One of the most exciting tasks in emergency medicine is the opportunity to manage the airway. In residency, it was incredibly exciting to manage an uncooperative patient or control a chaotic resuscitation by calling for medications, running through our intubation checklist, and then securing the airway. As a trainee, those days felt like I accomplished something substantial. And so it seemed that as soon as we watched the tube pass through the glottis, my attending and I were high-fiving ourselves on the way out of the room without a second thought as the respiratory therapists took over and worked their magic. Airway and disposition secured; off to the ICU!
Certainly, my detached attitude towards the ventilator was actually a side effect of the intimidation I felt when regarding its inscrutable buttons, dials, and waveforms. But as I worked with emergency department and ICU intensivists, I watched them fiddle with the dials, carefully optimizing for each individual patient’s physiology. Not only did they seem like they were the most confident and intelligent people in the room, but they could easily collaborate with the respiratory therapists because of their effortless command of the language of ventilators, which seemed to be the best place to start if I wanted to master the ventilator.
The following is a list of terms that will help any medical student, nurse, resident, or non-intensivist to jumpstart their ventilator education. Since the list is not comprehensive, I have also included a list of some amazing CriticalCareNow articles as well as my references to facilitate a deeper dive into all things ventilator management.
So take a carefully calibrated, deep breath and let’s get started!
Tidal Volume (TV) – The amount of volume delivered per breath, which is generally calculated based on the patient’s ideal or predicted body weight based on their height. A good starting point is 6-8 mL/kg, with the lower range favored in lung-protective scenarios like ARDS and the higher range favored in obstructive disease like asthma and COPD. A tidal volume that is too high can result in barotrauma.
Respiratory Rate (RR) – The number of breaths delivered per minute. In assist-control modes, the rate is a baseline but can change if the patient triggers their own breath (aka over-breathes).
Minute Ventilation (MV) – Defined as respiratory rate x tidal volume. Since tidal volume is relatively fixed (based on the patient’s height), the respiratory rate is usually adjusted when attempting to increase or decrease minute ventilation.
Fraction of inspired oxygen (FiO2) – This is the percentage of oxygen delivered per breath. Often started at 100% and then titrated down based on the patient’s oxygen requirement.
Positive End-Expiratory Pressure (PEEP) – The amount of pressure in the ventilator tubing and lungs at the end of each expiration or breath.
Inspiratory peak flow rate – When we take a breath, air travels quickly into our lungs and then slows as we reach the end of our breath. This is a decelerating pattern. When the ventilator delivers a breath with a peak flow rate, it delivers it at a constant pressure and then ends the breath.
I to E Ratio – The ratio of time designated for inspiration to the time assigned for expiration. A healthy person usually has an I:E ratio of 1:2, that is exhalation takes twice as long as inhalation. For chronic retainers, like those with COPD or asthma, you might want to decrease the I:E ratio (1:4 or 1:5) to allow for full exhalation and prevent air trapping due to breath stacking.
Peak Pressure – Represents the highest pressure in the entire system (ventilator + tubes + large airway + alveoli).
Plateau Pressure – Represents the amount of pressure in the small airway and alveoli, without airflow, which is determined by pressing the inspiratory hold button at the end of a breath. A plateau pressure > 30 cm H2O is a risk factor for barotrauma.
Driving Pressure – Represents the difference between the peak pressure and the PEEP. It is the pressure change during each breath.
Volume Assist-Control (AC) – This is the most common and simplest setting to use in the emergency department. It provides full respiratory support if the patient is not breathing on his or her own, but allows the patient to trigger a breath and still get a full breath. The tidal volume, respiratory rate, FiO2, PEEP, and inspiratory flow rate are set by the provider. When the ventilator delivers a breath, it will increase the pressure until the desired tidal volume is reached and then stop. Exhalation is passive.
Pressure Control (PC) – In this setting, the respiratory rate, the driving pressure, and inspiratory time (I-time) are selected. The ventilator will deliver a breath until the driving pressure is met (volume will vary depending on compliance), and then hold it for the selected I-time before terminating the breath. These breaths are given with decelerating inspiratory flow.
Pressure support – This setting allows the patient to initiate their own breath and then the ventilator helps to assist the patient reach the selected pressure. This setting allows the patient to set their own rate and pattern of breathing. It is often the desired setting when attempting to wean a patient off the ventilator or if they are intubated for a reason other than cardiopulmonary pathology (altered mental status, airway protection). It is important to note that there is no back-up rate so the patient should not be at risk of becoming apneic.
Pressure-Regulated Volume Control (PRVC) – After a desired tidal volume is chosen, the ventilator monitors each breath and adjusts the inspiratory pressure based on the prior breath to achieve the tidal volume. If the delivered volume is too low in one breath, it will increase the inspiratory pressure the next breath and vice versa. The breaths can be initiated by the ventilator or the patient and the breaths are given in a decelerating pattern. The variable settings are the same as volume control but the waveforms look like pressure control. It’s a hybrid of both worlds! If the patient is air hungry, however, it can lead to patient-ventilator dyssynchrony.
Synchronous Intermittent Mandatory Ventilation (SIMV) With Pressure Support – In this setting, the ventilator delivers a selected tidal volume (although pressure-control is also an option). The machine or the patient can initiate the breath, however, if it is the latter, the ventilator will detect it and time the next breath so as to not give a breath when the patient is exhaling (hence the “synchronous”). If the patient-initiated breath is less than the desired tidal volume, the ventilator can provide pressure support as needed.
Airway Pressure Release Ventilation (APRV) – When the lungs are contused or flooded, and therefore injured and collapsed, the repetitive recruitment of alveoli can lead to shear stress and further damage. APRV is a setting that is often misunderstood. By maintaining an elevated pressure with brief releases of breath to allow for ventilation, this mode maintains alveolar recruitment and prevents “atelectrauma.” Think CPAP with occasional short drops in pressure for CO2 clearance. This setting can be used for ARDS or refractory hypoxemia, and patients can initiate breaths on top of the continuous positive pressure. The selected settings include P-high (the pressure applied throughout the cycle), T-high (the length of time the pressure is applied for), P-low (the lowest pressure allowed when the breath releases; usually zero), and T-low (the length of time the breath is allowed to release before a new breath is initiated).
There are two important caveats. First, the names of certain settings on the ventilator are proprietary so that the same settings on different machines will have different names. It is important to know the ventilator you are working with. Second, ventilator management is a personal, point-of-pride for many intensivists, so opinions differ on optimal settings for various conditions and ICUs. I recommend trying to understand why certain doctors or respiratory therapists like the settings they use and take the best of what they have to offer as you develop your own practice. As always, read the literature, apply your knowledge, ask questions, trust but verify, and keep an open mind.
- When working in the emergency department or the ICU, it is not enough for medical students, nurses, residents, and non-intensivists to secure the airway and ignore how the ventilator works.
- After intubating a patient, understanding what settings to select based on their specific physiology will likely lead to better outcomes.
- The names of some settings are copyrighted so that the same settings on different machines will have different names. It is important to know the ventilator you are working with.
- Opinions vary on optimal ventilator settings. Take the best of what everyone will teach you and determine your own practice. Read the literature, apply your knowledge, ask questions, trust but verify, and keep an open mind.
Want to go on a deep dive? Check out some of CriticalCareNow’s other articles on ventilator management:
- The Vitals: Barotrauma by Obiajulu Anozie, MD (https://criticalcarenow.com/the-vitals-barotrauma/)
- Optimal PEEP by Seon Adams, RT (https://criticalcarenow.com/optimal-peep/)
- Differentiating Peak and Plateau Pressures by Komal Parikh, MD (https://criticalcarenow.com/differentiating-peak-and-plateau-pressures/)
- Peak Airway Pressure: Why The Fuss by Aman Thind, MD (https://criticalcarenow.com/peak-airway-pressure-why-the-fuss/)
- Riding the Waves: Ventilator Waveform Interpretation by Danelle Howard, RT (https://criticalcarenow.com/riding-the-waves/)
- Scott Weingart, MD, “Managing Initial Mechanical Ventilation in the Emergency Department”, Annals of Emergency Medicine, Volume 68, Number 5, November 2016.
- Ryan Pedigo, MD, “Ventilator Management of Adult Patients in the Emergency Department”, Emergency Medicine Practice, Volume 22, Number 7, July 2020.
- Kelly Crane, MCMSc, Pa-C, “What Are Your Vent Settings, Bud?” Avoiding Common Errors in the Emergency Department. Chapter 13. 2017. Wolters Kluwer. 2nd Edition. Philadelphia, PA.
- William Owens, MD. The Ventilator Book. 2012. First Draught Press. 2nd Edition. Columbia, SC.
- Brian J. Wright, MD, “Lung-protective Ventilation Strategies and Adjunctive Treatments for the Emergency Medicine Patient with Acute Respiratory Failure”, Emergency Medicine Clinics of North America, Volume 32, Issue 4, 2014, Pages 871-887, https://doi.org/10.1016/j.emc.2014.07.012.