mercredi 5 février 2020 

14h10 - 15h10


 
E08

Ventilation mécanique : de la physiologie à la clinique

MODÉRATEUR(S) :  Lise PIQUILLOUD (Lausanne, SUISSE ), Matthieu SCHMIDT (PARIS)  
  

Relationship between diaphragm thickening fraction and transdiaphragmatic pressure in healthy and mechanically ventilated patients: a breath by breath analysis

Orateur(s) :   Thomas POULARD (Paris) 

Auteur(s) :  Quentin FOSSÉ (Paris)   Jean luc GENNISSON (Orsay)   Marie cécile NIÉRAT (Paris)   Jean yves HOGREL (Paris)   Thomas SIMILOWSKI (Paris)   Alexandre DEMOULE (Paris)   Damien BACHASSON (Paris)   Martin DRES (Paris)  

14h10 - 14h25
Durée de la présentation : 10 min
Durée de la discussion : 5 min


Abstract : 
Relationship between diaphragm thickening fraction and transdiaphragmatic pressure in healthy and mechanically ventilated patients: a breath by breath analysis

Introduction / Rationale :
Diaphragm thickening fraction (TFdi) measured by ultrasound (US) is widely used in clinical research to evaluate diaphragm function in order to guide clinicians in providing optimal ventilator support. Studies reported TFdi cut-off values that could help in predicting weaning outcome in mechanically ventilated (MV) patients, but surprisingly, very little is known on the relationship between TFdi and the changes in transdiaphragmatic pressure (ΔPdi), the reference method. The present study investigated the relationship between ΔPdi and TFdi in healthy subjects and in MV patients.

Méthodes / Patients and Methods :
Pdi was monitored with gastric and esophageal catheters and US was performed at the zone of apposition of the right hemi-diaphragm. Healthy subjects breathed against an external inspiratory threshold load of 0-50% of maximal inspiratory pressure. MV patients were tested under several ventilator assistances before performing a spontaneous breathing trial. A breath by breath analysis was performed to confront ΔPdi and TFdi for a given breathing cycle. Pearson correlation coefficients (r) were used to determine within-individual and overall relationships between ΔPdi and TFdi.

Résultats / Results :
Fifteen healthy volunteers and 22 MV patients were studied. One healthy subject displayed a significant positive correlation between ΔPdi and TFdi (r=0.32, p<0.01). Only three of the 22 MV patients presented with a significant positive correlation between ΔPdi and TFdi (mean r=0.67, 95% CIs [0.41, 0.83] in patients with significant ΔPdi-TFdi correlation, all p<0.01). Overall relationship between ΔPdi and TFdi in MV patients was weak (R=0.17, 95% CIs [0.04, 0.29], p<0.05). Individual relationships between ΔPdi and TFdi and averaged values for every condition tested are presented in Fig. 1.

Discussion / Discussion :


Conclusion / Conclusion :
These findings show that TFdi does not generally correlate with Pdi suggesting that TFdi may not be used as a surrogate for Pdi. The explanations for this lack of correlation deserve further studies.
 

Accuracy of clinical estimation of the respiratory effort under pressure support ventilation

Orateur(s) :   Samuel TUFFET (Créteil) 

Auteur(s) :  François PERIER (Créteil)   Anne-fleur HAUDEBOURG (Créteil)   Nicolas DE PROST (Créteil)   Keyvan RAZAZI (Créteil)   Armand MEKONTSO DESSAP (Créteil)   Guillaume CARTEAUX (Créteil)  

14h25 - 14h40
Durée de la présentation : 10 min
Durée de la discussion : 5 min


Abstract : 
Accuracy of clinical estimation of the respiratory effort under pressure support ventilation

Introduction / Rationale :
One of the main aims of partial ventilatory support is to maintain the patient’s respiratory effort within a normal range. In clinical routine, the respiratory effort is assessed by clinical judgment, whose accuracy is unknown. In this study, we assessed the accuracy of clinical estimation of the respiratory effort under pressure support ventilation (PSV).

Méthodes / Patients and Methods :
In this prospective monocenter study, patients under mechanical ventilation were included within the first two days after switching from assist control ventilation to PSV. Flow, airway pressure, and esophageal pressure were recorded and respiratory effort indices were computed using the FluxMed device (MBMED). Respiratory effort was classified as normal (esophageal pressure time product (PTPes) between 50 and 150 cmH2O.s.min-1 (1)), insufficient (PTPes < 50 cmH2O.s.min-1) or excessive (PTPes > 150 cmH2O.s.min-1). A senior physician, a resident and a nurse were independently asked to clinically evaluate patient’s respiratory effort using a five levels scale: very low, low, normal, high and very high respiratory effort. Data are reported as median [1st-3rd quartile] or number (percentage).

Résultats / Results :
Thirty patients, aged 65 years [57-71], with a median SOFA score of 6 [4-9], were included so far. They had spent 9 days [6-12] under mechanical ventilation before inclusion. Median PTPes was 175 cmH2O.s.min-1 [98-244]. At the time of assessment, respiratory effort was insufficient in two patients (7%), normal in 10 (33%), and excessive in 18 (60%). Senior physician’s clinical estimation misclassified the respiratory effort in 12 patients (40%). Sensibility/specificity of the senior physician estimation to detect insufficient, normal and excessive respiratory effort were 0.50/0.89, 0.50/0.70 and 0.67/0.75, respectively. Accuracy of the resident and nurse evaluations was consistent with that of senior physician. By univariate analysis, higher SOFA score at inclusion (p=0.02) and higher age (p=0.03) were significantly associated with non-detection of excessive respiratory effort.

Discussion / Discussion :


Conclusion / Conclusion :
During the two days after switching from assist control ventilation to PSV, our preliminary data suggest that: 1/ excessive respiratory efforts are frequently observed and 2/ the clinical judgment frequently fails to adequately classify the level of respiratory effort, making the excessive efforts underdiagnosed.


1. the PLeUral pressure working Group (PLUG—Acute Respiratory Failure section of the European Society of Intensive Care Medicine), Mauri T, Yoshida T, Bellani G, Goligher EC, Carteaux G, et al. Esophageal and transpulmonary pressure in the clinical setting: meaning, usefulness and perspectives. Intensive Care Medicine. sept 2016;42(9):1360-73.
 

Influence of body mass index on respiratory mechanics in acute respiratory distress syndrome: a multicenter cohort study.

Orateur(s) :   Jean-Luc DIEHL (Paris) 

Auteur(s) :  Rémi COUDROY (Poitiers)   Damien VIMPERE (Paris)   Nadia AISSAOUI (Paris)   Romy YOUNAN (Paris)   Clotilde BAILLEUL (Paris)   Amélie COUTEAU-CHARDON (Paris)   Aymeric LANCELOT (Paris)   Emmanuel GUÉROT (Paris)   Chen LU (Toronto)   Laurent BROCHARD (Toronto, CANADA)  

14h40 - 14h55
Durée de la présentation : 10 min
Durée de la discussion : 5 min


Abstract : 
Influence of body mass index on respiratory mechanics in acute respiratory distress syndrome: a multicenter cohort study.

Introduction / Rationale :
Overweight and obesity are increasingly prevalent worldwide and account for about 30-40% of patients with acute respiratory distress syndrome (ARDS). How body mass index (BMI) influences respiratory mechanics in ARDS is unclear.

Méthodes / Patients and Methods :
This study is a secondary analysis of 2 cohorts of ARDS according to the Berlin definition: a bicenter Canadian study of 45 ARDS of any BMI enrolled in a prospective study (NCT02457741), and a French monocenter cohort of selected ARDS with a BMI > 40 kg/m2. Airway pressure, flow and esophageal pressure were collected in all patients and we report data at a set positive end-expiratory pressure (PEEP) of 5 cmH2O. Presence of complete airway closure and airway opening pressure were assessed using a low-flow inflation pressure-volume curve. End expiratory lung volume (EELV) was measured using the nitrogen washout/washin technique. The ratio EELV to predicted functional residual capacity was calculated.
Patients were sorted in 3 groups according to the World Health Organization overweight classification (BMI < 30, from 30 to < 40, and ≥ 40 kg/m2).

Résultats / Results :
Among the 54 patients included, 18 patients (34%) had BMI < 30 kg/m2, 16 (30%) between 30 and 40 kg/m2, and 19 (36%) ≥ 40 kg/m2. The median PaO2/FiO2 was 138 mmHg with a PEEP of 15 cmH2O, and mortality was 32% without difference across groups.
Airway closure occurrence increased with BMI (22%, 38% and 58%, p= 0.04). When present, airway opening pressure was 9.6 cmH2O (8.5-13.2) and similar between the 3 groups. With increasing BMI, total PEEP increased from 6.0 to 9.0 cmH2O between groups (p= 0.02). All values of esophageal pressure increased with BMI. End-expiratory esophageal pressure was strongly correlated with BMI (rho= 0.71, p<0.001), as illustrated in Figure 1. Consequently end-expiratory transpulmonary pressure decreased from -2.7 to -9.3 cm H2O with increasing BMI (p= 0.008). The ratio of EELV to predicted functional residual capacity was negatively correlated with end-expiratory pressure (Rho= -0.39, p= 0.01), but not with BMI.
Driving pressure and elastance of the respiratory system, chest wall and lung were similar across all ranges of BMI. Likewise, EELV was similar between groups.

Discussion / Discussion :


Conclusion / Conclusion :
In ARDS, increasing BMI is associated with increased occurrence of airway closure and increased values of esophageal pressure. Conversely, chest wall elastance is not influenced by BMI, as well as lung elastance. Including BMI in interpreting respiratory mechanics in ARDS patients can provide additional information for the clinical management.
 

Impact of tidal volume during the “transition period” following neuromuscular blockade cessation in ARDS: an observational study

Orateur(s) :   Safaa NEMLAGHI (Paris) 

Auteur(s) :  Anne-fleur HAUDEBOURG (Créteil)   François PERIER (Créteil)   Nicolas DE PROST (Créteil)   Keyvan RAZAZI (Créteil)   Guillaume VOIRIOT (Paris)   Muriel FARTOUKH (Paris)   Armand MEKONTSO DESSAP (Créteil)   Guillaume CARTEAUX (Créteil)  

14h55 - 15h10
Durée de la présentation : 10 min
Durée de la discussion : 5 min


Abstract : 
Impact of tidal volume during the “transition period” following neuromuscular blockade cessation in ARDS: an observational study

Introduction / Rationale :
Low tidal volume is the cornerstone of protective ventilation in the initial phase of ARDS (1). Whether such low tidal volume can still be achieved when the patient is allowed to breathe spontaneously under pressure support ventilation (PSV) is unknown. In moderate-to-severe ARDS patients receiving neuromuscular blockade, we assessed the tidal volume and its potential association with the outcome during the “transition period” following neuromuscular blockade.

Méthodes / Patients and Methods :
Retrospective observational study in two university intensive care units. Patients fulfilling moderate-to-severe ARDS criteria less than 72 hours after intubation and receiving neuromuscular blockers were included upon entry in the “transition period”. We defined the “transition period” as the 72 hours following neuromuscular blockers cessation. Ventilatory and hemodynamic parameters were recorded every 3 hours during the “transition period”. Primary outcome was the association between mean tidal volume under pressure support ventilation during the “transition period” and the 28-day mortality after adjustment for confounding factors. Data are reported as median [1st-3rd quartile] or number (percentage).

Résultats / Results :
One hundred nine patients were included, with a PaO2/FiO2 ratio of 100 mmHg [76-165] at intubation and 194 mm Hg [158-244] at inclusion and a SOFA score at 7 [4.5-10]. Patients had been ventilated two days [1-3.8] before inclusion. During the “transition period”, 88 patients (80.7%) were switched to PSV. The median duration of PSV was 42 hours [27-48]. The mean tidal volume under PSV was significantly lower in survivors than in non survivors at day 28 (7.1 ml/kg [6.3-7.9] vs. 7.8 ml/kg [6.8-9.4] respectively, p = 0.007). By multivariate analysis (Cox proportional hazards regression model), mean tidal volume during PSV remained independently associated with the 28-day mortality after adjusting for SOFA score and immunosuppression. Patients with a mean tidal volume above 8 mL/kg under PSV during the “transition period” had a lower cumulative probability of survival at day 28 as compared with others (Log rank test, p=0.008) (Figure 1).

Discussion / Discussion :


Conclusion / Conclusion :
In patients with moderate-to-severe ARDS, a higher tidal volume under PSV within the 72 hours following neuromuscular blockers cessation is independently associated with the 28-day mortality.

1. Papazian L, Aubron C, Brochard L, Chiche J-D, Combes A, Dreyfuss D, et al. Formal guidelines: management of acute respiratory distress syndrome. Ann Intensive Care. 2019 Dec;9(1):69.