Acute Respiratory Distress Syndrome (ARDS): What You Need

John Gallagher DNP, RN, CCNS, RRTAndrew Rice MSN,CRNA, ACNP-BC

Acute Respiratory Distress Syndrome (ARDS): What You Need to Know Today

Learning Objectives

• Identify current trends in the clinical management of ARDS during the COVID-19 Pandemic

• Make recommendations for caring for patients with ARDS during the COVID-19 Pandemic

Coronavirus (COVID-19)

• Novel bat-origin Coronavirus originating in Wuhan, Hubei, China– SARS-CoV-2 aka COVID-19

• Patients present with flu-like symptoms– Sore throat– Cough– Fever– Shortness of breath

COVID-19 Illness Severity

• 81% Mild (no or mild pneumonia)• 14% Severe disease

– Dyspnea, hypoxia, >50% lung involvement • 5% critical disease

– Respiratory failure, shock, or multiorgan dysfunction– Uncommon: only 13% need vasoactive agents

COVID-19 Related ARDS

• 3% – 17% COVID-19 develop ARDS• Late onset dyspnea (6.5 days)• ARDS develops ~2.5 days after dyspnea• Risk Factors: age, smoking, comorbidities, fever > 39*C

– Cardiac disease, DM, HTN, lung disease, CKD, cancer, obesity

Lab Findings with Worse Outcomes• Lymphopenia• Elevated liver enzymes• Elevated lactate dehydrogenase (LDH)• Elevated inflammatory markers (eg, C-reactive protein [CRP], ferritin)• Elevated D-dimer (>1 mcg/mL)• Elevated prothrombin time (PT)• Elevated troponin• Elevated creatine phosphokinase (CPK)• Normal procalcitonin with pneumonia, but elevated with ICU admission• Acute kidney injury

Patient Presentation

• Hypoxemia manifested by low oxygen saturation worsening with activity (hypoxic vasoconstriction?)– SpO2 < 90%

• High negative inspiratory effort in spontaneously breathing patients

• Improvement in oxygenation with invasive positive pressure ventilation– Lung compliance may be normal!!

Patient Presentation

• Worsening hypoxemia and lung compliance• Hypoxic pulmonary vasoconstriction/microemboli

– Elevated D-dimer• Cardiomyopathy/Myocarditis

– Viral cause– Right ventricular failure related to ARDS and PPV?

ARDS CriteriaPaO2/FiO2 Ratio

Mild* Moderate* Severe*200 – 300 100 - 200 < 100

• Acute onset (within 7 days)

• Bilateral opacities (CXR or CT)

• Alveolar edema is not related to cardiac failure or fluid overload– Does not require normal PCWP– Does not require absence of LA hypertension

* on CPAP/PEEP > 5 cm H2O

JAMA. 2012;307(23):2526-2533. doi:10.1001/jama.2012.5669

Radiologic Changes

• Ground glass opacities peripherally and basilar • Interlobular septal thickening

• Radiologic changed may be seen early in some cases before positive COVID screening results

• Not recommended: CXR or CT for screening/progression (staff/equipt contamination)

Lung Ultrasound• Thickened/Irregular pleural line • Multiple B-Lines• Subpleural consolidations• Air bronchograms• Localized pleural effusion possible

Copetti, R Cardiovasc Ultrasound 2008

B-Lines

COVID-19 Supportive Management

• Prone ventilation (prolonged, avoid early return to supine)• Conservative fluid therapy (except with sepsis)• Glucocorticoids?• Avoid aerosolization procedures (bronchoscopy, nebulizers)• Critical Care Management: nutritional support, VTE prophylaxis, stress

ulcer prophylaxis, fever management, etc. • Low intubation threshold

Management of Hypoxemia

• Supplemental low-flow oxygen– Lowest FiO2 necessary maintain SpO2 90% – 96%

• High-flow nasal Cannula?• Non-invasive positive pressure ventilation (NIPPV) ?• Intubation/Invasive PP ventilation

Non-Invasive Strategies

• HFNC– Aerosol virus

• Mask over the face

• NIPPV– Aerosol virus

• Filtration of the circuit

Non-Invasive Strategies –CPAP Hood– High Flow Set Up– Venturi

Decision to Intubate

• Delayed intubation ↑ risk to patient and HCW• Low Intubation threshold

– Rapid ARDS progression (hours)– Lack of improvement on >40 L/minute of high flow oxygen and a

fraction of inspired oxygen (FiO2) >0.6– Worsening hypercapnia– Hemodynamic instability or multiorgan failure

Intubation-Preparation• PPE- Full barrier precautions

– PAPR (powered air purifying respirator) or N-95 mask/faceshield

• Avoid awake intubation (cough aerosolization) • Most experienced operator/Limit those in the room (Neg press)• Video laryngoscope (distance and first pass success)

• Novel barrier approaches

https://www.apsf.org/wp-content/uploads/news-updates/2020/apsf-coronavirus-airway-management-infographic.pdf

https://www.nejm.org/doi/full/10.1056/NEJMc2007589?query=featured_coronavirusBarrier enclosure during endotracheal intubationApril 3rd 2020

Intubation

• Goals: Protect staff, successful first attempt, limit aerosolization• Pre-oxygenate 5 min (passive low-flow ie. nasal cannula) • RSI intubation – Do Not Mask Ventilate• Heat Moisture Exchanging Filter (HMEF) between airway and

BVM/Ventilator• Direct placement on the ventilator

https://www.apsf.org/wp-content/uploads/news-updates/2020/apsf-coronavirus-airway-management-infographic.pdf

ARDS CriteriaPaO2/FiO2 Ratio

Mild* Moderate* Severe*200 – 300 100 - 200 < 100

• Acute onset (within 7 days)

• Bilateral opacities (CXR or CT)

• Alveolar edema is not related to cardiac failure or fluid overload– Does not require normal PCWP– Does not require absence of LA hypertension

* on CPAP/PEEP > 5 cm H2O

JAMA. 2012;307(23):2526-2533. doi:10.1001/jama.2012.5669

Zone of↑ Risk

PLATEAU

Driving Pressure

PEEP

Alveolar Overdistension

Collapsed Alveoli

Inspiratory phase

Expiratory phase

Repeated Alveolar Close and Expansion (RACE)

“Milking” of surfactant from alveoli with repeat closure

Lung Protection

Marini, J. (2019) Critical Care, 23 (suppl 1):114

Lung Protective Ventilation Strategy

• Maintain Alveolar Pressure (plateau pressure) < 30 cm H2O– Low tidal volume ventilation 6 ml/kg of PBW (range 4-8 ml/kg PBW)

• PEEP to prevent end-tidal collapse/recruit– PEEP start lower (8-10 cm H2O) and titrate up

ARDSNet Protocol

• Low tidal volume• Prone ventilation

http://www.ardsnet.org/files/ventilator_protocol_2008-07.pdf

Evolution of Mechanical Ventilators

Volume Control Pressure Control

PEEPA/C

SIMVA/C

SIMV

Support

Dual Control

Ventilation Strategies• LTVV + PEEP

• Pressure Control Inverse Ratio (PC-IRV) + PEEP• Volume Targeted Pressure Modes • Biphasic Ventilation- spontaneous breathing mode

– BiPhasic/BiLevel– Airway Pressure Release Ventilation ( exp time < 1.0 sec)

Volume Targeted (Control)Ventilation (VCV)• Guaranteed tidal volume with each breath• Constant flowrate• Pressure varies based on resistance and compliance of

the lung and chest wall

Pressure

Flow

Pressure Targeted (Control) Ventilation (PCV)Fixed inspiratory pressure but Volume is variable• Inspiratory pressure & inspiratory time• Airway resistance, lung and chest wall compliance

Pressure

Flow

Pressure Control Inverse Ratio (PC-IRV)

50

25

50

I-Time E-Time I-Time

Time

Pressure

Auto-PEEP

50

25

50

I-Time E-Time I-Time

Time

Pressure

8

Set PEEPAuto- PEEP

P

F

Exp. Flow 50 - 80% of Peak

PCV PC-IRV

Auto PEEPMeasurement

ActualPEEP

Volume Assured Pressure Modes

Pressure Limited + Minimum Volume Guarantee• aka…

– Adaptive Pressure Control Modes– “Dual Control” Modes

Machine adjusts to changing lung mechanics to provide tidal volume within pressure limit

Volume Assured Pressure Modes

PCV + Volume Target

•Pressure Regulated Volume Control (PRVC)•Volume Support

•Volume Control Plus (VC+)•Volume Support

•Pressure Control Volume Guarantee (PCVG)

•Volume Targeted Pressure Control (VTPC)

•Adaptive Pressure Ventilation•Adaptive Support Ventilation

•Pressure Augmentation

Pressure

Flow

Pressure Regulated Volume Control

Points to Remember

• Guaranteed minimum tidal volume but not a constant tidal volume!!

• Tidal volume may not be achieve if lung compliance becomes low or pressure limit is set too low

• Excessive tidal volume if the patient generates excessive inspiratory efforts

Spontaneous Breaths

P

T

PEEPHI

PEEPLO

Spontaneous Breaths

PEEPHI

PPEEPLO

T

* * ** * * *† ††

Synchronized Transition†Spontaneous Breaths*

APRV

BiPhasic

Spontaneous Breaths

P

T

PEEPHI

PEEPLO

Biphasic Ventilation

Spontaneous Breaths

•Inspiratory Pressure Limit (PEEPHI)•PEEP (PEEPLOW)•Inspiratory time (Ti)•Rate (fx)•Pressure Support

• Biphasic• Bi-level• Bi-Vent• BIPAP• Duo PAP

APRV Characteristics• High CPAP level with a short expiratory releases at set intervals (rate)

• APRV always implies an inverse I:E ratio

• All spontaneous breathing is done at upper pressure level

PEEPHI

PPEEPLO

T

* * ** * * *† ††

Synchronized Transition†Spontaneous Breaths*

Alveolar Volumetric Changes in APRV

Insp.

Exp.

Conventional APRV

Insp. Exp.~~

Prone Positioning

Zone of Perfusion Zone of Ventilation

Prone for 12-16 hoursIn moderate to severe ARDS

Pulmonary Vasodilators

• Preferential distribution to ventilated alveoli

• Improvement in perfusion to ventilated areas

• Reduce Pulmonary Vascular Resistance (PVR)

• Reduce afterload of the RV

Nitric Oxide

Injection of gas into the distal ventilatorcircuit (minimize interaction with O2 )

– initial 20-40 ppm– maintain 2-10 ppmAdverse effects– methemaglobinemia– oxidant formation – vasoconstriction/hypoxemia (withdrawal)– possibly renal failure

Cardiovascular Effects of COVID-19

• Chest pain/palpitation• Dysrhythmias

– Atrial fibrillation– Tachydysrhythmias

• Heart failure• Cardiomyopathy• Troponin elevations• Cardiac Arrest

Chloroquine/Hydroxychloroquine• Prolonged QT• Torsades

Lopinavir/Ritonavir• Prolonged QT and PR interval• Coadministration with lovastatin

or simvastatin may result in rhabdomyolysis

Positive Pressure & RV Afterload

• Myocardial O2 demand• Reduced Coronary Artery BF (chamber dilation)

PPV/PEEP

Alveolar distention

Increased RV afterload

Hypoxic Vasoconstriction

Capillary compression

Alveolar collapse

Ventilator Availability• Critical care vents (fully functional)/BiPap machines• Use of emergency stockpile and industry production• Use of Anesthesia machines• Multiple patients on one machine-significant limitations

Goals of Ventilation

• Familiarity/experience with the chosen mode• Application/limitations across disease states

• Goals of the chosen strategy• Lung protection/recruitment/liberation

• Endpoints of success (failure)• Improved oxygenation/ventilation/compliance

•

• Patience…..• Recruitment and improvements may take hours

• Rapidly changing from one mode to another rarely helpful

• Especially if the team is unfamiliar with it

Goals of Ventilation

Parting Thoughts

• Identify overall patient ventilation goals• Ensure team familiarity with the chosen mode/strategy• Lung protection and recruitment early rather than Rescue• Patience.. Improvement may be gradual• Anticipate and prepare for associated complications• Monitoring change in patient parameters is everyone’s

responsibility

Resources• AANA

– https://www.aana.com/aana-covid-19-resources• APSF

– https://www.apsf.org/novel-coronavirus-covid-19-resource-center/• SCCM

– https://www.sccm.org/disaster• Center for Disease Control (CDC)

– https://www.cdc.gov/• https://online-learning.harvard.edu/course/mechanical-ventilation-

covid-19