Improving Oxygenation in ARDS
OVERVIEW
Refractory hypoxia, leading to dysoxia at the cellular level, can be difficult to manage in severe acute respiratory distress syndrome (ARDS)
- protective lung ventilation strategies should be used (e.g. ARDSNet protocol) to prevent worsening from ventilator-induced lung injury (VILI)
- many of the strategies commonly used lack a strong evidence base
- these strategies may help improve oxygenation in selected lung conditions other than ARDS, where there is a strong rationale
APPROACH
Basic measures
- increase FiO2 to improve PAO2
- increased PEEP
- increase surface area for gas exchange
- decrease atelectasis
- redistribution of lung water
General measures
- physio and suctioning
- sedation and paralysis
- decreased O2 consumption and CO2 production
- the ACURASYS trial found a mortality benefit with early atracurium neuromuscular blockade
- treat factors that increase metabolic demand; e.g. sepsis
- optimise fluid balance
- maximise cardiac output and oxygen delivery
- minimise interstitial overload
- optimise Hb
- optimal oxygen carriage and minimise immune and volume effects of transfusion
- diuretics
- albumin
- a small trial supports the use of concentrated albumin with frusemide in hypoproteinaemic ARDS patients
Optimise recruitment and FRC
- lung recruitment manoeuvre
- open collapsed alveoli, increased FRC and area available for gas exchange
- uncertain benefit; increased mortality in the ART trial
- increased I:E ratio towards 1:1 (from 1:1.5 to 1:2 which is a typical standard ratio)
- increases FRC, recruitment and PAO2
- inverse ratio ventilation
- longer time in inspiration with potential gas trapping
- provides autoPEEP above set PEEP with subsequent increase in FRC and area for gas exchange
- consider airway pressure release ventilation (APRV)
- unproven
- prone positioning
- better V/Q, improved mechanical advantage, less lung compression from abdominal and mediastinal contents
- improved mortality in severe ARDS in meta-analyses and PROSEVA trial
Optimise Flow to Ventilated Alveoli
- inhaled NO
- dilator delivered only to ventilated alveoli (evidence lacking)
- prostacyclin
— mproved perfusion to ventilated alveoli (evidence lacking)
Last Resorts
- tracheal gas insufflation
— decrease circuit dead space providing lower CO2 with relative increase in PAO2 - High-frequency oscillation ventilation (HFOV)
- no benefit in large RCTs (OSCAR and OSCILATE)
- VEno-venous extracorporeal membrane oxygenation (VV ECMO)
- improved oxygenation + lung rest and minimisation of ventilator associated lung injury
- supported by CESAR trial
References and Links
CCC Ventilation Series
Modes: Adaptive Support Ventilation (ASV), Airway Pressure Release Ventilation (APRV), High Frequency Oscillation Ventilation (HFOV), High Frequency Ventilation (HFV), Modes of ventilation, Non-Invasive Ventilation (NIV), Spontaneous breathing and mechanical ventilation
Conditions: Acute Respiratory Distress Syndrome (ARDS), ARDS Definitions, ARDS Literature Summaries, Asthma, Bronchopleural Fistula, Burns, Oxygenation and Ventilation, COPD, Haemoptysis, Improving Oxygenation in ARDS, NIV and Asthma, NIV and the Critically Ill, Ventilator Induced Lung Injury (VILI), Volutrauma
Strategies: ARDSnet Ventilation, Open lung approach, Oxygen Saturation Targets, Protective Lung Ventilation, Recruitment manoeuvres in ARDS, Sedation pauses, Selective Lung Ventilation
Adjuncts: Adjunctive Respiratory Therapies, ECMO Overview, Heliox, Neuromuscular blockade in ARDS, Prone positioning and Mechanical Ventilation
Situations: Cuff leak, Difficulty weaning, High Airway Pressures, Post-Intubation Care, Post-intubation hypoxia
Troubleshooting: Autotriggering of the ventilator, High airway and alveolar pressures / pressure alarm, Ventilator Dyssynchrony
Investigation / Indices: A-a gradient, Capnography and waveforms, Electrical Impedance Tomography, Indices that predict difficult weaning, PaO2/FiO2 Ratio (PF), Transpulmonary pressure (TPP)
Extubation: Cuff Leak Test, Extubation Assessment in ED, Extubation Assessment in ICU, NIV for weaning, Post-Extubation Stridor, Spontaneous breathing trial, Unplanned extubation, Weaning from mechanical ventilation
Core Knowledge: Basics of Mechanical Ventilation, Driving Pressure, Dynamic pressure-volume loops, flow versus time graph, flow volume loops, Indications and complications, Intrinsic PEEP (autoPEEP), Oxygen Haemoglobin Dissociation Curve, Positive End Expiratory Pressure (PEEP), Pulmonary Mechanics, Pressure Vs Time Graph, Pressure vs Volume Loop, Setting up a ventilator, Ventilator waveform analysis, Volume vs time graph
Equipment: Capnography and CO2 Detector, Heat and Moisture Exchanger (HME), Ideal helicopter ventilator, Wet Circuit
MISC: Sedation in ICU, Ventilation literature summaries
Journal articles
- Collins SR, Blank RS. Approaches to refractory hypoxemia in acute respiratory distress syndrome: current understanding, evidence, and debate. Respiratory care. 56(10):1573-82. 2011. [pubmed]
- Cortés I, Peñuelas O, Esteban A. Acute respiratory distress syndrome: evaluation and management. Minerva Anestesiol. 2012 Mar;78(3):343-57. [pubmed] [Free Full Text]
FOAM and web resources
- DerangedPhysiology.com — Ventilation strategy for ARDS
- Resus.ME — Don’t just pre-oxygenate: have an Oxygenation Strategy (2015)
Critical Care
Compendium
Chris is an Intensivist and ECMO specialist at The Alfred ICU, where he is Deputy Director (Education). He is a Clinical Adjunct Associate Professor at Monash University, the Lead for the Clinician Educator Incubator programme, and a CICM First Part Examiner.
He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives. He was one of the founders of the FOAM movement (Free Open-Access Medical education) has been recognised for his contributions to education with awards from ANZICS, ANZAHPE, and ACEM.
His one great achievement is being the father of three amazing children.
On Bluesky, he is @precordialthump.bsky.social and on the site that Elon has screwed up, he is @precordialthump.
| INTENSIVE | RAGE | Resuscitology | SMACC
