Simple Assist-Control Ventilation
This experience covers basic AC Mode Ventilation.
Your team has been launched for a 10 y/o, 45 kg, in respiratory failure. You opt to bring your transport ventilator inside the referring facility and start ventilatory support prior to loading back into your aircraft.
Simple Assist/Control (AC) Ventilation
By: Dan Turner, Retired UMMC Flight Nurse
Using mechanical ventilation is an essential part of critical care transport medicine and we all must have at least a basic understanding of how to perform such a critical care skill. I will admit to you that there are a few capabilities of some really fancy ventilators that I do not have experience with. Hence, this title, “ Simple Assist/Control Ventilation”. This experience will provide you with a very basic understanding of using a transport ventilator. For more advanced ventilator knowledge, I’d like to recommend you visiting my colleague, Charles Swearingen’s group or check out his many books on the topic. Ok, enough of all that—let’s get started. To demonstrate the benefits of AC Ventilation over Synchronized Intermittent Mandatory Ventilation (SIMV), I found a publicly available YouTube video for you to watch HERE
Now that we have that out of the way, let’s dig in! For this experience, we will cover the ventilator settings of:
Tidal Volume (TV)
Peak End Expiratory Pressure (PEEP)
TV is the amount of gas that will be delivered in order to aerate, oxygenate, and ventilate the lungs of our critically ill or injured patient. This setting should be 7-10 ml/kg of body weight. TVs that are too high will exert dangerously high pressure on the lungs, causing barotrauma and even collapse of a lung. How do we know if the pressure our ventilator is exerting is within a safe range? Great question! The answer is by monitoring the Peak Inspiratory Pressure (PIP) which will be visible on the ventilator itself. A good rule of thumb is to use as little as is necessary to cause a gentle, bilaterally equal chest rise and fall, indicating ideal oxygenation and ventilation (somewhere around a PIP of 20 cm H2O). I would suggest starting at a TV of 7 ml/kg of body weight and adjust as necessary to maintain oxygen saturations of 95-100% and an End Tidal CO2 (ETCO2) range of 35-45. Let’s just make life easier and shoot for an ETCO2 of 40.
The rate is how many breaths per minute that the ventilator is delivering. This should be around the expected age-specific parameters that you learned in school. The rate you choose will affect mostly the amount of exhaled carbon dioxide. The faster one breaths, the more CO2 that is “blown off”. Therefore, we can say that the faster the rate, the lower the amount of exhaled CO2 that will be noted.
Fraction of inspired oxygen (FiO2) is the percentage of the gas mixture being delivered that is oxygen. This can range from what is called “room air,” or 21% oxygen, all the way up to 100%, which is pure oxygen. What FiO2 should you use? Like TV, use as little as possible to maintain 02 saturation’s between 95-100%. Personally I always started at an FiO2 at 80%.
PEEP is the amount of tension maintained on the alveoli at the end of the exhalation phase of mechanical ventilation. PEEP settings are always age-specific. For kids from 0–12 years old, I would suggest a setting of 4 cm H2O. For ages 12 and older, use a setting of 5 cm H2O.
Ok, let’s look at a case study and work our newly-found ventilator magic.
Patient info: 10 y/o female in respiratory failure. Patient’s weight 45 kg
You’ve arrived, assessed, and moved her over to the aircraft stretcher. You’ve opted to bring in your transport ventilator and place her on it before loading into the aircraft. You place the ventilator settings as:Mode: Assist Control, TV: 315, Rate 24, FiO2 90%, PEEP 4.