Daily Archives: November 18, 2022

Academic Half Day 11/18/2022: Managing Respiratory Failure in the ICU Part 2

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Mechanical Ventilation in Severe Asthma

The effects of ventilatory pattern on hyperinflation, airway pressures, and circulation in mechanical ventilation of patients with severe air-flow obstruction – Am Rev Respir Dis 1987

  • Initial case series mentioned by Dr. Corbridge that described the relationship between minute ventilation, tidal volume, and inspiratory time on pulmonary hyperinflation in states of severe airflow obstruction

Mechanical ventilation for severe asthma – CHEST 2015

  • Helpful review of how to manage the ventilator in severe asthma

Management of life-threatening asthma – CHEST 2022

  • New CHEST review which provides more details on pharmacotherapies

Advanced Topics in ARDS and Ventilator Management

Acute Respiratory Distress Syndrome – Nat Rev Dis Primers 2019

  • Nice review which summarizes a lot of what we know about ARDS pathobiology

Comparison of the Berlin definition for acute respiratory distress syndrome with autopsy – Am J Respir Crit Care Med 2013

  • Important study which found that < 50% of autopsy specimens from patients who met Berlin Criteria for ARDS had diffuse alveolar damage on pathology. Pneumonia was the most common alternative finding

New Insights into Clinical and Mechanistic Heterogeneity of the Acute Respiratory Distress Syndrome: Summary of the Aspen Lung Conference 2021 – Am J Respir Cell Mol Bio 2022

  • Summary of discussions from Aspen Lung Conference. Provides a nice review of ARDS phenotyping including hypo and hyperinflammatory  phenotypes and implications for clinical trial design

The “baby lung” became an adult – Intensive Care Med 2016

  • Easy to ready summary of “baby lung” concept in ARDS

Driving pressure and survival in the acute respiratory distress syndrome – N Engl J Med 2015

  • Re-analysis of ARDS clinical trials which found that driving pressure was strongly associated with survival and that interventions which lowered delta P were associated with improved outcomes

Fifty Years of Research in ARDS. Spontaneous Breathing during Mechanical Ventilation. Risks, Mechanisms, and Management – Am J Respir Crit Care Med 2017 

  • Nice summary of potential risks and benefits of spontaneous breathing during ARDS. Discusses transpulmonary pressure and pendelluft

Setting PEEP in ARDS

Fifty Years of Research in ARDS. Setting Positive End-Expiratory Pressure in Acute Respiratory Distress Syndrome – Am J Respir Crit Care Med 2017

  • Part of 50 years of research in ARDS series (worth reading entire series). Review several approaches to setting PEEP including driving pressure, PV curves, and esophageal pressure monitoring

Liberation from Mechanical ventilation

Summary of ACCP/ATS Liberation from IMV guidelines on this blog 

Two foundational vent liberation trials to know:

A comparison of four methods of weaning patients from mechanical ventilation. Spanish Lung Failure Collaborative Group – N Engl J Med 1995

  • Landmark weaning trial which found T-piece was superior to weaning by pressure support or IMV

Comparison of three methods of gradual withdrawal from ventilator support during weaning from mechanical ventilation – Am J Respir Crit Care Med 1994

  • Using the specific weaning protocols in the trial, a progressive reduction in pressure support was superior to weaning by T-piece or SIMV

Journal Club

Early Active Mobilization during Mechanical Ventilation in the ICU – N Engl J Med 2022

  • In mechanically ventilated patients, an intervention to achieve the highest possible level of mobilization that was deemed safe during daily therapy did not improve outcomes and was associated with more adverse events compared to usual care

Anaglesia and Sedation in the ICU

2018 Clinical Practice Guidelines for the Prevention and Management of Pain, Agitation/Sedation, Delirium, Immobility, and Sleep Disruption in Adult Patients in the ICU,

 

 

 

Quantifying unintended exposure to high tidal volumes from breath-stacking dyssynchrony in ARDS: the BREATHE criteria,

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“Quantifying unintended exposure to high tidal volumes from breath-stacking dyssynchrony in ARDS: the BREATHE criteria,” Intensive Care Medicine, 2016, USA

Note: I am focusing on only one aspect of this paper, see the comments section for more details

Question: Using novel diagnostic criteria, how often does breath-stacking dyssynchrony (BSD) occur in pts with ARDS?

Study Type: Prospective observational study at 2 US hospitals

Study Population: Adult pts with ARDS placed on mechanical ventilation within the previous 24 hours were eligible provided they were ventilated in the assist-control mode. Exclusion criteria included chronic mechanical ventilation, neuromuscular disease compromising spontaneous ventilation, and impending withdrawal of full supportive care

Study Groups: Airflow and pressure were continuously recorded for 72 hours, coded by an analog-digital converter, and read directly into an analysis program. The flow-time waveform was integrated to calculate cumulative tidal volume change over consecutive machine inspiratory cycles. BSD was identified using the BREATHE criteria (consecutive inspiratory cycles + expiratory times <1 sec + expiratory volume between inspiratory cycles at least 2mL/kg PBW less than first inspiratory cycle volume + •120% set inspiratory time {for pressure-targeted breaths} + BSD TV •2mL/Kg PBW above intended TV) (essentially saying the pt inspires twice before fully exhaling the first breath). Medication administration and ventilator management were directed by the ICU team who were blinded to study analysis.

Primary Outcome: BSD as measured by the BREATHE criteria

Results: 33 pts were enrolled. Notable pt characteristics: mean age (57), shock (91%), pneumonia (83%), duration of MV prior to enrollment (16 hrs), death before discharge or day 28 (27%). Vent characteristics: VC+ (volume-targeted pressure control) (79%), VC (typical volume-cycled ventilation with a set flow rate) (21%), set TV (6 mL/kg PBW), RR (25), PEEP (10), FiO2 (50%), P/F (107). 1,841 hrs were recorded and 2,166,076 breaths were analyzed (80% without neuromuscular blockage). Observed BSD frequency was 27 (7-59) breaths/hr, peak hourly BSD frequency was 170 (55-394) breaths/hr. BSD frequency was sustained for more than 60 breaths/hr during 18% (1-37) of hrs recorded without NMB. TV during BSD was 11.3 (9.7-13.3) mL/kg PBW. Peak airway pressure minimally increased with BSD.

Caveats: Small sample size, 743 hours not recorded or included for various reasons, does not establish any connection between BSD and outcomes including ventilator-induced lung injury.

Take-home Point: Among pts with ARDS ventilated in assist-control mode, breath-stacking dyssynchrony occurs and exposes pts to potentially injurious tidal volume.

Commentary

  • The BREATHE criteria are fine, but for residents easier to just remember that BSD is “inspiratory flow triggered before complete expiration” (i.e., the pt is triggering a 2nd breath before fully exhaling the first).

  • I have purposely ignored one of the main aspects of this study: comparing the BREATHE criteria to other methods of measuring BSD. Unless you are really into reading about ventilator dyssynchrony, this part of the paper is less interesting than the more basic message that BSD occurs (sometimes quite often) in AC modes.

  • This paper is a nice reminder that when you are setting a tidal volume in either VC or VC+, this does not guarantee that this is the volume your pt will receive before exhaling. You may think your pt is receiving “lung-protective ventilation,” but frequent episodes of BSD may cause your pt to receive very large TVs (in the above study, an average Vt of 11 mL/kg PBW). These results highlight the importance of looking at ventilator waveforms in your pts and frequently evaluating synchrony.

  • Whether decreasing BSD improves outcomes remains to be seen. This is one of the proposed mechanisms by which early neuromuscular blockade may improve outcomes in ARDS but more studies are needed to prove this connection.