Tidal lung hysteresis to interpret PEEP-induced changes in compliance in ARDS patients.

BACKGROUND: In ARDS, the PEEP level associated with the best respiratory system compliance is often selected; however, intra-tidal recruitment can increase compliance, falsely suggesting improvement in baseline mechanics. Tidal lung hysteresis increases with intra-tidal recruitment and can help interpreting changes in compliance. This study aims to assess tidal recruitment in ARDS patients and to test a combined approach, based on tidal hysteresis and compliance, to interpret decremental PEEP trials. METHODS: A decremental PEEP trial was performed in 38 COVID-19 moderate to severe ARDS patients. At each step, we performed a low-flow inflation-deflation manoeuvre between PEEP and a constant plateau pressure, to measure tidal hysteresis and compliance. RESULTS: According to changes of tidal hysteresis, three typical patterns were observed: 10 (26%) patients showed consistently high tidal-recruitment, 12 (32%) consistently low tidal-recruitment and 16 (42%) displayed a biphasic pattern moving from low to high tidal-recruitment below a certain PEEP. Compliance increased after 82% of PEEP step decreases and this was associated to a large increase of tidal hysteresis in 44% of cases. Agreement between best compliance and combined approaches was accordingly poor (K = 0.024). The combined approach suggested to increase PEEP in high tidal-recruiters, mainly to keep PEEP constant in biphasic pattern and to decrease PEEP in low tidal-recruiters. PEEP based on the combined approach was associated with lower tidal hysteresis (92.7 ± 20.9 vs. 204.7 ± 110.0 mL; p < 0.001) and lower dissipated energy per breath (0.1 ± 0.1 vs. 0.4 ± 0.2 J; p < 0.001) compared to the best compliance approach. Tidal hysteresis ≥ 100 mL was highly predictive of tidal recruitment at next PEEP step reduction (AUC 0.97; p < 0.001). CONCLUSIONS: Assessment of tidal hysteresis improves the interpretation of decremental PEEP trials and may help limiting tidal recruitment and energy dissipated into the respiratory system during mechanical ventilation of ARDS patients.

Timing of inspiratory muscle activity detected from airway pressure and flow during pressure support ventilation: the waveform method.

BACKGROUND: Whether respiratory efforts and their timing can be reliably detected during pressure support ventilation using standard ventilator waveforms is unclear. This would give the opportunity to assess and improve patient-ventilator interaction without the need of special equipment. METHODS: In 16 patients under invasive pressure support ventilation, flow and pressure waveforms were obtained from proximal sensors and analyzed by three trained physicians and one resident to assess patient's spontaneous activity. A systematic method (the waveform method) based on explicit rules was adopted. Esophageal pressure tracings were analyzed independently and used as reference. Breaths were classified as assisted or auto-triggered, double-triggered or ineffective. For assisted breaths, trigger delay, early and late cycling (minor asynchronies) were diagnosed. The percentage of breaths with major asynchronies (asynchrony index) and total asynchrony time were computed. RESULTS: Out of 4426 analyzed breaths, 94.1% (70.4-99.4) were assisted, 0.0% (0.0-0.2) auto-triggered and 5.8% (0.4-29.6) ineffective. Asynchrony index was 5.9% (0.6-29.6). Total asynchrony time represented 22.4% (16.3-30.1) of recording time and was mainly due to minor asynchronies. Applying the waveform method resulted in an inter-operator agreement of 0.99 (0.98-0.99); 99.5% of efforts were detected on waveforms and agreement with the reference in detecting major asynchronies was 0.99 (0.98-0.99). Timing of respiratory efforts was accurately detected on waveforms: AUC for trigger delay, cycling delay and early cycling was 0.865 (0.853-0.876), 0.903 (0.892-0.914) and 0.983 (0.970-0.991), respectively. CONCLUSIONS: Ventilator waveforms can be used alone to reliably assess patient's spontaneous activity and patient-ventilator interaction provided that a systematic method is adopted.

Ethylene glycol poisoning requiring veno-arterial ECMO: A case report.

Supportive care is the cornerstone of the poisoned patient's treatment, waiting for eventual antidotes to act. We recently treated a case of a severe Ethylene Glycol intoxication with early-onset veno-arterial ECMO. The patient was taken to our Emergency Department with the suspicion of acute cerebrovascular accident, since he was found unconscious at home. The arterial blood gas and blood tests showed a severe metabolic acidosis with high serum lactates and creatinine levels. The cerebral Computed Tomography was negative. The rapid increase in serum lactates suggested Ethylene Glycol intoxication. Although the patient was not in shock yet, arterial and venous introducers were placed in to the femoral vessels so that when the patient showed the first signs of cardiogenic shock, veno-arterial ECMO could be initiated in a very short time. The hemodynamic state progressively improved and V-A ECMO was removed after 16 h of support with complete recovery.

Mechanical Ventilation Guided by Uncalibrated Esophageal Pressure May Be Potentially Harmful.

BACKGROUND: Esophageal balloon calibration was proposed in acute respiratory failure patients to improve esophageal pressure assessment. In a clinical setting characterized by a high variability of abdominal load and intrathoracic pressure (i.e., pelvic robotic surgery), the authors hypothesized that esophageal balloon calibration could improve esophageal pressure measurements. Accordingly, the authors assessed the impact of esophageal balloon calibration compared to conventional uncalibrated approach during pelvic robotic surgery. METHODS: In 30 adult patients, scheduled for elective pelvic robotic surgery, calibrated end-expiratory and end-inspiratory esophageal pressure, and the associated respiratory variations were obtained at baseline, after pneumoperitoneum-Trendelenburg application, and with positive end-expiratory pressure (PEEP) administration and compared to uncalibrated values measured at 4-ml filling volume, as per manufacturer recommendation. Data are expressed as median and [25th, 75th percentile]. RESULTS: Ninety calibrations were successfully performed. Chest wall elastance worsened with pneumoperitoneum-Trendelenburg and PEEP (19.0 [15.5, 24.6] and 16.7 [11.4, 21.7] cm H2O/l) compared to baseline (8.8 [6.3, 9.8] cm H2O/l; P < 0.0001 for both comparisons). End-expiratory and end-inspiratory calibrated esophageal pressure progressively increased from baseline (3.7 [2.2, 6.0] and 7.7 [5.9, 10.2] cm H2O) to pneumoperitoneum-Trendelenburg (6.2 [3.8, 10.2] and 16.1 [13.1, 20.6] cm H2O; P = 0.014 and P < 0.001) and PEEP (8.8 [7.7, 15.6] and 18.9 [16.3, 22.0] cm H2O; P < 0.0001 vs. baseline for both comparison; P < 0.001 and P = 0.002 vs. pneumoperitoneum-Trendelenburg) and, at each study step, they were persistently lower than uncalibrated esophageal pressure (P < 0.0001 for all comparisons). Overall, difference among uncalibrated and calibrated esophageal pressure was 5.1 [3.8, 8.4] cm H2O at end-expiration and 3.8 [3.0, 6.3] cm H2O at end-inspiration. Uncalibrated esophageal pressure swing was always lower than calibrated one (P < 0.0001 for all comparisons) with a difference of -1.0 [-1.8, -0.4] cm H2O. CONCLUSIONS: In a clinical setting with variable chest wall mechanics, uncalibrated measurements substantially overestimated absolute values and underestimated respiratory variations of esophageal pressure. Calibration could substantially improve mechanical ventilation guided by esophageal pressure.

Brief Report: A Case of Tramadol Overdose: Extracorporeal Life Support and Hemoperfusion as Life-Saving Treatment.

We describe the case of a 49-year-old woman with a Tramadol intoxication associated with multiorgan failure. Veno-arterial femoro-femoral extracorporeal life support (VA-ECLS) and hemoperfusion (HP) were used as rescue treatments. The emergency medical service found a woman at home unconscious. Once in the hospital, she was intubated and catecholamines support was immediately started for a severe shock. Brain CT was normal, whereas EEG revealed a metabolic encephalopathy pattern. Toxic levels of Tramadol and Quetiapine were detected. VA-ECLS was implanted due to persistent multiorgan failure, and HP with a charcoal cartridge was set to increase the Tramadol clearance. To quantify the charcoal cartridge's removal efficiency of Tramadol, Tramadol concentration was measured before and after the cartridge and before and after the treatment in the patient's blood. The charcoal cartridge showed good extraction ratio during the treatment and no significant rebound effect. VA-ECLS and HP allowed the patient to be weaned from vasoconstrictors and the resolution of the organ failures. These treatments might be lifesaving in the Tramadol intoxication.

Persistent pollutants: focus on perfluorinated compounds and kidney.

PURPOSE OF REVIEW: There is increasing interest in the environmental and human damage caused by pollutants. Big efforts are continuously made to monitor their levels and identify safe thresholds. For this purpose, an essential step is to prioritize harmful substances and understand their effect on human body. Perfluorinated compounds (PFCs) deserve particular attention because of their wide diffusion and potential correlation with different diseases including glucose intolerance, hyperlipidaemia, thyroid diseases, gestational diabetes mellitus and hypertension, testicular and genitourinary cancer as well as impaired kidney function. This review focuses on the renal effects of PFCs, with the attempt to clarify their occurrence and pathogenetic mechanisms. RECENT FINDINGS: We reviewed MEDLINE and EMBASE citations between 31 October 2017 and 31 May 2019 and selected human studies measuring PFCs exposure, kidney function markers and the ability of haemodialysis to remove PFCs from the circulating blood. It has been currently clarified that exposure to PFCs is linked with an impaired kidney function and that they can be removed by blood purification. SUMMARY: Further studies are required on the potential synergic negative effect of PFCs co-exposure with other pollutants as well as animal studies about the removal capacity of different haemodialysis membranes.

Assessment of Lung Aeration and Recruitment by CT Scan and Ultrasound in Acute Respiratory Distress Syndrome Patients.

OBJECTIVES: Lung ultrasound is commonly used to evaluate lung morphology in patients with acute respiratory distress syndrome. Aim of this study was to determine lung ultrasound reliability in assessing lung aeration and positive end-expiratory pressure-induced recruitment compared with CT. DESIGN: Randomized crossover study. SETTING: University hospital ICU. PATIENTS: Twenty sedated paralyzed acute respiratory distress syndrome patients: age 56 years (43-72 yr), body mass index 25 kg/m (22-27 kg/m), and PaO2/FIO2 160 (113-218). INTERVENTIONS: Lung CT and lung ultrasound examination were performed at positive end-expiratory pressure 5 and 15 cm H2O. MEASUREMENTS AND MAIN RESULTS: Global and regional Lung Ultrasound scores were compared with CT quantitative analysis. Lung recruitment (i.e., decrease in not aerated tissue as assessed with CT) was compared with global Lung Ultrasound score variations. Global Lung Ultrasound score was strongly associated with average lung tissue density at positive end-expiratory pressure 5 (R = 0.78; p < 0.0001) and positive end-expiratory pressure 15 (R = 0.62; p < 0.0001). Regional Lung Ultrasound score strongly correlated with tissue density at positive end-expiratory pressure 5 (rs = 0.79; p < 0.0001) and positive end-expiratory pressure 15 (rs = 0.79; p < 0.0001). Each step increase of regional Lung Ultrasound score was associated with significant increase of tissue density (p < 0.005). A substantial agreement was found between regional Lung Ultrasound score and CT classification at positive end-expiratory pressure 5 (k = 0.69 [0.63-0.75]) and at positive end-expiratory pressure 15 (k = 0.70 [0.64-0.75]). At positive end-expiratory pressure 15, both global Lung Ultrasound score (22 [16-27] vs 26 [21-29]; p < 0.0001) and not aerated tissue (42% [25-57%] vs 52% [39-67%]; p < 0.0001) decreased. However, Lung Ultrasound score variations were not associated with lung recruitment (R = 0.01; p = 0.67). CONCLUSIONS: Lung Ultrasound score is a valid tool to assess regional and global lung aeration. Global Lung Ultrasound score variations should not be used for bedside assessment of positive end-expiratory pressure-induced recruitment.

Modified Lung Ultrasound Score for Assessing and Monitoring Pulmonary Aeration.

Purpose Lung Ultrasound Score (LUSS) is a useful tool for lung aeration assessment but presents two theoretical limitations. First, standard LUSS is based on longitudinal scan and detection of number/coalescence of B lines. In the longitudinal scan pleura visualization is limited by intercostal space width. Moreover, coalescence of B lines to define severe loss of aeration is not suitable for non-homogeneous lung pathologies where focal coalescence is possible. We therefore compared longitudinal vs. transversal scan and also cLUSS (standard coalescence-based LUSS) vs. qLUSS (quantitative LUSS based on % of involved pleura). Materials and methods 38 ICU patients were examined in 12 thoracic areas in longitudinal and transversal scan. B lines (number, coalescence), subpleural consolidations (SP), pleural length and pleural involvement (> or ≤ 50 %) were assessed. cLUSS and qLUSS were computed in longitudinal and transversal scan. Results Transversal scan visualized wider (3.9 [IQR 3.8 - 3.9] vs 2.0 [1.6 - 2.5] cm, p < 0.0001) and more constant (variance 0.02 vs 0.34 cm, p < 0.0001) pleural length, more B lines (70 vs 59 % of scans, p < 0.0001), coalescence (39 vs 28 %, p < 0.0001) and SP (22 vs 14 %, p < 0.0001) compared to longitudinal scan. Pleural involvement > 50 % was observed in 17 % and coalescence in 33 % of cases. Focal coalescence accounted for 52 % of cases of coalescence. qLUSS-transv generated a different distribution of aeration scores compared to cLUSS-long (p < 0.0001). Conclusion In unselected ICU patients, variability of pleural length in longitudinal scans is high and focal coalescence is frequent. Transversal scan and quantification of pleural involvement are simple measures to overcome these limitations of LUSS.

Waveforms-guided cycling-off during pressure support ventilation improves both inspiratory and expiratory patient-ventilator synchronisation.

OBJECTIVE: To test the performance of a software able to control mechanical ventilator cycling-off by means of automatic, real-time analysis of ventilator waveforms during pressure support ventilation. DESIGN: Prospective randomised crossover study. SETTING: University Intensive Care Unit. PATIENTS: Fifteen difficult-to-wean patients under pressure support ventilation. INTERVENTIONS: Patients were ventilated using a G5 ventilator (Hamilton Medical, Bonaduz, Switzerland) with three different cycling-off settings: standard (expiratory trigger sensitivity set at 25% of peak inspiratory flow), optimised by an expert clinician and automated; the last two settings were tested at baseline pressure support and after a 50% increase in pressure support. MEASUREMENTS AND MAIN RESULTS: Ventilator waveforms were recorded and analysed by four physicians experts in waveforms analysis. Major and minor asynchronies were detected and total asynchrony time computed. Automation compared to standard setting reduced cycling delay from 407 ms [257-567] to 59 ms [22-111] and ineffective efforts from 12.5% [3.4-46.4] to 2.8% [1.9-4.6]) at baseline support (p < 0.001); expert optimisation performed similarly. At high support both cycling delay and ineffective efforts increased, mainly in the case of expert setting, with the need of reoptimisation of expiratory trigger sensitivity. At baseline support, asynchrony time decreased from 39.9% [27.4-58.7] with standard setting to 32% [22.3-39.4] with expert optimisation (p < 0.01) and to 24.4% [19.6-32.5] with automation (p < 0.001). Both at baseline and at high support, asynchrony time was lower with automation than with expert setting. CONCLUSIONS: Cycling-off guided by automated real-time waveforms analysis seems a reliable solution to improve synchronisation in difficult-to-wean patients under pressure support ventilation.

Combined ultrasound-CT approach to monitor acute exacerbation of interstitial lung disease.

BACKGROUND: Lung ultrasound is a bedside non-irradiating tool for assessment and monitoring of lung diseases. A lung ultrasound score based on visualized artefacts allows reliable quantification of lung aeration, and is useful to monitor mechanical ventilation setting, fluid resuscitation and antibiotic response in critical care. In the context of interstitial lung diseases associated to connective tissue disorders, lung ultrasound has been integrated to computed tomography for diagnosis and follow-up monitoring of chronic lung disease progression. CASE PRESENTATION: This case describes a severe acute exacerbation of interstitial lung disease associated to dermatomyositis-polymyositis requiring prolonged extra-corporeal life support. Lung ultrasound score was performed daily and allowed monitoring and guiding both the need of advanced imaging as computed tomography and immunosuppressive therapy. CONCLUSIONS: This case suggests lung ultrasound may be a useful monitoring tool for the response to immunosuppressive therapy in acute severe rheumatic interstitial lung disease, where chest X-ray is poorly informative, and transportation is at high risk.

Lung Ultrasound in Patients with Acute Respiratory Failure Reduces Conventional Imaging and Health Care Provider Exposure to COVID-19.

Lung ultrasound gained a leading position in the last year as an imaging technique for the assessment and management of patients with acute respiratory failure. In coronavirus disease 2019 (COVID-19), its role may be of further importance because it is performed bedside and may limit chest X-ray and the need for transport to radiology for computed tomography (CT) scan. Since February 21, we progressively turned into a coronavirus-dedicated intensive care unit and applied an ultrasound-based approach to avoid traditional imaging and limit contamination as much as possible. We performed a complete daily examination with lung ultrasound score computation and systematic search of complications (pneumothorax, ventilator-associated pneumonia); on-duty physicians were free to perform CT or chest X-ray when deemed indicated. We compared conventional imaging exams performed in the first 4 wk of the COVID-19 epidemic with those in the same time frame in 2019: there were 84 patients in 2020 and 112 in 2019; 64 and 22 (76.2% vs. 19.6%, p < 0.001) had acute respiratory failure, respectively, of which 55 (85.9%) were COVID-19 in 2020. When COVID-19 patients in 2020 were compared with acute respiratory failure patients in 2019, the median number of chest X-rays was 1.0 (1.0-2.0) versus 3.0 (1.0-4.0) (p = 0.0098); 2 patients 2 (3.6%) versus 7 patients (31.8%) had undergone at least one thoracic CT scan (p = 0.001). A self-imposed ultrasound-based approach reduces the number of chest X-rays and thoracic CT scans in COVID-19 patients compared with patients with standard acute respiratory failure, thus reducing the number of health care providers exposed to possible contamination and sparing personal protective equipment.

Technical aspects of bedside respiratory monitoring of transpulmonary pressure.

Transpulmonary pressure, that is the difference between airway pressure (Paw) and pleural pressure, is considered one of the most important parameters to know in order to set a safe mechanical ventilation in acute respiratory distress syndrome (ARDS) patients but also in critically ill obese patients, in abdominal pathologies or in pathologies affecting the chest wall itself. Transpulmonary pressure should rely on the assessment of intrathoracic pleural pressure. Esophageal pressure (Pes) is considered the best surrogate of pleural pressure in critically ill patients, but concerns about its reliability exist. The aim of this article is to describe the technique of Pes measurement in mechanically ventilated patients: the catheter insertion, the proper balloon placement and filling, the validation test and specific procedures to remove the main artifacts will be discussed.