Pneumomediastinum in COVID-19: a phenotype of severe COVID-19 pneumonitis? The results of the United Kingdom (POETIC) survey.

BACKGROUND: There is an emerging understanding that coronavirus disease 2019 (COVID-19) is associated with increased incidence of pneumomediastinum. We aimed to determine its incidence among patients hospitalised with COVID-19 in the United Kingdom and describe factors associated with outcome. METHODS: A structured survey of pneumomediastinum and its incidence was conducted from September 2020 to February 2021. United Kingdom-wide participation was solicited via respiratory research networks. Identified patients had SARS-CoV-2 infection and radiologically proven pneumomediastinum. The primary outcomes were to determine incidence of pneumomediastinum in COVID-19 and to investigate risk factors associated with patient mortality. RESULTS: 377 cases of pneumomediastinum in COVID-19 were identified from 58 484 inpatients with COVID-19 at 53 hospitals during the study period, giving an incidence of 0.64%. Overall 120-day mortality in COVID-19 pneumomediastinum was 195/377 (51.7%). Pneumomediastinum in COVID-19 was associated with high rates of mechanical ventilation. 172/377 patients (45.6%) were mechanically ventilated at the point of diagnosis. Mechanical ventilation was the most important predictor of mortality in COVID-19 pneumomediastinum at the time of diagnosis and thereafter (p<0.001) along with increasing age (p<0.01) and diabetes mellitus (p=0.08). Switching patients from continuous positive airways pressure support to oxygen or high flow nasal oxygen after the diagnosis of pneumomediastinum was not associated with difference in mortality. CONCLUSIONS: Pneumomediastinum appears to be a marker of severe COVID-19 pneumonitis. The majority of patients in whom pneumomediastinum was identified had not been mechanically ventilated at the point of diagnosis.

Reproducibility of 19 F-MR ventilation imaging in healthy volunteers.

PURPOSE: To assess the reproducibility of percentage ventilated lung volume (%VV) measurements in healthy volunteers acquired by fluorine (19 F)-MRI of inhaled perfluoropropane, implemented at two research sites. METHODS: In this prospective, ethically approved study, 40 healthy participants were recruited (May 2018-June 2019) to one of two research sites. Participants underwent a single MRI scan session on a 3T scanner, involving periodic inhalation of a 79% perfluoropropane/21% oxygen gas mixture. Each gas inhalation session lasted about 30 seconds, consisting of three deep breaths of gas followed by a breath-hold. Four 19 F-MR ventilation images were acquired per participant, each separated by approximately 6 minutes. The value of %VV was determined by registering separately acquired 1 H images to ventilation images before semi-automated image segmentation, performed independently by two observers. Reproducibility of %VV measurements was assessed by components of variance, intraclass correlation coefficients, coefficients of variation (CoV), and the Dice similarity coefficient. RESULTS: The MRI scans were well tolerated throughout, with no adverse events. There was a high degree of consistency in %VV measurements for each participant (CoVobserver1 = 0.43%; CoVobserver2 = 0.63%), with overall precision of %VV measurements determined to be within ± 1.7% (95% confidence interval). Interobserver agreement in %VV measurements revealed a high mean Dice similarity coefficient (SD) of 0.97 (0.02), with only minor discrepancies between observers. CONCLUSION: We demonstrate good reproducibility of %VV measurements in a group of healthy participants using 19 F-MRI of inhaled perfluoropropane. Our methods have been successfully implemented across two different study sites, supporting the feasibility of performing larger multicenter clinical studies.

Dynamic susceptibility contrast 19 F-MRI of inhaled perfluoropropane: a novel approach to combined pulmonary ventilation and perfusion imaging.

PURPOSE: To assess alveolar perfusion by applying dynamic susceptibility contrast MRI to 19 F-MRI of inhaled perfluoropropane (PFP). We hypothesized that passage of gadolinium-based contrast agent (GBCA) through the pulmonary microvasculature would reduce magnetic susceptibility differences between water and gas components of the lung, elevating the T2∗ of PFP. METHODS: Lung-representative phantoms were constructed of aqueous PFP-filled foams to characterize the impact of aqueous/gas phase magnetic susceptibility differences on PFP T2∗ . Aqueous phase magnetic susceptibility was modulated by addition of different concentrations of GBCA. In vivo studies were performed to measure the impact of intravenously administered GBCA on the T2∗ of inhaled PFP in mice (7.0 Tesla) and in healthy volunteers (3.0 Tesla). RESULTS: Perfluoropropane T2∗ was sensitive to modulation of magnetic susceptibility difference between gas and water components of the lung, both in phantom models and in vivo. Negation of aqueous/gas phase magnetic susceptibility difference was achieved in lung-representative phantoms and in mice, resulting in a ~2 to 3× elevation in PFP T2∗ (3.7 to 8.5 ms and 0.7 to 2.6 ms, respectively). Human studies demonstrated a transient elevation of inhaled PFP T2∗ (1.50 to 1.64 ms) during passage of GBCA bolus through the lung circulation, demonstrating sensitivity to lung perfusion. CONCLUSION: We demonstrate indirect detection of a GBCA in the pulmonary microvasculature via changes to the T2∗ of gas phase PFP within directly adjacent alveoli. This approach holds potential for assessing alveolar perfusion by dynamic susceptibility contrast 19 F-MRI of inhaled PFP, with concurrent assessment of lung ventilation properties, relevant to lung physiology and disease.

Optimized and accelerated 19 F-MRI of inhaled perfluoropropane to assess regional pulmonary ventilation.

PURPOSE: To accelerate 19 F-MR imaging of inhaled perfluoropropane using compressed sensing methods, and to optimize critical scan acquisition parameters for assessment of lung ventilation properties. METHODS: Simulations were performed to determine optimal acquisition parameters for maximal perfluoropropane signal-to-noise ratio (SNR) in human lungs for a spoiled gradient echo sequence. Optimized parameters were subsequently employed for 19 F-MRI of inhaled perfluoropropane in a cohort of 11 healthy participants using a 3.0 T scanner. The impact of 1.8×, 2.4×, and 3.0× undersampling ratios on 19 F-MRI acquisitions was evaluated, using both retrospective and prospective compressed sensing methods. RESULTS: 3D spoiled gradient echo 19 F-MR ventilation images were acquired at 1-cm isotropic resolution within a single breath hold. Mean SNR was 11.7 ± 4.1 for scans acquired within a single breath hold (duration = 18 s). Acquisition of 19 F-MRI scans at shorter scan durations (4.5 s) was also demonstrated as feasible. Application of both retrospective (n = 8) and prospective (n = 3) compressed sensing methods demonstrated that 1.8× acceleration had negligible impact on qualitative image appearance, with no statistically significant change in measured lung ventilated volume. Acceleration factors of 2.4× and 3.0× resulted in increasing differences between fully sampled and undersampled datasets. CONCLUSION: This study demonstrates methods for determining optimal acquisition parameters for 19 F-MRI of inhaled perfluoropropane and shows significant reduction in scan acquisition times (and thus participant breath hold duration) by use of compressed sensing.

Healthcare staff attitudes towards the use of electronic cigarettes ('e-cigarettes') compared with a local trust policy.

BACKGROUND: E-cigarette use has risen dramatically in recent years, despite uncertainty over long-term health effects and concerns regarding efficacy as a smoking cessation device. Currently, there is no legislation prohibiting use in public, though many trusts have extended the NHS Smokefree policy to include e-cigarettes. The successful implementation of such policy is, however, unclear. AIM: This study examined staff attitudes towards the use of e-cigarettes in a hospital environment with respect to enforcement of a local trust smoking policy. METHODS: A total of 79 healthcare professionals working at South Tyneside District Hospital, South Shields, completed a written questionnaire regarding use of e-cigarettes, particularly views on use in public and on hospital premises. Factors influencing the likelihood of individuals to challenge the use of e-cigarettes were assessed. RESULTS: In all, 45% of respondents thought that e-cigarettes should be allowed in public places, though a majority (62%) favoured use on hospital grounds compared to within hospital buildings (18%). Over 50% of respondents were unaware of trust policy relating to e-cigarettes and only 25% had ever challenged someone using a device. Roughly, one-third reported that they would still not challenge someone in future, despite being informed of trust policy. Fear of abuse was the most cited reason for not challenging. Expressed concerns of e-cigarette use related to fire risk, 'normalising' smoking behaviour and uncertainty of long-term effects. CONCLUSION: Most staff do not enforce trust policy regarding e-cigarette use. This reflects variation in opinion over use, poor awareness of the policy itself and perceived barriers to implementation, including fear of abuse. Addressing these issues through staff education sessions may help successful future implementation.