Registered Respiratory Therapist for 18 years working in all areas of healthcare. Professional interest is the nuances of mechanical ventilation and just learning new/old technology.
The Pre-brief
You get called to your patient’s bedside. Your patient is presenting with a COPD exacerbation, has shortness of breath, increased work of breathing, and is diaphoretic. The plan is to place the patient on BiPAP and start nebulizers. You place the patient on 12/6 to achieve a tidal volume of 400, but how do you adjust the rise time for better patient compliance and comfortability while achieving the best outcome?
What is Rise Time?
The speed at which inspiratory pressure increases to the set target pressure is known as the rise time on most BiPAPs. Adjustments in rise time can improve patient comfort/tolerability with BiPAP. Rise times generally go from 100ms to 600ms, with settings of 1 through 5. A setting of 1 is the fastest while a setting of 5 is the slowest. Adjustments in the rise time change the waveform delivery of the pressure, furthermore, affecting your I:E ratio.
Why is this important?
Adjusting the length of time needed to cycle from EPAP to IPAP can be very useful. BiPAP waveforms can be altered with the rise time by changing the angle of the pressure delivery. A faster rise time, setting 1, can result in a square waveform, where a slower rise time, setting 5, will be more sinusoidal.
This slope change allows the patient to get more or less inspiratory flow to reach the target pressure. Setting this will vary with different patient populations. COPD patients tend to need a faster inhalation and prolonged exhalation. A shorter rise time will aid in this style of breathing for this patient population. A restrictive or neuromuscular patient may need a longer rise time to allow for adequate gas exchange. Patients in acute respiratory failure may be flow starved, therefore, needing a shorter rise time to meet their inspiratory demands.
So how do you determine the correct rise time?
Examining the waveforms and minute ventilation will help ensure proper setting of the rise time. The goal with proper rise time is to reduce the work of breathing and increase patient comfort. Understanding the slope, along with clinical examination of the patient, will allow you to achieve this.
Asking your patients simple yes or no questions will also help achieve optimal rise time. These may seem like obvious questions, but simple terms are always best for your patient. Does your breathing feel easier? Do you feel like you can take a full breath? Is this tolerable? (I don’t use comfortable because for some BiPAP is never comfortable but they can tolerate it).
The Debrief
- Adjusting rise time properly can result in better outcomes
- Different patient populations may need different rise times
- If a patient is not tolerating BiPAP, think about adjusting the rise time
- Ask your patient simple questions to gauge if the rise time is optimal
References
- Johnson, K. G., & Johnson, D. C. (2015, October 23). Treatment of sleep-disordered breathing with positive airway pressure devices: technology update. Medical devices (Auckland, N.Z.). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4629962/#__sec8title.
