Physiologic Effects of ECMO in Patients with Severe Acute Respiratory Distress Syndrome.

RATIONALE: Blood flow rate affects mixed venous oxygenation (SvO2) during venovenous extracorporeal membrane oxygenation (ECMO), with possible effects on the pulmonary circulation and the right heart function. OBJECTIVES: We aimed at describing the physiologic effects of different levels of SvO2 obtained by changing ECMO blood flow, in patients with severe ARDS receiving ECMO and controlled mechanical ventilation. METHODS: Low (SvO2 target 70-75%), intermediate (SvO2 target 75-80%) and high (SvO2 target > 80%) ECMO blood flows were applied for 30 minutes in random order in 20 patients. Mechanical ventilation settings were left unchanged. The hemodynamic and pulmonary effects were assessed with pulmonary artery catheter and electrical impedance tomography (EIT). MEASUREMENTS AND MAIN RESULTS: Cardiac output decreased from low to intermediate and to high blood flow/SvO2 (9.2 [6.2-10.9] vs 8.3 [5.9-9.8] vs 7.9 [6.5-9.1] L/min, p = 0.014), as well as mean pulmonary artery pressure (34 ± 6 vs 31 ± 6 vs 30 ± 5 mmHg, p < 0.001), and right ventricle stroke work index (14.2 ± 4.4 vs 12.2 ± 3.6 vs 11.4 ± 3.2 g*m/beat/m2, p = 0.002). Cardiac output was inversely correlated with mixed venous and arterial PO2 values (R2 = 0.257, p = 0.031 and R2 = 0.324, p = 0.05). Pulmonary artery pressure was correlated with decreasing mixed venous PO2 (R2 = 0.29, p <0.001) and with increasing cardiac output (R2 = 0.378 p < 0.007). Measures of ventilation/perfusion mismatch did not differ between the three steps. CONCLUSIONS: In severe ARDS patients, increased ECMO blood flow rate resulting in higher SvO2 decreases pulmonary artery pressure, cardiac output, and right heart workload. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Bedside Selection of Positive End Expiratory Pressure by Electrical Impedance Tomography in Patients Undergoing Veno-Venous Extracorporeal Membrane Oxygenation Support: A Comparison between COVID-19 ARDS and ARDS from Other Etiologies.

BACKGROUND: The interest in protective ventilation strategies and individualized approaches for patients with severe illness on veno venous extracorporeal support has increased in recent years. Wide heterogeneity exists among patients with COVID-19 related acute respiratory distress syndrome (C-ARDS) and ARDS from other etiologies (NC-ARDS). EIT is a useful tool for the accurate analysis of regional lung volume distribution and allows for a tailored ventilatory setting. The aim of this work is to retrospectively describe the results of EIT assessments performed in patients C-ARDS and NC-ARDS undergoing V-V ECMO support. METHODS: A clinical EIT-guided decremental PEEP trail was conducted for all patients included in the study and mechanically ventilated. RESULTS: 12 patients with C-ARDS and 12 patients with NC-ARDS were included in the study for a total of 13 and 18 EIT evaluations, respectively. No significant differences in arterial blood gas, respiratory parameters, and regional ventilation before and after the EIT exam were recorded. The subset of patients with NC-ARDS whose EIT exam led to PEEP modification was characterized by a lower baseline compliance compared with the C-ARDS group: 18 (16-28) vs. 27 (24-30) (p = 0.04). Overdistension significantly increased at higher steps only for the NC-ARDS group. A higher percentage of overdistension was described in patients with NC-ARDS when compared with patients with C-ARDS. CONCLUSIONS: EIT is feasible in patients with COVID-19-associated ARDS on veno-venous extracorporeal support and may help in tailoring the PEEP setting. Overall, severe COVID-19-related ARDS presents respiratory characteristics similar to severe "classical" NC-ARDS. However, C-ARDS is associated with a lower risk of overdistension at a higher PEEP level compared with NC-ARDS.

Bag valve resuscitator versus Mapleson C circuit during manual ventilation: A bench top study.

BACKGROUND: Manual ventilation is life saving in critically ill patients. The lack of airway pressure monitoring makes it operator and device dependent. In this bench top-study, we compared a self- inflating bag valve resuscitator and a Mapleson C circuit during manual ventilation performed by critical care nurses under normal and pathologic conditions, with a special focus on delivered positive end expiratory pressure (PEEP). METHODS: Three different respiratory patterns (normal, restrictive and obstructive) were reproduced by a breathing simulator. Twenty nurses provided manual ventilation with a specific ventilatory pattern. Airway pressure, tidal volume and respiratory rate were recorded. Absolute value, error (difference between recorded and target values) and variability of PEEP were analysed. RESULTS: 3820 breathing traces were analysed. PEEP error was significantly higher with Mapelson C (43.3% vs 5.9% respectively, p < 0.001). This finding was confirmed regardless of operator skill and scenario. PEEP was more variable with Mapelson C (p < 0.05 in all scenarios). Ventilation of obstructive patients with Mapelson C resulted in higher PEEP levels compared to the reference value. Conversely, in the restrictive setting, PEEP was lower. Difference between PEEP and the minimum pressure recorded during the respiratory cycle was significantly higher with Mapelson C (p < 0.05). CONCLUSIONS: Manual ventilation with a Mapleson C circuit delivered a less accurate and less stable PEEP level compared to a self-inflating bag valve resuscitator.

Feasibility and physiological effects of prone positioning in non-intubated patients with acute respiratory failure due to COVID-19 (PRON-COVID): a prospective cohort study.

BACKGROUND: The COVID-19 pandemic is challenging advanced health systems, which are dealing with an overwhelming number of patients in need of intensive care for respiratory failure, often requiring intubation. Prone positioning in intubated patients is known to reduce mortality in moderate-to-severe acute respiratory distress syndrome. We aimed to investigate feasibility and effect on gas exchange of prone positioning in awake, non-intubated patients with COVID-19-related pneumonia. METHODS: In this prospective, feasibility, cohort study, patients aged 18-75 years with a confirmed diagnosis of COVID-19-related pneumonia receiving supplemental oxygen or non-invasive continuous positive airway pressure were recruited from San Gerardo Hospital, Monza, Italy. We collected baseline data on demographics, anthropometrics, arterial blood gas, and ventilation parameters. After baseline data collection, patients were helped into the prone position, which was maintained for a minimum duration of 3 h. Clinical data were re-collected 10 min after prone positioning and 1 h after returning to the supine position. The main study outcome was the variation in oxygenation (partial pressure of oxygen [PaO2]/fractional concentration of oxygen in inspired air [FiO2]) between baseline and resupination, as an index of pulmonary recruitment. This study is registered on ClinicalTrials.gov, NCT04365959, and is now complete. FINDINGS: Between March 20 and April 9, 2020, we enrolled 56 patients, of whom 44 (79%) were male; the mean age was 57·4 years (SD 7·4) and the mean BMI was 27·5 kg/m2 (3·7). Prone positioning was feasible (ie, maintained for at least 3 h) in 47 patients (83·9% [95% CI 71·7 to 92·4]). Oxygenation substantially improved from supine to prone positioning (PaO2/FiO2 ratio 180·5 mm Hg [SD 76·6] in supine position vs 285·5 mm Hg [112·9] in prone position; p<0·0001). After resupination, improved oxygenation was maintained in 23 patients (50·0% [95% CI 34·9-65·1]; ie, responders); however, this improvement was on average not significant compared with before prone positioning (PaO2/FiO2 ratio 192·9 mm Hg [100·9] 1 h after resupination; p=0·29). Patients who maintained increased oxygenation had increased levels of inflammatory markers (C-reactive protein: 12·7 mg/L [SD 6·9] in responders vs 8·4 mg/L [6·2] in non-responders; and platelets: 241·1 × 103/µL [101·9] vs 319·8 × 103/µL [120·6]) and shorter time between admission to hospital and prone positioning (2·7 days [SD 2·1] in responders vs 4·6 days [3·7] in non-responders) than did those for whom improved oxygenation was not maintained. 13 (28%) of 46 patients were eventually intubated, seven (30%) of 23 responders and six (26%) of 23 non-responders (p=0·74). Five patients died during follow-up due to underlying disease, unrelated to study procedure. INTERPRETATION: Prone positioning was feasible and effective in rapidly ameliorating blood oxygenation in awake patients with COVID-19-related pneumonia requiring oxygen supplementation. The effect was maintained after resupination in half of the patients. Further studies are warranted to ascertain the potential benefit of this technique in improving final respiratory and global outcomes. FUNDING: University of Milan-Bicocca.

Is there a relationship between dopamine and rhegmatogenous retinal detachment?

Dopamine and its receptors have been widely studied in the neurological conditions and in the retina. In this study, we evaluated the possible role of dopamine in rhegmatogenous retinal detachment (RRD) by comparing the amount of 3,4-dihydroxyphenylacetic acid (DOPAC), a surrogate index of retinal dopamine levels, in the vitreous sample of patients affected by RRD with those affected by macular pucker and vitreous hemorrhage. Our results showed that significantly higher levels of DOPAC were found in the vitreous sample of patients affected by RRD compared with those affected by vitreous hemorrhage and macular pucker (P = 0.002). Specifically, no trace of the substance was found in vitreous hemorrhage and macular pucker samples. A slightly significant positive correlation was found among DOPAC and post-operative best corrected visual acuity (r = 0.470, P = 0.049). No correlation was found between DOPAC and the days elapsed between diagnosis and surgery (P = 0.317). For the first time our findings suggest that DOPAC is released in RRD, but not in other retinal diseases such as vitreous hemorrhage and macular pucker. Moreover, we showed a correlation between visual acuity outcome and the amount of DOPAC in the vitreous. This might have a potential, although still unknown, implication in the pathogenesis of the disease and/or in the associated photoreceptors loss. This study was approved by the Ethics Committee of Rome Tor Vergata University Hospital (R.S.92.10) on September 24, 2010.