Written by HEMS Contributor: Amy Neglia, RN, MSN, ACNS-BC, CCRN, CMC, CFRN, C-NPT
Disclaimer: I am not a Respiratory Therapist (RT). I know that I also don’t look at ventilation quite like a Respiratory Therapist does. RT’s, you are great and I love you. My training was different than your training, so just know that this is a ventilator guide in “nurse speak.”
When I first became a flight nurse, I was pretty confident about many things in the Intensive Care world…Running a ventilator was not one of them. Sure, I knew how to interpret a blood gas, and I knew what basic settings were important for different types of patients.
However, when given the reigns to control another person’s ventilation, I didn’t’ really know what I was doing. Luckily, I have had some fantastic mentors, some opportunities for higher education and an appetite to learn, coupled with the intense fear of hurting/not helping patients. I have found that many flight nurses and paramedics are in the same boat. We think that we can get by with the settings we pick patients up on, or at least we can keep them “safe.” Is that good enough? Wouldn’t it be better to have some insight? This may be a very basic discussion for you… or it may change the way you manage your patients.
Alright… you are setting up the ventilator to transport a patient. How do you know what settings to choose? It depends on what you are aiming for. We have a few goals… oxygenation, ventilation, and lung injury prevention. Let’s begin by talking about modes, how to choose different settings and then we can work these goals into the equation.
Common Ventilator Modes
Assist Control (AC):
This mode gives a full tidal volume breath with every breath that is set on the ventilator AND every extra breath the patient takes above and beyond the set rate. Example: A set rate of 16 + 8 spontaneous breaths = 24 breaths at whatever VT is set on the ventilator.
- This is good for patients who were intubated for increased work of breathing (basically any respiratory problem); It makes it so they don’t have to work so hard. There is no pressure support to adjust – every breath is supported.
Synchronized Intermittent Mandatory Ventilation. (SIMV):
Mandatory breaths (RR that is set on the ventilator) are synchronized with the patient’s effort. Mandatory breaths are calculated by the set RR; If the set RR on the vent is 16, the vent gives a full tidal volume for 16 of the breaths the patient takes. Make sense?
- If the patient isn’t breathing on their own or not up to the set rate, then the ventilator initiates enough breaths to match that rate at the set VT.
- If the patient is breathing more than the set rate, the vent does not give VT to those extra breaths; The patient gets whatever size breath they take on their own. Example: Set rate of 16 + 8 spontaneous breaths = 16 breaths at VT 450 & 8 breaths at whatever VT the patient takes on their own.
- In SIMV, you can add inspiratory pressure to overcome the resistance of the ETT or increase the volume of spontaneous breaths. This helps the patient feel more comfortable and can help decrease the work of breathing. This is used with SIMV. So be kind and add a little Pressure Support (PS) to those extra breaths…consider setting the PS around 10 cm H2O less than the current Pplat.
There are two breath types to choose from when we have selected the mode: Volume Control and Pressure Control.
- Volume Control: The ventilator is set to deliver a predetermined volume with each breath
- Pressure Control: The ventilator delivers a breath to the patient up to a set pressure limit. When the limit is reached, the breath is terminated.
Volume control can be a little easier to manage…the ventilator puts volume in and you (the crew) watch to see how much volume comes out. Pressure control tends to be a little less intuitive. Which mode is preferred many times changes depending on geographic location and where the Intensivists/Medical Directors you trained with were taught. There are good arguments for both types. In many places, adults are ventilated on volume control and small children are ventilated on pressure control. A good rule of thumb. Don’t ventilate someone on a mode you aren’t’ comfortable using. A little more on Pressure Control:
Pressure Control (PC):
This mode allows the patient to take a “pressure-limited” breath. The patient gets whatever VT they can take up until a certain pressure value is reached; then the breath is terminated – so you are setting a pressure limit, not a delivered volume. VT is measured by looking at the exhaled volume (Vte).
- You may see these settings in PC: 15/5
- 15 is the set peak pressure.
- 5 represents PEEP.
- The patient takes a breath until the set PIP is reached and then the breath stops.
- Look at the exhaled volume.
- If you’re comfortable with the size of the breath, then great – leave the peak pressure where it is!
- Want more volume? Slowly increase the peak pressure and monitor for the desired exhaled volume.
- Want less volume? Try decreasing the peak pressure.
Let’s move on… how do we choose the rest of the settings?
Respiratory rate. Now don’t laugh…Do you know why you choose what you do? Who actually breaths at a respiratory rate of 12 per minute? Sleeping people and unconscious people do. Try and breathe at 12 times a minute right now… is it comfortable? It’s probably not comfortable for your patient either. If you have an overdose patient or some other patient that you intubated for airway protection, then 12 breaths/minute is fine. Otherwise, think more like 14-18 breaths per minute. If your patient came in breathing 30-40 times per minute and in distress, then they will need a higher rate. Don’t paralyze them to slow them down – they probably need this faster rate to oxygenate… and maybe correct their pH! And don’t worry – we’ll get into special situations later.
Here is the next piece to the puzzle: Tidal volume. Yes, 6-10mls/kg of ideal body weight is the rule… but it’s not always physiologic or comfortable for each patient. Example: An 80kg man @10mls/kg would have a tidal volume of 800mls – This would be like take a really, really deep breath, every time he breathes in – not comfortable. Our program and our Intensive Care Units use a height-based chart to figure tidal volume. That being said, most adults should have set tidal volumes between 400 and 600mls on the ventilator. If the tidal volume is set outside of these ranges, it should make you think twice: What’s the special reason?
If the patient has an increased respiratory rate, the tidal volumes will need to be lowered in order to prevent breath stacking, increased pressures, and hypocapnia. What’s more important than tidal volume? Minute Ventilation? Minute Ventilation (MV) = Respiratory Rate (RR) X Tidal Volume (VT).
Normal Adult MV is 6-9 Liters Per Minute (LPM), but pediatric MV is dependent on weight/age. Patients may need more or less MV depending on their disease process! If they are breathing over your set RR and you have an appropriate VT set, let them take >9 LPM; They need it! If their ETCO2 is low, they are likely compensating for acidosis or head injury! But… don’t force them to take >9 LPM without a purpose (ex: oxygenation… you are also watching their Peak Inspiratory Pressure’s (PIP) at the same time…). If you paralyze your patient or the patient is not initiating breaths, make sure they have a VT of at least 6 LPM! How many times have you put your patient on a RR of 12 and a VT of 500? Those setting give you the adult minimum MV of 6 LPM. What if you have a RR of 12 and a VT of 450? 5.4 LPM – This is not even meeting the patient’s basic needs.
Inspiratory Time/Inspiratory: Expiratory Ratio
How does Inspiratory Time (I-time) and the Inspiratory: Expiratory ratio (I:E ratio) fit in? I-time is how much time your patient gets to inspire when given a breath. The common adult range: 0.8-1.0 seconds. The expiratory time is how long the patient is given to exhale the breath. The I-Time and the RR determine the I:E ratio – how much time your patient gets to inhale versus exhale. Many adults will be comfortable with an I:E ratio from 1:1.5 to 1:2-ish. Patient’s with COPD and asthma need longer times to exhale and may need 1:3 or 1:4. (However, asthma and COPD patients still get pneumonia and sepsis; you may need to balance the potential for air-trapping with the patient’s needs based on their current condition: hypoxia and/or acidosis). Nobody likes to breathe 1:1… try it. It’s not comfortable. There are 2 ways to adjust the I:E ratio: RR and I-time.
|Respiratory Rate: Decreases||I:E Ratio: Increases|
|Respiratory Rate: Increases||I:E Ratio: Decreases|
|I-time: Decreases||I:E Ratio: Increases|
|I-time: Increases||I:E Ratio: Decreases|
Positive End Expiratory Pressure
Moving on to Positive End Expiratory Pressure, or PEEP – what is it? It’s the pressure left in the patient’s alveoli at the end of exhalation. Intrinsic PEEP is what the patient does for themselves and extrinsic PEEP is the PEEP that we give them with the ventilator. COPD’ers will have higher intrinsic PEEP, because they air trap, whereas the rest of us don’t.
Playing with the PEEP makes us feel like we are “doing something,” so we like to mess with it. PEEP on the vent is good for a few things…when you think of PEEP, think “oxygenation.” PEEP pushes junk out of the alveoli (pneumonia, pulmonary edema, pulmonary hemorrhage), stents the alveoli open (atelectasis, ARDS) and pushes down the diaphragm to allow the lungs to expand (Abdominal Compartment Syndrome, diaphragmatic injuries). COPD’ers tend to “auto-PEEP” (stent their alveoli open themselves) to try and get all of that air out… they get tired and have to work hard to do it, so if we give them peep, then they don’t have to work so hard to do it on their own (auto-PEEP). So… if you are increasing your PEEP, what is your reason? Pretty much everyone gets a PEEP of 5, which helps overcome the resistance of the ventilator circuit. It is common to see PEEP’s of 5-10. 10-15 is approaching what I like to call “super PEEP.” Super PEEP (15-20 or up to 24) may be needed, but monitor closely for signs of pneumothorax and always monitor your Plateau Pressures (Pplat). If you are reaching the need for super PEEP, consider consulting Intensivists for further management.
Lung Injury Prevention
We use the above settings to oxygenate and ventilate our patients. How do we make sure that we aren’t hurting them with our settings? Or how do we do our best to mitigate the short-term and long-term damage happening to really sick lungs?
I just mentioned Plateau Pressure – this is the pressure at the alveolar level. Increased pressure = alveolar damage (barotrauma). Healthy lungs should have Pplats <20cm H2O, where sick lungs should ideally have Pplats <30 cm H2O. Really sick lungs (ARDS, pulmonary hemorrhage) should be AT LEAST < 40 cm H2O (ARDSnet, 2008). If the patient’s Pplat is >40? Fix it fast (Find a way to decrease the pressures)!
Peak Inspiratory Pressure
While the Pplat is basically the pressure in the lower airways & alveoli, the Peak Inspiratory Pressure or PIP is the pressure in the upper airways (main branches, trachea) & ventilator tubing. The PIP should always be higher than the Pplat. If your PIP is increasing, think Dislodgement/Obstruction/Pneumothorax/Equipment check (DOPE) first! Check placement, suction the patient, check tubing & ETT for kinks, contemplate the possibility of pneumothoraces and consider giving nebulizer treatments.
- ALSO: think sedation! Maybe they are too awake and coughing/fighting the ventilator or maybe they need pain meds – negative pressure breathing is normal…but positive pressure breathing hurts!
- ALSO: Maybe you are trying to put too much volume in their lungs (VT)…so decrease VT and increase the RR to maintain MV and improve elevated Pplats!
- ALSO: Maybe they need more time to exhale (Decrease I-time)!
Now that we know a lot of the rules, when do they need to be broken? Or better yet, how can we manipulate them a little for different disease processes?
Increased Intracranial Pressure
SIMV is good for patients who have or are at risk for having increased Intracranial Pressure (ICP). The body is trying to blow off CO2 to shrink vessels in brain and decrease the ICP. SIMV allows these patients’ bodies to regulate the amount of carbon dioxide they exhale, regulate their pH and shrink their vessels. If we put them on AC, we are controlling how much carbon dioxide they blow off. Let the patient cause their own hypocarbia, but don’t force it on them unless you have a specific reason, such as a temporizing effort to reverse herniation (Stevens, Shoykhet & Cadena, 2015).
Severe asthmatics can’t exhale past obstruction and pressure builds up – too much pressure in the chest impairs cardiac function and can create hemodynamic compromise and cardiac arrest. Its okay to hypo-ventilate asthmatics a little (MV 5-6 LPM) and even allow some hypercarbia. If they do build up too much pressure or become peri-arrest, consider disconnecting the endotracheal tube and manually decompressing the chest (AHA, 2015) Sounds weird? Look it up!
Many times, these patients favor a decreased RR and an increased VT for COPD exacerbation. You may try to systematically match the patient’s auto-PEEP up to 80% with ventilator PEEP: this can decrease the work of breathing since the patient doesn’t have to work so hard to stent the alveoli open themselves (Mosier, et al., 2015). Auto-PEEP’ing 8 on top of a set PEEP of 5? Try turning the PEEP up to around 10.
Acute Respiratory Distress Syndrome (ARDS)/Pulmonary Hemorrhage
Have you walked in to pick up a patient and found that they had PIP’s in the 40’s or 50’s? Hard to oxygenate? For patients with ARDS/Pulmonary hemorrhage or refractory hypoxia and increased pressures, consider placing them on Lung Protective Ventilation (LPV). Not sure?
- Calculate the PF ratio: PaO2/FiO2 = <200? ARDS, <300? Acute Lung Injury (ALI)
Lung Protective Ventilation strikes a balance between oxygenation, ventilation, and lung injury prevention. Oxygenation and keeping PIP’s below 40mmHg is key. These patients may have permissive hypercarbia, as CO2 reduction is not the main goal. This happens through a step-wise process. Alternate increasing the FiO2 with increasing the PEEP, with an oxygenation goal of 88-92%. See the example below:
LPV generally starts with a VT of 6ml/kg. Then set your patient’s initial rate to their approximate baseline minute ventilation, not to exceed 35 breaths per minute. The plateau pressure goal is to maintain pressures ≤ 30 cm H2O. If the Pplat is >30cm H20, then consider decreasing the VT by up to 1ml/kg (minimum 4mls/kg). Remember: If you decrease the VT, then the RR must increase in order to keep the same MV. Normalizing CO2 is nice, but oxygenation is more important. PH management is also important, with the goal being a pH >7.3. However, unless you carry a way to check a blood gas in transport, the focus will remain on improving oxygenation and decreasing pressures (ARDSnet, 2008).
Whew! Are you still with me? How about a few management tips?
Ask yourself this question: What do they need and how do I give it to them? This should help get your patient where they need to go.
Why is my patient hypoxic?
- Is the O2 off in your vehicle?
- Is the FiO2 on your ventilator still at 21%?
- Does the patient need more FiO2? Sometimes, but sometimes its something else…
- Is the patient not getting enough VT to meet his/her oxygen requirements?
- Is the RR not high enough to meet the patient’s oxygen requirements?
- Do they need more PEEP to push junk out of the lungs?
- Position? Sit the patient up to get belly weight off of his/her diaphragm
- Remember: GOOD lung down… This helps with aeration of the lungs and can improve oxygenation.
Why is my patient hypercarbic?
- Is my CO2 sensor plugged up?
- Is the patient’s MV too low?
- The patient cannot exhale past obstructive lung disease (needs nebs)?
- Is the patient now ventilating a new area of lung previously not ventilated (may be expected)?
- Is my patient just getting worse despite my best efforts?
- Is my patient right main-stemmed? Where is the chin in kids? The endotracheal tube will follow chin position, so keep the head midline!
Why is my patient hypocarbic?
- Am “I” over-ventilating them? Then stop!
- Are they over-ventilating themselves?
- Look at the patient condition.
- Is the patient anxious or hurting? Fix it! (Fentanyl and Versed… big fan)
- Are they acidotic? Let them over-ventilate!
- Are they in respiratory distress? Work on optimizing vent settings, nebs, etc.
- Cold patients don’t make CO2 well
- Is the endotracheal tube still in the right hole?!
There are a lot of different alarms that may sound and a lot of them are specific to individual ventilators. There are two alarms that are universally easy to keep track of and easy to intervene on: High pressure and low pressure.
Why does the high-pressure alarm keep sounding?
- You need to relieve pressure somewhere!
- Try suctioning, unkink tubing, nebs
- Do they need sedation?
- Are you giving too much tidal volume?
- Do they need more time to exhale?
- Does the patient’s position need to change?
Why does the low-pressure alarm keep sounding?
- Did the ventilator tubing pop off of the patient?
- Did the tubing come off of the vent?
- Did the oxygen run out/not get turned on?
- Is the patient working so hard to breath, that they are “sucking” negative pressure?
Admittedly, there is a lot of basic information here, but do you think about it every time you transport a ventilated patient? Have you understood the ventilator changes you have made in the past? Think about what “comfortable to breath” is for your patient, and don’t forget to calculate minute ventilation. Keep the patient’s PIP’s and Pplat’s down and give them time to exhale. Remember, there are a lot of things that cause high and low pressure alarms…and try to remember how you, the patient and the ventilator are all working together to affect the patient’s breathing.
American Heart Association. (2015). Web-based Integrated 2010 & 2015 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care; Part 10: Special Circumstances of Resuscitation. Retrieved on August 21, 2018 from: file:///C:/Users/arneg/OneDrive/Desktop/New%20folder/Articles/Resuscitation/part-10-special-circumstances-of-resuscitation.pdf
ARDSnet: NIH NHBLI ARDS Clinical Network Mechanical Ventilation Protocol Summary. (2008). Retrieved on August 21, 2018 from: www.ardsnet.org/files/ventilator_protocol_2008-07.pdf
Mosier, J.M., Hypes, C., Joshi, R., Whitmore, S., Parthasarathy, S. & Cairns, C.P. (2015). Ventilator strategies and rescue therapies for management of acute respiratory failure in the emergency department. Annals of Emergency Medicine, 66(5), p.529-541.
Patel, B.K. (2018). Overview of mechanical ventilation. Merck Manual: Professional Edition. Retrieved on August 21, 2018 from: https://www.merckmanuals.com/professional/critical-care-medicine/respiratory-failure-and-mechanical-ventilation/overview-of-mechanical-ventilation
Stevens, R.D., Shoykhet, M & Cadena, R. (2015). Emergency Neurological Life Support: Intracranial hypertension & herniation. Neurocritical Care, 23(Suppl 2): S76–S82.