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