Bruno-Pierre Dubé

Coexistence and Impact of Limb Muscle and Diaphragm Weakness at Time of Liberation from Mechanical Ventilation in Medical Intensive Care Unit Patients

Rationale: Intensive care unit (ICU)‐ and mechanical ventilation (MV)‐acquired limb muscle and diaphragm dysfunction may both be associated with longer length of stay and worse outcome. Whether they are two aspects of the same entity or have a different prevalence and prognostic impact remains unclear. Objectives: To quantify the prevalence and coexistence of these two forms of ICU‐acquired weakness and their impact on outcome. Methods: In patients undergoing a first spontaneous breathing trial after at least 24 hours of MV, diaphragm dysfunction was evaluated using twitch tracheal pressure in response to bilateral anterior magnetic phrenic nerve stimulation (a pressure <11 cm H2O defined dysfunction) and ultrasonography (thickening fraction [TFdi] and excursion). Limb muscle weakness was defined as a Medical Research Council (MRC) score less than 48. Measurements and Main Results: Seventy‐six patients were assessed at their first spontaneous breathing trial: 63% had diaphragm dysfunction, 34% had limb muscle weakness, and 21% had both. There was a significant but weak correlation between MRC score and twitch pressure (&rgr; = 0.26; P = 0.03) and TFdi (&rgr; = 0.28; P = 0.01), respectively. Low twitch pressure (odds ratio, 0.60; 95% confidence interval, 0.45‐0.79; P < 0.001) and TFdi (odds ratio, 0.84; 95% confidence interval, 0.76‐0.92; P < 0.001) were independently associated with weaning failure, but the MRC score was not. Diaphragm dysfunction was associated with higher ICU and hospital mortality, and limb muscle weakness was associated with longer duration of MV and hospital stay. Conclusions: Diaphragm dysfunction is twice as frequent as limb muscle weakness and has a direct negative impact on weaning outcome. The two types of muscle weakness have only limited overlap.

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: Diagnostic Approaches and Management Strategies

The diaphragm is the main inspiratory muscle, and its dysfunction can lead to significant adverse clinical consequences. The aim of this review is to provide clinicians with an overview of the main causes of uni- and bi-lateral diaphragm dysfunction, explore the clinical and physiological consequences of the disease on lung function, exercise physiology and sleep and review the available diagnostic tools used in the evaluation of diaphragm function. A particular emphasis is placed on the clinical significance of diaphragm weakness in the intensive care unit setting and the use of ultrasound to evaluate diaphragmatic action.

Exploring cardio-pulmonary interactions by examining the ventilatory, pulmonary gas exchange, and heart rate kinetics response to high-intensity cycle exercise in COPD patients.

In this Commentary, we aim to discuss a paper by Nasis et al. recently published in this journal (Nasis et al., 2015). As a basis for our comment, we would like to begin with a presentation of some background information of the topic of the relationship between cardiac and pulmonary variables during exercise. Cardio-pulmonary interactions can be difficult to explore in healthy and in COPD patients, especially during exercise. One method allowing access to these interactions is the examination of the ventilatory, pulmonary gas exchange, and heart rate kinetics response to high-intensity exercise.

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.

Effects of aging and comorbidities on nutritional status and muscle dysfunction in patients with COPD

Chronic obstructive pulmonary disease (COPD) is a prevalent, complex and debilitating disease which imposes a formidable burden on patients and the healthcare system. The recognition that COPD is a multifaceted disease is not new, and increasing evidence have outlined the importance of its extra-pulmonary manifestations and its relation to other comorbid conditions in the clinical course of the disease and its societal cost. The relationship between aging, COPD and its comorbidities on skeletal muscle function and nutritional status is complex, multidirectional and incompletely understood. Despite this, the current body of knowledge allows the identification of various, seemingly partially independent factors related both to the normal aging process and to the independent deleterious effects of chronic diseases on muscle function and body composition. There is a dire need of studies evaluating the relative contribution of each of these factors, and their potential synergistic effects in patients with COPD and advanced age/comorbid conditions, in order to delineate the best course of therapeutic action in this increasingly prevalent population.

Stair-Climbing Capacity as a Marker of Improvement Following Pulmonary Rehabilitation

PURPOSE: The aim of this study was to explore the potential and safety of a stair-climbing test as a tool to monitor improvement following pulmonary rehabilitation (PR) in patients with chronic obstructive pulmonary disease (COPD). METHODS: Stair-climbing capacity was assessed in 139 patients with COPD before and after a comprehensive 8-week PR program, which included stair-climbing training. Stair-climbing capacity was assessed as the total number of flights of stairs climbed without stopping. A constant work rate endurance test (CET) was also performed before and after PR. Change in stair-climbing after PR (&Dgr;stairs) was compared and correlated to the change in endurance time (&Dgr;CET) and, for 40 patients, to the change in COPD assessment test (&Dgr;CAT) score. RESULTS: Most patients had moderate to severe COPD (mean forced expiratory volume in 1 second = 54% ± 20% predicted). Stair-climbing capacity, endurance time, and CAT score improved after PR (2.8 ± 1.4 vs 8.3 ± 3.3 flights, 408 ± 272 vs 717 ± 415 seconds, and 20.0 ± 6.4 vs 17.6 ± 6.6 units, respectively; P value for all < .001). &Dgr;stairs was moderately correlated to &Dgr;CET (r = 0.49; P < .001) and well correlated to &Dgr;CAT (r = −0.71; P < .001). Patients with greater change in &Dgr;stairs had better baseline resting lung function and aerobic capacity. No adverse events were reported during stair-climbing. CONCLUSION: Stair-climbing is responsive to training in patients with COPD and is correlated to the change in CAT score following PR. Although the test requires further standardization, it could eventually be used as a simple and safe way to assess improvement following interventions in COPD.

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.