Ventilating Asthma or COPD? I:E is NOT the Goal

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crashing ventilated patient
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Steve Haywood
Former Respiratory Therapist working to de-mystify the ventilator through hands-on workshops and online education. Additional interests include HFNC in CHF and COPD, Medical Education, and Tupperware.

The Pre-brief

In a ventilated patient with an acute COPD or asthma exacerbation, if your I:E ratio is greater than 1:4 you likely will create stacked breaths.  However, just because you have an I:E ratio of 1:5 does not mean that your patient will not stack breaths. It is all about how much time they have to exhale.  If you see the flow waveform below, you need to make changes to your ventilator!

COPD and Asthma patients are hypercapnic! We must drive down the CO2! We do this by maximizing the Effective Minute Ventilation. If your patient is stacking breaths, they will get no volume!

You must prevent Breath Stacking

To prevent breath stacking, do not aim for some magical I:E ratio, but rather make sure you give the patient as much time as they need to fully exhale. This will vary depending on the individual patient’s degree of airway resistance. You can have a favorable I:E ratio and still have insufficient time for your patient to exhale.

The following are some pearls to assist you in managing the intubated patient in an acute COPD or asthma exacerbation

Pearl – Treat the Obstructive Airway Disease.

The ventilator is a supportive device, not a  therapeutic device! It is simply buying your patient time. 

Make sure you are treating the underlying obstructive airway disease!

    • Albuterol
    • Ipratropium Bromide
    • Steroids
    • Magnesium (Asthma)
    • Ketamine (Asthma)
    • Azithromycin (COPD)
    • Epinepherine
    • Kitchen Sink

EDITORS COMMENTARY 

“[Azithromycin] is certainly standard of care in COPD but controversial in asthma; there no clear benefit. . . Similarly, I almost never use [magnesium] and ketamine in a COPD patient unless they have horrific bronchospasm.”

 – Matt Siuba

Pearl – Sedate/Paralyze the patient.

The patient will feel like they are suffocating! They will want to breathe fast due to acidemia and progressive air trapping! In a crashing asthma or COPD exacerbation patient, the patient’s spontaneous respiratory rate will result in breath stacking. Ketamine is a great choice for sedation because it has bronchodilatory properties. However, Ketamine will not suppress the respiratory drive so it should be used as an adjunct to other sedatives such as propofol. Many times, these patients will require paralysis in addition to sedation. Make sure to provide adequate deep sedoanalgesia first before paralysis

Pearl – Raise the Peak Pressure Alarm

In the crashing obstructive airway disease patient, the resistance will be increased significantly. This increased resistance will cause peak airway pressures to go quite high. Remember, peak airway pressures are not the actual pressures exerted on the alveoli. The plateau pressure is a more accurate representation of the pressures exerted on the alveoli.  Check the plateau pressures often as you increase the peak pressure alarm. In severe obstructive airway disease, you may need to increase this alarm as high as 80-90cmH2O. 

More on peak airway pressure and plateau pressure HERE and HERE.

The peak airway pressure alarm also serves as a pop-off valve to prevent barotrauma. With this alarm increased the patient is at increased risk of spontaneous pneumothorax, so consider setting it approximately 10 cmH2O above the current peak pressures. Check the plateau pressures often and ultrasound the lungs if there are significant changes to evaluate for spontaneous pneumothorax.

Pearl – Set the Tidal volume.

8mL/KG of Ideal Body Weight based on height. 

  • I do not like to go lower than 6-8mL/Kg because at least 2mL/Kg is going to be dead space ventilation.We need to maximize alveolar ventilation! In severe cases, you may need to raise the tidal volume to 9-10mL/Kg provided that the plateau pressures are still safe, in order to maintain a minimum minute ventilation and allow a low enough respiratory rate to provide the needed expiratory time. 
  • If you increase tidal volumes, watch the plateau pressures! Keep <30cmH2O!

Pearl – Hit the Reset Button

Empty the lungs!

You may reach a point of no return of stacked breaths. When the peak pressure is high and the plateau pressure is also high, the lungs are overdistended and you will not catch up. If this happens, you have to hit the reset button!

Disclosure: I do not know who first described this maneuver. It was not me. 

Disconnect the ventilator from the ETT. Next, push down on the anterior/lateral ribcage to force as much gas out of the chest as possible. 

This maneuver does not fix anything! It just hits the reset button so you can start over. The patient may ventilate well for a short amount of time after performing this maneuver. If the expiratory flow is not returning to baseline on the Flow/Time waveform (CLIP BELOW) your vent is still set poorly for your patient and you need to make changes.

Expiratory flow does not return to baseline. The patient is still air trapping. 

 If you see the peak pressures increasing with each breath, your vent is still set poorly for your patient and you need to make changes.

Peak pressures are steadily increasing as the patient’s lungs become overfilled with each breath. 

**IF THE PATIENT HAS COVID-19.**

Only do this if absolutely necessary. Everyone in the room needs full airborne precautions PPE before starting. After disconnecting the patient from the vent, immediately cap the end of the ventilator circuit and place a viral filter on the ETT.  

You may have to hit the reset button multiple times before you find your sweet spot of vent settings.

Pearl – Optimize the I time

Set the I-time short. I usually start at 0.6 seconds. If you shorten the I time too much, you will create turbulent flow. If the peak pressure alarm goes off with every inspiration with no volume delivered after you “hit the reset button”, you have turbulent flow. If this occurs, lengthen the I time in small increments until the tidal volume is delivered. 

A smaller tube will cause you to reach turbulent flow at a high I-time. Make sure you intubate with as large an ETT that is safe for your patient. 

Lowering the viscosity of the gas will allow higher velocity flow before turbulent flow is reached. I have run heliox through a ventilator, but we depleted the hospital’s entire supply of heliox rapidly! Additionally, you max out at a FiO2 of 40% with heliox.

Pearl – Optimize the E-time by lowering the RR.

If you see the flow pattern above, your patient is not fully exhaling. If you have already lowered the inspiratory time, the next step is to lower the respiratory rate until you see the expiratory flow return to baseline as seen below. 

Full exhalation of each breath

In addition to following the flow waveform, pressing the expiratory hold button will quantify the intrinsic peep. Intrinsic peep is the amount of gas retained in the lungs at the start of each breath. Depending on the brand of ventilator this will be expressed as a retained volume or retained pressure.

While lowering the respiratory rate seems counterintuitive when our patient is hypercapnic, if we do not allow the patient to fully exhale, ventilation efficiency (CO2 removal) is impaired. The respiratory rate may get into the single digits in severe Asthma/COPD Exacerbation! Do not be tempted to inappropriately raise the respiratory rate when the ABG shows a respiratory acidosis. If the patient begins to stack breaths, gas exchange will worsen. Many intensivists will allow the pH to drop as low as 7.15 without intervention. When the pH needs to be raised, consider attempting to raise the tidal volume instead of the respiratory rate to prevent breath stacking. As the patient improves, the respiratory rate could potentially be liberalized. (You should be aggressively treating with Albuterol, Ipratropium, Steroids, Kitchen Sink, Etc.)

Pro-tip: Increasing tidal volume always provides more bang for the minute ventilation buck than increasing respiratory rate.

The Debrief

Intubated patients with severe obstructive lung disease can be some of the most challenging to manage. 

  • Continue to dose albuterol and treat the underlying disease. 
  • You may have to hit the reset button while you optimize the ventilator. 
  • You may be able to increase the tidal volumes if the plateau pressures are low. 
  • As paralytics are added and spontaneous inspiration is removed, the respiratory mechanics change and turbulent flow may be reached at higher inspiratory times. The rate may need to be lowered even more. 
  • As you treat the disease, you may be able to increase the rate. 
  • While the process is broken down in a simple fashion, there is nothing simple about managing these patients. 
  • Look at your I:E ratio. You need to get it low (1:5 or lower), but do not fixate on it. It is all about giving the patient as much time as possible to exhale.

Other Helpful Hints

  • Be cautious of blebs on COPD patients. They can appear similar to a pneumothorax on ultrasound and putting a chest tube into a bleb can create a bronchopleural fistula that may require surgery. 
  • Consider ECMO. If you cannot oxygenate or ventilate your patient, ECMO can buy you time while you treat the underlying disease without destroying the lungs. 
  • Extracorporeal CO2 removal (ECCO2R) is another theoretically attractive option, but this is restricted to research studies in the United States at this time.

References

  1. Henderson, W., Pare, P., Ayas, N. (2016) Murray and Nadel’s Textbook of Respiratory Medicine, Sixth Edition, Saunders, Asthma Clinical Diagnosis and Treatment 42, 731-750.e7
  2. Henderson, W., Pare, P., Ayas, N. (2016) Murray and Nadel’s Textbook of Respiratory Medicine, Sixth Edition, Saunders, COPD Clinical Diagnosis and Management44, 767-785.e7
  3. Esmailian M, Koushkian Esfahani M, Heydari F. The Effect of Low-Dose Ketamine in Treating Acute Asthma Attack; a Randomized Clinical Trial. Emerg (Tehran). 2018;6(1):e21.
  4. Tiwari A, Guglani V, Jat KR. Ketamine versus aminophylline for acute asthma in children: A randomized, controlled trial. Ann Thorac Med. 2016;11(4):283-288. doi:10.4103/1817-1737.191874
  5. Salim Rezaie, “REBEL Cast Episode 11: The Crashing Asthmatic”, REBEL EM blog, June 1, 2015. Available at: https://rebelem.com/rebelcast-crashing-asthmatic/.

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