#206 Airway Management for the Non-Intensivist

April 13, 2020 | By Cyrus Askin

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.

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Credits

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

Sponsor

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.

Time Stamps

• 00:00 Sponsor – AccessMedicine by McGraw Hill http://bit.ly/MHCurbsiders 
• 00:15 Disclaimer, intro, guest bio
• 03:15 Guest one liner, chicken wings (Miller Lite marinade), career advice
• 07:40 Sponsor – AccessMedicine by McGraw Hill http://bit.ly/MHCurbsiders 
• 08:20 Case of hypoxemic respiratory failure; Rapid evaluation, initial labs
• 16:03 Initial assessment of a COVID-PUI; HFNC and non-invasive ventilation
• 23:40 Proning patients for hypoxemia
• 29:15 ARDS basics: diagnostic criteria, Brief Recap
• 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

1. 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.
2. 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.
3. 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.
4. Keep an eye on peak and plateau pressures: elevations in one or both have a differential diagnosis (see below) which can guide troubleshooting efforts.
5. 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.
6. Ventilator Dyssynchrony rarely means 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.
7. 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? 

Physical Exam: 

• 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

Disposition:

• 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

1. Simple nasal cannula, easy and effective up to 6LPM
2. 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.

3. 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
4. CPAP/BIPAP – in the US, generally this is not being done but could be in resourced strapped environments
5. Endotracheal intubation: When a patient is tired! This means you’ve got to keep checking in!

Proning? 

• Can help with hypoxemia, even when not intubated! (Scarvilli 2015)
• Can ask the awake patients to prone themselves.

ARDS Nuts & Bolts

Bilateral, diffuse opacification DDx (A) the lungs are injured or (B) florid heart failure – hence the general definition for ARDS: non-cardiogenic pulmonary edema.

Berlin Criteria – used to define ARDS (Thompson 2017)

• 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.
  1. Mild ARDS: <300
  2. Moderate ARDS: <200
  3. Severe ARDS: <100
  4. 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)
  1. 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).

Rate

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 decreases PCO2 (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

Tidal Volume

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 decreases PCO2 (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

Airway pressures (primarily Peak & Plateau) are the dependent variables (a function of the independent variables “dialed in” and the lungs themselves)

Peak pressure (P_peak): 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).
  1. 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 (P_plateau): 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.
• Differential diagnosis: Maybe it’s excessive PEEP, abdominal compartment syndrome, chest wall restriction / morbid obesity, worsening ARDS, pulmonary edema, worsening/progressive pneumonia (i.e. alveolar purulence), pneumothorax or a developing pleural effusion.

Lung Compliance 

Peak and plateau pressure give you information regarding compliance = ability of the lung to distend.

Example:

• Immediately following intubation, plateau pressure is measured at 30 cm H2O.
• Chest X-Ray is consistent with pulmonary edema, diuresis is successfully begun.
• Next day, plateau pressure is measured at 20 cm H2O.
• This means compliance has improved based upon the intervention!

What should be done after intubation?

• Immediately record peak and plateau pressures as a baseline.
  1. The plateau pressure after intubation, while the patient is still paralyzed, is more reliable than when a patient is spontaneously breathing while on the ventilator!
  2. These pressures will generally be recorded regularly by your respiratory therapist, thereafter.
• Get a blood gas after 30-60 minutes and make adjustments based upon PCO2, PAO2 and pH.
  1. Dr. Chung mentions that a pH above 7.25 is survivable  and means you have time to initiate other therapies without having to divert all your attention to acid-base management.
• In the absence of arterial access, venous blood gases are perfectly reasonable to assess blood CO2 levels and pH.
• Don’t forget the cutaneous oxygen saturation and end-tidal CO2 monitoring which can be used as real-time metrics to help guide ventilator adjustments.
• Consider calculating the oxygenation index (OI) regularly (Trachshel 2005):
  1. (FiO2 x Mean Airway Pressure) / PaO2
  2. 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.
  3. An OI <25 is associated with good outcomes.
  4. An OI of 25-40 is associated with 40% mortality.
  5. An OI of >40 should prompt consideration for extracorporeal membrane oxygenation (ECMO).

Lung protective ventilation: 

Keep an eye on both plateau pressure and volume, together (Neto 2012, Villar 2011).

• 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.

Troubleshooting.

• 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.
• Consider  pressure assist control sooner than in traditional ARDS.

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:

1. Lung Protection: Watch out for high plateau pressures and high tidal volumes.
2. Optimize PEEP: Usually done at the bedside through trial and error. 
   1. Useful increases in PEEP result in improved oxygenation. 
   2. Deleterious increases in PEEP manifest as hemodynamic instability
3. Prune – Dry lungs are happy lungs!  (FACTT 2006). Target dry lungs after the acute phase, once the patient is not requiring pressor support. 
   1. Loop diuretics, +/- albumin (Kitsios 2014). 
   2. Trend urine output and weight carefully
4. Prone – explored in the PROSEVA trial  (Guerin 2013)
5. Paralyze – somewhat controversial with mixed data. 
   1. ACURASYS  (Papazian 2010) – supportive of paralysis. 
   2. ROSE (PETAL Network 2019) – did not support early use of paralysis in ARDS.

Links

1. Internet Book of Critical Care (IBCC) Podcast by Dr. Josh Farkas – COVID-19
2. Dr. Jessica Bunin’s Video Lecture on Vent Basics for Non-Intensivists
3. COVID-19 Toolbox
4. One-Stop for some COVID-19 video content, also on the COVID-19 Toolbox Site

Goal

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.

Learning objectives

After listening to this episode listeners will…  

1. Appreciate the unique challenges faced by the medical community as pertaining to the current COVID-19 pandemic.
2. Be familiar with fundamentals of critical care as pertaining to airway management.
3. Define the diagnostic criteria of ARDS and appreciate early clinical signs that may indicate a patient is developing ARDS.
4. Review the various non-invasive methods of assisting with oxygenating & ventilating a patient (NC, NRB, HFNC, NIPPV, etc.) and any key contraindications.
5. Recognize signs suggestive of impending respiratory failure requiring invasive mechanical ventilation (i.e. indications for intubation).
6. Be familiar with basic ventilator parameters, basic terminology / modes.
7. Know initial vent settings for a patient with resp failure / ARDS based on ARDSnet data.
8. Have an approach to titrating vent settings based on physiologic parameters & the blood gas.
9. Know special considerations for management of ARDS in a patient with COVID-19.
10. Be familiar with advanced management strategies for patients with ARDS such as proning and paralysis

Disclosures

Dr. Chung reports no relevant financial disclosures. The Curbsiders report no relevant financial disclosures. 

Citation

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.