Respiratory drive, inspiratory effort, and work of breathing: review of definitions and non-invasive monitoring tools for intensive care ventilators during pandemic times. / Impulso, esfuerzo y trabajo respiratorio: revisión de definiciones y herramientas no invasivas de ventiladores de cuidados intensivos durante tiempos de pandemia.

Technological advances in mechanical ventilation have been essential to increasing the survival rate in intensive care units. Usually, patients needing mechanical ventilation use controlled ventilation to override the patients respiratory muscles and favor lung protection. Weaning from mechanical ventilation implies a transition towards spontaneous breathing, mainly using assisted mechanical ventilation. In this transition, the challenge for clinicians is to avoid under and over assistance and minimize excessive respiratory effort and iatrogenic diaphragmatic and lung damage. Esophageal balloon monitoring allows objective measurements of respiratory muscle activity in real time, but there are still limitations to its routine application in intensive care unit patients using mechanical ventilation. Like the esophageal balloon, respiratory muscle electromyography and diaphragmatic ultrasound are minimally invasive tools requiring specific training that monitor respiratory muscle activity. Particularly during the coronavirus disease pandemic, non invasive tools available on mechanical ventilators to monitor respiratory drive, inspiratory effort, and work of breathing have been extended to individualize mechanical ventilation based on patients needs. This review aims to identify the conceptual definitions of respiratory drive, inspiratory effort, and work of breathing and to identify non invasive maneuvers available on intensive care ventilators to measure these parameters. The literature highlights that although respiratory drive, inspiratory effort, and work of breathing are intuitive concepts, even distinguished authors disagree on their definitions.

Los avances tecnológicos de la ventilación mecánica han sido parte esencial del aumento de la sobrevida en las unidades de cuidados intensivos. Desde la conexión a la ventilación mecánica, comúnmente se utiliza ventilación controlada sin la consecuente participación de los músculos respiratorios del paciente, con el fin de favorecer la protección pulmonar. El retiro de la ventilación mecánica implica un periodo de transición hacia la respiración espontánea, utilizando principalmente ventilación mecánica asistida. En esta transición, el desafío de los clínicos es evitar la sub y sobre asistencia ventilatoria, minimizando el esfuerzo respiratorio excesivo, daño diafragmático y pulmonar inducidos por la ventilación mecánica. La monitorización con balón esofágico permite mediciones objetivas de la actividad muscular respiratoria en tiempo real, pero aún hay limitaciones para su aplicación rutinaria en pacientes ventilados mecánicamente en la unidad de cuidados intensivos. Al igual que el balón esofágico, la electromiografía de los músculos respiratorios y la ecografía diafragmática son herramientas que permiten monitorizar la actividad muscular de la respiración, siendo mínimamente invasivas y con requerimiento de entrenamiento específico. Particularmente, durante la actual pandemia de enfermedad por coronavirus se ha extendido el uso de herramientas no invasivas disponibles en los ventiladores mecánicos para monitorizar el impulso (drive), esfuerzo y trabajo respiratorio, para promover una ventilación mecánica ajustada a las necesidades del paciente. Consecuentemente, el objetivo de esta revisión es identificar las definiciones conceptuales de impulso, esfuerzo y trabajo respiratorio utilizadas en el contexto de la unidad de cuidados intensivos, e identificar las maniobras de medición no invasivas disponibles en los ventiladores de cuidados intensivos para monitorizar impulso, esfuerzo y trabajo respiratorio. La literatura destaca que, aunque los conceptos de impulso, esfuerzo y trabajo respiratorio se perciben intuitivos, no existe una definición clara. Asimismo, destacados autores los definen como conceptos diferentes.

The use of head helmets to deliver noninvasive ventilatory support: a comprehensive review of technical aspects and clinical findings.

A helmet, comprising a transparent hood and a soft collar, surrounding the patient's head can be used to deliver noninvasive ventilatory support, both as continuous positive airway pressure and noninvasive positive pressure ventilation (NPPV), the latter providing active support for inspiration. In this review, we summarize the technical aspects relevant to this device, particularly how to prevent CO2 rebreathing and improve patient-ventilator synchrony during NPPV. Clinical studies describe the application of helmets in cardiogenic pulmonary oedema, pneumonia, COVID-19, postextubation and immune suppression. A section is dedicated to paediatric use. In summary, helmet therapy can be used safely and effectively to provide NIV during hypoxemic respiratory failure, improving oxygenation and possibly leading to better patient-centred outcomes than other interfaces.

A physiological approach to understand the role of respiratory effort in the progression of lung injury in SARS-CoV-2 infection.

Deterioration of lung function during the first week of COVID-19 has been observed when patients remain with insufficient respiratory support. Patient self-inflicted lung injury (P-SILI) is theorized as the responsible, but there is not robust experimental and clinical data to support it. Given the limited understanding of P-SILI, we describe the physiological basis of P-SILI and we show experimental data to comprehend the role of regional strain and heterogeneity in lung injury due to increased work of breathing.In addition, we discuss the current approach to respiratory support for COVID-19 under this point of view.

COVID-19: minimising contaminated aerosol spreading during CPAP treatment.

BACKGROUND: The COVID-19 pandemic has raised concern for healthcare workers getting infected via aerosol from non-invasive respiratory support of infants. Attaching filters that remove viral particles in air from the expiratory limb of continuous positive airway pressure (CPAP) devices should theoretically decrease the risk. However, adding filters to the expiratory limb could add to expiratory resistance and thereby increase the imposed work of breathing (WOB). OBJECTIVE: To evaluate the effects on imposed WOB when attaching filters to the expiratory limb of CPAP devices. METHODS: Two filters were tested on three CPAP systems at two levels of CPAP in a mechanical lung model. Main outcome was imposed WOB. RESULTS: There was a minor increase in imposed WOB when attaching the filters. The differences between the two filters were small. CONCLUSION: To minimise contaminated aerosol generation during CPAP treatment, filters can be attached to expiratory tubing with only a minimal increase in imposed WOB in a non-humidified environment. Care has to be taken to avoid filter obstruction and replace filters as recommended.

Inspiratory effort and breathing pattern change in response to varying the assist level: A physiological study.

AIM: To describe the response of breathing pattern and inspiratory effort upon changes in assist level and to assesss if changes in respiratory rate may indicate changes in respiratory muscle effort. METHODS: Prospective study of 82 patients ventilated on proportional assist ventilation (PAV+). At three levels of assist (20 %-50 %-80 %), patients' inspiratory effort and breathing pattern were evaluated using a validated prototype monitor. RESULTS: Independent of the assist level, a wide range of respiratory rates (16-35br/min) was observed when patients' effort was within the accepted range. Changing the assist level resulted in paired changes in inspiratory effort and rate of the same tendency (increase or decrease) in all but four patients. Increasing the level in assist resulted in a 31 % (8-44 %) decrease in inspiratory effort and a 10 % (0-18 %) decrease in respiratory rate. The change in respiratory rate upon the change in assist correlated modestly with the change in the effort (R = 0.5). CONCLUSION: Changing assist level results in changes in both respiratory rate and effort in the same direction, with change in effort being greater than that of respiratory rate. Yet, neither the magnitude of respiratory rate change nor the resulting absolute value may reliably predict the level of effort after a change in assist.