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MAR
25

Because I Was Inverted: What You Need to Know About APRV

APRV-Cover

The nurse approaches you as you're taking off your helmet and wheeling the stretcher into the ED from the helipad. 

"We can't get his pulse ox up! We have tried EVERYTHING!"

 This is a small outlying community access hospital and they rarely meet you at the door. Original page was a 43 year old male who is being transferred back to a tertiary care center to receive higher level pulmonary and critical care (they are even using the E word).

The patient presented to the community hospital by EMS with a five day complaint of progressive shortness of breath. 

Nurse Report: 

  • Presented profoundly dyspneic and hypoxic and failed a trial of BiPAP (yah, I know its a trademark name..psh).
  • Intubated and placed on a ventilator.
  • Remains hypoxic with dangerously elevated airway pressures, despite multiple ventilator adjustments.
  • Chest X-ray reveals widespread “ground-glass” opacities. 

Upon your arrival, you find the patient laying on ED stretcher with high pressure alarms sounding.

His vital signs are a heart rate of 154, blood pressure of 170/100 and a pulse ox of 74%.

Current Ventilator Setting:

  • Volume – Assist Control
  • Rate: 24
  • Tidal Volume: 450ml's
  • PEEP: 22 cmh2O
  • FiO2 of 100%
  • Pplat 48 cmh2O

An ABG was obtained just as you arrived with revealed a pH of 7.15, CO2 of 55.3, HCO3 of 21 and PaO2 of 53. 

Given the patient’s hypoxia in spite of increased PEEP, elevated plateau pressures and ventilator desynchrony, you discuss transitioning the patient to airway pressure release ventilation (APRV) with medical control - medical control agrees. 

Anyone who has been in critical care transport for any length of time has had to transition a patient from one mode of ventilation to another, usually from pressure to volume or vice versa. But with APRV being available on some transport ventilators, it is important to have a sound understanding of this mode, as well as its utility for when it may be an option. 

APRV has a reputation of being a somewhat "new form" of ventilation when in actuality it has been utilizing for over three decades, however it has become more prominent as of late, especially in Acute Respiratory Distress Syndrome (ARDS) and Acute Lung Injury (ALI). APRV has been found to be safe and effective in both of these disease states. However, it is important to note, that APRV has not been shown to have an improved mortality benefit. Though it has shown to improve oxygenation, shorten mechanical ventilator duration and ICU length of stay.

APRV is a pressure-limited, time triggered, time cycled, inverse ratio ventilation which allows for spontaneous breathing.It is a form of open lung ventilation, which alternates  between high and low pressures for a predetermined length of time while allowing spontaneous breathing similar to Continuous Positive Airway Pressure (CPAP).

The beauty of APRV is that it allows spontaneous breathing between both inspiratory and expiratory phases. Should the patient have no respiratory effort, APRV becomes a form of inverse ratio, pressure limited ventilation.

So what does all this mean exactly? It is equivalent  to sticking your head out the window going 50mph and being pulled back in for a half a second and repeating this process over and over again.  

UNDERSTANING THE VERNACULAR 

APRV comes with its own vernacular, which may cause some  apprehension to clinicians that are not familiar with the terminology and their meaning. 

With conventional ventilation we are all familiar with the standard settings of rate, tidal volume or pressure, PEEP and FiO2. With APRV there are four main settings; Pressure High, Pressure Low, Time High and Time Low, in addition to FiO2. These four settings determine how much pressure will be given over a defined period of time. 

 To even further complicate matters different manufactures use different names for APRV. It is also important to note that with the different names there may be subtitle differences in their specific mode.

The Highs & Lows: 

With APRV there are two set pressure: Pressure High (P high) and Pressure Low (P low) which occur over two defined periods of time: Time High (T high) and Time Low (T Low). Pressure high and Time high as well as Pressure low and Time low occur in conjunction with one another. 

Pressure high is the upper pressure level most commonly thought of as the CPAP pressure or inspiratory pressure. Time high is the length of time of which pressure high is spent and will be significantly longer than that of time low.

During Pressure High, which can occurs up to 80-90% of the ventilator cycle based on the Time High, alveolar recruitment in addition to the maintenance of lung volumes, occur through an open lung ventilation approach creating a prolonged increase in mean airway pressure resulting in near constant lung recruitment.

Pressure low, is the lower pressure level or the expiratory pressure. Time low is the shorter of the two times and is the expiratory time or release phase. 

During the release phase, it allows for ventilation and CO2 removal. Given the short time that this release occurs, it prevents alveolar decruitment but is long enough to create an acceptable tidal volume.

Spontaneous Breathing 

With APRV allowing the patient to breath spontaneously during all portions of ventilation, it leads to increased patient comfort, decreased sedation, minimized atelectasis and improved gas exchange. It also leads to patient-ventilator synchrony leading to a decreased need for neuro muscular blockade. 

 

The Good & The Bad: 

Advantages: 

  • Lung protective ventilation strategy 
  • Alveolar Recruitment 
  • Improved oxygenation & hemodynamics 
  • Ability to main spontaneous breathing and patient-ventilator synchrony 
  • Decreased sedative & neuromuscular blockade usage 

 

Disadvantages: 

  • Potential Volutrauma 
  • Increased Work of Breathing 
  • Dynamic Hyperinflation

 

PULLING THE APRV TRIGGER 

Unfortunately there is not a well-established recommendation of when a patient should be transitioned from conventional ventilator settings to APRV. In my experience, from a in-hospital perspective some will employ APRV early in the patient’s clinical course where as others will use it a salvage type therapy. So these suggestions my thoughts, which are worth very little....

 

From a transport perspective, I think APRV should be given consideration in the patient with refractory hypoxia despite escalating PEEP, dangerously elevated plateau pressures despite the use of lung protective ventilation strategies  or the patient who is hypoxic and dyssynchronous with the ventilator despite corrective management. 

In both of these scenarios I believe APRV will be beneficial given the maximization of alveolar recruitment during P and T high, creating the prolonged elevation of mean airway pressure as well as the prevention of decruitment during the release phase. I also believe that APRV would be extremely beneficial in the patient with desynchrony as the patient would have the ability to breath spontaneously throughout the entirety of the ventilator cycle, leading to improved patient comfort.

Again, with there being no well-established recommendation of who and when a patient should be transitioned to APRV, it is important for the clinician to analyze all of the information they have at that time and make a decision based on the options that have available, as to if the patient may benefit in transitioning to APRV. 

 

P High: 30

The P High is going to be set to your desired plateau pressure and should be kept below 35 in order to prevent overdistention. When transitioning a patient to APRV from another conventional mode of ventilation, the previously utilized plateau pressure can be utilized as the P High.  

P Low: 0

The P Low is set to 0 to optimize the expiratory flow. 

T High: 4 or greater 

T High should be set greater than 4. 

A T High below 4 will have a negative affect mean airway pressure. The T high should be occur greater than 90% of the ventilation cycle and is the main determinant of the release frequency, with the frequency  being between 10-14. As the number of frequencies increase alveolar decruitment can occur.  

Release Frequency = 60 / (T High + T Low)

T Low: 0.5

T low is the most important of the four parameters. A T Low that is too short may result in inadequate exhalation and hypercapnia. A  prolonged T low can lead to alveolar decruitment. 

Selecting the appropriate release time will result in adequate ventilation while curtailing alveolar decruitment. Minute Volume will be dependent a T low in addition to patient respiratory effort. 

Patient Management:

Hypoxemia

  • Increase P High, T High or both 
  • Increase FiO2 

Hypercapnia:

When utilizing APRV you will likely encounter some degree of hypercapnia which is usually well tolerated.

  • Decrease T High in increments of 0.5 seconds. 
    • By shorting T High, there will be more releases. (T High should generally not be decreased to less than 4 seconds)
  • Increase P High. Increasing 
    • P High will increase delta P (P High – P Low).

Hypocarbia:

  • Increase T High in increments of 5 seconds 
    • By increasing T high, there will be fewer releases. 
  • Decrease P High 
    • By decreasing P High, delta P will lower. 
      • Monitor oxygenation and be aware of possible decruitment. 

 

 

I would be remiss if I didn’t recommend both Ventilator Management: A Pre-Hospital Perspective and Ventilator Management: Advanced Concepts in Critical Care as exceptional texts on ventilator management as supplaments to this acticle. 

Will you consider APRV in refractory hypoxia? 

 

References:

Farkas, J. (2017, November 19). APRV Guideline. Retrieved March 1, 2020, from https://emcrit.org/squirt/aprv/

Frawley, P. M., & Habashi, N. M. (2004). Airway pressure release ventilation and pediatrics: theory and practice. Critical Care Nursing Clinics of North America16(3), 337–348. doi: 10.1016/j.ccell.2004.04.003

Hess, D., & Kacmarek, R. M. (2019). Essentials of mechanical ventilation. New York: McGraw-Hill Education.

Marino, P. L. (2014). Marinos the Icu book. Wolters Kluwer Health.

Nader Habashi: Airway Pressure Release Ventilation (APRV) – A mechanistic and physiologic view. (n.d.). Retrieved from http://marylandccproject.org/core-content/nader-habashi-airway-pressure-release-ventilation-aprv-mechanistic-physiologic-view/

 

 

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MAR
12

The Haunting: Foregoing our Faults


 

No one in emergency medicine wakes up in the morning and plans on going out of their way to make errors in patient care. We strive for perfection when treating our patients, at least most of us. We make clinical decisions to the best of our ability from what we have accrued in education, what resources we have at our disposal and what mistakes we have learned from time and experience in our careers.  

When I began my career as a paramedic, I unfortunately took everything I heard from instructors, command staff and others opinions and ideology towards other clinicians. I let it infect me. I mean, they were my mentors, peers and experienced clinicians I had looked up to. Why not ingest everything they tell me?  “So practice and observe everything they tell you. But do not do what they do. For they do not practice what they preach." Man, I wish I would have applied that earlier in my career but we live and learn right? 

Until I began to progress into a position of leadership, as well as beginning to gain influence from great mentors in and outside of the job, did I realize that these traits were not improving our organization or the organizations around us. Unfortunately, it was beginning to become a part of my personality. Absolutely shameful as I look back and see the kind of conversation I became a part of to make our organization appear better than the ones surrounding us.

There were resentful and judgemental opinions toward others involved in patient care in outside facilities, volunteer and other pre-hospital organizations. This became a part of a culture. Working at the hospital, how many times has someone transferred care to your facility and given the report en route or at bedside and you or someone else says “oh, its insert flight program here” or “of course, its insert EMS organization here." Even when EMS arrives at nursing facilities, "how much do you want to bet this patient is in septic shock." Why not help them? Why not educate them? Why not attempt to see where they are coming from? As a clinician, if you have more education with the matter at hand, why not reach out and provide it for them? When we get back to base, station or stock the trauma bay for the next patient, where is our own post-incident review? I am not talking a debrief of “well it went well with what we had." Please stop saying this. I cringe every time I hear that statement. No questions? No criticism of our own care? Why? Well, we are the best to do it, right? Even if we did make any mistakes, why would we open them up to others and let everyone know our imperfections of care, realizing there is room for improvement of our own performance, policies and guidelines. This is a perfect example of a teachable moment. 

 

  

 

After all of this, when we transfer the patient to the next level of care, we clock out and go home. The possibility of discussing, correcting and managing future errors in care dissipates when we lay our head down at night, never to be spoken of or heard again. Atleast until these faults of ourself and others come back to haunt us. The circle of animosity and not educating others or ourselves continues into the next shift to repeat itself over and over and over again. We are all guilty. Whether it is out of pure frustration, lack of sleep or repeated instances. 

 

This develops into a constant framework of vindication, unwillingness to expose our own failures and the inability to educate ourselves and those around us who might have made any errors involved in the process of patient care. What are we teaching our new employees and students? Even clinicians outside of our organization who were wanting an opportunity of employment with us but now see our ego and remarks. This occurs quite often in organizations with anyone above or below them in size, education and performance. No one is without sin.  

 

Society overall has a negative outlook on failure and mistakes in general, especially when it applies to the setting of patient care. This begins with certain clinicians within the organization and leadership permitting their behavior, if not themselves, to float along like that particle of dust in your attic when you turn the light on watching it settle on others. They lack self-reflection and humility and don't take the steps necessary to correct errors surrounding patient care. 

 

 

I find it funny how much of an impact working in a negative environment can give you such humility and further character, as long as you are self aware of the environment you are in. I am personally grateful for that experience. Where as an organization that is doing things correctly, at least most the time, I can’t say you would acquire certain traits and mentality. It is fairly easy to drift through a high-caliber work environment without constant negativity and conflict and not read between the lines. Though, when things are not going well in a constantly negative environment, you acquire how not to manage people, how not to build character, how not to prioritize, how not to communicate and the list goes on. When things are going right, it is hard to notice and acquire the attributes at times that are meant to achieve overall organizational success. You usually will not go out of your way to say “things are so fluent and operable here, what can I improve?”. No, most of the time, you start asking questions when you and the others around you are digging yourself out of a hole, asking how the hell did we get to this point and where do we go from here? 

 

We don’t wake up one day and become an attending at an emergency department or a respiratory therapist with 10 years experience, or even a flight paramedic/nurse with a major flight program. Not every hospital, HEMS or EMS organization has the same resources, same patient contact or same education. Remember where you came from and realize that every moment of failure or wrong approach can be educational. You are doing nothing to improve the outcome of patient care or improving others by constantly belittling but offering no solution for the next patient. Remember, they are calling you. They are transferring the patient to you. They want help. They need help. Offer help and advice. Don't be condescending. 

 

As someone with any influence in any organization, in any position, become that “elite” clinician who helps initiate this culture of understanding and attempts to first use these moments in care as a learning opportunity instead of making our employees or outside personnel terrified at the possibility of embarrassment or discipline. At the end of the day, we are here for the patient, no? Give our future patients the best care possible and withdraw the possibility of that same error returning to haunt us and those around us.

 

Failure is inevitable. What will you do as an individual or organization, to create a culture without animosity and the ability to learn from yourself and others?  It starts with a choice. Be the change you want to see the next time you walk through that door.  

 

 

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