Management of primary blast lung injury: a comparison of airway pressure release versus low tidal volume ventilation

BackgroundPrimary blast lung injury (PBLI) presents as a syndrome of respiratory distress and haemoptysis resulting from explosive shock wave exposure and is a frequent cause of mortality and morbidity in both military conflicts and terrorist attacks. The optimal mode of mechanical ventilation for managing PBLI is not currently known, and clinical trials in humans are impossible due to the sporadic and violent nature of the disease.MethodsA high-fidelity multi-organ computational simulator of PBLI pathophysiology was configured to replicate data from 14 PBLI casualties from the conflict in Afghanistan. Adaptive and responsive ventilatory protocols implementing low tidal volume (LTV) ventilation and airway pressure release ventilation (APRV) were applied to each simulated patient for 24 h, allowing direct quantitative comparison of their effects on gas exchange, ventilatory parameters, haemodynamics, extravascular lung water and indices of ventilator-induced lung injury.ResultsThe simulated patients responded well to both ventilation strategies. Post 24-h investigation period, the APRV arm had similar PF ratios (137 mmHg vs 157 mmHg), lower sub-injury threshold levels of mechanical power (11.9 J/min vs 20.7 J/min) and lower levels of extravascular lung water (501 ml vs 600 ml) compared to conventional LTV. Driving pressure was higher in the APRV group (11.9 cmH2O vs 8.6 cmH2O), but still significantly less than levels associated with increased mortality.ConclusionsAppropriate use of APRV may offer casualties with PBLI important mortality-related benefits and should be considered for management of this challenging patient group

Mathematical and Computational Modelling in Critical Illness

Mathematical and computational modelling are assuming a prominent role in investigating the complex pathophysiological states and therapeutic strategies in critical illness. This editorial briefly illustrates the models of the respiratory and cardiovascular systems developed in the last decades, and their advantages and disadvantages with respect to traditional methods of research, i.e. trials in humans and animals. The future direction and application of these high-fidelity and highly integrated models will be to facilitate the development of bedside patient-clones to guide the clinical management of critically ill patients

The impact of video games on ultrasound-guided regional anesthesia skills

Background: There is an association between video game practice and laparoscopic expertise in trainee surgeons. Ultrasound-guided regional anesthesia has many parallels with laparoscopic surgery. The aim of this study was to explore whether video game experience is associated with enhanced performance in a simulated ultrasound-guided task in novice operators.Methods: In this prospective observational study, 60 medical student volunteers were recruited. Following characterization of video game experience, they underwent an assessment of visuospatial abilities. Following standardized teaching, the recruits’ technical performance of an ultrasound-guided needle task was assessed for overall quality by global rating scale [GRS].Results: Out of a total possible GRS score of 35, gamers compared to non-gamers demonstrated 5.2 (95% CI 1.9, 8.4) units of better performance. Gamers also performed better in mental rotation test (MRT) scores (Difference 4.1, 95% CI 1.2, 7.0) .Conclusion: Video game practice is associated with increased mental rotation ability and enhanced technical performance in a simulated ultrasound-guided task

Effect of variable pre-oxygenation endpoints on safe apnoea time using high flow nasal oxygen for women in labour: a modelling investigation

BackgroundStudies of pulmonary denitrogenation (pre-oxygenation) in obstetric populations have shown high flow nasal oxygen therapy (HFNO) is inferior to facemask techniques. HFNO achieves median end-tidal oxygen fraction (FE′O2) of 0.87 after 3 min. As HFNO prolongs safe apnoea times through apnoeic oxygenation, we postulated that HFNO would still extend safe apnoeic times despite the lower FE′O2 after pre-oxygenation.MethodsThe Interdisciplinary Collaboration in Systems Medicine simulation suite, a highly integrated, high-fidelity model of the human respiratory and cardiovascular systems, was used to study the effect of varying FE′O2 (60%, 70%, 80%, and 90%) on the duration of safe apnoea times using HFNO and facemask techniques (with the airway open and obstructed). The study population consisted of validated models of pregnant women in active labour and not in labour with BMI of 24, 35, 40, 45, and 50 kg m−2.ResultsHFNO provided longer safe apnoeic times in all models, with all FE′O2 values. Labour and increased BMI reduced this effect, in particular a BMI of 50 kg m−2 reduced the improvement in apnoea time to 1.8–8.5 min (depending on the FE′O2), compared with an improvement of more than 60 min in the subject with BMI 24 kg m−2.ConclusionsDespite generating lower FE′O2, HFNO provides longer safe apnoea times in pregnant subjects in labour. Care should be taken when used in patients with BMI ≥50 kg m−2 as the extension of the safe apnoea time is limited

Effect of oxygen fraction on airway rescue: a computational modelling study

© 2020 British Journal of Anaesthesia Background: During induction of general anaesthesia, patients frequently experience apnoea, which can lead to dangerous hypoxaemia. An obstructed upper airway can impede attempts to provide ventilation. Although unrelieved apnoea is rare, it continues to cause deaths. Clinical investigation of management strategies for such scenarios is effectively impossible because of ethical and practical considerations. Methods: A population-representative cohort of 100 virtual (in silico) subjects was configured using a high-fidelity computational model of the pulmonary and cardiovascular systems. Each subject breathed 100% oxygen for 3 min and then became apnoeic, with an obstructed upper airway, during induction of general anaesthesia. Apnoea continued throughout the protocol. When arterial oxygen saturation (SaO2) reached 20%, 40%, or 60%, airway obstruction was relieved. We examined the effect of varying supraglottic oxygen fraction (FO2) on the degree of passive re-oxygenation occurring without tidal ventilation. Results: Relief of airway obstruction during apnoea produced a single, passive inhalation (caused by intrathoracic hypobaric pressure) in all cases. The degree of re-oxygenation after airway opening was markedly influenced by the supraglottic FO2, with a supraglottic FO2 of 100% providing significant and sustained re-oxygenation (post-rescue PaO2 42.3 [4.4] kPa, when the airway rescue occurred after desaturation to SaO2 60%). Conclusions: Supraglottic oxygen supplementation before relieving upper airway obstruction improves the effectiveness of simulated airway rescue. Management strategies should be implemented to assure a substantially increased pharyngeal FO2 during difficult airway management

Evaluating Current Guidelines for Cardiopulmonary Resuscitation using an Integrated Computational Model of the Cardiopulmonary System

ObjectiveWe aimed to use a high-fidelity computational model that captures key interactions between the cardiovascular and pulmonary systems to investigate whether current CPR protocols could potentially be improved.MethodsWe developed and validated the computational model against available human data. We used a global optimisation algorithm to find CPR protocol parameters that optimise the outputs associated with return of spontaneous circulation in a cohort of 10 virtual subjects.ResultsCompared with current protocols, myocardial tissue oxygen volume was more than 5 times higher, and cerebral tissue oxygen volume was nearly doubled, during optimised CPR. While the optimal maximal sternal displacement (5.5 cm) and compression ratio (51%) found using our model agreed with the current American Heart Association guidelines, the optimal chest compression rate was lower (67 compressions min−1). Similarly, the optimal ventilation strategy was more conservative than current guidelines, with an optimal minute ventilation of 1500 ml min−1 and inspired fraction of oxygen of 80%. The end compression force was the parameter with the largest impact on CO, followed by PEEP, the compression ratio and the CC rate.ConclusionsOur results indicate that current CPR protocols could potentially be improved. Excessive ventilation could be detrimental to organ oxygenation during CPR, due to the negative haemodynamic effect of increased pulmonary vascular resistance. Particular attention should be given to the chest compression force to achieve satisfactory CO. Future clinical trials aimed at developing improved CPR protocols should explicitly consider interactions between chest compression and ventilation parameters

Utility of Driving Pressure and Mechanical Power to Guide Protective Ventilator Settings in Two Cohorts of Adult and Pediatric Patients With Acute Respiratory Distress Syndrome: A Computational Investigation

Objectives: Mechanical power and driving pressure have been proposed as indicators, and possibly drivers, of ventilator-induced lung injury. We tested the utility of these different measures as targets to derive maximally protective ventilator settings.Design: A high-fidelity computational simulator was matched to individual patient data and used to identify strategies that minimize driving pressure, mechanical power, and a modified mechanical power that removes the direct linear, positive dependence between mechanical power and positive end-expiratory pressure.Setting: Interdisciplinary Collaboration in Systems Medicine Research Network.Subjects: Data were collected from a prospective observational cohort of pediatric acute respiratory distress syndrome from the Children’s Hospital of Philadelphia (n = 77) and from the low tidal volume arm of the Acute Respiratory Distress Syndrome Network tidal volume trial (n = 100).Interventions: Global optimization algorithms evaluated more than 26.7 million changes to ventilator settings (approximately 150,000 per patient) to identify strategies that minimize driving pressure, mechanical power, or modified mechanical power.Measurements and Main Results: Large average reductions in driving pressure (pediatric: 23%, adult: 23%), mechanical power (pediatric: 44%, adult: 66%), and modified mechanical power (pediatric: 61%, adult: 67%) were achievable in both cohorts when oxygenation and ventilation were allowed to vary within prespecified ranges. Reductions in driving pressure (pediatric: 12%, adult: 2%), mechanical power (pediatric: 24%, adult: 46%), and modified mechanical power (pediatric: 44%, adult: 46%) were achievable even when no deterioration in gas exchange was allowed. Minimization of mechanical power and modified mechanical power was achieved by increasing tidal volume and decreasing respiratory rate. In the pediatric cohort, minimum driving pressure was achieved by reducing tidal volume and increasing respiratory rate and positive end-expiratory pressure. The Acute Respiratory Distress Syndrome Network dataset had limited scope for further reducing tidal volume, but driving pressure was still significantly reduced by increasing positive end-expiratory pressure.Conclusions: Our analysis identified different strategies that minimized driving pressure or mechanical power consistently across pediatric and adult datasets. Minimizing standard and alternative formulations of mechanical power led to significant increases in tidal volume. Targeting driving pressure for minimization resulted in ventilator settings that also reduced mechanical power and modified mechanical power, but not vice versa

Effect of mental rotation skills training on ultrasound-guided regional anaesthesia task performance by novice operators: a rater-blinded, randomised, controlled study

© 2020 British Journal of Anaesthesia Background: The effect of mental rotation training on ultrasound-guided regional anaesthesia (UGRA) skill acquisition is currently unknown. In this study we aimed to examine whether mental rotation skill training can improve UGRA task performance by novice operators. Methods: We enrolled 94 volunteers with no prior experience of UGRA in this randomised controlled study. After a baseline mental rotation test, their performance in a standardised UGRA needling task was independently assessed by two raters using the composite error score (CES) and global rating scale (GRS). Volunteers with low baseline mental rotation ability were randomised to a mental rotation training group or a no training group, and the UGRA needling task was repeated to determine the impact of the training intervention on task performance. The study primary outcome measure was UGRA needling task CES measured before and after the training intervention. Results: Multivariate analyses controlling for age, gender, and previous performance showed that participants exposed to the training intervention made significantly fewer errors (CES B=-0.66 [standard error, SE=0.17];

Optimising respiratory support for early COVID-19 pneumonia : a computational modelling study

Optimal respiratory support in early COVID-19 pneumonia is controversial and remains unclear. Using computational modelling, we examined whether lung injury might be exacerbated in early COVID-19 by assessing the impact of conventional oxygen therapy (COT), high-flow nasal oxygen therapy (HFNOT), continuous positive airway pressure (CPAP), and noninvasive ventilation (NIV). Using an established multi-compartmental cardiopulmonary simulator, we first modelled COT at a fixed FiO (0.6) with elevated respiratory effort for 30 min in 120 spontaneously breathing patients, before initiating HFNOT, CPAP, or NIV. Respiratory effort was then reduced progressively over 30-min intervals. Oxygenation, respiratory effort, and lung stress/strain were quantified. Lung-protective mechanical ventilation was also simulated in the same cohort. HFNOT, CPAP, and NIV improved oxygenation compared with conventional therapy, but also initially increased total lung stress and strain. Improved oxygenation with CPAP reduced respiratory effort but lung stress/strain remained elevated for CPAP >5 cm H O. With reduced respiratory effort, HFNOT maintained better oxygenation and reduced total lung stress, with no increase in total lung strain. Compared with 10 cm H O PEEP, 4 cm H O PEEP in NIV reduced total lung stress, but high total lung strain persisted even with less respiratory effort. Lung-protective mechanical ventilation improved oxygenation while minimising lung injury. The failure of noninvasive ventilatory support to reduce respiratory effort may exacerbate pulmonary injury in patients with early COVID-19 pneumonia. HFNOT reduces lung strain and achieves similar oxygenation to CPAP/NIV. Invasive mechanical ventilation may be less injurious than noninvasive support in patients with high respiratory effort