Martin Dres

Neurally adjusted ventilatory assist improves patient–ventilator interaction during postextubation prophylactic noninvasive ventilation*

Objectives:To compare the respective impact of pressure support ventilation and naturally adjusted ventilatory assist, with and without a noninvasive mechanical ventilation algorithm, on patient–ventilator interaction. Design:Prospective 2-month study. Setting:Adult critical care unit in a tertiary university hospital. Patients:Seventeen patients receiving a prophylactic postextubation noninvasive mechanical ventilation. Interventions:Patients were randomly mechanically ventilated for 10 mins with: pressure support ventilation without a noninvasive mechanical ventilation algorithm (PSV-NIV–), pressure support ventilation with a noninvasive mechanical ventilation algorithm (PSV-NIV+), neurally adjusted ventilatory assist without a noninvasive mechanical ventilation algorithm (NAVA-NIV–), and neurally adjusted ventilatory assist with a noninvasive mechanical ventilation algorithm (NAVA-NIV+). Measurements and Main Results:Breathing pattern descriptors, diaphragm electrical activity, leak volume, inspiratory trigger delay, inspiratory time in excess, and the five main asynchronies were quantified. Asynchrony index and asynchrony index influenced by leaks were computed. Peak inspiratory pressure and diaphragm electrical activity were similar for each of the four experimental conditions. For both pressure support ventilation and neurally adjusted ventilatory assist, the noninvasive mechanical ventilation algorithm significantly reduced the level of leakage (p < .01). Inspiratory trigger delay was not affected by the noninvasive mechanical ventilation algorithm but was shorter in neurally adjusted ventilatory assist than in pressure support ventilation (p < .01). Inspiratory time in excess was shorter in neurally adjusted ventilatory assist and PSV-NIV+ than in PSV-NIV– (p < .05). Asynchrony index was not affected by the noninvasive mechanical ventilation algorithm but was significantly lower in neurally adjusted ventilatory assist than in pressure support ventilation (p < .05). Asynchrony index influenced by leaks was insignificant with neurally adjusted ventilatory assist and significantly lower than in pressure support ventilation (p < .05). There was more double triggering with neurally adjusted ventilatory assist. Conclusions:Both neurally adjusted ventilatory assist and a noninvasive mechanical ventilation algorithm improve patient–ventilator synchrony in different manners. NAVA-NIV+ offers the best compromise between a good patient–ventilator synchrony and a low level of leaks. Clinical studies are required to assess the potential clinical benefit of neurally adjusted ventilatory assist in patients receiving noninvasive mechanical ventilation. Trial Registration:Clinicaltrials.gov Identifier NCT01280760.

Critical illness-associated diaphragm weakness

Diaphragm weakness is highly prevalent in critically ill patients. It may exist prior to ICU admission and may precipitate the need for mechanical ventilation but it also frequently develops during the ICU stay. Several risk factors for diaphragm weakness have been identified; among them sepsis and mechanical ventilation play central roles. We employ the term critical illness-associated diaphragm weakness to refer to the collective effects of all mechanisms of diaphragm injury and weakness occurring in critically ill patients. Critical illness-associated diaphragm weakness is consistently associated with poor outcomes including increased ICU mortality, difficult weaning, and prolonged duration of mechanical ventilation. Bedside techniques for assessing the respiratory muscles promise to improve detection of diaphragm weakness and enable preventive or curative strategies. Inspiratory muscle training and pharmacological interventions may improve respiratory muscle function but data on clinical outcomes remain limited.

Ultrasound evaluation of diaphragm function in mechanically ventilated patients: comparison to phrenic stimulation and prognostic implications

Rationale In intensive care unit (ICU) patients, diaphragm dysfunction is associated with adverse clinical outcomes. Ultrasound measurements of diaphragm thickness, excursion (EXdi) and thickening fraction (TFdi) are putative estimators of diaphragm function, but have never been compared with phrenic nerve stimulation. Our aim was to describe the relationship between these variables and diaphragm function evaluated using the change in endotracheal pressure after phrenic nerve stimulation (Ptr,stim), and to compare their prognostic value. Methods Between November 2014 and June 2015, Ptr,stim and ultrasound variables were measured in mechanically ventilated patients <24 hours after intubation (‘initiation of mechanical ventilation (MV)’, under assist-control ventilation, ACV) and at the time of switch to pressure support ventilation (‘switch to PSV’), and compared using Spearmans correlation and receiver operating characteristic curve analysis. Diaphragm dysfunction was defined as Ptr,stim <11 cm H2O. Results 112 patients were included. At initiation of MV, Ptr,stim was not correlated to diaphragm thickness (p=0.28), EXdi (p=0.66) or TFdi (p=0.80). At switch to PSV, TFdi and EXdi were respectively very strongly and moderately correlated to Ptr,stim, (r=0.87, p<0.001 and 0.45, p=0.001), but diaphragm thickness was not (p=0.45). A TFdi <29% could reliably identify diaphragm dysfunction (sensitivity and specificity of 85% and 88%), but diaphragm thickness and EXdi could not. This value was associated with increased duration of ICU stay and MV, and mortality. Conclusions Under ACV, diaphragm thickness, EXdi and TFdi were uncorrelated to Ptr,stim. Under PSV, TFdi was strongly correlated to diaphragm strength and both were predictors of remaining length of MV and ICU and hospital death.

Diaphragm dysfunction during weaning from mechanical ventilation: an underestimated phenomenon with clinical implications

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2018. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2018. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.

Pleural effusion in difficult weaning from mechanical ventilation

Objectives To describe the incidence of pleural effusion in patients who failed a first spontaneous breathing trial (SBT) and to describe the characteristics of these patients. Methods We conducted a prospective observational study in three medical ICU. All mechanically ventilated patients were screened daily. In patients who failed their first SBT, a pleural ultrasonography was performed and the presence of PE was qualitatively quantified according to a 4-steps classification: 0: no PE; 1: small PE; 2: moderate PE and 3: large PE. In addition the main clinical characteristics of patients were collected. For statistical analysis, patients with classes 0 and 1 were regrouped, as were patients with classes 2 and 3. Results From November 2014 to March 2015, 336 patients were screened and 56 (17%) failed their first SBT. Among them, 28 patients (50%) had no PE, 18 patients (32%) had small PE (left or right), 8 (14%) patients had moderate PE and 2 (4%) patients had large PE. Patients with moderate and large PE stayed longer in ICU (19 ± 7 vs. 9 ± 7 days, p < 0.01) and had a longer duration of mechanical ventilation (14 ± 9 vs. 24 ± 12 days, p < 0.01) as compared with patients without PE and with small PE. Patients with moderate or large PE and patients without PE or with small PE shared similar characteristics at admission (age: 66 ± 14 and 61 ± 15 and SAPS 2: 55 ± 18 53 ± 15, p > 0.05). Shock as the cause of initiation of mechanical ventilation was more frequent in patients with moderate and large PE as compared to patients without and small PE (40% vs. 4%, p < 0.01). Only one patient with a large PE had a pleural evacuation but without clinical improvement. Conclusions Significant pleural effusion is often detected in difficult to wean patients (18%), and is associated with shock state as the reason for mechanical ventilation. The interest of pleural drainage in this population deserves further studies.

Ultrasonographically diagnosed diaphragmatic dysfunction and weaning failure from mechanical ventilation in critically ill patients.

Clinical data suggest that diaphragmatic dysfunction (DD) is associated with difficult weaning from mechanical ventilation. However, studies focusing specifically on diaphragmatic function in this setting are scarce. OBJECTIVE To predict the outcome of a spontaneous breathing trial (SBT) through the ultrasonographic assessment of diaphragmatic and intercostal muscle function.

Noninvasive Ventilatory Support in Acute Respiratory Distress Syndrome

The current ventilation strategy of acute respiratory distress syndrome (ARDS) is based on the use of lung-protective invasive ventilation. Since invasive ventilation is associated with potentially severe complications, there is a growing interest for alternative ventilatory support such as noninvasive ventilation (NIV) and heat and humidified high-flow oxygenation through nasal cannula (1). While NIV exerts evidenced beneficial effects in patients presenting with severe exacerbation of chronic obstructive pulmonary disease or cardiogenic pulmonary edema, the use of NIV in acute hypoxemic respiratory failure related to early ARDS is still debated. Moreover, NIV can also be deleterious in some patients, mostly by delaying needed intubation (2). There is a high interest for high-flow oxygenation through nasal cannula. High-flow oxygenation through nasal cannula has been investigated in adults with acute hypoxemic respiratory failure with interesting findings. The exact positioning of this technique needs more assessment as well as determining its mechanisms of action (3). Immunocompromised patients are a subset of patients in whom the effect of NIV has been shown to be beneficial. However, the improved prognosis of these patients over the recent years, even under mechanical ventilation, necessitates a reappraisal of its effects (4). Lastly, an important emerging concern comes from the fact that some non-intubated patients with a high respiratory drive may develop an injurious breathing pattern and self-inflict lung injury. The optimal treatment may then be sedation, intubation, and application of a lung-protective ventilation.

Noninvasive Ventilation: Do Not Tolerate Intolerance

Noninvasive ventilation (NIV) has been used to treat acute respiratory failure in various settings for more than 2 decades. There is now strong evidence that NIV saves lives.[1][1] The most clearly established indications for NIV are acute-on-chronic respiratory failure resulting from exacerbations

Reliability of diaphragmatic ultrasonography to detect diaphragm dysfunction in critically ill patients

The gold standard to diagnose diaphragmatic dysfunction (DD) is the measurement of the intra-thoracic depression is response to a bilateral stimulation of the phrenic nerves (Ptr,stim). This technique is costly, requires expertise and is not widely available at the bedside. On the opposite, ultrasonography is easy to perform but has not been compared.

Impact of sepsis on the dynamics of diaphragmatic function in patients under mechanical ventilation

Sepsis and mechanical ventilation are both risk factors of diaphragmatic dysfunction (DD) in critically ill patients. The evolution of diaphragmatic function under mechanical ventilation in septic and non-septic patients has not been described.