Ventilator Alphabet Soup
About six months ago, my daughter was placed on a ventilator. It wasn’t the first time—she was intubated and ventilated as an infant for a period of time—but my head was spinning with all of the acronyms, settings, and readings. After lots of research and repeated explanations from the respiratory therapists, I finally got most of it down.
My daughter now uses a ventilator daily, and we are still in alphabet soup land! Since it is critically important for you as a parent to know and understand your child’s ventilator settings, this article will compile some of the most common acronyms and terms used with ventilators.
The First Alphabet Soup: Ventilator Modes
Even before you get to all the settings on the ventilator, there is the matter of ventilator modes. Unfortunately, the names for these aren’t entirely standardized, which makes it tricky.
In general, modes fall into two categories, pressure modes and volume modes. Pressure modes give a set amount of pressure to the lungs (kind of like the force of the air blowing in). This pressure causes the lungs to expand. Volume modes instead regulate how much volume of air is put into the lungs (kind of like the size of the breath), and the pressure varies to make sure the volume remains steady.
Pressure modes are used more commonly in children. Some pressure modes include the following, listed from least invasive to most invasive:
- CPAP or Continuous Positive Airway Pressure mode: In CPAP mode, a constant amount of pressure is given every time a breath is taken, both during inspiration and expiration. This mode is very commonly used for children using a CPAP machine with a mask.
- S or Spontaneous mode: This is the most typical BiPAP mode used for children with a BiPAP machine and a mask. It gives a higher level of pressure every time a spontaneous breath is taken, followed by a lower level of pressure during exhalation.
- S/T or Spontaneous/Timed mode: This is another typical BiPAP mode that is also often used for children with trachs. It gives a higher level of pressure every time a spontaneous breath is taken, followed by a lower level of pressure during exhalation. It also has a back-up rate, meaning if spontaneous breaths are not taken regularly, the ventilator will initiate breaths.
- PC-SIMV or Pressure Control-Synchronized Intermittent Mandatory Ventilation: This is a common mode for children with trachs/vents. It gives mandatory machine-initiated breaths, but allows the child to take his or her own breaths, with or without pressure assistance, between the mandatory breaths.
- Pressure Control mode: Depending on the ventilator, this mode may have a slightly different meaning. For example, on a Trilogy, this mode will assist a spontaneous breath, while on other ventilators, strict control of breathing is initiated. On the Trilogy, this mode is like S/T mode, except every breath, whether patient-initiated or machine-initiated, has the same length of inspiration (inspiratory time). On other ventilators, this mode provides strict control with no patient-initiated breaths.
- T or Timed mode: This is a BiPAP mode that is not used very often. The ventilator gives mandatory breaths at regular intervals, completely ignoring any breaths initiated by the child.
Volume modes are also used in children with trachs or children who are intubated, and on some occasions non-invasively. These include the following, from least invasive to most invasive:
- AC or Assist Control mode: This mode allows a patient-initiated breath or a machine-initiated breath when the child does not breathe. It delivers a set tidal volume during inhalation.
- SIMV or Synchronized Intermittent Mandatory Ventilation: This mode is also common, and delivers a set tidal volume on inspiration. It gives a mandatory breath initiated by the ventilator, while additional breaths initiated by the child can be pressure supported.
- PRVC or Pressure Regulated Volume Control: This is a hybrid mode that is used for patients unexpected to wean on their settings. It provides both control of the tidal volume on inhalation, as well as a controlled or limited pressure setting. Breaths may be patient or machine-initiated.
- Control Ventilation: This mode is less common, and gives a set tidal volume at regular intervals, ignoring any breaths initiated by the child.
The Second Alphabet Soup: Vent Settings and Readings
Just when you finally think you have mastered all the abbreviations associated with ventilator modes, then you get to the settings. The alphabet soup runs wild here!
First we will start with the basic settings for inhalation and exhalation pressure:
- IPAP: When using a BiPAP device or a vent in a BiPAP mode, IPAP or Inspiratory Positive Airway Pressure is the term used for the amount of pressure being given as your child inhales.
- EPAP: EPAP is the exact opposite of IPAP and stands for Expiratory Positive Airway Pressure. It is the amount of pressure that continues even while your child is exhaling. EPAP is always the same or lower than IPAP. The purpose of EPAP is to keep the smallest airways (alveoli) open so they do not collapse on exhale.
- PIP: PIP or Peak Inspiratory Pressure is the term used in ventilator modes for the highest level of pressure reached on inhale. This can be used as a pressure setting if your child needs a certain amount of pressure, or it can be a reading of the highest level of pressure reached on inhale in a volume mode. When used as a setting, it is roughly equivalent to IPAP.
- PEEP: PEEP stands for Positive End-Expiratory Pressure, which is a setting that keeps the pressure at a certain level during the exhalation. PEEP is roughly equivalent to EPAP and is also used to keep the smallest airways (alveoli) open so they do not collapse on exhale.
Other terms include the following:
- Tidal Volume: Tidal Volume is the amount of air that has expanded the lungs. On ventilators, this is typically used as a setting to determine what volume a patient will receive in volume modes. It may be expressed as the total volume of air, but more often it is expressed as a certain air volume for each kilogram of weight of the child. Tidal volume is usually used as a setting, whereas Vte (see below) is used as a reading of what the volume actually is.
- Vte: Vte stands for Exhaled Tidal Volume and is the volume of air that is exhaled. This is an important reading, especially when in pressure modes, because it represents how much air is expanding the lungs.
- Vti: Vti stands for Inhaled Tidal Volume and is the actual volume of air that is inhaled. This reading is not used as often, except in patients who are actively inhaling.
- Rate: Rate is the respiratory rate, which can be a setting (the number of breaths required per minute) or a reading of the actual number of breaths a child is taking.
- Minute Ventilation: Minute ventilation is a little bit more complicated. It is basically the total amount of air that went in and out of a child in one minute.
- MAP: MAP stands for Mean Airway Pressure and is the average pressure over a full breath, including inhale and exhale. With the exception of high frequency ventilators, this is normally a reading and not a setting.
- Inspiratory Time: This is a setting which indicates how long the inhale should be, or a reading of how long an inhalation actually is on a spontaneous breath.
- I:E Ratio: The I:E ratio is simply an expression of the ratio between the length of time it takes to inhale and the length of time it takes to exhale.
- Peak Flow: Peak flow is the maximum amount of air flow, measured in liters per minute, during a breath.
- BPM: Breaths per minute.
- LPM: Liters per minute, which is used to indicate the amount of oxygen or flow of air that is given to a child.
- Leak: The leak is the amount of air that is leaking out with each breath. This is of particular concern in children on non-invasive ventilation who tend to leak air out of a mask or their mouth.
- FiO2: On a ventilator, FiO2 is the amount of oxygen measured as a percentage of the total amount of air given. For example, room air is 21% oxygen. Anything over 21% means additional oxygen is being given.
- AVAPS: This is technically a mode, which allows you to set target volumes in a pressure mode.
Embrace the Alphabet Soup
It can be very hard to learn all of the acronyms and terms associated with ventilators, even for nurses and medical professionals! Take them one at a time, starting with the most important ones, such as your child’s settings. Over time you will learn to understand all of them and what they mean, including what actions you can take to improve your child’s breathing.
Just for fun: After reading this article, who can guess what needs to be fixed for the child on the vent shown in the picture above?
Author: Susan Agrawal • Date: 3/30/2012