Expiratory Muscle Activity Counteracts Positive End-Expiratory Pressure and Is Associated with Fentanyl Dose in Patients with Acute Respiratory Distress Syndrome

Rationale: Hypoxemia during mechanical ventilation might be worsened by expiratory muscle activity, which reduces end-expiratory lung volume through lung collapse. A proposed mechanism of benefit of neuromuscular blockade in acute respiratory distress syndrome (ARDS) is the abolition of expiratory efforts. This may contribute to the restoration of lung volumes. The prevalence of this phenomenon, however, is unknown. Objectives: To investigate the incidence and amount of end-expiratory lung impedance (EELI) increase after the administration of neuromuscular blocking agents (NMBAs), clinical factors associated with this phenomenon, its impact on regional lung ventilation, and any association with changes in pleural pressure. Methods: We included mechanically ventilated patients with ARDS monitored with electrical impedance tomography (EIT) who received NMBAs in one of two centers. We measured changes in EELI, a surrogate for end-expiratory lung volume, before and after NMBA administration. In an additional 10 patients, we investigated the characteristic signatures of expiratory muscle activity depicted by EIT and esophageal catheters simultaneously. Clinical factors associated with EELI changes were assessed. Measurements and Main Results: We included 46 patients, half of whom showed an increase in EELI of >10% of the corresponding Vt (46.2%; IQR, 23.9-60.9%). The degree of EELI increase correlated positively with fentanyl dosage and negatively with changes in end-expiratory pleural pressures. This suggests that expiratory muscle activity might exert strong counter-effects against positive end-expiratory pressure that are possibly aggravated by fentanyl. Conclusions: Administration of NMBAs during EIT monitoring revealed activity of expiratory muscles in half of patients with ARDS. The resultant increase in EELI had a dose-response relationship with fentanyl dosage. This suggests a potential side effect of fentanyl during protective ventilation.

Comorbidity burden conditions the prognostic performance of D-dimer in elderly patients with acute pulmonary embolism

INTRODUCTION

The prognostic accuracy of D-dimer for risk assessment in acute Pulmonary Embolism (APE) patients may be hampered by comorbidities. We investigated the impact of comorbidity burden (CB) by using the Charlson Comorbidity Index (CCI), on the prognostic ability of D-dimer to predict 30 and 90-day mortality in hemodynamically stable elderly patients with APE.

METHODS

All patients aged >65 years with normotensive APE, consecutively evaluated in the Emergency Department since 2010 through 2014 were included in this retrospective cohort study. Area under the curve (AUC) and ½ Net Reclassification Improvement (NRI) were calculated.

RESULTS

Study population: 162 patients, median age: 79.2 years. The optimal cut-off value of CCI score for predicting mortality was ≤1 (Low CB) and >1 (High CB), AUC = 0.786. Higher levels of D-dimer were associated with an increased risk death at 30 (HR = 1.039, 95%CI:1.000-1.080, p = 0.049) and 90 days (HR = 1.039, 95%CI:1.009-1.070, p = 0.012). When added to simplified Pulmonary Embolism Severity Index (sPESI) score, D-dimer increased significantly the AUC for predicting 30-day mortality in Low CB (AUC = 0.778, 95%CI:0.620-0.937, ½NRI = 0.535, p = 0.015), but not in High CB patients (AUC = 0.634, 95%CI:0.460-0.807, ½ NRI = 0.248, p = 0.294). Similarly, for 90-day mortality D-dimer increased significantly the AUC in Low CB (AUC = 0.786, 95%CI:0.643-0.929, ½NRI = 0.424, p-value = 0.025), but not in High CB patients (AUC = 0.659, 95%CI:0.541-0.778, ½NRI = 0.354, p-value = 0.165).

CONCLUSION

In elderly patients with normotensive APE, comorbidities condition the prognostic performance of D-dimer, which was found to be a better predictor of death in subjects with low CB. These results support multimarker strategies for risk assessment in this population.