Choosing initial ventilator settings

Selecting initial ventilator settings is frequently tested on both the TMC-RRT and clinical simulation board exams. Therefore, it is crucial that respiratory therapy students have a thorough understanding of initial ventilator setting selection.

Before we get started, an important concept to understand is that acceptable initial ventilator settings are different than the ventilator settings used when making changes. This is because when choosing initial ventilator settings we don’t yet have arterial blood gas, or lung compliance data to guide our choices.

For example, the recommended initial mandatory rate is 10 to 20 breaths per minute. However, we may increase this rate beyond 20 once we’re able to analyze arterial blood gas, airway pressures, and hemodynamic data collected while the patient is on the ventilator.

With that said, let’s review initial ventilator settings.

Mode

Students should take comfort that initial mode selection is not emphasized by the NBRC to determine if an answer is correct or not. This is probably due to the vast number of ventilator modes that exist. Also, there is no universal naming system for ventilator modes. This creates confusion as similar modes may have entirely different names depending on the manufacturer.

Furthermore, patients can be effectively ventilated using any form of volume or pressure control. As long as the tidal volume is set appropriately when using volume control (6-8 ml/kg of predicted body weight), or the inspiratory pressure is set appropriately when using pressure control (20-30 cm H2O), any of these modes will work. Therefore, modes such as A/C, SIMV, PRVC and pressure control are all acceptable initial modes of ventilation on the RRT board exam.

Modes such as high frequency oscillation and Jet ventilation are also not used as an initial mode of ventilation. CPAP delivered through an advanced airway may be used if the patient does not require ventilatory support.

Tidal volume

First, be sure to base the tidal volume on the patient’s predicted body weight (PBW). This is important because a patient’s lung capacity does not change as they gain or lose weight. Using an overweight patient’s given weight in the exam question could provide a dangerously high tidal volume. Therefore, any time the patient’s height is given in the exam question, be sure to calculate the patient’s predicted body weight.

Use 6-8 ml/kg of predicted body weight (PBW) for most patients

Use 4-6 ml/kg of predicted body weight for patients suspected of ARDS

Forumula:

PBW male: 50 + 2.3(inches tall – 60)

PBW female: 45.5 + 2.3(inches tall – 60)

Example: Calculate the predicted body weight of a 65 inch male patient

50 + 2.3(65-60)

50 + 2.3(5)

50 + 11.5

PBW = 61.5 kg

Mandatory rate

10-20 breaths/minute

An important point to keep in mind when selecting the mandatory rate is to ensure the patient receives an adequate minute ventilation. For example, if you choose a tidal volume of 400 ml and a mandatory rate of 10 breaths per minute, the minute ventilation would be only 4 LPM. This is below the recommended minute ventilation of at least 5 LPM. So when using a low tidal volume, you should also consider using a mandatory rate that is high enough to provide at least 5 LPM minute ventilation.

FiO2

Selecting the correct FiO2 can be a bit of a mystery on the RRT board exams. However, if you keep these bullet points in mind, you should be successful:

• Try to avoid using a high FiO2 in patient’s with COPD
• Use 100% oxygen following intubation due to emergencies.
• If following intubation the SpO2 is 100%, you can use a lower FiO2.
• Generally 100% is a good starting point for most patients until we can see how their SpO2 and arterial blood gases respond.

PEEP

2-6 cm H2O

If the patient is suspected of having ARDS, it is acceptable to use a therapeutic level of PEEP beginning as high as 10 cm H2O. Keep in mind, the patient’s hemodynamics should be stable to use a high PEEP.

• Do not use a high PEEP level in patient’s with unstable cardiac function. For example, a patient who has just undergone CPR should not receive PEEP greater than 5 cm H2O.
• If the patient was on CPAP prior to intubation, set the PEEP level the same as the CPAP level.
• If the patient was on BiPAP prior to intubation, set the PEEP level the same as the EPAP level.

Now apply these guidelines to the following example simulation question. What would you choose?

If you chose the last choice: VC, A/C ventilation, FiO2 0.60, mandatory rate 18, Vt 450 mL, PEEP 10 cm H2O you are correct!