTS: The median value of PEEP in the individualized group was 10 cm H2O. The incidence of clinically significant PPCs was significantly lower in the individualized PEEP group compared with that in the fixed PEEP group (26 of 67 [38.8%] vs 42 of 67 [62.7%], relative risk = 0.619, 95% confidence intervals, 0.435-0.881; P = .006). The overall severity of PPCs and the area of atelectasis were also significantly diminished in the individualized PEEP group. Higher respiratory compliance during surgery and improved intra- and postoperative oxygenation was observed in the individualized group. No significant differences were found in other outcomes between the 2 groups, such as ICU admission rate or 30-day mortality. CONCLUSIONS: The application of individualized PEEP based on minimum driving pressure may effectively decrease the severity of atelectasis, improve oxygenation, and reduce the incidence of clinically significant PPCs after open upper abdominal surgery.

Avoid the Trap: Nonexpanding Lung.

Nonexpanding lung is a mechanical complication in which part of the lung is unable to expand to the chest wall, preventing apposition of the visceral and parietal pleura. This can result from various visceral pleural disease processes, including malignant pleural effusion and empyema. Nonexpanding lung can be referred to as trapped lung or lung entrapment, both with distinct clinical features and management strategies. Early evaluation of pleural effusions is important to address underlying causes of pleural inflammation and to prevent the progression from lung entrapment to trapped lung. Some patients with trapped lung will not experience symptomatic relief with pleural fluid removal. Therefore, misrecognition of trapped lung can result in patients undergoing unnecessary procedures with significant cost and morbidity. We reviewed the current understanding of nonexpanding lung, which included causes, common presentations, preventative strategies, and recommendations for clinical care.

Analysis of the therapeutic effect and prognosis in 86 cases of rib fractures and atelectasis.

BACKGROUND: The aim of the present study was to explore the therapeutic effect and prognosis in patients with rib fractures and atelectasis after thoracic trauma in order to provide a basis for clinical decision-making in primary hospitals. METHODS: A retrospective study was conducted on 86 patients admitted to our hospital between January 2016 and May 2020 with rib fractures and atelectasis after thoracic trauma. On the basis of the chest computed tomography scans taken at the time of discharge, the patients were divided into two groups: the reexpansion group and the non-reexpansion group. The two groups were compared with respect to the changes observed in the patients' levels of blood oxygen saturation (SpO2) and pulmonary function, the presence of secondary pulmonary or thoracic infection, the time of chest tube drainage, the length of hospitalization, the cost of hospitalization, and the patients' level of satisfaction with their quality of life 3 months after discharge. RESULTS: In the reexpansion group, there were significant differences in the levels of SpO2 and pulmonary function measured before and after pulmonary reexpansion (P < 0.05). Compared with the non-reexpansion group, the patients in the reexpansion group had a lower incidence of secondary pulmonary and thoracic infection and a higher level of satisfaction with their quality of life after discharge; these differences were statistically significant (P < 0.05). There was no statistical significance between the two groups with respect to the time of chest tube drainage or the length of hospitalization (P > 0.05). However, the cost of hospitalization was significantly higher in the reexpansion group than in the non-reexpansion group (P < 0.05). CONCLUSIONS: The patients in the pulmonary reexpansion group had a lower incidence of complications and a better prognosis than the patients in the non-reexpansion group.

Indices of acceleration atelectasis and the effect of hypergravity duration on its development.

NEW FINDINGS: What is the central question of the study? The aim was to determine the effects of duration of acceleration in the cranial-caudal direction (+Gz) on acceleration atelectasis and identify measurement techniques that can be used to assess it. What is the main finding and its importance? Non-invasive measurement of acceleration atelectasis using electrical impedance tomography and estimates of pulmonary shunt provide more detailed assessment of acceleration atelectasis than traditional forced vital capacity measures. Using these techniques, it was found that as little as 30 s of exposure to +Gz acceleration can cause acceleration atelectasis. The results of the present study will allow a more accurate and detailed assessment of acceleration atelectasis in the future. ABSTRACT: Recently, there have been reports of acceleration atelectasis during fast jet flight despite the use of systems designed to minimize this. Before further investigation of this, indices suitable for use in applied settings and identification of acceleration durations that elicit it are required. Fifteen non-aircrew subjects underwented five centrifuge exposures lasting 15, 30, 60 and 2 × 90 s with a plateau of +5 Gz (acceleration in the cranial-caudal direction) while breathing 94% O2 during all but one control exposure (21% O2 ). Lung volumes and gas exchange limitation were assessed after each exposure. Regional lung impedance and compliance were measured after Gz exposure using electrical impedance tomography and the forced oscillatory technique, respectively. The presence of acceleration atelectasis was confirmed by reductions of 10-17% in vital and inspiratory capacity after 60 and 90 s Gz exposures (P < 0.05) and resulted in reduced regional lung impedance and a gas exchange limitation of 8.1 and 12.5%, respectively (P < 0.05). There was also a small but significant decrease in regional lung impedance after 30 s exposures. Functional residual capacity and lung compliance were unchanged in atelectatic lungs (P > 0.05). In the majority of individuals, >60 s of Gz exposure while breathing 94% O2 causes acceleration atelectasis. Electrical impedance tomography and the measurement of gas exchange limitation provide useful indicators of acceleration atelectasis. Acceleration atelectasis exerts its effects primarily through basal lung closure and reflex inspiratory limitation, both of which can be reversed by performing three maximal inspiratory breathing manoeuvres.

Caring for Patients with Spinal Cord Injuries.

The column in this issue is supplied by Juan Jose Olivero, MD, who was a nephrologist at Houston Methodist Hospital and a member of the hospital's Nephrology Training Program before his retirement in 2019. Dr. Olivero obtained his medical degree from the University of San Carlos School of Medicine in Guatemala, Central America, and completed his residency and nephrology fellowship at Baylor College of Medicine in Houston, Texas. He currently serves on the journal's editorial board and is editor of the "Points to Remember" section.

Central Airway Collapse, an Underappreciated Cause of Respiratory Morbidity.

Dyspnea, cough, sputum production, and recurrent respiratory infections are frequently encountered clinical concerns leading patients to seek medical care. It is not unusual for a well-defined etiology to remain elusive or for the therapeutics of a presumed etiology to be incompletely effective. Either scenario should prompt consideration of central airway pathology as a contributor to clinical manifestations. Over the past decade, recognition of dynamic central airway collapse during respiration associated with multiple respiratory symptoms has become more commonly appreciated. Expiratory central airway collapse may represent the answer to this diagnostic void. Expiratory central airway collapse is an underdiagnosed disorder that can coexist with and mimic asthma, chronic obstructive pulmonary disease, and bronchiectasis. Awareness of expiratory central airway collapse and its spectrum of symptoms is paramount to its recognition. This review includes clear definitions, diagnostics, and therapeutics for this challenging condition. We performed a narrative review through the PubMed (MEDLINE) database using the following MeSH terms: airway collapse, tracheobronchomalacia, tracheomalacia, and bronchomalacia. We include reports from systematic reviews, narrative reviews, clinical trials, and observational studies from 2005 to 2020. Two reviewers evaluated potential references. No systematic reviews were found. A total of 28 references were included into our review. Included studies report experience in the diagnosis and/or treatment of dynamic central airway collapse; case reports and non-English or non-Spanish studies were excluded. We describe the current diagnostic dilemma, highlighting the role of dynamic bronchoscopy and tracheobronchial stent trial; outline the complex therapeutic options (eg, tracheobronchoplasty); and present future directions and challenges.

Lung pulse visualized through pleural effusion as a diagnostic sign of complete obstructive atelectasis of the left lung in a critical patient with respiratory failure. / Pulso pulmonar visualizado a través de derrame pleural como signo diagnóstico de atelectasia obstructiva completa del pulmón izquierdo en paciente crítico con insuficiencia respiratoria.

Complete obstructive atelectasis occurs when mucous or a foreign body obstruct one of the main bronchi. Several lung ultrasound signs have been associated with this entity. We describe the case of a patient admitted to the surgical critical care unit in whom lung ultrasound led to a diagnosis of complete obstructive atelectasis, and the presence of pleural effusion provided direct visualization of lung pulse, a sign that has only previously been described by interpreting ultrasound artifacts.

Effects of intraoperative individualized PEEP on postoperative atelectasis in obese patients: study protocol for a prospective randomized controlled trial.

BACKGROUND: Obese patients undergoing general anesthesia and mechanical ventilation during laparoscopic abdominal surgery commonly have a higher incidence of postoperative pulmonary complications (PPCs), due to factors such as decreasing oxygen reserve, declining functional residual capacity, and reducing lung compliance. Pulmonary atelectasis caused by pneumoperitoneum and mechanical ventilation is further aggravated in obese patients. Recent studies demonstrated that individualized positive end-expiratory pressure (iPEEP) was one of effective lung-protective ventilation strategies. However, there is still no exact method to determine the best iPEEP, especially for obese patients. Here, we will use the best static lung compliance (Cstat) method to determine iPEEP, compared with regular PEEP, by observing the atelectasis area measured by electrical impedance tomography (EIT), and try to prove a better iPEEP setting method for obese patients. METHODS: This study is a single-center, two-arm, prospective, randomized control trial. A total number of 80 obese patients with body mass index ≥ 32.5 kg/m2 scheduled for laparoscopic gastric volume reduction and at medium to high risk for PPCs will be enrolled. They will be randomly assigned to control group (PEEP5 group) and iPEEP group. A PEEP of 5 cmH2O will be used in PEEP5 group, whereas an individualized PEEP value determined by a Cstat-directed PEEP titration procedure will be applied in the iPEEP group. Standard lung-protective ventilation methods such as low tidal volumes (7 ml/kg, predicted body weight, PBW), a fraction of inspired oxygen ≥ 0.5, and recruitment maneuvers (RM) will be applied during and after operation in both groups. Primary endpoints will be postoperative atelectasis measured by chest electrical impedance tomography (EIT) and intraoperative oxygen index. Secondary endpoints will be serum IL-6, TNF-α, procalcitonin (PCT) kinetics during and after surgery, incidence of PPCs, organ dysfunction, length of in-hospital stay, and hospital expense. DISCUSSION: Although there are several studies about the effect of iPEEP titration on perioperative PPCs in obese patients recently, the iPEEP setting method they used was complex and was not always feasible in routine clinical practice. This trial will assess a possible simple method to determine individualized optimal PEEP in obese patients and try to demonstrate that individualized PEEP with lung-protective ventilation methods is necessary for obese patients undergoing general surgery. The results of this trial will support anesthesiologist a feasible Cstat-directed PEEP titration method during anesthesia for obese patients in attempt to prevent PPCs. TRIAL REGISTRATION: www.chictr.org.cn ChiCTR1900026466. Registered on 11 October 2019.

Higher age and obesity limit atelectasis formation during anaesthesia: an analysis of computed tomography data in 243 subjects.

BACKGROUND: General anaesthesia is increasingly common in elderly and obese patients. Greater age and body mass index (BMI) worsen gas exchange. We assessed whether this is related to increasing atelectasis during general anaesthesia. METHODS: This primary analysis included pooled data from previously published studies of 243 subjects aged 18-78 yr, with BMI of 18-52 kg m-2. The subjects had no clinical signs of cardiopulmonary disease, and they underwent computed tomography (CT) awake and during anaesthesia before surgery after preoxygenation with an inspired oxygen fraction (FIO2) of >0.8, followed by mechanical ventilation with FIO2 of 0.3 or higher with no PEEP. Atelectasis was assessed by CT. RESULTS: Atelectasis area of up to 39 cm2 in a transverse scan near the diaphragm was seen in 90% of the subjects during anaesthesia. The log of atelectasis area was related to a quadratic function of (age+age2) with the most atelectasis at ∼50 yr (r2=0.08; P<0.001). Log atelectasis area was also related to a broken-line function of the BMI with the knee at 30 kg m-2 (r2=0.06; P<0.001). Greater atelectasis was seen in the subjects receiving FIO2 of 1.0 than FIO2 of 0.3-0.5 (12.8 vs 8.1 cm2; P<0.001). A multiple regression analysis, including a quadratic function of age, a broken-line function of the BMI, and dichotomised FIO2 (0.3-0.5/1.0) adjusting for ventilatory frequency, strengthened the association (r2=0.23; P<0.001). PaO2 decreased with both age and BMI. CONCLUSIONS: Atelectasis during general anaesthesia increased with age up to 50 yr and decreased beyond that. Atelectasis increased with BMI in normal and overweight patients, but showed no further increase in obese subjects (BMI ≥30 kg m-2). Therefore, greater age and obesity appear to limit atelectasis formation during general anaesthesia.

Risks from Breathing Elevated Oxygen.

INTRODUCTION: Effects of breathing gas with elevated oxygen partial pressure (Po2) and/or elevated inspired oxygen fraction (FIo2) at sea level or higher is discussed. High FIo2 is associated with absorption problems in the lungs, middle ear, and paranasal sinuses, particularly if FIo2 > 80% and small airways, Eustachian tubes, or sinus passages are blocked. Absorption becomes faster as cabin altitude increases. Pulmonary oxygen toxicity and direct oxidative injuries, related to elevated Po2, are improbable in flight; no pulmonary oxygen toxicity has been found when Po2 < 55 kPa [418 Torr; 100% O2 higher than 15,000 ft (4570 m)]. Symptoms with Po2 of 75 kPa [520 Torr; 100% O2 at 10,000 ft (3050 m)] were reported after 24 h and the earliest signs at Po2 of 100 kPa (760 Torr, 100% O2 at sea level) occurred after 6 h. However, treatment for decompression sickness entails a risk of pulmonary oxygen toxicity. Elevated Po2 also constricts blood vessels, changes blood pressure control, and reduces the response to low blood sugar. With healthy lungs, gas transport and oxygen delivery are not improved by increasing Po2. Near zero humidity of the breathing gas in which oxygen is delivered may predispose susceptible individuals to bronchoconstriction.Shykoff BE, Lee RL. Risks from breathing elevated oxygen. Aerosp Med Hum Perform. 2019; 90(12):1041-1049.

Unilateral Lung Recruitment Maneuver for Massive Atelectasis in a Child With Glenn Circulation: A Case Report.

A 9-year-old girl with Glenn circulation suffered from massive atelectasis of the left lung caused by bleeding during cardiac catheterization. The atelectasis resulted in frequent hypoxia leading to oxygen saturation (SpO2) of 40%-50%. In the intensive care unit, we performed a unilateral lung recruitment maneuver (ULRM) for 2 days. The ULRM involved placement of a bronchial blocker in the right main bronchus and application of continuous positive airway pressure to the left lung without hemodynamic deterioration. Eventually, SpO2 improved to 80%-85%. ULRM can be a treatment option for unilateral atelectasis in a child with Glenn circulation.

A novel technique with double catheter suctioning for clearing away the left lung atelectases: Selective left bronchial aspiration (SeLBA).

INTRODUCTION: Atelectasis is a common problem in intensive care units. It usually occurs due to airway obstruction caused by pulmonary secretions. As the left main bronchus angulates from carina more sharply, suctioning of the secretions from left side is less effective, causing failure in treatment of left lung atelectases. If chest physiotherapy and medical treatment fail, bronchoscopy should be considered; but it requires experience, time, effort and a higher cost. OBJECTIVES: To evaluate the success of a novel method "selective left bronchial aspiration (SeLBA)" in the treatment of left lung atelectases. METHODS: The study consisted of 10 patients who suffered left lung atelectasis and treated with double catheter suctioning technique, SeLBA in Pediatric Intensive Care Unit of Hacettepe University Ihsan Dogramaci Children's Hospital between June 2017 and February 2019. The outcomes were evaluated by comparing the chest X-rays before and after the procedure. RESULTS: All of the patients' atelectases resolved successfully by SeLBA procedure. CONCLUSION: We introduce this novel technique of reopening the atelectased left lung as a rapid, safe and practical alternative for bronchoscopic clear away.

Analysis of different levels of positive end-expiratory pressure during lung retrieval for transplantation: an experimental study.

Atelectasis and inadequate oxygenation in lung donors is a common problem during the retrieval of these organs. Nevertheless, the use of high positive end-expiratory pressure (PEEP) is not habitual during procedures of lung retrieval. Twenty-one Sprague-Dawley male consanguineous rats were used in the study. The animals were divided into 3 groups according to the level of PEEP used: low (2 cmH2O), moderate (5 cmH2O), and high (10 cmH2O). Animals were ventilated with a tidal volume of 6 mL/kg. Before lung removal, the lungs were inspected for the presence of atelectasis. When atelectasis was detected, alveolar recruitment maneuvers were performed. Blood gasometric analysis was performed immediately. Finally, the lungs were retrieved, weighed, and submitted to histological analysis. The animals submitted to higher PEEP showed higher levels of oxygenation with the same tidal volumes PO2=262.14 (PEEP 2), 382.4 (PEEP 5), and 477.0 (PEEP 10). The occurrence of atelectasis was rare in animals with a PEEP of 10 cmH2O, which therefore required less frequent recruitment maneuvers (need for recruitment: PEEP 2=100%, PEEP 5 =100%, and PEEP 10=14.3%). There was no change in hemodynamic stability, occurrence of pulmonary edema, or other histological injuries with the use of high PEEP. The use of high PEEP (10 cmH2O) was feasible and probably a beneficial strategy for the prevention of atelectasis and the optimization of oxygenation during lung retrieval. Clinical studies should be performed to confirm this hypothesis.

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

BACKGROUND: Although a high inspired oxygen fraction (FiO2) is commonly used in paediatric anaesthesia, the impact on postoperative lung function is unclear. We compared lung volume, ventilation heterogeneity, and respiratory mechanics in anaesthetised children randomised to receive low or high FiO2 intraoperatively. METHODS: In a double-blind randomised controlled trial, children scheduled for elective surgery were randomly assigned FiO2 100% (n=29) or FiO2 80% (n=29) during anaesthesia induction and emergence. During maintenance of anaesthesia, participants assigned FiO2=100% at induction/emergence received FiO2=80% (FiO2>0.8 group); those randomised to FiO2=80% at induction/emergence received FiO2=35% intraoperatively (FiO2 [0.8→0.35 group]). During spontaneous breathing, we measured the (i) functional residual capacity (FRC) and lung clearance index (ventilation inhomogeneity) by multiple-breath nitrogen washout; and (ii) airway resistance and respiratory tissue elastance by forced oscillations, before operation, after discharge from the recovery room, and 24 h after operation. Mean (95% confidence intervals) are reported. RESULTS: Fifty eight children (12.9 [12.3-13.5] yr) were randomised; 22/29 (high group) and 21/29 (low group) children completed serial multiple-breath nitrogen washout measurements. FRC decreased in the FiO2>0.8 group after discharge from recovery (-12.0 [-18.5 to -5.5]%; P=0.01), but normalised 24 h later. Ventilation inhomogeneity increased in both groups after discharge from recovery, but persisted in the FiO2>0.8 group 24 h after surgery (6.1 [2.5-9.8%]%; P=0.02). Airway resistance and respiratory elastance did not differ between the groups at any time point. CONCLUSIONS: FiO2>0.8 decreases lung volume in the immediate postoperative period, accompanied by persistent ventilation inhomogeneity. These data suggest that FiO2>0.8 should be avoided in anaesthetised children with normal lungs. CLINICAL TRIAL REGISTRATION: NCT02384616.

Tidal changes in PaO2 and their relationship to cyclical lung recruitment/derecruitment in a porcine lung injury model.

BACKGROUND: Tidal recruitment/derecruitment (R/D) of collapsed regions in lung injury has been presumed to cause respiratory oscillations in the partial pressure of arterial oxygen (PaO2). These phenomena have not yet been studied simultaneously. We examined the relationship between R/D and PaO2 oscillations by contemporaneous measurement of lung-density changes and PaO2. METHODS: Five anaesthetised pigs were studied after surfactant depletion via a saline-lavage model of R/D. The animals were ventilated with a mean fraction of inspired O2 (FiO2) of 0.7 and a tidal volume of 10 ml kg-1. Protocolised changes in pressure- and volume-controlled modes, inspiratory:expiratory ratio (I:E), and three types of breath-hold manoeuvres were undertaken. Lung collapse and PaO2 were recorded using dynamic computed tomography (dCT) and a rapid PaO2 sensor. RESULTS: During tidal ventilation, the expiratory lung collapse increased when I:E <1 [mean (standard deviation) lung collapse=15.7 (8.7)%; P<0.05], but the amplitude of respiratory PaO2 oscillations [2.2 (0.8) kPa] did not change during the respiratory cycle. The expected relationship between respiratory PaO2 oscillation amplitude and R/D was therefore not clear. Lung collapse increased during breath-hold manoeuvres at end-expiration and end-inspiration (14% vs 0.9-2.1%; P<0.0001). The mean change in PaO2 from beginning to end of breath-hold manoeuvres was significantly different with each type of breath-hold manoeuvre (P<0.0001). CONCLUSIONS: This study in a porcine model of collapse-prone lungs did not demonstrate the expected association between PaO2 oscillation amplitude and the degree of recruitment/derecruitment. The results suggest that changes in pulmonary ventilation are not the sole determinant of changes in PaO2 during mechanical ventilation in lung injury.