Pitfalls & Pearls in the COVID-19 Era with Medical Intensivist Dr. Kevin Chung
Breathe easy with these airway management principles and expert tips for managing the patient with COVID-19 related lung disease (i.e. pneumonia, hypoxemia, ARDS). In the COVID-19 era, non-intensivists are being called upon to care for critically ill patients across the globe. At the Curbsiders, we understand that this can be a stressful proposition! Therefore, we’ve enlisted the help of the renowned medical intensivist & USUHS Chair of Medicine, Dr. Kevin Chung (@chungk1031) to teach us what we need to know about airway management in these challenging times.
Written and Produced by: Cyrus Askin MD, Michael Rose MD, Kathleen Hiltz MD
Show Notes: Cyrus Askin MD
Infographic: Elena Gibson, MD
Cover Art: Dr. Kate Grant MBChB DipGUMed
Hosts: Matthew Watto MD, FACP; Paul Williams MD, FACP; Cyrus Askin, MD
Editor: Matthew Watto MD, FACP (written materials); Clair Morgan of nodderly.com
Guest: COL Kevin Chung, MD, FACP
AccessMedicine is the acclaimed online medical resource that features Harrison’s Principles of Internal Medicine and more trusted content from the best minds in medicine. Visit AccessMedicine to learn more:http://bit.ly/MHCurbsiders.
33:22 Mechanical ventilation: Initial settings, following the blood gas
40:55 Peak and plateau pressure, Lung compliance and Troubleshooting a high pressures
51:30 Ventilator dyssynchrony; Lung compliance and traditional ARDS vs COVID-19 lungs
62:55 Advanced ARDS – The 5 Ps of therapy and differences with COVID-19
68:10 Take home points; Plugs; Outro
Airway Management Pearls
High flow nasal cannula (HFNC): Start at 10-20 LPM and 100% FIO2 and ask patients to breathe in through their nose, out through their mouth and purse their lips to generate PEEP.
In general, basic mechanical ventilation can be thought of us in terms of volume assist control and pressure assist control – the former being more common / intuitive, where a tidal volume is set versus the latter where expiratory and inspiratory pressures are set.
In volume control assist ventilation (AC/VC): fraction of inspired oxygen (FiO2) and positive end-expiratory pressure (PEEP) can be adjusted to improve oxygenation while respiratory rate (RR) and tidal volume (VT) can be adjusted to improve ventilation.
Keep an eye on peak and plateau pressures: elevations in one or both have a differential diagnosis (see below) which can guide troubleshooting efforts.
Compliance refers to how easily the lung distends – this should be regularly assessed (by plateau pressure) to guide therapy and should improve over time with therapy.
Ventilator Dyssynchrony rarelymeans the patient is suffering from a sedation deficiency: consider making adjustments to the ventilator, including flow or trying a different ventilator mode. When in doubt, call your friendly neighborhood intensivist for help.
ARDS is defined via the Berlin Criteria and graded in severity using the P:F ratio. Proning, paralyzing, optimizing PEEP and pruning (diuresing) are strategies to help patients with advanced ARDS.
Airway Management for the Non-Intensivist – Notes
Initial Patient Contact & Assessment
In the context of the current COVID-19 pandemic, hypoxemia with bilateral chest X-ray findings upon presentation is concerning.
Do not stop being a good internist! Consider a broad differential.
Hx of heart disease?
Hx of CHF?
Other viral illnesses?
Be quick! Make note of accessory muscle use.
Listen for evidence of murmur, perhaps a quick lung exam – make sure to use proper PPE!
Labs: ABG (or VBG) with lactate, brain natriuretic peptide (BNP), procalcitonin, respiratory viral PCR panel, COVID-19 PCR (keeping in mind the specificity > sensitivity, as Dr. Watto pointed out – consider getting two or even three in patients with a high pretest probability).
Procalcitonin: very high procalcitonin can suggest a bacterial process which is either the primary pathology or may suggest coinfection .
Kashlak Pearl!: the coronavirus tested for on the respiratory viral PCR panel is not the novel coronavirus
These patients should be strongly considered for admission, close monitoring with continuous pulse oximetry, and supplemental oxygen should be provided as needed.
Would further consider admission to the intensive care unit, especially if oxygen needs on admission are greater than a standard nasal cannula (> 6LPM).
An Approach to the Airway: COVID-19 Edition
Look at the patient – if talking and completing sentences, that’s good.
Heavy breathing, conversational dyspnea, accessory muscle use… think about non-invasive ventilation vs. intubation.
Lots of controversy over what is and is not aerosol generating – we just don’t know enough to speak intelligently on this.
Dr. Chung’s approach
Simple nasal cannula, easy and effective up to 6LPM
Beyond, consider face mask or non-rebreather (NRB)
Kashlak Pearl: In a tachypneic patient, the O2 reservoir on a non-rebreather is not terribly helpful due to poor seal, so face mask and NRB are effectively equivalent.
High-flow nasal cannula: Many options, generally go up to 40 LPM
Titrate up, usually starting at 10-20 LPM
Can adjust flow and oxygen percentage (FiO2)
Coach the patient: breath in throw the nose, out through the mouth with pursed lips
The pursed lips helps to generate intrinsic PEEP – which can be comparable to PEEP provided from non-invasive positive pressure ventilation (Sotello 2015)
Is this an aerosol generating procedure? We don’t know, but Dr. Chung recommends negative pressure room and facemask for the patient if this is done
For healthcare-workers entering the room, PPE to include, at a minimum bouffant cap, N-95 face mask, eye/face shield, gown and double gloves (sandwiching the gown sleeves) per Dr. Chung
CPAP/BIPAP – in the US, generally this is not being done but could be in resourced strapped environments
Endotracheal intubation: When a patient is tired! This means you’ve got to keep checking in!
Generally require some degree of Positive End Expiratory Pressure or PEEP (5 cm H2O or more) however, if the patient is on high-flow nasal cannula or non-invasive positive pressure ventilation, a presumptive diagnosis can be considered (per Dr. Chung)
Bilateral infiltrates, without a cardiogenic cause (based upon clinical judgement).
Degrees of ARDS: based on P:F ratio (PaO2 / FiO2, i.e. the ratio of the partial pressure of oxygen in arterial blood to the fraction of inhaled oxygen) – normal is 400-500.
Mild ARDS: <300
Moderate ARDS: <200
Severe ARDS: <100
Mortality increases as a function of severity
Mechanical Ventilation 101 (& 102)
Easiest thought of in terms of Volume targeted and Pressure targeted.
Most common modes: Volume Assist Control (AC/VC) & Pressure Assist Control (AC/PC)
Assist: every breath, whether it is patient-triggered or machine-triggered, is fully supported based upon the parameters entered
Trigger: what causes the breath
Patient-triggered: the patient volitionally generates flow or negative pressure which results in an assisted breath.
Machine-triggered: the machine, based upon the set respiratory rate, delivers a breath.
Volume Assist Control
Most prevalent mode and mode of choice for most patients.
Independent Variables (things that you set) are rate, tidal volume, fraction of inhaled oxygen or oxygen percentage (FiO2) and positive end expiratory pressure (PEEP).
Breaths per minute, adjusted based upon patient’s intrinsic respiratory rate (if applicable), increasing the machine rate –> increases minute ventilation (respiratory rate x tidal volume) and thus decreasesPCO2 (decreasing acidosis / promoting alkalosis) while decreasing the rate has the reverse effect, assuming the patient is not breathing above the set rate (i.e., if a patient is conscious and breathing 16 times a minute, setting the rate to 10 or 12 will have no effect).
Default: ~12 breaths per minute
May start at 18 or 20 – it all depends on what the patient was doing before intubation
Volume (mL) in every breath that is either machine or patient triggered
Volume should be based on ideal body weight, starting at approximately 6mL/Kg of ideal body weight per ARDSnet.
Increasing tidal volume –> increases minute ventilation (respiratory rate x tidal volume) and thus decreasesPCO2 (decreasing acidosis / promoting alkalosis) while decreasing has the reverse effect.
Minimizing / optimizing the tidal volume through this strategy reduces volutrauma which is seen when the tidal volume delivered is inappropriately high for a patient and can contribute to over-distention.
Positive End Expiratory Pressure (PEEP)
The minimum pressure that is always delivered by the ventilator to “splint” open the airways / alveoli and improve oxygenation.
Set initially between 5 and 8 cm H2O in most cases
Dr. Chung says: set the PEEP to the patient.
Increasing PEEP should improve oxygenation.
Fraction of Inhaled Oxygen (FiO2)
The fraction or percentage of oxygen in the inhaled air.
Atmospheric FiO2 is 0.21 (21%).
Generally, initial FiO2 for a patient should be 1.00 (or 100%) which can then be titrated down as tolerated.
Increased FiO2 should improve the patient’s oxygenation.
Airway pressures (primarily Peak & Plateau) are the dependent variables (a function of the independent variables “dialed in” and the lungs themselves)
Peak pressure (Ppeak): the highest pressure registered by the ventilator, measured at the end of the endotracheal tube (ETT).
Measured with every breath.
Increases in airway resistance will increase the peak such as a patient biting on the ETT, a kink in tubing / disconnection, bronchospasm, mucus plug(s).
Troubleshooting elevated Peak pressure: Consider inserting a bite block / increasing sedation, run the tubing, provide bronchodilator therapy or mucolytic therapy vs. bronchoscopy. (CAUTION: Would be very careful regarding bronchoscopy in COVID-19!!)
Mean airway pressure
Also should be monitored, reported by the ventilator.
This is the average pressure generated during the respiratory cycle.
Used to calculate the oxygenation index (see below).
Plateau pressure (Pplateau): the pressure “seen” at the alveoli (technically trans-alveolar pressure).
This should be monitored regularly.
Determined via a manual inspiratory hold (i.e. must be measured).
How do you do that? A button on the ventilator,, when pressed, will continue to deliver a breath for a specified period of time, rather than releasing to allow for exhalation and the next breath.
This allows the ventilator to calculate the plateau pressure.
A goal plateau pressure is < 30 cm H2O, pressures beyond this can lead to barotrauma (i.e. alveolar damage due to excessive alveolar pressures)(Fan 2017).
Elevated peak & plateau pressure?
Dr. Chung: It’s not about the airway, it’s about everything around the airway compressing alveoli.
May be more helpful than P:F ratio as it takes into account the pressure required to achieve a certain PaO2, effectively differentiating between the patient with a PEEP of 5 from the patient with a PEEP of 14 who have the same P:F ratio.
An OI <25 is associated with good outcomes.
An OI of 25-40 is associated with 40% mortality.
An OI of >40 should prompt consideration for extracorporeal membrane oxygenation (ECMO).
Lung protective ventilation is predicated upon minimization of both plateau pressure and tidal volume with a goal of supporting a patient through recovery, to include management of their acid-base status.
It is important to monitor tidal volume and plateau pressure to minimize the potential for iatrogenic lung injury.
A few words on Pressure Assist Control
Similar to volume assist control however, instead of setting a tidal volume and PEEP, you set an inspiratory pressure and expiratory pressure (independent variables) which result in a tidal volume (dependent variable).
A respiratory rate and FiO2 are still set in the same way they are set in volume assist control .
If a patient’s average tidal volumes increase without changes to their pressure settings, this indicates improved compliance…Of course, the converse is true.
Reductions in PCO2 can be achieved through:
Increasing the respiratory rate.
Increasing the “Delta P” also known as the driving pressure. This is done by increasing the difference between the inspiratory pressure and the expiratory pressure.
Patient ventilator dyssynchrony
This can be seen when the patient’s intrinsic respiratory rate, “desired” tidal volumes or desired flow are poorly matched to the ventilator.
This manifests as the patient appearing “uncomfortable” – grimace, irritability, tachycardia, possibly high-pressures on the ventilator.
Increasing flow: default is usually 60 LPM, can increase to 80 LPM or 100 LPM.
Perform a pressure assist control trial.
Provides variable flow which allows you to determine the flow the patient “desires”.
Once this is determined, you could consider switching the patient back to volume assist control, using the measured flow from your “pressure assist trial”.
Increase the tidal volume: consider going from 6 mL/kg IBW to 8 mL/Kg IBW.
Sedation: sometimes, increasing sedation/analgesia is appropriate but this should not be the first move – instead, try to adjust settings / modes, with the help of an intensivist, until you find a setting that works for the patient.
Mechanical Ventilation in COVID-19 & Advanced ARDS
In Dr. Chung’s experience, many COVID-19 patients are intubated with very compliant lungs.
Consider higher tidal volumes in these patients, 8-10 mL/Kg of IBW.
Consider lower PEEP if higher PEEP is not necessary.
Considerpressure assist control sooner than in traditional ARDS.
If we get a patient that has a plateau pressure of 30…what should register in your mind is, ‘oh my gosh I’m dealing with a really stiff lung…these lungs are really sick’.
COL Kevin Chung MD
Sometimes, patients with COVID-19 behave like more typical ARDS with initial plateau pressures in excess of 30 (i.e. they have poor compliance)… what can be done?
Consider Dr. Chung’s 5 Ps:
Lung Protection: Watch out for high plateau pressures and high tidal volumes.
Optimize PEEP: Usually done at the bedside through trial and error.
Useful increases in PEEP result in improved oxygenation.
Deleterious increases in PEEP manifest as hemodynamic instability
Prune – Dry lungs are happy lungs! (FACTT 2006). Target dry lungs after the acute phase, once the patient is not requiring pressor support.
Listeners will be equipped with the basics to provide ventilatory support, to include the use of mechanical ventilation, for critically ill patients in the COVID-19 era.
After listening to this episode listeners will…
Appreciate the unique challenges faced by the medical community as pertaining to the current COVID-19 pandemic.
Be familiar with fundamentals of critical care as pertaining to airway management.
Define the diagnostic criteria of ARDS and appreciate early clinical signs that may indicate a patient is developing ARDS.
Review the various non-invasive methods of assisting with oxygenating & ventilating a patient (NC, NRB, HFNC, NIPPV, etc.) and any key contraindications.
Recognize signs suggestive of impending respiratory failure requiring invasive mechanical ventilation (i.e. indications for intubation).
Be familiar with basic ventilator parameters, basic terminology / modes.
Know initial vent settings for a patient with resp failure / ARDS based on ARDSnet data.
Have an approach to titrating vent settings based on physiologic parameters & the blood gas.
Know special considerations for management of ARDS in a patient with COVID-19.
Be familiar with advanced management strategies for patients with ARDS such as proning and paralysis
Dr. Chung reports no relevant financial disclosures. The Curbsiders report no relevant financial disclosures.
Chung, K, Askin C, Rose M, Hiltz K, Gibson E, Williams PN, Watto MF. “206 Airway Management for the Non-Intensivist”. The Curbsiders Internal Medicine Podcast. http://thecurbsiders.com/episode-list 04/13/2020.