We Have No Beds: Ventilator Series
Reading a Ventilator Screen
Before diving into a specific mode of ventilation, we should address what you see on a ventilator screen first. What do all these abbreviations mean?…
Note: the pictures and order of descriptions reflect the Puritan-Bennett 840 ventilator. However, most of the information will reflect most ventilators in general even if presented in a different format.
Understanding the CONTROL Panel
- Determines manner in which breaths and tidal volume will be delivered.
- Assist Control (AC), Synchronized Intermittent Mechanical Ventilation (SIMV), Pressure Support (PS)/Spontaneous, Bilevel…to name a few.
- Respiratory rate that is set manually.
- Volume Control (VC)
- Tidal volume is set by the controller to be delivered to the airways, while pressure is variable.
- Most common means of delivering a tidal volume in mechanical ventilation.
- Pressure Control (PC)
- A peak pressure is set to be delivered to the airways, while tidal volume is variable.
- Alternative means of delivering a tidal volume in mechanical ventilation.
- Ideal for patients whose airway pressures need to be strictly controlled.
- Pressure Support, not to be confused with pressure control.
- Provides a small amount of pressure to the airway during inspiration to overcome the resistance made by the endotracheal tube (ETT).
- Usually used alone during weaning (spontaneous breathing trials-SBT) or added to SIMV mode (Synchronized Intermittent Mechanical Ventilation).
- It can only be used if the ventilator mode allows for spontaneous breaths to be taken.
- Pressure or flow trigger.
- Senses patient’s effort to take a spontaneous breath.
- Pressure Trigger: negative pressure from patient attempting to take a breath translates to pressure dropping below baseline thus triggering a breath.
- Flow Trigger: flow sensed from patient attempting to take a breath and seen as a flow rise above the baseline thus triggering a breath.
- Simply the oxygen level that is set to be delivered to the patient.
- Ranges from 0.21 (21%, room air) to 1.0 (100%).
- Determines flow, or how the tidal volume is delivered.
- Square Flow diagram: constant flow
- Ramp Flow diagram: decelerating flow
- Expiratory Sensitivity
- Controls when inspiration turns off and expiration is allowed.
- You will usually see ESens 25% on the control panel which means once the inspiratory flow decreases to 25% of the initial peak flow, inspiration ceases and expiration starts.
- Changing the percentage affects the I:E (Inspiratory:Expiratory) ratio by affecting the time spent in inspiration (the smaller the percentage the longer the inspiratory time and vise versa).
- May set a higher percentage in obstructive patients to prevent air trapping (shorter I, longer E).
- May set a lower percentage in restrictive patients to increase tidal volume (longer I, shorter E).
- Positive End Expiratory Pressure
- Pressure applied to airway as patient exhales.
- Commonly set at 5cmH20.
- Helps with oxygenation through alveolar recruitment.
Now, before you get overwhelmed, you will usually only have to directly deal with a few of these parameters. Typically, what you report on rounds or give to the respiratory therapist as your “basic settings” is what you will have to manipulate. Make sure to know how to change the mode, rate, TV, FiO2 and PEEP. As for everything else…you can ask for help.
Understanding the REAL TIME Screen
Flashing box (“C”, “S”)
- “C” (green color) for “Controlled” breath, meaning machine triggered
- “S” (orange color) for “Spontaneous” breath, meaning patient initiated breath
(seen on Puritan Bennett 840; other ventilators may not have this icon)
- Peak airway pressure, a measure of airway resistance
- Mean airway pressure
- Thought to reflect alveolar pressure and can be used to correlate risk of barotrauma.
- Measured PEEP in airway.
- Inspiratory: Expiratory ratio representing the time spent in each.
- normal I:E is 1:2 or 1:3 with more prolonged expiratory times being in obstructive patterns (1:4).
- Actual respiratory rate of the patient (rate set plus spontaneous or triggered breaths).
- Tidal volume expired, which should be very close to the set tidal volume.
- Can be used to evaluate if the patient is pulling adequate tidal volumes in spontaneous modes.
- Expired Minute ventilation, TV x RR = MV
- Correlates to the patient’s (fTOT x Vte) on the ventilator screen.
When placing a patient on a ventilator the initial settings are mode, rate, TV, PEEP, and FiO2. The other settings have defaults that can be changed for specific patient populations. Future posts will address what the settings actually are and how you chose. For now start checking out the ventilators you will be working with and make sure you understand how to read the screens.
Benjamin D. Singer, MD et. al. “Basic Invasive Mechanical Ventilation.” Southern Medical Journal: 2009:102(12):1238-1245.
David W. Woodruff, RN, MS, CNS, CCRN. “A Quick Guide to Ventilator Essentials.” Modern Medicine Network: Sept, 2005. http://www.modernmedicine.com/modern-medicine/content/tags/copd/quick-guide-vent-essentials.
Dean R. Hess, PhD, RRT, FAARC. “Ventilator Waveforms and the Physiology of Pressure Support Ventilation.” Respiratory Care: 2005;50(2):166-183.
Terry L. Forrette, MHS, RRT. “Transitioning from Mechanical Ventilation.” Medscape Pulmonary Medicine: 2006. http://www.medscape.org/viewarticle/528367_9.