David R. Janz

Clinical Characteristics and Outcomes Are Similar in ARDS Diagnosed by Oxygen Saturation/Fio2 Ratio Compared With Pao2/Fio2 Ratio

BACKGROUND Oxygen saturation as measured by pulse oximetry/Fio2 (SF) ratio is highly correlated with the Pao2/Fio2 (PF) ratio in patients with ARDS. However, it remains uncertain whether SF ratio can be substituted for PF ratio for diagnosis of ARDS and whether SF ratio might identify patients who are systemically different from patients diagnosed by PF ratio. METHODS We conducted a secondary analysis of a large observational prospective cohort study. Patients were eligible if they were admitted to the medical ICU and fulfilled the Berlin definition of ARDS with hypoxemia criteria using either the standard PF threshold (PF ratio ≤ 300) or a previously published SF threshold (SF ratio ≤ 315). RESULTS Of 362 patients with ARDS, 238 (66%) received a diagnosis by PF ratio and 124 (34%) by SF ratio. In a small group of patients who received diagnoses of ARDS by SF ratio who had arterial blood gas measurements on the same day (n = 10), the PF ratio did not meet ARDS criteria. There were no major differences in clinical characteristics or comorbidities between groups with the exception of APACHE (Acute Physiology and Chronic Health Evaluation) II scores, which were higher in the group diagnosed by PF ratio. However, this difference was no longer apparent when arterial blood gas-dependent variables (pH, Pao2) were removed from the APACHE II score. There were also no differences in clinical outcomes including duration of mechanical ventilation (mean, 7 days in both groups; P = .25), duration of ICU stay (mean, 10 days vs 9 days in PF ratio vs SF ratio; P = .26), or hospital mortality (36% in both groups, P = .9). CONCLUSIONS Patients with ARDS diagnosed by SF ratio have very similar clinical characteristics and outcomes compared with patients diagnosed by PF ratio. These findings suggest that SF ratio could be considered as a diagnostic tool for early enrollment into clinical trials.

A Multicenter, Randomized Trial of Ramped Position vs Sniffing Position During Endotracheal Intubation of Critically Ill Adults

BACKGROUND: Hypoxemia is the most common complication during endotracheal intubation of critically ill adults. Intubation in the ramped position has been hypothesized to prevent hypoxemia by increasing functional residual capacity and decreasing the duration of intubation, but has never been studied outside of the operating room. METHODS: Multicenter, randomized trial comparing the ramped position (head of the bed elevated to 25°) with the sniffing position (torso supine, neck flexed, and head extended) among 260 adults undergoing endotracheal intubation by pulmonary and critical care medicine fellows in four ICUs between July 22, 2015, and July 19, 2016. The primary outcome was lowest arterial oxygen saturation between induction and 2 minutes after intubation. Secondary outcomes included Cormack‐Lehane grade of glottic view, difficulty of intubation, and number of laryngoscopy attempts. RESULTS: The median lowest arterial oxygen saturation was 93% (interquartile range [IQR], 84%‐99%) with the ramped position vs 92% (IQR, 79%‐98%) with the sniffing position (P = .27). The ramped position appeared to increase the incidence of grade III or IV view (25.4% vs 11.5%, P = .01), increase the incidence of difficult intubation (12.3% vs 4.6%, P = .04), and decrease the rate of intubation on the first attempt (76.2% vs 85.4%, P = .02), respectively. CONCLUSIONS: In this multicenter trial, the ramped position did not improve oxygenation during endotracheal intubation of critically ill adults compared with the sniffing position. The ramped position may worsen glottic view and increase the number of laryngoscopy attempts required for successful intubation. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT02497729; URL: www.clinicaltrials.gov

The role of red blood cells and cell-free hemoglobin in the pathogenesis of ARDS

The primary focus of research into the pathophysiology of the acute respiratory distress syndrome (ARDS) has been on the interaction between the lung, underlying causes of ARDS, and the role of white blood cells and platelets in contributing to lung injury. Given a lack of specific therapies for this common complication of critical illness, further insight into the pathophysiology of this syndrome is greatly needed to develop targeted interventions. The red blood cell (RBC) has been reported to undergo deleterious changes in critical illness and be present in the alveoli of patients with ARDS. Release of RBC contents is known to be injurious in other conditions but has only recently been studied in critical illness and ARDS. The contribution of the RBC to ARDS represents a new avenue of research that may produce new, targeted therapies for this deadly syndrome.

Cell-free hemoglobin: a novel mediator of acute lung injury

Patients with the acute respiratory distress syndrome (ARDS) have elevated levels of cell-free hemoglobin (CFH) in the air space, but the contribution of CFH to the pathogenesis of acute lung injury is unknown. In the present study, we demonstrate that levels of CFH in the air space correlate with measures of alveolar-capillary barrier dysfunction in humans with ARDS (r = 0.89, P < 0.001) and in mice with ventilator-induced acute lung injury (r = 0.89, P < 0.001). To investigate the specific contribution of CFH to ARDS, we studied the impact of purified CFH in the mouse lung and on cultured mouse lung epithelial (MLE-12) cells. Intratracheal delivery of CFH in mice causes acute lung injury with air space inflammation and alveolar-capillary barrier disruption. Similarly, in MLE-12 cells, CFH increases proinflammatory cytokine expression and increases paracellular permeability as measured by electrical cell-substrate impedance sensing. Next, to determine whether these effects are mediated by the iron-containing heme moiety of CFH, we treated mice with intratracheal hemin, the chloride salt of heme, and found that hemin was sufficient to increase alveolar permeability but failed to induce proinflammatory cytokine expression or epithelial cell injury. Together, these data identify CFH in the air space as a previously unrecognized driver of lung epithelial injury in human and experimental ARDS and suggest that CFH and hemin may contribute to ARDS through different mechanisms. Interventions targeting CFH and heme in the air space could provide a new therapeutic approach for ARDS.

A Multicenter Randomized Trial of a Checklist for Endotracheal Intubation of Critically Ill Adults

BACKGROUND: Hypoxemia and hypotension are common complications during endotracheal intubation of critically ill adults. Verbal performance of a written, preintubation checklist may prevent these complications. We compared a written, verbally performed, preintubation checklist with usual care regarding lowest arterial oxygen saturation or lowest systolic BP experienced by critically ill adults undergoing endotracheal intubation. METHODS: A multicenter trial in which 262 adults undergoing endotracheal intubation were randomized to a written, verbally performed, preintubation checklist (checklist) or no preintubation checklist (usual care). The coprimary outcomes were lowest arterial oxygen saturation and lowest systolic BP between the time of procedural medication administration and 2 min after endotracheal intubation. RESULTS: The median lowest arterial oxygen saturation was 92% (interquartile range [IQR], 79‐98) in the checklist group vs 93% (IQR, 84‐100) with usual care (P = .34). The median lowest systolic BP was 112 mm Hg (IQR, 94‐133) in the checklist group vs 108 mm Hg (IQR, 90‐132) in the usual care group (P = .61). There was no difference between the checklist and usual care in procedure duration (120 vs 118 s; P = .49), number of laryngoscopy attempts (one vs one attempt; P = .42), or severe life‐threatening procedural complications (40.8% vs 32.6%; P = .20). CONCLUSIONS: The verbal performance of a written, preprocedure checklist does not increase the lowest arterial oxygen saturation or lowest systolic BP during endotracheal intubation of critically ill adults compared with usual care. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT02497729; URL: www.clinicaltrials.gov.

Cell-Free Hemoglobin-mediated Increases in Vascular Permeability. A Novel Mechanism of Primary Graft Dysfunction and a New Therapeutic Target

RATIONALE Cell-free hemoglobin (CFH) is a potent oxidant associated with poor clinical outcomes in a variety of clinical settings. Recent studies suggest that acetaminophen (APAP), a specific hemoprotein reductant, can abrogate CFH-mediated oxidative injury and organ dysfunction. Preoperative plasma CFH levels are independently associated with primary graft dysfunction (PGD) after lung transplant ( 1 ). OBJECTIVES Our objectives were to determine whether CFH would increase lung vascular permeability in the isolated perfused human lung and whether APAP would limit these effects. METHODS Human lungs declined for transplant were inflated and perfused with Dulbeccos modified Eagle medium/5% albumin at a pulmonary artery pressure of 8-12 mm Hg. After steady state was achieved, CFH (100 mg/dl) was added to the perfusate ± APAP (15 μg/ml). Lung permeability was measured by continuous monitoring of lung weight gain and by extravasation of Evans blue dye-labeled albumin from the vasculature into bronchoalveolar lavage. To test the mechanism of increased permeability, human pulmonary microvascular endothelial cells were exposed to CFH (0.5 mg/ml) ± APAP (160 μM) for 24 hours and permeability was assessed by electrical cell-substrate impedance sensing. MEASUREMENT AND MAIN RESULTS In the isolated perfused human lung, CFH increased lung permeability over 2 hours compared with control lungs (12% vs. 2% weight gain from baseline, P = 0.03). Increased vascular permeability was confirmed by a 4.8-fold increase in Evans blue dye-labeled albumin in the airspace compared with control lungs. Pretreatment with APAP prevented lung weight gain (P = 0.06 vs. CFH). In human pulmonary microvascular endothelial cells, CFH increased monolayer permeability (P = 0.03 vs. control), and this was attenuated by APAP (P = 0.045 vs. CFH). CONCLUSIONS Circulating CFH increases vascular permeability in the isolated perfused human lung and paracellular permeability in lung microvascular endothelial cells. These effects may explain the association of plasma CFH levels with PGD. The hemoprotein reductant APAP attenuates the effects of CFH and merits further exploration as a potential therapy for PGD prevention.

Manual ventilation to prevent hypoxaemia during endotracheal intubation of critically ill adults: protocol and statistical analysis plan for a multicentre randomised trial

Introduction Hypoxaemia is the most common complication during endotracheal intubation of critically ill adults, and it increases the risk of cardiac arrest and death. Manual ventilation between induction and intubation has been hypothesised to decrease the incidence of hypoxaemia, but efficacy and safety data are lacking. Methods and analysis The Preventing Hypoxemia with Manual Ventilation during Endotracheal Intubation trial is a prospective, multicentre, non-blinded randomised clinical trial being conducted in seven intensive care units in the USA. A total of 400 critically ill adults undergoing endotracheal intubation will be randomised 1:1 to receive prophylactic manual ventilation between induction and endotracheal intubation using a bag-valve-mask device or no prophylactic ventilation. The primary outcome is the lowest arterial oxygen saturation between induction and 2 min after successful endotracheal intubation, which will be analysed as an unadjusted, intention-to-treat comparison of patients randomised to prophylactic ventilation versus patients randomised to no prophylactic ventilation. The secondary outcome is the incidence of severe hypoxaemia, defined as any arterial oxygen saturation of less than 80% between induction and 2 min after endotracheal intubation. Enrolment began on 2 February 2017 and is expected to be complete in May 2018. Ethics and dissemination The trial was approved by the institutional review boards or designees of all participating centres. The results will be submitted for publication in a peer-reviewed journal and presented at one or more scientific conferences. Trial registration number NCT03026322; Pre-results.

Derivation and validation of a two-biomarker panel for diagnosis of ARDS in patients with severe traumatic injuries

Background Acute respiratory distress syndrome (ARDS) is common after severe traumatic injuries but is underdiagnosed and undertreated. We hypothesized that a panel of plasma biomarkers could be used to diagnose ARDS in severe trauma. To test this hypothesis, we derived and validated a biomarker panel in three independent cohorts and compared the diagnostic performance to clinician recognition of ARDS. Methods Eleven plasma biomarkers of inflammation, lung epithelial and endothelial injury were measured in a derivation cohort of 439 severe trauma patients. ARDS status was analyzed by two-investigator consensus, and cases were required to meet Berlin criteria on intensive care unit (ICU) day 1. Controls were subjects without ARDS during the first 4 days of study enrollment. A multivariable logistic regression model was used to generate probabilities for ARDS. A reduced model with the top two performing markers was then tested in two independent validation cohorts. To assess clinical diagnosis of ARDS, medical records in the derivation cohort were systematically searched for documentation of ARDS diagnosis made by a clinical provider. Results Among 11 biomarkers, the combination of the endothelial injury marker angiopoietin-2 (Ang-2) and the lung epithelial injury marker receptor for advanced glycation endproducts (RAGE) provided good discrimination for ARDS in the derivation cohort (area under the curve (AUC)=0.74 (95% CI 0.67 to 0.80). In the validation cohorts, the AUCs for this model were 0.70 (0.61 to 0.77) and 0.78 (0.71 to 0.84). In contrast, provider assessment demonstrated poor diagnostic accuracy for ARDS, with AUC of 0.55 (0.51 to 0.60). Discussion A two-biomarker panel consisting of Ang-2 and RAGE performed well across multiple patient cohorts and outperformed clinical providers for diagnosing ARDS in severe trauma. Clinical application of this model could improve both diagnosis and treatment of ARDS in patients with severe trauma. Level of evidence Diagnostic study, level II.

Effect of Interhospital ICU Relocation on Patient Physiology and Clinical Outcomes

Relocation of large numbers of critically ill patients between hospitals is sometimes necessary and the risks associated with relocation may be high. In the setting of adherence to an interhospital intensive care unit (ICU) relocation protocol, we aimed to determine whether the interhospital relocation of all ICU patients in a single day is associated with changes in vital signs, device removal, and worse clinical outcomes. We conducted a prospective, observational, cohort study of all critically ill adults admitted to a tertiary medical center’s ICUs on the day of a planned hospital relocation and exposed to interhospital ICU relocation compared with unexposed critically ill adults. Changes in vital signs were evaluated by the before-and-after interhospital relocation measurement of vital signs, and clinical outcomes were collected for all patients. A total of 699 patients were admitted to the ICU during the observation period, 24 of whom were exposed to interhospital ICU relocation on a single day. The median interhospital transport duration was 28 minutes (interquartile range: 24-35) and 29% of patients were receiving invasive mechanical ventilation. Patients exposed to interhospital ICU relocation had no significant change in any vital sign measurement and no devices were unintentionally removed. Inhospital mortality was similar (8.3%) to patients not exposed to interhospital ICU relocation (9.2%, P > .99). In the setting of adherence to an ICU relocation protocol, the interhospital ICU relocation of all critically ill adults during a single day is not associated with changes in vital signs, device removal, or worse clinical outcomes.

Early exposure to hyperoxia and mortality in critically ill patients with severe traumatic injuries

BackgroundHyperoxia is common early in the course of resuscitation of critically ill patients. It has been associated with mortality in some, but not all, studies of cardiac arrest patients and other critically ill cohorts. Reasons for the inconsistency are unclear and may depend on unmeasured patient confounders, the timing and duration of hyperoxia, population characteristics, or the way that hyperoxia is defined and measured. We sought to determine whether, in a prospectively collected cohort of mechanically ventilated patients with traumatic injuries with and without head trauma, higher maximum partial pressure of arterial oxygen (PaO2) within 24 hours of admission would be associated with increased risk of in-hospital mortality.MethodsCritically ill patients with traumatic injuries undergoing invasive mechanical ventilation enrolled in the Validating Acute Lung Injury biomarkers for Diagnosis (VALID) study were included in this study. All arterial blood gases (ABGs) from the first 24 hours of admission were recorded. Primary analysis was comparison of the highest PaO2 between hospital survivors and non-survivors.ResultsA total of 653 patients were evaluated for inclusion. Of these, 182 were not mechanically ventilated or did not have an ABG measured in the first 24 hours, leaving 471 patients in the primary analysis. In survivors, the maximum PaO2 was 141 mmHg (median, interquartile range 103 - 212) compared to 148 mmHg (IQR 105 - 209) in non-survivors (p = 0.82). In the subgroup with head trauma (n = 266), the maximum PaO2 was 133 mmHg (IQR 97 - 187) among survivors and 152 mmHg (108 - 229) among nonsurvivors (p = 0.19). After controlling for age, injury severity score, number of arterial blood gases, and fraction of inspired oxygen, maximum PaO2 was not associated with increased mortality (OR 1.27 for every fold increase of PaO2 (95% CI 0.72 - 2.25).ConclusionsIn mechanically ventilated patients with severe traumatic injuries, hyperoxia in the first 24 hours of admission was not associated with increased risk of death or worsened neurological outcomes in a setting without brain tissue oxygenation monitoring.