It’s important for providers of all levels to know how to set ventilator settings and other ventilator management basics.
Scenerio: You are covering a very busy ER and your patient in respiratory failure you was just intubated. The Registered Respiratory Therapist (RRT) consults you on what ventilator settings you want the patient to be placed on. You can either:
- Defer to the RRT’s expertise or
- Provide the RRT with patient-centered initial ventilator settings and make changes to those settings based on patient response.
So what do you do? A better understanding of ventilator management will improve the outcome of either decision.
Ventilator Management 101: Ask the Questions
The purpose of this post is to provide you with a better understanding of basic ventilator management and be able to make informed decisions on patient care. The questions listed below will provide the framework for discussion on the basics of managing patients on mechanical ventilation (MV):
- Question 1: Why did the patient need to be intubated and what is the expected timeframe that s/he will need MV?
- Question 2: How much ventilatory support does the patient need?
- Question 3: Which mode of ventilation?
- Question 4: How much Vt (tidal volume) should the patient receive?
- Question 5: What is the rate that you should set the ventilator on?
- Question 6: What is the FiO2 that you should start with?
- Question 7: What is the PEEP that you should start with?
- Question 8: Is the patient comfortable on the ventilator?
- Question 9: What are other factors to consider for a patient on MV?
Question 1: Why did the patient needed to be intubated and what is the expected timeframe s/he will need MV?
There are many indications for intubation and they will result in either a patient sustaining respiratory failure or impending respiratory failure. The most frequent indications are:
- altered mental status (AMS) leading to inability to protect the airway (seizure, overdose ingestion)
- profound impairment in gas exchange (severe asthma, COPD exacerbation), and
- severe impairment in acid-base balance (sepsis, severe DKA).
For example, a person who overdosed on 2 full bottles of buproprion may experience AMS and need to be intubated for airway protection. Likewise, a patient who has sustained a GTC seizure and had aspirated would also need airway protection.
However, a person with COPD exacerbation may not be able to compensate further and develop severe impairment in gas exchange.
The indications for intubation and the patient’s co-morbidities help predict how long a patient will require MV:
- A person who is healthy but is altered due to overdose ingestion will not likely need to be MV for more than a few days versus a person with advanced COPD presenting with a severe exacerbation, where it may take days or a week to reverse the inflammatory process.
- Likewise, a person may be on the ventilator postoperatively because s/he was too sleepy and needed a little more time to wake up from the anesthesia. His/her time on MV may be only an hour to a few hours.
Question 2: How much support does the patient need?
This is very individualized and is based on the indication for intubation.
The postoperative patient who is too sleepy to safely extubate may be spontaneously breathing, but needs just a little more Vt to prevent atelectasis from developing. The appropriate ventilator setting may be spontaneous mode with pressure support to help overcome the resistance of the ETT and to provide a little more volume to each breath s/he takes (This is called CPAP with PS).
On the other hand, a s/p CPR patient will need full MV support.
Questions 3: Which mode of ventilation?
There are essentially 3 basic modes of ventilation: Assist control (AC), SIMV, and CPAP
- AC: there is volume controlled (VC) and pressure controlled (PC)
- VC: the tidal volume you set is guaranteed but the corresponding pressure generating from that will vary based on how compliant the patient’s lungs are. This is the peak airway pressure or also known as the peak inspiratory pressure (PIP)
- PC: the pressure that you set is constant, but the volume able to be generated will vary based on the patient’s lung compliance.
Which one is better? Either is fine, but the most basic ventilator mode utilized is VC.
Because of the constant Vt, the patient’s minute ventilation is constant. This is what you want if you are trying to control ventilation. If you have trouble oxygenating your patient, perhaps changing to PC mode may help, especially with alveolar recruitment.
In either mode, the patient can breathe above the set rate; however, each breath will always be a controlled breath and there is NO synchronization between the patient’s effort and when the ventilator is due provide a set breath.
This may create ventilator dyssynchrony if the patient is not adequately sedated.
SIMV is synchronized mandatory minute ventilation – meaning that you set a minimum rate and Vt. That is mandatory minute ventilation part.
- If the patient breathes at the time the ventilator is due to give a set breath, the ventilator will synchronize with the patient’s breath.
- In between the mandatory breaths, the patient can breathe on his/her own. PS is usually added to aid in comfort and increase the patient’s spontaneous Vt.
CPAP means continuous positive airway pressure. The patient must be breathing spontaneously and must achieve an adequate Vt to prevent atelectasis and impairment in gas exchange. PS may be added to aid in comfort by decreasing airway resistance and increase Vt.
Question 4: How much Vt should the patient receive?
The Vt is the volume of air moved into and out of the lungs during each ventilation cycle.
- The Vt should be set based on the patient’s predicted body weight (PBW).
- PBW Male: 50 + 2.3[height in inches-60]
- PBW Female: 45.5 + 2.3[height in inches-60]
- In VC mode, set the Vt around 6-8ml/kg of PBW
- If the pressure generated is too high, the ventilator has a safety measure to cut off the breath and generates a high pressure alarm.
- In PC, adjust the pressure so achieve a Vt of 6-8ml/kg of PBW.
- Remember that volume will vary as compliance changes (such as after a dose of Lasix for flash pulmonary edema). This may result in under ventilation or volutrauma.
Question 5: What rate should you set the ventilator to?
Let’s review minute ventilation:
- Minute ventilation is the amount of gas entering (or leaving) the lungs per minute.
- It is the product of Vt and RR (Vt xRR)
- Typical Minute Ventilation in a 70kg adult male, calculating at 8ml/kg at 12BPM = 6.7LPM.
The minute ventilation IS different from alveolar ventilation. Alveolar ventilation takes into account the anatomic dead space in the airway – that is air that does not involve in gas exchange.
This is important because a patient who is breathing fast and shallow will have the same minute ventilation as a patient who is breathing deep and slow, but the first patient will develop respiratory failure because s/he will not have adequate alveolar ventilation. The rate set is on the ventilator is usually 12-16BPM; however, this will depend on the indication for intubation and patient co-morbidities.
For example, if you set a rate for 15bpm, the ventilator will give a breath every 4 seconds. The ventilator will provide an I:E ratio based on the rate you set and the flow to deliver the breath (other ventilators have sophisticated modes to adjust inspiratory time or flow).
- A typical I:E ratio is 1:3. However, 1:4 maybe indicated in a person with obstructed lung disease.
After setting the Vt based on the PBW and the RR, calculate the minute ventilation to see if this is appropriate. Assess for adequacy of chest rise. Auscultate the lung fields.
Question 6: What is the initial FiO2 set to?
For ease, set it on 100% (some will refer to it as 1.0 or 0.7 for 70% oxygen).
Titrate FiO2 based on SpO2 or arterial blood gas.
Question 7: What PEEP should I set?
Let’s begin by differentiating PEEP from CPAP.
- PEEP is positive end expiratory pressure. PEEP is utilized to prevent collapse of the alveoli by application of a distending pressure so that the alveoli can be partially opened after each breath.
- Without PEEP, the alveoli have to reopen on each breath and this can create shearing injury.
- PEEP ranges from 0cmH20 to about 20cmH20 (may be higher but the risk far outweighs the benefit).
- In general, increasing PEEP in patients with conditions like ARDS helps improve oxygenation so that you do not have to increase the FiO2.
- CPAP is continuous pressure that is present in both inspiration and expiration and applies to spontaneously breathing patient
Starting at a PEEP of 5cmH20 for patients that have no major lung parenchymal disorder is reasonable.
It is believed that we have physiologic PEEP of 3-5cmH20; thus, when we are intubated, the loss of the glottis closure result in loss of physiologic PEEP.
Question 8: Is the patient comfortable on the ventilator?
It is critical that the patient is comfortable on the ventilator. Some patients, depending on co-morbidities, may need more or less sedation.
- Some of the sedations utilized in the ICU are: Propofol, Dexmedetomidine, Fentanyl, Midazolam.
- However, despite an adequate amount of sedation administered, patients may still buck the vent (ventilator dyssynchrony).
- If you decide to administer a neuromuscular blocking agent such as vecuronium or rocuronium, use it sparingly and ensure the patient is receiving adequate sedation or anxiolytic.
Questions 9: What are some other considerations in managing a mechanically ventilated patient?
- Obtain a chest radiography post intubation, while it is critical that you assess ETT placement, you also need to review the entire chest film.
- The ETT should be around 4cm above the carina.
- Take note of the size of the ETT and placement (cm) in relation to the patient’s teeth/lip.
- Obtain an arterial blood gas approximately 30 minutes to an hour post-intubation.
- Apply care bundles to prevent VAP (Keep HOB 30 degrees, sedation holiday to assess readiness for extubation, oral care).
- Provide GI and DVT Prophylaxis.
Ventilator Management In Short
In conclusion, the patient’s comorbidities drive the reason for intubation and ventilator settings. When placing a patient on MV, I would suggest placing a patient on VC mode, Vt 6-8ml/kg of PBW, Rate 12-16, FiO2 100%, and PEEP of 5cmH20. Obtain a chest radiograph for ETT placement but be sure to assess the whole chest for any abnormalities. Obtain an arterial blood gas approximately 30 minutes to an hour post-intubation and make the necessary adjustments based on clinical picture and objective data. Adjust Vt and RR to manage ventilation; PEEP and FiO2 for oxygenation. Remember to provide adequate sedation and measures to prevent ventilator associated PNA. Don’t forget GI and DVT prophylaxis, if no contraindication.
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