Acute Lung InjuryandARDS

Andreas CredeEmergency Medicine Registrar

OverviewIntroductionDefinitionPathophysiologyTreatmentNew StuffReferences

Introduction1st described 1967 (Ashbaugh et al)Incidence 1.5 -7.5/ 100000 population28 day mortality 25 30%1Diagnosis clinical

DefinitionAcute onset (

Risk FactorsAlcoholismGenetic predisposition

CausesDirect Injury1PneumoniaAspirationDrowningAmniotic fluid and fat embolismAlveolar haemorrhageSmoke, toxic gas inhalationReperfusion (incl rapid drainage pleural effusion)Unilateral lung re-implantation

CausesIndirect Injury1Severe SepsisMassive transfusionShockPancreatitisSalicylate/ narcotic overdoseAnaphylaxisCardiopulmonary bypass

DifferentialLVFFluid overloadMitral stenosisLymphangitis carcinomatosisInterstitial lung disease1

Respiratory Failure

HistologicallyExudative Phase3 Neutrophilic InfiltrateAlveolar HaemorrhageProteinaceous Pulmonary OedemaCytokines (TNF, IL1,8) Inflammation Oxidative Stress and Protease Activity Surfactant ActivityAtelectasis

HistologicallyElastase- induced capillary and alveolar damage3 Alveolar flooding Fluid clearanceCapillary thrombosis Anticoagulant proteins Procoagulant proteins (Tissue Factor) Anti- fibrinolytic Protein (Plasminogen Activator Inhibitor)

Post Acute PhaseFibroproliferative Phase3Variable time periodFibrosisChronic InflammationNeovascularisationResolution3Improvement of hypoxaemiaImproved dead space and lung complianceResolution radiographic abnormalitiesCan take up to 1 yearResidual restrictive or obstructive picture

Long TermChronic Respiratory DiseaseMuscle FatigueMuscle WastingWeakness

TreatmentVentilationFluid ManagementSteroidsOther Stuff

VentilationTidal VolumesPEEPPositioningWeaning Protocols

Tidal VolumeRecommended 4-6ml/kg4High tidal volumes4Overdistention of alveoliLocal inflammatory response resulting in systemic inflammationTNF, IL6, IL10,

Tidal Volume4Low tidal volume ventilationWeight Predicted not actualPlateau Pressure 30cm H2OResp Rate Titrated to pH 7.3-7.45PEEP and FiO2 Adjusted to maintain saturationLow tidal volume may result in hypercarbiaARMA (Respiratory Management in ALI/ARDS Trial)NaHCO3 infusions/ hyperventilation to maintain pH

Tidal VolumesSame sedation strategiesNo duration of ventilationHigh frequency oscillatory ventilation shown no benefit over low tidal volume ventilation 30 day mortality not statistically significant (37% vs 52%, p=0.10)Earlier recovery from hypoxiaOnly ventilation strategy shown to reduce mortality (40% - 31%)4

PEEP Recommendation: lowest PEEP/ FiO2 to maintain saturationRecruits collapsed alveoliIn dependant regionsOver-distends in non-dependant regions Repetitive opening/ closing of alveoli: airway damageEndothelial/ epithelial stretch injury with subsequent capillary injurySimilar cytokine response as tidal volume

PEEP

PEEPALVEOLI Trial4Higher PEEP = improved oxygenationIn hospital mortality equal btw high and low PEEPTime on ventilator similarDuration non- pulmonary organ failure equal

PEEPAdverse effects of PEEP Cardiac outputVolutrauma Lung water High VA/Q Dead space Endothelial permeability Epithelial permeability Bronchial blood flow

Fessler, ARRD 1993

PEEP + Lung PerfusionPermutt, JAP 1961

PEEPSome EndpointsBest PaO2Lowest ShuntBest O2 deliveryBest lung perfusionPlateau Pressure 30cm H2OOptimise aeration on CTPressure/ volume curve becomes concave

PositioningProne positioning1,4Redistribution of blood & ventilation to least affected areas of lungSecretion clearanceShifts mediastinum anteriorly assists recruitment of atelectatic areas? reduce lung injuryReduced lung compression by abdominal contents

Supine Ventilation 40% lung volume under lung, especially patients with large hearts

Prone Ventilation

Effect of Blood Flow in Prone Positioning7Percent Flow25500SupineDorsalVentral

PositioningProne position4Transient improvement PaO2/FiO2No improvement: survival/ time on ventilator/ time in ICURole:High FiO2High plateau pressures

Weaning ProtocolsReduce duration of mechanical ventilation vs patients managed by IMV protocol4Daily spontaneous breathing trial430-120 mins unassisted ventilation4 Criteria before commencementSome reversal of underlying causePEEP 8cm H2O/ FiO2 50%Haemodynamic stabilityAbility to initiate inspiratory effort

Fluid Management

Fluid ManagementFluid movement regulated by:Starling equationVessel wallAbility to filter fluidSelective permeability to proteins

Fluid Management

Fluid ManagementStudy of conservative vs liberal fluid management560 day mortality: 25.5 vs 28.4% p=0.301st 28 days ventilator free: 14.6 vs 12.1 p

SteroidsTheoretical use to inflammatory response associated with ARDS62006 study6No 60 day mortality (28.6% vs 29.2% p= 0.10)Use of steroids 14+ days post onset: mortality need for vasopressors ventilator and shock free days neuromuscular weaknessShort term improvement in oxygenation

Other stuffExtracorporeal membrane oxygenationImprovement in oygenationNo long term survivalVasodilatorsImproved oygenationNo long term survivalKetoconazolePentoxyfillineNutritional modificationAntioxidantsSurfactantB2 stimulants1

Emergency Department SummaryPREVENT!Low tidal volume ventilationRestrict PEEPRestrict Fluids (if possible)Initiate Weaning ProtocolSupine Ventilation

ConclusionMany theoretical therapiesOnly proven strategy to improve survival is low tidal volume ventilationTherapies to reduce number of days needing scarce resources valuable in our setting

Thank You

References1. Wheeler, A.P. and Bernard, G.R. 2007,Acute Lung Injury and the Acute Respiratory Distress Syndrome: A Clinical Review. Lancet; 369: 1553652. The Acute Respiratory Distress Syndrome Network. 2000, Ventilation With Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome. N Engl J Med; 342:1301-083 Plantadosi, C.A and Schwartz, D.A. 2004, The Acute Respiratory Distress Syndrome. Ann Intern Med; 141:460-470.4. Girard, T>D> and Bernard,G.R. 2007, Mechanical Ventilation in ARDS: A State-of-the-Art Review. Chest; 131;921-9295. The National Heart, Lung and Blood Institue Acute Respiratory Distress Syndrome Clinical Trials Network. 2006, Comparison of Two Fluid-Management Strategies in Acute Lung Injury. N Engl J Med; 354:2564-756. The National Heart, Lung and Blood Institue Acute Respiratory Distress Syndrome Clinical Trials Network. 2006, Efficacy and Safety of Corticosteroids for Persistent Acute Respiratory Distress Syndrome. N Engl J Med; 354:1671-847. www.slideshare.net