Assisted mechanical ventilation: the future is now!

Respiratory drive, inspiratory effort, and work of breathing: review of definitions and non-invasive monitoring tools for intensive care ventilators during pandemic times

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 patient’s 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 patient’s 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.

Accuracy of Algorithms and Visual Inspection for Detection of Trigger Asynchrony in Critical Patients : A Systematic Review

Objective

This study aimed to summarize the accuracy of the different methods for detecting trigger asynchrony at the bedside in mechanically ventilated patients.

Method

A systematic review was conducted from 1990 to 2020 in PubMed, Lilacs, Scopus, and ScienceDirect databases. The reference list of the identified studies, reviews, and meta-analyses was also manually searched for relevant studies. The reference standards were esophageal pressure catheter and/or electrical activity of the diaphragm. Studies were assessed following the QUADAS-2 recommendations, while the review was prepared according to the PRISMA criteria.

Results

One thousand one hundred and eleven studies were selected, and four were eligible for analysis. Esophageal pressure was the predominant reference standard, while visual inspection and algorithms/software comprised index tests. The trigger asynchrony, ineffective expiratory effort, double triggering, and reverse triggering were analyzed. Sensitivity and specificity ranged from 65.2% to 99% and 80% to 100%, respectively. Positive predictive values reached 80.3 to 100%, while the negative predictive values reached 92 to 100%. Accuracy could not be calculated for most studies.

Conclusion

Algorithms/software validated directly or indirectly using reference standards present high sensitivity and specificity, with a diagnostic power similar to visual inspection of experts.

Patient–Ventilator Interaction Testing Using the Electromechanical Lung Simulator xPULM™ during V/A-C and PSV Ventilation Mode

During mechanical ventilation, a disparity between flow, pressure and volume demands of the patient and the assistance delivered by the mechanical ventilator often occurs. This paper introduces an alternative approach of simulating and evaluating patient–ventilator interactions with high fidelity using the electromechanical lung simulator xPULM™. The xPULM™ approximates respiratory activities of a patient during alternating phases of spontaneous breathing and apnea intervals while connected to a mechanical ventilator. Focusing on different triggering events, volume assist-control (V/A-C) and pressure support ventilation (PSV) modes were chosen to test patient–ventilator interactions. In V/A-C mode, a double-triggering was detected every third breathing cycle, leading to an asynchrony index of 16.67%, which is classified as severe. This asynchrony causes a significant increase of peak inspiratory pressure (7.96 ± 6.38 vs. 11.09 ± 0.49 cmH2O, p < 0.01)) and peak expiratory flow (−25.57 ± 8.93 vs. 32.90 ± 0.54 L/min, p < 0.01) when compared to synchronous phases of the breathing simulation. Additionally, events of premature cycling were observed during PSV mode. In this mode, the peak delivered volume during simulated spontaneous breathing phases increased significantly (917.09 ± 45.74 vs. 468.40 ± 31.79 mL, p < 0.01) compared to apnea phases. Various dynamic clinical situations can be approximated using this approach and thereby could help to identify undesired patient–ventilation interactions in the future. Rapidly manufactured ventilator systems could also be tested using this approach.

Neurally adjusted ventilatory assist in acute respiratory failure: a randomized controlled trial

PURPOSE

We hypothesized that neurally adjusted ventilatory assist (NAVA) compared to conventional lung-protective mechanical ventilation (MV) decreases duration of MV and mortality in patients with acute respiratory failure (ARF).

METHODS

We carried out a multicenter, randomized, controlled trial in patients with ARF from several etiologies. Intubated patients ventilated for ≤ 5 days expected to require MV for ≥ 72 h and able to breathe spontaneously were eligible for enrollment. Eligible patients were randomly assigned based on balanced treatment assignments with a computerized randomization allocation sequence to two ventilatory strategies: (1) lung-protective MV (control group), and (2) lung-protective MV with NAVA (NAVA group). Allocation concealment was maintained at all sites during the trial. Primary outcome was the number of ventilator-free days (VFDs) at 28 days. Secondary outcome was all-cause hospital mortality. All analyses were done according to the intention-to-treat principle.

RESULTS

Between March 2014 and October 2019, we enrolled 306 patients and randomly assigned 153 patients to the NAVA group and 153 to the control group. Median VFDs were higher in the NAVA than in the control group (22 vs. 18 days; between-group difference 4 days; 95% confidence interval [CI] 0 to 8 days; p = 0.016). At hospital discharge, 39 (25.5%) patients in the NAVA group and 47 (30.7%) patients in the control group had died (between-group difference - 5.2%, 95% CI - 15.2 to 4.8, p = 0.31). Other clinical, physiological or safety outcomes did not differ significantly between the trial groups.

CONCLUSION

NAVA decreased duration of MV although it did not improve survival in ventilated patients with ARF.

Implementation of Neurally Adjusted Ventilatory Assist (NAVA): Patient characteristics and staff experiences

OBJECTIVE

The objective of the study was to describe the implementation of Neurally Adjusted Ventilatory Assist (NAVA) by characteristics of patients receiving NAVA and by staff-experienced opportunities and barriers.

METHODS

Design. A retrospective review of hospital records of mechanically ventilated patients over two time periods after implementation, as well as a questionnaire survey and interviews with staff.

SETTING

A secondary Danish ICU.

PARTICIPANTS

ICU patients, nurses, and intensivists.

INTERVENTION

Implementation of NAVA, which included theoretical education, bedside training, and frequent updates.

MAIN OUTCOME MEASURE

Evaluation of NAVA implementation measured by characteristics of patients receiving NAVA and staff experiences with NAVA.

RESULTS

A total of 311 patients were included. Hereof 43 (27%) and 68 (44%) patients, respectively, had recieved NAVA. The patients receiving NAVA had higher severity scores and more hours on ventilators. A total of 35 nurses (76%) and 16 physicians (64%) completed the questionnaire. Most clinicians found, to a high (43%) or very high (41%) degree, that NAVA was an effective therapy option. Furthermore, 77% did not experience any barriers regarding NAVA therapy. The main advantages experienced with NAVA were increased patient comfort, respiratory synchrony with the ventilator, and improved opportunities for monitoring patient respiratory performance. The main disadvantage was the need for additional theoretical and practical knowledge.

CONCLUSION

Despite staff experience of NAVA as a beneficial treatment option, more than half of the patients did not receive NAVA treatment two years after the start of its implementation. Implementation of a therapy which is substantially different to earlier practices is complicated.

Oxygen Therapeutics and Mechanical Ventilation Advances

Advances in intensive care unit (ICU) therapeutics are plentiful and rooted in technological enhancements as well as recognition of patient care priorities. A plethora of new devices and modes are available for use to enhance patient safety and support liberation from mechanical ventilation while preserving oxygenation and carbon dioxide clearance. Increased penetrance of closed loop systems is one means to reduce care variation in appropriate populations. The intelligent design of the ICU space needs to integrate the footprint of that device and the data streaming from it into a coherent whole that supports patient, family, and caregivers.

Neurally adjusted ventilatory assist in patients with acute respiratory failure: study protocol for a randomized controlled trial

Background

Patient-ventilator asynchrony is a common problem in mechanically ventilated patients with acute respiratory failure. It is assumed that asynchronies worsen lung function and prolong the duration of mechanical ventilation (MV). Neurally Adjusted Ventilatory Assist (NAVA) is a novel approach to MV based on neural respiratory center output that is able to trigger, cycle, and regulate the ventilatory cycle. We hypothesized that the use of NAVA compared to conventional lung-protective MV will result in a reduction of the duration of MV. It is further hypothesized that NAVA compared to conventional lung-protective MV will result in a decrease in the length of ICU and hospital stay, and mortality.

Methods/design

This is a prospective, multicenter, randomized controlled trial in 306 mechanically ventilated patients with acute respiratory failure from several etiologies. Only patients ventilated for less than 5 days, and who are expected to require prolonged MV for an additional 72 h or more and are able to breathe spontaneously, will be considered for enrollment. Eligible patients will be randomly allocated to two ventilatory arms: (1) conventional lung-protective MV (n = 153) and conventional lung-protective MV with NAVA (n = 153). Primary outcome is the number of ventilator-free days, defined as days alive and free from MV at day 28 after endotracheal intubation. Secondary outcomes are total length of MV, and ICU and hospital mortality.

Discussion

This is the first randomized clinical trial examining, on a multicenter scale, the beneficial effects of NAVA in reducing the dependency on MV of patients with acute respiratory failure.

Trial registration

ClinicalTrials.gov website (NCT01730794). Registered on 15 November 2012.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-016-1625-5) contains supplementary material, which is available to authorized users.