Recruitment pattern of the diaphragm and extradiaphragmatic inspiratory muscles in response to different levels of pressure support

Increasing Sweep Gas Flow Reduces Respiratory Drive and Dyspnea in Nonintubated Venoarterial Extracorporeal Membrane Oxygenation Patients: A Pilot Study

BACKGROUND

Data on assessment and management of dyspnea in patients on venoarterial extracorporeal membrane oxygenation (ECMO) for cardiogenic shock are lacking. The hypothesis was that increasing sweep gas flow through the venoarterial extracorporeal membrane oxygenator may decrease dyspnea in nonintubated venoarterial ECMO patients exhibiting clinically significant dyspnea, with a parallel reduction in respiratory drive.

METHODS

Nonintubated, spontaneously breathing, supine patients on venoarterial ECMO for cardiogenic shock who presented with a dyspnea visual analog scale (VAS) score of greater than or equal to 40/100 mm were included. Sweep gas flow was increased up to +6 l/min by three steps of +2 l/min each. Dyspnea was assessed with the dyspnea-VAS and the Multidimensional Dyspnea Profile. The respiratory drive was assessed by the electromyographic activity of the alae nasi and parasternal muscles.

RESULTS

A total of 21 patients were included in the study. Upon inclusion, median dyspnea-VAS was 50 (interquartile range, 45 to 60) mm, and sweep gas flow was 1.0 l/min (0.5 to 2.0). An increase in sweep gas flow significantly decreased dyspnea-VAS (50 [45 to 60] at baseline vs. 20 [10 to 30] at 6 l/min; P < 0.001). The decrease in dyspnea was greater for the sensory component of dyspnea (-50% [-43 to -75]) than for the affective and emotional components (-17% [-0 to -25] and -12% [-0 to -17]; P < 0.001). An increase in sweep gas flow significantly decreased electromyographic activity of the alae nasi and parasternal muscles (-23% [-36 to -10] and -20 [-41 to -0]; P < 0.001). There was a significant correlation between the sweep gas flow and the dyspnea-VAS (r = -0.91; 95% CI, -0.94 to -0.87), between the respiratory drive and the sensory component of dyspnea (r = 0.29; 95% CI, 0.13 to 0.44) between the respiratory drive and the affective component of dyspnea (r = 0.29; 95% CI, 0.02 to 0.54) and between the sweep gas flow and the alae nasi and parasternal (r = -0.31; 95% CI, -0.44 to -0.22; and r = -0.25; 95% CI, -0.44 to -0.16).

CONCLUSIONS

In critically ill patients with venoarterial ECMO, an increase in sweep gas flow through the oxygenation membrane decreases dyspnea, possibly mediated by a decrease in respiratory drive.

EDITOR’S PERSPECTIVE

Advanced waveform analysis of diaphragm surface EMG allows for continuous non-invasive assessment of respiratory effort in critically ill patients at different PEEP levels

BACKGROUND

Respiratory effort should be closely monitored in mechanically ventilated ICU patients to avoid both overassistance and underassistance. Surface electromyography of the diaphragm (sEMGdi) offers a continuous and non-invasive modality to assess respiratory effort based on neuromuscular coupling (NMCdi). The sEMGdi derived electrical activity of the diaphragm (sEAdi) is prone to distortion by crosstalk from other muscles including the heart, hindering its widespread use in clinical practice. We developed an advanced analysis as well as quality criteria for sEAdi waveforms and investigated the effects of clinically relevant levels of PEEP on non-invasive NMCdi.

METHODS

NMCdi was derived by dividing end-expiratory occlusion pressure (Pocc) by sEAdi, based on three consecutive Pocc manoeuvres at four incremental (+ 2 cmH2O/step) PEEP levels in stable ICU patients on pressure support ventilation. Pocc and sEAdi quality was assessed by applying a novel, automated advanced signal analysis, based on tolerant and strict cut-off criteria, and excluding inadequate waveforms. The coefficient of variations (CoV) of NMCdi after basic manual and automated advanced quality assessment were evaluated, as well as the effect of an incremental PEEP trial on NMCdi.

RESULTS

593 manoeuvres were obtained from 42 PEEP trials in 17 ICU patients. Waveform exclusion was primarily based on low sEAdi signal-to-noise ratio (Ntolerant = 155, 37%, Nstrict = 241, 51% waveforms excluded), irregular or abrupt cessation of Pocc (Ntolerant = 145, 35%, Nstrict = 145, 31%), and high sEAdi area under the baseline (Ntolerant = 94, 23%, Nstrict = 79, 17%). Strict automated assessment allowed to reduce CoV of NMCdi to 15% from 37% for basic quality assessment. As PEEP was increased, NMCdi decreased significantly by 4.9 percentage point per cmH2O.

CONCLUSION

Advanced signal analysis of both Pocc and sEAdi greatly facilitates automated and well-defined identification of high-quality waveforms. In the critically ill, this approach allowed to demonstrate a dynamic NMCdi (Pocc/sEAdi) decrease upon PEEP increments, emphasising that sEAdi-based assessment of respiratory effort should be related to PEEP dependent diaphragm function. This novel, non-invasive methodology forms an important methodological foundation for more robust, continuous, and comprehensive assessment of respiratory effort at the bedside.

MUltiparametric Score for Ventilation Discontinuation in Intensive Care Patients: A Protocol for an Observational Study

BACKGROUND

Mechanical ventilation significantly improves patient survival but is associated with complications, increasing healthcare costs and morbidity. Identifying optimal weaning times is paramount to minimize these risks, yet current methods rely heavily on clinical judgment, lacking specificity.

METHODS

This study introduces a novel multiparametric predictive score, the MUSVIP (MUltiparametric Score for Ventilation discontinuation in Intensive care Patients), aimed at accurately predicting successful extubation. Conducted at Santo Stefano Hospital's ICU, this single-center, observational, prospective cohort study will span over 12 months, enrolling adult patients undergoing invasive mechanical ventilation. The MUSVIP integrates variables measured before and during a spontaneous breathing trial (SBT) to formulate a predictive score.

RESULTS

Preliminary analyses suggest an Area Under the Curve (AUC) of 0.815 for the MUSVIP, indicating high predictive capacity. By systematically applying this score, we anticipate identifying patients likely to succeed in weaning earlier, potentially reducing ICU length of stay and associated healthcare costs.

CONCLUSION

This study's findings could significantly influence clinical practices, offering a robust, easy-to-use tool for optimizing weaning processes in ICUs.

Analysis and applications of respiratory surface EMG: report of a round table meeting

Surface electromyography (sEMG) can be used to measure the electrical activity of the respiratory muscles. The possible applications of sEMG span from patients suffering from acute respiratory failure to patients receiving chronic home mechanical ventilation, to evaluate muscle function, titrate ventilatory support and guide treatment. However, sEMG is mainly used as a monitoring tool for research and its use in clinical practice is still limited-in part due to a lack of standardization and transparent reporting. During this round table meeting, recommendations on data acquisition, processing, interpretation, and potential clinical applications of respiratory sEMG were discussed. This paper informs the clinical researcher interested in respiratory muscle monitoring about the current state of the art on sEMG, knowledge gaps and potential future applications for patients with respiratory failure.

Sensory interventions to relieve dyspnoea in critically ill mechanically ventilated patients

BACKGROUND

In critically ill patients receiving mechanical ventilation, dyspnoea is frequent, severe and associated with an increased risk of neuropsychological sequelae. We evaluated the efficacy of sensory interventions targeting the brain rather than the respiratory system to relieve dyspnoea in mechanically ventilated patients.

METHODS

Patients receiving mechanical ventilation for ≥48 h and reporting dyspnoea (unidimensional dyspnoea visual analogue scale (Dyspnoea-VAS)) first underwent increased pressure support and then, in random order, auditory stimulation (relaxing music versus pink noise) and air flux stimulation (facial versus lower limb). Treatment responses were assessed using Dyspnoea-VAS, the Multidimensional Dyspnea Profile and measures of the neural drive to breathe (airway occlusion pressure (P 0.1) and electromyography of inspiratory muscles).

RESULTS

We included 46 patients (tracheotomy or intubation n=37; noninvasive ventilation n=9). Increasing pressure support decreased Dyspnoea-VAS by median 40 mm (p<0.001). Exposure to music decreased Dyspnoea-VAS compared with exposure to pink noise by median 40 mm (p<0.001). Exposure to facial air flux decreased Dyspnoea-VAS compared with limb air flux by median 30 mm (p<0.001). Increasing pressure support, but not music exposure and facial air flux, reduced P 0.1 by median 3.3 cmH2O (p<0.001).

CONCLUSIONS

In mechanically ventilated patients, sensory interventions can modulate the processing of respiratory signals by the brain irrespective of the intensity of the neural drive to breathe. It should therefore be possible to alleviate dyspnoea without resorting to pharmacological interventions or having to infringe the constraints of mechanical ventilation lung protection strategies by increasing ventilatory support.

Surface electromyography to quantify neuro-respiratory drive and neuro-mechanical coupling in mechanically ventilated children

BACKGROUND

The patient's neuro-respiratory drive, measured as electrical activity of the diaphragm (EAdi), quantifies the mechanical load on the respiratory muscles. It correlates with respiratory effort but requires a dedicated esophageal catheter. Transcutaneous (surface) monitoring of respiratory muscle electromyographic (sEMG) signals may be considered a suitable alternative to EAdi because of its non-invasive character, with the additional benefit that it allows for simultaneously monitoring of other respiratory muscles. We therefore sought to study the neuro-respiratory drive and timing of inspiratory muscles using sEMG in a cohort of children enrolled in a pediatric ventilation liberation trial. The neuro-mechanical coupling, relating the pressure generated by the inspiratory muscles to the sEMG signals of these muscles, was also calculated.

METHODS

This is a secondary analysis of data from a randomized cross-over trial in ventilated patients aged < 5 years. sEMG recordings of the diaphragm and parasternal intercostal muscles (ICM), esophageal pressure tracings and ventilator scalars were simultaneously recorded during continuous spontaneous ventilation and pressure controlled-intermittent mandatory ventilation, and at three levels of pressure support. Neuro-respiratory drive, timing of diaphragm and ICM relative to the mechanical ventilator's inspiration and neuro-mechanical coupling were quantified.

RESULTS

Twenty-nine patients were included (median age: 5.9 months). In response to decreasing pressure support, both amplitude of sEMG (diaphragm: p = 0.001 and ICM: p = 0.002) and neuro-mechanical efficiency indices increased (diaphragm: p = 0.05 and ICM: p < 0.001). Poor correlations between neuro-respiratory drive and respiratory effort were found, with R²: 0.088 [0.021-0.152].

CONCLUSIONS

sEMG allows for the quantification of the electrical activity of the diaphragm and ICM in mechanically ventilated children. Both neuro-respiratory drive and neuro-mechanical efficiency increased in response to lower inspiratory assistance. There was poor correlation between neuro-respiratory drive and respiratory effort.

TRIAL REGISTRATION

ClinicalTrials.gov ID NCT05254691. Registered 24 February 2022, registered retrospectively.

Obstructive Sleep Apnea and Role of the Diaphragm

Obstructive sleep apnea (OSA) causes multiple local and systemic pathophysiological consequences, which lead to an increase in morbidity and mortality in patients suffering from this disorder. OSA presents with various nocturnal events of apnoeas or hypopneas and with sub-clinical airflow limitations during wakefulness. OSA involves a large percentage of the population, particularly men, but the estimate of OSA patients could be much broader than data from the literature. Most of the research carried out in the muscle field is to understand the causes of the presence of chronic nocturnal desaturation and focus on the genioglossus muscle and other muscles related to dilating the upper airways. Sparse research has been published regarding the diaphragm muscle, which is the main muscle structure to insufflate air into the airways. The article reviews the functional anatomy of the muscles used to open the upper respiratory tract and the non-physiological adaptation that follows in the presence of OSA, as well as the functional anatomy and pathological adaptive aspects of the diaphragm muscle. The intent of the text is to highlight the disparity of clinical interest between the dilator muscles and the diaphragm, trying to stimulate a broader approach to patient evaluation.

Dyspnea and the electromyographic activity of inspiratory muscles during weaning from mechanical ventilation

Rationale

Dyspnea, a key symptom of acute respiratory failure, is not among the criteria for spontaneous breathing trial (SBT) failure. Here, we sought (1) to determine whether dyspnea is a reliable failure criterion for SBT failure; (2) to quantify the relationship between dyspnea and the respective electromyographic activity of the diaphragm (EMGdi), the parasternal (EMGpa) and the Alae nasi (EMGan).

Methods

Mechanically ventilated patients undergoing an SBT were included. Dyspnea intensity was measured by the Dyspnea-Visual Analogic Scale (Dyspnea-VAS) at the initiation and end of the SBT. During the 30-min SBT or until SBT failure, the EMGdi was continuously measured with a multi-electrode nasogastric catheter and the EMGan and EMGpa with surface electrodes.

Results

Thirty-one patients were included, SAPS 2 (median [interquartile range]) 53 (37‒74), mechanically ventilated for 6 (3‒10) days. Seventeen patients (45%) failed the SBT. The increase in Dyspnea-VAS along the SBT was higher in patients who failed (6 [4‒8] cm) than in those who passed (0 [0‒1] cm, p = 0.01). The area under the receiver operating characteristics curve for Dyspnea-VAS was 0.909 (0.786–1.032). The increase in Dyspnea-VAS was significantly correlated to the increase in EMGan (Rho = 0.42 [0.04‒0.70], p < 0.05), but not to the increase in EMGpa (Rho = − 0.121 [− 0.495 to − 0.290], p = 0.555) and EMGdi (Rho = − 0.26 [− 0.68 to 0.28], p = 0.289).

Conclusion

Dyspnea is a reliable criterion of SBT failure, suggesting that Dyspnea-VAS could be used as a monitoring tool of the SBT. In addition, dyspnea seems to be more closely related to the electromyographic activity of the Alae nasi than of the diaphragm.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13613-022-01025-5.

Accessory and Expiratory Muscles Activation During Spontaneous Breathing Trial: A Physiological Study by Surface Electromyography

Background

The physiological and prognostical significance of accessory and expiratory muscles activation is unknown during a spontaneous breathing trial (SBT). We hypothesized that, in patients experiencing weaning failure, accessory and expiratory muscles are activated to cope with an increased respiratory workload.

Purpose

To describe accessory and expiratory muscle activation non-invasively by surface electromyography (sEMG) during an SBT and to assess differences in electrical activity (EA) of the inspiratory and expiratory muscles in successful vs. failing weaning patients.

Methods

Intubated patients on mechanical ventilation for more than 48 h undergoing an SBT were enrolled in a medical and surgical third-level ICU of the University Teaching Hospital. Baseline characteristics and physiological variables were recorded in a crossover physiologic prospective clinical study.

Results

Of 37 critically ill mechanically ventilated patients, 29 (78%) patients successfully passed the SBT. Rapid shallow breathing index (RSBI) was higher in patients who failed SBT compared with the successfully weaned patients at baseline and over time (group-by-time interaction p < 0.001). EA of both the diaphragm (EAdi_surf) and of accessory muscles (ACC_surf) was higher in failure patients compared with success (group-by-time interaction p = 0.0174 and p < 0.001, respectively). EA of expiratory muscles (ESP_surf) during SBT increased more in failure than in weaned patients (group-by-time interaction p < 0.0001).

Conclusion

Non-invasive respiratory muscle monitoring by sEMG was feasible during SBT. Respiratory muscles EA increased during SBT, regardless of SBT outcome, and patients who failed the SBT had a higher increase of all the inspiratory muscles EA compared with the patients who passed the SBT. Recruitment of expiratory muscles—as quantified by sEMG—is associated with SBT failure.

Acute intermittent hypoxia and respiratory muscle recruitment in people with amyotrophic lateral sclerosis: A preliminary study

Respiratory failure is the main cause of death in amyotrophic lateral sclerosis (ALS). Since no effective treatments to preserve independent breathing are available, there is a critical need for new therapies to preserve or restore breathing ability. Since acute intermittent hypoxia (AIH) elicits spinal respiratory motor plasticity in rodent ALS models, and may restore breathing ability in people with ALS, we performed a proof-of-principle study to investigate this possibility in ALS patients. Quiet breathing, sniff nasal inspiratory pressure (SNIP) and maximal inspiratory pressure (MIP) were tested in 13 persons with ALS and 10 age-matched controls, before and 60 min post-AIH (15, 1 min episodes of 10% O₂, 2 min normoxic intervals) or sham AIH (continuous normoxia). The root mean square (RMS) of the right and left diaphragm, 2nd parasternal, scalene and sternocleidomastoid muscles were monitored. A vector analysis was used to calculate summated vector magnitude (Mag) and similarity index (SI) of collective EMG activity during quiet breathing, SNIP and MIP maneuvers. AIH facilitated tidal volume and minute ventilation (treatment main effects: p < 0.05), and Mag (ie. collective respiratory muscle activity; p < 0.001) during quiet breathing in ALS and control subjects, but there was no effect on SI during quiet breathing. SNIP SI decreased in both groups post-AIH (p < 0.005), whereas Mag was unchanged (p = 0.09). No differences were observed in SNIP or MIP post AIH in either group. Discomfort was not reported during AIH by any subject, nor were adverse events observed. Thus, AIH may be a safe way to increase collective inspiratory muscle activity during quiet breathing in ALS patients, although a single AIH presentation was not sufficient to significantly increase peak inspiratory pressure generation. These preliminary results provide evidence that AIH may improve breathing function in people with ALS, and that future studies of prolonged, repetitive AIH protocols are warranted.

Proportional assist ventilation relieves clinically significant dyspnea in critically ill ventilated patients

INTRODUCTION

Dyspnea is common and often severe symptom in mechanically ventilated patients. Proportional assist ventilation (PAV) is an assist ventilatory mode that adjusts the level of assistance to the activity of respiratory muscles. We hypothesized that PAV reduce dyspnea compared to pressure support ventilation (PSV).

PATIENTS AND METHODS

Mechanically ventilated patients with clinically significant dyspnea were included. Dyspnea intensity was assessed by the Dyspnea-Visual Analog Scale (D-VAS) and the Intensive Care-Respiratory Distress Observation Scale (IC-RDOS) at inclusion (PSV-Baseline), after personalization of ventilator settings in order to minimize dyspnea (PSV-Personalization), and after switch to PAV. Respiratory drive was assessed by record of electromyographic activity of inspiratory muscles, the proportion of asynchrony was analyzed.

RESULTS

Thirty-four patients were included (73% males, median age of 66 [57-77] years). The D-VAS score was lower with PSV-Personalization (37 mm [20‒55]) and PAV (31 mm [14‒45]) than with PSV-Baseline (62 mm [28‒76]) (p < 0.05). The IC-RDOS score was lower with PAV (4.2 [2.4‒4.7]) and PSV-Personalization (4.4 [2.4‒4.9]) than with PSV-Baseline (4.8 [4.1‒6.5]) (p < 0.05). The electromyographic activity of parasternal intercostal muscles was lower with PAV and PSV-Personalization than with PSV-Baseline. The asynchrony index was lower with PAV (0% [0‒0.55]) than with PSV-Baseline and PSV-Personalization (0.68% [0‒2.28] and 0.60% [0.31‒1.41], respectively) (p < 0.05).

CONCLUSION

In mechanically ventilated patients exhibiting clinically significant dyspnea with PSV, personalization of PSV settings and PAV results in not different decreased dyspnea and activity of muscles to a similar degree, even though PAV was able to reduce asynchrony more effectively.

Weaning the patient: between protocols and physiology

PURPOSE OF REVIEW

Ventilator weaning forms an integral part in critical care medicine and strategies to shorten duration are rapidly evolving alongside our knowledge of the relevant physiological processes. The purpose of the current review is to discuss new physiological and clinical insights in ventilator weaning that help us to fasten liberation from mechanical ventilation.

RECENT FINDINGS

Several new concepts have been introduced in the field of ventilator weaning in the past 2 years. Approaches to shorten the time until ventilator liberation include frequent spontaneous breathing trials, early noninvasive mechanical ventilation to shorten invasive ventilation time, novel ventilatory modes, such as neurally adjusted ventilatory assist and drugs to enhance the contractile efficiency of respiratory muscles. Equally important, ultrasound has been shown to be a versatile tool to monitor physiological changes of the cardiorespiratory system during weaning and steer targeted interventions to improve extubation outcome.

SUMMARY

A thorough understanding of the physiological adaptations during withdrawal of positive pressure ventilation is extremely important for clinicians in the ICU. We summarize and discuss novel insights in this field.