# Respiratory Care Flow Rates/ Student needs help!

- 0Nov 14, '11 by SearchYourSoulHi. I am a respiratory care student in my first year. I know this is a nursing forum but I have found lots of help in the past on this site.

I am confused about inspiratory flow rates. The specific question is this:

Your patient has a Vt of 0.8 L, a reapiratory rate of 12 br/m with an inspiratory time of 1.2 seconds. What is your patient's inspiratory flow rate?

I also have another question too:

You set up a T-piece with an FiO2 of 0.4 using a full E cylinder with oxygen flow meter set at 12 l/m. What is the total flow of the system?

If someone can please help me with these. I am struggling some in this area.

Thank you so much. - 8,612 Visits
- 3Nov 15, '11 by
*JustBeachyNurse*I'm going out on a limb, but if I had this question in nursing school my answer would be "call the respiratory therapist". We never got into such detail about flow rates other than the basics. - 1Nov 15, '11 by SanFranSRNAHi I am a student nurse anesthetis. I'm going to offer in input but this is from anesthesia point of view. Inspiratory flow rate (IFR) is measured Liter/minute. IFR determines how quickly the breath is delivery. How I determine what flow rate to set is depending on the tidal volume. If I am giving much larger Tidal volume (usually not the case), I will set the inspiratory flow rate a little longer. For example, T.V of 900ml Rate 10 BPM, I:E of 1.3: 2. How that helps.

Now on to the second question. The total flow of the system is 12 L/min... If you are using a full cylinder O2 E tank. A full E tank has 660L of O2. If you are running a flow rate of 12L/min it will give you 55 mins. Here is the math. 660L/ 12L/min = 55 minNRSKarenRN likes this. - 1Nov 15, '11 by PetERNurse0.8 L / 1.2 sec = 0.67 L/sec = 40 L/min IFR (which of course is affected by rise time)

If your O2 flow rate is 12 L/min, but that is only 40% of your system's flow, your total system flow is:

12 / 0.4 = 30 L/min

and yes your tank will last about 55 minutes.Esme12 likes this. - 4Nov 15, '11 by GilaRRTThese are fundamental, first semester respiratory student calculations. Please, get help and look at tutoring. Do not fall behind and good luck.

As already discussed the inspiratory flow is simply how many ml per second multiplied by 60 and a conversion to liters to get liters per minute. 0.67 L/sec = 40 L/min.

The second question involves air entrainment calculations. It is NOT asking for duration. You can use the magic box formula or do the following:

1) Find your air entrainment ratio:

100-40 = 60, 40-20 = 20 --> 60:20 = 3:1

2) Add the ratio:

3+1= 4

3) Take the product of the number above and the flow of oxygen:

4* 12 = 48

48 L/min is the total flow delivered in this situation.Last edit by GilaRRT on Nov 15, '11 :**Reason**: 3) - 3Nov 15, '11 by nerdtonurse?:bowingpur

Wow, guys. This is why I just pick up the phone and punch the code for respiratory.... - 2Nov 15, '11 by BiffbradfordOxygen can be considered a drug like any other, nothing wrong with knowing how to administer it.JulieL and NRSKarenRN like this.
- 1Nov 15, '11 by PetERNurseBrain fart. Gila is right. Have to first calc your air2 ratio, your air flow, and add that to your o2 flow. Have never seen the cool add the ratio trick. Allows you to skip a step. Thanks Gila!GilaRRT likes this.